Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy

Haun, C.; Vann, C.; Osburn, S.; Mumford, P.; Roberson, P.; Romero, M.; Fox, C.; Johnson, C.; Parry, H.; Kavazis, A.; Moon, J.; Badsia, V.; Mwashote, B.; Ibeanusi, V.; Young, K.; Roberts, M.

doi:10.1101/596049

bioRxiv · 10.1101/596049

Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy

Haun, C.·Vann, C.·Osburn, S.·Mumford, P.·Roberson, P.·Romero, M.·Fox, C.·Johnson, C.·Parry, H.·Kavazis, A.·Moon, J.·Badsia, V.·Mwashote, B.·Ibeanusi, V.·Young, K.·Roberts, M.

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Abstract

Cellular adaptations that occur during skeletal muscle hypertrophy in response to high-volume resistance training are not well-characterized. Therefore, we sought to explore how actin, myosin, sarcoplasmic protein, mitochondrial, and glycogen concentrations were altered in individuals that exhibited mean skeletal muscle fiber cross-sectional area (fCSA) hypertrophy following 6 weeks of high-volume resistance training. Thirty-one previously resistance-trained, college-aged males (mean {+/-} standard deviation: 21{+/-}2 years, 5{+/-}3 training years) had vastus lateralis (VL) muscle biopsies obtained prior to training (PRE), at week 3 (W3), and at week 6 (W6). Muscle tissue from 15 subjects exhibiting PRE to W6 VL mean fCSA increases ranging from 320-1600 m2 was further interrogated using various biochemical and histological assays as well as proteomic analysis. Seven of these individuals donated a VL biopsy after refraining from training 8 days following the last training session (W7) to determine how deloading affected biomarkers. The 15 fCSA hypertrophic responders experienced a +23% increase in mean fCSA from PRE to W6 (p<0.001) and, while muscle glycogen concentrations remained unaltered, citrate synthase activity levels decreased by 24% (p<0.001) suggesting mitochondrial volume decreased. Interestingly, both myosin and actin concentrations decreased ~30% from PRE to W6 (p<0.05). Phalloidin-actin staining similarly revealed actin concentrations per fiber decreased from PRE to W6. Proteomic analysis of the sarcoplasmic fraction from PRE to W6 indicated 40 proteins were up-regulated (p<0.05), KEGG analysis indicated that the glycolysis/gluconeogenesis pathway was upregulated (FDR sig. <0.001), and DAVID indicated that the following functionally-annotated pathways were upregulated (FDR value <0.05): a) glycolysis (8 proteins), b) acetylation (23 proteins), c) gluconeogenesis (5 proteins) and d) cytoplasm (20 proteins). At W7, sarcoplasmic protein concentrations remained higher than PRE (+66%, p<0.05), and both actin and myosin concentrations remained lower than PRE (~-50%, p<0.05). These data suggest that short-term high-volume resistance training may: a) reduce muscle fiber actin and myosin protein concentrations in spite of increasing fCSA, and b) promote sarcoplasmic expansion coincident with a coordinated up-regulation of sarcoplasmic proteins involved in glycolysis and other metabolic processes related to ATP generation. Interestingly, these effects seem to persist up to 8 days following training.

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Haun, C., Vann, C., Osburn, S., Mumford, P., Roberson, P., Romero, M., Fox, C., Johnson, C., Parry, H., Kavazis, A., Moon, J., Badsia, V., Mwashote, B., Ibeanusi, V., Young, K., Roberts, M.. 2019-04-02. Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy. https://doi.org/10.1101/596049

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