Gait & Posture 49 (2016) 19–24 Contents lists available at ScienceDirect Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost Full length article Gait initiation time is associated with the risk of multiple falls—A population-based study Michele L Callisayaa,b,* , Leigh Blizzarda , Kara Martinc, Velandai K Srikanthb,a a Menzies Institute for Medical Research Tasmania, University of Tasmania, Hobart, Tasmania, Australia Southern Clinical School, Monash Medical Centre, Monash University, Clayton, Victoria, Australia c Cancer Council Victoria, Cancer Epidemiology and Intelligence Division, Melbourne, Victoria, Australia b A R T I C L E I N F O A B S T R A C T Article history: Received November 2015 Received in revised form 26 May 2016 Accepted June 2016 Aims: In a population-based study of older people to examine whether 1) overall gait initiation (GI) time or its components are associated with falls and 2) GI under dual-task is a stronger predictor of falls risk than under single-task Methods: Participants aged 60–85 years were randomly selected from the electoral roll GI was obtained with a force platform under both single and dual-task conditions Falls were ascertained prospectively over a 12-month period Log multinomial regression was used to examine the association between GI time (total and its components) and risk of single and multiple falls Age, sex and physiological and cognitive falls risk factors were considered as confounders Results: The mean age of the sample (n = 124) was 71.0 (SD 6.8) years and 58.9% (n = 73) were male Over 12 months 21.8% (n = 27) of participants reported a single fall and 16.1% (n = 20) reported multiple falls Slower overall GI time under both single (RR all per 100 ms 1.28, 95%CI 1.03, 1.58) and dual-task (RR 1.14, 95%CI 1.02, 1.27) was associated with increased risk of multiple, but not single falls (p < 0.05) Multiple falls were also associated with slower time to first lateral movement under single-task (RR 1.90 95%CI 0.59, 1.51) and swing time under dual-task condition (RR 1.44 95%CI 1.08, 1.94) Conclusion: Slower GI time is associated with the risk of multiple falls independent of other risk factors, suggesting it could be used as part of a comprehensive falls assessment Time to the first lateral movement under single-task may be the best measures of this risk ã 2016 Elsevier B.V All rights reserved Keywords: Gait initiation Gait Accidental falls Physical examination Older people Population based Introduction Falls occur in over 30% of people older than 60 years living in the community in a one-year period [1], and can result in injury, loss of independence and nursing home admission [2] Identified risk factors for falls include impaired physiological (e.g muscle strength, gait, balance) and psychological factors (e.g mood, processing speed and attention), with a greater number of impairments increasing the risk [3] However, falls remain a significant problem with further investigation of risk factors required in order to identify and prevent older people from falling Falls can occur during gait initiation (GI)—the transition stage from standing still to steady state walking [4] Previous studies have found the slower GI time is associated with impairment in * Corresponding author at: Menzies Institute for Medical Research Tasmania, University of Tasmania Private Bag 23, Hobart, Tasmania, Australia E-mail addresses: Michele.callisaya@utas.edu.au (M L Callisaya), Leigh.Blizzard@utas.edu.au (L Blizzard), Kara.Martin@cancervic.org.au (K Martin), Velandai.Srikanth@monash.edu (V.K Srikanth) http://dx.doi.org/10.1016/j.gaitpost.2016.06.006 0966-6362/ã 2016 Elsevier B.V All rights reserved both physiological and cognitive falls-risk factors [5], and prevention of a fall often requires a quick change in posture or a protective step Taken together these factors indicate that poorer GI time may provide a good summary measure of an individual’s falls-risk GI can be described by its three components: Time to the first lateral movement (FLM); FLM to when the lead foot leaves the platform; and from foot off to contact with the adjacent surface [5,6] GI time increases whilst performing a simultaneous task in older people [6], such as talking to another person This is thought to be due to the increased load on executive and attentional resources, which may be limited in older age, and result in slower GI The competition for attention between the cognitive and GI tasks may further increase risk of falls [7–9] Examining the