Muhammad Ali reportedly abstained for six weeks before a fight. Coaches have been passing the rule down for a century, and athletes repeat it to each other in changing rooms as settled fact. It even has a folk mechanism: aggression, testosterone, "conserved energy".
A systematic review of nine studies says something else.
What the review found
The present evidence suggests that sexual activity the day before competition does not exert any negative impact on performance, even though high-quality, randomized controlled studies are urgently needed.
That is the sentence from the conclusion[1]. Its second half is worth as much attention as its first, because the authors state plainly that the design of the available studies is not strong and probably does not reflect real-life situations.
The one exception, up close
The review carries a caveat that has taken on a life of its own online: that a negative effect occurs when less than two hours pass between intercourse and the test.
That caveat comes from a single study. Boone and Gilmore, 1995, eleven sedentary men — not athletes[2].
What it actually found:
- Maximal aerobic power, oxygen pulse and double product — unaffected.
- The only significant differences were in heart rate at 5 and 10 minutes of the recovery phase in the test run about two hours after intercourse.
- In the test performed later the same day, the differences were gone.
So where does the belief come from
Probably from two things at once. First, "the night before" cannot be separated from what people do around it: a later bedtime, alcohol, less sleep. Those are variables with well-documented effects on performance, and none of them is sex.
Second, pre-competition rituals work whether or not they have a mechanism. An athlete who believes abstinence strengthens him gets predictability and a sense of control, and those are worth more than most supplements.
There is no reason to take such a ritual away from anybody. There is a reason not to sell it as a research finding, because the research says something more modest: the day before makes no difference, and everything beyond that was measured on eleven men off the sofa.