Mechanisms Regulating Resistance Training Mediated Hypertrophy in Human Skeletal Muscle

It is well established that resistance training induces muscle hypertrophy, although the mechanisms and influence of biological sex are unclear. The extent of post-exercise myofibrillar protein synthesis (MyoPS), satellite cells (SC) and dietary amino acids to promote muscle hypertrophy have generally been investigated independently in controlled lab based settings and predominately in males; therefore this dissertation systematically examined how MyoPS, SC and dietary amino acids are influenced by acute resistance exercise, resistance training and sex in a single study. Ten young men (~23.0 y) and women (~23.0 y) completed a single bout of resistance exercise before and after 8-weeks of whole-body resistance training with muscle biopsies of the vastus lateralis taken immediately prior to, 24-, and 48-hours after each bout. Study 1 displayed, irrespective of acute exercise or training status, males had greater rates of integrated MyoPS over 48 h, and regardless of sex, post-exercise MyoPS was positively related to muscle hypertrophy only in the trained state. In Study two, irrespective of sex and acute resistance exercise, resistance training induced SC accretion in only type II fibers, and the change in pre – post type II SC content was related to type II muscle fiber hypertrophy. In Study 3, the incorporation of post-exercise dietary amino acids into contractile myofibrillar and non-contractile sarcoplasmic proteins was reduced in the trained state, regardless of sex, suggesting less reliance of dietary amino acids to sustain post-exercise MyoPS in the in trained state. We also observed that, irrespective of sex and acute resistance exercise, resistance training promoted greater mechanistic target of rapamycin (mTOR) proximity to the cell periphery and capillaries and concomitant colocalization with the lysosome suggesting an increased efficiency to sequester dietary amino acids and activate MyoPS in the trained state. Males had greater post-exercise mTOR colocalization with the lysosome, which may in part, explain the greater rates of MyoPS. Based on these studies, it appears that resistance exercise in the trained state is reflective of hypertrophic adaptations, through MyoPS and SC content, and may result in less reliance of dietary amino acids. These changes may be underpinned by altered intracellular mTOR redistribution with training.

Department dc:contributor.department

Kinesiology and Physical Education

Year dc:date.issued

2021

Author dc:creator

• Sawan, Sidney Abou Sawan

Advisor dc:contributor.advisor

• Moore, Daniel R

• amino acids
• dietary protein
• muscle protein synthesis
• resistance exercise
• skeletal muscle
• stable isotopes

Handle dc:identifier.uri

http://hdl.handle.net/1807/111419

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/111419