sport polymer

Applied Ergonomics 1984, 15.4, 259-279 Ergonomics in sport Exercise and sports equipment: Some ergonomics aspects T. Reilly and A. Lees Department of Sport & Recreation Studies, Liverpool Polytechnic, Byrom Street, Liverpool L3 3AF, UK Sports equipment encompasses a gamut of devices used in laboratory, training and competitive contexts and these form the content of this paper. Ergometers range in sophistication from friction braked stationary bicycles to computer controlled simulators which incorporate exercise modes specific to the athletic user. These are now used in training, as experimental devices and in some instances for competition purposes. Training equipment exhibits a similar emphasis on exercise specificity, safety being an important aspect of its use. Design of projectiles for sporting activities has mainly reflected their traditional modes of use, the introduction of synthetic materials having some ergonomics implications. Similarly, materials science and design technology have contributed innovations in equipment for racquet sports and hitting implements. The changes have tended to be associated with availability of new materials for product construction and have implications for safety and skill in the transition to using the new products. Ski equipment design illustrates ergonomics factors in interfacing the performer with the sporting environment and how equipment has progressed by regenerative design processes. Enhancement of performance in some sports must be accompanied by an awareness of safety requirements: where appropriate, risks to participants should be reduced by use of protective clothing and equipment. Enforced validation of protective equipment is recommended to raise safety levels in certain sports and the safety of spectators must not be neglected. Human factors criteria can then be applied in monitoring, officiating and spectating at sporting events. Keywords: Exercise, sports equipment, training Introduction Consideration of the characteristics of the equipment used in sport is an important aspect of interfacing the performer with the sporting environment. Historically, equipment was fabricated to enhance and extend human capabilities: gradually, as equipment in everyday use became more extensive and refined, various forms of competition involving skill in using equipment evolved. These equipment developments varied from vaulting poles, racquets for games, projectiles, aquatic shells, to locomotory aids such as skis, skates, cycles and motor propelled vehicles. In other sports, appropriate shoes, clothing and protective equipment have been fabricated to promote the safety and efficiency of performance. As competition in top-flight sport has grown increasingly intense, much creativity has been applied by engineers in attempting to launch new artefacts to be used by the champion performers. Where the quality of new equipment provided a crucial advantage to the user - as evident in the introduction of glassfibre vaulting poles, aerodynamic javelins, turbo-charged Formula 1 racing car engines or 'jumbo' sized lawn tennis racquets - the novel feature is generally adopted by competitors to eschew entering the contest at a disadvantage. In other cases the details of the designs, such as the keel of the Australian yacht in the 1983 America's Cup contest, may be kept secret until victory is secure. Attention has also been focused on accessory equipment such as sports shoes and clothing and the need to improve their comfort and protective functions. Besides, technology is now extensively utilised in the provision of equipment to help officiating at sports contests, enhance training methods, improve information presentation to the audience and allow precise measurements of human capacities under controlled laboratory conditions. It is apparent that sports equipment can be broadly defined to refer to a gamut of materials used in recreational, training, competition and experimental contexts. These areas provide the scope of the current article. The requirements of competition mainly dictate the trends and developments in the other spheres. For competition to be possible and performances to be comparable on a worldwide basis standardisation is necessary, a factor not always mandatory with industrial products. National standards are fixed by the governing body appropriate to the sport in question, which invariably has to adopt the standards of the parent 0003-6870/84/04 0259-21 $03.00 Q 1984 Butterworth & Co (Publishers) Ltd Applied Ergonomics December 1984 259 Ergonomics in sport international governing body and these largely determine the constraints on designers of new equipment. In baseball the specifications for the ball were determined in 1872 and for the bat in 1876, both still applying today. In contrast, specifications in machine sports and aquatic activities are regularly modified to accommodate the ingenuity of new designers, who are spurred on by the rewards that accompany sporting successes. Whether governing bodies hinder or encourage new developments in equipment, designers must work within the limits of the specifications laid down in the rules for the sport. They also have to consider what implications use of their product may have for training and injury occurrence. Many sports activities do not have an inherent heavy call for equipment in competitive contexts, yet practitioners use sophisticated hardware in training to optimise their preparation. This applies, for example, to the training of runners and swimmers. Similarly, elaborate analytical systems are available for measurement of biophysical and perceptual-motor capacities so that athletic potential may be predicted and adaptations to training regimes monitored. Measurement of fitness variables has become increasingly refined with the recognition of the multivariate nature of fitness (Ostyn et al, 1980) and its specificity for the activity in question. Additionally, laboratory methodologies in the sports sciences have progressed in sophistication and these have overlapped into training contexts with an increased use of ergometers for specific training purposes as welt as for testing. The transfer illustrates the possibility of cross- fertilisation of ideas from theory to practice. Ergometers Conventionally, practitioners used field tests such as the Cooper 12-min run test and a maximum weight lift to measure endurance and muscular strength capacity respectively, and for monitoring improvement with training regimes (Reiliy, 1981). Such tests were relatively simple to execute and were closely related to sporting activities. Similarly the Harvard Step Test (Brouha, 1943) required only simple equipment and so for some time was widely adopted for use in military, industrial and sports institutions. The introduction of cycle ergometers into exercise physiology laboratories fostered a sharper interest in fitness testing and medical screening under exercise conditions where the rate of work could be quantified and controlled and the physiological reaction to that work rate could be monitored. The outcome was that numerous facilities became available in developed countries for exercise stress testing. The possibility of estimating human power output and energy expenditure during stationary cycling led to the acceptance of friction or hydraulically braked bicycle ergometers in training for positive health and body-weight control. Use of cycle ergometers flourished in commercially based fitness clubs