Work-matched High-intensity Interval And Moderate-intensity Continuous Training Adaptations On 17 Lactate Threshold Methods In Females

Abstract

PURPOSE: to compare exercise training effects on 17 lactate threshold methods to 6 weeks (3x/week) of high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT) in females. METHODS: 24 healthy sedentary females (mean ± SD: peak oxygen uptake 30.0 ± 3.2 mLᐧkg-1ᐧmin-1, peak power output 151 ± 21 W, body mass index 23.4 ± 2.6 kgᐧm-2) were randomly assigned to either HIIT or MICT. Participants performed a step-incremental test on a cycle ergometer (3-min stages of 25-W increments, starting at 25 W) pre- and post-training. The HIIT group (N = 12) performed a 10-min warm-up (power output (PO) at 70% of the maximal heart rate (HRmax)), and four 4-min intervals (PO at 90% HRmax) interspersed with 4-min recovery at 30 W. The MICT group (N = 12) performed 60-min continuous cycling (PO at 90% of the first lactate turning-point (LT1)). Lactate thresholds were analyzed as: Log-log, onset of blood lactate accumulation (OBLA, N = 5), fixed value above baseline (Bsln+, N = 3), Dmax and its modified versions (N = 5), lactate turning-points (LT1 and LT2), and the minimal lactate-intensity ratio (LTratio). A two-way analysis of variance was used to test differences within (post versus pre) and between groups. Additionally, the width of confidence intervals (CIwidth) from the delta change was calculated for each method and group. RESULTS: In the HIIT group, the intensity derived from all the methods significantly increased after training (p < 0.01), except for LTratio (p = 0.6). In the MICT group, the intensity from OBLA, Bsln+, and the modified Dmax methods significantly increased after training (p < 0.05), whereas Log-log, Dmax, LT1, LT2, and LTratio did not improve significantly (p > 0.05). The HIIT group showed a higher increase in intensity from the Dmax methods, and in LT1 and LT2 compared with the MICT group (p < 0.05). No differences were observed between the groups in the improvements of Log-log, OBLA, Bsln+, and LTratio. OBLA at 3.5 and 4.0 mM, and Dmax presented the narrowest CIwidth (range 7 - 12 W), while Bsln+ 0.5 mM, Bsln+ 1.0 mM, and Log-log had the widest CIwidth (range 24 - 32 W). CONCLUSIONS: In healthy sedentary females, improvements of the Dmax methods, LT1, and LT2 were superior in the HIIT group. The lowest intra-individual variability in response to training was observed in the Dmax and OBLA at 3.5 and 4.0 mM methods.