Walking Economy Research Articles

Walking economy and exercise efficiency in successful weight loss maintainers

PurposeFollowing short-term weight loss, the energetic cost of transport decreases and exercise efficiency increases. Whether changes persist during long-term weight maintenance is unknown. MethodsWe compared walking economy and exercise efficiency in weight loss maintainers (WLM, maintaining ≥13.6 kg weight loss for ≥1 year), controls without obesity (NC, BMI similar to current BMI of WLM), and controls with overweight/obesity (OC, BMI similar to pre-weight loss BMI of WLM). Energy expenditure (EE) and respiratory quotient were measured using indirect calorimetry at rest, while standing, and during treadmill walking. Gross and net energetic cost of transport (J/kg/m) was measured during level treadmill walking at 0.75, 1.12, and 1.52 m/s. Gross, net, and delta efficiency (%) were measured during inclined treadmill walking (2 %, 4 %, and 6 % grade) and a constant speed (1.12 m/s). ResultsWLM (n = 32, BMI: 23.8 ± 2.3 kg/m2) and NC (n = 28, BMI: 22.7 ± 1.6 kg/m2) had significantly lower EE (kJ/min) compared to OC (n = 26, BMI: 33.0 ± 4.5 kg/m2) during rest, standing, and walking (p < 0.01). Net energetic cost of transport was significantly lower in WLM compared to OC at 1.12 and 1.52 m/s (p < 0.05). Net efficiency was significantly greater in WLM compared to OC while walking (p ≤ 0.05). There were no significant differences between WLM and NC for any measures of economy or efficiency. ConclusionWLM had lower walking economy and greater walking efficiency compared to OC, but there were no differences between WLM and NC. Thus, individuals maintaining significant weight loss may be successful with long-term weight loss, in part, due to resistance against adaptive reductions in walking energetics.

Relationships of post-stroke fatigue with mobility, recovery, performance, and participation-related outcomes: a systematic review and meta-analysis.

Effective post-stroke mobility, recovery, performance, and participation are key goals for stroke survivors. However, these outcomes may be hindered by post-stroke fatigue (PSF), which can affect numerous aspects of post-stroke mobility, recovery, performance, functioning, community participation, and return to work. This review aimed to assess the scientific evidence on the relationship between PSF and mobility function, functional recovery, functional performance, and participation-related outcomes among stroke survivors. A comprehensive search of Cochrane Central, PubMed, Embase, and Web of Science (WoS) databases was conducted from inception to December 2023. Observational, cross-sectional, and longitudinal studies were included. The methodological quality of the included studies was assessed using the National Institute of Health's quality assessment tool, while the risk of bias was assessed using the Quality in Prognostic Studies tool. A total of 28 studies (n = 2,495 participants, 1,626 men, mean age ranging from 52.5 ± 9.5 to 71.1 ± 9.9 years) were included. The data analysis was conducted using narrative and quantitative synthesis. Fixed and random effects meta-analyses were conducted to explore the relationships between PSF and relevant outcomes. Chronic PSF was found to have significant negative correlations with mobility (meta r = -0.106, p < 0.001), balance performance (meta r = -0.172; 95%; p = 0.004), and quality of life (meta r = -0.647; p < 0.001). It also showed significant positive correlations with stroke impairment (meta r = 0.144, p < 0.001) and disability (meta r = 0.480, p < 0.001). Additionally, exertion/acute PSF had significantly negative correlations with walking economy (meta r = -0.627, p < 0.001) and walking endurance (meta r = -0.421, p = 0.022). The certainty of evidence was deemed moderate for these relationships. Our findings indicate that higher levels of PSF are associated with poorer mobility, balance, and participation, as well as greater disability and stroke impairment. Future studies, especially prospective longitudinal and randomized controlled trials, are warranted to substantiate our findings. PROSPERO, identifier: CRD42023492045.

