Neuromuscular adaptations after 12 weeks of light‐ vs. heavy‐load power‐oriented resistance training in older adults

Abstract

This study aimed to determine the specific adaptations provoked by power‐oriented resistance training using light (LL‐PT, 40% 1‐RM) vs. heavy (HL‐PT, 80% 1‐RM) loads in older adults. Using a randomized within‐subject study design, 45 older adults (>65 years) completed an 8‐week control period (CTR) followed by 12 weeks of unilateral LL‐PT vs. HL‐PT on a leg press. The 1‐RM, theoretical force at zero velocity ( F 0 ), maximal unloaded velocity ( V 0 ), and maximal muscle power ( P max ) were determined through a force‐velocity relationship test. Isometrically, the rate of force development (RFD) and the corresponding muscle excitation of the knee extensor muscles were assessed. In addition, muscle cross‐sectional area (CSA) and architecture of two quadriceps muscles were determined. Changes after CTR, LL‐PT and HL‐PT were compared using linear mixed models. HL‐PT provoked greater improvements in 1‐RM and F 0 (effect size (ES) = 0.55‒0.68; p < 0.001) than those observed after LL‐PT (ES = 0.27−0.47; p ≤ 0.001) (post hoc treatment effect, p ≤ 0.057). By contrast, ES of changes in V 0 was greater in LL‐PT compared to HL‐PT (ES = 0.71, p < 0.001 vs. ES = 0.39, p < 0.001), but this difference was not statistically significant. Both power training interventions elicited a moderate increase in P max (ES = 0.65‒0.69, p < 0.001). Only LL‐PT improved early RFD (ie, ≤100 ms) and muscle excitation (ES = 0.36‒0.60, p < 0.05). Increased CSA were noted after both power training programs (ES = 0.13‒0.35, p < 0.035), whereas pennation angle increased only after HL‐PT (ES = 0.37, p = 0.004). In conclusion, HL‐PT seems to be more effective in improving the capability to generate large forces, whereas LL‐PT appears to trigger greater gains in movement velocity in older adults. However, both interventions promoted similar increases in muscle power as well as muscle hypertrophy.