individual components of GI under single and dual-task may assist in further refining the assessment of falls risk and design of effective intervention programs Previous findings have differed in the relationship between GI [8,10–12] or stepping tests [13] and falls risk, with some reporting an increased risk under single [12,13] or dual-task [8,11,12], while 20 M.L Callisaya et al / Gait & Posture 49 (2016) 19–24 others reported no association under single-task [8,10] Conflicting findings may be explained by the use of differing samples including volunteers [8,10] or residents from retirement villages [11–13] or by retrospective falls ascertainment, potentially leading to recall bias [8,10,11,13] To our knowledge there has only been one prospective study, where slower step execution times were associated with recurrent falls [12] This study included volunteers from retirement homes which may not be generalizable to all older people living in the community Therefore, in a population-based sample of older people the aims of this study were to examine whether: 1) overall GI time or its components were associated with falls 2) GI time under dualtask was a stronger predictor of falls risk than under single-task 3) Whether associations between GI and falls were independent of other physiological and psychological factors We hypothesized that overall GI time under dual-task would be the strongest predictor of falls independent of other falls risk factors Methods 2.1 Participants The sample consisted of 128 consecutive participants who completed the GI task from the Tasmanian Study of Cognition and Gait (TASCOG), starting in 2007 The overall larger TASCOG study (n = 431) commenced in 2005 and randomly selected residents from the Southern Tasmanian Electoral roll aged between 60–85 years using age- and sex-stratified random sampling Participants were excluded if they resided in a nursing home, were unable to walk without the use of a gait aid or if there were any contraindications to having a MRI scan Participants with Parkinson’s disease and dementia were excluded due their know effects on GI and falls The Southern Tasmanian Health and Medical Human Research Ethics Committee approved this study and written consent was obtained from all participants Measures 3.1 Gait initiation GI was measured under single- and dual-task using a 200 Hz AccuGait force-platform and Advanced Mechanical Technology Inc.-NetForce software as described previously [5] Participants stood on the force-platform with heels spaced by cm and at approximately a 10 degree angle [6] In the single-task condition participants were asked to start walking in response to a buzzer activated at random times Under the dual-task condition the participant was asked to count backwards in threes from a number that varied with each trial Six trials were performed for each task alternating between the two As previously described [5] we examined components of GI (see Fig 1), using a program written in Visual basic 6.0: Time from stimulus to FLM (change in mediolateral velocity of >100 mm/s in the centre of pressure towards the swing leg as detected by the force plate and provided by Netforce software); Transfer time: FLM to toe off of the leading foot (the second time velocity crossed mm/s after FLM); Swing time: time from toe off to foot contact (the beginning of a continual drop in vertical force that passed 75% of baseline) We also examined the overall time from stimulus to initial contact of the leading foot as this measures was found to be the most strongly associated with a falls risk score comprising of physiological measures [5] The median of the six trials was calculated as this was found to be the best summary index across trials [5] Fig Force plate data provided by AMTI-NETsoftware illustrating the components of gait initiation Legend: First (red) line = time to first lateral movement (change in med-lateral velocity of >100m/s); Second (blue) line = toe off (the second time velocity crosses mm/s after the first lateral movement; Third (green) line = foot contact of swing leg (the beginning of a continual drop in vertical force that passed 75% of baseline) 3.2 Falls Participants were sent a falls questionnaire and a pre-paid envelope every months for 12 months A fall was defined as ‘an unexpected event in which the participant comes to rest on the ground, floor or lower level’ [14] Participants were also asked to keep a falls calendar to record any falls If a participant did not return a