PEOPLE WITH TRANSTIBIAL amputation lose the anklefoot

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1 123 ORIGINAL ARTICLE The Effects of Prosthetic Foot Design on Physiologic Measurements, Self-Selected Walking Velocity, and Physical Activity in People With Transtibial Amputation Miao-Ju Hsu, PhD, PT, David H. Nielsen, PhD, PT, Suh-Jen Lin-Chan, PhD, PT, Donald Shurr, MA, PT, CPO ABSTRACT. Hsu MJ, Nielsen DH, Lin-Chan SJ, 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: Objective: To investigate the physiologic differences during multispeed treadmill walking and physical activity profiles for the Otto Bock C-Walk foot (C-Walk), Flex-Foot, and solid ankle cushion heel () foot in people with transtibial amputation. Design: A repeated-measures design with 3 prostheses. Setting: Research laboratory. Participants: Eight men with unilateral transtibial amputation. Interventions: Not applicable. Main Outcome Measures: Physiologic responses (energy expenditure, gait efficiency, exercise intensity, rating of perceived exertion [RPE]) during multispeed treadmill walking (53.64, 67.05, 80.46, 93.87, m/min) test were analyzed with 2-way repeated-measures analysis of variance (ANOVA). One-way ANOVA was employed to analyze foot-type differences for self-selected walking velocity (SSWV), and steps per day (daily activity). Analysis of covariance was used to analyze foot-type differences with SSWV as the covariable for the physiologic measurements. Results: The C-Walk had a trend of improved physiologic responses compared with the ; however, no foot-type differences were statistically significant. Compared with the C-Walk and, the Flex-Foot showed no significant differences in energy expenditure and gait efficiency, but significantly lower percentage of age-predicted maximum heart rate and RPE values. Conclusions: The energy storing-releasing feet appeared to have certain trends of improved gait performance compared with the ; however, not many objective foot-type differences were significantly noted. Further studies with a larger sample size are suggested. Key Words: Amputation; Heart rate; Oxygen consumption; Physical fitness; Prostheses and implants; Prosthesis design; Rehabilitation. From the Institute and Faculty of Physical Therapy, National Yang Ming University, Taipei City, Taiwan (Hsu); Graduate Program in Physical Therapy and Rehabilitation Science, University of Iowa, Iowa City, IA (Nielsen, Shurr); and School of Physical Therapy, Texas Woman s University, Dallas, TX (Lin-Chan). Supported by a grant from the Otto Bock Group, Minneapolis, MN. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Correspondence to Miao-ju Hsu, PhD, Institute and Faculty of Physical Therapy, National Yang Ming University, No.155, LiNong St 2 Sec, Pei-Tou District, Taipei City, Taiwan, mjhsu@ym.edu.tw. Reprints are not available from the author /06/ $32.00/0 doi: /j.apmr by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation PEOPLE WITH TRANSTIBIAL amputation lose the anklefoot complex and associated muscle function. Even though compensation is possible through the recruitment of substitute muscles at the ipsilateral and contralateral hips and knees, 1-4 research has shown that the gait of individuals with transtibial amputation is less efficient, requires increased energy expenditure, and produces a higher relative exercise intensity. 1,5,6 The study by Waters et al 7 of subjects with vascular and traumatic transtibial amputation showed that the subjects with vascular amputation expended 55% more kcal kg 1 m 1 at the self-selected walking velocity (SSWV), and the subjects with traumatic amputation expended 25% more kcal kg 1 m 1, compared with subjects with nonpathologic gait at SSWV. Prosthesis design has been a contributing factor to variations in these outcome parameters. One of the most common energy-storing prosthetic feet currently available on the market is the Flex-Foot. a From a design perspective, the construction of the Flex-Foot provides dynamic function and allows energy to be stored through compression of an internal plate during heel contact and early stance with subsequent energy release during late stance and push-off The 1C40 Otto Bock C-Walk foot (C-Walk) b is among the newest energy-storing prostheses on the market. The main features of this prosthetic foot include the carbon fiber reinforced plastic spring elements (C-spring and base spring) and a control spring (fig 1). 11 Due to its unique design, the C-Walk is claimed to allow people with transtibial amputation to walk smoothly and comfortably at slow as well as higher walking speeds and also for use in recreational activities. Research on the interprosthesis comparison between the Flex-Foot and C-Walk is lacking. Physiologic assessment is an important aspect in evaluating efficacy of foot types. In gait studies of prosthetic foot types, the most commonly used physiologic variables include energy expenditure, gait efficiency, relative exercise intensity, and rating of perceived exertion (RPE). Gait efficiency has been defined as energy expenditure per distance traveled and is derived from the ratio of the oxygen consumption divided by the walking speed. 5,12 Measuring oxygen consumption requires expensive equipment and trained personnel, which are not always available. Therefore, heart rate and RPE have been used in many studies for physiologic monitoring. The exercise heart rate, expressed as a percentage of age-predicted maximum heart rate (%APMHR [exercise heart rate/age-predicted maximum heart rate] 100), has been used to indicate the relative exercise intensity during ambulation. 13 Most investigations on assessing gait performance with various prostheses have been done in laboratory settings. Nevertheless, those tests fail to represent the lifestyle or the full

