Abstract:

Exoskeletons that improve locomotion economy typically are engineered to reduce users’ limb joint mechanical work or moments. Yet, limb joint dynamics do not necessarily reflect muscle dynamics, which dictate whole-body metabolic energy expenditure. Here, we hypothesize that exoskeletons primarily reduce user metabolic energy expenditure across locomotion conditions by reducing active muscle volume.

Key Points

• Center of mass, limb joint, and muscle mechanical do not explain well how exoskeletons alter locomotion economy.
• Limb joint dynamics do not necessarily reflect the underlying muscle dynamics across locomotion conditions.
• Active muscles are the primary drivers of whole-body metabolic energy expenditure during locomotion. Consequently, exoskeletons likely need to consider muscle dynamics to optimize locomotion economy.
• During walking and hopping with an exoskeleton, muscle force generation is a better correlate to locomotion economy than previously measured mechanical work parameters.
• Tracking muscle length changes in vivo may help provide reasonably accurate active muscle volume calculations.
• Future exoskeleton controllers may incorporate real-time muscle physiology measures to update device characteristics and maintain minimal active muscle volume and metabolic energy expenditure across locomotion conditions.