Exercise response variability: Random error or true differences in exercise response?

Islam, Hashim; Gurd, Brendon J.

doi:10.1113/ep089015

Cited by 7 publications

(8 citation statements)

References 6 publications

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“…Similar findings of negligible variation attributable to the intervention itself have been reported in other interventions (Islam & Gurd, 2020), including the effect of exercise training on maximal oxygen consumption (Williamson et al, 2017) and weight loss (Williamson et al, 2018), in a pain management intervention in adults with chronic musculoskeletal pain (Watson et al, 2021), and in changes in muscle size and strength following resistance training (Dankel et al, 2020). Collectively, these findings support consideration of more holistic approaches to intervention delivery.…”

Section: Discussionsupporting

confidence: 64%

Individual Participant Data Meta-Analysis Provides No Evidence of Intervention Response Variation in Individuals Supplementing With Beta-Alanine

Esteves

Swinton

Sale

et al. 2021

International Journal of Sport Nutrition and Exercise Metabolism

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Currently, little is known about the extent of interindividual variability in response to beta-alanine (BA) supplementation, nor what proportion of said variability can be attributed to external factors or to the intervention itself (intervention response). To investigate this, individual participant data on the effect of BA supplementation on a high-intensity cycling capacity test (CCT110%) were meta-analyzed. Changes in time to exhaustion (TTE) and muscle carnosine were the primary and secondary outcomes. Multilevel distributional Bayesian models were used to estimate the mean and SD of BA and placebo group change scores. The relative sizes of group SDs were used to infer whether observed variation in change scores were due to intervention or non-intervention-related effects. Six eligible studies were identified, and individual data were obtained from four of these. Analyses showed a group effect of BA supplementation on TTE (7.7, 95% credible interval [CrI] [1.3, 14.3] s) and muscle carnosine (18.1, 95% CrI [14.5, 21.9] mmol/kg DM). A large intervention response variation was identified for muscle carnosine (σIR = 5.8, 95% CrI [4.2, 7.4] mmol/kg DM) while equivalent change score SDs were shown for TTE in both the placebo (16.1, 95% CrI [13.0, 21.3] s) and BA (15.9, 95% CrI [13.0, 20.0] s) conditions, with the probability that SD was greater in placebo being 0.64. In conclusion, the similarity in observed change score SDs between groups for TTE indicates the source of variation is common to both groups, and therefore unrelated to the supplement itself, likely originating instead from external factors such as nutritional intake, sleep patterns, or training status.

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Section: Discussionsupporting

confidence: 64%

Individual Participant Data Meta-Analysis Provides No Evidence of Intervention Response Variation in Individuals Supplementing With Beta-Alanine

Esteves

Swinton

Sale

et al. 2021

International Journal of Sport Nutrition and Exercise Metabolism

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“…However, our results also revealed non‐meaningful interindividual variability (i.e., positive SD IR values not exceeding the SWC; Table 1) or no evidence of interindividual differences in trainability (i.e., a negative SD IR value; Table 1) for roughly half of our outcomes (Table 1). These latter findings add to the growing body of evidence indicating that observed responses contain a large degree of random measurement error and/or within‐subject variability (Islam et al ., 2020 a ; Williamson et al., 2018) – observations that raise concerns for whether researchers, clinicians or coaches can accurately quantify an individual's true response to exercise training (Islam & Gurd, 2020). Accordingly, our findings suggest that it is inappropriate, and perhaps erroneous, to assume that variability in observed skeletal muscle responses to continuous exercise training reflects interindividual differences in trainability.…”

Section: Discussionmentioning

confidence: 99%

Examining interindividual differences in select muscle and whole‐body adaptations to continuous endurance training

Bonafiglia

Islam

Preobrazenski

et al. 2021

Experimental Physiology

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Studies have interpreted a wide range of morphological and molecular changes in human skeletal muscle as evidence of interindividual differences in trainability.However, these interpretations fail to account for the influence of random measurement error and within-subject variability. The purpose of the present study was to use the standard deviation of individual response (SD IR ) statistic to test the hypothesis that interindividual differences in trainability are present for some but not all skeletal muscle outcomes. Twenty-nine recreationally active males (age: 21 ± 2 years; BMI: 24 ± 3 kg/m 2 ; VO 2 peak ; 45 ± 7 ml/kg/min) completed 4 weeks of continuous training (REL; n = 14) or control (n = 15). Maximal enzyme activities (citrate synthase and β-hydroxyacyl-CoA dehydrogenase), capillary density, fibre type composition, fibre-specific succinate dehydrogenase activity and substrate storage (intramuscular triglycerides and glycogen), and markers of mitophagy (BCL2interacting protein 3 (BNIP3), BNIP3-like protein, parkin and PTEN-induced kinase 1)were measured in vastus lateralis samples collected before and after the intervention.We also calculated SD IR values for VO 2 peak , peak work rate and the onset of blood lactate accumulation for the REL group and a separate group that exercised at the negative talk test stage. Although positive SD IR values -indicating interindividual differences in trainability -were obtained for aerobic capacity outcomes, maximal enzyme activities, capillary density, all fibre-specific outcomes and BNIP3 protein content, the remaining outcomes produced negative SD IR values indicating a large degree of random measurement error and/or within-subject variability. Our findings question the interpretation of heterogeneity in observed responses as evidence of interindividual differences in trainability and highlight the importance of including control groups when analysing individual skeletal muscle response to exercise training.

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“…Inadvertently, the current literature is flooded with analyses that lack appropriate control conditions, potentially leading to incorrect conclusions. We hope this commentary, along with the original article by Islam and Gurd (2020), serves to increase awareness of the influence of random error and the importance of incorporating control conditions for proper data interpretation, particularly in the setting of secondary analyses focused on identifying responders versus nonresponders. Rigorous training in statistics and research methods, whether in the classroom, at conferences or more informally, through journal club discussions, should continue to be promoted among physiologists.…”

Section: Impact and Futurementioning

confidence: 99%

“…As elegantly articulated by Islam and Gurd in their recently published article entitled, ‘ Exercise response variability: Random error or true differences in exercise response? ’ (Islam & Gurd, 2020), an important consideration here is whether such heterogeneity in response to an intervention is attributed to: (i) a differential, but inherent, physiological response (one that is reproducible) among individuals; or (ii) the influence of random error (i.e., noise attributable to technical and/or biological sources). In such instances, close attention should also be paid to the statistical approach adopted for such secondary analysis, as elaborated below.…”

Section: The Problemmentioning

confidence: 99%

Identifying responders versus non‐responders: Incorporation of controls is required for sound statistical inference

Padilla

Leary

Limberg

2020

Experimental Physiology

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Exercise response variability: Random error or true differences in exercise response?

Cited by 7 publications

References 6 publications

Individual Participant Data Meta-Analysis Provides No Evidence of Intervention Response Variation in Individuals Supplementing With Beta-Alanine

Individual Participant Data Meta-Analysis Provides No Evidence of Intervention Response Variation in Individuals Supplementing With Beta-Alanine

Examining interindividual differences in select muscle and whole‐body adaptations to continuous endurance training

Identifying responders versus non‐responders: Incorporation of controls is required for sound statistical inference

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