Walking Economy Research Articles

Assessment of aerobic capacity and walking economy of unilateral transfemoral amputees

Studies of the maximal oxygen uptake (VO(2max)) of transfemoral amputees have mostly used protocols that activate a relatively small muscle mass. Consequently, transfemoral amputee VO(2max) may be systematically underestimated, and the validity of these test protocols is questionable. (1) Investigate validity and reliability of a VO(2max) walking protocol and (2) compare the VO(2max) of a transfemoral amputee group with a group of matching controls. (1) Randomized crossover study: walking versus running VO(2max) for the control group and (2) case-control study: transfemoral amputees versus control group VO(2max). Twelve transfemoral amputees and control participants performed a walking VO(2max) test with increasing treadmill inclinations to voluntary exhaustion. The control group also completed a running ("gold-standard") VO(2max) test. Mean (standard deviation) control group VO(2max) following walking and running was similar, that is, 2.99 (0.6) L min(-1) and 3.09 (0.7) L min(-1), respectively. Mean (standard deviation) transfemoral amputee walking VO(2max) was 2.14 (0.8) L min(-1) (compared to CON; p < 0.01). Mean intraclass correlation coefficient of repeated VO(2) measurements was 0.97, and within-subjects standard deviation was 60 mL min(-1). The walk protocol is valid. Walking VO(2max) of transfemoral amputees was 40% lower compared to control group. Reliability of the walking protocol is comparable to other walking protocols. Clinical relevance The design, alignment, and materials of prostheses are important for effective ambulation. Cardio-respiratory fitness is, however, also important in this regard, and a low fitness may compromise health and independent living. Hence, transfemoral amputees with low physical fitness should engage in regular physical activity to improve health, gait capacity, and independency.

The Effect of Exercise on Fitness and Performance-Based Tests of Function in Intermittent Claudication: A Systematic Review

Exercise is a widely accepted treatment known to improve walking ability in persons with peripheral arterial disease (PAD); however, it has not been confirmed as to whether exercise improves fitness and performance-based function and, consequently, performance of activities of daily living (ADL). This systematic review aims to identify whether any mode of structured exercise improves physical fitness or performance-based tests of function and whether improvement in walking ability is related to an improvement in these outcomes. Eligible studies included randomized controlled trials (RCTs) using an exercise intervention for the treatment of intermittent claudication with fitness (including the 6-min walk (6MW), aerobic capacity, shuttle and muscle strength) tests and performance-based tests of function as the outcomes. STUDY APPRAISAL AND METHODS: Assessment of study quality was performed using a modified version of the Physiotherapy Evidence Database Scale (PEDro). Relative effect sizes, mean differences (MDs) and 95 % confidence intervals were calculated and adjusted via Hedges' bias-corrected for small sample sizes. Regression analyses were performed to establish relationships between walking ability and fitness outcomes. Twenty-four RCTs met the inclusion criteria: 19 aerobic training interventions and 5 progressive resistance training (PRT). In total 924 participants (71 % male) were studied; with few participants over 75 years of age and the mean ankle brachial index was mean ± standard deviation (SD) 0.66 ± 0.06. The most common outcome measured was aerobic capacity (52 % of trials), which improved by 8.3 % ± 8.7 % on average. Although there were no significant relationships, up to 16 % of the variance in walking distances can be explained by changes in walking economy. Muscle strength was measured in only five trials, improving by 42 % ± 74 % on average. There was a strong significant relationship between change in plantar flexor muscle strength and change in initial claudication time (r = 0.99; p = 0.001) and absolute claudication time (r = 0.75; p = 0.05) measured on a treadmill across trials measuring this muscle group. The 6MW distance was measured in only 14 % of trials. Walking and PRT significantly improved 6MW initial claudication distance (MD range 52-129 m) and total walking distance (MD range 36-108 m) in studies that measured this outcome. Only one trial assessed performance-based tests of function, and they did not improve significantly. Although data are limited, there is a strong significant relationship between plantar flexor muscle strength and treadmill walking ability. More research is needed to assess improvements in walking economy at specific timepoints and whether this translates to improvements in claudication outcomes and measurements pertaining to muscle strength. Future trials should focus on interventions that improve lower limb muscle strength and assess muscle strength, power and endurance across a variety of lower extremity muscle groups in order to understand these relationships further. The 6MW, muscle strength and performance-based tests of function such as chair stand, balance scale, stair climb and gait speed are understudied in PAD. Future trials should examine the effects of exercise on performance-based tests of function, which may predict actual ADL performance and incident disability.

