Ageing is a complex, multifactorial phenomenon. The existence of biolo
gic rhythms as well as the study of their modifications or their alter
ations in the aged are useful and pertinent to understand the biologic
age. These modifications, if any, may be interpreted as a change in t
he adaptability of aged subjects to environmental factors. The loss or
decrease of adaptation capacity with ageing is worth quantifying. Thi
s paper rounds up the question.