A repetition (rep) is the fundamental unit of work in weight training, representing one complete, controlled execution of an exercise. It begins at the starting position, moves through the full range of motion, and returns to the start, completing a cycle of muscle contraction and relaxation. This movement cycle allows trainees to systematically measure and track their physical efforts.
The Anatomy of a Repetition
A repetition is a distinct sequence of muscle actions divided into three primary phases, each corresponding to a different type of muscular contraction. The concentric phase is the lifting or shortening action, where the muscle overcomes the resistance, such as pushing a barbell up during a bench press or standing up during a squat.
The eccentric phase is the controlled lowering or lengthening of the muscle under tension, like slowly descending into the bottom of a squat or lowering the barbell to the chest. Eccentric contractions are capable of generating significantly more force than concentric contractions and cause greater mechanical stress on the muscle fibers, which is important for growth and strength development. The isometric phase is a static hold where the muscle is generating force without changing length, such as pausing briefly at the bottom of a squat or holding a plank.
The speed at which these phases are performed is known as tempo, often expressed as a four-digit code representing the time in seconds for each phase. Controlling the tempo, particularly slowing down the eccentric phase, increases the time under tension (TUT), a metric linked to muscle growth by maximizing mechanical tension on the muscle fibers. Varying the tempo modifies the training stimulus without necessarily changing the weight on the bar.
Repetitions in Context: Sets and Volume
Repetitions are grouped into a set, a sequence of repetitions performed consecutively before a rest period. For example, performing 10 squats constitutes one set of 10 repetitions. The total number of repetitions and sets performed defines the overall training volume, a primary driver of adaptation.
Training volume is often calculated by multiplying the total repetitions by the load used, providing a metric that integrates effort and quantity. Intensity is monitored using self-assessment tools.
Rate of Perceived Exertion (RPE) uses a 1-to-10 scale to subjectively rate the difficulty of a set, with 10 being maximum effort. A more specific measure is Reps In Reserve (RIR), which estimates how many more repetitions could have been performed before reaching muscle failure. For instance, an RIR of 2 means the trainee stopped the set two repetitions short of failure.
Matching Rep Ranges to Training Goals
The repetition range is systematically manipulated to target specific physiological adaptations. Lifting in the low-repetition range (1 to 5 reps per set) focuses on maximizing strength gains. This range requires a high percentage of maximum lifting capacity (85% to 100% of 1RM), which enhances the nervous system’s ability to recruit motor units.
A moderate repetition range, generally defined as 6 to 12 repetitions per set, is considered optimal for hypertrophy, or muscle growth. This range uses a moderate load, usually between 65% and 80% of 1RM, and maximizes the metabolic stress and time under tension necessary to stimulate muscle fiber repair and growth. The high-repetition range involves performing 15 or more repetitions per set with lighter loads.
Training with high repetitions focuses on improving muscular endurance and fatigue resistance. The continuous effort improves the muscle’s ability to sustain contractions and clear metabolic byproducts. These ranges are guidelines, and some muscle growth can occur outside the traditional hypertrophy zone if the set is taken close to muscle failure.