Metabolic Responses to 4 Different Body Weight-Supported Locomotor Training Approaches in Persons With Incomplete Spinal Cord Injury

ObjectiveTo describe metabolic responses accompanying 4 different locomotor training (LT) approaches. DesignSingle-blind, randomized controlled trial. SettingRehabilitation research laboratory, academic medical center. ParticipantsIndividuals (N=62) with minimal walking function due to chronic motor-incomplete spinal cord injury. InterventionParticipants trained 5 days/week for 12 weeks. Groups were treadmill-based LT with manual assistance (TM), transcutaneous electrical stimulation (TS), and a driven gait orthosis (DGO) and overground (OG) LT with electrical stimulation. Main Outcome MeasuresOxygen uptake (V˙o2), walking velocity and economy, and substrate utilization during subject-selected “slow,” “moderate,” and “maximal” walking speeds. ResultsV˙o2 did not increase from pretraining to posttraining for DGO (.00±.18L/min, P=.923). Increases in the other groups depended on walking speed, ranging from .01±.18m/s (P=.860) for TM (slow speed) to .20±.29m/s (P=.017) for TS (maximal speed). All groups increased velocity but to varying degrees (DGO, .01±.18Ln[m/s], P=.829; TM, .07±.29Ln[m/s], P=.371; TS, .33±.45Ln[m/s], P=.013; OG, .52±.61Ln[m/s], P=.007). Changes in walking economy were marginal for DGO and TM (.01±.20Ln[L/m], P=.926, and .00±.42Ln[L/m], P=.981) but significant for TS and OG (.26±.33Ln[L/m], P=.014, and .44±.62Ln[L/m], P=.025). Many participants reached respiratory exchange ratios ≥1 at any speed, rendering it impossible to statistically discern differences in substrate utilization. However, after training, fewer participants reached this ceiling for each speed (slow: 9 vs 6, n=32; moderate: 12 vs 8, n=29; and maximal 15 vs 13, n=28). ConclusionsDGO and TM walking training was less effective in increasing V˙o2 and velocity across participant-selected walking speeds, while TS and OG training was more effective in improving these parameters and also walking economy. Therefore, the latter 2 approaches hold greater promise for improving clinically relevant outcomes such as enhanced endurance, functionality, or in-home/community ambulation.

Relation Between Aerobic Capacity and Walking Ability in Older Adults With a Lower-Limb Amputation

ObjectivesTo determine the relative aerobic load, walking speed, and walking economy of older adults with a lower-limb prosthesis, and to predict the effect of an increased aerobic capacity on their walking ability. DesignCross-sectional. SettingHuman motion laboratory at a rehabilitation center. ParticipantsConvenience sample of older adults (n=36) who underwent lower-limb amputation because of vascular deficiency or trauma and able-bodied controls (n=21). InterventionsNot applicable. Main Outcome MeasuresPeak aerobic capacity and oxygen consumption while walking were determined. The relative aerobic load and walking economy were assessed as a function of walking speed, and a data-based model was constructed to predict the effect of an increased aerobic capacity on walking ability. ResultsPeople with a vascular amputation walked at a substantially higher (45.2%) relative aerobic load than people with an amputation because of trauma. The preferred walking speed in both groups of amputees was slower than that of able-bodied controls and below their most economical walking speed. We predicted that a 10% increase in peak aerobic capacity could potentially result in a reduction in the relative aerobic load of 9.1%, an increase in walking speed of 17.3% and 13.9%, and an improvement in the walking economy of 6.8% and 2.9%, for people after a vascular or traumatic amputation, respectively. ConclusionsCurrent findings corroborate the notion that, especially in people with a vascular amputation, the peak aerobic capacity is an important determinant for walking ability. The data provide quantitative predictions on the effect of aerobic training; however, future research is needed to experimentally confirm these predictions.

