Effects of high intensity continuous and intermittent training strategies used for endurance development on cardio-vascular responses

Abstract

Purpose of the present study was to examine the potential effects of five high intensity training (HIT) models on central and peripheral components of VO_2max. We analysed O₂ consumption (VO₂), cardiac output (Q), stroke volume (SV), heart rate (HR) and arteriovenous O₂ difference (a-vO_2diff) in different regimes of HIT during loading and recovery periods. Eight well-trained male competitive cyclists take part in the study (age: 22.1±3.1 years; body mass: 66.2±8.5 kg; height: 175.4±5.2 cm; body fat: 7.2%±1.1%; O_2max: 64±5.61 mL∙min^-1∙kg^-1). Following familiarization sessions, VO_2max was determined, and then, maximal SV, HR, Q and a-vO_2diff (SV_max), (HR_max), (Q_max), (a-vO_{2diff_max}) were evaluated individually using exercise intensities corresponding to 40 to 110% of VO_2max separately, by nitrous-oxide re-breathing (N₂O_RB) method. Thereafter, training models were performed as; HIT₁: 16 repetitions with power at ~110% of VO_2max for 45-sec (16×45-sec, p@~110%VO_2max) with 1:1 work and recovery (w/r) ratio; HIT₂: 4×3-min at p@~93%VO_2max with 1:1 w/r ratio; HIT₃: alternating the power between VO_2max (1-min) and anaerobic threshold (4-min) × 5 repetitions; HIT₄: 25-min constant-load, HIT₅: 6×30-sec at 7,5% body weight with 1:7 w/r ratio. All participants reached exhaustion at all tested HIT models. After the repeated-measures analyses, possible significant differences were investigated by post-hoc LSD/Wilcoxon. T_spent above 95% of VO_2max was higher in HIT₂ session than other exercise modalities (p<0.05). However, amongst all protocols T_spent above 90% of VO_2max were not statistically different amongst exercise modalities, except HIT₅ (p>0.05); T_spent at VO_2max was lowest in HIT₅ (p<0.05). T_spent at Q_max was higher in HIT₂ and HIT₃ sessions than HIT₁, HIT₂ and HIT₅ (p<0.05). T_spent at SV_max was higher in HIT₃ and HIT₄ modalities than HIT₁ and HIT₂. T_spent at 95% of HR_max was higher in HIT₂ session than other exercise modalities (p<0.05). T_spent at a-vO_{2diff_max} was higher in HIT₁ and HIT₂ than HIT₃, HIT₄ and HIT₅ (p<0.05). These results show that different exercise modalities reaching similar VO_2max levels may be effective in the development of central or peripheral components associated with VO_2max. It may be said that continuous HIT modalities seems to have a higher potential to improve central part of VO_2max, while intermittent HIT modalities seems better for peripheral one.