The objective of Ibis work is to study the effects of aerobic and anaerobic physical training upon the maximum amplitude of Hoffman's reflex (Hmáx) and the direct motor response (Máx) and upon the reason Hmáx/Mmáx, parameters that were evaluated with electrophysiological routine technique. For that purpose, the work was developed with sedentary female people with an average age of 19.4+1.5 years, which divided into two groups were training for two months on a rolling platform (aerobic) and strength machine (anaerobic). During the aerobic training Hmáx increased in 72.7% (p 0.0001) and Hmáx/Mmáx was modified from 36.9 to 71.1% (p 0.0001). During the anaerobic training Hmáx decreased in 76.9% (p= 0.0002) and Hmáx/Mmáx was modified from 36.3 to 8.7% (p 0.0001). Mmáx didn't suffer modifications. ln a conclusion we can say that the central nervous system, at the spine level has enough plasticity to adapt to different kinds of physical training and that the evaluation of Hoffman's reflex could be utilized to find athletically talented people and to follow the temporal way of the neuromuscular adaptation in athletes from different sport areas.El objetivo del trabajo fue estudiar los efectos del entrenamiento físico aeróbico y anaeróbico sobre la amplitud máxima del reflejo de Hoffmann (Hmáx), la respuesta motora directa (Mmáx) y sobre la razón Hmáx/Mmáx, parámetros que fueron evaluados con técnica electrofisiológica de rutina. Para ello se trabajó con sujetos sedentarios de sexo femenino de edad promedio de 19.4 (1.5 años, los que divididos en dos grupos entrenaron durante dos meses en plataforma rodante (aeróbico) y máquina de fuerza (anaeróbico). Con el entrenamiento aeróbico Hmáx aumentó en 72.7 % (p