Personal and ubiquitous computing vol 9 issue 1 jan 2005

Pers Ubiquit Comput (2005) 9: 1–5 DOI 10.1007/s00779-004-0259-x O R I GI N A L A R T IC L E Andrea Szymkowiak Ỉ Kenny Morrison Ỉ Peter Gregor Prveen Shah Ỉ Jonathan J Evans Ỉ Barbara A Wilson A memory aid with remote communication using distributed technology Received: October 2003 / Accepted: 15 February 2004 / Published online: April 2004 Ó Springer-Verlag London Limited 2004 Abstract Electronic memory aids have been used successfully to give reminders to individuals with memory problems These aids usually present short action reminders that are acknowledged by the user The recent enhancement of handheld computers with wireless technology has rendered them multi-functional and presents an opportunity to be exploited to meet the demands of the user This paper describes the architecture of an electronic memory aid system we have developed and are currently evaluating with memory-impaired participants In addition to providing action prompts, the developed system allows data entry not only on the device itself, but also from other stations Hence, the memory-impaired user and third parties can remotely enter data into the device, depending on the skills of the user The system also remotely monitors users’ acknowledgements of reminders and allows third parties to initiate further actions where appropriate Keywords Elderly Æ Memory-impaired users Æ Personal digital assistant Æ Remote communication A Szymkowiak (&) Division of Psychology, School of Social and Health Sciences, University of Abertay Dundee, Dundee, DD1 1HG, UK E-mail: shtas@abertay.ac.uk K Morrison Ỉ P Gregor Applied Computing, University of Dundee, Dundee, DD1 4HN, UK P Shah Ỉ J J Evans Ỉ B A Wilson The Oliver Zangwill Centre, Princess of Wales Hospital, Lynn Road, Ely, Cambridgeshire, CB6 1DN, UK Introduction: designing for non-average people Memory problems are often associated with ageing [1] and they are among the most common effects of brain injury Electronic memory aids have been successfully used to provide action cues to people who have problems remembering everyday tasks such as taking a shower or preparing tea [2] The provision of short cues is usually sufficient rather than a detailed description of the action [3] to remind users of the task The efficiency of electronic devices as memory aids has been evaluated for numerous devices such as a pager [4], mobile phone [5], the Voice Organiser (handheld dictaphone) [6], and handheld computers or personal digital assistants (PDAs) [7, 8, 9, for a review see 10] The pager, which requires the touch of a button to acknowledge an action prompt, is effective for the memory-impaired user because it is simple to use [11] However, learning to use electronic organisers often produces great problems for this user group [12] and may require prolonged or repeated training [8] In conjunction with research that shows that memoryimpaired people benefit from errorless training procedures [13], it is evident that the training required to learn how to use the electronic memory aid should be minimal and should produce as few errors as possible In contrast, current time-management software running on PDAs requires at least some training for the average user Although the ease of use of such software applications varies across the range of devices available and the platform used (e.g EPOC/PalmOS/ PocketPC/Symbian), they are not designed for memory-impaired or elderly people This is crucial given the suggestion that memory impairment reduces the ability of users to build conceptual models of the working interface [14] and that older people might experience a decline in working memory [15] The need for a customised interface for specific user groups is, however, highlighted by other researchers [9] Their study showed that customising the interface of PDAs for a group of brain-injured users enabled them to successfully use these devices as memory aids Based on these reported findings we surmise that the use of electronic devices as memory aids presents a challenge for the memory-impaired users Two major factors to be considered are the ease of the interaction with the device and, related to this, the degree of customisation required for a particular user group Additional usability issues for the use of small portable devices are also essential: a report on WAP usability (Wireless Application Protocol—the technology used to access the Internet from mobile phones) [16] gives detailed evidence of the problems of creating usable systems for small screens found on mobile phones and PDAs for average users Scrolling pages, screen layout and the use of images and text all contribute to a difficult usability problem which can only complicate the use of these technologies as an external memory aid for the non-average, e.g the elderly or memory-impaired user The elderly user group may also experience declining visual acuity, contrast sensitivity and reduced sensitivity to colour, particularly blue-green tones (for a review see [17]), all of which make a small PDA interface difficult or impossible to see When combined with difficulties in control of fine movement [18] and the impact this would have on the ability to manage a small touch screen device, older, memory-impaired people present a user group with very specific needs in this design area The readiness of users to take up assistive technology is naturally another component that affects its use Besides insight into the need to use a memory aid [9], the support of family and professional carers can be of great importance [19] The possibility of integrating relatives or professionals in the assistive process may facilitate the use of new technology It is suggested that this can be achieved with the implementation of a remote communications system, the features of which we will discuss in the next sections 2.1 The design rationale for the PDA as memory aid For the memory-impaired or elderly user, the factors discussed in the introduction suggest an interface with clearly displayed functionality that minimises the load on working memory This implies intuitive usability that results in minimal training and visibly maintains the structure of the system at all times, avoiding the use of deep menu structures, as these are problematic for elderly users [20] Given the hardware limitations of small handheld devices, such as reduced display size, this presents a major design challenge The memory aid/ PDA that we are currently using, a Siemens SX45, is running the Windows CE 3.0 Pocket PC operating system The PDA is equipped with a 240 · 320 pixels (approx 60 · 78 mm) touch screen, a non-reflective TFT LCD with 65,536 colours The PDA weighs about 300 g and its dimensions are 124 · 87 · 26 mm We decided that four major functions should be clearly visible on the default display A menu structure was not deemed useful to avoid users becoming disoriented on the small display The device in Fig depicts the interface of the PDA we are currently evaluating with users Four major A memory aid with remote communication We have developed a memory aid system that we are currently evaluating with memory-impaired people in a rehabilitation clinic The memory aid system consists of a PDA that the memory-impaired user can operate but that can also be remotely accessed by third parties on a PC with access to the Internet In the latter case, the user would contact the administrator or carer to enter data into a central database on the Internet for them and thus is in control of which data are entered Data are periodically synchronised between the device and the central Internet database, and thus can be looked up by the memory-impaired person on the device as well as by a third person monitoring this database In the following section we will describe the rationale used in the design of the PDA as well as that behind the idea of remote communication Fig Shown is a picture of the prototype interface currently evaluated The device comprises four major functions, 1) looking at today’s entries, 2) looking at a calendar to select a day, 3) accessing diary info (such as birthdays and people), and 4) modifying the diary, which can be accessed by tapping the virtual ‘‘buttons’’ on the interface functions, 1) looking at today’s entries, 2) looking at a calendar to select a day, 3) accessing diary info (such as birthdays and people), and 4) modifying the diary have been selected It was suggested that the user would mainly be interested in viewing today’s task, as this is the behaviour that is most relevant for them Thus, the button to activate this function was placed in a prominent position on the display The user can go backwards or forwards by a day by tapping the buttons labelled ‘‘-Day’’ and ‘‘+Day’’ respectively A click on the clock in the right upper corner displays the current time The user can always go back to this default display, irrespective of where they are, by the tapping of, at the most, two buttons Scrolling through the Entry list in the middle of the screen allows users to browse through entries The length of the list depends on the number of entries and therefore is dependent on the habits of a particular user For all other displays involving the scroll bar the number of pages to scroll through has been limited to at most 1/2 to keep scrolling to a minimum It is suggested that the acknowledgment of action prompts by the user allows easy interaction with the device, usually by the tap of a button upon receiving a text or voice message As handheld computers are usually equipped with touch screens, virtual buttons that are sufficient in size can be displayed on the screen Thus, to a certain extent, the design of the interface can actually circumvent hardware limitations such as tiny buttons As depicted in Fig 2, the user has two alternatives in responding to an alarm occurring together with a reminder: either to acknowledge it with no further reminders or to acknowledge it with the option to be reminded again by tapping one of the two ‘‘buttons’’ This gives the user control over the presentation of reminders and accounts for situations in which the user cannot comply with an action prompt because of situational factors; for example, the user could be using the bathroom or sitting in a movie theatre when an alarm occurs Being able to defer a reminder allows the user to select a place and time to act on the reminder Acknowledging action prompts appears to be a simple task However, interacting with the device to enter events or data appears to be a greater challenge, as the reliance on menu structures, even if shallow, hides some of the functions of the device at certain times, which might be problematic for users with memory problems While we strive to obtain maximal usability in the design of the PDA as a memory aid, depending on the characteristics of the user, wireless technology can facilitate the interaction between the user and the device by creating flexibility for data entry Generally, memory-impaired