Muscle Strength And Size Correlations At Baseline And Following Unilateral Resistance Training

Abstract

Traditional theory has linked muscular size and muscular strength at baseline and following resistance training, though recent studies have challenged the independence of these traits, especially within the context of chronic resistance training. We previously completed a large study of strength and size changes with 12 weeks of progressive resistance training in previously untrained adults. PURPOSE: We examined the effects of progressive resistance training on the relationship between muscle volume (VOL) and muscle strength, measured as both dynamic (one repetition maximum; 1-RM) and isometric (maximal voluntary contraction; MVC) strength. We further tested for sex differences in these relationships. METHODS: 665 healthy young (18>age>40) and untrained individuals (254 men and 411 women) were tested. Muscle volume (by magnetic resonance imaging) and strength (1-RM and MVC) measures were taken before and after 12-weeks of resistance training of the non-dominant biceps/triceps. Subjects trained with progressively increasing weights twice per week using biceps preacher curl, biceps concentration curl, standing biceps curl, overhead triceps extension, and triceps kickback. We used Pearson correlations to test strength-size relationships in the entire cohort and within sex both at baseline and percent change following training. RESULTS: Weak to moderate correlations were seen at baseline: VOL-1-RM (r=0.43 in all, 0.32 in women and 0.14 in men, all p<0.01) and VOL-MVC (r=0.34 in all, 0.19 in women and 0.28 in men, all p<0.01). Following training, specific relationships between percent changes in strength and size were: VOL-1-RM (r=0.04 in all, p=0.3; 0.13 in women, p=0.006; and 0.14 in men, p=0.03) and VOL-MVC (r=0.13 in all, p<0.01; 0.19 in women, p<0.01; and 0.12 in men, p=0.054). CONCLUSION: At baseline, significant but weak correlations exist between strength and size, regardless of sex. Following training, correlations became weaker, and even insignificant for change in volume to change in 1-RM in the whole cohort and change in volume to change in MVC in men. Together, these data provide evidence that isometric and dynamic strength are complex traits, especially following resistance training, that are affected by factors beyond size.