Obesity does not impair walking economy across a range of speeds and grades

Despite the popularity of walking as a form of physical activity for obese individuals, relatively little is known about how obesity affects the metabolic rate, economy, and underlying mechanical energetics of walking across a range of speeds and grades. The purpose of this study was to quantify metabolic rate, stride kinematics, and external mechanical work during level and gradient walking in obese and nonobese adults. Thirty-two obese [18 women, mass = 102.1 (15.6) kg, BMI = 33.9 (3.6) kg/m(2); mean (SD)] and 19 nonobese [10 women, mass = 64.4 (10.6) kg, BMI = 21.6 (2.0) kg/m(2)] volunteers participated in this study. We measured oxygen consumption, ground reaction forces, and lower extremity kinematics while subjects walked on a dual-belt force-measuring treadmill at 11 speeds/grades (0.50-1.75 m/s, -3° to +9°). We calculated metabolic rate, stride kinematics, and external work. Net metabolic rate (Ė net/kg, W/kg) increased with speed or grade across all individuals. Surprisingly and in contrast with previous studies, Ė net/kg was 0-6% less in obese compared with nonobese adults (P = 0.013). External work, although a primary determinant of Ė net/kg, was not affected by obesity across the range of speeds/grades used in this study. We also developed new prediction equations to estimate oxygen consumption and Ė net/kg and found that Ė net/kg was positively related to relative leg mass and step width and negatively related to double support duration. These results suggest that obesity does not impair walking economy across a range of walking speeds and grades.

Effects of high-resistance circuit training in an elderly population

The aim of this study was to determine the efficacy of a program of high-resistance circuit (HRC) training, and to compare the effects of HRC to traditional heavy strength (TS) training on strength, muscle size, body composition and measures of cardiovascular fitness in a healthy elderly population. Thirty-seven healthy men and women (61.6±5.3years) were randomly assigned to HRC (n=16), TS (n=14), or a control group (CG, n=7). Training consisted of weight lifting twice a week for 12weeks. Before and after the training, isokinetic peak torque in the upper and lower body, and body composition (dual X-ray absorptiometry) were determined. In addition, cardiovascular parameters were evaluated during an incremental treadmill test. Both HRC and TS groups showed significant increases in isokinetic strength (p<0.001), and the increase was significantly greater in the experimental groups than in CG (p<0.03). There were significant increases in lean mass (HRC, p<0.001; TS, p=0.025) and bone mineral density (HRC, p=0.025; TS, p=0.018) in the experimental groups. Only HRC showed a significant decrease in fat mass (p=0.011); this decrease was significantly greater in HRC than in CG (p=0.039). There were significant improvements in walking economy in the HRC group (p<0.049), although there were no statistical differences between groups. There were no changes in any variables in CG. Hence, HRC training was as effective as TS for improving isokinetic strength, bone mineral density and lean mass. Only HRC training elicited adaptations in the cardiovascular system and a decrease in fat mass.

Walking Economy During Cued versus Non-Cued Treadmill Walking in Persons with Parkinson's Disease

Gait impairment is common in Parkinson's disease (PD) and may result in greater energy expenditure, poorer walking economy, and fatigue during activities of daily living. Auditory cueing is an effective technique to improve gait; but the effects on energy expenditure are unknown. To determine whether energy expenditure differs in individuals with PD compared with healthy controls and if auditory cueing improves walking economy in PD. Twenty participants (10 PD and 10 controls) came to the laboratory for three sessions. Participants performed two, 6-minute bouts of treadmill walking at two speeds (1.12 m·sec-1 and 0.67 m·sec-1). One session used cueing and the other without cueing. A metabolic cart measured energy expenditure and walking economy was calculated (energy expenditure/power). PD had worse walking economy and higher energy expenditure than control participants during cued and non-cued walking at the 0.67 m·sec-1 speed and during non-cued walking at the 1.12 m·sec-1. With auditory cueing, energy expenditure and walking economy worsened in both participant groups. People with PD use more energy and have worse walking economy than adults without PD. Walking economy declines further with auditory cuing in persons with PD.

