Reps for Muscle Hypertrophy
Your dedication to regular weight training may fall short without the use of proper program design principles. For example, you may be unknowingly sabotaging your fitness results by performing too few or too many reps. Combining proper repetition, loading and set ranges optimizes your time in the gym and ensures muscle building success.
Principle of Specificity
Muscles adapt specifically to imparted demands, as stated by the National Strength and Conditioning Association. A well designed weightlifting program manipulates training variables based on goal-specific guidelines. For example, repetitions performed dictate endurance, strength or hypertrophic outcomes. Because features of muscular function rely on various physiological pathways, you must target those pathways specifically for change to occur.
Muscle Fibers and Weight Training
Although muscle fibers slide against each other during all movement, the increased loading associated with weight training causes microscopic fiber tears. Loading-induced fiber damage heals during rest and results in increased fiber diameter and greater muscle mass. Therefore, reps for muscular hypertrophy must enable optimal fiber damage. Optimal fiber damage requires adequate loading in addition to repeated motion.
Repetitions for Hypertrophy
According to the American Council on Exercise, hypertrophy requires eight to 12 repetitions, while increased endurance requires 12 to 20 and strength enhancement calls for one to eight repetitions. Hoping for hypertrophy while performing 12 to 20 – or one to eight – sets usually garners unintended results.
Effect on Loading
Unfortunately, requirements for muscular hypertrophy move beyond advantageous rep ranges. In fact, optimal loading and goal-specific repetition guidelines influence each other. For example, loads of 70 to 80 percent of your maximal ability boost muscle fiber friction and subsequent hypertrophy, as stated by ACE. Hypertrophic adaptations decrease with loads lighter than 70 percent maximal ability – regardless of repetitions performed. As an easy rule, if your chosen load allows greater than 12 repetitions, it is likely too light to cause muscle growth.
Effect on Sets
Performing two to six sets increases training volume – a product of weight lifted, repetitions performed and number of sets. ACE lists high-intensity, high-volume exercise stress as the primary stimulus to muscle hypertrophy. Specified loads are considered high-intensity, and recommended sets and reps contribute further to high volume. ACE suggests resting 30 to 120 seconds between sets to allow maximal effort on all sets performed. In addition to hypertrophy, increased training volume produces larger amounts of fiber damage and subsequent post-exercise muscle soreness. Consult a doctor before starting a weightlifting program.
- “American Council on Exercise Personal Trainer Manual”; American Council on Exercise; 2003
- "Essentials of Strength Training and Conditioning"; National Strength and Conditioning Association; 2000
Melissa Ross began writing professionally in 2009, with work appearing in various online publications. She has been an American Council on Exercise certified personal trainer since 2006. Ross holds a Bachelor of Science in kinesiology from California Polytechnic State University, San Luis Obispo and a Master of Science in kinesiology from California State University, Fullerton.