Mixed
In trained individuals, resistance training to momentary failure produces significant strength increases regardless of repetition duration (from 2s:4s to 30s:30s:30s), provided load and time-under-load are matched.
If you are already trained, you do not need to slow down your reps to get stronger. Whether you lift at a normal speed (2s concentric, 4s eccentric) or extremely slowly (10s or 30s phases), you will gain the same amount of strength as long as you lift a load that makes you fail between 7-10 reps (for normal speed) or 3-5 reps (for slow speed). Focus on reaching failure, not on how fast you move the weight. This allows you to choose a speed that feels best for your joints or schedule.
Analyses revealed significant increases in strength for all exercises but no between-group differences... Repetition duration does not affect the increases in strength in trained participants where exercise is performed to momentary failure.
Why this rating
Randomized controlled trial with matched load/TUL, but lacks a non-training control and uses predictive 1RM rather than true 1RM.
Source
Neither repetition duration nor number of muscle actions affect strength increases, body composition, muscle size, or fasted blood glucose in trained males and females
Luke Carlson et al. · Applied Physiology Nutrition and Metabolism · 2018
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