Mechanical and energetic consequences of rolling foot shape in human walking

During human walking, the center of pressure under the foot progresses forward smoothly during each step, creating a wheel-like motion between the leg and the ground. This rolling motion might appear to aid walking economy, but the mechanisms that may lead to such a benefit are unclear, as the leg is not literally a wheel. We propose that there is indeed a benefit, but less from rolling than from smoother transitions between pendulum-like stance legs. The velocity of the body center of mass (COM) must be redirected in that transition, and a longer foot reduces the work required for the redirection. Here we develop a dynamic walking model that predicts different effects from altering foot length as opposed to foot radius, and test it by attaching rigid, arc-like foot bottoms to humans walking with fixed ankles. The model suggests that smooth rolling is relatively insensitive to arc radius, whereas work for the step-to-step transition decreases approximately quadratically with foot length. We measured the separate effects of arc-foot length and radius on COM velocity fluctuations, work performed by the legs and metabolic cost. Experimental data (N=8) show that foot length indeed has much greater effect on both the mechanical work of the step-to-step transition (23% variation, P=0.04) and the overall energetic cost of walking (6%, P=0.03) than foot radius (no significant effect, P>0.05). We found the minimum metabolic energy cost for an arc foot length of approximately 29% of leg length, roughly comparable to human foot length. Our results suggest that the foot's apparently wheel-like action derives less benefit from rolling per se than from reduced work to redirect the body COM.

Inferior Exercise Economy in Children: Perpetuating a Myth?

It is one of the most established, well-documented pieces of dogma in the pediatric exercise physiology literature: compared with adults, children exhibit a greater metabolic requirement to move body mass—an inferior exercise economy—during weight-bearing exercise (1,7). In a typical example provided by Unnithan and Eston, 9–10 year old boys had a 24% greater mass-relative oxygen demand while running on a treadmill at 9.6 km h-1 compared with 18–25 year old men (47 ml kg-1 min-1 versus 38 ml kg-1 min-1; 15). Cross-sectional studies indicate that this economy improves with increasing age. In an early study, Skinner et al. demonstrated a progressive decline in metabolic demand during uphill treadmill walking from 46 ml kg-1 min-1 in a group of 6–8 year old children to 41 ml kg-1 min-1 in a cohort of 12–16 year old youth (13). Longitudinal studies have verified this trend. In the Amsterdam Growth, Health, and Fitness Study, data from 192 subjects showed a mean decrease in VO2 per kg from 37.6 to 30.3 ml kg-1 min-1 between the ages of 13 and 27 years (16). Rowland et al. determined treadmill walking economy at 3.25 mph and 8% grade annually for five years in children beginning at age 9 years (9). Mass-relative oxygen uptake fell progressively over this time span from an initial mean value of 31.0 ml kg-1 min-1 to 26.5 ml kg-1 min-1. The findings have been remarkably consistent: metabolic cost per kg body mass at a given exercise load progressively decreases in a continuum through the growing years. VO2/kg at a given treadmill speed and grade setting can be predicted to decline by an average of approximately 1.0 ml kg-1 min-1 for each year of increasing age until midlate adolescence. From the perspective of developmental exercise physiology, this “wasteful gait” of children has been considered as a disadvantage in their capacity for endurance exercise compared with adults. “The high metabolic cost of walking and running,” it has been suggested, “makes the small child less of an ‘aerobic machine” (1). From a more pragmatic standpoint, the progressive change in exercise economy

Resonance in Human Walking Economy: How Natural Is It?

Abstract Locomotion and movement economy are cornerstone topics in movement science. Modeling the leg as ahybrid mass-spring pendulum shows walking economy should be optimized when stride frequency matchesthe resonant frequency of the limb. Human walking is described as self-optimizing because mean preferred(PSF) and modeled resonant (RSF) stride frequencies usually are statistically equivalent, but this depictionmay not be fully justified. Purpose: To more thoroughly examine the self-optimization characterization andthe consequences of obligating use of the RSF. Methods : Forty-seven individuals of diverse staturescompleted 3 consecutive days of preferred walking trials on a treadmill where stride rate, stride length,walking speed, heart rate and walking economy measures were made under steady state heart rate conditions.Anthropometric measures were taken to build a hybrid model of the leg and model the RSF. Reliability acrossdays was evaluated via repeated measures analysis of variance (ANOVA) and intra-class correlation (α=.05)and correlations were calculated for PSF and RSF. A separate sample of 20 participants walked under 3conditions, (1) completely preferred; (2) at the original preferred speed using the RSF; and (3) with theoption to establish a new preferred speed while using the RSF.

