Introduction

It has long been known that endurance training induces a multitude of metabolic and morphological adaptations that improve the resistance of the trained musculature to fatigue and enhance endurance capacity and/or exercise performance (13). Accumulating evidence now suggests that many of these adaptations can be modified by nutrient availability (9-11, 21). Growing evidence suggests that training with reduced muscle glycogen using a ‘train twice every second day’ compared to a more traditional ‘train once daily’ approach can enhance the acute training response (29) and markers representative of endurance training adaptation after short-term (3-10 wk) training interventions (8, 16, 30). Of note is that the superior training adaptation in these previous studies was attained despite a reduction in maximal self-selected power output (16, 30). The most obvious factor underlying the reduced intensity during a second training bout is the reduction in muscle glycogen availability.