users have carers or relatives who also function as carers Usually, individuals with severe memory problems regularly visit a clinic in which administrative and/or health care personnel can take care of their needs Thus, task sharing between the user and carers or administrative staff regarding the interactions with the PDA/memory aid can be achieved, alleviating the problems users might have when learning how to use the device In particular, this task sharing can be achieved by allowing carers or administrative staff to access the PDA over the Internet, while the user is interacting with the device, thereby creating a remote communication system The system that we have developed incorporates this facility and we will discuss its architecture next 2.2 The architecture of the remote communication memory aid Fig Shown is a picture of the prototype interface currently evaluated The user has two alternatives in responding to an alarm occurring together with a reminder: either to acknowledge it with no further reminders or to acknowledge it with the option to be reminded again by tapping one of the two ‘‘buttons’’ The recent development of PDAs using wireless technology has rendered them multi-functional and presents an opportunity to be exploited to meet the demands of the user For example, in addition to providing action prompts, a PDA could allow data entry on the device itself but also from other stations (see Fig 3) Hence, users, carers or even administrative staff can enter data remotely into the device, thus creating the flexibility of data entry depending on the characteristics and needs of the user A typical interaction scenario could be as follows: the memory-impaired user has acquired the skill to acknowledge reminders by tapping a button on the device, but data entry presents a challenge to be met at a later stage For the present, a carer or administrative staff can enter reminders (for example, a reminder for tonight’s dinner) into the user’s PDA using a browser on his PC to enter the reminder into a database on a server Fig The architecture of the memory aid (PDA) with remote communication Data entry and monitoring can be achieved remotely from various stations, by administrative personnel, carers or relatives equipped with PCs with access to the Internet Both data entry and monitoring are achieved by synchronisation between the PDA and the server In this case the memory-impaired user would contact a carer to enter the data for them The data entries are synchronised between the server database and the PDA at specific times, thus allowing for relatively short intervals between the time of data entry and the time the prompt is due Repeated action prompts on a daily or weekly basis can be entered into the device, as users often request reminders for routine actions such as taking medication, and is functionality which has been implemented in recent memory aids [9, 21] Once the user has mastered one particular function of the device, s/he might attempt to learn additional functions For instance, s/he might enter reminders or other data such as details on individuals, thus reducing the need for the intervention of the carer or administrative staff In addition to being able to enter reminders from various stations, the fact that reminders can be entered using an ordinary PC circumvents the problems of small display sizes to enter detailed information For example, once the user has mastered data entry functions, s/he could enter contact details for a particular person such as their name and phone number into the PDA If more details are required, the carer or even the user can enter this additional information using a PC with a large screen size Thus, different data can be entered using different devices but the user of the PDA can access them at any time The user controls who enters which data, depending on their needs and skills We have discussed issues pertaining to data entry into the device in the previous section However, having distributed technology also allows carer or administrative staff to monitor remotely if a user has acknowledged a reminder and—if that is not the case—to initiate further actions such as contacting a carer A typical scenario could be the user failing to acknowledge a reminder prompting him/her to take medication The device would then prompt the user again to take the medication If the user still does not acknowledge the reminder, the device would automatically update the server to indicate that this reminder has not been acknowledged Once this has happened, administrative staff could take further action such as calling the user or the carer At present, the acknowledgement of reminders has to be checked by a user (administrative staff) who can take appropriate action and contact a carer if necessary but these tasks could be further automated in such a way that actions can be initiated from the server station, without the intervention of a third party For example, once the system has detected that the user has not responded to a high priority reminder (e.g ‘‘take the yellow heart pill now’’) a call could be automatically initiated on the server end, contacting a carer with an automated call to his (mobile) phone to ask him to contact the user This functionality provides the carer with the means to monitor the user’s behaviour if necessary and may thus alleviate the worry of the carer when the user does not acknowledge a particular reminder It should be noted that the memory aid shares a drawback with