Concurrent strength and endurance training reportedly compromises strength gains and the ability to produce explosive movements. Possible reasons for compromises in strength-power adaptations with concurrent training are an increased likelihood of overtraining; differences in the organization of neuromuscular recruitment patterns; alterations in the concentrations of various hormones and differences in activation or repression of various anabolic/catabolic processes at the muscular level; and shifts in protein isozymes such as myosin. Recent research suggests that strength training may enhance endurance performance, although there are reasons to believe that resistance training can also be detrimental. Further research is necessary to determine the extent to which strength adaptations are compromised with concurrent training, and the mechanism(s) by which combined training negatively affects strength. It is recommended that the training of athletes takes into account the physiological demands of the sport and unique needs of the individual athlete in designing a training program in order to optimize performance.
J. Chromiak, D. R. Mulvaney
Journal of Strength and Conditioning Research