2 124 ENERGY STORING-RELEASING PROSTHETIC FEET, Hsu Fig 1. The basic structure of the C-Walk. Abbreviation: CFRP, carbon fiber reinforced plastic. extent of the daily activities of people with transtibial amputation. The pedometer is a step-counter consisting of a miniature pendulum transducer that swings with each step and registers the number of steps on an internal counter. The pendulum mechanism is driven by oscillation of the pelvis during gait. The use of pedometers has shown promise in monitoring physical activity in various populations, including individuals with pathologic gait Pedometry may possibly be a useful tool to indicate the contrasts in physical activity levels due to the use of different types of prosthesis by individuals with transtibial amputation. The purpose of this study was to investigate the physiologic differences in gait (energy expenditure, gait efficiency, exercise intensity, RPE) for the C-Walk, Flex-Foot, and solid ankle cushion heel () foot b during multispeed treadmill walking (53.64, 67.05, 80.46, 93.87, m/min, SSWV) in people with transtibial amputation. A secondary purpose involved pedometry determined foot-type comparisons of daily physical activity profiles. We hypothesized that the C-Walk and Flex- Foot were superior to the foot on the parameters measured. METHODS We recruited eight men without significant medical problems other than unilateral traumatic transtibial amputation. Subjects had experience in prosthesis use for at least 1 year, were proficient walkers and had adequate exercise tolerance to achieve a treadmill walking speed of m/min without undue difficulty. The prestudy foot types of the subjects were 3 Flex-Foots, 2 ReFlex Vertical Shock Pylons, 1 foot, 1 Flex-Walk, and 1 Icon-Allurion. We obtained written informed consent from each subject in accordance with the Human Subjects Review Committee of the College of Medicine at the University of Iowa prior to admittance into the study. Subjects were required to undergo 3 separate test sessions according to foot type (C-Walk, Flex-Foot, foot). To ensure adequate prosthesis acclimation, subjects were asked to wear the relevant test foot for 4 weeks prior to laboratory testing. Several prosthetists were involved in fitting and alignment of the prostheses. However, the same prosthetist was responsible for all 3 tested feet for a respective subject. Each subject used a standard socket for all 3 tested prosthetic feet. General selection criteria for a prosthetic foot were based on the subject s foot size and body weight. For the Flex-Foot, in addition to foot size and body weight, impact level (high, medium, low) based on the subject s physical activity level was also considered. As a general reference, the Day Activity Score inventory 18 was used to evaluate the physical activity level of the subjects. The descriptive data of subjects are presented in table 1. A 2-factor (speed, type of prosthesis) repeated-measures design involving multiple speed treadmill walking (53.64, 67.05, 80.46, 93.87, m/min, SSWV) was employed for the physiologic assessment of each prosthesis. The dependent physiologic assessment variables included energy expenditure (oxygen consumption [in ml kg 1 min 1 ]), gait efficiency, relative exercise intensity, and RPE. Gait efficiency was calculated from oxygen consumption divided by speed ([ml kg 1 min 1 ]/[m/min] ml kg 1 m 1 ). The relative exercise intensity was expressed as (%APMHR [exercise heart rate/age-predicted maximum heart rate] 100). A repeated-measures design was used for daily activity and SSWV assessments. The dependent variables included the pedometers mean step counts per day and the SSWV. The foot-type testing order was nonrandomized. All subjects attended a preliminary session, which included general orientation to test procedures, familiarization with the RPE scale, practice of treadmill walking, instructions on using the pedometer and recording the daily activity log, and instructions on completing all necessary paperwork. In addition to the practice session, 3 test sessions on separate days at 1-month intervals were required. Each subject tested a single prosthesis per test session. The C-Walk was scheduled on either the first or the second test session, as was the. The test order of these 2 prosthetic feet was counterbalanced between the first and the second sessions. In response to subjects interest in and suggestions on the Flex-Foot, subjects were recruited back for a third test session, which was the