most other electronic prompting devices, i.e that acknowledging a reminder does not necessarily equate to actually executing the action The user could acknowledge an action reminder, but then, being temporarily distracted by other events, still forget to execute the action or even intentionally omit to execute it The development of systems that monitor behaviour, such as in telemonitoring systems [e g 22] and ‘‘smart’’ homes, integrated with the use of prompting devices may be a possible answer to this challenge Conclusions The review on the usability of electronic devices as memory aids in this paper highlights difficulties for memory-impaired users in the learning required to use such devices In addition, other researchers have pointed out serious usability challenges with respect to design of WAP-based interfaces for the average user However, the degree to which the device allows task sharing between the user and a carer or administrative staff can greatly facilitate the challenges users encounter when using the device This can take the pressure off the user to use all functions of the device at once Instead, the users can slowly get accustomed to the functionality of the device at their own pace and have at the same time the assurance that carers can take care of their needs, while they take advantage of the functionality with which the device provides them We conclude that there is great potential in the use of recent technologies by non-average users such as elderly or memory-impaired people, if customisation and interface design reflect the needs and demands of the user Automatically contacting the carer if the user fails to acknowledge reminders would be a further extension of our memory aid system, and is to be implemented at a later stage Exploiting distributed technology and the advantages it provides in data entry and monitoring can contribute to a usable system With the advance of multimodal devices that allow picture/video transmission in addition to text- and graphics-based information, the future potential of distributed communication systems for social care is huge At present, our system is mainly graphics based but new technologies should also allow the use of speech or audio based interactions Evaluating our current system with users is showing the extent to which we have produced a usable and efficient memory aid system that may incorporate more sophisticated technology in the future Given that memory impairments are related to ageing [1] combined with an increase in the number of older adults from 11 to 14 million within the next 25 years in Britain [23], the use of technologies which can maintain independence for older and memory impaired people may result in huge savings for the health care system Acknowledgements This research is funded by Grant 2006/394 from the Health Foundation, Older People Programme References Huppert FA, Johnson T, Nickson J (2000) High prevalence of prospective memory impairment in the elderly and in earlystage dementia: findings from a population based study App Cog Psych 14:S63-S81 Wilson BA, Evans JJ, Emslie H, Malinek V (1997) Evaluation of NeuroPage: a new memory aid J Neurol Neurosur Psych 63:113–115 Harris JE (1992) Ways to help memory In: Wilson BA, Moffat N (eds) Clinical management of memory problems, Chapman & Hall, London Wilson BA, Emslie HC, Quirk K, Evans JJ (2001) Reducing everyday memory and planning problems by means of a paging system: a randomised control and crossover study J Neurol Neurosur Psych 70:477–482 Wade TK, Troy JC (2001) Mobile phones as a new memory aid: a preliminary investigation using case studies Brain Inj 15:305–320 van den Broek MD, Downes J, Johnson Z, Dayus B, Hilton N (2000) Evaluation of an electronic memory aid in the neuropsychological rehabilitation of prospective memory deficits Brain Inj 14:455–462 Kim HJ, Burke DT, Dowds MM, George J (1999) Utility of a microcomputer as an external memory aid for a memory-impaired head injury patient during in-patient rehabilitation Brain Inj 13:147–150 Kim HJ, Burke DT, Dowds MM, Robinson Boone KA, Park GJ (2000) Electronic memory aids for an outpatient brain injury: follow-up findings Brain Inj 14:187–196 Wright P, Rogers N, Hall C et al (2001) Comparison of pocket-computer memory aids for people with brain injury Brain Inj 15:787–800 10 Inglis EA, Szymkowiak A, Gregor P, Newell AF, Hine N, Shah P, Evans JJ, Wilson BA (in press) Issues surrounding the usercentred development of a new interactive memory aid Int J Univ Acc Info Soc 11 Wilson BA, Emslie HC, Quirk K, Evans JJ (1999) George: learning to live independently with NeuroPage Rehab Psych 44:284–296 12 Wilson BA, Moffat N (1984) Rehabilitation of memory for everyday life In: Harris JE, Morris PE (eds) Everyday memory, actions and absent-mindedness, Academic Press, London 13 Evans JJ, Wilson BA, Schuri U et al (2000) A comparison of ‘‘errorless’’ and ‘‘trial-and-error’’ learning methods for teaching individuals with acquired memory deficits Neuropsych Rehab 10: 67–101 14 Zajicek M, Morrissey W (2001) Speech output for older visually impaired adults In: Blandford A, Vanderdonckt J, Gray P (eds) Interaction without frontiers, in: Joint Proceedings of HCI 2001 and IHM 2001, Lille, France, September 2001 15 Salthouse TA (1994) The ageing of working memory Neuropsychology 8:535–543 16 Ramsey M, Nielsen J (2000) WAP usability de´ja` vu: 1994 all over again Nielsen Norman Group, Fremont, CA 17 Hawthorn D (2000) Possible implications of aging for interface