questionnaire they were followed-up with a phone call Any participant not reporting a fall and returning fewer than 10 months of questionnaires was excluded Those who fell once during the 12-month period were classified as having a single fall and those that fell more than once were classified as having multiple falls 3.3 Physiological and psychological falls risk measures Physiological factors were measured using the short form of the Physiological Profile Assessment [15] (visual contrast sensitivity [dB] using the Melbourne Edge Test; proprioception (cm) using a lower limb matching task, with a vertical protractor placed between participant legs; isometric quadriceps strength [kg] using a spring gauge; simple reaction time (ms) using a light stimulus and press of a switch; postural sway (mm) using a swaymeter to measure body displacement at the waist level while standing on a foam mat for 30 s); gait speed (cm/s) was obtained using the 4.6 metre GaitRite mat as previously described [1] Psychosocial factors included: mood using the Geriatric Depression Scale (short version) [16] and scores >5 were classified as depressed; executive function/attention was assessed with the Victoria Stroop test (time to read a list of coloured words printed in non-corresponding colours of ink, e.g the participant reads the colour of ink, not the colour word) [17] and the Digit Symbol Coding subtest of the Weschler Adult Intelligence Scale—Third Edition (time to match a list of symbols with corresponding digits) [18] M.L Callisaya et al / Gait & Posture 49 (2016) 19–24 3.4 Other measures A standardised questionnaire was used to obtain participants medical history including any history of hypertension, diabetes mellitus, stroke, dementia and Parkinson’s disease 21 (p < 0.05); Fig and Table There was also a significant difference (p 0.05) 5.2 Gait initiation and single falls Data analysis Differences between those in the full study and those in the GI sub-study were calculated using chi squared analysis (x2) and ttests as appropriate Log multinomial regression was used to estimate the relative risk of single and multiple falls for GI (components and overall time) under single- and dual-task Gait initiation was presented in 100 ms units to more clearly describe associations for the regression analyses All models were adjusted for age and sex Other falls risk measures of physiological and psychological function were added to the models if associated with falls and the relevant variable changed the coefficient of the GI measure by more than 10% Analyses were conducted using STATA version 12.1 (StataCorp, TX, USA) Results Four participants were excluded (one person had a diagnosis of Parkinson’s disease and had missing falls data), leaving 124 participants Ninety four percent of participants (n = 117) returned all six questionnaires During the 12 months follow-up, 62.1% (n = 77) reported no falls and 37.9% (n = 47) reported any fall Of those who fell, 21.8% (n = 27) a single fall and 16.1% (n = 20) reported two or more falls Table provides the baseline characteristics of participants The mean age of the sample was 71.0 (SD 6.6) years and 58.9% (n = 73) were male Those not included were slightly older (p = 0.03), walked more slowly (p = 0.02), but had better proprioception (p < 0.001) and edge contrast sensitivity (p = 0.02) 5.1 Difference in gait initiation time under single and dual-task Overall GI under dual-task (mean 1224.2 ms, SD 307.9) was significantly slower than under single-task (1079.9 ms, SD 184.5) in the overall sample (p < 0.001), and for each category of falls After adjusting for age and sex there was no significant increase in the risk of a single fall for overall GI time (single-task: RR per 100 ms increase 1.07, 95% CI 0.88, 1.30; dual-task RR per 100 ms increase1.03, 95% CI 0.92, 1.15), or for any of its components (Table 3) 5.3 Gait initiation and multiple falls After adjusting for age and sex, slower overall GI time under single-task (RR per 100 ms increase 1.28, 95% CI 1.03, 1.58) and dual-task (RR per 100 ms increase 1.14, 95% CI 1.02, 1.27) was associated with increased risk of multiple falls For example the risk of multiple falls increased 28% per 100 ms under single-task and 14% under dual-task Slower time to FLM under single-task (RR per 100 ms increase 1.90 95%CI 1.23, 2.94) and slower swing time under dual-task (RR per 100 ms increase 1.44, 95%CI 1.08, 1.94) were also associated with multiple falls We tested whether the associations between GI