Flex-Foot test. To ensure acclimation to the specific prosthesis for testing purposes, the subject wore the prosthesis to be tested for the month prior to each test session. During the same period, the subject was given a light-weight, battery-operated Yamax Digiwalker pedometer, c which he used to count his daily number of steps. The pedometer was positioned slightly anterior to the crest of the iliac on the side of the amputation. The subject put on the pedometer as soon as he arose in the morning; at the end of each day, he recorded the total steps for the day and reset the pedometer to zero for use the next morning. The subject was asked to continuously record each day s total for 1 month. The data from the pedometer were averaged and expressed as steps per day. To ensure the correct use of the pedometer, telephone follow-up calls were done. Each of the test sessions involved an SSWV treadmill test and a multiple speed treadmill walking test. A 20-minute recovery period was provided between the SSWV test and the multiple speed treadmill test. Table 1: Descriptive Data for the Subjects Variable Mean SD Range Age (y) Body weight (kg) Height (m) Stump length (m) Prosthesis experience (y) Mass of C-Walk (kg)* Mass of Flex-Foot (kg)* Mass of (kg)* Day Activity Scale (U) Abbreviation: SD, standard deviation. *Refers to the entire prosthetic limb. Day Activity Scale scores 18 range from 70 to 50 with following categories: very high, 30; high, 10 to 29; average, 1 to9;restricted, 40 to 10; inactive, 40.

3 ENERGY STORING-RELEASING PROSTHETIC FEET, Hsu 125 The protocol for the SSWV test was a modified version of that reported by Holt et al. 19 The initial speed was 67.05m/min. The subject walked on the treadmill at this speed for 30 seconds, and then, with the direction from the subject, the experimenter increased or decreased the speed in increments of 5.36m/min each 30 seconds until a comfortable speed was found. The subject then walked at this comfortable speed with 2.68m/min increment, 30-second speed adjustments being made as indicated by the subject. Continuous walking for 2 minutes with no requested speed adjustment constituted the SSWV. During the test, no feedback of the actual treadmill speed was provided to the subject. To ensure that the speed chosen was consistent, 1 repeated trial was conducted with the same procedure. The average of the 2 SSWV trials was used in the final data analysis. The multiple speed walking test employed a continuous, progressive protocol, which consisted of a preliminary 4-minute resting stage involving data collection with the subject in a standing position, followed by six 4-minute walking exercise stages (53.64, 67.05, 80.46, 93.87, m/min, SSWV). The testing protocol ordered the SSWV exercise stage according to its relative speed. Following the treadmill test, a 2- to 3-minute cool-down period was provided at 67.05m/min. A chair was placed at the end of the treadmill in the event that the subject needed to sit down. During the treadmill test, we measured oxygen consumption by the open-circuit, breath-by-breath method with a MedGraphics CardiO 2 metabolic cart. d Heart rate was recorded by the radiotelemetry system. e A modified chest manubrium V5 (CM5) recording electrode lead system was used. Prior to the application of the electrodes, the selected sites were prepared by cleaning and rubbing with alcohol pads. Procedures to record the heart rate were conducted as previously reported. 6,13 Heart rate and oxygen consumption were monitored continuously, however, the last 1-minute, steady-state values were averaged and used for the data analysis. At each walking stage, RPE was recorded during the final minute. The gait efficiency and the %APMHR were calculated for each walking stage. To verify the accuracy of the pedometer for subjects with transtibial amputation, we administered a validity test during the multiple speed treadmill test. The validity test involved comparing the pedometer step count to the step count determined from a mechanical handheld counter. The accuracy of the pedometer was calculated as (100 [absolute value of {the number of steps recorded from the pedometer actual number of steps} / actual number of steps] 100). The statistical analysis was performed using the Statistical Analysis System f for Windows library program provided by the University of Iowa. Means and standard deviations (SDs) were calculated for each dependent variable. We used 2-way repeated-measures analysis of variance (ANOVA) to test for main effects and the interaction of foot type (C-Walk and Flex-Foot vs ) versus speed of ambulation (53.64, 67.05, 80.46, 93.87, m/min) for each physiologic measurement Energy Expenditure (ml o 2 kg -1 min -1 ) Speed (m /m in ) (energy expenditure, gait efficiency, %APMHR, RPE) for the treadmill walking tests. One-way ANOVA was employed to analyze foot-type differences for SSWV, and steps per day (daily activity). Analysis of covariance (ANCOVA) was used to analyze foot-type differences with SSWV as the covariable for the physiologic measurements (energy expenditure, gait efficiency, %APMHR, RPE). Tukey-Kramer follow-up tests were performed