Energy neutral: the human foot and ankle subsections combine to produce near zero net mechanical work during walking

Abstract

The human foot and ankle system is equipped with structures that can produce mechanical work through elastic (e.g., Achilles tendon, plantar fascia) or viscoelastic (e.g., heel pad) mechanisms, or by active muscle contractions. Yet, quantifying the work distribution among various subsections of the foot and ankle can be difficult, in large part due to a lack of objective methods for partitioning the forces acting underneath the stance foot. In this study, we deconstructed the mechanical work production during barefoot walking in a segment-by-segment manner (hallux, forefoot, hindfoot, and shank). This was accomplished by isolating the forces acting within each foot segment through controlling the placement of the participants’ foot as it contacted a ground-mounted force platform. Combined with an analysis that incorporated non-rigid mechanics, we quantified the total work production distal to each of the four isolated segments. We found that various subsections within the foot and ankle showed disparate work distribution, particularly within structures distal to the hindfoot. When accounting for all sources of positive and negative work distal to the shank (i.e., ankle joint and all foot structures), these structures resembled an energy-neutral system that produced net mechanical work close to zero (−0.012 ± 0.054 J/kg).

The foot is more than a spring: human foot muscles perform work to adapt to the energetic requirements of locomotion

“…Small errors in estimates of the velocity of the contact points, joint centres and insertion locations of the MTU may also explain some of this difference. Our estimate of foot contact work during the level stepping task is also in agreement with previous data using similar approaches to quantify the energetic function 0 -1 of the foot during locomotion [12]. The magnitude of energy absorbed by the plantar MTU (4.5 J) in level walking was similar but higher than that reported in running at 3.1 m s 21 (3.1 J) [41].…”

“…Secondly, using estimates for speed and force as described in the next section, the work performed by the plantar MTU was calculated. Thirdly, we applied a unified deformable segment analysis to quantify the instantaneous power of the foot as it interacts with the ground, as explained previously [11,12], termed the foot contact model.…”

“…The depiction of the foot as an elastic spring is based on in situ cadaveric observations of the PA straining in response to longitudinal arch (LA) compression and recoiling as the LA rebounds [6]. Recent in vivo evidence suggests that the energetic behaviour of the foot during constant speed locomotion is more akin to that of a viscous spring-damper system, rather than a purely elastic spring [11,12]. We have recently shown that a greater proportion of absorbed energy is dissipated by structures within the foot at higher running & 2019 The Author(s) Published by the Royal Society.…”

Number of Segments Within Musculoskeletal Foot Models Influences Ankle Kinematics and Strains of Ligaments and Muscles

“…16 It should be noted that the rigid body assumption in all MFMs in the current study may lead to errors, which may be overcome with the use of a deformable foot model in future studies. 31,32 In contrast to the large differences between 2MFM versus 3MFM and 2MFM versus 5MFM, the differences between 3MFM and 5MFM were much smaller, which suggested a greater similarity between them. The similarity may arise from the fact that both models include the MTP joint, because hopping requires a considerable MTP joint range of motion, which is captured by the 3MFM and 5MFM.…”

“…In other words, IK uses different bony landmarks to calculate ankle joint angles depending on the respective MFM, which may consequently generate different motions . It should be noted that the rigid body assumption in all MFMs in the current study may lead to errors, which may be overcome with the use of a deformable foot model in future studies …”