Clinical Sciences 1223
Energy Costs & Performance of Transtibial Amputees & Non-amputees during Walking & Running
Affiliations
Key words ▶ carbon fiber prosthetic feet ● ▶ energy storing and return ● prosthetic feet ▶ gait efficiency ●
L. J. Mengelkoch1, J. T. Kahle2, M. J. Highsmith2, 3 1
Doctor of Physical Therapy Program, University of St. Augustine for Health Sciences, St. Augustine, United States School of Physical Therapy & Rehabilitation Sciences, University of South Florida, Tampa, United States 3 Center for Neuromusculoskeletal Research, University of South Florida, Tampa, United States 2
Abstract
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This study compared energy costs and performance differences of walking and running for transtibial amputee (TTA) and matched non-amputee runners. TTA were tested with 3 prosthetic feet: traditional foot, SACH; general purpose, energy storing and return (ESAR) foot, Renegade; running-specific ESAR foot, Nitro. During walking, VO2 and gait efficiency (GE) were similar between prosthetic feet. VO2 was increased (21–33 %) and GE was decreased for TTA compared to controls. Self-selected walking speed (SSWS) was slower for SACH (4–6 %) compared to Renegade and Nitro but SSWS for TTA was slower (16–22 %) than controls. Dur-
Introduction
▼ accepted after revision May 05, 2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1382056 Published online: August 21, 2014 Int J Sports Med 2014; 35: 1223–1228 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Dr. Larry J. Mengelkoch Doctor of Physical Therapy Program University of St. Augustine for Health Sciences 1 University Blvd. 32086 St. Augustine United States Tel.: + 1/904/826/0084 ext. 1255 Fax: + 1/904/827 0069 [email protected]
The use of energy storing and return (ESAR) carbon fiber prosthetic feet potentially allows lower extremity amputees to ambulate with a more functional and energy efficient gait [19]. A brief description of the general biomechanical principal of ESAR carbon fiber feet is that during initialmid stance phases of gait, the prosthetic foot compresses and stores potential energy. During terminal stance the prosthetic foot decompresses to its original shape and the energy stored in the prosthetic foot is then returned to help propel the limb forward, effectively providing a push-off [15]. ESAR feet have multiple categories. One category is a general purpose walking and running foot, which incorporates a carbon fiber keel and ankle [15]. Another category is a running-specific foot, which incorporates a carbon fiber, C-shaped keel, but has no heel [15]. A common traditional prosthetic foot is the solid ankle cushioned heel (SACH) [4]. It consists of a rigid keel (solid ankle) that terminates at a level that approximates the metatarsophalangeal joints. It has a cushioned heel that provides pas-
ing running, VO2 was increased (8–18 %) and GE was decreased using SACH and Renegade, compared to Nitro. During running, VO2 was greater (9–38 %), GE was decreased and SSRS was slower (17–30 %) for TTA, than controls. VO2 peak was similar for controls and TTA using Nitro, but peak running speed was slower for TTA. In conclusion, during walking energy costs are mostly similar between prosthetic feet, but ESAR feet likely provide faster SSWS for TTA. During running, energy costs and performance are improved for TTA using Nitro. Nonetheless, for all prosthetic feet conditions, TTA demonstrated an energy cost and performance disadvantage during walking and running compared to non-amputee runners.
sive plantarflexion in early stance and molded foam toes that allow the toes to passively hyperextend during late stance. The SACH foot is lightweight, inexpensive and functionally useful for walking [4, 8–10, 14], but few studies have analyzed this foot during running [9]. The reported energy costs of walking for persons with transtibial amputation due to non-vascular causes using traditional and ESAR prosthetic feet is widely varying. Some studies have reported that energy costs during walking for transtibial amputees (TTA) compared to non-amputees are similar [10]. Others have reported that TTA walk more slowly (11 %) and experience greater energy costs (16 %) than non-amputees at self-selected pace [5]. The variability of energy costs in these studies may be related to differences in gait speed, differences in prosthetic components within TTA groups, variability in prosthetic fittings, and differences in physical characteristics and fitness levels between TTA and non-amputee controls. Fewer studies are available reporting energy costs for persons with transtibial amputation (due to non-vascular causes) during running
Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
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Authors
[1, 9, 21]. Nonetheless, there has been considerable media controversy and scholarly debate [12, 20] on whether running-specific ESAR prosthetic feet provide amputee runners an unfair biomechanical and energy expenditure advantage. Currently there is insufficient evidence to determine if specialized prosthetic running feet provide a distinct advantage for amputee runners. Weyand et al. [21] reported that the metabolic costs during near Olympic-level sprint performance for an elite bilateral TTA runner and intact-limb elite runners are mostly similar. They also observed that the bilateral TTA runner and intact-limb elite runners obtained similar peak running speeds. However, the study found substantial biomechanical differences between the TTA runner and intact-limb elite runners. The TTA runner had significantly shorter aerial and swing times resulting in more rapid repositioning of limbs, and longer ground contact times to apply force. Conversely, the ground reaction forces produced by the TTA runner were significantly less than the intactlimb elite runners, indicating a force impairment for the TTA runner. Together these factors resulted in a functional trade-off (i. e., no advantage) in producing peak running speed for the TTA runner. Since this report, the author team has become divided concerning the issue of whether a prosthetic foot can provide an advantage [12, 20]. Brown et al. [1] compared the energy costs of running for recreational TTA runners using running-specific ESAR prosthetic feet to control non-amputee runners. They reported that while TTA using running-specific ESAR feet did not did not gain a physiological advantage over non-amputee runners, they did have similar energy costs and obtained similar peak running speeds as non-amputees runners. Given the wide range of ambulatory energy costs reported using traditional & ESAR feet from the limited available evidence and the recent debate regarding an unfair biomechanical or energy cost advantages TTAs may gain when using running-specific ESAR prosthetic feet, more research is warranted. The purpose of this study was to 1.) compare the energy costs of walking and running for TTA runners using traditional and ESAR prosthetic feet to matched non-amputee runners; 2.) clarify potential performance benefits of running-specific ESAR prosthetic feet.
Methods
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Subjects 3 male, unilateral, TTA runners with amputation due to nonvascular causes (trauma, n = 1; bone cancer, n = 1; congenital, n = 1) and 3 male, non-amputee control runners matched by age, physical characteristics and physical activity levels were recruited for this study. Participants were healthy, recreational runners who trained ≥ 4 h · wk − 1, for ≥ 1 years and competed regularly in competitive running events. The study was conducted in accordance with ethical standards approved by the International Journal of Sports Medicine [6]. The study protocol was approved by the University of South Florida’s Institutional Review Board, and each study participant provided written informed consent.