Customized passive-dynamic ankle–foot orthoses can improve walking economy and speed for many individuals post-stroke

BackgroundPassive-dynamic ankle–foot orthoses (PD-AFOs) are often prescribed to address plantar flexor weakness during gait, which is commonly observed after stroke. However, limited evidence is available to inform the prescription guidelines of PD-AFO bending stiffness. This study assessed the extent to which PD-AFOs customized to match an individual’s level of plantar flexor weakness influence walking function, as compared to No AFO and their standard of care (SOC) AFO.MethodsMechanical cost-of-transport, self-selected walking speed, and key biomechanical variables were measured while individuals greater than six months post-stroke walked with No AFO, with their SOC AFO, and with a stiffness-customized PD-AFO. Outcomes were compared across these conditions using a repeated measures ANOVA or Friedman test (depending on normality) for group-level analysis and simulation modeling analysis for individual-level analysis.ResultsTwenty participants completed study activities. Mechanical cost-of-transport and self-selected walking speed improved with the stiffness-customized PD-AFOs compared to No AFO and SOC AFO. However, this did not result in a consistent improvement in other biomechanical variables toward typical values. In line with the heterogeneous nature of the post-stroke population, the response to the PD-AFO was highly variable.ConclusionsStiffness-customized PD-AFOs can improve the mechanical cost-of-transport and self-selected walking speed in many individuals post-stroke, as compared to No AFO and participants’ standard of care AFO. This work provides initial efficacy data for stiffness-customized PD-AFOs in individuals post-stroke and lays the foundation for future studies to enable consistently effective prescription of PD-AFOs for patients post-stroke in clinical practice.Trial Registration: NCT04619043.

Increased Metabolic Demand During Nighttime Walking in Hilly Forest Terrain While Wearing Night Vision Goggles.

Foot-borne soldiers sometimes carry out nighttime operations. It has previously been reported an elevated metabolic demand and impaired walking economy during outdoor walking on a gravel road in darkness wearing night vision goggles (NVG), compared with wearing a headlamp. The aim of the present study was to evaluate the effect of wearing NVG while walking in a hilly forest terrain and compare the results between experienced and inexperienced NVG users. At nighttime, two different groups, inexperienced (five men and six women) and experienced (nine men) NVG users, walked 1.1 km at a self-selected comfortable pace in a hilly forest. Part I was mainly uphill, and Part II was mainly downhill. Walks were performed wearing a headlamp (light), monocular NVG (mono), binocular NVG (bino), or mono with a 25 kg extra weight (backpack). Walking economy calculated from oxygen uptake in relation to body mass and covered distance (V̇O2 (mL/[kg · km])), heart rate, gait, and walking speed were measured. In both groups, walking economy was deteriorated in all three conditions with limited vision (mono, bino, and backpack) compared to the light condition, both during Part I (mono/bino, experienced: +26/+25%, inexperienced: +34/+28%) and Part II (mono/bino, experienced: +44/+46%, inexperienced: +63/+49%). In the backpack condition, the relative change of walking economy was greater for the inexperienced group than the experienced group: Part I (experienced: +46%, inexperienced: +70%), Part II (experienced: +71%, inexperienced: +111%). Concurrently, the step length was shorter in all three conditions with limited vision during Part I (mono/bino/backpack, experienced: -7/-7/-15%, inexperienced: -12/-12/-19%) and Part II (mono/bino/backpack; experienced: -8/-8/-14%, inexperienced: -17/-15/-24%) than in the light condition. The experienced NVG users walked faster during all conditions, but there was no difference in heart rate between groups. Despite that foveal vision using NVG is adequate, it appears that the mechanical efficiency during nighttime walking in hilly terrain was markedly lower while wearing NVG than with full vision, regardless of whether the soldier was an experienced or inexperienced NVG user. Moreover, the walking economy was even more affected when adding the 25-kg extra weight. It is probable that the deteriorated mechanical efficiency was partly due to the shorter step length in all three conditions with limited vision.