designers Interact Comput 12:507–528 18 Vercruyssen M (1996) Movement control and the speed of behaviour In: Fisk AD, Rogers WA (eds) Handbook of human factors and the older adult, Academic Press, San Diego, CA 19 Kapur N (1995) Memory aids in the rehabilitation of memory disordered patients In: Baddeley AD, Wilson BA, Watts FN (eds) Handbook of memory disorders, Wiley, Chichester, UK 20 Freudenthal D (2001) Age differences in the performance of information retrieval tasks Behav Info Technol 20:9-22 21 Wright P, Rogers N, Hall C, Wilson B, Evans J, Emslie H (2001) Enhancing an appointment diary on a pocket computer for use by people after brain injury Int J Rehab Res 24:299– 308 22 Doughty K, Costa J (1997) Continuous automated telecare assessment of the elderly J Telemed Tele 3:23–25 23 HMSO (1998) Population trends Her Majesty’s Stationary Office, London Pers Ubiquit Comput (2005) 9: 6–19 DOI 10.1007/s00779-004-0269-8 O R I GI N A L A R T IC L E James F Knight Ỉ Anthony Schwirtz Ỉ Fotis Psomadelis Chris Baber Æ Huw W Bristow Æ Theodoros N Arvanitis The design of the SensVest Received: 29 September 2003 / Accepted: 15 March 2004 / Published online: 26 June 2004 Ó Springer-Verlag London Limited 2004 Abstract The SensVest is an item of wearable technology that measures, records and transmits aspects of human physical performance such as heart rate, temperature and movement The SensVest has been designed for use by science teachers and students to meet their requirements This paper reports the stages undertaken to design the SensVest, from determining appropriate methods of assessing human performance, to considerations of mounting the technology on the body Trials have shown that concessions need to be made with ease of use and cost to ensure that the data collected is reliable and usable, with an awareness of the sensors’ limitations By designing the SensVest with the wearer in mind a system has been developed that is comfortable, does not inhibit normal performance and is wearable User trials have shown that meaningful, reliable and useful data can be collected using the SensVest Keywords SensVest Ỉ Ergonomics Ỉ Wearable computer Ỉ Design Ỉ Energy expenditure Introduction This paper presents work undertaken as part of a European project to investigate science teaching in schools The paper is split into two main parts The first part sets up the aims of the project and discusses the rationale for choices made in deciding what technology will be incorporated in the wearable so that it meets the aims of the project The second part discusses the design J F Knight (&) Æ A Schwirtz Æ C Baber Æ H W Bristow T N Arvanitis Department of Electronic, Electrical and Computer Engineering, School of Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK E-mail: j.f.knight@eee-fs7.bham.ac.uk F Psomadelis ANCO S.A R&D Division, 44, Syngrou Avenues, 117 42 Athens, Greece and ergonomic considerations in producing the wearable and the evaluations of the prototypes before presenting the final design Part 1: Requirements of the SensVest 2.1 The SensVest The SensVest was originally designed for use in the Lab of Tomorrow project.1 While the Lab of Tomorrow focussed on the collection of data for education, it is proposed that the resultant design offers a means of collecting data in a wide variety of work-related studies and could be of interest to ergonomists, sports scientists and members of the medical profession There are three ways in which data from real world activities can be recorded The first is to effectively make the world the laboratory This requires that the environment be fitted with sufficient sensors to monitor, measure and record human activities, e.g camera-based systems Commercially available vision systems are typically very expensive, although the Lab of Tomorrow consortium has successfully developed a low-cost tracking system However, these systems require that activity be performed within the calibration volume of space covered by the vision system, which has implications for the type of activity that can be analysed Furthermore, the vision system could require post-processing to be able to derive human performance data from the images Alternatively, people could be bought into a laboratory and asked to perform examples of everyday tasks While such an approach might be more cost-effective, in terms of equipment, it produces problems relating to the ‘‘naturalness’’ of activities that can The Lab of Tomorrow project is a European project with partners from Greece, Germany, Italy, Austria and England The aim of the project is to develop technologies that can be used to enhance the learning experience Specifically, the aim is to measure scientific variables from everyday activities, which can be used as the basis of science lessons be recorded in the laboratory For example, asking someone to perform tasks under observation in the laboratory could lead to a different activity than that observed in the normal environment Furthermore, people could be limited as to their range of movement in that they must remain within the envelope of the sensors A third approach involves people effectively carrying the laboratory with them In this scenario the person has the sensors to measure relevant scientific variables with them at all times In this approach, the sensors not bind the person to a location and thus expands the envelope of situations to which the sensors can be taken The aim of this paper is to report the design aspect of the wearable system