Mechanical energy profiles of the combined ankle–foot system in normal gait: Insights for prosthetic designs

Journal of Experimental Biology

Takahashi

Sawicki

2015

Self Cite

107

Measuring biomechanical work performed by humans and other animals is critical for understanding muscle-tendon function, jointspecific contributions and energy-saving mechanisms during locomotion. Inverse dynamics is often employed to estimate jointlevel contributions, and deformable body estimates can be used to study work performed by the foot. We recently discovered that these commonly used experimental estimates fail to explain whole-body energy changes observed during human walking. By re-analyzing previously published data, we found that about 25% (8 J) of total positive energy changes of/about the body's center-of-mass and >30% of the energy changes during the Push-off phase of walking were not explained by conventional joint-and segment-level work estimates, exposing a gap in our fundamental understanding of work production during gait. Here, we present a novel Energy-Accounting analysis that integrates various empirical measures of work and energy to elucidate the source of unexplained biomechanical work. We discovered that by extending conventional 3 degree-of-freedom (DOF) inverse dynamics (estimating rotational work about joints) to 6DOF (rotational and translational) analysis of the hip, knee, ankle and foot, we could fully explain the missing positive work. This revealed that Push-off work performed about the hip may be >50% greater than conventionally estimated (9.3 versus 6.0 J, P=0.0002, at 1.4 m s −1). Our findings demonstrate that 6DOF analysis (of hipknee-ankle-foot) better captures energy changes of the body than more conventional 3DOF estimates. These findings refine our fundamental understanding of how work is distributed within the body, which has implications for assistive technology, biomechanical simulations and potentially clinical treatment.

Section: Key Scientific Implicationssupporting

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Six degree-of-freedom analysis of hip, knee, ankle and foot provides updated understanding of biomechanical work during human walking

Journal of Experimental Biology

Takahashi

Sawicki

2015

Self Cite

107

“…3D). Much of this work is potentially attributable to the foot, where activity of intrinsic muscles (25), motion of the metatarsophalangeal joint, and deformation of heel pad and plantar tissues (26,27) yield a combined foot power profile (37,40,41) that is qualitatively similar to the soft tissue push-off contributions computed in this study. Some of the observed work may in fact be performed actively by muscle (25), but since foot work was not explicitly estimated in this analysis, their contributions get lumped into the soft tissue estimate.…”

Section: Discussionsupporting

confidence: 58%

Soft Tissue Deformations Contribute to the Mechanics of Walking in Obese Adults

Medicine &Amp; Science in Sports &Amp; Exercise

Board

et al. 2015

Obesity not only adds to the mass that must be carried during walking, but also changes body composition. Although extra mass causes roughly proportional increases in musculoskeletal loading, less well understood is the effect of relatively soft and mechanically compliant adipose tissue. Purpose To estimate the work performed by soft tissue deformations during walking. The soft tissue would be expected to experience damped oscillations, particularly from high force transients following heel strike, and could potentially change the mechanical work demands for walking. Method We analyzed treadmill walking data at 1.25 m/s for 11 obese (BMI > 30 kg/m2) and 9 non-obese (BMI < 30 kg/m2) adults. The soft tissue work was quantified with a method that compares the work performed by lower extremity joints as derived using assumptions of rigid body segments, with that estimated without rigid body assumptions. Results Relative to body mass, obese and non-obese individuals perform similar amounts of mechanical work. But negative work performed by soft tissues was significantly greater in obese individuals (p= 0.0102), equivalent to about 0.36 J/kg vs. 0.27 J/kg in non-obese individuals. The negative (dissipative) work by soft tissues occurred mainly after heel strike, and for obese individuals was comparable in magnitude to the total negative work from all of the joints combined (0.34 J/kg vs. 0.33 J/kg for obese and non-obese adults, respectively). Although the joints performed a relatively similar amount of work overall, obese individuals performed less negative work actively at the knee. Conclusion The greater proportion of soft tissues in obese individuals results in substantial changes in the amount, location, and timing of work, and may also impact metabolic energy expenditure during walking.

“…Thus, none of these experimental methods provides a definitive answer on how work performed by muscletendon units about the ankle transfers to nonadjacent segments, or how (mechanistically) ankle push-off facilitates economical gait. Given that both the foot (distal to the ankle) and the knee are estimated to perform substantial negative work during Push-off (Siegel et al, 1996;Takahashi and Stanhope, 2013;Zelik et al, 2015a), some of the ankle push-off work may not directly accelerate the swing limb, nor the COM. Rather, a portion of ankle push-off might instead serve to offset simultaneous energy absorption or dissipation elsewhere in the body (e.g.…”

Section: Limitations Of This Perspectivementioning

confidence: 99%

A unified perspective on ankle push-off in human walking

Journal of Experimental Biology

Adamczyk

2016

115

Muscle-tendon units about the ankle joint generate a burst of positive power during the step-to-step transition in human walking, termed ankle push-off, but there is no scientific consensus on its functional role. A central question embodied in the biomechanics literature is: does ankle push-off primarily contribute to leg swing, or to center of mass (COM) acceleration? This question has been debated in various forms for decades. However, it actually presents a false dichotomy, as these two possibilities are not mutually exclusive. If we ask either question independently, the answer is the same: yes! (1) Does ankle push-off primarily contribute to leg swing acceleration? Yes. (2) Does ankle push-off primarily contribute to COM acceleration? Yes. Here, we summarize the historical debate, then synthesize the seemingly polarized perspectives and demonstrate that both descriptions are valid. The principal means by which ankle push-off affects COM mechanics is by a localized action that increases the speed and kinetic energy of the trailing push-off limb. Because the limb is included in body COM computations, this localized segmental acceleration also accelerates the COM, and most of the segmental energy change also appears as COM energy change. Interpretation of ankle mechanics should abandon an either/ or contrast of leg swing versus COM acceleration. Instead, ankle push-off should be interpreted in light of both mutually consistent effects. This unified perspective informs our fundamental understanding of the role of ankle push-off, and has important implications for the design of clinical interventions (e.g. prostheses, orthoses) intended to restore locomotor function to individuals with disabilities.