A Study of the Effect of the Difference in Energy Stored in Two Prosthetic Feet Made of Carbon Fiber Amputated Below the Knee on the Efficiency of Walking

ESAR feet are prosthetic feet with carbon fiber parts that store mechanical energy while standing and release it during propulsion. It is believed to reduce the metabolic energy needed for walking, and to promote the economy of walking. However, there is little scientific evidence to support this claim. This study aimed to compare the energy storage properties of two prosthetic feet made of carbon fiber using the P-Walk, G-Walk, and Podium devices developed for gait analysis, which is a systematic examination of human movement, enabling phasing, estimation of musculoskeletal performance, and determination of kinematic and motor parameters. The amount of energy was calculated for each of the feet using the load deflection test, and the results showed that the new artificial foot with an energy of 6.186 joules showed a great improvement in the results of the tests compared to the old artificial foot with an energy of 3.403 joules. The Podium device tests showed a significant improvement in walking patterns and pressure distribution after using a new foot. The pressure distribution became almost equal on both sides, and the angular deviation of COP decreased from -7 to 1.3 degrees. Ground reaction force vector tilt results also improved, with a body angle of 0 degrees and inclination varying slightly depending on the tibiofemoral angle for males. P-Walk results reveal left-sided static test pressure distribution, exposing amputees to osteoarthritis risk and revealing lack of confidence in prosthetic foot. After use the new prosthetic foot, amputees press more on right foot, indicating balance restoration. The G-Walk device shows the effectiveness of both healthy left and prosthetic foot when walking on an amputated right leg when use the new prosthetic foot. The amputated side's performance is similar to a healthy limb, with minimal difference and within normal limits. Walking cadence and speed values are within normal ranges, while stride length and step length are outside normal ranges for both sides. Obliquity results show a small difference in pelvic angles due to weak pelvic muscles, but these are close to standard values for prosthetic foot use. The amputee's opinions about the evaluation of the new prosthetic foot were good when using the T-score by 61.0 with a rate of 86.4%. It was a significant improvement compared to the old foot with an evaluation of 53.6 by 63.9%.

Treadmill walking economy is not affected by body fat and body mass index in adults.

To determine whether body fat and body mass index (BMI) affect the energy cost of walking (Cw; J/kg/m), ventilation, and gas exchange data from 205 adults (115 females; percent body fat range = 3.0%-52.8%; BMI range = 17.5-43.2 kg/m2) were obtained at rest and during treadmill walking at 1.34 m/s to calculate gross and net Cw. Linear regression was used to assess relationships between body composition indices, Cw, and standing metabolic rate (SMR). Unpaired t-tests were used to assess differences between sex, and one-way ANOVA was used to assess differences by BMI categories: normal weight, <25.0 kg/m2; overweight, 25.0-29.9 km/m2; and obese, ≥30 kg/m2. Net Cw was not related to body fat percent, fat mass, or BMI (all R2 ≤ 0.011). Furthermore, mean net Cw was similar by sex (male: 2.19 ± 0.30 J/kg/m; female: 2.24 ± 0.37 J/kg/m, p = 0.35) and across BMI categories (normal weight: 2.23 ± 0.36 J/kg/m; overweight: 2.18 ± 0.33 J/kg/m; obese: 2.26 ± 0.31, p = 0.54). Gross Cw and SMR were inversely associated with percent body fat, fat mass, and BMI (all R2 between 0.033 and 0.270; all p ≤ 0.008). In conclusion, Net Cw is not influenced by body fat percentage, total body fat, and BMI and does not differ by sex.

Habitually wearing high heels may improve user walking economy in any footwear.