developed for the Lab of Tomorrow project Specifically, the paper will focus on aspects of mounting the technology on the body and the ergonomic considerations taken into account when doing this In effect this paper demonstrates the processes undertaken to get the appropriate technology on the body in a suitable manner Indeed, a major aspect of this paper is to determine what the terms ‘‘appropriate’’ and ‘‘suitable’’ mean in the context of developing a wearable system 2.2 Defining technical requirements Having the sensors with the person at all times was selected as the approach most appropriate to measure activity in the real world Within this approach there are two sub-methods: the first is to have the sensors embedded into the tools or equipment that the person uses; the second is to attach the sensors to the people themselves This second option is beneficial in that it ensures that the sensors are with the person at all times, can be used to measure activities and not require the manipulation of some artefact Consequently, these sensors act passively, recording data without requiring that the users perform some extraneous activity Attaching technology to the body has received considerable interest in the form of wearable computing [1, 2] Within the area of wearable computing wearing sensors is not novel A number of researchers have used body mounted sensors to try to determine such aspects as the wearer’s position, posture and activity state with the aim of developing computer systems that are context aware [for example 3, 4] Other wearable sensor systems have been developed to measure a range of physiological variables For example BODYMEDIA have produced the SensWear Pro Armband, which monitors skin and ambient temperature, the galvanic skin response and movement from a device which is worn on the upper arm This is marketed as a product for weight management, wellness, assisted living, fitness, sleep monitoring and scientific research The SensVest differs from these other wearable systems in that it has been developed specifically as a teaching tool As such it has been designed with the end user in mind (i.e a student) and the use of the data collected for the role of teaching Although the SensVest may ultimately use the same or similar sensors as those used in other systems the context of their use dictated that a specific product be designed and developed Many of the systems discussed above may be wearable but may not be suitable when the wearer is engaged in strenuous physical activity The positioning of the sensors is also important The SensWear records movement from a device on the upper arm; this would be unsuitable for situations where the wearer is engaged in considerable physical activity but with little arm movement, for example, cycling As such the design of the SensVest had to consider where, and in what situations, the device will be worn and also what data would be appropriate 2.2.1 Determining metrics Taking into account that the focus of the project is the development of a device for use by schoolchildren, discussions with educationalists and teachers were held to determine what aspects of performance they would like to record From these discussions two concepts were proposed The first involves measurements of human movement that can be applied to Newtonian physics with the emphasis on assessing variables such as: force, displacement, velocity and acceleration The second was a measure of the energy expended by a person while carrying out various tasks 2.2.1.1 Measuring movement The intention for measuring aspects of movement in this project is to apply the data to concepts underpinned by Newtonian physics As such measurements of displacement, velocity, acceleration and force are pertinent Measurements such as these in human movement applications come under the province of biomechanics An assessment of biomechanical techniques proffered numerous ways of assessing movement However, most of these methods involve using equipment, which is separate from the assessed performer and are set up in calibrated areas Examples of these systems may involve digitising a video or cine image, or they may use automatic opto-electronic tracking systems, which use either passive body markers (for example Kinemetrics, MacReflex, ELITE, Motion Analysis, Peak, Vicon and CODA) or active markers (for example, Selspot, IROS and Watsmart) However, as one aim is to be able to measure students performing everyday activities it was deemed inappropriate to restrict the student to one specific calibrated location (i.e a laboratory or classroom) As such, these systems were rejected The requirement was for devices that could be worn and transported into the real world This is achievable with the use of accelerometers Accelerometers incorporate a mass mounted on a cantilever beam or spring attached to a housing As the housing accelerates, because of its inertia, the mass lags behind, deforming the beam This deformation is measured either using strain gauges or piezo-electric devices, which gives a measure of the acceleration For this project accelerometers were deemed most appropriate, as they are small, lightweight, wearable and relatively cheap They can also be used to measure the accelerations of body segments (e.g arms and legs individually) and if mounted on the trunk, the acceleration of the body There are a number of considerations that must be taken into account when using accelerometers; for instance, they give no indication of a segment’s