to promote physical well-being of members changing from a sedentary to a more active use of leisure time. These ergometers were also the chosen mode of exercise when tests of aerobic and physical working capacity, such as VO 2 max and PWC 170 (Sjostrand, 1960), were conducted. ThougIa'2he Monark cycle ergometer is still a fundamental item of equipment for general use in exercise testing, its limitations for specific purposes are now recognised and many alternatives are commercially available. Electrically braked cycles overcome the difficulties of acquiring precise control of the work rate encountered in using their friction-braked predecessors by not having to depend on dictating the pedal frequency. Power output is f'txed; the resistance, which is provided by the electro- magnetic field set up by rotating copper discs, accommodates to changes in pedalling frequency so that it alters inversely with changes in the pedal rate to maintain power output constant. Even so, changing the pedalling rate while keeping power output constant will affect metabolic responses to exercise (Hughes et al, 1982). The force bicycle used by Davies et al (1984) has the cranks drawn by a variable speed motor so that maximum force production and power output at pre-determined pedalling speeds can be calculated when the cycle is linked to a computer. The Fitron cycle developed by Cybex Inc (Ronkonkoma, NY) is isokinetic, allowing the pedalling rate to be f'Lxed in advance, the resistance accommodating to the effort exerted by the individual. The resistance in the Dynavit (Garrick Co, London) cycle (Fig. 1) is computer-controlled so that an incremental work test to maximum effort or a steady-rate regime can be set pre-start. An ear plethysmographic system linked to the cycle permits concomitant monitoring and recording of the heart rate. Other ergometric systems utilise feedback from the user's physiological responses to exercise, as is the case in 'heart-rate controlled ergometry'. This facility is enormously helpful to clinicians and to Fig. 1 Computer controlled cycle ergorneter with accessory pulse rate and blood pressure monitor 260 Applied Ergonomics December 1984 Ergonomics in sport supervisors of exercise programmes prescribed to cardiac patients and coronary risk individuals: it is now available in the current range of treadmills as well as in cycle ergometers. Motorised running treadmills provide an alternative mode of precisely controlling the exercise load The VO 2 is • ax generally found to be about 8% higher when measurer~ on a treadmill compared with that measured on a cycle ergometer (~,strand and Rodahl, 1977). Current treadmills have a number of improved features including more compliant belts for greater shock absorption on landing, easy-to-use safety harnesses and emergency stop controls. A facility for declining as well as inclining the belt has promoted experimental interest in downhill locomotion (Pimental et al, 1982). Self-propelled belts compare favourably with electrically driven treadmills in enabling maximum running effort to be elicited (Davies et al, 1981) and this has helped their acceptance for general fitness training. Recognition of the specificity of fitness has led to the development of a range of ergometers appropriate to demands integral to individual sports. Astrand and Englesson (1972) reported the design of a swimming flume for use in physiological testing of swimmers which has subsequently been utilised for fundamental investigations of swimming actions (Holmer, 1972; Clarys and Lewillie, 1975). Similarly, tanks with rotating water channels are used in studies of oarsmen and canoeists, or of their respective crafts. These laboratory facilities are expensive and are available in but a few well-equipped sports science research centres such as the University of Tsukuba, Tokyo University, and research institutions in Stockholm, Buffalo, Milan and Brussels. The facilities may also be used for fundamental studies of the behaviour of new water-sports equipment such as sailboards (Gregory and I~es, 1981). Where research funds are less generously provided, dry land simulators of water sports may be employed. A 'Biokinetic Swim Bench' (Isokinetics Inc, Mountain View, CA, Fig. 2) which partially accommodates to the input of effort and which allows duplication of the pattern of arm and shoulder involvement in pulling through the water in the swimming stroke has been used for fitness testing (Sharp et al, 1982). Similarly, an isokinetic swim bench can be utilised for fundamental research in the physiology of swimming (Swaine and Reilly, 1983). How closely the hydrodynamic forces during the pulling action are simulated has not been demonstrated. Rowing and canoe ergometers which incorporate hydraulic, mechanical or electrical resistance mechanisms and which mimic the actions of the competitive events are also being utilised (Cooper, 1982; Dal Monte et al, 1981). Competitive cyclists can use their own machines on rollers and a wind load simulator for more realistic reproduction of road conditions in the laboratory (Firth, 1981). For skiers, treadmill rails have been modified to accommodate work with ski poles as well as leg movements; for proficient cross-country skiers, VO 2 max values in excess of their treadmill running VO 2 max are then found (Bergh, 1982). Arm ergometry is now recognised as necessary for specific function testing of arm-trained athletes, modes including arm cranking, turning and bending being employed (Mangum et al, 1983), though it is also possible to modify conventional cycle ergometers as occasion demands. Mobile underwater ergometers permit control and measurement of divers' work output during swimming at ocean depths up to 30 m and are becoming more reliable during extended use (Dwyer, 1977). The linking of automatic systems for expiratory gas analysis to conventional ergometers has considerably enhanced the productivity of many sports research laboratories. On-line systems using dedicated microprocessors make measurement of VO 2 max and VE max routine, consecutive computations being performed every 30 s or every 60 s. Additionally, it has been suggested, sub-maximal indices of the ability to sustain high intensity exercise may be obtained from the disproportionate increase in minute ventilation with increased work loads (Wasserman et al, 1973) though the interpretation of the break-point in ventilation Fig. 2 Swim bench simulator used for research, fitness testing and training of swimmers Applied Ergonomics December 1984 261 Ergonomics in sport and its relationship to metabolic acidosis are still the subject of controversy (Hughes et al, 1982; Brooks and Fahey, 1984). Similarly, fast-response analysers have permitted measurement of breath-by-breath expirations and so accelerated the understanding of the kinetics of the acute response to exercise. The Wilmore-Costill adaptation to standard automatic systems allows for calibration of analytical equipment concomitant with measurements during exercise, thereby easing the task of the exercise test technician. The importance of anaerobic power in explosive activities has directed the attention of exercise scientists towards its measurement. Margaria and co-workers (1966) described a stair run test for calculation of alactacid anaerobic power, the equipment needed comprising a stairway of suitable dimensions and switch pads or photo cell assemblies connected to electronic timers on appropriate steps. A modification of this test