2. General purpose ESAR foot (Renegade™; Freedom Innova▶ Fig. 1b); 3. Run-specific ESAR foot (Nitro™; tions, Irvine, CA; ● ▶ Fig. 1c). TTA participants Freedom Innovations, Irvine, CA; ● had each prosthetic foot condition fitted to their prosthesis by the study’s prosthetists (JTK & MJH). TTA participants then accommodated to each prosthetic foot for a minimum of 2 weeks and performed a minimum of 3–4 exercise training sessions prior to testing. To ensure the assignment of the order of testing for the 3 prosthetic feet conditions was balanced and randomized, a block randomization method was used [11]. All possible combinations of testing order were determined for the 3 prosthetic feet conditions (i. e., 9) and balanced into 3 blocks. Each block was typed onto one sheet of standardized paper, folded equally and placed in an unmarked sealed opaque envelop. The 3 envelopes were then placed into an opaque cardboard box, which was then closed and rotated for 1 min to shuffle the envelopes. Each of the 3 participants was then assigned their testing sequence by blindly choosing an envelope from the opaque box [3].
Exercise testing procedures For exercise testing, participants reported to the laboratory in the morning following a minimum 8 h fasting period and had refrained from exercise for approximately 48 h. Participants performed peak effort exercise testing for each test condition using an incremental treadmill (Quinton TM65™; Cardiac Science, Waukesha, WI) walking and running protocol. Testing began at 40.2 m · min − 1, 0 % grade. Speed increased every 2 min by 13.4 m · min − 1. If the participant was able to complete the running stage at 241.4 m · min − 1, 0 % grade, then grade was increased by 2 % for each additional stage until the participant reached his peak exercise tolerance. Approximately 48–72 h prior to exercise testing, participants came to the laboratory for a treadmill familiarization session. During the familiarization session individual self-selected walking and running speeds (SSWS and SSRS) were determined for each prosthetic foot condition for TTA and non-amputee control runners, and programed into their exercise test(s).
Measurements The primary energy expenditure measurement for this study was oxygen uptake (VO2) measured continuously by breath-bybreath gas exchange analysis (Vmax Encore 229™; Care Fusion, Palm Springs, CA). Calibration of the metabolic cart was performed immediately prior to testing. Flow volume measures were calibrated using a 3L syringe, and gas analyzers were calibrated to known gas mixtures. For TTA, body weight measurements without their prosthesis were used for VO2 (ml O2 · kg − 1 · min − 1) measurements relative to body weight.
Study design The study utilized a repeated measures design with case-control matching. Each TTA participant was tested with 3 prosthetic feet conditions: 1. Traditional prosthetic foot – SACH (K08 SACH ▶ Fig. 1a); Strider™; Kingsley Manufacturing Co. Costa Mesa, CA; ●
Fig. 1 3 prosthetic feet conditions: a Solid ankle cushioned heel (SACH) foot; b General purpose energy storing and return (ESAR) Renegade foot; c Run-specific ESAR Nitro foot.
Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
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Table 1 Physical characteristics and peak performance responses of transtibial amputee (TTA) and non-amputee control runners. TTA age (years) height (cm) weight (kg) % fat VO2 peak (ml O2 · kg − 1 · min − 1) peak speed (m · min − 1) peak grade %
Results
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▶ Table 1 compares physical characteristics and peak perform●
ance responses of TTA and non-amputee control runners. TTA weighed significantly less (p ≤ 0.05), but were closely matched to non-amputee control runners in other physical characteristics. TTA and non-amputee control runners achieved similar VO2 peak values, but peak running speeds were significantly slower (p ≤ 0.05) for TTA. During exercise testing TTA participants performed to their peak exercise tolerance for each prosthetic foot condition. TTA subjects thus had variable end-points for each prosthetic foot condition. Each subject completed all walking speed stages. All control subjects were able to run at or beyond 214 m · min − 1, whereas only one TTA runner could complete this stage/speed of the test while using the Nitro run-specific foot. The Renegade ESAR foot was used by all TTA runners up to 160.6 m · min − 1, whereas the SACH foot had a TTA runner drop out prior to initiating running.
Significant difference from control, p ≤ 0.05
25 VO2 (ml•O2•kg–1•min–1)
Data were entered into a database and verified for accuracy, completeness and normality. Paired t-tests were used to compare physical characteristics and peak performance responses between TTA and non-amputee control runners. VO2 and GE data were averaged over the final 20 s of each ambulatory speed. Mean values for VO2 and GE at each ambulatory speed were compared using a mixed model ANOVA. A repeated measures ANOVA was used for comparison of the 3 prosthetic feet conditions for the TTA group. A one-way ANOVA was used for the comparison of the non-amputee control runners to the TTA group’s 3 prosthetic feet conditions. It was expected that during running, TTA participants would have variable speed/stage end-points for peak exercise tolerance for each prosthetic foot condition. Thus, as higher speeds were attained, we expected some TTA participants would drop out and there would be missing data for the TTA group for some prosthetic foot conditions [18]. We used the following intentionto-treat strategy for imputation of missing data. At any ambulatory speed/stage, where the number of TTA participants was less than 3 for a prosthetic foot condition, the mean value substitution method [2], which is also referred to as the missing patient’s own group mean or MOWN technique [17], was utilized. That is, the mean value for the available subjects was determined and imputed for the missing subject’s data points for that prosthetic foot condition. Statistical analyses were performed using SPSS software (Version 20, SPSS Inc. Chicago, IL). For all procedures statistical significance was p ≤ 0.05. Values are reported as means ± standard deviation (SD).
35.3 ± 9.0 175.5 ± 10.2 79.4 ± 8.2 17.2 ± 4.8 50.7 ± 9.3 232.5 + 15.5 2.0 ± 2.0
Values are mean ± SD †
Data analysis
Control
35.3 ± 10 174.6 ± 10.6 68.6 ± 9.9 † 18.7 ± 6.6 51.6 ± 7.8 201.2 ± 13.4 † 0.0 ± 0.0
20 15 10 5 0
40.2
53.6
67.1
80.5
93.9
Speed (m•min– 1) Control
Nitro
Renegade
SACH
Fig. 2 Mean ( ± SD) energy expenditure (VO2) of 3 prosthetic feet conditions for transtibial amputees (TTA) compared to non-amputee controls during walking. All subjects completed all walking stages. Energy expenditure was similar between all TTA feet conditions and controls at 40.2 m · min − 1 speed. At speeds 53.6, 67.1, 80.5 and 93.9, energy expenditure was similar between TTA for all feet conditions but significantly greater (p ≤ 0.05) for all TTA feet conditions compared to controls.
Energy expenditure responses during fixed walking and running speeds During walking at fixed speeds, mean (± SD) energy expenditure costs (VO2) were similar between prosthetic feet conditions for ▶ Fig. 2). At all but the slowest walking speed TTA (● (40.2 m · min − 1) energy costs were significantly greater (p ≤ 0.05) for TTA with all prosthetic feet conditions compared to nonamputee controls: SACH, 21–33 % greater; Renegade: 23–28 % greater; Nitro: 28–32 % greater. ▶ Fig. 3), mean (± SD) energy During running at fixed speeds (● expenditure costs were significantly increased (p ≤ 0.05) for TTA using the SACH and Renegade prosthetic feet compared to the Nitro prosthetic foot: SACH 8–18 % greater; Renegade 8–18 % greater. During running, energy costs were significantly greater (p ≤ 0.05) for TTA with all prosthetic feet conditions compared to non-amputee controls: SACH 28–36 % greater; Renegade 27–38 % greater; Nitro 9–32 % greater.
