Twenty-two males with at least 6 months of training experience and the ability to bench at least bodyweight were recruited. After establishing 1RM, the subjects performed two protocols on separate days:

1. Three sets of 12 reps at 60% of 1RM on Smith machine bench press, 3 minutes rest between sets. Rep duration was 3 seconds: 1.5 seconds eccentric and 1.5 seconds concentric (lowering and lifting phase of each rep).
2. Three sets of 6 reps at 60% of 1RM on Smith machine bench press, 3 minutes rest between sets. Rep duration was 6 seconds: 3 seconds eccentric and 3 seconds concentric.

Total time under tension per set for each trial was 36 seconds.

EMG of the anterior deltoid, pec major, and triceps were recorded. Lactate values were assessed prior to exercise, 1 minute after each set, and every 3 minutes for 12 minutes following the final set.

• EMG was higher during the protocol with shorter rep duration.
• EMG was higher in all the muscles during the shorter rep duration protocol.
• Lactate values were higher during that protocol as well after each set. They remained elevated for longer post workout too.

The increased muscle activity during the shorter rep duration, along with the higher lactate values, show a clear winner in the time under tension battle. With TUT equal (36 seconds), doing more reps seems to be the winner via increased activation and greater lactate levels, indicating greater metabolic stress.

So instead of slowing down your reps in a workout to increase time under tension, simply add a few more reps with a faster rep speed.

1. Lacerda LT et al. Variations in repetition duration and repetition numbers influence muscular activation and blood lactate response in protocols equalized by time under tension. J Strength Cond Res. 2016 Jan;30(1):251-8. PubMed.