Effects of increased intensity of intermittent training in runners with differing V̇O₂ kinetics

The purpose of this study was to test the hypothesis that athletes having a slower oxygen uptake (V̇O₂) kinetics would benefit more, in terms of time spent near V̇O_2max, from an increase in the intensity of an intermittent running training (IT). After determination of V̇O_2max, vV̇O_2max (i.e. the minimal velocity associated with V̇O_2max in an incremental test) and the time to exhaustion sustained at vV̇O_2max (T _lim), seven well-trained triathletes performed in random order two IT sessions. The two IT comprised 30-s work intervals at either 100% (IT_100%) or 105% (IT_105%) of vV̇O_2max with 30-s recovery intervals at 50% of vV̇O_2max between each repeat. The parameters of the V̇O₂ kinetics (td₁, τ₁, A₁, td₂, τ₂, A₂, i.e. time delay, time constant and amplitude of the primary phase and slow component, respectively) during the T _lim test were modelled with two exponential functions. The highest V̇O₂ reached was significantly lower (P<0.01) in IT_100% run at 19.8 (0.9) km^.h⁻¹ [66.2 (4.6) ml^.min^−1.kg⁻¹] than in IT_105% run at 20.8 (1.0) km^.h⁻¹ [71.1 (4.9) ml^.min^−1.kg⁻¹] or in the incremental test [71.2 (4.2) ml^.min^−1.kg⁻¹]. The time sustained above 90% of V̇O_2max in IT_105% [338 (149) s] was significantly higher (P<0.05) than in IT_100% [168 (131) s]. The average T _lim was 244 (39) s, τ₁ was 15.8 (5.9) s and td₂ was 96 (13) s. τ₁ was correlated with the difference in time spent above 90% of V̇O_2max (r=0.91; P<0.01) between IT_105% and IT_100%. In conclusion, athletes with a slower V̇O₂ kinetics in a vV̇O_2max constant-velocity test benefited more from the 5% rise of IT work intensity, exercising for longer above 90% of V̇O_2max when the IT intensity was increased from 100 to 105% of vV̇O_2max.