Gait efficiency during self-selected walking and running speeds At SSWS, GE was similar between prosthetic feet conditions for ▶ Fig. 4). However, GE was significantly lower (more effiTTA (● cient; p ≤ 0.05) for non-amputee controls compared to all prosthetic feet conditions for TTA. SSWS was significantly slower
Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
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Because SSWS and SSWR are variable between subjects, a relative measure that integrates speed and energy costs is needed to determine gait efficiency (GE). The criterion measure for GE is defined as energy expenditure per meter traveled and determined from the ratio of VO2 divided by ambulation speed (ml O2 · kg − 1 · m − 1) [8]. The lower the value for GE, the more efficient the gait. For TTA, body weight and body composition measurements were determined without their prosthesis. Percent body fat was determined using air displacement plethysmography with measured thoracic gas volume (BOD POD GS™; COSMED, Rome, Italy).
70 65 60 55 50 45 40 35 30 25 20 15 10 5 0
2
2 1
1
1
1
2 1
1
Peak running speed responses 134.1
147.5
160.9
174.3
187.8
201.2
214.6
–1
Speed (m• min ) Control
Nitro
Renegade
SACH
Fig. 3 Mean (± SD) energy expenditure (VO2) of 3 prosthetic feet conditions for transtibial amputees (TTA) compared to non-amputee controls during running. All control subjects completed all running stages. When TTA subject(s) dropped out of a running stage, the number of TTA subjects completing that speed-stage is indicated in the respective column. Energy expenditure was significantly greater (p ≤ 0.05) for all TTA feet conditions compared to controls at all running speeds (134.1– 214.6 m · min − 1). During running, there were no significant differences in energy expenditure between the SACH and Renegade feet conditions. Energy expenditure was significantly greater (p ≤ 0.05) for the SACH and Renegade feet conditions compared to the Nitro foot condition at all running speeds.
0.4 Gait Efficiency (ml•O2•kg– 1•m–1)
At SSRS, GE was significantly improved (p ≤ 0.05) for the Nitro prosthetic foot compared to SACH and Renegade prosthetic feet ▶ Fig. 4). However, GE was significantly lowest (most for TTA (● efficient; p ≤ 0.05) for non-amputee control runners compared to TTA for all prosthetic feet conditions. At SSRS, the SACH foot was significantly slower (13–16 %; p ≤ 0.05) compared to the Renegade and Nitro feet. Similar to SSWS, SSRS for all prosthetic feet conditions were significantly slower (17–30 %; p ≤ 0.05) for TTA than non-amputee controls.
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 64.4
67.1
68.8
82.3
123.4 142.4 146.6 176.1
Speed (m•min–1) Walking Control
Running Nitro
Renegade
SACH
Fig. 4 Gait efficiency (ml O2 · kg − 1 · m − 1) of 3 prosthetic feet conditions (SACH, Renegade, Nitro) for transtibial amputees compared to nonamputee controls at self-selected walking and running speeds (SSWS and SSRS). During SSWS and SSRS gait efficiency was significantly lower (p ≤ 0.05; i. e., improved) for controls compared to TTA for all prosthetic feet conditions. Furthermore, SSWS and SSRS were significantly faster (p ≤ 0.05) for controls compared to TTA for all prosthetic feet conditions. Gait efficiency during SSWS was similar between TTA feet conditions, while SSWS was significantly faster (p ≤ 0.05) for Renegade and Nitro compared to SACH. For TTA gait efficiency during SSRS was significantly lower (p ≤ 0.05; i. e., improved) for Nitro compared to SACH and Renegade. SSRS was significantly faster (p ≤ 0.05) for Renegade and Nitro compared to SACH. The number of subjects completing each test condition was n = 3, except SSRS for SACH condition, where it was n = 2.
(p ≤ 0.05) for the SACH foot compared to Renegade and Nitro feet (4–6 %). Additionally, SSWS for all prosthetic feet conditions were significantly slower (16–22 %; p ≤ 0.05) for TTA than nonamputee controls.
A functional difference in peak running speed (mean ± SD) was observed between prosthetic feet conditions for TTA and non-amputee control runners. TTA ran slowest using the SACH foot (peak speed = 154.2 ± 28.4 m · min − 1, 0 ± 0 % grade); moderately faster with the Renegade foot (peak speed = 178.8 + 20.5 m · min − 1, 0 % ± 0 % grade); and fastest with the Nitro foot (peak speed = 201.2 + 13.4 m · min − 1, 0 ± 0 % grade). Although TTA using the Nitro foot, obtained similar VO2 peak levels as non-amputee con▶ Table 1), peak running speed at VO peak was trol runners (● 2 significantly (p ≤ 0.05) faster for non-amputee control runners (peak speed = 232.5 + 15.5 m · min − 1, 2 ± 2 % grade).
Discussion
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When TTA walked at both fixed speeds and at SSWS, no significant differences were observed among the 3 prosthetic feet conditions for energy expenditure (VO2) and GE. However, TTA demonstrated significantly increased energy costs and decreased GE compared to non-amputee controls. At SSWS, TTA demonstrated improved speed with the Renegade and Nitro compared to the SACH, but SSWS for TTA were significantly slower for all prosthetic feet conditions compared to non-amputee controls. Our study is in agreement with the earlier study by Gailey et al. [5] who reported that the energy costs of walking for TTA are significantly increased and SSWS are slower compared to nonamputee controls. However, a major limitation of their study was the great variability in prosthetic components used by TTA subjects. While more current studies have investigated the effect of foot type and energy cost during walking for TTA, the literature has shown inconsistent results. Nielsen et al. [14] reported decreased energy costs and improved GE for TTA using the general purpose ESAR Flex-Foot compared to the traditional SACH foot at fixed walking speeds. Conversely, Hsu et al. [9] reported that energy costs and GE were similar for TTA using the ESAR Flex-Foot and SACH foot but were improved using another type of general purpose ESAR foot (Re-Flex VSP). In another study, Hsu et al. [8] found similar results to the current study in that energy costs for TTA using the traditional SACH foot and 2 general purpose ESAR feet (Flex-Foot and C-Walk) were similar at fixed walking speeds and SSWS. The study by Hsu et al. [10] is perhaps the most contrary to our findings. These researchers reported that during walking at fixed speeds TTA had similar energy costs and GE as non-amputee controls at all walking velocities using the ESAR Re-Flex VSP foot. Furthermore, they reported that TTA had similar energy costs and GE as non-amputee controls using the Flex-Foot and SACH foot at slower walking velocities, but increased energy costs and decreased GE at faster walking velocities. Possible reasons for differences between the present study and these studies were differences in the physical activity levels
Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
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VO2 (ml O2•kg– 1•min– 1)
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added into the calculation of the VO2 (ml O2 · kg − 1 · min − 1) measurements relative to body weight. Since the prosthesis does not consume oxygen this can introduce a systematic error in their VO2 measurements. For example, the mean (+ SD) weight of the running-specific Nitro prosthesis in our study was 1.5 (± 0.5) kg. If a relatively similar prosthetic weight value were subtracted out from the body weight values in their VO2 measurements, the denominator value becomes reduced and VO2 values would be increased. Thus, there may possibly be a significant difference (increase) in VO2 (energy expenditure) for TTA runners compared to non-amputee controls in their study.