for use on a cycle ergometer was developed by Pirnay and Crielaard (1980). Dal Monte (1980) developed a similar protocol for use on the treadmill by strain gauging the front raft which was gripped by the subject as he ran. Lakomy (1984) described how a non-motorised treadmill could be instrumented for measuring the power generated during sprinting: the applied force and .the belt speed are measured, while a harness is passed around the waist to secure the subject to the treadmill. Alternatively, peak power and corollary observations can be obtained by means of a force platform, the methodology for its use as an ergometer being described by Cavagna (1975). The Wingate 'anaerobic test' (Bar-Or, 1981) can be performed on a cycle ergometer to distinguish two aspects of anaerobic power: accessory transducers enable measurement to be made of peak power over 5 s and mean power over a 30 s all-out test. These are taken as representative of maximal alactacid and lactacid anaerobic power respectively. Fig. 3 shows how results can be presented by means of a computer with measurements of power production for each second. A study of 18 young male swimmers demonstrated high correlations for both mean power (r = 0.81) and peak power (r = 0-81) with sprint swimming velocity when the Wingate test was modified for use on a Biokinetic Swim Bench: the relationships were still significant when data were normalised for age and body weight, though the relationship weakened as the distance swum was increased (Bayley and Reilly, 1984). Measurement of muscular strength can be important in identifying predispositions to injury (Reilly, 1981) as well as in indicating fitness status. Conventional methods of testing have employed dynamometers, cable tensiometry or strain gauging assemblies to measure peak isometric tension. Ergometers have been designed for eccentric as well as concentric muscular exercise: exercise on the model reported by Knuttgen and co-workers (1982) consists of cycling activity of the legs against the rotational movements of an electric motor, the direction in which the pedal crankshaft of the ergometer is driven being dependent on whether concentric or eccentric work is desired. Use of isokinetic equipment such as that of Cybex Inc allows dynamic measurements to be made and at a variety of speeds of contraction. The 'Kin-Com' computer controlled system (Chattecx Corp, Chattenooga, TN) overcomes some of the torque overshoot problems (Sapega etal, 1982) associated with earlier variable resistance machines and permits control '3MEJECT NHNEIT REILLY ~UBJECT BODY blEIGPIT: 7(~.5 TEST FIODIE ILEGS LOC~(KP> I 5 POWER OUTPUT (WATTS) : d ME~I I~OMER RT 5 SECS I 6(;I ME~ PO~aER RT 5 SECS(WAT~ MESCal ~l~ RT UB SECS¢ 5', MERN POWER RT 1~ SECS (Wf ~ POMIER ~T 15 SECS| 5| I~ POkeR RT 15 SEDS <k~ PIE~iN POb~I~R liT 21El SECS : 4~ M~$ l~R FIT 20 SECS (~N ME.RH POWER RT 25 ~ECS= 4: ~ pCI~ER RT 725 SEC ~, , HI MI£RH Pr~IE~ R1 -'~ sEr':,,w~" P$1EN,I pOI4EI~ DVER 3;0 ;EC;: ME~; POHE~ OVE~ dE, '~E':=, I 6(;6 • 8 T. KO,I~4> t 9.4581~3 558.4 55e. 4 (WRTT.KG.IE~4~ i 7.9~36738 4~B.2 ( M~TT. KO. E414 > I ~;. ~11 t34752 430. qTT.~'C,.BW, : 6. l~?Oe14~ ITT. ~ G, ~;tl ~ ; 5.24~226-¢~5 '~EC~, I.I~TT./ G,E:HJ I 7.~4444445 Fig. 3 Results of 'Wingate Anaerobic Test' on one subject with power production computed for every second of the 30 s test of torque as well as speed in concentric and eccentric actions. Variable resistance has been incorporated into a range of ergometers by Cybex Inc, following the commercial success of its knee extension model; the Ornithron, Uppe body ergometer' and the Fitron cycle are examples. The pattern of changes in torque and peak power with increasing speeds of contraction on isokinetic equipment is Used in some laboratories to estimate fibre type distributions in the involved muscles. The extremely high correlation between sprint free style swimming and power achieved on a 'Biokinetic Swim Bench' (Sharp et al, [982)demonstrates the potential of such ergometric apparatus for fitness testing. The techniques are readily ac~ptable to sports practitioners for monitoring biophysical capacities since the methods are non-invasive. In summary, ergometers now ran_ ge according to the type of muscle action permissible. Increasing emphasis is also placed on the need to match the etgemetric mode to specific needs of the user. Computer linked systems in er[ometry enhance the ease of exercise testing and reduce the risks attendant on strenuous exercise to the subject. 262 Applied Ergonomics December 1984 Ergonomics in sport Training equipment Increased systemisation of training regimes for elite athletes has spawned the design of various training machines and items of equipment. The most prominent is the use of resistance modes to accustom active muscles to work against supra-normal loads. Weight training has been adopted by most sportsmen, astute choice of the training stimulus being made to match the activity in question. The risks of incurring back, knee or wrist injuries with heavy weight training are documented (Reilly, 1978) and various types of ergometers have been used as alternatives. The risk of injury is not totally eliminated during heavy exercise if free weights are replaced by a weight-machine: a study by Andrews et a! (1983) showed that though greater strength development may accompany the use of a typical squat machine compared with a similar barbell exercise, a greater shear force at certain joints may also be involved. Free weights cannot present the maximum training stimulus throughout the complete range of movements. Isokinetic equipment, which incorporates a speed governor in the apparatus to allow variable resistance according to the effort produced, has proved superior to conventional progressive resistance and to isometric strength training methods (Thistle et al, 1967). An alternative practice is to use cams designed according to typical human strength curves so that the resistance is altered with the angle of contraction at whatever joint is involved. The 'Nautilus' (De Land, Florida) and 'Polaris' (San Diego, CA) systems incorporate this principle of accommodating resistance and overcome a limiting feature of the current isokinetic machines in that eccentric as well as concentric actions are permitted. Weight throwers and swimmers have traditionally employed weighted pulleys which permit exercising with the specific patterning of the muscle actions of the competitive event while the current 'Biokinetic Swim Benches' provide feedback on the forces produced and the work accomplished. Running harnesses have been used by runners to condition their muscles to work against supra-normal resistance, while weighted clothing and weighted boots have been employed by jumpers, sprinters and gymnasts. The versatility of resistance training is illustrated by the utilisation of multi-station equipment, such systems now being designed on ergonomics criteria (Fig. 4). Typically a twelve-station apparatus incorporates stations for arm, leg and trunk work which are adaptable for flexion or extension exercise while resistance is provided by either body weight, loaded stacks, isokinetic machines or pulley systems (Reilly and Thomas, 1978). The use of circuit weight-training has been validated for training the cardiovascular system (Gettman et al, 1982; Reilly, 1983). Multi-station equipment can be used for training specific muscle groups or for general conditioning of team squads. The Masolet (Oslo) 'sequence' system