when significant main effects of foot type existed. A level of P less than.05 was adopted for the determination of statistical significance. Intraclass correlation coefficient (ICC) analyses were performed to examine test-retest reliability for the SSWV, according to foot type. RESULTS All subjects completed the SSWV and multiple-speed walking tests from to m/min on the treadmill without difficulties. However, as for data on pedometers during the 1-month accommodation interval, we had missing data on 4 tests (C-Walk, Flex-Foot, tests for 1 subject; Flex-Foot test for another subject) due to subjects sporadic noncompliance. The statistical analysis was adjusted for this unbalanced design. The energy expenditure group means for subjects with transtibial amputation during walking from to m/ min with the C-Walk, Flex-Foot, and are graphically presented in figure 2. During walking, oxygen consumption increased with speed in a curvilinear fashion for all subjects, regardless of foot type. The energy expenditure of the Flex- Foot appeared to be slightly less than that of the, and the C- Wa lk Fig 2. Group means and SEs for energy expenditure (in mlo 2 kg 1 min 1 ) during walking from to m/min (N 8). Table 2: Summary ANOVA Results for Oxygen Uptake, %APMHR, Gait Efficiency, and RPE During Walking From to m/min Variable Degrees of Freedom Oxygen Uptake (mlo 2 kg 1 min 1 ) %APMHR Gait Efficiency (mlo 2 kg 1 m 1 ) RPE F P F P F P F P Foot * * Speed * * * * Foot by speed *Significant difference (P.05).

4 126 ENERGY STORING-RELEASING PROSTHETIC FEET, Hsu %APMHR Speed (m/min) C-Walk Fig 3. Group means and SEs of relative exercise intensity (%AP- MHR) during walking from to m/min (N 8). Gait Efficiency (mlo 2 kg -1 m -1 ) Sp eed (m/min) C-Walk differences between the Flex-Foot and the appeared to progressively increase with increases in walking speed. The C-Walk appeared to have lower oxygen consumption values at and 80.46m/min when compared with the Flex-Foot. However, the ANOVA results revealed the differences between foot types were not significant (table 2). The %APMHR group means and standard errors (SEs) for the subjects walking from to m/min with the C-Walk, Flex-Foot, and are graphically presented in figure 3. During walking, %APMHR increased with speed in a curvilinear fashion for all subjects. The between foot-type differences slightly increased with increases in walking speed. The Flex-Foot appeared to have lowest %APMHR, followed by the C-Walk, and then the across all walking speeds from to m/min. The ANOVA results showed that the differences between foot types were statistically significant (see table 2). The Tukey-Kramer follow-up tests in table 3 revealed those significant differences between the Flex-Foot versus the C-Walk and the. However, no significant difference was found between the C-Walk and the. The gait efficiency group means for subjects during walking from to m/min with the C-Walk, Flex-Foot, and are graphically presented in figure 4. The lower the value for gait efficiency, the more efficient the gait. During progressively increasing speeds of walking, a parabolic (downwardly oriented concave) curve was seen in all subjects. The C-Walk and the Flex-Foot appeared to be more efficient compared with the across all tested walking speeds, and with greater differences between the C-Walk and the at mid-range speeds (67.05 and 80.46m/min), with greater differences between the Flex-Foot and the at the higher walking speeds (93.87 and m/min). The ANOVA results revealed the differences between foot types, however, the results were not statistically significant (see table 2). Fig 4. Group means and SEs of gait efficiency (in mlo 2 kg 1 m 1 ) during walking from to m/min (N 8). The RPE group means and SEs for the subjects walking from to m/min with the C-Walk, Flex-Foot, and are graphically presented in figure 5. As illustrated, during walking, RPE increased with speed. The RPE of the Flex-Foot appeared to be lower compared with the C-Walk and across all walking speeds. Compared with the, the RPE of the C-Walk appeared to be less at the 2 lower speeds, and 67.05m/min, but higher at 80.46, 93.87, and m/min. The ANOVA results revealed that the differences between foot types were significant (see table 2). As shown in table 3, Tukey-Kramer adjusted follow-up test revealed those significant differences between the Flex-Foot versus the C-Walk and. The Flex-Foot appeared to have significantly lower RPE than the C-Walk and. However, no significant difference was found between the C-Walk and. The test-retest reliability ICCs for the SSWV were high and statistically significant. The ICCs were.926 (P.000),.972 (P.000), and.926 (P.000) for the C-Walk, Flex-Foot, and, respectively. The SSWV group means and SDs for the subjects walking with the C-Walk, Flex-Foot, and are presented in table 4. The subjects appeared to choose the RPE C-Walk Table 3: Summary of the Tukey-Kramer Follow-Up Analysis for %APMHR and RPE Analysis %APMHR RPE C-Walk Flex-Foot.040*.007* C-Walk Flex-Foot.003*.002* *Significant difference (P.05). 5 Speed (m/min) Fig 5. Group means and SEs of RPE during walking from to m/min (N 8).