Study Limitations and Future Study
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The primary limitation for this study was sample size. It was difficult to recruit TTA participants who met the relatively high level of training for our study’s inclusion criteria. However, our study design utilized case-control matching with repeated measures, which is a well-accepted methodological approach to studying rare conditions, i. e., in this case well-conditioned TTA runners [7, 13, 16]. A primary benefit reported from utilizing this approach is thorough study of available subjects. In terms of disadvantages for such designs, 2 types of bias are commonly described: sampling and observation/recall. In terms of observation bias, we attempted to minimize this by utilizing oxygen uptake, a highly objective measurement, as the study’s primary outcome measure to determine energy expenditure and gait efficiency [8]. Additionally, TTA had accommodation periods for the prosthetic feet conditions, and all subjects had a testing familiarization session before actual testing occurred. In terms of sampling bias our study had well defined inclusion criteria for participants, and thus our results may be generalizable only to TTA with these characteristics. For future study we are planning to follow the same study design and investigate the energy efficiency of these same 3 prosthetic feet during walking and running in transfemoral amputee runners compared to non-amputee control runners.
Conclusion
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For clinical relevance, our data suggest that for TTA walking on level surfaces, energy costs are mostly similar between prosthetic feet conditions, but ESAR feet likely provide faster SSWS. For TTA performing distance-type running, energy costs are reduced and GE, SSRS & peak speed are improved using the running-specific ESAR Nitro foot compared to the traditional SACH foot and general purpose ESAR Renegade foot. Nonetheless, for all prosthetic feet conditions, TTA runners demonstrated an energy cost and performance disadvantage during walking and running compared to matched non-amputee runners.
Acknowledgements
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This study was funded by the University of South Florida’s Signature Interdisciplinary Program in Cardiovascular Research Award # 10009-614101. We wish to thank Freedom Innovations, Irvine, CA, for providing the Renegade and Nitro prosthetic feet for the study.
Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
and conditioning of TTA subjects, differences in accommodation periods for each foot type, differences in prosthetic fittings, differences in randomization and allocation concealment techniques, and, in some studies [8, 9, 14], the lack of non-amputee control subjects for comparison. In the current study we observed that the run-specific ESAR Nitro foot provided TTA reduced energy costs and improved GE, SSRS & peak speed during distance-type running compared to the SACH and ESAR Renegade feet. However, a major finding in our study was that TTA runners using the run-specific ESAR Nitro foot expended significantly more energy at every speed and ran slower at VO2 peak than closely matched non-amputee control runners. Thus, in our study TTA runners using the runspecific ESAR Nitro foot demonstrated an energy cost and performance disadvantage compared to non-amputee control runners. These results differ from other running studies. Hsu et al. [9] reported results that were similar to what they observed during walking, in which energy costs and GE were similar for TTA using the ESAR Flex-Foot and SACH foot, but were improved using another type of general purpose ESAR foot (Re-Flex VSP). Major factors limiting the comparison of their findings with those of the current study are that their study did not describe specific inclusion criteria for TTA participants concerning their run training history, their TTA running speeds during testing were much slower (120.69–147.5 m · min − 1 vs. 134.1–214.6 m · min − 1), their study lacked a non-amputee control group and did not test a run-specific ESAR foot. In the study by Weyand et al. [21] these researchers reported that the metabolic costs during near Olympic-level sprint performance for an elite bilateral TTA runner and intact-limb elite runners, are mostly similar. Since the Weyand et al. [21] study involved high-intensity sprint running in a single case, and our study involved high-intensity distance-type running it is reasonable to suggest that inferences from each study’s finding could be limited to their respective running settings. The running study that most closely matches the conditions of the current study is the study reported by Brown et al. [1]. Recreational TTA runners using running-specific ESAR prosthetic feet were compared to control non-amputee runners. They reported that TTAs using running-specific ESAR feet had similar energy costs at all speeds and obtained similar peak running speeds as non-amputees. The mean peak running speed and peak VO2 values of TTA runners in the Brown et al. [1] study were 254.8 ± 32.2 m · min − 1 and 56.3 ± 7.6 ml O2 · kg − 1 · min − 1. The mean peak running speed and peak VO2 values of TTA runners in the current study were 201.2 ± 13.4 m · min − 1 and 51.6 ± 7.8 ml O2 · kg − 1 · min − 1. These data indicate both studies involved well-trained recreational TTA runners, but the TTA runners in the Brown et al. [1] study were slightly more fit than the TTA runners in the current study. Brown et al. [1] concluded that although TTAs using running-specific ESAR feet performed similarly to non-amputee controls, they did not gain a physiological advantage over non-amputee runners. We suggest 2 potential methodological differences in the Brown et al. [1] study compared to our study may contribute to the difference in results. In the Brown et al. [1] study subjects used their own running prosthesis, which indicates variability in both the type/brand of running-specific ESAR foot and standardization of prosthetic fittings. In the present study, all subjects utilized the same running-specific ESAR Nitro foot and were fitted by the same study prosthetists (JTK & MJH). Another concern is that in the Brown et al. [1] study, the weight of the prosthesis was
Conflicts of interest: The authors declare no conflict of interest. References 1 Brown MB, Millard-Stafford ML, Allison AR. Running-specific prostheses permit energy cost similar to nonamputees. Med Sci Sports Exerc 2009; 41: 1080–1087 2 Buhi ER, Goodson P, Neilands TB. Out of sight, not out of mind: strategies for handling missing data. Am J Health Behav 2008; 32: 83–92 3 Doig GS, Simpson F. Randomization and allocation concealment: a practical guide for researchers. J Crit Care 2005; 20: 187–191 4 Edelstein JE. Prosthetic feet: state of the art. Phys Ther 1988; 68: 1874–1881 5 Gailey RS, Wenger MA, Raya M, Kirk N, Erbs K, Spyropoulos P, Nash MS. Energy expenditure of trans-tibial amputees during ambulation at self-selected pace. J Prosthet Orthot 1994; 18: 84–91 6 Harriss DJ, Atkinson G. Ethical standards in sports and exercise science research: 2014 update. Int J Sports Med 2013; 34: 1025–1028 7 Hartung DM, Touchette D. Overview of clinical research design. Am J Health-Syst Pharm 2009; 66: 398–408 8 Hsu M-J, Nielsen DH, Lin-Chan S-J, Shurr D. The effects of prosthetic foot design on physiologic measurements, self-selected walking velocity, and physical activity in people with transtibial amputation. Arch Phys Med Rehabil 2006; 87: 123–129 9 Hsu M-J, Nielsen DH, Yack HJ, Shurr DG. Physiological measurements of walking and running in people with transtibial amputations with 3 different prostheses. J Orthop Sports Phys Ther 1999; 29: 526–533 10 Hsu M-J, Nielsen DH, Yack J, Shurr DG, Lin S-J. Physiological comparisons of physically active persons with transtibial amputation using static and dynamic prostheses versus persons with nonpathological gait during multiple-speed walking. J Prosthet Orthot 2000; 12: 60–69 11 Kang M, Ragan BG, Park JH. Issues in outcomes research: an overview of randomization techniques for clinical trials. J Athl Train 2008; 43: 215–221
