Time to exhaustion during severe intensity running: response following a single bout of interval training

 The primary aim of this study was to examine any change in performance caused by a fatiguing interval training session (TS). A secondary aim of this study was to examine the change in oxygen uptake (V˙O2) during moderate and severe intensity running, and the relationship with the change in performance. Seven male runners [mean age 24 (SD 6) years, height 1.79 (SD 0.06) m, body mass 67.9 (SD 7.6) kg, maximal oxygen uptake (V˙O2max) 4.14 (SD 0.49) l · min−1] were studied. The V˙O2 during moderate and severe intensity running and running performance were studied immediately prior to, 1 h following, and 72 h following TS. The TS was performed on a treadmill, and consisted of six bouts of 800 m at 1 km · h−1 below the velocity at V˙O2max (vV˙O2max), with 3-min rest intervals. Performance was also assessed at 1 km · h−1 below vV˙O2max, in the form of time to exhaustion (tlim). The V˙O2 and heart rate (fc) were assessed both during the severe intensity performance trial, and the moderate intensity run at 50% vV˙O2max. Whilst a significant change was observed in running performance and the V˙O2 during both moderate and severe intensity running prior to and following TS, no relationship was observed between the magnitude of change in these variables. At 1 h following TS, tlim had decreased by 24%, V˙O2 during moderate intensity running had increased by 2%, and the difference in V˙O2 between 2 min 45 s and the end of severe intensity running had increased by 91% compared with values recorded prior to TS. At 1 h following TS, ƒc had also increased significantly during moderate intensity running by 5% compared to the value recorded prior to TS. These findings demonstrated that TS resulted in a reduction in performance, and that the relationship between running performance and V˙O2 during running may be altered under conditions of prolonged fatigue.