Exercise is a form of stress. Sun light is a form of stress also & differnt people can handle intense sun light better then others i.e., An albino is @ one end of spectrum & can handle very small amounts of stress from sun light & a black individual @ the other end of the spectrum & can handle a lot more stress from intense sun light & then there is everyone in between in regaeds to the amount of intense sun light they can handle.
There is also a wide range in regards to stress from exercise individuals can handle compared to others.
Anarobic exercise produces far more stress then arobic exercise
An individual only has x amount of recovery ability period & it is best to use wisely.
Off track below because Iam not sure if your doing anarobic exercise but I use the concept to judge my use limited supply of recovery ability
If an individual is doing weight training, then adds areobics & starts getting weaker they are most likely adding to much arobics
By keeping a journal one can tell if they are over training based on thier increase or decrease in strength levels
Of course one could also cut back on the anarobic exercise (weight training) so more recovery ability could be used for arobic exercise.