Time Under tension (TUT) which was coined by a strength coach named Charles Poliquin indicated that the amount of time a muscel is "under tension" or (contracted against resistance) is the best way to stimulate muscel growth. How do you count TUT? During reps. Not by the amount of time you spend on one body part. For example: you perfrom barbell curls with a count of 4 seconds up, 2 second pause at top, and 5 seconds down. That looks like this 4-2-4 or 10 seconds per rep. If you perform 8 repitions at that speed, your biceps will be under resistive tension for 80 seconds (or 1 min. 20 sec. per set)