Exercise for People in Early- or Mid-Stage Parkinson Disease: A 16-Month Randomized Controlled Trial

Exercise confers short-term benefits for individuals with Parkinson disease (PD). The purpose of the study was to compare short- and long-term responses among 2 supervised exercise programs and a home-based control exercise program. The 16-month randomized controlled exercise intervention investigated 3 exercise approaches: flexibility/balance/function exercise (FBF), supervised aerobic exercise (AE), and home-based exercise (control). This study was conducted in outpatient clinics. The participants were 121 individuals with PD (Hoehn & Yahr stages 1-3). The FBF program (individualized spinal and extremity flexibility exercises followed by group balance/functional training) was supervised by a physical therapist. The AE program (using a treadmill, bike, or elliptical trainer) was supervised by an exercise trainer. Supervision was provided 3 days per week for 4 months, and then monthly (16 months total). The control group participants exercised at home using the National Parkinson Foundation Fitness Counts program, with 1 supervised, clinic-based group session per month. Outcomes, obtained by blinded assessors, were determined at 4, 10, and 16 months. The primary outcome measures were overall physical function (Continuous Scale-Physical Functional Performance [CS-PFP]), balance (Functional Reach Test [FRT]), and walking economy (oxygen uptake [mL/kg/min]). Secondary outcome measures were symptom severity (Unified Parkinson's Disease Rating Scale [UPDRS] activities of daily living [ADL] and motor subscales) and quality of life (39-item Parkinson's Disease Quality of Life Scale [PDQ-39]). Of the 121 participants, 86.8%, 82.6%, and 79.3% completed 4, 10, and 16 months, respectively, of the intervention. At 4 months, improvement in CS-PFP scores was greater in the FBF group than in the control group (mean difference=4.3, 95% confidence interval [CI]=1.2 to 7.3) and the AE group (mean difference=3.1, 95% CI=0.0 to 6.2). Balance was not different among groups at any time point. Walking economy improved in the AE group compared with the FBF group at 4 months (mean difference=-1.2, 95% CI=-1.9 to -0.5), 10 months (mean difference=-1.2, 95% CI=-1.9 to -0.5), and 16 months (mean difference=-1.7, 95% CI=-2.5 to -1.0). The only secondary outcome that showed significant differences was UPDRS ADL subscale scores: the FBF group performed better than the control group at 4 months (mean difference=-1.47, 95% CI=-2.79 to -0.15) and 16 months (mean difference=-1.95, 95% CI=-3.84 to -0.08). Absence of a non-exercise control group was a limitation of the study. Findings demonstrated overall functional benefits at 4 months in the FBF group and improved walking economy (up to 16 months) in the AE group.

Effect of High Aerobic Intensity Interval Treadmill Walking in People With Chronic Stroke: A Pilot Study With One Year Follow-Up

Objective: To determine the physiological and functional responses from high aerobic intensity treadmill walking in 4 x 4-minute intervals in people with chronic stroke and to evaluate the feasibility of this mode of training. Method: This was a baseline control trial with 1 year follow-up in an outpatient rehabilitation setting at a university hospital. Eight people with chronic stroke participated in and completed the study. Their mean age was 48.9 (± 10.6) years. We tested uphill treadmill walking in 4 x 4-minute work periods at an intensity between 85% and 95% of peak heart rate from initial maximal treadmill testing. There were 3-minute active breaks between the intervals. The main outcome measures were peak oxygen uptake (VO2peak) and walking economy (Cw). Overall compliance and adverse events determine the feasibility. Results: VO2peak increased from 2.32 (± 0.44) to 2.60 (± 0.55) L • min–1 post training (P = .003). Walking economy (Cw) improved from 1.12 (± 0.15) to 1.04 (± 0.18) L • min–1 (P = .043). At 1 year follow-up, VO2peak was 2.59 (±0.58) L • min –1 and was not significantly different from posttraining measurement (P = 1.00). Cw was 1.19 (± 0.15) L • min–1 at 1 year follow-up and thus was worse than post training (P = .023). Functional improvements were found in the 6-minute walk test (6MWT) (P = .020), 10-meter walk test (10MWT) (P = .032), and Timed Up and Go test (TUG) (P = .002) at post tests. Conclusions: High aerobic intensity interval treadmill walking significantly increased VO2peak and improved Cw in these subjects. The training was feasible and may have important implications for cardiovascular health and future rehabilitation programs in this population.