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Energy Costs & Performance of Transtibial Amputees & Non-amputees during Walking & Running
Affiliations
Key words ▶ carbon fiber prosthetic feet ● ▶ energy storing and return ● prosthetic feet ▶ gait efficiency ●
L. J. Mengelkoch1, J. T. Kahle2, M. J. Highsmith2, 3 1
Doctor of Physical Therapy Program, University of St. Augustine for Health Sciences, St. Augustine, United States School of Physical Therapy & Rehabilitation Sciences, University of South Florida, Tampa, United States 3 Center for Neuromusculoskeletal Research, University of South Florida, Tampa, United States 2
Abstract
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This study compared energy costs and performance differences of walking and running for transtibial amputee (TTA) and matched non-amputee runners. TTA were tested with 3 prosthetic feet: traditional foot, SACH; general purpose, energy storing and return (ESAR) foot, Renegade; running-specific ESAR foot, Nitro. During walking, VO2 and gait efficiency (GE) were similar between prosthetic feet. VO2 was increased (21–33 %) and GE was decreased for TTA compared to controls. Self-selected walking speed (SSWS) was slower for SACH (4–6 %) compared to Renegade and Nitro but SSWS for TTA was slower (16–22 %) than controls. Dur-
Introduction
▼ accepted after revision May 05, 2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1382056 Published online: August 21, 2014 Int J Sports Med 2014; 35: 1223–1228 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Dr. Larry J. Mengelkoch Doctor of Physical Therapy Program University of St. Augustine for Health Sciences 1 University Blvd. 32086 St. Augustine United States Tel.: + 1/904/826/0084 ext. 1255 Fax: + 1/904/827 0069 [email protected]
The use of energy storing and return (ESAR) carbon fiber prosthetic feet potentially allows lower extremity amputees to ambulate with a more functional and energy efficient gait [19]. A brief description of the general biomechanical principal of ESAR carbon fiber feet is that during initialmid stance phases of gait, the prosthetic foot compresses and stores potential energy. During terminal stance the prosthetic foot decompresses to its original shape and the energy stored in the prosthetic foot is then returned to help propel the limb forward, effectively providing a push-off [15]. ESAR feet have multiple categories. One category is a general purpose walking and running foot, which incorporates a carbon fiber keel and ankle [15]. Another category is a running-specific foot, which incorporates a carbon fiber, C-shaped keel, but has no heel [15]. A common traditional prosthetic foot is the solid ankle cushioned heel (SACH) [4]. It consists of a rigid keel (solid ankle) that terminates at a level that approximates the metatarsophalangeal joints. It has a cushioned heel that provides pas-
ing running, VO2 was increased (8–18 %) and GE was decreased using SACH and Renegade, compared to Nitro. During running, VO2 was greater (9–38 %), GE was decreased and SSRS was slower (17–30 %) for TTA, than controls. VO2 peak was similar for controls and TTA using Nitro, but peak running speed was slower for TTA. In conclusion, during walking energy costs are mostly similar between prosthetic feet, but ESAR feet likely provide faster SSWS for TTA. During running, energy costs and performance are improved for TTA using Nitro. Nonetheless, for all prosthetic feet conditions, TTA demonstrated an energy cost and performance disadvantage during walking and running compared to non-amputee runners.
sive plantarflexion in early stance and molded foam toes that allow the toes to passively hyperextend during late stance. The SACH foot is lightweight, inexpensive and functionally useful for walking [4, 8–10, 14], but few studies have analyzed this foot during running [9]. The reported energy costs of walking for persons with transtibial amputation due to non-vascular causes using traditional and ESAR prosthetic feet is widely varying. Some studies have reported that energy costs during walking for transtibial amputees (TTA) compared to non-amputees are similar [10]. Others have reported that TTA walk more slowly (11 %) and experience greater energy costs (16 %) than non-amputees at self-selected pace [5]. The variability of energy costs in these studies may be related to differences in gait speed, differences in prosthetic components within TTA groups, variability in prosthetic fittings, and differences in physical characteristics and fitness levels between TTA and non-amputee controls. Fewer studies are available reporting energy costs for persons with transtibial amputation (due to non-vascular causes) during running
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Authors
[1, 9, 21]. Nonetheless, there has been considerable media controversy and scholarly debate [12, 20] on whether running-specific ESAR prosthetic feet provide amputee runners an unfair biomechanical and energy expenditure advantage. Currently there is insufficient evidence to determine if specialized prosthetic running feet provide a distinct advantage for amputee runners. Weyand et al. [21] reported that the metabolic costs during near Olympic-level sprint performance for an elite bilateral TTA runner and intact-limb elite runners are mostly similar. They also observed that the bilateral TTA runner and intact-limb elite runners obtained similar peak running speeds. However, the study found substantial biomechanical differences between the TTA runner and intact-limb elite runners. The TTA runner had significantly shorter aerial and swing times resulting in more rapid repositioning of limbs, and longer ground contact times to apply force. Conversely, the ground reaction forces produced by the TTA runner were significantly less than the intactlimb elite runners, indicating a force impairment for the TTA runner. Together these factors resulted in a functional trade-off (i. e., no advantage) in producing peak running speed for the TTA runner. Since this report, the author team has become divided concerning the issue of whether a prosthetic foot can provide an advantage [12, 20]. Brown et al. [1] compared the energy costs of running for recreational TTA runners using running-specific ESAR prosthetic feet to control non-amputee runners. They reported that while TTA using running-specific ESAR feet did not did not gain a physiological advantage over non-amputee runners, they did have similar energy costs and obtained similar peak running speeds as non-amputees runners. Given the wide range of ambulatory energy costs reported using traditional & ESAR feet from the limited available evidence and the recent debate regarding an unfair biomechanical or energy cost advantages TTAs may gain when using running-specific ESAR prosthetic feet, more research is warranted. The purpose of this study was to 1.) compare the energy costs of walking and running for TTA runners using traditional and ESAR prosthetic feet to matched non-amputee runners; 2.) clarify potential performance benefits of running-specific ESAR prosthetic feet.
