Time Under Tension

Time under tension is the duration of muscular effort during a resistance exercise repetition or set. It is usually expressed in seconds and includes the time spent lifting, lowering, and holding the resistance. Recording it adds information that a repetition count alone cannot provide .¹

The duration of a repetition depends on its individual phases. The muscle may shorten while producing force, lengthen while resisting a load, or maintain a position during a pause. Adding the durations of these phases gives the repetition's time under tension. Repeating that movement accumulates time across the set, so the same number of repetitions can involve different durations of effort .¹

Time under tension describes duration, but does not fully describe the exercise stimulus. The load, movement range, and distribution of time between phases also matter. Two sets can have equal total time under tension yet produce different immediate muscular and metabolic responses when their repetition numbers and durations differ. A longer duration therefore does not, by itself, establish that a set is more effective .^1,2