The habitual use of high-heeled footwear may structurally remodel user leg muscle tendons, thereby altering their functional capabilities. High heels set users' ankles in relatively plantarflexed positions, causing calf muscle tendons to operate at relatively short lengths. Habitually operating muscle tendons at relatively short lengths induces structural remodeling that theoretically affects muscle metabolism. Because structural changes occur within the body, the user's locomotor metabolism may change in any footwear condition (e.g., conventional shoes, barefoot). Here, we studied the influence of habitual high-heel use on users' leg muscle-tendon structure and metabolism during walking in flat-soled footwear. We tested eight participants before and after 14 wk of agreeing to wear high heels as their daily shoes. Overall, participants who wore high heels >1,500 steps per day, experienced a 9% decrease in their net metabolic power during walking in flat-soled footwear (d = 1.66, P ≤ 0.049), whereas participants who took <1,000 daily steps in high heels did not (d = 0.44; P = 0.524). Across participants, for every 1,000 daily steps in high heels, net metabolic power during walking in flat-soled footwear decreased 5.3% (r = -0.73; P = 0.040). Metabolic findings were partially explained (r2 = 0.43; P = 0.478) by trending shorter medial gastrocnemius fascicle lengths (d = 0.500, P = 0.327) and increased Achilles tendon stiffness (d = 2.889, P = 0.088). The high-heel intervention did not alter user walking stride kinematics in flat-soled footwear (d ≤ 0.567, P ≥ 0.387). While our limited dataset is unable to establish the mechanisms underlying the high-heel-induced walking economy improvement, it appears that prescribing specific footwear use can be implemented to alter user muscle-tendon properties and augment their function in any shoes.NEW & NOTEWORTHY Habitually wearing high-heeled footwear structurally remodels leg muscle tendons and improves user walking economy, regardless of worn attire.

Physiological responses during walking in men and women with intermittent claudication.

Miyasato et al. show that peak oxygen consumption, walking economy, anaerobic threshold, and cardiovascular responses (heart rate, blood pressure, and rate pressure product) during walking were similar between men and women with peripheral artery disease and intermittent claudication. There were no differences in the physiological responses to walking between men and women with intermittent claudication. Sex per se is not a factor that demands changes in walking prescription for patients with intermittent claudication. Peak oxygen consumption (VO2peak), anaerobic threshold, walking economy, and cardiovascular responses during walking are used to guide and monitor walking training in patients with peripheral artery disease and intermittent claudication. Women with peripheral artery disease and intermittent claudication present greater impairments than men, and evaluating training markers according to sex for decisions regarding walking prescription in this population is important. This study aimed to compare VO2peak, walking economy, anaerobic threshold, and cardiovascular responses during walking in men and women with peripheral artery disease and intermittent claudication. Forty patients (20 men and 20 women with similar baseline characteristics) underwent a cardiopulmonary treadmill test (3.2km/h and 2% increase in slope every 2 minutes until maximal leg pain). The VO2 and rate-pressure product were assessed. Data from men and women were compared using t-tests. There were no significant differences between men and women (VO2peak: 15.0±4.8 versus 13.9±2.9mL∙kg-1∙min-1, p=0.38; walking economy: 9.6±2.7 versus 8.4±1.6mL∙kg-1∙min-1, p=0.09; anaerobic threshold: 10.5±3.2 versus 10.5±2.2mL∙kg-1∙min-1, p=0.98; rate pressure product at 1st stage: 13,465± 2,910 versus 14,445±4,379bpm∙mmHg, p=0.41; and rate pressure product at anaerobic threshold:13,673±3,100 versus 16,390±5,870bpm∙mmHg, p=0.08 and rate pressure product at peak exercise: 21,253±6,141 versus 21,923±7,414bpm∙mmHg, p=0.76, respectively). Men and women with peripheral artery disease and similar baseline characteristics presented similar responses to walking, suggesting that decisions regarding walking prescription and monitoring can be made regardless of sex in this specific population.

Change In Walking Economy After Resistance Training With Weight Gain In Young Adult Athletes

Change In Walking Economy After Resistance Training With Weight Gain In Young Adult Athletes

Analysis of Walking Economy after Sleeve Gastrectomy in Patients with Severe Obesity.