initial condition (i.e position, orientation or velocity) They are gravity sensitive This means that their output represents the vector sum of the gravity and kinematic acceleration To derive accurate acceleration additional information regarding segmental orientation is needed Without this additional information, the user must either assume that any movement was linear so that the gravity component can be subtracted using a resting value, or that the gravity component is negligible in relation to the acceleration measured by the movement of the body The accelerometer signal tends to drift over time causing a low-frequency noise effect that increases with time This means that the accelerometer has to be regularly calibrated If attached to clothing or the skin errors can occur due to the relative movement clothing or skin makes with soft tissue To overcome this problem the accelerometer must be mounted on the body as tightly as possible The accelerometer can be delicate and is easily broken if dropped so some care has to be taken when handling it These considerations dictate that the wearer be aware of the limitations Ultimately, the value of the data depends on the required accuracy of the user 2.2.1.2 Measuring the energy expenditure The most common method used in sports and exercise science is to measure the amount of oxygen consumed This involves collecting samples of gas breathed into a bag or directly into a gas analyser This method, though, was deemed inappropriate for this project, as the equipment is expensive and usually fixed to one location Portable devices exist [5, 6] but these are cumbersome to use, especially for long-term free movement [7] and as it involves attaching breathing equipment to the face it is uncomfortable and restricts verbal communication [8] 2.2.1.3 Measuring the heart rate Measuring the heart rate is a commonly used measure of assessing energy expenditure and is attractive as a direct linear relationship between the oxygen uptake and the heart rate at moderate to high intensities of exercise has been found [9] During physical activity aerobic respiration uses oxygen to produce energy Calculating the amount of oxygen consumed therefore gives an estimation of the energy expended during physical activity As a linear relationship has been found between oxygen uptake and heart rate at moderate to high intensities of exercise a measure of heart rate can be used to provide this estimate More accurate estimates for the prospective users of the SensVest (i.e adolescents) would involve using relationships developed from the same age range The heart rate max can be estimated using the equation: HRmax = 220 À age (in years) So, for example a 15-year old max heart rate is 205 Estimates of maximum oxygen consumption (VO2max) can be taken from published data Thus, the VO2max for 15-year old males is 59 ml/min kg [10] With an average body weight of 57 kg [11] an estimated VO2max for a 15-year-old male is thus 3.36 l/min Taking an average heart rate during a physical activity of, say, 160 bpm, for example, this translates into a heart rate of approximately 78% max A heart rate of 78% max relates to an oxygen consumption of approximately 70% VO2max [9], which corresponds to 2.35 l/min (i.e 70% of 3.36 l/min) For each litre of oxygen consumed approximately 20 kJ of energy is liberated Therefore, an estimation of oxygen consumption from heart rate can be used to estimate the energy expenditure For example, our 15 year old male basketball player with a heart rate of 160 bpm was expending energy at a rate of 47 kJ/min As such, estimates of energy expenditure based on the heart rate can easily be made 2.2.1.4 Methods of heart rate measurement Table shows a number of ways of measuring the heart rate that were considered for the SensVest In essence there are two main methods of measuring heart rate: one is to measure the pulse rate from an artery (for example, inserting the microphone, the pressure bulb and the plethysmography in Table 1), and the other is to measure the electrical signal that stimulates the heart to contract (for example, the lead ECG and the heart rate monitor in Table 1) Of the two methods, that of measuring the pulse was initially the most attractive These methods are generally cheaper and as they not involve attaching technology to the skin of the chest are more convenient in terms of pupils putting on the SensVest in environments where others may be present For the initial prototype of the SensVest the heart rate was measured using the insert microphone and the pressure bulb These methods involved attaching sensors to the wrist or hand and were attractive because they were cheap and easy to use Unfortunately, being affected by hand and finger movements they were found to be highly susceptible to noise during trials, and as such they were deemed unreliable Subsequent prototypes investigated the use of plethysmography, but this was also found to be unreliable (see Table 1) Therefore, the idea of measuring the pulse had to be discarded for that of measuring the electrical signal of the heart Using a lead ECG method proved promising; however it was not very practical Setting up the equipment and preparing the wearer was time-consuming and was uncomfortable for the wearer, specifically when the adhesive electrodes Table Measuring heart rate methods Method Technique Cost (£) Attachment point and method Power Comment/findings from trials consumption (mW) Insert microphone Microphone detects pulse on surface artery