This book began with an experimental study of the effect of perinatal malnutrition on locomotor parameters in adult female rats during the oestrous cycle. The ovarian cycle of the rats was determined by means of a vaginal smear between the 60th and 90th day of age. The locomotor activity of adult Wistar females was analysed from day 60 to day 65 during the fertile and non-fertile phases of the ovarian cycle. We observed a reduction in the weight and physical characteristics of the malnourished group compared with the fed group. In the next stage, in humans developed at the Université de Technologie de Compiègne (UTC) - France, we examine the effects of possible variations in the menstrual cycle on strength, voluntary activation and reflex excitability in the sural triceps muscle group in young women. All the parameters analysed: muscle twitch kinetics, amplitudes and latencies Tmax, Tmin, Hmax, Mmax, were not affected by the phases of the menstrual cycle. The neuromuscular efficiency for Tmax and Mmax were not modified during the phases of the menstrual cycle.