Obesity is associated with a higher energy cost of walking which affects activities of daily living. Bariatric surgery with sleeve gastrectomy (SG) has beneficial effects on weight loss and comorbidities. The aim of this study was to analyze the impact of SG on walking economy in subjects with severe obesity. This observational cohort study included all patients with morbid obesity who were considered suitable candidates for SG between June 2017 and June 2019. Each patient underwent an incremental cardiopulmonary exercise test on a treadmill (modified Bruce protocol) one month before and six months after SG. Data on the energy cost of walking were recorded during three protocol stages (stage 0-slow flat walking: speed 2.7 km/h, slope 0%; stage ½-slow uphill walking: speed 2.7 km/h, slope 5%; stage 1-fast uphill walking: speed 4.0 km/h, slope 8%). 139 patients with morbid obesity (78% women; age 44.1 ± 10.7 years; BMI 42.5 ± 4.7 kg/m2) were included in the study. At six months post-SG, patients presented with a significantly decreased body weight (-30.5 ± 17.2 kg; p < 0.05), leading to an average BMI of 31.6 ± 4.2 kg/m2. The net energy cost of walking (measured in J/m and J/kg/m) of the subjects was lower compared to pre-SG at all three protocol stages. This improvement was also confirmed when the subjects were grouped by gender and obesity classes. After a significant weight loss induced by SG, regardless of the severity of obesity and gender, patients exhibited a lower energy expenditure and an improved walking economy. These changes make it easier to perform daily routines and may facilitate an increase in physical activity.

Delta economy of walking is not associated with body mass index in physically inactive adults

PURPOSE: Published data on the relationship between body mass index (BMI; kg/m2) and energy cost of walking is inconsistent. The aim of this study was to determine whether the increased energy expenditure (EE) that occurs with increased walking speed (defined as delta economy) is associated with BMI. The primary hypothesis was that BMI does not influence delta economy. METHODS: Insufficiently active adults (total n = 187[GG1], males n = 87, females n = 100, BMI = 20.0-39.5 kg/m2,18-60 years) walked on the treadmill at 2, 3, and 4 miles per hour (mph) while ventilation and gas exchange were measured with an indirect calorimetry system (Jaeger Oxycon Mobile) for determination of oxygen consumption (VO2), carbon dioxide production (VCO2), and respiratory exchange ratio (RER). VO2 and RER were used to calculate EE (w/kg). Each subject walked for six minutes at each speed. Only the last three minutes of EE per stage were used after verification of steady state. Delta economy was captured by analyzing the slope of change of VO2 across walking speeds. Two methodologies were employed to quantify the slope: a novel technique using polynomial random coefficient regression (PRCR) and the traditional delta economy (TDE) method of calculating change in EE for a change in speed. Two key PRCR components were generated: linear and quadratic coefficients. TDE was determined for three speed changes: 2-3 mph, 3-4 mph, and 2-4 mph. The relationship with each of these to BMI was examined via Pearson product-moment correlation with α set at 0.05. RESULTS: BMI was not associated with either the linear ( r = 0.01, p = 0.87) or quadratic ( r = 0.08, p = 0.28) PRCR coefficients. There was no relationship between BMI and TDE at any of the speed intervals: 2-3 mph ( r = 0.07, p = 0.32), 3-4 mph ( r = 0.05, p = 0.53), or 2-4 mph ( r = 0.01, p = 0.87). CONCLUSION: In this sample of inactive adults, BMI did not influence traditional delta economy or the linear and quadratic coefficients from the PRCR model. Consequently, our results indicate that the considerable between-subject variability in all measures of walking economy is not affected by BMI. A strength of this study is the large sample size, which reduces the likelihood of sampling bias that might be present in previously published studies with much smaller sample sizes. This analysis was conducted on a baseline dataset collected as part of a project funded from a grant from the National Cancer Institute at the National Institutes of Health (R01CA198915). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Powered Hip Exoskeleton Reduces Residual Hip Effort Without Affecting Kinematics and Balance in Individuals With Above-Knee Amputations During Walking.

