In the bodybuilding world, it's not uncommon to see individuals train with a constant tension technique. Typically, this is achieved by avoiding locking out the joints in an exercise. For instance, in a constant tension squat, you avoid locking out the knees, thereby maintaining constant tension on the quadriceps.

Two studies by Tanimoto et al. assessed how keeping constant tension on a muscle compares to allowing the muscle to briefly rest between repetitions. Both these studies found no difference between the two methods, suggested constant tension is no more effective than normal repetition execution.

Three other studies technically fit into the constant tension research. In these studies, a full range of motion was compared to a partial range of motion that maintained constant tension.

Two of these studies are very similar in design (Goto et al. and Pinto et al.). In these two studies, a partial range of motion that used only the midrange of motion of the exercise was compared to a full range of motion. Unfortunately, the two studies conflict, the study by Goto et al. found the partial range of motion to be superior to a full range of motion, whereas the study by Pinto et al. found the full range of motion to be superior to the partial range of motion.

So, these two studies cannot inform us of the effectiveness of a partial range of motion that applies constant tension via the midrange of motion.

However, the third study by Pedrosa et al. is quite interesting. They found that a partial range of motion performed at long muscle lengths produced greater muscle hypertrophy than a full range of motion. A partial range of motion at long muscle lengths is (a lot of the time) a constant tension. We've covered this study in more detail in a previous video on range of motion. Nevertheless, perhaps this study suggests that a constant tension could be superior for muscle growth if it is applied via a partial range of motion at long muscle lengths. Although, more research would undoubtedly be required before fully concluding this.

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References:
Goto et al. https://pubmed.ncbi.nlm.nih.gov/31034...
Pinto et al. https://pubmed.ncbi.nlm.nih.gov/22027...
Tanimoto et al. 1 https://pubmed.ncbi.nlm.nih.gov/18978...
Schoenfeld et al. rep range metaanalysis https://pubmed.ncbi.nlm.nih.gov/28834...
Lopez et al. rep range metaanalysis https://pubmed.ncbi.nlm.nih.gov/33433...
Schoenfeld et al. rep tempo metaanalysis https://pubmed.ncbi.nlm.nih.gov/25601...
Tanimoto et al. 2 https://pubmed.ncbi.nlm.nih.gov/16339...