Does testosterone supplementation increase muscle size and strength in men?

From: NEJM

Journal rating:
rating: 100%
Study Quality:
rating: 85%

Overall Reliability

Article Quality:
rating: 65%
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  • 43 healthy men


  • Participants were randomly assigned to one of four groups: placebo with no exercise, testosterone with no exercise, placebo plus exercise, and testosterone plus exercise.
  • The men received injections of 600 mg of testosterone enanthate or placebo weekly for 10 weeks.
  • The men in the exercise groups performed standardised weight-lifting exercises three times weekly.
  • Before and after the treatment period, fat-free mass was determined by underwater weighing, muscle size was measured by magnetic resonance imaging, and the strength of the arms and legs was assessed by bench-press and squatting exercises, respectively.


  • Among the men in the no-exercise groups, those given testosterone had greater increases than those given placebo in muscle size in their arms (mean change in triceps area, 424 vs. -81mm) and legs (change in quadriceps area, 607 vs. -131mm) and greater increases in strength in the bench-press (9 vs. -1kg) and squatting exercises (16 vs. 3 kg).
  • The men assigned to testosterone and exercise had greater increases in fat-free mass (6.1kg) and muscle size (triceps area, 501mm2; quadriceps area, 1174mm2) than those assigned to either no-exercise group, and greater increases in muscle strength (bench-press strength, 22kg; squatting- exercise capacity, 38 kg) than either no-exercise group.
  • Neither mood nor behaviour was altered in any group.


  • Yes (with confidence); especially when combined with strength training.


Editors Notes

  • The training consisted of a cycle of weight lifting at heavy intensity (90 percent of the maximal weight the man lifted for one repetition before the start of training), light intensity (70 percent of the pretraining one- repetition maximal weight), and medium intensity (80 percent of this maximal weight) on three nonconsecutive days each week. Regardless of the actual weights lifted, the training was held constant at four sets with six repetitions per set (a set is the number of complete repetitions of an exercise followed by rest).
  • Because previous research had demonstrated increases in strength of approximately 7 percent for the bench-press exercise and 12 percent for the squatting exercise after four to five weeks of training, the weights were increased correspondingly during the final five weeks of training in relation to the initial intensity. The number of sets was also increased from four to five, but the number of repetitions per set remained constant.