described by MacDonald (1983) demonstrates how agility and joint flexibility can also be improved. Additionally, the multi-station machines are relatively safe for novices to use since free weights are not involved and the apparatus has proved effective in fitness training of industrial workers on- site as well as in training competitive athletes (Reilly, 1979a). Practitioners recognise the difficulty of isolating a speed training stimulus from that producing effects on muscular strength or muscle power. Nevertheless, various regimes and apparatus have been designed for improving speed of limb movements. Boxing speedballs have been utilised by sprinters reputedly for speeding up arm movements with a positive transfer to leg speed, the existence of the neurophysiological mechanism for effecting the transfer being unclear. Experimental work has shown that forced fast movements, induced on a treadmill or cycle ergometer, can result in Fig. 4 Multi station training equipment (Reilly and Thomas, 1978) Applied Ergonomics December 1984 263 Ergonomics in sport increased speeds of contraction when the assistance is withdrawn (Dintiman, 1974). Downhill ramps are used in indoor arenas in the training of long jumpers to permit a faster acceleration in the run-up and achieve an economy of energy output over a complete training session. In these cases the principle is one of speed assistance rather than provision of resistance to increase the load on contracting muscles. Similarly, the exploitation of energy stored in eccentric contractions for a subsequent concentric action has been incorporated into the design of training machines, so permitting the development of muscular power and speed of contraction. Consequently various bounding and depth- jumping drills, collectively known as plyometrics, are practised by many athletes (Reilly, 1981). For this reason weight training racks may include a facility to concentrate on weight lowering exercises where greater loads can be handled than in lifting, and many multi-station devices allow eccentric as well as concentric actions. An adverse after- effect is the muscle stiffness associated with vigorous eccentric contractions. A range of artefacts has also been developed for training of individuals, temporarily or permanently impaired. Hydrotherapy pools are generally accepted as important means of providing resistance to muscle action in water. As body mass is buoyed up by water, this is a useful training mode for handicapped and injured athletes since the strain involved in lifting body weight against gravity is avoided. Harnesses are used for suspending the individual in water while simulating the running action; for example, to gave the injured runner an opportunity to maintain training status. Glaser et al (1980) reported the use and validation of wheel- chair ergometers which permitted progressive arm training for semiplegics. Special lightweight wheelchairs have been designed for wheelchair marathon racing, thereby reducing the energy demands of propulsion and enhancing performance in the competitive event. Passive methods of inducing training effects, such as electrical stimulation of muscle (Hudlicka. 1983), or cycloid vibration for joint flexibility (Atha and Wheatley, 1976) have potential applications to the injured as well as to top competitors whose active regimes can thereby be augmented. Another aspect of equipment design which has captivated sports engineers is how skills training can be optimised by use of simulators. The golfer's groove, designed to forcibly guide the club head in a predetermined path, has not stood up well to validation studies (Skrinar and Hoffmann, 1977). The 'golf trainer', a device which permits measurement of club head accelerations and decelerations in driving, and prediction of resultant ball flight characteristics, provides useful immediate feedback to the golfer. Comparable benefit is offered if portable video-recording systems are used in field conditions, the visual feedback being most effective when employed in conjunction with expert comments of a mentor. Relays of lights which are tripped in sequence are used by the sides of running tracks and swimming lanes as aids to pace judgement, though the extent to which this transfers to competition has not been documented. Some simulators avoid the discomfort, risk or expense of realistic practices. Golf driving ranges are popular in Japan where entry to a golf course is both difficult to gain and expensive. Sailboarding can be simulated on dry land with artificial provision of wind at selected velocities and directions on the sail, so the individual can learn without the discomfort of repeated immersions. Similarly, a man-powered flight simulator was designed (Evans and Reilly, 1979) to enable optimal control configurations to be determined betore the Kroemer prize for man-powered flight was won by the Gossamer machine. Team skills such as rugby scrummaging may be practised on scrummaging racks whose designs range in complexity from makeshift wooden structures to sophisticated hydraulic systems with force transducers attached. Such devices cannot adequately represent the finer points of the game when the effort of the squad is co- ordinated as in coping with a wheel or turn of the scrum. Individual tackle dummies are widely used in teaching tackling skills in American football as well as in Rugby football, and injuries due to imperfect execution of practice tackles can thereby be reduced. Simulation of environmental conditions can also be a useful strategy for training purposes. Climbing walls allow difficult manoeuvres to be attempted in the gymnasium and afford an opportunity of testing new mountaineering equipment without the necessity of incurring the risks attendant on high mountain climbs. Artificial ski slopes provide the novice with the opportunity of acquiring basic skills prior to experiencing the ski slopes and are a popular recreation facility in sports centres in the United Kingdom where good ski conditions are rare. In neither case has the magnitude of the transfer of skill to the realistic condition been thoroughly established. A portable simulator of altitude hypoxia may be worn as a back-pack in preparation for skiing, mountaineering, or athletic performance at moderate to high altitudes. In a previously unpublished study by Clucus, McClean and Reilly at Liverpool Polytechnic the use of such equipment (PO 2 Aerobic Exerciser Inspir Air Corporation, Westlake Village, CA)whilst cycling on an ergometer at a toad of 200W was found to elevate various physiological responses significantly over normal conditions. The heart rate increased by a mean value of 8 beats/min (n = 12), perceived exertion was raised and blood PO 2 was reduced to a value compatible with expectations at an altitude of 2300 m. The system recirculates expired air and mixes it with inspired ambient air to reduce the partial pressure of inspired O 2 , CO 2 being absorbed in a canister on the back pack. Respiratory responses to wearing the equipment were shown by Berryhill and Williams (1984) to be dissimilar to those associated with exercise at altitude, suggesting that hypoxic stress was incompletely simulated. The validity of its use to improve performance potential at sea level is even more contentious. Simulators of heat stress (e g, environmental chamber or sauna bath) can also be effective in promoting adaptive responses that benefit endurance performers when that exercise is conducted in the heat. Use of sweat suits by American footballers to promote sweating and weight loss in early season practices is dangerous because of the risk of heat injury involved when evaporative heat loss is hindered. Compression chambers comprise an important facility in the training of divers and are an essential mode of therapy in the event of decompression sickness. Acceptance of simulators is the basis of many machines used in holiday and gaming resorts. Ofteal their popularity spawns competitions in their own right. Hence ski competitions are held on artificial ski slopes or on grass courses while competitive climbs are held on 'climbing walls'. 