Stretching Increases IGF1, Protein Synthesis

Muscle growth in response to mechanical stimuli : a study looking at electrical stimulation, stretching and its effect on muscle growth. This was shared around the Discord channel, and it by itself is an interesting concept.

This was a 3 day experiment looking at muscle growth stimulated by either/both stretch and electrical stimulation in the extensor digitorum longus muscle of a rabbit.

>digitorum longus muscle

Wanna see my longus muscle, babe? ( ͡° ͜ʖ ͡°)

From the abstract itself, and my commentary:

Continuous electrical stimulation failed to change muscle protein turnover or growth.

Translation: Electrical stimulation of muscle itself doesn’t result in hypertrophy.

Static stretch caused significant adaptive growth, with increases in c-fos, c-jun, and insulin-like growth factor I (IGF-I; 12-fold) mRNA levels, and protein (19%), RNA (128%), and DNA (45%) contents. Both the fractional (138%) and total (191%) rates of protein synthesis increased with stretch, correlating with increased ribosomal capacities.

Important markers for muscle growth increasing due to stretching - IGF1 increasing 12x over baseline is significant, as is 191% increase in the rate of protein synthesis.

Combining stretch and electrical stimulation increased the mRNA concentration of IGF-I (40-fold). The adaptive growth was greater (35%), with massive increases in the nucleic acids (185 and 300%), ribosomal capacities (230%), and the rates of protein synthesis (345 and 450%).

Combined stretch and electrical stimulation increased IGF1 40x and protein synthesis 3-4x. Adaptive growth (+35%) refers to repair and growth of a muscle after being used.


Arnold was famous for posing between sets. Arnold believed that posing between sets allowed him to gain mastery over the muscles he was training and lengthen the individual muscles for more complete development. Lengthening the muscles, or stretching, is a parallel I see between the research and real life. As Arnold believed, combining stretching and contraction of the muscle seems to increase many of the important markers that support hypertrophy.

Unless you work out at home, I don’t think those in the gym would appreciate you posing in the mirror between sets. However, stretching between sets is unlikely to cause harm and if this research holds true in a real world setting (never a given) will support muscle growth.