Cross-education Effects After High Versus Low Frequency, Volume-matched Grip Strength Training.

Abstract

Unilateral strength training can attenuate muscle mass and strength losses in an opposite immobilized limb. Traditional unilateral training programs that yield these cross-education effects cause inter-limb asymmetry by inducing hypertrophy and strength increases in the trained limb. A higher frequency training program with lower per session volume may attenuate trained limb hypertrophy but still yield cross-education effects, lowering inter-limb asymmetry. PURPOSE: To determine the effects of a high frequency (HF) vs. low frequency (LF) volume-matched 4-week isometric grip strength training program on cross-education of strength. METHODS: Nineteen healthy right-handed participants (age 24±5 years) were randomly assigned to one of two groups: HF (n=10) and LF (n=9). Participants were tested twice before and once after a 4-week, unilateral (right) grip strength training program totaling 120 maximal repetitions per week. HF trained twice per day, 5 days per week, 2 sets of 6 repetitions per session. LF trained 3 days per week, 5 sets of 8 repetitions per session. Measures included maximal isometric grip strength (grip dynamometer) and wrist flexion (NORM dynamometer), muscle thickness (ultrasound), muscle activation (EMG) and voluntary activation (twitch-interpolation). RESULTS: A significant time main effect (p<0.001) was observed for isometric grip strength where both limbs increased from pre to post with no differences between groups (LF right: 42.4±12.2 to 46.6±11.1 kg; LF left: 38.6±10.5 to 42.0±10.4 kg; HF right: 47.6±13.6 to 50.5±13.5 kg; HF left: 43.9±11.9 to 47.6±13.3 kg). Muscle thickness significantly increased in both groups in the right limb only (R: 3.93±0.44 to 4.04±0.45 cm, p<0.05; L: 3.88±0.51 to 3.88±0.49 cm, p=0.897). EMG burst activity (normalized to the maximal M wave), maximal isometric wrist flexion torque, and voluntary activation of the forearm muscles did not change significantly from pre to post training in either arm (p=0.256 to 0.831). CONCLUSION: As predicted, both LF and HF training programs were effective for inducing cross-education of grip strength to the untrained limb; however, contrary to our hypothesis, both programs induced similar hypertrophy in the trained limb. These findings have implications for rehabilitation strategies after unilateral injury.