The effects of strength training on isometric force production symmetry in recreationally trained males

The purpose of this investigation was to determine what effect a bilateral strength training regimen has on isometric force production symmetry and if changes in force production symmetry can be accounted for by differences in pre-intervention strength levels. Design: Sixteen recreationally trained males (1-RM squat: 146.8 23.0 kg.) were assigned to two groups for the 7-week training intervention: strong (S) and weak (W) based on pre-training squat isometric peak force allometrically scaled (IPFa) at 120 knee angle. Methods: Subjects completed a 7-week training intervention following a block-periodized model and were tested on measures of dynamic (1RM squat) and isometric (isometric squat at 90 and 120 knee angle) strength pre-and post-intervention. The degree of bilateral lower limb asymmetry was calculated as a percentage where 0% symmetry index (SI) indicates perfect symmetry on the isometric squat. Results: ANCOVA results showed no statistical difference between groups for all dependent variables when pre-intervention IPFa 120 scores were used as the covariate. Paired t-tests results showed both groups statistically improved 1RM squat and IPFa 120 (p < 0.05). IPFa 120 SI decreased statistically from pre-training in the W group (p = 0.03). Independent t-test results showed the W group had statistically larger pre-intervention SI scores for IPFa 90 (p = 0.045) and IPFa 120 (p = 0.007); however this difference was no longer present following strength training. There was a strong inverse relationship between pooled IPFa 120 and IPFa 120 SI (r = -0.64, p = 0.004).