Methods
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Subjects 3 male, unilateral, TTA runners with amputation due to nonvascular causes (trauma, n = 1; bone cancer, n = 1; congenital, n = 1) and 3 male, non-amputee control runners matched by age, physical characteristics and physical activity levels were recruited for this study. Participants were healthy, recreational runners who trained ≥ 4 h · wk − 1, for ≥ 1 years and competed regularly in competitive running events. The study was conducted in accordance with ethical standards approved by the International Journal of Sports Medicine [6]. The study protocol was approved by the University of South Florida’s Institutional Review Board, and each study participant provided written informed consent.
2. General purpose ESAR foot (Renegade™; Freedom Innova▶ Fig. 1b); 3. Run-specific ESAR foot (Nitro™; tions, Irvine, CA; ● ▶ Fig. 1c). TTA participants Freedom Innovations, Irvine, CA; ● had each prosthetic foot condition fitted to their prosthesis by the study’s prosthetists (JTK & MJH). TTA participants then accommodated to each prosthetic foot for a minimum of 2 weeks and performed a minimum of 3–4 exercise training sessions prior to testing. To ensure the assignment of the order of testing for the 3 prosthetic feet conditions was balanced and randomized, a block randomization method was used [11]. All possible combinations of testing order were determined for the 3 prosthetic feet conditions (i. e., 9) and balanced into 3 blocks. Each block was typed onto one sheet of standardized paper, folded equally and placed in an unmarked sealed opaque envelop. The 3 envelopes were then placed into an opaque cardboard box, which was then closed and rotated for 1 min to shuffle the envelopes. Each of the 3 participants was then assigned their testing sequence by blindly choosing an envelope from the opaque box [3].
Exercise testing procedures For exercise testing, participants reported to the laboratory in the morning following a minimum 8 h fasting period and had refrained from exercise for approximately 48 h. Participants performed peak effort exercise testing for each test condition using an incremental treadmill (Quinton TM65™; Cardiac Science, Waukesha, WI) walking and running protocol. Testing began at 40.2 m · min − 1, 0 % grade. Speed increased every 2 min by 13.4 m · min − 1. If the participant was able to complete the running stage at 241.4 m · min − 1, 0 % grade, then grade was increased by 2 % for each additional stage until the participant reached his peak exercise tolerance. Approximately 48–72 h prior to exercise testing, participants came to the laboratory for a treadmill familiarization session. During the familiarization session individual self-selected walking and running speeds (SSWS and SSRS) were determined for each prosthetic foot condition for TTA and non-amputee control runners, and programed into their exercise test(s).
Measurements The primary energy expenditure measurement for this study was oxygen uptake (VO2) measured continuously by breath-bybreath gas exchange analysis (Vmax Encore 229™; Care Fusion, Palm Springs, CA). Calibration of the metabolic cart was performed immediately prior to testing. Flow volume measures were calibrated using a 3L syringe, and gas analyzers were calibrated to known gas mixtures. For TTA, body weight measurements without their prosthesis were used for VO2 (ml O2 · kg − 1 · min − 1) measurements relative to body weight.
Study design The study utilized a repeated measures design with case-control matching. Each TTA participant was tested with 3 prosthetic feet conditions: 1. Traditional prosthetic foot – SACH (K08 SACH ▶ Fig. 1a); Strider™; Kingsley Manufacturing Co. Costa Mesa, CA; ●
Fig. 1 3 prosthetic feet conditions: a Solid ankle cushioned heel (SACH) foot; b General purpose energy storing and return (ESAR) Renegade foot; c Run-specific ESAR Nitro foot.
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Table 1 Physical characteristics and peak performance responses of transtibial amputee (TTA) and non-amputee control runners. TTA age (years) height (cm) weight (kg) % fat VO2 peak (ml O2 · kg − 1 · min − 1) peak speed (m · min − 1) peak grade %
Results
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▶ Table 1 compares physical characteristics and peak perform●
ance responses of TTA and non-amputee control runners. TTA weighed significantly less (p ≤ 0.05), but were closely matched to non-amputee control runners in other physical characteristics. TTA and non-amputee control runners achieved similar VO2 peak values, but peak running speeds were significantly slower (p ≤ 0.05) for TTA. During exercise testing TTA participants performed to their peak exercise tolerance for each prosthetic foot condition. TTA subjects thus had variable end-points for each prosthetic foot condition. Each subject completed all walking speed stages. All control subjects were able to run at or beyond 214 m · min − 1, whereas only one TTA runner could complete this stage/speed of the test while using the Nitro run-specific foot. The Renegade ESAR foot was used by all TTA runners up to 160.6 m · min − 1, whereas the SACH foot had a TTA runner drop out prior to initiating running.
Significant difference from control, p ≤ 0.05
25 VO2 (ml•O2•kg–1•min–1)
Data were entered into a database and verified for accuracy, completeness and normality. Paired t-tests were used to compare physical characteristics and peak performance responses between TTA and non-amputee control runners. VO2 and GE data were averaged over the final 20 s of each ambulatory speed. Mean values for VO2 and GE at each ambulatory speed were compared using a mixed model ANOVA. A repeated measures ANOVA was used for comparison of the 3 prosthetic feet conditions for the TTA group. A one-way ANOVA was used for the comparison of the non-amputee control runners to the TTA group’s 3 prosthetic feet conditions. It was expected that during running, TTA participants would have variable speed/stage end-points for peak exercise tolerance for each prosthetic foot condition. Thus, as higher speeds were attained, we expected some TTA participants would drop out and there would be missing data for the TTA group for some prosthetic foot conditions [18]. We used the following intentionto-treat strategy for imputation of missing data. At any ambulatory speed/stage, where the number of TTA participants was less than 3 for a prosthetic foot condition, the mean value substitution method [2], which is also referred to as the missing patient’s own group mean or MOWN technique [17], was utilized. That is, the mean value for the available subjects was determined and imputed for the missing subject’s data points for that prosthetic foot condition. Statistical analyses were performed using SPSS software (Version 20, SPSS Inc. Chicago, IL). For all procedures statistical significance was p ≤ 0.05. Values are reported as means ± standard deviation (SD).
35.3 ± 9.0 175.5 ± 10.2 79.4 ± 8.2 17.2 ± 4.8 50.7 ± 9.3 232.5 + 15.5 2.0 ± 2.0
Values are mean ± SD †
Data analysis
Control
35.3 ± 10 174.6 ± 10.6 68.6 ± 9.9 † 18.7 ± 6.6 51.6 ± 7.8 201.2 ± 13.4 † 0.0 ± 0.0
20 15 10 5 0
40.2
53.6
67.1
80.5
93.9
Speed (m•min– 1) Control
Nitro
Renegade
SACH
Fig. 2 Mean ( ± SD) energy expenditure (VO2) of 3 prosthetic feet conditions for transtibial amputees (TTA) compared to non-amputee controls during walking. All subjects completed all walking stages. Energy expenditure was similar between all TTA feet conditions and controls at 40.2 m · min − 1 speed. At speeds 53.6, 67.1, 80.5 and 93.9, energy expenditure was similar between TTA for all feet conditions but significantly greater (p ≤ 0.05) for all TTA feet conditions compared to controls.
