Sperm are said to be strong when they are able to move or their motility is high. Normal sperm count is 40 millions per ml and 2-3 ml ejaculate is normal. At least 60% sperms should be motile and out of these motile sperms 20%-30% should be fast moving. You can improve the motility of the sperms by eating good diets rich in vitamin E or taking vitamin E supplements.