and multiple falls were independent of other physiological or psychological falls risk measures In the majority of cases the addition of these other measures did not change the associations between GI and multiple falls The exception was for the addition of gait speed to the association between FLM and multiple falls under single-task The association was reduced, but slower time to FLM remained significantly associated with falls (RR 1.66 95%CI 1.01, 2.73) Discussion In this population-based study of older community-dwelling people, slower overall GI time under single and dual-task was associated with increased risk of multiple falls The strength of association was slightly stronger under the single compared with dual-task condition Slower time to FLM conferred the strongest risk of falls under single-task and swing time the strongest risk Table Baseline characteristics of the sample Characteristic Included in analysis (n = 124) No falls (n = 77) Single fall (n = 27) Multiple falls (n = 20) Age (mean SD) Sex (% male) Height, cm (mean SD) Weight, kg (mean SD) 71.0 73 167.8 80.5 6.8 58.9 10.0 16.3 70.2 48 168.5 80.5 6.6 62.3 9.8 14.1 71.3 14 166.0 80.7 5.3 51.9 9.5 14.7 73.5 9.0 167.1 80.2 9.0 45.0 11.0 25.1 Medical history, n (%) Hypertension Diabetes Depression, GDS > Falls, previous 12m Gait speed, cm/s 59 15 13 116.4 47.6 12.1 3.23 10.4 19.7 35 8.0 4.0 120.0 45.5 10.4 1.30 5.2 19.4 14 5.0 0.0 115.4 51.9 18.5 0.00 0.0 15.9 10 1.0 9.0 104.0 50.0 5.0 15.0 45.0 20.7 Cognitive Variables Stroop colour time (s) Symbol Search 37.9 23.3 19.0 7.2 37.7 23.9 19.1 7.2 38.4 22.7 22.0 7.2 37.9 22.2 14.8 7.5 Physiological factors Reaction time (ms) Knee extension (kg) Body sway (mm) Proprioception (deg) Edge contrast sensitivity (dB) 225.3 32.7 29.4 1.9 21.1 31.8 13.0 12.5 1.3 1.8 223.4 34.4 29.7 2.0 21.1 28.1 13.7 13.7 1.4 1.9 222.4 30.4 26.7 1.9 21.4 26.4 12.4 8.5 1.1 1.6 236.8 27.9 30.6 1.8 20.5 47.6 11.7 13.3 1.2 1.8 SD = standard deviation; GDS = Geriatric Depression Scale 22 M.L Callisaya et al / Gait & Posture 49 (2016) 19–24 Fig Overall gait initiation time and its components under single and dual-task by falls status *p < 0.05 for difference with gait initiation under single task Table Overall gait initiation time and its components by falls status GI time, mean SD (ms) Included in analysis (n = 124) No falls (n = 77) Single fall (n = 27) Multiple falls (n = 20) Overall single Overall dual FLM single FLM dual Transfer single Transfer dual Swing single Swing dual 1079.9 1224.2 240.1 383.0 494.8 483.9 345.1 357.3 1049.7 1175.2 227.5 353.9 487.5 479.6 334.8 341.7 1102.6 1258.7 239.72 420.6 508.7 481.9 354.2 356.2 1165.6 1366.5 289.0 444.3 504.3 503.1 372.4 419.1 184.5 307.9 78.6 221.0 103.8 111.8 84.0 117.1 156.9 235.7 58.0 170.4 102.0 118.6 74.9 84.5 181.5 330.9 79.2 288.4 114.2 89.1 59.7 52.7 254.3 456.9 121.7 277.0 98.6 115.3 130.6 226.9 GI = Gait initiation; SD = standard deviation; FLM = first lateral movement Table Regression models of the association of gait initiation (GI) time with risk of a single and multiple falls (n = 124) No falls n = 77 (62.1%) One fall n = 27 (21.8%) Multiple falls n = 20 (16.1%) RR* 95%CI RR* 95%CI Time to FLM Single task Dual task 0.94 1.07 0.59, 1.51 0.93, 1.23 1.90 1.12 1.23, 2.94 0.94, 1.23 Transfer time Single task Dual task 1.13 0.97 0.12,1.54 0.73,1.28 1.06 1.09 0.74,1.52 0.81,1.45 Swing time Single task Dual task 1.16 0.96 0.75,1.78 0.70,1.32 1.46 1.44 0.90, 2.38 1.08,1.94 Overall GI time Single task Dual task 1.07 1.03 0.88, 1.30 0.92 1.15 1.28 1.14 1.03, 1.58 1.02, 1.27 All models adjusted for age and sex; RR = relative risk; CI = confidence intervals; FLM = first lateral movement; *per 100 ms under dual-task These results were independent of gait speed and other falls risk factors, supporting the addition of GI to comprehensive falls risk assessments This study has a number of strengths It is the first prospective study to our knowledge to examine the association between GI and falls risk in a population-based sample By using a multinomial regression approach, we were able to model the relative risk of GI under single and dual-task for both single and multiple falls We carefully examined the independence of associations from other falls risk factors Furthermore, we used sophisticated quantitative measures of both GI, its components and other falls risk factors Our study has some limitations It is possible that the initial trial M.L Callisaya et al / Gait & Posture 49 (2016) 19–24 may give a more real life