What is hypertrophy?
Hypertrophy is the enlargement of existing muscle fibers. It is triggered primarily by mechanical tension during resistance training and carried out in the hours afterward by muscle protein synthesis.
Mechanical tension as the primary stimulus
The literature discusses three mechanisms that trigger hypertrophy: mechanical tension, metabolic stress, and muscle microtrauma (Schoenfeld, 2010). Mechanical tension is now considered the primary driver — metabolic stress and microtrauma play supporting roles, but they aren't what makes or breaks growth.
Myofibrillar vs. sarcoplasmic
Myofibrillar hypertrophy refers to an increase in the contractile elements of a muscle fiber. Sarcoplasmic hypertrophy describes growth in the non-contractile volume — fluid, enzymes, and glycogen. Both forms have been demonstrated in controlled training studies (Haun et al., 2019).
What hypertrophy requires
Three basic conditions have to be in place: enough weekly training volume, a steady increase in demand through progressive overload, and an energy intake that at least covers maintenance. If any one of these is missing, muscle growth slows down or stalls entirely.
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- Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. J Strength Cond Res, 24(10). PubMed
- Schoenfeld, B. J., & Grgic, J. (2020). Effects of range of motion on muscle development during resistance training interventions: A systematic review. SAGE Open Med, 8. PubMed
- Haun, C. T., et al. (2019). A Critical Evaluation of the Biological Construct Skeletal Muscle Hypertrophy. Front Physiol, 10. PubMed
- Damas, F., et al. (2016). The development of skeletal muscle hypertrophy through resistance training. Sports Medicine, 48(4). PubMed