5 ENERGY STORING-RELEASING PROSTHETIC FEET, Hsu 127 Table 4: Group Data for SSWV and Daily Activity for the C-Walk, Flex-Foot, and Variable C-Walk Flex-Foot SSWV (m/min) Physical activity (steps/d) NOTE. Values are mean SD. highest SSWV while walking with the Flex-Foot, followed by the C-Walk, and then the. However, the ANOVA results revealed no significant differences between foot type (F 1.48, P.26). Based on the unequalness of the SSWV, additional analyses of the physiologic measurements were performed with ANCOVA using the SSWV as the covariable. The ANCOVA results showed no significant differences between foot types on energy expenditure (F.15, P.866), %APMHR (F.10, P.903), gait efficiency (F.15, P.864), and RPE (F.15, P.863). Pedometers were used to assess subjects daily activities. The validity test of pedometers showed the accuracy of the pedometer was 93.8% 6.5%. Four daily records (C-Walk, Flex-Foot, and data for 1 subject, Flex-Foot data for another subject) were missing due to subjects sporadic noncompliance. The daily activity (in steps/d) group means and SDs based on 4-week data collection periods for the subjects with the C-Walk, Flex-Foot, and are presented in table 4. The daily activity for the Flex-Foot was the highest, followed by the, and then the C-Walk. However, the ANOVA results revealed no significant foot-type differences were found (F 3.56, P.06). DISCUSSION The energy expenditure in people with transtibial amputation was higher than that of people with nonpathologic gait at similar speeds, and the increased energy expenditure became more apparent with increasing walking speeds. Nielsen et al 6 reported that during walking from to m/min, people with nonpathologic gait required energy expenditure from 9.00 to 16.43mLO 2 kg 1 min 1, while people with traumatic transtibial amputation spent an average of to 26.25mLO 2 kg 1 min 1. Our subjects required an average of 9.97 to 19.00mLO 2 kg 1 min 1 during walking at the same range of speeds. The increased energy expenditure seen in persons with transtibial amputation during walking was possibly associated with altered kinematics and kinetics of gait due to the loss of ankle function. 1,2,4 However, it is interesting to note that the differences in energy expenditure between our subjects with transtibial amputation and those with nonpathologic gait were less than in Nielsen s report. Similarly, Fisher and Gullickson 5 reported that people with traumatic transtibial amputation expended an average of 20% more energy than people with nonpathologic gait during treadmill walking from to 90.12m/min. In contrast, the present study showed only about a 10% increase in the persons with transtibial amputation during the functional walking speeds from to m/min. A possible explanation may be that the subjects in the current study were all physically active. As reported in table 1, the Day Activity Scale group mean was U, indicating that they were at high to very high activity scale levels in individuals with lower extremity amputation. 18 However, physical activity level was not reported in Nielsen s and Fisher s studies. In addition, Nielsen 6 showed that the Flex-Foot was superior to the at speeds above 53.64m/min. This was not supported by our statistical results. A possible explanation may be that the subjects we recruited in the present study were more motor adept because several of them participated in sports in their leisure time. In general, our subjects appeared to have accommodated to their disability well and were able to adapt to the shortcomings of the foot better than the subjects in Nielsen s study. Thus, the differential functional advantages between the static and the dynamic Flex-Foot were minimized. This study supports that the relation between gait efficiency and speed is a parabolic curve, which has been reported in the literature both in people with nonpathologic gait and in those with transtibial amputation. 5,6,8,12 As shown in figure 4, the Flex-Foot appeared to be more advantageous at the higher walking speeds. One might speculate that the Flex-Foot could be more beneficial than the to people with transtibial amputation who are engaged in more activities involving higher walking speeds, jogging, or running. However, because this was not supported by the statistical results of our study, more research with a larger sample size is needed to clarify this speculation. The results of previous studies indicated that the optimal gait efficiency in people with nonpathologic gait usually occurred at a range from to 100m/min, with the most frequently reported value being 80.46m/min, while people with