264 Applied Ergonomics December 1984 Ergonomics in sport Recent examples of the progression of ergometers from experimental to training and competition use are the tread- mill relay races inaugurated by 'Power-jog' machines in 1983. A typical competition involves team work to cover the maximum distance in a set time. Efficient performance involves skills specific to the simulator so that pronounced changes in belt speed are minimised as individual team members alternate on the treadmill. EQUIPMENT FOR PLA Y Intrinsic to many sports is the use of equipment as an essential element in play. Ergonomic factors in the design and use of selected categories of products are now considered. Projectiles Projectiles are used in sports to demonstrate individual abilities in achieving distance or accuracy or both. Their design and construction are based on either practical grounds or historical tradition, and often reflect their mode of use. Where permissible, the developments which have occurred have been to enhance performance, or reduce injury potential. The projectiles used in athletics are the discus, shot, javelin and hammer, and are all based on historical design. Little change in their shape, size and mass has been allowed by the sport's governing body. The exception to this has been the development of the aerodynamic javelin in which modifications to its shape and weight distribution have occurred. This has been largely as a result of the use of new materials ( aluminium alloy) for its construction. The shot and hammer are of heavy metal (usually iron) construction and of uniform density. They have changed little over the years. The discus is of wooden construction, with a protective thin metal rim and weighted centre, which enables a higher rotational velocity to be achieved at release. A discus of rubber construction is available for practice, giving similar mass and inertia properties to its equivalent for competition, but improving durability. Special versions of both shot (loose shot) and discus (rubber) are manufactured so that they are suitable for use indoors. The rules of competition allow different weights to be used by junior and female athletes, and are a reflection of the differences in the strength and size of these participant groups. The weights and sizes allowed have been chosen arbitrarily and not on the basis of scientific investigation. Archery is another historic event with its origins extending back to primitive man, and the bow and arrow have received considerable development and refinement over the intervening years. The modern wooden arrow has a tip of steel construction for penetration and durability, and a plastic nock at the rear which is durable and provides a means for orientating the arrow correctly. Three feathers are used, and these are glued to the shaft at a slight angle so that a spin about the longitudinal axis is caused during flight, producing spin stability (Butler, 1968). The target arrow is made as light as possible so that a given kinetic energy wilt result in a higher release velocity, and a smaller drop of the arrow from its initial line of flight, thus aiding accuracy in target shooting. Field or hunting arrows need to be of sturdier construction, and this is achieved by increasing the shaft's diameter. The extra weight of the arrow demands Fig. 5 A modern bow that larger feathers are used for aerodynamic stability, which also increases air resistance. Glassfibre and aluminium are two other materials used for the construction of arrows and the consistency possible in their manufacture means that they can be produced to be both robust and highly accurate. Aluminium arrows are considered to be the best for accuracy (Butler, 1968). The manner in which an arrow is constructed is one factor affecting the accuracy to which it can be shot. The characteristics of the bow and the archer are also important. The bow is designed to help impart a consistent quantity of energy to the arrow, and to help in its aim at the target. The length of draw can be determined by the position of the arrow on the arrow rest, and it can be set perpendicular to the bow string by marking a 'nocking-point' at the appropriate place. The angle at which it is released can be determined by using the bow sight on the grip of the bow. The modern bow is distinguished by large weights attached to the bow by long rods (Fig. 5). Their purpose is to increase the bar's moment of inertia to rotation resulting from the recoil of the bow string during the release of the arrow. This is in part a compensation for the asymmetrical bow body, caused by the need to have a clear view along the arrow and through the bow sights. These additions to the bow vary from archer to archer. They represent a level of 'fine tuning' of the bow to the archer which is essential in a sport that demands consistent high-accuracy performance. It is then Applied Ergonomics December 1984 265 Ergonomics in sport left to the archer to make the necessary adjustments in order to cope with changing environmental conditions. The speed and strength at which the arrow is released may lead to injury of the archer from the recoiling bow string. Archery gloves are used to protect the fingers of the pulling hand from the pressures associated with the high tension in the bow string and its small area of contact. Arm guards are used to protect the supporting ann from being grazed by the bowstring. Traditionally leather has been used but as the speed and strength of the bow has increased it has been necessary to add steel reinforcements to gloves and arm guards. Soong (1974)has suggested a bow design which enables the maximum amount of strain energy stored in the bow to be imparted to the arrow. This theoretical treatment enabled him to comment on the mass of the bow, its initial curvature, stiffness distribution, length of the bow and the length of the bowstring. The generation of maximum velocity has implications for accuracy as mentioned already. Man himself is a projectile in many sports events even though he is not often thought of as such and this sometimes has an impact on sports equipment. In the pole vault the introduction of the glassfibre pole enabled performance to be enhanced and Hay (1971) has analysed the energy transfers that occur when these poles are used. The other jumping events rely on the athlete himself and the rules prohibit any attempt to enhance performance artificially; thus the maximum thickness of the shoe sole is 25 mm in the high jump and any springs or elastic type materials in the shoe are not allowed. With these restrictions the enhancement of performance has occurred as a result of improved fitness and better jumping techniques rather than by equipment. Dyson (1977) described the evolution of techniques and the effect that this has had on the height cleared. The most notable