Increasing muscle size offers several advantages for team-sport athletes. For example, strength and power potential are increased with larger muscle cross-sectional area, which can be transferred to performance qualities like sprinting, jumping and changing direction. Increased muscle mass can be useful for collision-sport athletes who benefit from the added armor and weight gain depending on positional requirements. Given that muscle growth is a key objective of many strength and conditioning programs, it would be useful for coaches to understand the training factors that have the largest influence on stimulating gains in muscle hypertrophy.
Schoenfeld (2010) describes 3 primary factors that elicit a hypertrophic response. Each of which ultimately increase the activation and proliferation of satellite cells that are responsible for protein synthesis (i.e., muscle accretion).
- Mechanical Tension – Greater resistance (i.e., weight on the bar) will create increased tension on muscle fibers. This mechanical stimulus (i.e., stretch and deformation of the muscle fiber) is transduced to a chemical stimulus that activates the AKT/mTOR pathway that ultimately increases protein synthesis. This is particularly enhanced from eccentric contractions.
- Muscle Damage – Repeated contractions against resistance results in microtrauma to myfibrils. This results in an inflammatory response which attracts neutrophils, macrophages and lymphocytes to clear cell debris and stimulate the release of pro-inflammatory myokines (e.g., IL-6) which subsequently stimulate protein synthetic response via satellite cell proliferation and differentiation.
- Metabolic Stress – Metabolic by-products from glycolysis accumulate during a bout of resistance training. Metabolites such as lactate, Pi, and H+ act as osmolytes within the muscle which increase fluid entry into the muscle cell causing cellular swelling. As the cell swells, the integrity of its structure is threatened (similar to filling a balloon up with water). However, instead of popping like a balloon, adaptive mechanisms result in increased protein synthesis to increase the size and strength of the cell structure.
To maximize hypertrophy, it is likely that a variety of intensities, rep ranges and volumes are required. However, general guidelines recommend that multiple sets in the 6-12 rep range with 60-90 seconds rest between sets are a great starting point for stimulating muscle growth. This will enable sufficient mechanical tension, create muscle damage and increase metabolic stress, all critical factors for inducing skeletal muscle hypertrophy.
Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. The Journal of Strength & Conditioning Research, 24(10), 2857-2872.