Development of a non-damaging high-intensity intermittent running protocol.

The aim of the present study was to devise a non-damaging high-intensity intermittent running protocol. Ten healthy active men completed high-intensity interval running (8× 3-min bouts at 90% of maximal oxygen uptake interspersed with 3-min recovery) on a motorized treadmill under normal laboratory temperatures. Mean heart rate and rating of perceived exertion significantly increased during the intermittent protocol (the first bout, 15.3± 1.2; the final bout, 18.6± 0.9; P< 0.001). Blood lactate concentrations were significantly elevated following bout 1 compared with resting values (1.2± 0.3 mmol/L vs 5.4± 2.4 mmol/L; P = 0.03). However, no significant reduction in maximal voluntary contraction was observed immediately after completing the last exercise bout (623.9± 143.6 N) or during the subsequent 7-d period compared to pre-exercise values (P = 0.59). Creatine kinase (CK) concentrations were not significantly increased following exercise or during the subsequent 7-d period (P = 0.96). Myoglobin (Mb) content was significantly increased following exercise (P = 0.01), however, values returned towards pre-exercise concentrations after 24 h. These results indicate that the high-intensity intermittent running protocol induced changes in physiological and subjective indices that are consistent with the effects of acute fatigue as opposed to those changes normally associated with exercise-induced muscle damage. This exercise protocol can therefore be used to investigate the influence of high-intensity exercise from physiological responses to molecular adaptation.