Connecting the legs with a spring improves human running economy

Simpson, Cole S.; Welker, Cara Gonzalez; Uhlrich, Scott D.; Sketch, Sean M.; Jackson, Rachel W.; Delp, Scott L.; Collins, Steven H.; Selinger, Jessica C.; Hawkes, Elliot W.

doi:10.1242/jeb.202895

Cited by 47 publications

(48 citation statements)

References 56 publications

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“…Moreover, they performed five 7-min experimental walking trials wearing the exoskeleton. Previous studies show that adaptation time could potentially affect metabolic rates [ 42 , 43 ]. Thus, it may be possible that with prolonged exposure to using the exoskeleton, subjects may have adopted locomotor strategies that could potentially affect metabolic rates.…”

Section: Discussionmentioning

confidence: 99%

Passive-elastic knee-ankle exoskeleton reduces the metabolic cost of walking

Etenzi¹,

Borzuola

Grabowski

2020

J NeuroEngineering Rehabil

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Background Previous studies have shown that passive-elastic exoskeletons with springs in parallel with the ankle can reduce the metabolic cost of walking. We developed and tested the use of an unpowered passive-elastic exoskeleton for walking that stores elastic energy in a spring from knee extension at the end of the leg swing phase, and then releases this energy to assist ankle plantarflexion at the end of the stance phase prior to toe-off. The exoskeleton uses a system of ratchets and pawls to store and return elastic energy through compression and release of metal springs that act in parallel with the knee and ankle, respectively. We hypothesized that, due to the assistance provided by the exoskeleton, net metabolic power would be reduced compared to walking without using an exoskeleton. Methods We compared the net metabolic power required to walk when the exoskeleton only acts at the knee to resist extension at the end of the leg swing phase, to that required to walk when the stored elastic energy from knee extension is released to assist ankle plantarflexion at the end of the stance phase prior to toe-off. Eight (4 M, 4F) subjects walked at 1.25 m/s on a force-measuring treadmill with and without using the exoskeleton while we measured their metabolic rates, ground reaction forces, and center of pressure. Results We found that when subjects used the exoskeleton with energy stored from knee extension and released for ankle plantarflexion, average net metabolic power was 11% lower than when subjects walked while wearing the exoskeleton with the springs disengaged ( p = 0.007), but was 23% higher compared to walking without the exoskeleton ( p < 0.0001). Conclusion The use of a novel passive-elastic exoskeleton that stores and returns energy in parallel with the knee and ankle, respectively, has the potential to improve the metabolic cost of walking. Future studies are needed to optimize the design and elucidate the underlying biomechanical and physiological effects of using an exoskeleton that acts in parallel with the knee and ankle. Moreover, addressing and improving the exoskeletal design by reducing and closely aligning the mass of the exoskeleton could further improve the metabolic cost of walking.

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Section: Discussionmentioning

confidence: 99%

Passive-elastic knee-ankle exoskeleton reduces the metabolic cost of walking

Etenzi¹,

Borzuola

Grabowski

2020

J NeuroEngineering Rehabil

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“…For example, an ankle exoskeleton developed by Collins et al, composed of springs and clutches, reduced energy cost of walking by an average of 7.2% at normal walking speeds 29 . Similar metabolic cost reductions have also been observed in running, including a spring-loaded exoskeletons assisting at the hip (~8%) 30 and an 'exotendon' that connected the two feet with a spring (~6.4%) 31 . Additionally, our 7.1% reduction in fast walking is much greater than previous results by Roy and Stefanyshyn, achieving only ~1% reduction with similar passive insoles during running 21 .…”