Energy expenditure responses during fixed walking and running speeds During walking at fixed speeds, mean (± SD) energy expenditure costs (VO2) were similar between prosthetic feet conditions for ▶ Fig. 2). At all but the slowest walking speed TTA (● (40.2 m · min − 1) energy costs were significantly greater (p ≤ 0.05) for TTA with all prosthetic feet conditions compared to nonamputee controls: SACH, 21–33 % greater; Renegade: 23–28 % greater; Nitro: 28–32 % greater. ▶ Fig. 3), mean (± SD) energy During running at fixed speeds (● expenditure costs were significantly increased (p ≤ 0.05) for TTA using the SACH and Renegade prosthetic feet compared to the Nitro prosthetic foot: SACH 8–18 % greater; Renegade 8–18 % greater. During running, energy costs were significantly greater (p ≤ 0.05) for TTA with all prosthetic feet conditions compared to non-amputee controls: SACH 28–36 % greater; Renegade 27–38 % greater; Nitro 9–32 % greater.
Gait efficiency during self-selected walking and running speeds At SSWS, GE was similar between prosthetic feet conditions for ▶ Fig. 4). However, GE was significantly lower (more effiTTA (● cient; p ≤ 0.05) for non-amputee controls compared to all prosthetic feet conditions for TTA. SSWS was significantly slower
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Because SSWS and SSWR are variable between subjects, a relative measure that integrates speed and energy costs is needed to determine gait efficiency (GE). The criterion measure for GE is defined as energy expenditure per meter traveled and determined from the ratio of VO2 divided by ambulation speed (ml O2 · kg − 1 · m − 1) [8]. The lower the value for GE, the more efficient the gait. For TTA, body weight and body composition measurements were determined without their prosthesis. Percent body fat was determined using air displacement plethysmography with measured thoracic gas volume (BOD POD GS™; COSMED, Rome, Italy).
70 65 60 55 50 45 40 35 30 25 20 15 10 5 0
2
2 1
1
1
1
2 1
1
Peak running speed responses 134.1
147.5
160.9
174.3
187.8
201.2
214.6
–1
Speed (m• min ) Control
Nitro
Renegade
SACH
Fig. 3 Mean (± SD) energy expenditure (VO2) of 3 prosthetic feet conditions for transtibial amputees (TTA) compared to non-amputee controls during running. All control subjects completed all running stages. When TTA subject(s) dropped out of a running stage, the number of TTA subjects completing that speed-stage is indicated in the respective column. Energy expenditure was significantly greater (p ≤ 0.05) for all TTA feet conditions compared to controls at all running speeds (134.1– 214.6 m · min − 1). During running, there were no significant differences in energy expenditure between the SACH and Renegade feet conditions. Energy expenditure was significantly greater (p ≤ 0.05) for the SACH and Renegade feet conditions compared to the Nitro foot condition at all running speeds.
0.4 Gait Efficiency (ml•O2•kg– 1•m–1)
At SSRS, GE was significantly improved (p ≤ 0.05) for the Nitro prosthetic foot compared to SACH and Renegade prosthetic feet ▶ Fig. 4). However, GE was significantly lowest (most for TTA (● efficient; p ≤ 0.05) for non-amputee control runners compared to TTA for all prosthetic feet conditions. At SSRS, the SACH foot was significantly slower (13–16 %; p ≤ 0.05) compared to the Renegade and Nitro feet. Similar to SSWS, SSRS for all prosthetic feet conditions were significantly slower (17–30 %; p ≤ 0.05) for TTA than non-amputee controls.
0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 64.4
67.1
68.8
82.3
123.4 142.4 146.6 176.1
Speed (m•min–1) Walking Control
Running Nitro
Renegade
SACH
Fig. 4 Gait efficiency (ml O2 · kg − 1 · m − 1) of 3 prosthetic feet conditions (SACH, Renegade, Nitro) for transtibial amputees compared to nonamputee controls at self-selected walking and running speeds (SSWS and SSRS). During SSWS and SSRS gait efficiency was significantly lower (p ≤ 0.05; i. e., improved) for controls compared to TTA for all prosthetic feet conditions. Furthermore, SSWS and SSRS were significantly faster (p ≤ 0.05) for controls compared to TTA for all prosthetic feet conditions. Gait efficiency during SSWS was similar between TTA feet conditions, while SSWS was significantly faster (p ≤ 0.05) for Renegade and Nitro compared to SACH. For TTA gait efficiency during SSRS was significantly lower (p ≤ 0.05; i. e., improved) for Nitro compared to SACH and Renegade. SSRS was significantly faster (p ≤ 0.05) for Renegade and Nitro compared to SACH. The number of subjects completing each test condition was n = 3, except SSRS for SACH condition, where it was n = 2.
(p ≤ 0.05) for the SACH foot compared to Renegade and Nitro feet (4–6 %). Additionally, SSWS for all prosthetic feet conditions were significantly slower (16–22 %; p ≤ 0.05) for TTA than nonamputee controls.
A functional difference in peak running speed (mean ± SD) was observed between prosthetic feet conditions for TTA and non-amputee control runners. TTA ran slowest using the SACH foot (peak speed = 154.2 ± 28.4 m · min − 1, 0 ± 0 % grade); moderately faster with the Renegade foot (peak speed = 178.8 + 20.5 m · min − 1, 0 % ± 0 % grade); and fastest with the Nitro foot (peak speed = 201.2 + 13.4 m · min − 1, 0 ± 0 % grade). Although TTA using the Nitro foot, obtained similar VO2 peak levels as non-amputee con▶ Table 1), peak running speed at VO peak was trol runners (● 2 significantly (p ≤ 0.05) faster for non-amputee control runners (peak speed = 232.5 + 15.5 m · min − 1, 2 ± 2 % grade).
