THE ROLE OF METABOLITES IN STRENGTH TRAINING .2. SHORT VERSUS LONG ISOMETRIC CONTRACTIONS

The role of intramuscular metabolite changes in the adaptations follow ing isometric strength training was examined by comparing the effect o f short, intermittent contractions (IC) and longer, continuous (CC) co ntractions. In a parallel study, the changes in phosphate metabolites and pH were examined during the two protocols using whole-body nuclear magnetic resonance spectroscopy (NMRS). Seven subjects trained three time per week for 14 weeks. The right leg was trained using four sets of ten contractions, each lasting 3 s with a 2-s rest period between e ach contraction and 2 min between each set. The left leg was trained u sing four 30-s contractions with a 1-min rest period between each. Bot h protocols involved isometric contractions at 70% of a maximum volunt ary isometric contraction (MVC). The MVC, length:tension and force:vel ocity relationships and cross-sectional area (CSA) of each leg were me asured before and after training. The increase in isometric strength w as significantly greater (P = 0.041) for the CC leg (median 54.7%; P = 0.022) than for IC (31.5%; P = 0.022). There were no significant diff erences between the two protocols for changes in the length:tension or force:velocity relationships. There were significant increases in mus cle CSA for the CC leg only. NMRS demonstrated that the changes in pho sphate metabolites and pH were greater for the CC protocol. These find ings suggest that factors related to the greater metabolite changes du ring CC training results in greater increases in isometric strength an d muscle CSA.