Maximal Strength Training Enhances Strength and Functional Performance in Chronic Stroke Survivors

This study aimed to demonstrate that maximal strength training improves muscle strength and to assess the effect of training on function, aerobic status, and quality-of-life among chronic stroke survivors. Ten patients acted as their own controls for 4 wks, before an 8-week training intervention. Patients trained 3 days/wk, with four sets of four repetitions at 85%-95% one repetition maximum in unilateral leg press and plantarflexion with an emphasis on maximal mobilization of force in the concentric phase. After training, leg press strength improved by 30.6 kg (75%) and 17.8 kg (86%); plantarflexion strength improved by 35.5 kg (89%) and 28.5 kg (223%) for the unaffected and affected limbs, respectively, significantly different from the control period (all P < 0.01). The 6-min walk test improved by 13.9 m (within training period; P = 0.01), and the Timed Up and Go test time improved by 0.6 secs (within training period; P < 0.05). There were no significant changes in walking economy, peak aerobic capacity, Four-Square Step Test, or health-related quality-of-life after training. Maximal strength training improved muscle strength in the most affected as well as in the nonaffected leg and improved Timed-Up-And-Go time and 6-min walk distance but did not alter Four-Step Square Test time, aerobic status, or quality-of-life among chronic stroke survivors.

Why Does Walking Economy Improve after Weight Loss in Obese Adolescents?

This study tested the hypothesis that the increase in walking economy (i.e., decrease in net metabolic rate per kilogram) after weight loss in obese adolescents is induced by a lower metabolic rate required to support the lower body weight and maintain balance during walking. Sixteen obese adolescent boys and girls were tested before and after a weight reduction program. Body composition and oxygen uptake while standing and walking at four preset speeds (0.75, 1, 1.25, and 1.5 m·s⁻¹) and at the preferred speed were quantified. Net metabolic rate and gross metabolic cost of walking-versus-speed relationships were determined. A three-compartment model was used to distinguish the respective parts of the metabolic rate associated with standing (compartment 1), maintaining balance and supporting body weight during walking (compartment 2), and muscle contractions required to move the center of mass and limbs (compartment 3). Standing metabolic rate per kilogram (compartment 1) significantly increased after weight loss, whereas net metabolic rate per kilogram during walking decreased by 9% on average across speeds. Consequently, the gross metabolic cost of walking per unit of distance-versus-speed relationship and hence preferred walking speeds did not change with weight loss. Compartment 2 of the model was significantly lower after weight loss, whereas compartment 3 did not change. The model showed that the improvement in walking economy after weight loss in obese adolescents was likely related to the lower metabolic rate of the isometric muscular contractions required to support the lower body weight and maintain balance during walking. Contrastingly, the part of the total metabolic rate associated with muscle contractions required to move the center of mass and limbs did not seem to be related to the improvement in walking economy in weight-reduced individuals.

Effects of a 6-month exercise program pilot study on walking economy, peak physiological characteristics, and walking performance in patients with peripheral arterial disease

The purpose of this study was to examine the effects of a 6-month exercise program on submaximal walking economy in individuals with peripheral arterial disease and intermittent claudication (PAD-IC). Participants (n = 16) were randomly allocated to either a control PAD-IC group (CPAD-IC, n = 6) which received standard medical therapy, or a treatment PAD-IC group (TPAD-IC; n = 10) which took part in a supervised exercise program. During a graded treadmill test, physiological responses, including oxygen consumption, were assessed to calculate walking economy during submaximal and maximal walking performance. Differences between groups at baseline and post-intervention were analyzed via Kruskal–Wallis tests. At baseline, CPAD-IC and TPAD-IC groups demonstrated similar walking performance and physiological responses. Postintervention, TPAD-IC patients demonstrated significantly lower oxygen consumption during the graded exercise test, and greater maximal walking performance compared to CPAD-IC. These preliminary results indicate that 6 months of regular exercise improves both submaximal walking economy and maximal walking performance, without significant changes in maximal walking economy. Enhanced walking economy may contribute to physiological efficiency, which in turn may improve walking performance as demonstrated by PAD-IC patients following regular exercise programs.