A unilateral, lightweight powered hip exoskeleton has been shown to improve walking economy in individuals with above-knee amputations. However, the mechanism responsible for this improvement is unknown. In this study we assess the biomechanics of individuals with above-knee amputations walking with and without a unilateral, lightweight powered hip exoskeleton. We hypothesize that assisting the residual limb will reduce the net residual hip energy. Eight individuals with above-knee amputations walked on a treadmill at 1 m/s with and without a unilateral powered hip exoskeleton. Flexion/extension assistance was provided to the residual hip. Motion capture and inverse dynamic analysis were performed to assess gait kinematics, kinetics, center of mass, and center of pressure. The net energy at the residual hip decreased from 0.05±0.04 J/kg without the exoskeleton to -0.01±0.05 J/kg with the exoskeleton (p = 0.026). The cumulative positive energy of the residual hip decreased on average by 18.2% with 95% confidence intervals (CI) (0.20 J/kg, 0.24 J/kg) and (0.16 J/kg, 0.20 J/kg) without and with the exoskeleton, respectively. During stance, the hip extension torque of the residual limb decreased on average by 37.5%, 95% CI (0.28 Nm/kg, 0.36 Nm/kg), (0.17 Nm/kg, 0.23 Nm/kg) without and with the exoskeleton, respectively. Powered hip exoskeleton assistance significantly reduced the net residual hip energy, with concentric energy being the main contributor to this change. We believe that the reduction in residual hip extension torque during early stance is the main contributor to this reduction. This analysis shows that by assisting the residual hip, the exoskeleton significantly decreased the net hip energy produced by the residual limb, which may explain the improvements in walking economy previously observed.

Fascicle dynamics of the tibialis anterior muscle reflect whole-body walking economy

Humans can inherently adapt their gait pattern in a way that minimizes the metabolic cost of transport, or walking economy, within a few steps, which is faster than any known direct physiological sensor of metabolic energy. Instead, walking economy may be indirectly sensed through mechanoreceptors that correlate with the metabolic cost per step to make such gait adaptations. We tested whether velocity feedback from tibialis anterior (TA) muscle fascicles during the early stance phase of walking could potentially act to indirectly sense walking economy. As participants walked within a range of steady-state speeds and step frequencies, we observed that TA fascicles lengthen on almost every step. Moreover, the average peak fascicle velocity experienced during lengthening reflected the metabolic cost of transport of the given walking condition. We observed that the peak TA muscle activation occurred earlier than could be explained by a short latency reflex response. The activation of the TA muscle just prior to heel strike may serve as a prediction of the magnitude of the ground collision and the associated energy exchange. In this scenario, any unexpected length change experienced by the TA fascicle would serve as an error signal to the nervous system and provide additional information about energy lost per step. Our work helps provide a biomechanical framework to understand the possible neural mechanisms underlying the rapid optimization of walking economy.

Combining an Artificial Gastrocnemius and Powered Ankle Prosthesis: Effects on Transtibial Prosthesis User Gait.

Walking is more difficult for transtibial prosthesis users, partly due to a lack of calf muscle function. Powered ankle prostheses can partially restore calf muscle function, specifically push-off power from the soleus. But one limitation of a powered ankle is that emulating the soleus does not restore the multi-articular function of the gastrocnemius. This missing function may explain elevated hip and knee muscle demands observed in individuals walking on powered ankles. These elevated demands can make walking more fatiguing and impact mobility. Adding an Artificial Gastrocnemius to a powered ankle might improve gait for prosthesis users by reducing the prosthesis-side hip and knee demands. This work investigates if an Artificial Gastrocnemius reduced prosthesis-side hip or knee demands for individuals walking with a powered ankle providing high levels of push-off. We performed two case series studies that examined the effects that a passive elastic Artificial Gastrocnemius has on joint moment-impulses when prosthesis users walked with a powered ankle. We found that hip moment-impulse was reduced during stance when walking with an Artificial Gastrocnemius for six of seven participants. The Artificial Gastrocnemius effects on knee kinetics were variable and subject-specific, but in general, it did not reduce the knee flexor or extensor demands. The Artificial Gastrocnemius should be further explored to determine if reduced hip demands improve mobility or the user's quality of life by increasing the distance they can walk, increasing walking economy, or leading to increased physical activity or community engagement.

