Purpose This doctoral dissertation aimed at 1) examining the haematological adaptations to high-intensity interval training (HIT) in well-trained athletes (Study I) and 2) investigating the exercise responses and effects of one-legged HIT in normoxia and hypoxia (Study II).
Methods In Study I, 27 male and eight female well-trained (VO2max: 63.7 7.7 ml/kg/min; age: 27 3 years) athletes were randomly assigned to the HIT (HITG, N = 19) or the control group (CG, N = 16). Thirteen recreationally active (VO2max: 46.7 10.3 ml/kg/min; age: 26 3 years) participants were recruited for Study II and were randomly assigned to the hypoxic (HG, N= 7) or the normoxic (NG, N= 6) HIT training group. In Study I, the HITG performed eleven HIT sessions over a three week period, consisting of four 4 min interval bouts at an exercise intensity of 90-95% of the individual maximal heart rate (HRmax), separated by 4-min active recovery periods. Before and 5 2 days after the intervention, total haemoglobin mass (tHb-mass), blood volume (BV) and plasma volume (PV) were determined by the CO-rebreathing method. VO2max was assessed in a laboratory treadmill test. The athletes of the CG maintained their usual endurance and strength training during the three week intervention period. In Study II, both groups completed nine HIT sessions in three weeks. The NG performed the training in normoxia (FiO2: 0.21; 600 m) and the HG in hypoxia (FiO2: 0.126; 4500 m). Each session consisted of 4 x 4 min one-legged cycling at 90% of HRmax separated by 4 min recovery periods. Before and after the intervention period, VO2max and peak power output (Wmax) and responses to submaximal cycling (100 and 150 watts) were assessed in a laboratory two-legged cycling test.
Results Study I: tHb-mass (from 753 124 to 760 121 g), BV (from 5.6 0.8 to 5.6 0.9 l) and PV (from 3.2 0.5 to 3.2 0.5 l) remained unchanged after HIT and did not show an interaction (group x time). Within the HITG, VO2max improved from baseline by +3.5% (p = 0.011), but remained unchanged in the CG. No interaction (group x time) was seen for VO2max. The HITG showed a significant reduction in HRmax compared to the baseline measurement (-2.3%, p 0.001), but HRmax remained unchanged in the CG. There was a significant interaction (group x time) for HRmax (p = 0.006). Study II: Peak power output significantly improved within both groups (9.6 4.8% and 12.6 8.9% for HG and NG, respectively) with no significant interaction (p = 0.277). However, VO2max only significantly increased after training in hypoxia from 45.4 10.1 to 50.0 9.8 ml/min/kg (10.8 6.0%; p = 0.002) with no significant interaction (p = 0.146). The maximal O2-pulse improved within the HG and demonstrated a significant interaction (p = 0.040).
Conclusions We conclude that eleven HIT sessions added to usual training did neither improve VO2max nor haematological parameters compared to the CG. One-legged cycling training significantly improved VO2max and peak power output. Training under hypoxic conditions may generate greater effects on VO2max than a similar training in normoxia and is considered as a promising training method for improving cardiorespiratory fitness.