Do Between-limb Strength Differences in the Elbow Flexors Affect Their Neuromuscular and Strength Adaptations to Short-term Strength Training?

Abstract

Purpose. The present study quantified between-limb responses to strength training in the stronger (STR) versus weaker (WEA) elbow flexors in participants with symmetric (SYM) or asymmetric (ASY) 1-RM strength. Methods. Neural, hypertrophic and strength adaptations to 4 weeks (3∙wk-1) of unilateral elbow flexion training of both arms were examined in 24 participants (6 men and 6 women in each group) who had not undertaken strength training in the past 12 months. Changes in one-repetition maximum load (1-RM strength), isokinetic (20°·s-1 and 210°·s-1) and isometric (MVIC) strength and rate of force development (RFD) as well as muscle activation (EMG; normalised to maximum M-wave amplitude) and size (CSAFlexor) were measured. Transcranial magnetic stimulation was used to assess motor evoked potential amplitude (MEP) and cortical silent period duration (cSP). Results. Following training, significant increases in 1-RM strength (SYM, STR: ∆ = 2.4±1.1 kg, WEA: ∆ = 1.9±1.1 kg; ASY, STR: ∆ = 1.8±0.7 kg, WEA: ∆ = 1.7±0.7 kg) and CSAFlexor (SYM, STR: ∆ = 107±98 mm2, WEA: ∆ = 121±64 mm2; ASY, STR: ∆ = 108±73 mm2, WEA: ∆ = 105±65 mm2) were observed, although they were not different between arms in either group. Increases in isokinetic strength were also detected, but only in STR (SYM: 20°·s-1, 210°·s-1; ASY: 20°·s-1). No statistical changes were detected in MVIC, RFD, EMG, MEP or cSP. Correlation analyses demonstrated both similarities and differences in the between-limb responses when comparing the groups. Conclusion. Between-limb responses to strength training in participants with and without strength symmetry were similar, although isokinetic strength increases were only observed in the stronger arms. However, the correlation results suggest that individual differences exist between the groups, signalling that between-limb responses can differ in individuals with and without strength asymmetry.