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 h igh-intensity exercise was examined following a bout of interval running. W ell-trained endurance runners were split into an experimental group [maximu m oxygen uptake, (V) over dot O-2max 4.73 (0.39) l.min(-1)] and a reliabili ty group [(V) over dot O-2max 4.77 (0.26) l.min(-1)]. The experimental grou p 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 thr eshold and (V) over dot O-2max; tests 1 and 2, respectively). The slow comp onent 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 exercis e, i.e. Delta(V) over dot O2(6-3) The Delta(V) over dot O2(6-3) was the sam e 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 mag nitude 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 expe rimental group was observed in the absence of any significant change in bod y mass, core temperature or blood lactate concentration, either at the star t or end of tests 1 or 2. It is concluded that similar mechanisms may be re sponsible for the slow component of (V) over dot O-2 kinetics and for the f atigue following the training session. It has been suggested previously tha t this mechanism may be linked primarily to changes within the active limb, with the recruitment of alternative and/or additional less efficient fibre s.