example of performance in an unfamiliar environment When we examined only the first trial (results not shown) there was no meaningful differences in risk of falls when compared to the summary measure of all six trials Participants stood with their heels spaced by cm as previously described [6], which may have influenced stability for some participants [19] We used numerical counting backwards in s for the dual-task, but did not record if there were any errors It is therefore unknown whether participants prioritised one task over the other, or if other types of dual-tasks, such as verbal fluency or a more difficult serial s task may have been more sensitive [20] Finally, it would have been interesting to compare findings to the risk of falls under a dual-task continuous walking condition, or to examine whether fear of falling or prior injuries from falls were associated with gait initiation and falling, but these data were not available GI time was not associated with single falls over 12 months This is in agreement with a study of people from retirement homes [12], as well as previous findings that impaired physiological and cognitive measures [21,1] are not associated with single falls It is possible that single falls are due to factors not measured in this study, such as dizziness or incontinence Alternatively they may be healthy older people undertaking risky or adventurous activities that put them at risk of an isolated fall Our results add substantially to the body of evidence demonstrating that, in community dwelling older people, slower overall GI time increases the risk of multiple falls under both single and dual-task conditions Previous studies have been conflicting, particularly under single-task, with one study reporting slower stepping times to the front or to the side were associated with falls [13], whilst others found no association with a single-task step execution task [10,11] Differences may be due to the retrospective ascertainment of falls leading to recall bias [10,11,13], methods of classifying falls, or the different types of stepping tests utilised Prior studies also included people from retirement villages making the results less generalizable to all community dwelling older people [11,13] In the only prospective study [12] of volunteers from retirement homes, slower step execution times under both single and dual-task were associated with increased odds of multiple falls [12], which is in agreement with results from our population-based study Although overall GI time and swing time under dual-task were associated with multiple falls, the associations were not meaningfully stronger than under single-task condition as hypothesised In fact the strength of association was slightly stronger under single task, although confidence intervals were wide This finding is surprising, but in agreement with the only other prospective study of people in retirement homes [12] It is possible that during the dual-task condition those at high risk of falls pay more attention to the gait initiation task (“the posture first” strategy)[22] Further investigation is needed as to whether increasing the difficulty or type of dual-task test is important [23,24], and the cost of the cognitive task should be measured Overall, our findings suggest that GI under dual-task is not a sufficiently sensitive measure to increase the discrimination of multiple fallers over the single-task condition in this population Of the components of GI, slower time to FLM showed the strongest association with multiple falls, under single-task and overall This is consistent with our previous finding that time to FLM was the component most consistently associated with physiological and cognitive falls risk factors [5] These stronger associations may be explained by the fine control required in transferring weight medio-laterally when moving from standing still to a new posture In contrast swing time was the only component associated with falls under dual-task Swing phase requires neuromuscular power to bring the leg forward whilst balancing on the stance leg [25] The increased demands of the 23 swing phase may explain why it was associated with multiple falls under the more difficult dual-task condition However, swing time under single-task showed a similar strength of association, and may have been significant in a larger sample Our results are different to those of Melzer et al [12] who reported recurrent fallers were slower during transfer and swing time under single task