The response depends on the type of training activity performed in addition to its aims. If the session involves a fairly intensive or extensive workout, aimed for example at improving certain muscle qualities (such as strength or stamina), a reasonable recovery period is imperative to give the body time to build new structures (enzymes, mitochondria, muscle fibres, etc.). Furthermore, in the case of particularly exhausting sessions, it is required to replenish energy reserves.

MINIMUM RECOVERY TIMES
Each type of characteristic stimulated will require different recovery times but, in principle, for a subject undergoing training of normal intensity, a 24-hr interval is sufficient; on the other hand, beginners should not ideally train more than every other day for at least the first two to three months. In the case of workouts which are particularly stressful on the joints, muscles and tendons, it is certainly preferable, particularly for the elderly and less active, to insert at least one to two rest days between two successive workouts. In such cases, the body must also reinforce these structures in order to prevent them from being damaged.

MAXIMUM TIME BETWEEN SESSIONS
Conversely, too long a time between one session and the next would lead to the positive gains from the first session being completely negated. In fact, any improvements the body makes to stimulated muscles (increased strength, stamina and so on), are only retained if they are maintained on a regular basis, otherwise they are lost since the body no longer has a need for them. Of course, the maximum interval between two successive workouts depends on the type or quality of the sessions but, for the average person, an interval of four days can already be deemed to be excessive.

WEIGHT LOSS AND METABOLIC DISORDERS
It is a completely different matter for those who are overweight or who suffer from metabolic disorders such as diabetes: in these cases daily physical activity is almost an obligation. Where exercise for weight loss is concerned, it is important to note that the bodyfs hormones respond to increased activity by increasing appetite or the capacity to absorb food, thereby increasing calorie intake. The result is that, within the space of a few days, the body re-establishes a balance, compensating for extra calorie burn with a higher calorie intake. Therefore if exercise is not prescribed in combination with a calorie restricted diet, on training days the balance will be maintained. However, on rest days calorie intake will be higher than calorie burn because more food is being consumed. Rest days between sessions therefore lead to additional weight gain, despite regular exercise. In such cases, it is essential to perform a small amount of exercise every day which, amongst other considerations, should not be too intense if weight loss is the objective. Finally in the case of diabetes sufferers, exercise has a positive effect on hormone levels, although it is necessary to adapt the subjectfs medication in response to this change. The subject is better able to manage this situation if the exercise time, duration and intensity are always the same every day; on the other hand if active and inactive days are alternated, such as by changing the time or type of exercise, it may be difficult to regulate the intake of medication.