Acute caffeine intake increases muscle strength and endurance Original paper

In this meta-analysis of randomized controlled trials, supplementation with caffeine before resistance exercise increased upper-body and lower-body muscle strength and muscle endurance in young men.

The effect of acute supplementation with caffeine, compared with a placebo, on muscle strength (measured using one-repetition maximum; 1RM) and muscle endurance (measured using the maximum number of repetitions completed) during resistance training.

A total of 251 participants (average ages of 17–29; 82% men, 18% women).

A meta-analysis of 14 randomized controlled trials was performed. The dose of caffeine ranged from 2 to 11 mg per kilogram of body weight. The timing of supplementation was either 45 or 60 minutes before exercise. Muscle strength/endurance was measured for the upper body in 6 trials, for the lower body in 1 trial, and for both the upper and lower body in 7 trials.

In the trials that reported this information, the load lifted during the muscle endurance tests was low (<60% 1RM) in 2 trials, moderate (60%–85% 1RM) in 6 trials, and high (≥85% 1RM) in 3 trials.

Compared with a placebo, caffeine increased muscle strength and muscle endurance, both in upper-body and lower-body exercise tests.

In subgroup analyses, caffeine increased muscle strength in the trials with the following characteristics:

• Administered ≥6 mg/kg (but not trials that administered <6 mg/kg)
• Administered caffeine 45 minutes before exercise (but not trials that administered caffeine 60 minutes before exercise)
• Recruited men (but not trials that recruited women).

Also, caffeine increased muscle endurance in the trials that involved moderate or high loads (but not in the trials that used low loads) and in the trials that recruited men (but not in the trials that recruited women).

The methodological quality was rated good for 11 trials and excellent for 3 trials.