Neither total muscle activation nor co-activation explains the youthful walking economy of older runners

Publication date: Available online 20 July 2018

Source: Gait & Posture

Author(s): Owen N. Beck, Alena M. Grabowski, Justus D. Ortega

Abstract

Background

Older adults (≥65 years) exhibited greater metabolic rates during walking (worse walking economy) compared to young adults. Yet, previous research suggests that habitual running, but not habitual walking, exercise mitigates the age-related deterioration of walking economy.

Research Question

Does total leg muscle activation and/or agonist-antagonist co-activation explain the superior walking economy of older runners versus older walkers? Methods: We quantified metabolic power, leg muscle activation, and co-activation in older walkers and older runners during walking at 0.75, 1.25, and 1.75 m/s.

Results

Neither total stride (each speed p ≥ 0.024), stance- (each speed p ≥ 0.217), nor swing- (each speed p ≥ 0.170) phase EMG amplitude differed between older walkers and older runners at 0.75, 1.25, or 1.75 m/s. Stride averaged medial gastrocnemius and biceps femoris activation were less in older runners than older walkers at 1.25 and 1.75 m/s (all p ≤ 0.025). We also calculated shank, thigh, and overall (shank and thigh) agonist-antagonist leg muscle co-activation over each stride phase and the only difference between groups was a greater shank co-activation in older runners at 0.75 m/s (p = 0.024). Across groups, stride, stance-, and swing-phase total muscle activation positively correlated with gross metabolic power (R² = 0.58-0.66; all p < 0.001). Paradoxically, across groups, stride, stance-, and swing-phase muscle co-activation indices were negatively correlated with gross metabolic power (R² = 0.08-0.29; all p ≤ 0.007).

Significance

Neither total leg muscle activation nor co-activation explains the superior walking economy of older runners versus older walkers.

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