I. Mujika et S. Padilla, Detraining: Loss of training-induced physiological and performance adaptations. Part I Short term insufficient training stimulus, SPORT MED, 30(2), 2000, pp. 79-87
Detraining is the partial or complete loss of training-induced adaptations,
in response to an insufficient training stimulus. Detraining characteristi
cs may be different depending on the duration of training cessation or insu
fficient training. Short term detraining (less than 4 weeks of insufficient
training stimulus) is analysed in part I of this review, whereas part II w
ill deal with long term detraining (more than 4 weeks of insufficient train
ing stimulus). Short term cardiorespiratory detraining is characterised in
highly trained athletes by a rapid decline in maximal oxygen uptake (V over
dot(2max)) and blood volume. Exercise heart rate increases insufficiently
to counterbalance the decreased stroke volume, and maximal cardiac output i
s thus reduced. Ventilatory efficiency and endurance performance are also i
mpaired. These changes are more moderate in recently trained individuals. F
rom a metabolic viewpoint, short term inactivity implies an increased relia
nce on carbohydrate metabolism during exercise, as shown by a higher exerci
se respiratory exchange ratio, and lowered lipase activity, GLUT-4 content,
glycogen level and lactate threshold. At the muscle level, capillary densi
ty and oxidative enzyme activities are reduced. Training-induced changes in
fibre cross-sectional area are reversed, but strength performance declines
are limited. Hormonal changes include a reduced insulin sensitivity, a pos
sible increase in testosterone and growth hormone levels in strength athlet
es, and a reversal of short term training-induced adaptations in fluid-elec
trolyte regulating hormones.