A Systematic Review Examining the Approaches Used to Estimate Interindividual Differences in Trainability and Classify Individual Responses to Exercise Training

Abstract

Background: Many reports describe statistical approaches for estimating interindividual differences in trainability and classifying individuals as “responders” or “non-responders.” The extent to which studies in the exercise training literature have adopted these statistical approaches remains unclear.Objectives: This systematic review primarily sought to determine the extent to which studies in the exercise training literature have adopted sound statistical approaches for examining individual responses to exercise training. We also (1) investigated the existence of interindividual differences in trainability, and (2) tested the hypothesis that less conservative thresholds inflate response rates compared with thresholds that consider error and a smallest worthwhile change (SWC)/minimum clinically important difference (MCID).Methods: We searched six databases: AMED, CINAHL, EMBASE, Medline, PubMed, and SportDiscus. Our search spanned the aerobic, resistance, and clinical or rehabilitation training literature. Studies were included if they used human participants, employed standardized and supervised exercise training, and either: (1) stated that their exercise training intervention resulted in heterogenous responses, (2) statistically estimated interindividual differences in trainability, and/or (3) classified individual responses. We calculated effect sizes (ESIR) to examine the presence of interindividual differences in trainability. We also compared response rates (n = 614) across classification approaches that considered neither, one of, or both errors and an SWC or MCID. We then sorted response rates from studies that also reported mean changes and response thresholds (n = 435 response rates) into four quartiles to confirm our ancillary hypothesis that larger mean changes produce larger response rates.Results: Our search revealed 3,404 studies, and 149 were included in our systematic review. Few studies (n = 9) statistically estimated interindividual differences in trainability. The results from these few studies present a mixture of evidence for the presence of interindividual differences in trainability because several ESIR values lay above, below, or crossed zero. Zero-based thresholds and larger mean changes significantly (both p < 0.01) inflated response rates.Conclusion: Our findings provide evidence demonstrating why future studies should statistically estimate interindividual differences in trainability and consider error and an SWC or MCID when classifying individual responses to exercise training.Systematic Review Registration: [website], identifier [registration number].

Progressive resistance training for children with cerebral palsy: A randomized controlled trial evaluating the effects on muscle strength and morphology

“…For example on the impairment level, muscle weakness, muscle size and the contribution of muscle size deficits to muscle weakness showed inter-individual variation ( Hanssen et al, 2021 ). Moreover, in adult populations, PRT has been shown to cause a wide range of responses ( Hubal et al, 2005 ; Ahtiainen et al, 2016 ; Bonafiglia et al, 2021 ). Therefore, it might be interesting for future research to identify which child might respond well to PRT based on baseline characteristics like age, gender, SMC, functional ability, topographical distribution, strength or muscle size deficits.…”

Human skeletal muscle mitochondrial responses to single‐leg intermittent or continuous cycle exercise training matched for absolute intensity and total work

“…Renewed interest in the topic of physiological responses to INT training 3 has reignited debate regarding the nature of the exercise stimulus for promoting training‐induced increases in mitochondrial content 4,5 . A limitation inherent to between‐group comparisons of INT and CONT training is inter‐individual differences in training responses 6 . One strategy to address this concern is the use of unilateral exercise to facilitate a within‐subject comparison of responses to two different training interventions, that is, between limbs 7 .…”

“…4,5 A limitation inherent to between-group comparisons of INT and CONT training is inter-individual differences in training responses. 6 One strategy to address this concern is the use of unilateral exercise to facilitate a within-subject comparison of responses to two different training interventions, that is, between limbs. 7 MacInnis et al 8 showed using a singleleg cycling model that short-term INT training elicited superior increases in biomarkers of mitochondrial content compared to CONT training matched for total work.…”

Inter-individual variations in response to aerobic and resistance training in hypertensive older adults

“…In order to reduce the risk of misclassifying participants, responders should be classified as individuals whose observed change in a given outcome exceeds the minimal clinical important difference (MCID) after accounting for random measurements (a.k.a. technical errors) [14]. Methods that do not consider MCID and technical errors may, therefore, inflate response rates [14].…”