The Influence Of Arch Stiffness On Walking Metabolic Cost

The Influence of Arch Stiffness on Walking Metabolic CostDaniel J. Davis; John H. ChallisThe Pennsylvania State University, University Park, PAWalking is a common activity of daily living and is typically metabolically efficient. An evolutionary theory proposes that human foot arch stiffness aids in this efficiency. Many of the computational musculoskeletal models used to examine the metabolic cost of gait have failed to incorporate the complexity of the foot, modeling it as a single rigid segment. This ignores the behavior of joints like the midtarsal joint (i.e., the arch), influences the mechanics of the more commonly studied ankle and knee joints, and hampers our understanding of energetically optimal gait. PURPOSE: To determine the influence of midtarsal joint stiffness on midtarsal joint energetics and the metabolic cost of simulated walking. METHODS: A two-dimensional musculoskeletal model was developed in OpenSim. A torsional spring at the midtarsal joint represented passive tissues and/or differences in shoe/orthotic properties. An optimal control problem was solved to produce muscle excitation time-series that generated walking gait for five different midtarsal joint stiffness conditions. The problem’s objective function included terms for minimizing the sum of muscle excitations squared, and the discrepancies with experimental joint angles, joint angular velocities, and ground reaction forces. Midtarsal joint energetics were assessed by estimating the work performed about the joint. The metabolic cost of the stance phase of walking was estimated using modeled muscle behavior. RESULTS: The magnitude of positive, negative, and net work performed about the arch and the estimated metabolic cost of stance generally decreased with increasing midtarsal joint stiffness (Table 1). CONCLUSION: Arch stiffness influences the metabolic cost of simulated walking, with differences of close to 5% between the stiffest and most compliant conditions. - Midtarsal Joint Stiffness Condition 300 Nm/rad 500 Nm/rad 700 Nm/rad 900 Nm/rad 1100 Nm/rad Midtarsal Joint Positive work [x10-2 J/kg] 18.51 11.60 9.61 5.19 4.55 Negative Work [x10-2 J/kg] -13.21 -8.92 -7.44 -5.50 -4.35 Net Work [x10-2 J/kg] 5.30 2.68 2.17 -0.31 0.20 Gross metabolic cost [J/m/kg] 2.45 2.43 2.42 2.36 2.32