Time under tension is one of the most commonly discussed concepts in the science of hypertrophy, and yet it remains poorly understood.

Technically, time under tension should be a good measure of the dosage of the hypertrophic stimulus provided by a workout. Unfortunately, researchers have as yet been unable to make connect time under tension with the amount of muscle growth that results, under all circumstances.

Indeed, there are many conflicting reports in the literature, some of which suggest that time under tension is closely linked to the amount of muscle growth that occurs after strength training, while others suggest it is not.

Research has reported a dose-response relationship between training volume and hypertrophy, but no such relationship between lifting (concentric phase) tempo and muscle growth, despite tempo being a very effective way for increasing the duration of time spent performing a set of a strength training exercise.

In my view, this confusion arises because we have traditionally not defined which muscle fibers are being subjected to tension, nor have we defined the level of tension that must be experienced. Indeed, when all muscle fibers are activated, and the tension is high, time under tension can be linked to the hypertrophy that results from training.

If we fix these problems with our definition of time under tension, I believe that these inconsistencies mostly disappear.

Let me explain.