2989. The time at which exercise is most proper, depends on such a variety of concurrent circumstances, that it does not admit of being regulated by any general rules, and must therefore be collected from the observations made on the effects of air, food, drink, &c.
2990. With respect to the duration of exercise, there are other particulars, relative to a greater or less degree of fatigue attending the different species and utility of it in certain states of the mind and body, which must determine this consideration as well as the preceding.
2991. That exercise is to be preferred which, with a view to brace and strengthen the body, we are most accustomed to, as any unusual one may be attended with a contrary effect.
2992. Exercise should be begun and finished gradually, never abruptly.
2993. Exercise in the open air has many advantages over that used within doors.