“Although there is obviously a training stimulus beyond which any additional load or stimulus does not induce further desired adaptation, the control mechanisms for the adaptive process require regular periods of overload…..”

“However, an imbalance between training frequency and subsequent recovery may give rise to an accumulation of training stress that results in a suboptimal adaptation response in skeletal muscle, termed overtraining. Therefore, the frequency of overload is important in defining the training stimulus, with adequate recovery required to ensure optimal muscle adaptation.”

V.Coffey, et al
Effect of High-Frequency Resistance Exercise on Adaptive Responses in Skeletal Muscle
Medicine & Science in Sports & Exercise…..Volume 39 #12…..December 2007…..page 2135-2144

“The production of reactive oxygen and nitrogen species……”

“Low to moderate doses of reactive oxygen and nitrogen species play a role in muscle adaptation to endurance training, but an overwhelming increase in reactive oxygen and nitrogen species may lead to increased cell apoptosis and immunosuppression, fatigued states and underperformance.”

N.A. Lewis, et al
Redox Homeostasis in the Elite Endurance Athlete
Sports Medicine.....Volume 45 #3.....March 2015....page 379