Fig. 2.

Graphical representation of the proposed theoretical principles of exercise adaptation. In GSDs, we suggest distinguishing exercise adaptation principles between disorders of muscular glycolysis and those of glycogenolysis, and further differentiating glycogenolysis disorders based on the presence or absence of the second wind phenomenon. In all these subcategories, anaerobic alactic exercise, which relies on phosphagens as energy substrates, might be performed safely. Nevertheless, future research may explore whether Cr supplementation might be beneficial in GSDs for enhancing the ability to perform repeated bouts of short-duration, high-intensity exercise. In fact, it is well known that repeating such activities leads to a rapid depletion of PCr and a concomitant increase in glycolytic activity (Gaitanos et al., 1993). Therefore, Cr supplementation, by increasing muscular Cr concentration and enhancing PCr resynthesis (Greenhaff et al. 1994), could potentially increase tolerance to these activities by delaying reliance on carbohydrate metabolism, thus prolonging safety during such exercise performance