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It has been suggested that time spent at a high fraction of maximal oxygen consumption (% V ˙ $\dot{\mathrm{V}}$ O 2max ) plays a decisive role for adaptations to interval training. However, previous studies examining how interval sessions should be designed to achieve a high % V ˙ $\dot{\mathrm{V}}$ O 2max have exclusively been performed in males. The present study compared the % V ˙ $\dot{\mathrm{V}}$ O 2max attained during three different 6 × 8 min interval protocols, in female (n = 11; V ˙ $\dot{\mathrm{V}}$ O 2max , 62.5 (6.4) mL · min -1 ·kg -1 ) and male (n = 8; V ˙ $\dot{\mathrm{V}}$ O 2max , 81.0 (5.2) mL · min -1 ·kg -1 ) cyclists. Mean power output during work intervals were identical across the three interval protocols, corresponding to the cyclist's 40 min maximal effort (PO 40min ): (1) 30 s intervals at 118% of PO 40min interspersed with 15 s active recovery at 60% (30/15), (2) constant pace at 100% of PO 40min (CON), and (3) altering between 60 s intervals at 110% and 60 s at 90% of PO 40min (60/60). Additionally, the study explored whether the m. vastus lateralis characteristics of the cyclists (fiber type proportion, capillarization, and citrate synthase activity) were associated with the % V ˙ $\dot{\mathrm{V}}$ O 2max attained during the interval sessions. Overall, mean % V ˙ $\dot{\mathrm{V}}$ O 2max and time ≥90% of V ˙ $\dot{\mathrm{V}}$ O 2max were higher during 30/15 compared to CON (86.7 (10.1)% and 1123 (787) s versus 85.0 (10.4)% and 879 (779) s, respectively; both p ≤ 0.01) and 60/60 (85.6 (10.0)% and 917 (745) s, respectively; both p ≤ 0.05), while no difference was observed between 60/60 and CON (both p ≥ 0.36). During interval sessions, % V ˙ $\dot{\mathrm{V}}$ O 2max and time ≥90% of V ˙ $\dot{\mathrm{V}}$ O 2max did not differ between sexes. Skeletal muscle characteristics were not related to % V ˙ $\dot{\mathrm{V}}$ O 2max  during interval sessions. In conclusion, well-trained cyclists demonstrate highest % V ˙ $\dot{\mathrm{V}}$ O 2max during 30/15, irrespective of sex and skeletal muscle characteristics., (© 2024 The Author(s). European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.)

It has been suggested that time at a high fraction (%) of maximal oxygen uptake (VO 2max ) plays a decisive role for adaptations to interval training. Yet, no study has, to date, measured the % of VO 2max during all interval sessions throughout a prolonged training intervention and subsequently related it to the magnitude of training adaptations. Thus, the present study aimed to investigate the relationship between % of VO 2max achieved during an interval training intervention and changes in endurance performance and its physiological determinants in well-trained cyclists. Twenty-two cyclists (VO 2max 67.1 (6.4) mL·min -1  ·kg -1 ; males, n = 19; females, n = 3) underwent a 9-week interval training intervention, consisting 21 sessions of 5 × 8-min intervals conducted at their 40-min highest sustainable mean power output (PO). Oxygen uptake was measured during all interval sessions, and the relationship between % of VO 2max during work intervals and training adaptations were investigated using linear regression. A performance index was calculated from several performance measures. With higher % of VO 2max during work intervals, greater improvements were observed for maximal PO during the VO 2max test (R 2 adjusted  = 0.44, p = 0.009), PO at 4 mmol·L -1 [blood lactate] (R 2 adjusted  = 0.25, p = 0.035), the performance index (R 2 adjusted  = 0.36, p = 0.013), and VO 2max (R 2 adjusted  = 0.54, p = 0.029). Other measures, such as % of maximal heart rate, were related to fewer outcome variables and exhibited poorer session-to-session repeatability compared to % of VO 2max . In conclusion, improvements in endurance measures were positively related to the % of VO 2max achieved during interval training. Percentage of VO 2max was the measure that best reflected the magnitude of training adaptations., (© 2024 The Author(s). European Journal of Sport Science published by Wiley‐VCH GmbH on behalf of European College of Sport Science.)

Purpose and Methods: To test whether heat training performed as 5 × 50-min sessions per week for 5 wk in a heat chamber (CHAMBER) or while wearing a heat suit (SUIT), in temperate conditions, increases hemoglobin mass (Hb mass ) and endurance performance in elite cyclists, compared with a control group (CON-1). Furthermore, after the 5-wk intervention, we tested whether three sessions per week for 3 wk with heat suit (SUIT main ) would maintain Hb mass elevated compared with athletes who returned to normal training (HEAT stop ) or who continued to be the control group (CON-2)., Results: During the initial 5 wk, SUIT and CHAMBER increased Hb mass (2.6% and 2.4%) to a greater extent than CON-1 (-0.7%; both P < 0.01). The power output at 4 mmol·L -1 blood lactate and 1-min power output ( Wmax ) improved more in SUIT (3.6% and 7.3%, respectively) than CON-1 (-0.6%, P < 0.05; 0.2%, P < 0.01), whereas this was not the case for CHAMBER (1.4%, P = 0.24; 3.4%, P = 0.29). However, when SUIT and CHAMBER were pooled this revealed a greater improvement in a performance index (composed of power output at 4 mmol·L -1 blood lactate, Wmax , and 15-min power output) than CON-1 (4.9% ± 3.2% vs 1.7% ± 1.1%, respectively; P < 0.05). During the 3-wk maintenance period, SUIT main induced a larger increase in Hb mass than HEAT stop (3.3% vs 0.8%; P < 0.05), which was not different from the control (CON-2; 1.6%; P = 0.19), with no differences between HEAT stop and CON-2 ( P = 0.52)., Conclusions: Both SUIT and CHAMBER can increase Hb mass , and pooling SUIT and CHAMBER demonstrates that heat training can increase performance. Furthermore, compared with cessation of heat training, a sustained increase in Hb mass was observed during a subsequent 3-wk maintenance period, although the number of weekly heat training sessions was reduced to 3., (Copyright © 2022 by the American College of Sports Medicine.)