title: Six degree-of-freedom analysis of hip, knee, ankle and foot provides updated understanding of biomechanical work during human walking.
abstract: Measuring biomechanical work performed by humans and other animals is critical for understanding muscle-tendon function, joint-specific contributions and energy-saving mechanisms during locomotion. Inverse dynamics is often employed to estimate joint-level 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 hip-knee-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.
authors: Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37212, USA Department of Physical Medicine and Rehabilitation, Vanderbilt University, Nashville, TN 37212, USA Laboratory of Neuromotor Physiology, Santa Lucia Foundation, Rome 00179, Italy karl.zelik@vanderbilt.edu.
authors: Karl E
authors: KE
authors: Zelik
authors: Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC 27695, USA.
authors: Kota Z
authors: KZ
authors: Takahashi
authors: Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill, Raleigh, NC 27695, USA.
authors: Gregory S
authors: GS
authors: Sawicki
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000502:physiology*; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D016138:Walking; D055815:Young Adult
keywords: Biomechanics; Foot work; Gait analysis; Inverse dynamics; Joint work; Mechanical work