The Henneman Size Principle

Dr. Henneman’s discovery of the “size principle” in 1957 explains the order in which motor units are recruited. This principle is widely discussed in exercise science classrooms. Among strength and conditioning experts, focus is given to hypertrophy, force production, and the rate of force production. However, regardless of the desired adaptation, high threshold motor unit recruitment is crucial. The physiological response of motor unit recruitment is essential for skeletal muscle hypertrophy, maximum force production, and high rates of force production. But, just because high threshold motor units are recruited isn’t the be-all-end-all for gaining muscle. This video will explain a bit more and then after, I’ll discuss some extra points not fully discussed in the video (because I didn’t want a crazy long video).

It is important to understand that activating high-threshold motor units through explosive training does not necessarily lead to muscle gain. When training for power or explosiveness, it is common to stop at a power or velocity cut-off. To ensure that the training objective of explosiveness is met, it is recommended to end a set when there is a 20% reduction in velocity. This approach was recommended by Strength Coach Dan Baker from Australia and it’s the approach we take at Ascend Perform.

To achieve hypertrophy, it is essential to increase the time under tension and the fatigue of the muscle leads to slower repetitions. This increased tension prompts an increase in myosin and actin cross-bridging, which activates the mechano–receptor, as mentioned in the video.


As expressed in the video, many individuals fail to consume adequate protein for muscular development. Based on the extensive guidance from trusted experts on this matter, the general recommended protein intake should amount to approximately 1 gram per pound of lean body weight. Furthermore, the quality of protein is crucial in ensuring sufficient levels of leucine, the amino acid responsible for protein synthesis. At Ascend Perform, we prefer taking essential amino acids during workouts to lower the catabolic affects of training. Post training we recommend Designs For Sport whey protein hydrolysate.


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