transtibial amputation ranged from to 90m/min, with the most frequently reported values below 70m/min. 1,6,8,12,20 Our present study showed that optimal gait efficiency in people with transtibial amputation occurred at approximately 80.46m/ min for the C-Walk and, and slightly above for the Flex-Foot (see fig 4); the optimal gait efficiency for all 3 feet appeared to occur at the higher end of the range reported in the literature. This finding may be because our subjects had traumatic etiologies. In addition, our subjects were more physically active and adept in adjusting to the handicaps of walking due to amputation. Similarly, Lehmann et al 8 investigated foot-type differences (Flex-Foot, Seattle foot, ) in people with transtibial amputation during walking and running and found optimal gait efficiency occurring around 90m/min, regardless of foot type. Their subjects appeared to be quite fit and were able to run up to 200m/min, which may explain why the optimal gait efficiency occurred at higher speeds and also, why minimizing of the foot-type differences was seen. The Flex-Foot had significantly lower relative exercise intensity than the C-Walk and. One possible explanation may be the loss of muscle mass associated with transtibial amputation. Research on arm exercise compared with leg exercise has revealed that arm exercise, with smaller muscle mass, evokes higher heart rate responses. 21,22 Because of loss of muscle mass, the stress experienced by people with transtibial amputation may be heightened and thus foot-type differences magnified. Another explanation may be psychologic factors. Research has shown heart rate is affected by factors such as depression, anxiety, and perceptions of fatigue. 12,23 In this study, general feedback from all subjects favored the Flex-Foot the most, followed by the C-Walk and then. This suggests that, possibly, the subjects felt most comfortable

6 128 ENERGY STORING-RELEASING PROSTHETIC FEET, Hsu when they were walking with the Flex-Foot, which may have further reduced the relative exercise intensity. Also, we may speculate that the Flex-Foot may have some advantages that help subjects reduce the level of stress during walking. Klute et al 24 indicated that the stiffness of the heel and fore-foot keel of a prosthetic foot may be an important factor associated with the level of soft tissue trauma resulting from loading on the residual limb during walking. Because the Flex-Foot appeared to have higher foot compliance than the, the Flex-Foot may lessen the discomfort that subjects experienced on the residual stump during walking, enabling them to walk more comfortably and smoothly. Accordingly, these indirect effects may have influenced the foot-type differences seen for the %APMHR and the RPE measurements. Because the testing protocol in the present study involved treadmill walking, the SSWV was determined for the treadmill and not for overground walking. The SSWV in people with nonpathologic gait has been reported from 74.3 to 100m/min, with the most frequently reported value being 80.5m/min. In contrast, in people with transtibial amputation, the SSWV ranged from 48 to 90m/min. 4,5,8,25 This population has been reported in the literature to have an SSWV up to 44% lower than that of people with nonpathologic gait. Different characteristics of subjects between studies, such as differences in physical fitness, the cause of amputation, height, and age, may contribute to this wide range of the SSWV seen in people with amputation. According to the SSWV test on the treadmill in our current study, the SSWV showed a 12%, 11%, and 13% lower velocity than that of people with nonpathologic gait for the C-Walk, Flex-Foot, and, respectively. This finding was in agreement with previous studies revealing that the SSWV in people with transtibial amputation was decreased. 1,5,7 The 2 energy-storing prosthetic feet that we investigated, the C-Walk and Flex-Foot, appeared to improve the SSWV compared with the ; however, the differences did not reach statistical significance. This result disagreed with the studies of Nielsen 6 and Synder 26 and colleagues, which showed the Flex- Foot improved the SSWV compared with the. Characteristics of subjects, such as physical fitness level and cause of amputation (traumatic vs dysvascular amputation) may contribute to this disagreement. However, our findings agreed with the studies of Lehmann 8 and Torburn 27 and colleagues. Nevertheless, in our study, the SSWV was approximately 70m/min for the C-Walk and the Flex-Foot, and 67m/min for the. In contrast, Lehmann demonstrated the SSWV was 90m/min for subjects walking with the Flex-Foot and, which appears to exceed the reported average value of 80.5m/min for people with nonpathologic gait. Differences in physical fitness, height, and age between subjects in our current study and those in Lehmann s study may help explain the difference in the SSWV. The SSWV has been shown to occur at the optimal gait efficiency in people with nonpathologic gait and people with transtibial amputation. 