The fantasy is that ejaculation comes from the testicles. Actually leaves you weakened. The fact is that nothing comes from the testicles. The sperm do their maturation outside the testicles. All the fluid that carries the sperm comes from the glands.
Sex is a great tranquilliser.
If you want to sleep well before a race, make love . . . I've done that before a race. I always run well. I think the real point is to continue your normal lifestyle. If you enjoy a lot of sex, go on doing it.