change in technique was the introduction of the Fosbury Flop, which enabled Richard Fosbury to win the Olympic Gold Medal in 1968 (Arlott, 1975). The technique is now well known but an important consideration is that after the jump the landing must be taken on the back. Only when sufficiently soft surfaces for landing on were introduced to this event on a widespread basis could this technique have been practised and used. Injuries still result from this type of landing due to inadequate landing beds or their faulty positioning. Trampolining and gymnastics are also sports in which man projects himself. The equipment used reflects the ever increasing difficulty of the moves the performer wishes to achieve. In trampolining the bed construction and spring strengths govern what height the performer may achieve. This in turn gives him more time in order to perform the more complex stunts. Trampolining is a relatively new sport (the first official championships were in the USA in 1954) and the materials used now have not changed greatly since the sport's inception. In gymnastics and acrobatics, a sprung floor is an essential feature of contemporary floor routines. The resilience of the floor reduces the magnitude of the impact forces (a positive safety feature) but also allows energy to be stored and utilised by the gymnast in his performance. Similar principles are utilised in the spring board or trampette for enhancing take off in vaulting events. As a consequence of the greater heights achieved a soft energy absorbing surface or mattress for landing is requiredin order to avoid unnecessary injury. The ultimate landing surface is that provided by a safety net which avoids all contact with hard surfaces. The ability of man to perform complex manoeuvres is beyond his understanding of how they are performed, The computer has been an essential toot for enabling biomechanical analyses to be undertaken in order to uncover the scientific principles of performance. Van Gheluwe and Duquet (1977)have investigated ~mnastic movements, Yeadon (1981 ) has analysed trampoline somersaults, while Ramey (1979) has investigated athletics jumps. Hatze (1983) has attempted to simulate many types of human motion including long jumping, and Miller (1971) has performed a useful simulation of springboard diving. While the computer is not used directly, its processing power has enabled these studies to throw some light on the main mechanical factors which are involved in the performance of complex skills. This knowledge has been of use to both performers and their coaches to help not only in the understanding of the actions which they perform but also in improving their performances. Sports ball design and i~rfornmne~ A sports ball is a general term given to an object which is thrown, hit, kicked or passed between persons as an essential ingredient of a game or sport; Often sports balls are spherical in shape, but this need not necessarily be the case. Common examples of spherical sports balls are those used in soccer, tennis and golf. Unusual examples of sports balls are the ellipsoid shaped ball used in rugby, the American football and the puck used in ice hockey. The size, shape and weight of sports balls have often been determined by the nature of the gam e during its evolution, and in many cases the available materials provided certain limitations on ball construction, and hence design: A further restriction has invariably been imposed by the governing bodies of the respective sports, who have placed limits to factors such as ball diameter, weight, resilience, mode of construction and colour. Shape, mass and size The shape of a sports ball is closely associated with its function. The most common shape is one which is spherical, and this allows the ball to roll easily, to be projected through the air, and to be thrown, hit and caught easily without any regard to the orientation of the ball It gives the best air flow characteristics for a non-specialised aerodynamic shape and can take advantage of spin about any axis both in movement through the air or in bouncing off a rigid surface. Shapes which deviate from this reflect the special requirements of the game. For example, in rugby the ellipsoid ball promotes its handling during the game, and in ice hockey the puck is required to slide rather than roll over the ice. The mass of a sports ball is closely related to that part of the human body or striking implement which is used to catch or propel it. Those balls which are used primarily by the hand have a mass which is easily controlled by the musculature of the upper body. If a ball is too light the arm muscles involved in the throwing action can contract quickly 266 Applied Ergonomics December 1984 Ergonomics in sport but with little force and so the power delivered to the ball is small (Wilkie, 1976). If the ball is too heavy the musculature of the arm is used to support the ball and is generally too weak to propel it effectively. Kunz (1974) has shown that there is an optimum ball mass for the generation of maximum release velocity, which lies between 0.1 and 0-2 kg. The size of the ball for hand throws determines the nature of the throwing action and consequently the release velocity. The baseball and the cricket ball are convenient sizes for holding in one hand and thus enable the user to take full advantage of the sequential nature of the body rotations involved in throwing for maximum release velocity. Hoshikawa and Toyoshima (1976) have shown that skilled one-hand throw relies on considerable body rotation and that the sequence begins with hip rotation which can be initiated by a step forward with the leg contra-lateral to the throwing arm, followed by rotation of the shoulder and elbow about the body and finally arm extension. With this action release velocities for skilled men have been shown to be above 40 m/s (Atwater, 1979). As the size of the ball increases beyond about 0.15 m diameter, modifications to the hand and arm position supporting the ball and throwing action are required. The fingers cannot grasp the ball firmly and the hand must now be placed underneath the ball to give it support, and to ensure that when thrown the propelling force is directed close to the centre of mass of the ball. This is observed in the games of handball, netball and basketball. As the diameter of the ball is increased it becomes more difficult to produce the lateral rotation of the forearm (which results in a 'leading elbow') necessary for high velocity throws (Cooper and Glassow, 1976) and so the ball is pushed rather than thrown, with the hand at all times above the level of the elbow. In games where the rules allow it, two hands are often preferred. This gives security in catching the ball, but restricts the throwing action by forcibly bringing the ball closer to the body and reducing the radius of rotation of the ball from the rotational axis through the body (Lees, 1984). Thus as a result of the ball size, release velocities are reduced and the ranges of ball flight are restricted. This means that less space is required for these games and in particular games such as netball, volleyball and basketball can all take place within a relatively small indoor area. Large heavy 'medicine' balls have in the past been popular for exercise and strength training. To aid catching in wet or cold conditions, gloves are often worn. The goalkeeper in soccer has long been observed to do this, as have players in Gaelic football. More recently