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Biomechanics

Biomechanics - Poster Session D

Poster E4 - MUSCULOSKELETAL MODELING TO EVALUATE THE INFLUENCE OF CARBON FIBER INSOLES ON GAIT METABOLIC COST

Friday, October 25, 2024
3:30 PM - 4:30 PM EST
Location: Exhibit Hall E, F & G

Introduction:  Humans frequently choose to walk at a speed that corresponds with the minimum metabolic energy expenditure per unit distance [1]. Factors such as age, muscular disorders, and neurological conditions, which affect approximately 10% of all U.S. adults [2], can increase the amount of energy necessary to complete daily activities. This increased energy expenditure can potentially lead to increased fatigue, injury risk, and healthcare costs [3,4,5], negatively affecting an individual’s quality of life. To address this, various assistive devices have been developed to reduce lower limb energy demands. Carbon fiber insoles are a low-cost assistive device that have the potential to reduce the whole-body metabolic cost of walking, but the contributions from individual muscles have yet to be elucidated [6,7]. Elucidating the effects of carbon fiber insoles on specific muscles would facilitate design improvements to better reduce injury and optimize lower limb energy expenditure. Musculoskeletal modeling and simulation informed by motion capture and direct muscle measurements can provide insights into individual-specific muscle mechanics which are not possible to assess in vivo [8]. The objective of this study was to generate computational musculoskeletal simulations from subject-specific models to examine the effects of footwear stiffness via carbon fiber insoles on lower-limb muscle energy expenditure. These simulations were compared with previous experimental data including lower-limb joint kinematics, soleus fascicle dynamics, and trends in whole-body energy expenditure.

Materials and

Methods:  One participant (male, 1.69 m, 68.5 kg) who completed the experimental protocol by Ray & Takahashi [6] was chosen at random for initial pilot simulations. In brief, Ray & Takahashi [6] collected data from motion capture, cine B-mode ultrasound, indirect calorimetry, and electromyography data as participants walked on a treadmill at three different speeds (1.25, 1.75, and 2.0 m/s) with three different footwear stiffness conditions in a block randomized order. The footwear stiffness conditions consisted of a standardized shoe (Reebok RealFlex Train) with no carbon fiber insole (low stiffness), a 1.6 mm carbon fiber insole (medium stiffness), and a 3.2 mm carbon fiber insole (high stiffness). For this analysis, one speed (1.25 m/s; a typical walking speed) was examined. A lower extremity model (OpenSim’s gait2354 model [8]) was first scaled to align with participant anthropometry and inertial properties. To represent the stiffening effect of the carbon fiber insoles, a torsional spring was added to the model’s metatarsophalangeal (MTP) joint with values obtained from 3-point bending tests [6]. Inverse kinematics was then employed to estimate model joint angles from measured marker trajectories. Finally, residual reduction and computed muscle control were used to solve for muscle control values that produced consistent kinematic and kinetic results (Figure 1) [8,9]. Whole-body and muscle-specific metabolic costs were calculated and summed across each joint for the simulated stride (biarticular muscles were partitioned based on the ratio of the moment arms at each joint [10]).

Results, Conclusions, and Discussions: The power fluctuations about the experimental distal foot and simulated MTP joint showed similar trends during the stance phase (Figure 1). The net work performed by the distal foot structures in vivo with increasing footwear stiffness varied in a similar pattern as the net work performed about the MTP joint with increasing torsional spring stiffness: -6.7, -7.6, and -0.9 J compared with -8.4, -13.9, and -2.7 J, respectively. The stance-averaged soleus fascicle shortening velocity decreased with increasing stiffness in both the experimental and simulated data: 23.52% (med) and 46.97% (high) relative to the low stiffness condition experimentally, and 36.07% (med) and 38.62% (high) relative to the low stiffness condition in the simulation, respectively. Additionally, the experimental and simulated metabolic cost of transport varied similarly, with greater relative decreases (1.29% and 2.63%, respectively) in the medium stiffness condition compared with the higher stiffness condition (0.32% and 2.44%, respectively) (Figure 2). Simulated muscles crossing the ankle joint consumed less energy with increasing torsional spring stiffness (Figure 3).
Similarities across the distal foot mechanical energetics and soleus fascicle shortening velocity trends between experimental and simulated data provide preliminary validation for modeling the muscle-specific metabolic costs that are difficult to determine in vivo. Specifically, the decrease in energy consumed by the ankle joint musculature with increasing torsional spring stiffness agrees well with bioenergetic modeling of experimental data of footwear stiffness modifications [11]. The main limitation of the model is the lack of anatomical markers to define specific joints and body segments. For example, no trunk markers were used in the experimental protocol. Therefore, the model’s pelvis was constrained to produce an upright trunk posture which may have altered lower limb gait dynamics. Additionally, only one marker distal to the MTP joint was used experimentally, decreasing the confidence in that joint’s kinematics and kinetics. This initial modelling framework requires further refinement but has the potential to be used to better understand individual muscle contributions to whole-body metabolic cost. This improved understanding can help to design future assistive devices aimed at reducing the energy requirements of those with mobility impairment.

Acknowledgements (Optional):  Acknowledgements: This work was supported by SPUR from the Office of Undergraduate Research at the University of Utah, NIH R01AR081287 awarded to KZT, and NIH T32TR004394 awarded to DJD. The authors would like to acknowledge Samuel F. Ray for collecting the experimental data associated with this study.

References:
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