Training specificity is considered important for strength training, although the functional and underpinning physiological adaptations to different types of training, including brief explosive contractions, are poorly understood. This study compared the effects of 12-wks of explosive-contraction (ECT, n=13) vs. sustained-contraction (SCT, n=16) strength training vs. control (CON, n=14) on the functional, neural, hypertrophic, and intrinsic contractile characteristics of healthy young men. Training involved 40 isometric repetitions (x3/wk): contracting as fast and hard as possible for ~1 s (ECT); or gradually increasing to 75% of maximum voluntary torque (MVT) before holding for 3 s (SCT). Torque and EMG during maximum and explosive contractions, torque during evoked octet contractions, and total quadriceps muscle volume (QUADSVOL) were quantified pre- and post-training. MVT increased more after SCT than EST (23 vs. 17%; effect size [ES]=0.69), with similar increases in neural drive, but greater QUADSVOL changes after SCT (8.1 vs. 2.6%; ES=0.74). ECT improved explosive torque at all time points (17-34%; 0.54≤ES≤0.76) due to increased neural drive (17-28%), whereas only late-phase explosive torque (150 ms, +12%; ES=1.48) and corresponding neural drive (18%) increased after SCT. Changes in evoked torque indicated slowing of the contractile properties of the muscle-tendon unit after both training interventions. These results showed training-specific functional changes that appeared to be due to distinct neural and hypertrophic adaptations. ECT produced a wider range of functional adaptations than SCT, and given the lesser demands of ECT this type of training provides a highly efficient means of increasing function.
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