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

Abstract

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 homogeneous chronic adaptations manifest over time among individuals, as a result of exposure to more homogeneous exercise stimuli elicited by threshold-based practices.

Determination of exercise intensity domains during upright versus supine cycling: a methodological study

“…Determining exercise intensity domains for well-tolerated longer durations of exercise is challenging, both during the upright ( Meyler, Bottoms & Muniz-Pumares, 2021 ; Keir, Pogliaghi & Murias, 2018 ) and supine cycling model. Compared to upright, supine exercise is characterized by slower O 2 transport ( Dillon et al, 2021 ), greater skeletal muscle deoxygenation ( Goulding et al, 2021a ), and a greater type II fibre activation cycling ( Goulding et al, 2021a , 2021b ), altogether likely leading to earlier exercise cessation.…”

“…For almost a century, cardiopulmonary exercise testing (CPET) has been the gold standard of integrative physiologic assessment ( Hill & Lupton, 1923 ), and is widely implemented as the diagnostic tool in both clinical and research settings to provide functional insights regarding general health and exercise tolerance ( Kaminsky et al, 2017 ; Guazzi et al, 2017 ; Wasserman et al, 2020 ). However, researchers are still investigating the nuances of the moderating factors, including biological, physiological, biomechanical, and methodological aspects related to CPET ( Meyler, Bottoms & Muniz-Pumares, 2021 ). The pertinent stages, such as the rate of oxygen uptake (V̇O 2 ) at the gas exchange threshold (GET) and the respiratory compensation point (RCP), provide objective outputs for clinicians and exercise physiologists to tailor personalised exercise interventions that can optimize overall cardiorespiratory health and performance while avoiding premature fatigue development.…”

“…For example, Smirl et al (2016) prescribed an exercise intensity domain by determining the % of HR relative to the maximum HR attained during incremental exercise. Crucially, exercise intensity domains were not categorised through gas exchange parameters for the corresponding PO, which has recently been identified as potentially misleading ( Jamnick et al, 2020 ; Zuccarelli et al, 2018 ; Meyler, Bottoms & Muniz-Pumares, 2021 ). Although recent studies have identified that V̇O 2 peak is progressively reduced when moving from an upright position into a supine during cycling ( Dillon et al, 2021 ), there is limited understanding of supine exercise intensity boundaries precisely determined from ramp CPET.…”

Causes and Consequences of Interindividual Response Variability: A Call to Apply a More Rigorous Research Design in Acute Exercise-Cognition Studies

“…In the literature, there is empirical evidence (Ross et al, 2015;Bonafiglia et al, 2016;Montero and Lundby, 2017) and a strong theoretical rationale (Pickering and Kiely, 2018;Herold et al, 2019;Gronwald et al, 2020b;Herold et al, 2020c;Meyler et al, 2021) that the individual responsiveness to exercise can be influenced by modifying the dose of exercise by adjusting the exercise prescription. However, a recent article emphasizes that larger mean changes rather than the reduction in interindividual variability, are responsible for the better responsiveness after adjusting the exercise prescription (e.g., higher training frequency, longer training duration) (Bonafiglia et al, 2021b).…”

“…Thus, we strongly advocate for the investigation of alternative approaches of exercise intensity prescriptions in the field of exercise-cognition science (Herold et al, 2019(Herold et al, , 2020b. Based on recent overview articles on this topic (Mann et al, 2013;Jamnick et al, 2020;Meyler et al, 2021), we recommend to use submaximal anchors of respiratory or/and metabolic parameters (e.g., ventilatory or lactate thresholds) as a proxy of aerobic and anaerobic threshold marker for exercise intensity prescription. A limitation of threshold concepts, which needs to be acknowledged, is that depending on the intensity domain, some of the threshold concepts are more valid than others (Jamnick et al, 2020).…”