Biological and methodological factors affecting VO2max response variability to endurance training and the influence of exercise intensity prescription

© 2021 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society. This is an open access article under the terms of the Creative Commons Attribution License. https://creativecommons.org/licenses/by/4.0/Changes in cardiorespiratory fitness (CRF) in response to endurance training (ET) exhibit large variations, possibly due to a multitude of biological and methodological factors. It is acknowledged that ~20% of individuals may not achieve meaningful increases in CRF in response to ET. Genetics, the most potent biological contributor, has been shown to explain ~50% of response variability, whilst age, sex, and baseline CRF appear to explain a smaller proportion. Methodological factors represent the characteristics of the ET itself including the type, volume, and intensity of exercise, as well as the method used to prescribe and control exercise intensity. Notably, methodological factors are modifiable and, upon manipulation, alter response rates to ET, eliciting increases in CRF regardless of an individual’s biological predisposition. Particularly, prescribing exercise intensity relative to a physiological threshold (e.g. ventilatory threshold) is shown to increase CRF response rates compared to when intensity is anchored relative to a maximum physiological value (e.g. maximum heart rate). It is, however, uncertain whether the increased response rates are primarily attributable to reduced response variability, greater mean changes in CRF, or both. Future research is warranted to elucidate whether more homogenous chronic adaptations manifest over time among individuals, as a result of exposure to more homogenous exercise stimuli elicited by threshold-based practices.Peer reviewe

A Multi-Center Comparison of VO2peak Trainability Between Interval Training and Moderate Intensity Continuous Training

There is heterogeneity in the observed VO2peak response to similar exercise training, and different exercise approaches produce variable degrees of exercise response (trainability). The aim of this study was to combine data from different laboratories to compare VO2peak trainability between various volumes of interval training and Moderate Intensity Continuous Training (MICT). For interval training, volumes were classified by the duration of total interval time. High-volume High Intensity Interval Training (HIIT) included studies that had participants complete more than 15 min of high intensity efforts per session. Low-volume HIIT/Sprint Interval Training (SIT) included studies using less than 15 min of high intensity efforts per session. In total, 677 participants across 18 aerobic exercise training interventions from eight different universities in five countries were included in the analysis. Participants had completed 3 weeks or more of either high-volume HIIT (n = 299), low-volume HIIT/SIT (n = 116), or MICT (n = 262) and were predominately men (n = 495) with a mix of healthy, elderly and clinical populations. Each training intervention improved mean VO2peak at the group level (P \u3c 0.001). After adjusting for covariates, high-volume HIIT had a significantly greater (P \u3c 0.05) absolute VO2peak increase (0.29 L/min) compared to MICT (0.20 L/min) and low-volume HIIT/SIT (0.18 L/min). Adjusted relative VO2peak increase was also significantly greater (P \u3c 0.01) in high-volume HIIT (3.3 ml/kg/min) than MICT (2.4 ml/kg/min) and insignificantly greater (P = 0.09) than low-volume HIIT/SIT (2.5 mL/kg/min). Based on a high threshold for a likely response (technical error of measurement plus the minimal clinically important difference), high-volume HIIT had significantly more (P \u3c 0.01) likely responders (31%) compared to low-volume HIIT/SIT (16%) and MICT (21%). Covariates such as age, sex, the individual study, population group, sessions per week, study duration and the average between pre and post VO2peak explained only 17.3% of the variance in VO2peak trainability. In conclusion, high-volume HIIT had more likely responders to improvements in VO2peak compared to low-volume HIIT/SIT and MICT

A novel gravity-induced blood flow restriction model augments ACC phosphorylation and PGC-1α mRNA in human skeletal muscle following aerobic exercise: a randomized crossover study

This study tested the hypothesis that a novel, gravity-induced blood flow restricted (BFR) aerobic exercise (AE) model will result in greater activation of the AMPK–PGC-1α pathway compared with work rate-matched non-BFR. Thirteen healthy males (age: 22.4 ± 3.0 years; peak oxygen uptake: 42.4 ± 7.3 mL/(kg·min)) completed two 30-min work rate-matched bouts of cycling performed with their legs below (CTL) and above their heart (BFR) at ∼2 weeks apart. Muscle biopsies were taken before, immediately, and 3 h after exercise. Blood was drawn before and immediately after exercise. Our novel gravity-induced BFR model led to less muscle oxygenation during BFR compared with CTL (O2Hb: p = 0.01; HHb: p 0.05). In conclusion, gravity-induced BFR is a viable BFR model that demonstrated an important role of AMPK signalling on augmenting PGC-1α mRNA. Novelty Gravity-induced BFR AE reduced muscle oxygenation without impacting muscle activation, advancing gravity-induced BFR as a simple, inexpensive BFR model. Gravity-induced BFR increased PGC-1α mRNA and ACC phosphorylation more than work rate-matched non-BFR AE. This is the first BFR AE study to concurrently measure blood catecholamines, muscle activation, and muscle oxygenation.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A systematic upregulation of nuclear and mitochondrial genes is not present in the initial post-exercise recovery period in human skeletal muscle

The purpose of the current investigation was to determine if an exercise-mediated upregulation of nuclear and mitochondrial-encoded genes targeted by the transcriptional co-activator peroxisome-proliferator-activated receptor gamma co-activator-1 alpha (PGC-1α) occurs in a systematic manner following different exercise intensities in humans. Ten recreationally active males (Age: 23 ±3 yrs; VO2peak: 41.8 ±6.6 mL/kg/min) completed two acute bouts of work-matched interval exercise at ~73% (LO) and ~100% (HI) of work rate at VO2peak in a randomized cross-over design. Muscle biopsies were taken before (Pre), immediately after (Post), and 3 hours into recovery (3hr) following each exercise bout. A main effect of time (pThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Does blood lactate predict the chronic adaptive response to training: A comparison of traditional and talk test prescription methods

The purpose of this study was to test the hypotheses that: 1) inter-individual variability in acute blood lactate responses during exercise at 65% of peak work rate (WRPEAK; REL) will predict variability in the chronic responses to exercise training, and 2) exercising at an intensity that causes uncomfortable speech production (negative [NEG] talk test [TT] stage) elicits high acute blood lactate responses and large adaptations to training. Twenty-eight participants competed four weeks of exercise training consisting of REL (n: 14) NEG (TT, n: 14). Fifteen additional participants were assigned to a no-exercise control group (CTL, n: 15). In REL, acute blood lactate responses during the first training session significantly predicted changes in VO2peak (r=0.69) after training. TT resulted in consistently high acute blood lactate responses. REL and TT improved (pThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Acute upregulation of PGC-1α mRNA correlates with training-induced increases in SDH activity in human skeletal muscle

The purpose of the present study was to determine if acute responses in pgc-1α, vegfa, sdha, and gpd1/2 mRNA expression predict their associated chronic skeletal muscle molecular (SDH/GPD activity and substrate storage) and morphological (fibre type composition and capillary density) adaptations following training. Skeletal muscle biopsies were collected from fourteen recreationally active men (age: 22.0 ± 2.4 years) before (PRE) and 3 hours after (3HR) the completion of an acute bout of SIT (eight, 20-second intervals at ~170% VO2peak work rate separated by 10 seconds of recovery). Participants then completed 6 weeks of SIT 4 times per week with additional biopsies after 2 (MID) and 6 (POST) weeks of training. Acute increases in pgc-1α mRNA strongly predicted increases in SDH activity (a marker of oxidative capacity) from PRE and MID to POST (PRE-POST: r = 0.81, r2 = 0.65, pThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author