Reductions in testosterone are not indicative of exercise performance decrement in male endurance athletes.

Our findings indicate that the participants of an 18 week intensive endurance exercise training program experienced significant (p < 0.001) reductions in resting testosterone (-25 to -45% decrease from pre-training), with some reaching the clinical criteria for androgen deficiency during the training regimen. Nonetheless, none of the participants displayed any running performance decrement, in fact, the opposite occurred (+18.6% improvement; p < 0.05). These preliminary findings suggest acute decreases in testosterone in and of itself may not be entirely indicative of a compromised exercise performance potential although elements of reproductive and bone health may still be compromised.