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bioRxiv · 10.1101/2025.02.13.638001

Bilateral neuromuscular adaptation to acute unilateral resistance exercise in healthy older adults

Gamage, N. N.·Altheyab, A.·Guo, Y.·Phillips, B. E.·Opie, G. M.·Semmler, J. G.·Atherton, P.·Piasecki, M.
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Abstract

IntroductionResistance exercise (RE) enhances functionality in older adults and has proven effective as a means of cross-education in scenarios of unilateral disuse. However, the extent to which older adults demonstrate cross-limb transfer at the motor unit (MU) level following a single bout of unilateral RE is unclear. MethodsThirteen healthy older adults (74.9 {+/-} 4.8 years; 5 females) underwent bilateral neuromuscular assessments pre- and post- a single bout of unilateral RE consisting of 3-4 sets of 8-12 repetitions of leg extension of the dominant (exercise) leg, at 75% of 1 repetition maximum, performed to failure. Maximum voluntary contraction (MVC) and force steadiness (FS) were measured. Central and peripheral features of individual MU were recorded using high-density surface electromyography and intramuscular electromyography (HDs/iEMG), during contractions normalised to 25% MVC. ResultsFollowing unilateral RE, MVC reduced in exercise (-14.8%, p < 0.001) and control (-6.9%, p = 0.003) legs, with reduced FS performance in the exercise leg compared to the control (p = 0.002). MU firing rate increased during contractions normalised to 25% baseline MVC in the exercised leg (p < 0.05), with no adaptation in the control leg (p > 0.05). All iEMG recorded measures of MU potentials remained unchanged in both legs (all p > 0.05). ConclusionAcute unilateral RE leads to bilateral MVC reduction in older males and females, demonstrating the cross-limb transfer effect. However, adaptation of MU features was only apparent in the exercised limb, and mechanisms underlying the force decline in the non- exercised limb remain uncertain.

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Gamage, N. N., Altheyab, A., Guo, Y., Phillips, B. E., Opie, G. M., Semmler, J. G., Atherton, P., Piasecki, M.. 2025-02-17. Bilateral neuromuscular adaptation to acute unilateral resistance exercise in healthy older adults. https://doi.org/10.1101/2025.02.13.638001

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