Section: Discussionmentioning

confidence: 55%

Gearing Up the Human Ankle-Foot System to Reduce Energy Cost of Fast Walking

Ray

Takahashi

2020

Sci Rep

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During locomotion, the human ankle-foot system dynamically alters its gearing, or leverage of the ankle joint on the ground. Shifting ankle-foot gearing regulates speed of plantarflexor (i.e., calf muscle) contraction, which influences economy of force production. Here, we tested the hypothesis that manipulating ankle-foot gearing via stiff-insoled shoes will change the force-velocity operation of plantarflexor muscles and influence whole-body energy cost differently across walking speeds. We used in vivo ultrasound imaging to analyze fascicle contraction mechanics and whole-body energy expenditure across three walking speeds (1.25, 1.75, and 2.0 m/s) and three levels of foot stiffness. Stiff insoles increased leverage of the foot upon the ground (p < 0.001), and increased dorsiflexion rangeof-motion (p < 0.001). Furthermore, stiff insoles resulted in a 15.9% increase in average force output (p < 0.001) and 19.3% slower fascicle contraction speed (p = 0.002) of the major plantarflexor (Soleus) muscle, indicating a shift in its force-velocity operating region. Metabolically, the stiffest insoles increased energy cost by 9.6% at a typical walking speed (1.25 m/s, p = 0.026), but reduced energy cost by 7.1% at a fast speed (2.0 m/s, p = 0.040). Stiff insoles appear to add an extra gear unavailable to the human foot, which can enhance muscular performance in a specific locomotion task. Humans take advantage of the functional interplay between the ankle joint and distal structures in the foot to walk and run effectively. Moreover, the plantarflexor muscle-tendon structures generate forces that help the body remain upright 1-3 and move the body forward from one step to the next 4,5. During walking or running, these muscles operate within favorable regions of force-length 6 and force-velocity (i.e., near isometric or low speeds) relationships 7-9 to produce force economically. Force production of the plantarflexors is facilitated by a gearing or lever-like function of the distal structures in the foot 10. In particular, structures like the toes, arch, and intrinsic muscles 11 can influence how the ground reaction force propagates underneath the foot, which in turn alters the force requirement of the ankle plantarflexor muscle-tendon unit. The ratio of the lever arms of the output ground reaction force and the input plantarflexor muscle-tendon force about the ankle 10 , termed gear ratio, can influence action of the plantarflexor muscles (Fig. 1). A high gear ratio can facilitate slower shortening of the plantarflexor muscles 12,13 , which could enhance force production, owing to the force-velocity relationship 14,15. The ability to modulate ankle-foot gear ratio may then help to maintain optimal function in different locomotor tasks, including steady-state walking, running 8,16,17 , and maximal-acceleration push-off 10,16. Common, everyday devices like footwear can alter the gearing-like function of the foot, consequently altering locomotor performance 13,16,18. For example, insole materials that minimize deflection aro...

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“…Passive exoskeletons for metabolic rate reduction 1 in running and walking are popular in the research community because of their innovative design as well as the perspective of usability, low weight, and affordable cost 1,[3][4][5][6] . Nevertheless, as for the active ones, passive exoskeletons have not fulfilled the desired expectations yet.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, the performance of these devices in metabolic rate reduction and comfort increment is very sensitive to users' kinematic and the compliance profiles of elastic parts. As a result, (1) adaptation of compliant elements (devising a semi-passive exoskeleton) 17,18 as well as (2) modification of subjects' kinematic by training 3 are two solutions for improving the performance of a full-passive exoskeleton. To materialize these two approaches for an assistive device, a low-cost and simple compliance adaptation method and a quantitative straight-forward kinematic measure for subject training are required.…”

Section: Introductionmentioning

confidence: 99%

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A Kinematic Index for Estimation of Metabolic Rate Reduction in Running withI-RUN

Aftabi

Nasiri

Ahmadabadi

2020

Preprint

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In this paper, we target multiple goals related to our passive running assistive device, called I-RUN. The major goals are: (1) finding the main reason behind individual differences in benefiting from our assistive device at the muscles level, (2) devising a simple measure for on-line I-RUN stiffness tuning, and creating a lab-free simple kinematic measure for (3) estimating metabolic rate reduction as well as (4) training subjects to maximize their benefit from I-RUN. Our approach is using some extensive data-driven OpenSim simulation results employing a generic lower limb model with 92-muscles and 29-DOF.It is observed that there is a significant relation between the hip joints kinematic and changes in the metabolic rate in the presence of I-RUN. Accordingly, a simple kinematic index is devised to estimate metabolic rate reduction. This index not only explains individual differences in metabolic rate reduction but also provides a quantitative measure for training subjects to maximize their benefits from I-RUN.The simulation results also re-confirm our hypothesis that “reducing the forces of two antagonistic mono-articular muscles is sufficient for involved muscles’ total effort reduction”. Consequently, we introduce a two-muscles EMG-based metric for the on-line tuning of I-RUN.

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Connecting the legs with a spring improves human running economy

Cited by 47 publications

References 56 publications

Passive-elastic knee-ankle exoskeleton reduces the metabolic cost of walking

Passive-elastic knee-ankle exoskeleton reduces the metabolic cost of walking

Gearing Up the Human Ankle-Foot System to Reduce Energy Cost of Fast Walking

A Kinematic Index for Estimation of Metabolic Rate Reduction in Running withI-RUN

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