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Repetitions, Strength, and Endurance

Earlier this week, I read a social media post from a fitness personality that warrants a response. The message, and I paraphrase, was as follows:
Heavy weights with fewer reps builds strength.
Lighter weights and more reps builds endurance.
This particular fitness “celebrity” is not to blame. To be clear, this message (and its kin, heavy weights build large muscles and lighter weights tone muscles) is likely the single most pervasive myth in exercise. It is so frequently repeated that it is almost woven into the fabric of fitness folklore. But as the adage goes, no matter how often a myth is repeated, and no matter how many people believe it, it is still a myth. And unfortunately, this particular mythical axiom has sent well-intended exercisers in pursuit of a strength training dichotomy that does not exist. A close examination of the scientific research reveals that muscle strength and muscle endurance are not separate trainable entities, but instead, are inextricably linked. When you improve your muscle strength (your ability to lift a heavier weight for fewer repetitions) your muscle endurance (your ability to lift a lighter weight for more repetitions) improves in almost a linear manner; and vice versa.
In a 2004 review published in the Journal of Exercise Physiology, researchers Smith and Bruce-Low concluded that, “The weight of scientific evidence, therefore, does not support the idea that different numbers of repetitions have differential effects on muscular strength and endurance.” In a 2004 review published in the Journal of Exercise Physiology, researchers Carpinelli, Otto, and Winett concluded that“All these studies strongly suggest that within a reasonable range of repetitions, approximately 3 to 20, there does not appear to be a specific number of repetitions (e.g., 4-6, 7-10, 12-15, etc.) that will elicit more favorable gains in muscular strength, power, or hypertrophy.” In a 2008 review published in the Journal of Exercise Science and Fitness, Carpinelli corroborated this finding stating, “The preponderance of studies strongly suggest that effective resistance training simply requires the selection of a desired range of repetitions, which is based on a personal preference rather than a specific goal, and a progression of the resistance to stay within the desired range of repetitions.” 
Stated otherwise, it does not matter how many reps you perform, as long as you reach momentary muscle failure.  It does not matter if “failure” is reached on your 5th rep or your 19th rep. 
A few practical applications and corollaries of this principle:
  • A marathon runner need not focus on muscle endurance by exclusively performing a higher number of reps. She may perform 6 reps or 15 reps and her results will be the same.
  • A football player need not focus on muscle strength by performing 3-5 repetitions with an extremely heavy weight. He may perform 3-5 repetitions but he will produce the same results with 25 repetitions.
  • Strength training as a whole becomes much less complicated because the number of reps and the amount of weight used is of much less importance than previously assumed.
  • The focus of each exercise should be on reaching the point of momentary muscle fatigue, not a predetermined number of repetitions.
  • One exception/clarification: If you are training to perform a 1-rep maximum (you’re trying to bench press as much as possible for 1 rep, for example); then you SHOULD perform sets with more weight and less reps but NOT because this makes you stronger; instead, using heavier weights for fewer reps refines or improves your skill (lifting a heavy weight one time is a skill).

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