There are many physical effects of overtraining and overexercising including fatigue, mood issues, anxiety, decreased immunity and fat storage. When we overexercise, our cortisol levels elevate and this can cause many undesirable effects!The Side Effects of Overexercising and Overtraining - 013 19:46 There are many physical effects of overtraining and overexercising including fatigue, mood issues, anxiety, decreased immunity and fat storage. When we overexercise, our cortisol levels elevate and this can cause many undesirable effects!