The performance and aerobic endurance effects of high-intensity versus moderate-intensity continuous running

The aim of the present study was to investigate the performance and aerobic endurance effects of high-intensity (HICR) versus moderate-intensity continuous running (MICR), which were nonmatched for total work. Twenty healthy recreational athletes (aged 28 ± 5 years) were randomly assigned to an HICR, MICR, or no-intervention control (C) group. The HICR group (n = 7) performed a 20-min strenuous, almost exhausting, run above lactate threshold (LT) at ∼88% of maximal heart rate (HR_max), whereas the MICR group (n = 7) performed a 40-min run at ∼80% HR_max. Both the HICR and MICR groups performed 3 intervention sessions a week, in addition to ∼60% of their regular aerobic exercise, for 10 weeks. The C group (n = 6) performed regular physical exercise throughout the study. Time to exhaustion, during a ∼4-8-min ramp test procedure, was significantly increased by 23% and 24% (P < 0.01) following HICR or MICR, respectively, with no significant difference in the change in time to exhaustion (P = 1.00) at pre- to post-training between the 2 training modalities (HICR and MICR). In the HICR group, maximal oxygen consumption and velocity at LT increased significantly by 5.0% and 6.8% (P < 0.01), respectively. The MICR group increased relative maximal oxygen consumption (mL·kg^-1·min^-1) significantly by 4.7% (P < 0.05), whereas the pulmonary respiratory gas-exchange ratio was significantly decreased at a submaximal workload by 4.2% (P < 0.01), indicating enhanced fat oxidation. No performance or physiological effects were observed in the C group. The present study indicates that even with a substantially lower total energy turnover, HICR can be as performance enhancing as MICR. Moreover, HICR can increase maximal aerobic power, whereas MICR may enhance fat oxidation.