Does Muscle Hypertrophy Relate To Resistance Training-Induced Changes In Myofibrillar Protein Synthesis In Women?

Abstract

Resistance exercise (RE) elevates skeletal muscle myofibrillar protein synthesis (MyoPS) for up to 48h, which can be measured under ‘free-living’ conditions using deuterium oxide (D2O). The accumulation of repeated bouts of RE (resistance training—RT) results in skeletal muscle hypertrophy, which in men has been reported to correlate with post-RE ‘free-living’ MyoPS only in the trained state. However, the impact of training status on acute responses to RE and their relationship to hypertrophic adaptations has yet to be investigated in women. PURPOSE: The present study examined the MyoPS response over 48h of recovery from an acute bout of RE in the untrained (UT) and trained (T) state to determine its association with hypertrophic adaptations in women. METHODS: Ten recreationally active young women (23±5 yr, 62.3±12.0 kg, 23.7±7.4 % body fat; mean±SD) underwent ~8 wk of supervised whole-body RT (4 x 10 repetitions, 75% 1 repetition maximum (1RM), 3x/wk). Whole-body fat free mass (FFM; BODPOD), vastus lateralis muscle thickness (MT; B-mode ultrasound) and 1RM for each completed exercise were measured in the UT and T state to quantify training responses. MyoPS was measured during the mid-follicular phase (day 3-9 of the menstrual cycle) at rest pre-training and for 48h following the first and final bout of RE using orally administered D2O. Muscle biopsies were obtained at pre-RE (0h), 24h and 48h post-RE to determine MyoPS in both the UT and T state. RESULTS: Following RT, there was a ~3.4% increase in FFM (49.3±6.4 vs. 51.0±6.9 kg; P < 0.001) and ~8.8% increase in MT (2.31±0.39 vs. 2.50±0.38 cm; P < 0.05). Representative 1RM strength increased for bench press and leg press exercise (28.5±5.8 kg vs. 38.7±9.8 kg and 151.6±63.5 vs. 259.3±92.7 kg, respectively; P < 0.01). Forthcoming analysis will determine if: i) training alters the post-exercise MyoPS response, and; ii) whether muscle hypertrophy correlates with acute MyoPS in the UT and/or T state. CONCLUSIONS: Women responded favourably to ~8 wk of RT with significant gains in FFM, MT and 1RM strength. Ongoing analysis will provide insight into the potential relationship between acute muscle protein synthesis and training-induced hypertrophy in the understudied female population. Supported by the Natural Sciences and Engineering Research Council of Canada.