the New Zealand national rugby team were observed to wear gloves during an international match against the British Lions. Protective mitts are also worn in baseball, softball, and gauntlets in hockey in order to protect against the forces of impact with the ball. Sports balls which are used primarily with the feet tend to be of the size and weight suitable for foot contact. The leg is stronger, and can move less quickly than the hand, therefore the weight of the kicked ball can reasonably be greater than the thrown ball. The soccer ball is a good example. With a diameter of 0.22 m and a mass of 0-435 kg it allows the characteristics of the kicking foot to be optimally used. Similar shapes and masses are found in the Rugby ball and American football, although the latter is lighter and is used also by the hand for one-handed throws. Release velocities in all three sports have generated velocities of 30 m/s in soccer (Plagenhoef, 1971), 34 m/s in rugby (Aitchison and Lees, 1983) and 30 m/s in American football (Kermond, 1979). The size of the playing areas are similar in all three cases, and until recently this meant that they were all constrained to outdoor locations. Of ergonomics interest is the variation in the ball size used for younger players. Both the ball size and mass are reduced for junior teams in the field games just referred to, the full sized ball only being used for adult teams. In most cases changes in ball size and mass cannot be made to account for individual differences in hand size. The ellipsoid shape of the Rugby and American football has another advantage. Introduced primarily for ease of handling in a game in which the ball is both handled and kicked, its shape enables a degree of stability to be generated in flight. Spin about the longitudinal axis is responsible for 'spin stability' and is a characteristic feature of skilled kicking in rugby and skilled throwing in American football. The use of racquets and other striking implements adds a new dimension to the size and mass requirements of sports balls. It has already been remarked that the hand can generate higher velocities than the foot, and this is because of the greater number of segments involved in the sequential build-up of velocity. With an implement extended to the arm as an extra segment the velocities generated are potentially even greater. In golf, for example, the club head velocity at impact is 70 m/s (Daish, 1972). Such high velocity impacts would produce enormous forces and torques on the musculature of the body if it were not for the mass of the ball being kept low. Thus in golf, squash, racquetball, badminton and tennis (0.06 kg) the ball mass is considerably lower than in hand or foot sports. In the case of baseball and cricket, the mass of the ball is higher (0" 16 kg) but the striking action is two-handed and the length of the bat is restricted. Despite the reduced ball mass, forces and torques generated can be high. Hatze (1976) found that torques generated in baseline shots in tennis can be as large as 23 Nm. In competitive racquet games these forces and torques can lead to injury, and a common complaint is 'tennis elbow' - an inflammation of the lateral epicondyle of the humerus. The usual cure is rest, but its occurrence can be prevented by using a racquet and style of play which reduce the force loadings on the forearm. In games where the ball mass or projectile is extremely light (table tennis and the shuttlecock in badminton) the forces and torques generated on the body are considerably reduced, but, as a consequence, both games are dominated by the aerodynamic forces acting on the projectile in flight. The performance characteristics in these cases are a direct result of the materials used for their manufacture. Materials and construction Many sports balls have traditionally used the materials and methods of construction available at the time of the conception of the game, although recent advances in materials technology have enabled changes to be made, Applied Ergonomics December 1984 267 Ergonomics in sport often improving the performance of the ball and at the same time reducing its cost. Materials Leather has always been a traditional material and its continued popularity in many forms of manufactured goods is a testament to its versatility. It is often favoured due to its combination of durability, pliability, softness of feel and resistance to wear, tearing and splitting. Ball softness is an important quality where contact is likely with the unprotected parts of the body. Leather used to construct modern sports balls is often treated to prevent water absorption, fungal growth and in the case of the rugby ball to enhance grip when wet. Synthetic laminate materials are now seriously challenging the dominance that leather has had for ball manufacture, as similar qualities can be produced in these materials. Plastics have been used for many years to mass-produce cheap versions of sports balls but they have generally lacked the weight or softness of the traditional materials. In games where either leather or synthetic materials are allowed by the rules, investigations as to their various merits have been undertaken. Mathers and Flatten (1982) measured the rebound resilience of leather and synthetic basketballs on four different types of playing surface. They found that although the leather ball rebounded significantly higher on all surfaces than the synthetic ball, both male and female subjects were unable to perceive any visual differences between two types of bali. In a similar experiment, Eccles (unpublished observations, Liverpool Polytechnic 1980) investigated the rebound resilience of plastic and two weights of leather netballs. It was found that there was no significant difference between the heavy leather and plastic balls, and the light leather ball rebounded less than the others. However, the internal pressure of the ball affected its resilience and in netball this is specified only in vague terms. When blown to a higher pressure the plastic ball produced a greater rebound height than did the leather ones. Two games deserve special mention with regard to materials used. In badminton the projectile has traditionally been made of leather covered cork and feathers. Shuttlecocks of these materials are still favoured by tournament players, although the cheapness and robustness of the modem plastic and foam version is preferred for practice. This dual use is typical of the regard given to the different materials used and has important implications for players. The two types of shuttlecock have different flight characteristics and so skills are developed under one set of conditions while the skills are used in competitive matches under a different set of conditions. The differences may be small but become more and more important as the playing level increases. A lack of consistency in manufacture may also produce similar effects. Golf has had an interesting history of ball materials and construction which is well described by Cochran and Stobbs (1968). Before the game had come under the guidance of a controlling body, the golf ball was a leather pouch tightly packed with feathers. The cheaper version of the time was a ball shaped from a special type of wood. This had better flight properties, and being cheaper soon became accepted. The modern golfball appeared in about 1900, and it was constructed with rubber thread tightly wound around a solid core. This was encased in a durable cover, which