EFFECT OF EXERCISE-INDUCED MUSCLE DAMAGE ON THE BLOOD LACTATE RESPONSE TO INCREMENTAL EXERCISE IN HUMANS

Eccentric muscle actions are known to induce temporary muscle damage, delayed onset muscle soreness (DOMS) and muscle weakness that may pers ist for several days. The purpose of the present study was to determin e whether DOMS-inducing exercise affects blood lactate responses to su bsequent incremental dynamic exercise. Physiological and metabolic res ponses to a standardised incremental exercise task were measured two d ays after the performance of an eccentric exercise bout or in a contro l (no prior exercise) condition. Ten healthy recreationally active sub jects (9 male, 1 female), aged 20 (SD 1) years performed repeated ecce ntric muscle actions during 40 min of bench stepping (knee high step; 15 steps.min(-1)). Two days after the eccentric exercise, while the su bjects experienced DOMS, they cycled on a basket loaded cycle ergomete r at a starting work rate of 150 W, with increments of 50 W every 2 mi n until fatigue. The order of the preceding treatments (eccentric exer cise or control) was randomised and the treatments were carried out 2 weeks apart. Two days after the eccentric exercise, all subjects repor ted leg muscle soreness and exhibited elevated levels of plasma creati ne kinase activity (P < 0.05). Endurance time and peak (V) over dot O- 2 during cycling were unaffected by the prior eccentric exercise. Minu te volume, respiratory exchange ratio and heart rate responses were si milar but venous blood lactate concentration was higher (P < 0.05) dur ing cycling after eccentric exercise compared with the control conditi on. Peak blood lactate concentration, observed at 2 min post-exercise was also higher [12.6 (SD 1.4) vs 10.9 SD (1.3) mM; P < 0.01]. The hig her blood lactate concentration during cycling exercise after prior ec centric exercise may be attributable to an increased rate of glycogeno lysis possibly arising from an increased recruitment of Type II muscle fibres. It follows that determination of lactate thresholds for the p urpose of fitness assessment in subjects experiencing DOMS is not appr opriate.