6,8,12 However, it is of interest to note that in our current study, regardless of foot type, the SSWV found on the treadmill test occurred at a lower speed than the speed at optimal gait efficiency. In contrast, Lehmann s study showed the SSWV tested overground occurred at a similar speed with that of the optimal gait efficiency during multiple speed treadmill test for the Flex-Foot, Seattle foot, and. A contributing factor to this inconsistency may be treadmill versus overground walking. Though research appears to show no significant differences in energy cost during walking on the treadmill versus overground, 28 no literature was found to demonstrate differences on SSWV for treadmill versus overground walking. Factors such as anxiety of subjects and variations in protocols used to test the SSWV may possibly cause differences between the SSWV tested on the treadmill and that tested overground. Further research is needed to verify this assumption. With heightened attention on the relation between physical inactivity and cardiovascular diseases, the changes of lifestyle in people with amputation due to different prosthetic feet appear to be of interest when assessing the efficacy of various foot types. Pedometry has been shown to successfully monitor physical activity in various populations, including people with pathologic gait. However, our research is the first study to utilize pedometry to evaluate foot type-related difference in physical activity in persons with transtibial amputation. In our study, the daily activity (steps/d) of the subjects was evaluated via pedometry during the 4-week acclimation periods for the respective test foot type. The validity test of the pedometer on the treadmill test revealed that the accuracy of the pedometer was about 93.8%, which was within the range (87.5% 99.3%) reported in the literature. 17,29,30 The Flex-Foot appeared to have an approximate 30% and 26% increase in daily physical activity compared with the C-Walk and the, respectively. The ANOVA results revealed that the Flex-Foot did not significantly improve physical activity; however, with a P value (P.06) approaching P equal to.05, the 30% and 26% increase in daily physical activity appeared to be clinically significant. CONCLUSIONS The energy storing-releasing prosthetic feet, the C-Walk and Flex-Foot, are speculated to improve gait performance compared with the traditional foot, the, and have advantages to allow people with transtibial amputation to participate in more vigorous physical activities, such as brisk walking. Our assessments based on physiologic measurements, SSWV, and daily activity aspects demonstrated certain trends of improved gait performance compared with the ; however, not many objective foot-type differences were significantly noted. Nevertheless, these conclusions are based on our small sample size of 8 physically active persons with traumatic amputation during constrained walking on a treadmill. More research has to be done to investigate whether those foot-type differences are clinically important. Future studies with a larger sample size are suggested. In addition, consideration should be given to the characteristics of subjects, such as physically active versus sedentary people with transtibial amputation, and the etiology of amputation. References 1. Breakey J. Gait of unilateral below-knee amputees. Orthot Prosthet 1976;30: Culham EG, Peat M, Newell E. Below-knee amputation: a comparison of the effect of the foot and single axis foot on electromyographic patterns during locomotion. Prosthet Orthot Int 1986;10: Hurley GR, McKenny R, Robinson M, Zadravec M, Pierrynowski MR. The role of the contralateral limb in below-knee amputee gait. Prosthet Orthot Int 1990;14: Winter DA, Sienko SE. Biomechanics of below-knee amputee gait. Biomechanics 1988;21: Fisher SV, Gullickson G. Energy cost of ambulation in health and disability: a literature review. Arch Phys Med Rehabil 1978;59: Nielsen DH, Shurr DG, Golden JC, Meier K. Comparison of energy cost and gait efficiency during ambulation in below-knee amputees using different prosthetic feet a preliminary report. J Prosthet Orthot 1988;1:24-31.

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