and transfer time under dual-task These differences may be due to the older (mean age recurrent fallers 78.8 years), and potentially frailer population, or the differing protocol involving stepping in different directions Our study has some important clinical implications Slower GI was associated with multiple falls independent of gait speed, suggesting GI provides additional information over this commonly recommended functional test We and others have found that slower times for GI [5,13] are associated with poorer performance in simple reaction time [5,13], muscle strength [4,5,13], balance [5,13] and cognition [5,13], suggesting GI may provide a good summary measure of an individual’s ability to cope with a range of impairments However, our findings were also independent of these tests, indicating that GI in response to an external cue represents a measure of functional response time that is important in order to prevent a fall, and which is not captured by other physiological and cognitive tests We used a relatively expensive force plate to measure GI that may only be available in a gait laboratory However simpler and cheaper devices such as inertial sensors [26] or a timed measure of repetitive stepping [27] may provide alternatives for measuring overall GI time in the clinic Further work is needed to determine whether using a stopwatch to time the response from an external cue to heel strike could be validated with force plate data It is also currently unknown whether improving GI times can prevent falls This might be achieved by targeting factors associated with slower initiation times such as leg strength or balance through exercise programs [28], or by practicing dual-task GI as a repetitive exercise [29] Commercially available games such as the dance video gaming mat may also help to improve step execution times, in a fun and engaging format [30,31] Randomised controlled trials are required to confirm such programs can reduce the number of falls in older people In conclusion slower GI time increased the risk of multiple falls independent of other risk factors, but with no added benefit of measurement under dual-task conditions Time to the first lateral movement under single-task may be the best measures of this risk Conflicts of interest There are no conflicts of interest Funding This work was supported by the National Health and Medical Research Council (NHMRC) Grants 403000 and 491109 and an Australian Physiotherapy Research Foundation Grant S0014877 MC is funded by an NHRMC Early Career Fellowship LB is funded by an NHMRC Career Development Fellowship VS is a recipient of a National Heart Foundation/National Health and Medical Research Council (NHMRC) Career Development Fellowship and NHMRC project grants Financial sponsors played no role in the design, execution, analysis and interpretation of data, or writing of the study Conflicts of interest There are no conflicts of interest 24 M.L Callisaya et al / Gait & Posture 49 (2016) 19–24 References [1] M.L Callisaya, L Blizzard, M.D Schmidt, K.L Martin, J.L McGinley, L.M Sanders, et al., Gait, gait variability and the risk of multiple incident falls in older people: a population-based study, Age Ageing 40 (2011) 481–487 [2] A.J Campbell, M.J Borrie, G.F Spears, S.L Jackson, J.S Brown, J.L Fitzgerald, Circumstances and consequences of falls experienced by a community population 70 years and over during a prospective study, Age Ageing 19 (1990) 136–141 [3] M.E Tinetti, M Speechley, S.F Ginter, Risk factors for falls among elderly persons living in the community, N Engl J Med 319 (1988) 1701–1707 [4] M Henriksson, H Hirschfeld, Physically active older adults display alterations in gait initiation, Gait Posture 21 (2005) 289–296 [5] K Martin, L Blizzard, M Garry, R Thomson, J McGinley, V Srikanth, Gait initiation in older people?Time to first lateral movement may be the measure of choice, Gait Posture 34 (2011) 374–378 [6] I Melzer, L.I Oddsson, The effect of a cognitive task on voluntary step execution in healthy elderly and young individuals, J Am Geriatr Soc 52 (2004) 1255–1262 [7] A.K Coppin, A Shumway-Cook, J.S Saczynski, K.V Patel, A Ble, L Ferrucci, et al., Association of executive function and performance of dual-task physical tests among older adults: analyses from the InChianti study, Age Ageing 35 (2006) 619–624 [8] K Uemura, M Yamada, K Nagai, M Shinya, N Ichihashi, Effect of dual-tasking on the center of pressure trajectory at gait initiation in elderly fallers and nonfallers, Aging