Fig. 4. Potential roles for lactate signalling during exercise of increasing intensity. At the onset of exercise, elevated lactate concentrations signal increased ventilatory drive and vasodilation, whilst sparing glucose and glycogen stores. As exercise intensity moves to the moderate zone, the increase in lactate mimics hypoxic conditions and triggers a number of adaptive responses. In this zone, lactate may also be involved with the transition to carbohydrate metabolism by inhibiting lipolysis. At severe exercise intensities, lactate acts as a peripheral signal to indicate exercise stress, whilst also maintaining the integrity of the muscle. High levels of lactate signal severe exercise stress and exercise is terminated, possibly through a central governor mechanism. Abbreviations: La, lactate; BLa, blood lactate; PRO, lactate protection; Glu, glucose; FA, fatty acid; EP, epinephrine; NEP, nor-epinephrine; VENT, increased ventilatory drive; VASD, vasodilation; W_max, maximal power output.