Discussion
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When TTA walked at both fixed speeds and at SSWS, no significant differences were observed among the 3 prosthetic feet conditions for energy expenditure (VO2) and GE. However, TTA demonstrated significantly increased energy costs and decreased GE compared to non-amputee controls. At SSWS, TTA demonstrated improved speed with the Renegade and Nitro compared to the SACH, but SSWS for TTA were significantly slower for all prosthetic feet conditions compared to non-amputee controls. Our study is in agreement with the earlier study by Gailey et al. [5] who reported that the energy costs of walking for TTA are significantly increased and SSWS are slower compared to nonamputee controls. However, a major limitation of their study was the great variability in prosthetic components used by TTA subjects. While more current studies have investigated the effect of foot type and energy cost during walking for TTA, the literature has shown inconsistent results. Nielsen et al. [14] reported decreased energy costs and improved GE for TTA using the general purpose ESAR Flex-Foot compared to the traditional SACH foot at fixed walking speeds. Conversely, Hsu et al. [9] reported that energy costs and GE were similar for TTA using the ESAR Flex-Foot and SACH foot but were improved using another type of general purpose ESAR foot (Re-Flex VSP). In another study, Hsu et al. [8] found similar results to the current study in that energy costs for TTA using the traditional SACH foot and 2 general purpose ESAR feet (Flex-Foot and C-Walk) were similar at fixed walking speeds and SSWS. The study by Hsu et al. [10] is perhaps the most contrary to our findings. These researchers reported that during walking at fixed speeds TTA had similar energy costs and GE as non-amputee controls at all walking velocities using the ESAR Re-Flex VSP foot. Furthermore, they reported that TTA had similar energy costs and GE as non-amputee controls using the Flex-Foot and SACH foot at slower walking velocities, but increased energy costs and decreased GE at faster walking velocities. Possible reasons for differences between the present study and these studies were differences in the physical activity levels
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VO2 (ml O2•kg– 1•min– 1)
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added into the calculation of the VO2 (ml O2 · kg − 1 · min − 1) measurements relative to body weight. Since the prosthesis does not consume oxygen this can introduce a systematic error in their VO2 measurements. For example, the mean (+ SD) weight of the running-specific Nitro prosthesis in our study was 1.5 (± 0.5) kg. If a relatively similar prosthetic weight value were subtracted out from the body weight values in their VO2 measurements, the denominator value becomes reduced and VO2 values would be increased. Thus, there may possibly be a significant difference (increase) in VO2 (energy expenditure) for TTA runners compared to non-amputee controls in their study.
Study Limitations and Future Study
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The primary limitation for this study was sample size. It was difficult to recruit TTA participants who met the relatively high level of training for our study’s inclusion criteria. However, our study design utilized case-control matching with repeated measures, which is a well-accepted methodological approach to studying rare conditions, i. e., in this case well-conditioned TTA runners [7, 13, 16]. A primary benefit reported from utilizing this approach is thorough study of available subjects. In terms of disadvantages for such designs, 2 types of bias are commonly described: sampling and observation/recall. In terms of observation bias, we attempted to minimize this by utilizing oxygen uptake, a highly objective measurement, as the study’s primary outcome measure to determine energy expenditure and gait efficiency [8]. Additionally, TTA had accommodation periods for the prosthetic feet conditions, and all subjects had a testing familiarization session before actual testing occurred. In terms of sampling bias our study had well defined inclusion criteria for participants, and thus our results may be generalizable only to TTA with these characteristics. For future study we are planning to follow the same study design and investigate the energy efficiency of these same 3 prosthetic feet during walking and running in transfemoral amputee runners compared to non-amputee control runners.
Conclusion
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For clinical relevance, our data suggest that for TTA walking on level surfaces, energy costs are mostly similar between prosthetic feet conditions, but ESAR feet likely provide faster SSWS. For TTA performing distance-type running, energy costs are reduced and GE, SSRS & peak speed are improved using the running-specific ESAR Nitro foot compared to the traditional SACH foot and general purpose ESAR Renegade foot. Nonetheless, for all prosthetic feet conditions, TTA runners demonstrated an energy cost and performance disadvantage during walking and running compared to matched non-amputee runners.
Acknowledgements
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This study was funded by the University of South Florida’s Signature Interdisciplinary Program in Cardiovascular Research Award # 10009-614101. We wish to thank Freedom Innovations, Irvine, CA, for providing the Renegade and Nitro prosthetic feet for the study.
Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
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and conditioning of TTA subjects, differences in accommodation periods for each foot type, differences in prosthetic fittings, differences in randomization and allocation concealment techniques, and, in some studies [8, 9, 14], the lack of non-amputee control subjects for comparison. In the current study we observed that the run-specific ESAR Nitro foot provided TTA reduced energy costs and improved GE, SSRS & peak speed during distance-type running compared to the SACH and ESAR Renegade feet. However, a major finding in our study was that TTA runners using the run-specific ESAR Nitro foot expended significantly more energy at every speed and ran slower at VO2 peak than closely matched non-amputee control runners. Thus, in our study TTA runners using the runspecific ESAR Nitro foot demonstrated an energy cost and performance disadvantage compared to non-amputee control runners. These results differ from other running studies. Hsu et al. [9] reported results that were similar to what they observed during walking, in which energy costs and GE were similar for TTA using the ESAR Flex-Foot and SACH foot, but were improved using another type of general purpose ESAR foot (Re-Flex VSP). Major factors limiting the comparison of their findings with those of the current study are that their study did not describe specific inclusion criteria for TTA participants concerning their run training history, their TTA running speeds during testing were much slower (120.69–147.5 m · min − 1 vs. 134.1–214.6 m · min − 1), their study lacked a non-amputee control group and did not test a run-specific ESAR foot. In the study by Weyand et al. [21] these researchers reported that the metabolic costs during near Olympic-level sprint performance for an elite bilateral TTA runner and intact-limb elite runners, are mostly similar. Since the Weyand et al. [21] study involved high-intensity sprint running in a single case, and our study involved high-intensity distance-type running it is reasonable to suggest that inferences from each study’s finding could be limited to their respective running settings. The running study that most closely matches the conditions of the current study is the study reported by Brown et al. [1]. Recreational TTA runners using running-specific ESAR prosthetic feet were compared to control non-amputee runners. They reported that TTAs using running-specific ESAR feet had similar energy costs at all speeds and obtained similar peak running speeds as non-amputees. The mean peak running speed and peak VO2 values of TTA runners in the Brown et al. [1] study were 254.8 ± 32.2 m · min − 1 and 56.3 ± 7.6 ml O2 · kg − 1 · min − 1. The mean peak running speed and peak VO2 values of TTA runners in the current study were 201.2 ± 13.4 m · min − 1 and 51.6 ± 7.8 ml O2 · kg − 1 · min − 1. These data indicate both studies involved well-trained recreational TTA runners, but the TTA runners in the Brown et al. [1] study were slightly more fit than the TTA runners in the current study. Brown et al. [1] concluded that although TTAs using running-specific ESAR feet performed similarly to non-amputee controls, they did not gain a physiological advantage over non-amputee runners. We suggest 2 potential methodological differences in the Brown et al. [1] study compared to our study may contribute to the difference in results. In the Brown et al. [1] study subjects used their own running prosthesis, which indicates variability in both the type/brand of running-specific ESAR foot and standardization of prosthetic fittings. In the present study, all subjects utilized the same running-specific ESAR Nitro foot and were fitted by the same study prosthetists (JTK & MJH). Another concern is that in the Brown et al. [1] study, the weight of the prosthesis was
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Mengelkoch LJ et al. Energy Costs & Performance … Int J Sports Med 2014; 35: 1223–1228
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
1228 Clinical Sciences
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