Achilles' new heel: Shock absorbing, gait assisting and energy harvesting

Humans have evolved to walk highly efficiently to conserve energy, making it challenging to develop assistive and energy-harvesting devices for walking. Herein, we report a heel pad-based assistance device for walking that not only optimizes the energetic economy of walking and prevents plantar fasciitis but also harvests energy from heel impact. Our footwear-embedded device improves the walking economy by offering shock absorption and walking assistance, while simultaneously providing energy-harvesting functions. We demonstrate that the use of our device reduces the activation of the gastrocnemius and soleus muscles during the foot strike by 5.8 ± 1.0 % and 4.1 ± 0.6 %, respectively. The collisional energy conserved from the impact at the touchdown is transformed into 3.8 ± 0.3 watts of electrical power (mean ± SEM). Compared with walking in normal shoes, the energy savings with the device imply that walking endurance could be increased by as much as 10 % without extra effort from the wearer. Our findings demonstrate the potential of the heel pad-based device that enhances the energy economy of walking and human bipedal locomotion.

Modulating Multiarticular Energy during Human Walking and Running with an Unpowered Exoskeleton.

Researchers have made advances in reducing the metabolic rate of both walking and running by modulating mono-articular energy with exoskeletons. However, how to modulate multiarticular energy with exoskeletons to improve the energy economy of both walking and running is still a challenging problem, due to the lack of understanding of energy transfer among human lower-limb joints. Based on the study of the energy recycling and energy transfer function of biarticular muscles, we proposed a hip-knee unpowered exoskeleton that emulates and reinforces the function of the hamstrings and rectus femoris in different gait phases. The biarticular exo-tendon of the exoskeleton assists hamstrings to recycle the kinetic energy of the leg swing while providing hip extension torque in the swing phase. In the following stance phase, the exo-tendon releases the stored energy to assist the co-contraction of gluteus maximus and rectus femoris for both hip extension and knee extension, thus realizing the phased modulation of hip and knee joint energy. The metabolic rate of both walking (1.5 m/s) and running (2.5 m/s) can be reduced by 6.2% and 4.0% with the multiarticular energy modulation of a hip-knee unpowered exoskeleton, compared to that of walking and running without an exoskeleton. The bio-inspired design method of this study may inspire people to develop devices that assist multiple gaits in the future.

Changes in submaximal and maximal measures of cardio-respiratory fitness resulting from 6-days of mountain walking

ABSTRACT Trekking is a popular activity associated with cardiovascular benefits. The aim of the present study was to investigate changes in the submaximal heart rate, oxygen uptake, oxygen pulse, and blood lactate concentration associated with a 6-day mountain walk. Over a 12-year period, 134 male (age 21.0 ± 1.4 years) and 124 female undergraduates (age 20.8 ± 1.6 years) participated. Three days before the trek submaximal and maximal laboratory measures were made on participants walking on a motorized treadmill using a breath-by-breath system to measure oxygen uptake (VO2) during exercise. Oxygen uptake and heart rate were recorded during steady-state exercise at treadmill gradients 0, 4, 8, 12, and 16%. Measurements were made, at the same time of day, two days after the trek. There were significant improvements in both the walking economy and the relative exercise intensity (%VO2max) at submaximal treadmill gradients 0-16%. Post-trek, heart rate was lower while oxygen pulse was higher, at each treadmill gradient. There was a significant increase in the maximal oxygen uptake for men (+2.7%) and women (+2.9%). The results of the present study suggest that improvements in cardiorespiratory fitness are associated with a 6-day mountain walk with no sex difference in the exercise response. .

Real-Time Locomotion Recognition Algorithm for an Active Pelvis Orthosis to Assist Lower-Limb Amputees