The improvement of walking speed after cardiac rehabilitation is associated with the reduction in the metabolic cost of walking in older persons

BackgroundTo walk a given distance older persons consume more metabolic energy than younger adults across all speeds. As physical activity interventions improve a variety of physical performance measures in older persons, including walking speed, in this study we hypothesized that the improvement of walking speed might be associated with the reduction of the metabolic cost of walking and we tested our hypothesis in a selected sample of older patients receiving cardiac rehabilitation. MethodsIn 120 patients (88 men and 32 women, mean age 74.1 years±SD 5.0) we assessed energy expenditure during the 6-min Walk Test (6mWT) before and after the rehabilitation using a portable system for direct calorimetry. ResultsOn the 6mWT performed after the rehabilitation patients significantly increased total energy expenditure (28.0kcal±SD 8.3 vs. 25.7kcal±SD 7.6, p<0.001), the distance walked (398m±SD 93 vs. 343m±SD 95, p<0.001) and, consequently, walking speed (1.11m/s±SD 0.26 vs. 0.95m/s±SD 0.26, p<0.001) while the metabolic cost of walking, i.e. the amount of energy used to move a body mass of 1kg for a distance of 1m, was significantly reduced (1.00cal/kg/m±SD 0.19 vs. 1.11cal/kg/m±SD 0.32, p<0.001). ConclusionsIn older patients receiving cardiac rehabilitation the improvement of walking speed is associated with the improvement of walking economy. This might be a contributory factor to the favourable effects of physical activity interventions on physical performance measures.

The effects of a controlled energy storage and return prototype prosthetic foot on transtibial amputee ambulation

The lack of functional ankle musculature in lower limb amputees contributes to the reduced prosthetic ankle push-off, compensations at other joints and more energetically costly gait commonly observed in comparison to non-amputees. A variety of energy storing and return prosthetic feet have been developed to address these issues but have not been shown to sufficiently improve amputee biomechanics and energetic cost, perhaps because the timing and magnitude of energy return is not controlled. The goal of this study was to examine how a prototype microprocessor-controlled prosthetic foot designed to store some of the energy during loading and return it during push-off affects amputee gait. Unilateral transtibial amputees wore the Controlled Energy Storage and Return prosthetic foot (CESR), a conventional foot (CONV), and their previously prescribed foot (PRES) in random order. Three-dimensional gait analysis and net oxygen consumption were collected as participants walked at constant speed. The CESR foot demonstrated increased energy storage during early stance, increased prosthetic foot peak push-off power and work, increased prosthetic limb center of mass (COM) push-off work and decreased intact limb COM collision work compared to CONV and PRES. The biological contribution of the positive COM work for CESR was reduced compared to CONV and PRES. However, the net metabolic cost for CESR did not change compared to CONV and increased compared to PRES, which may partially reflect the greater weight, lack of individualized size and stiffness and relatively less familiarity for CESR and CONV. Controlled energy storage and return enhanced prosthetic push-off, but requires further design modifications to improve amputee walking economy.

Systematic Variation of Prosthetic Foot Spring Affects Center-of-Mass Mechanics and Metabolic Cost During Walking

Lower-limb amputees expend more energy to walk than non-amputees and have an elevated risk of secondary disabilities. Insufficient push-off by the prosthetic foot may be a contributing factor. We aimed to systematically study the effect of prosthetic foot mechanics on gait, to gain insight into fundamental prosthetic design principles. We varied a single parameter in isolation, the energy-storing spring in a prototype prosthetic foot, the controlled energy storage and return (CESR) foot, and observed the effect on gait. Subjects walked on the CESR foot with three different springs. We performed parallel studies on amputees and on non-amputees wearing prosthetic simulators. In both groups, spring characteristics similarly affected ankle and body center-of-mass (COM) mechanics and metabolic cost. Softer springs led to greater energy storage, energy return, and prosthetic limb COM push-off work. But metabolic energy expenditure was lowest with a spring of intermediate stiffness, suggesting biomechanical disadvantages to the softest spring despite its greater push-off. Disadvantages of the softest spring may include excessive heel displacements and COM collision losses. We also observed some differences in joint kinetics between amputees and non-amputees walking on the prototype foot. During prosthetic push-off, amputees exhibited reduced energy transfer from the prosthesis to the COM along with increased hip work, perhaps due to greater energy dissipation at the knee. Nevertheless, the results indicate that spring compliance can contribute to push-off, but with biomechanical trade-offs that limit the degree to which greater push-off might improve walking economy.

