Acute hypoxia alters lactate threshold in chronic altitude residents

At an identical workload, blood lactate concentration ([La]) is higher in acute hypoxia (H) versus normoxia (N). However, in altitude-acclimatized individuals, the lactate response to incremental exercise in H and with various VO2max protocols is less clear. Subjects (N = 16) residing at moderate altitude completed VO2max tests on a cycle ergometer in N and H (FIO2 = 0.15) using ramp (R) and step (S) protocols. Gas exchange data were obtained breath-by-breath during exercise. Blood samples were obtained for measurement of blood [La]. One-way ANOVA with repeated measures was used to examine differences between lactate threshold (LT) and blood [La] among the various protocols. LT was significantly higher (p2max) and H (67.2 ? 9.6 %VO2max) versus R (59.7 ? 8.9 %VO2max). At VO2max, blood [La] was higher (p>0.05) in R compared to S and H. At 50 %VO2max, blood [La] was significantly higher (p<0.05) in S (2.0 ? 0.4 mmol/L) compared to R (1.7 ? 0.3 mmol/L and H (1.7 ? 0.6 mmol/L). In subjects acclimatized to altitude, the type of protocol used and gas fraction inspired alter the lactate response to incremental exercise. A standardized protocol for LT assessment is recommended to decrease discrepancies in LT between studies

Incidence of the oxygen plateau at VO2max during exercise testing to volitional fatigue

The purpose of this study was to better clarify the VO2 response to exercise to VO2max by comparing data derived from different time averaging intervals and exercise protocols. Sixteen active subjects (12 men and 4 women, mean age, height, weight, and VO2max = 31.6±8.9 yr, 172.0±6.6 cm, 70.8±12.7 kg, 3,212±652 mL/min) completed three different VO2max tests on a cycle ergometer (a 25 Watt/min ramp protocol (R), a 75 Watt/3 min step protocol (S), and a 25 Watt/min ramp protocol (H) under hypoxic conditions (FIO2 = 15%, P B = 635 mm Hg) on separate days. During each test, subjects breathed humidified air from a Tissot tank, and breath-by-breath gas exchange was obtained by a Medical Graphics metabolic cart. All breath-by-breath data were smoothed using an 11-breath moving average. These data were then time-averaged into 15, 30, and 60 s sampling intervals. Criteria for attainment of VO 2max included two of the following: RER ≥ 1.1, maximal heart rate (HR) within 10 b/min of the calculated value, or an O2 plateau (ΔVO2 ≤ 50 mL/min) with an increase in power output. Average VO2max was significantly lower (F (2, 30) = 84.37, p 2max was significantly lower (F (2, 30) = 12.26, p 2 for all protocols combined were 100, 100, 57 and 8% for the 11 breath, 15 s, 30 s and 1 min averaging, respectively. Data of the change in VO2 between VO2max and the closest neighboring data point revealed that variability was greatest for the longer time averaged data. This response was similar for each protocol. These findings show that shorter sampling intervals (breath-by-breath and 15 s) are most suitable for the detection of the VO2 plateau during progressive exercise to VO 2max. In addition, ramp and step protocols produce similar results, and acute normobaric hypoxia does not decrease the incidence of a VO2 plateau at VO2max using 11 breath or 15 s time averaging procedures

Attenuated Metabolic and Cardiorespiratory Responses to Isoenergetic High-Intensity Interval Exercise of Short Versus Long Bouts

Purpose To compare the metabolic, cardiorespiratory and perceptual responses to three isoenergetic high-intensity interval exercise (HIIE) protocols of different bout duration and an isoenergetic continuous exercise protocol. Methods Eleven healthy males (age, 28 ± 6 yr) performed four 20-min cycling trials of equal mean power output 1 wk apart. Participants cycled either continuously (CON) or intermittently with 10 s (HIIE10), 30 s (HIIE30), or 60 s (HIIE60) bouts at intensities corresponding to 49% (CON) or 100% of power at peak oxygen uptake (VO2peak). Recovery intervals during the HIIE trials were 15, 45, and 90 s, respectively. Results Average VO2 was similar in the HIIE trials (2.29 ± 0.42, 2.20 ± 0.43, and 2.12 ± 0.45 L·min-1, for HIIE10, HIIE30, and HIIE60, respectively), whereas in CON (2.02 ± 0.38 L·min-1), it was lower than HIIE10 (P = 0.002) and HIIE30 (P = 0.043). Average pulmonary ventilation (VE) was higher in HIIE60 compared with HIIE10, HIIE30, and CON (75.8 ± 21.8 L·min-1 vs 64.1 ± 14.5 L·min-1, 64.1 ± 16.2 L·min-1, and 54.0 ± 12.5 L·min-1, respectively, P < 0.001). The peak values and oscillations of VO2 and VE in HIIE60 were higher compared with all other trials (P < 0.001). Blood lactate concentration was higher in HIIE60 compared with HIIE10, HIIE30, and CON from the fifth minute onward, reaching 12.5 ± 3.5, 7.2 ± 2.1, 7.9 ± 2.9, and 4.9 ± 1.6 mmol·L-1, respectively, at the end of exercise (P < 0.001). RPE was higher and affective responses were lower in HIIE60 compared with all other trials toward the end of exercise (P < 0.001). Conclusions These findings highlight the importance of bout duration in HIIE, since shorter bouts resulted in attenuated metabolic and cardiorespiratory responses, lower RPE and feelings of displeasure compared with a longer bout, despite equal total work, duration, and work-to-recovery ratio. These results may have implications for the prescription of HIIE in various populations. © Lippincott Williams & Wilkins

Effects of exercise structure and modality on physiological and perceptual responses to exercise

This study examined the effect of exercise mode and intensity on physiological and perceptual responses to exercise. Twelve active adults (6 men and 6 women, age 5 21.7 6 1.6 years) initially performed incremental testing on the treadmill (TM) and cycle ergometer (CE) to assess maximal oxygen uptake (VO2max) and ventilatory threshold (VT). During the next 4 visits in a randomized order, subjects performed 20 minutes of moderate-intensity continuous exercise (MICE) at an intensity 20% below VT on the TM (TMMICE) and cycle ergometer (CEMICE) as well as time-matched high-intensity interval exercise (HIIE; 10 1-minute bouts at workload equal to 20% above VT followed by 1-minute active recovery) on both modes (TMHIIE and CEHIIE). During exercise, gas exchange data, blood lactate concentration, and perceptual responses (rating of perceived exertion, affective valence, and enjoyment) were assessed. Heart rate (p, 0.001) and V.O2 (p, 0.001) were higher in response to TMHIIE vs. CEHIIE as well as TMMICE vs. CEMICE. Blood lactate concentration was higher (p 5 0.003) in response to CEHIIE vs. TMHIIE. The rating of perceived exertion was significantly higher (p, 0.001) in TMMICE compared with CEMICE which showed the most positive affective valence (p 5 0.009). Enjoyment was similar across all bouts (p 5 0.11). Treadmill-based HIIE leads to higher heart rate and VO2 vs. CEHIIE, although there was no difference in affective valence or enjoyment. Practitioners aiming to optimize the cardiorespiratory response to moderate or interval exercise in their clientele should recommend TM running rather than cycling. © 2021 National Strength and Conditioning Associatio