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) over dot O-2) 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) over dot O-2max) 4.14 (SD 0.49)l . min(-1)] were studied. The (V) over dot O-2 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) over dot O-2max (v((V) over dot O2max)) with 3-min rest intervals. Performance was also assessed at 1 km . h(-1) below v((V) over dot O2max), in the form of time to exhaustion (t(lim)). The (V) over dot O-2 and heart rate (f(c)) were assessed both during the severe intensity performance trial, and the moderate intensity run at 50% v((V) over dot O2max). Whilst a significant change was observed in running performance and the (V) over dot O-2 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, t(lim) had decreased by 24%, (V) over dot O-2 during moderate intensity running had increased by 2%, and the difference in (V) over dot O-2 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, f(c) 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) over dot O-2 during running may be altered under conditions of prolonged fatigue

Oxygen Uptake During High-Intensity Running: Response Following a Single Bout of Interval Training

Elevated oxygen uptake ((V) over dot O-2) during moderate-intensity running following a bout of interval running training has been studied previously. To further investigate this phenomenon, the (V) over dot O-2 response to high-intensity exercise was examined following a bout of interval running. Well-trained endurance runners were split into an experimental group [maximum oxygen uptake, (V) over dot O-2max 4.73 (0.39) l.min(-1)] and a reliability group [(V) over dot O-2max 4.77 (0.26) l.min(-1)]. The experimental group completed a training session (4 x 800 m at 1 km.h(-1) below speed at (V) over dot O-2max, with 3 min rest between each 800-m interval). Five minutes prior to, and Ih following the training session, subjects completed 6 min 30 s of constant speed, high-intensity running designed to elicit 40% Delta (where Delta is the difference between (V) over dot O-2 at ventilatory threshold and (V) over dot O-2max; tests 1 and 2, respectively). The slow component of (V) over dot O-2 kinetics was quantified as the difference between the (V) over dot O-2 at 6 min and the (V) over dot O-2 at 3 min of exercise, i.e. Delta(V) over dot O2(6-3) The Delta(V) over dot O2(6-3) was the same in two identical conditions in the reliability group [mean (SD): 0.30 (0.10) l.min(-1) vs 0.32 (0.13) l.min(-1)]. In the experimental group, the magnitude of the slow component of (V) over dot O-2 kinetics was increased in test 2 compared with test 1 by 24.9% [0.27 (0.14) l.min(-1) vs 0.34 (0.08) l.min(-1), P < 0.05]. The increase in Delta(V) over dot O2(6-3) in the experimental group was observed in the absence of any significant change in body mass, core temperature or blood lactate concentration, either at the start or end of tests 1 or 2. It is concluded that similar mechanisms may be responsible for the slow component of (V) over dot O-2 kinetics and for the fatigue following the training session. It has been suggested previously that this mechanism may be linked primarily to changes within the active limb, with the recruitment of alternative and/or additional less efficient fibres