Powered hip exoskeletons, in combination with passive prostheses, have been recently proposed to improve the economy and pattern of walking of lower-limb amputees within clinical scenarios. However, for everyday life support, a real-time control strategy that can accurately recognize different locomotion modes and transitions is required. In this letter, we proposed a novel locomotion recognition algorithm for an Active Pelvis Orthosis designed to assist people with lower-limb amputation, in quasi-static (sit-to-stand/stand-to-sit) and dynamic locomotion modes (walking and stairs negotiation). Two finite-state machines were combined to recognize in real-time the participants’ locomotion, one was a rule-based algorithm and one was based on four linear discriminant analysis classifiers. Four transfemoral amputees took part in the experiments and performed a circuit of tasks in two conditions, namely in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">transparent mode</i> (the exoskeleton was controlled to provide null output impedance), and in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">assistive mode</i> (the exoskeleton was controlled to output an assistive torque consistently with the locomotion mode recognized by the algorithm), to test the algorithm in real-time conditions. The median (25 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 75 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> percentile) between-subjects recognition accuracy was 94.8% (93.4%, 96.5%) with user-dependent models. Offline analysis on user-independent models with leave-one-subject-out validation resulted in between-subjects recognition accuracy equal to 95.9% (94.0%, 97.8%). The results of this study pave the way for future experimentations of the technology in ecological scenarios.

ARTE index revisited: linking biomarkers of cardiometabolic health with free-living physical activity in postmenopausal women.

Activity-related energy expenditure (AEE) correlates with physical activity volume; however, between-person differences in body size and walking economy (net V̇o2) can influence AEE. The ratio of total energy expenditure (TEE) and resting energy expenditure (REE) estimates physical activity level (PAL) relative to body mass, yet does not account for variance in walking economy. The activity-related time equivalent (ARTEwalk) circumvents such constraints by adjusting for individual-specific walking economy. Herein, we compared AEE, PAL, and ARTEwalk index in a cohort (n = 81) of postmenopausal women while examining possible associations with biomarkers of cardiometabolic health. Secondary analyses were performed on postmenopausal women dichotomized above/below age group 50th percentile for body fat percent. TEE was reduced by 10% for the thermogenesis of digestion wherein AEE was calculated by subtracting REE from adjusted TEE. PAL was calculated as the ratio of TEE/REE. AEE was divided by the mean net energy expenditure of nongraded walking to calculate the ARTEwalk index. Between-group differences were not detected for AEE or PAL. However, the ARTEwalk index revealed that participants with less adiposity were more physically active (258 ± 149 vs. 198 ± 115 min·day-1; P = 0.046; g = 0.46). AEE and PAL did not correlate with cardiorespiratory fitness or biomarkers of cardiometabolic health. Cardiorespiratory fitness (r = 0.32), arterial elasticity (r = 0.24), total cholesterol/HDL-c ratio (r = -0.22), and body fat% (r = -0.24) were correlated with ARTEwalk. The ARTEwalk index may offer utility in detecting possible differences in physical activity volume among postmenopausal women and appears better associated with cardiometabolic biomarkers compared with AEE or PAL.

Improving Walking Economy With an Ankle Exoskeleton Prior to Human-in-the-Loop Optimization.

Lower limb robotic exoskeletons have shown the capability to enhance human locomotion for healthy individuals or to assist motion rehabilitation and daily activities for patients. Recent advances in human-in-the-loop optimization that allowed for assistance customization have demonstrated great potential for performance improvement of exoskeletons. In the optimization process, subjects need to experience multiple types of assistance patterns, thus, leading to a long evaluation time. Besides, some patterns may be uncomfortable for the wearers, thereby resulting in unpleasant optimization experiences and inaccurate outcomes. In this study, we investigated the effectiveness of a series of ankle exoskeleton assistance patterns on improving walking economy prior to optimization. We conducted experiments to systematically evaluate the wearers' biomechanical and physiological responses to different assistance patterns on a lightweight cable-driven ankle exoskeleton during walking. We designed nine patterns in the optimization parameters range which varied peak torque magnitude and peak torque timing independently. Results showed that metabolic cost of walking was reduced by 17.1 ± 7.6% under one assistance pattern. Meanwhile, soleus (SOL) muscle activity was reduced by 40.9 ± 19.8% with that pattern. Exoskeleton assistance changed maximum ankle dorsiflexion and plantarflexion angle and reduced biological ankle moment. Assistance pattern with 48% peak torque timing and 0.75 N·m·kg−1 peak torque magnitude was effective in improving walking economy and can be selected as an initial pattern in the optimization procedure. Our results provided a preliminary understanding of how humans respond to different assistances and can be used to guide the initial assistance pattern selection in the optimization.