is now plastic. Variations in the flight characteristics of the ball can be produced by varying the tightness of the rubber windings. Balls which are more tightly wound are termed high- compression balls. They not only fly further but they produce a harder impact and an unpleasant shock force which is transmitted to the hand. Construction Sports balls are constructed so that they are either hollow or solid. Hollow balls have a large size to mass ratio. They can be made large as in the case of the basketball, to enable catching and reduce throwing velocities, without incurring a penalty of increased mass. Hollow balls generally have little form or structure of their own and are pressurisod to provide this. The degree of internal air pressure also affects their resilience, i e, the height to which they will bounce. In virtually all cases the laws of the game def'me the acceptable range of internal pressure, and the resilience of the ball is quantified by its coefficient of restitution. This value for a wide variety of sports balls is given by Plagcnhoef (1971) and Hay (1973). The limits set for the coefficient of restitution refer to the playability of the ball at the lower level, and to safety considerations at the higher level. If the ball is insufficiently resilient then too much energy is required to play with it (as with a squash ball on a cold day). A bali which is too resilient is also too hard and this will cause large impact forces when in contact with any unprotected part of the body. Balls constructed with a solid interior tend to be small in size, so that their size to mass ratio is appropriate for the game Golf, hockey, baseballs and cricket balls are good examples. The baseball and cricket balls are both involved with striking and hand catching, and with the high velocities generated, injuries to the hand (as well as other parts of the body if mis- caught) can occur. In baseball padded gloves are used to protect the hand, while in cricket special catching techniques are adopted in order to reduce the impact force. In indoor racquet sports where the bali is small, eye injuries are becoming more common. Existing eye protection devices often fail to prevent the ball from entering the eye socket. As a result an American Society for Testing Materials standard has been issued to cover eye protectors (Sports Medicine Bulletin 1983). The golf ball is characterised by two official sizes, the American ball of diameter 41-1 mm and the English ball of diameter 42-7 mm. In order to conform to size and mass restrictions, the size of the inner core used must vary. This in turn will lead to a difference in moment of inertia of the ball which will affect its rotational velocity when struck off centre. Cochran and Stobbs (1968) considered the various merits of each and concluded that the larger ball tends to fly higher and as a consequence carry less far. Although small differences in performance do exist, it was felt that these are marginal compared with the day-to-day variations in a player's own performance. This is one difference in design which should not show any resultant differences in practice. The surface characteristics of a ball may have a marked effect on performance. The golf ball described above has a dimple depth which is very carefully controlled so as to give it optimum aerodynamic characteristics. The backspin 268 Applied Ergonomics December 1984 [...]... racing cyclists Franks, I.M t983 Communication to the Sport and Science Conference (University of Liverpool) Computer assisted sports evaluation 1980 In: Lubich,T., and Venerando,A.(Eds) Sports Cardiology Aulo Gaggi, Bologna Physiological classification of sports activities and cardiovascular function GetUnan, L.R., Ward, P., and H ~ , R.D 1982 MedSciSports and Exercise, 14, 229-234 A Dal Monte, A., Leonardi,... Ergonomics in sport Gregory, R.S., and Lees, A 1981 Proceedings Sport and Science (Crewe and Alsager College) The quantification of sailboard performance In: Burwitz, L., Lees, A., ReiUy, T., and Sanderson, F.H (Eds) pp 185-194 Hatze, H 1976 Med Sci Sports, 8, 88-95 Forces and duration of impact, and grip tightness during the tennis stroke Hatze, H 1983 J Sports Sciences, 1, 3-12 Computerisation of sports... training: design and validation of a prototype Ryan, A.J., and Allman, F.L 1974 Sports Medicine Academic Press, New York Sanderson, F.H 1981 In" Reilly, T (Ed) Sports Fitness and Sports Injuries Faber and Faber, London Injuries in racket sports, pp 175 182 278 Applied Ergonomics December 1984 Sanderson, F.H., and Way, K.P.M 1977 Brit J Sports Med ! 1, 188 The development of' objective methods of game analysis... Applied Ergonomics December 1984 275 Ergonomics in sport Berryhill, R.A., and Wilfiams, K.R 1984 Med Sci Sports Exercise, 16, 123 (Abstract) Physiological responses to the PO 2 Aerobic Exerciser Bishop, P.J 1976 Ergonomics, 19, 451-464 Head protection in sport with particular application to ice hockey Bishop, P.J., Kozey, J., and Caldwell, G 1982 Phys Sports Med, 10, 63-69 Performance of eye protectors... ski bindings In: ASME International Conference on Medical Devices and Sports Equipment, San Francisco, 18-20 August Johnson, R.J., and Pope, M.H 1982 Phys SportsMed, 10, 49-55 Ski binding biomechanics Johnson, R.J., Pope, M.H., and Ettlinger, C.F 1974 JSportsMed, 2, 299-367 Ski injuries and equipment function Jones, C.M 1979 Harpers Sports, 15 March, 20-24 The evolution of racket design Lees, A 1984... surface, depending instead on the feel of an arbitrary heel plant into the ground The progress of polymer technology and the growth of synthetic surfaces for outdoor sports Ergonomics in sport (Tipp and Watson, 1982) may eventually render such subjective judgements obsolete The introduction of technological aids to sport is based on the initiative of the relevant international federations Usually the innovation... and Saraniti, A 1982 Med Sci Sports and Exercise, I4, 368-375 The nature of torque 'overshoot' in Cybex isokinetic dyamometry Sharp, R.L., Troup, J.P., and Costill, D.L 1982 Med Sci Sports and Exercise t4, 53-56 Relationship between power and spring freestyle swimming Soong, T.S 1974 In: ASME Mechanics and Sport Bluestein, J.L.(Ed) 85 100 An optimally designed archery Sports Medicine Bulletin 1983... Weightman, D., and Brown, R:C 1975 BritJSportsMed, 9, 136-141, Injuries in eleven selected sports Whitman, G 1974 In: Biomechanics IV Nelson R.C and Morehouse, C.A Ergonomics in sport (Eds) University Park Press, Baltimore, pp 243-249 Biomechanical research and release bindings in alpine skiing Wicks, J.R., Oldridge, M.B., Cameron, B.J., and Jones, N.L 1983 Med Sci Sports and Exercise, 15, 224-231 Arm... Wheatley, D.W 1976 BritJSportsMed, 10, 26-34 Joint mobility changes due to low frequency vibration and stretching exercise Atwater, A.E 1979 Exercise and Sport Sciences Reviews, 7, 43-85 Biomechanics of overarm throwing movements and of throwing injuries Bar-Or, O 1981 Symbiosis, 13, 157 172 Le test anaerobic de Wingate a cricket ball Bayley, K., and Reilly, T 1984 Proceedings Society of Sports Sciences Conference... needed to combat the specific hazards presented in some sports Motor racing suits may need to offer cooling as well as fire proofing because of the heat stress and risk of fire involved Many machine sports also require the wearing of ear protectors by pit staff as well as drivers because of the high noise levels experienced Wet suits for aquatic sportsmen enable users to tolerate sustained periods of