Percent Body Fat is Negatively Correlated to Walking Efficiency in a Group of Obese and Nonobese Men and Women

The influence of body mass index and percent body fat on walking economy is uncertain, and may depend on the population studied. PURPOSE: We examined the relationship between body mass index (BMI: weight (kg)/height (m2), % body fat (%BF) and exercise VO2 during treadmill walking in subjects varying considerably in BMI (18.0 to 50.3) and %BF (15.5 to 52.0). METHODS: 20 males (age: 25.3 ± 6.4 yr.; ht: 176.0 ± 8.1 cm; wt: 95.8 ± 33.4 kg; BMI: 30.3 ± 8.9; % BF: 31.5 ± 8.2) and 21 females (age: 26.6 ± 6.5 yr.; ht: 167.5 ± 23.7 cm; wt: 79.1 ± 23.7 kg; BMI: 27.9 ± 8.0; % BF: 37.6 ± 10.7) completed exercise sessions consisting of level-grade treadmill walking at 1.1 mph (0.5 m/sec), 1.7 mph (0.75 m/sec), 2.2 mph (1.0 m/sec), 2.8 mph (1.25 m/sec), 3.4 mph (1.5 m/sec), 3.9 mph (1.75 m/sec), and 4.5 mph (2.00 m/sec). Subjects exercised for 5 min at each speed, while pulmonary ventilation and gas exchange were measured continuously. %BF was assessed by dual-energy X-ray absorptiometry. Metabolic cost (J/kg/m) was calculated by dividing metabolic power by walking speed, and preferred walking speed was determined from the time required to walk 70 m along a level sidewalk. The relationship between VO2 and walking speed was examined by way of polynomial random coefficient regression (PRCR) that generated linear and quadratic coefficients.. RESULTS: As expected, the VO2 vs. walking speed relationship was curvilinear. Only the quadratic coefficients of the PRCR analysis were significantly correlated with %BF (r = 0.45; p = 0.004) and BMI (r = 0.32; p = 0.039). These results were consistent with the finding that quadratic regression coefficients were significantly higher (p=0.008) in subjects with %BF above the median. The quadratic coefficients of the PRCR were also significantly inversely correlated with minimum metabolic cost speed (r = -0.85; p < 0.001) and preferred walking speed (r = -0.55; p < 0.0001). CONCLUSION: These results suggest that %BF adversely affects walking energy expenditure, primarily by increasing the rate of VO2 increase ("delta VO2") as walking speed increases. In our subjects this was most noticeable at the faster walking speeds, and may explain in part why subjects with high %BF, i.e., those with the greatest PRCR quadratic coefficients, had the lowest preferred walking speeds and lowest minimum metabolic cost walking speeds.

Human leg model predicts ankle muscle-tendon morphology, state, roles and energetics in walking.

A common feature in biological neuromuscular systems is the redundancy in joint actuation. Understanding how these redundancies are resolved in typical joint movements has been a long-standing problem in biomechanics, neuroscience and prosthetics. Many empirical studies have uncovered neural, mechanical and energetic aspects of how humans resolve these degrees of freedom to actuate leg joints for common tasks like walking. However, a unifying theoretical framework that explains the many independent empirical observations and predicts individual muscle and tendon contributions to joint actuation is yet to be established. Here we develop a computational framework to address how the ankle joint actuation problem is resolved by the neuromuscular system in walking. Our framework is founded upon the proposal that a consideration of both neural control and leg muscle-tendon morphology is critical to obtain predictive, mechanistic insight into individual muscle and tendon contributions to joint actuation. We examine kinetic, kinematic and electromyographic data from healthy walking subjects to find that human leg muscle-tendon morphology and neural activations enable a metabolically optimal realization of biological ankle mechanics in walking. This optimal realization (a) corresponds to independent empirical observations of operation and performance of the soleus and gastrocnemius muscles, (b) gives rise to an efficient load-sharing amongst ankle muscle-tendon units and (c) causes soleus and gastrocnemius muscle fibers to take on distinct mechanical roles of force generation and power production at the end of stance phase in walking. The framework outlined here suggests that the dynamical interplay between leg structure and neural control may be key to the high walking economy of humans, and has implications as a means to obtain insight into empirically inaccessible features of individual muscle and tendons in biomechanical tasks.