Clin Exp Res 24 (2012) 152–156 [9] T Herman, A Mirelman, N Giladi, A Schweiger, J.M Hausdorff, Executive control deficits as a prodrome to falls in healthy older adults: a prospective study linking thinking, walking, and falling, J Gerontol A Biol Sci Med Sci 65 (2010) 1086–1092 [10] K Uemura, M Yamada, K Nagai, N Ichihashi, Older adults at high risk of falling need more time for anticipatory postural adjustment in the precrossing phase of obstacle negotiation, J Gerontol A Biol Sci Med Sci 66 (2011) 904–909 [11] I Melzer, I Kurz, D Shahar, M Levi, L Oddsson, Application of the voluntary step execution test to identify elderly fallers, Age Ageing 36 (2007) 532–537 [12] I Melzer, I Kurz, D Shahar, L.I Oddsson, Do voluntary step reactions in dual task conditions have an added value over single task for fall prediction? A prospective study, Aging Clin Exp Res 22 (2010) 360–366 [13] S.R Lord, R.C Fitzpatrick, Choice stepping reaction time: a composite measure of falls risk in older people, J Gerontol A Biol Sci Med Sci 56 (2001) M627– 32 [14] S.E Lamb, E.C Jorstad-Stein, K Hauer, C Becker, Development of a common outcome data set for fall injury prevention trials: the prevention of falls network Europe consensus, J Am Geriatr Soc 53 (2005) 1618–1622 [15] S.R Lord, H.B Menz, A Tiedemann, A physiological profile approach to falls risk assessment and prevention, Phys Ther 83 (2003) 237–252 [16] J.A Yesavage, T.L Brink, T.L Rose, O Lum, V Huang, M Adey, et al., Development and validation of a geriatric depression screening scale: a preliminary report, J Psychiatr Res 17 (1982) 37–49 [17] O Spreen, E Strauss, A Compendium of Neuropsychological Tests, Administration, Norms, and Commentary, ed., Oxford University Press, New York, 1998 [18] D Weschler, Weschler Adult Intelligence Scale, Psychological Corporation, New York, 1997 [19] E Dalton, M Bishop, M.D Tillman, C.J Hass, Simple change in initial standing position enhances the initiation of gait, Med Sci Sports Exerc 43 (2011) 2352– 2358 [20] J.M Hausdorff, A Schweiger, T Herman, G Yogev-Seligmann, N Giladi, Dualtask decrements in gait: contributing factors among healthy older adults, J Gerontol A Biol Sci Med Sci 63 (2008) 1335–1343 [21] K.L Martin, L Blizzard, V.K Srikanth, A Wood, R Thomson, L.M Sanders, Cognitive function modifies the effect of physiological function on the risk of multiple falls—a population-based study, J Gerontol A Biol Sci Med Sci (2013) [22] A Shumway-Cook, M Woollacott, K.A Kerns, M Baldwin, The effects of two types of cognitive tasks on postural stability in older adults with and without a history of falls, J Gerontol A Biol Sci Med Sci 52 (1997) M232–40 [23] A Zijlstra, T Ufkes, D.A Skelton, L Lundin-Olsson, W Zijlstra, Do dual tasks have an added value over single tasks for balance assessment in fall prevention programs? A mini-review, Gerontology 54 (2008) 40–49 [24] O Beauchet, C Annweiler, V Dubost, G Allali, R.W Kressig, S Bridenbaugh, et al., Stops walking when talking: a predictor of falls in older adults, Eur J Neurol 16 (2009) 786–795 [25] M.D Fox, S.L Delp, Contributions of muscles and passive dynamics to swing initiation over a range of walking speeds, J Biomech 43 (2010) 1450–1455 [26] G Bonora, I Carpinella, D Cattaneo, L Chiari, M Ferrarin, A new instrumented method for the evaluation of gait initiation and step climbing based on inertial sensors: a pilot application in Parkinson’s disease, J Neuroeng Rehabil 12 (2015) 45 [27] J.L Medell, N.B Alexander, A clinical measure of maximal and rapid stepping in older women, J Gerontol A Biol Sci Med Sci 55 (2000) M429–33 [28] S.R Lord, S Castell, Physical activity program for older persons: effect on balance, strength, neuromuscular control, and reaction time, Arch Phys Med Rehabil 75 (1994) 648–652 [29] K Uemura, M Yamada, K Nagai, H Tateuchi, S Mori, B Tanaka, et al., Effects of dual-task switch exercise on gait and gait initiation performance in older adults: preliminary results of a randomized controlled trial, Arch Gerontol Geriatr 54 (2012) e167–71 [30] D Schoene, S.R Lord, K Delbaere, C Severino, T.A Davies, S.T Smith, A randomized controlled pilot study of home-based step training in older people using videogame technology, PLoS One (2013) e57734 [31] G Pichierri, A Coppe, S Lorenzetti, K Murer, E.D de Bruin, The effect of a cognitive-motor intervention on voluntary step execution under single and dual task conditions in older adults: a randomized controlled pilot study, Clin Interv Aging (2012) 175–184