Contralateral Adaptations After Unilateral Power Training in Older Adults: The Effect of Intensity of Load

This study aimed to investigate the effect of training intensity on contralateral adaptations following unilateral power-oriented resistance training (PT) in older adults. This secondary analysis of a within-person randomized controlled trial included 45 older adults (≥ 65 years; 25 women). After an 8-week control period (n = 45), part of the participants completed 12 weeks of a volume load-matched PT on one lower limb using either light loads (40% 1-RM, n = 9) or heavy loads (80% 1-RM, n = 10), while the contralateral limb did not exercise. Unilateral performance was assessed before and after each period through isometric tests (maximal isometric force, rate of force development, and muscle excitation) and dynamic tests (1-RM, maximal muscle power and maximal unloaded velocity determined through a force-velocity relationship test). Additionally, mid-thigh muscle mass and whole-body physical function were assessed. Linear mixed models were conducted to compare the effect (Cohen's d) of training intensity on the efficacy and magnitude of the contralateral adaptations and their impact on physical function. No contralateral adaptations were observed in any of the isometric tests. In contrast, untrained limbs showed comparable improvements in 1-RM (d = 0.35-0.42; p ≤ 0.001) and maximal muscle power (d = 0.49-0.54; p ≤ 0.001) regardless of PT intensity. Only heavy-load PT improved maximal unloaded velocity in the contralateral untrained limb (d = 0.68; p ≤ 0.001), while mid-thigh muscle mass (d = 0.24; p ≤ 0.013) and whole-body physical function assessed through the timed up-and-go test improved only after light-load PT (d = -0.74; p < 0.001). In conclusion, unilateral PT induced significant contralateral gains in dynamic muscle strength and power, regardless of training intensity, with heavier loads enhancing velocity-specific adaptations. Notably, light-load PT induced mild hypertrophy in the contralateral untrained limb and whole-body physical function, which might be particularly relevant for enhancing the intrinsic capacity of older adults. Trial Registration: ClinicalTrials.gov ID: NCT03724461.