FUNCTIONAL MRI OF MUSCLE USE AND MUSCLE TRAUMA WITH RESISTANCE EXERCISE 673

Abstract

This study employed functional magnetic resonance imaging (MRI) to compare muscle use and subsequent muscle trauma evoked by conventional free weight exercise versus exercise performed with minimal eccentric loading. Two groups of 10 non-weight-trained young adults matched for age, gender, height and weight performed 5 sets of 10 seated overhead presses at loads chosen to elicit failure by the final set, on either free weights (FW) or the Nordic Flex Gold system (NFG), which emphasizes isokinetic, concentric actions. Standard T2-weighted axial spin-echo MR images were acquired at 1.5 cm intervals along the length of the brachial region before, immediately after, and 24 hours after exercise. Fractional triceps brachii muscle recruitment, as indicated by net percentage of muscle cross sectional area exhibiting acute T2 elevation, was identical for the two exercise groups (FW: 67.3 ± 1.8%, NFG: 68.0 ± 2.4%; means ± SE, n = 10). This T2 increase evoked acutely by muscle use is known to abate rapidly (T1/2 < 30 min), but T2 then gradually increases over several days, purportedly reflecting muscle trauma. 24 hr post-exercise, net T2 elevation was visible in substantially more muscle area in the FW (12.3 ± 2.5%) than in the NFG group (0.8± 2.2%). These results suggest that elimination of most of the eccentric loading from an exercise does not significantly compromise muscle use but may substantially lessen the development of muscle trauma that has also been previously demonstrated by biopsy studies even in moderate-load eccentric exercise.