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].
Highlights
In 1999, the seminal Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study reported individual cardiorespiratory fitness responses ranging from approximately −100 to +1,000 ml/min following 20 weeks of supervised and standardized aerobic exercise training (Bouchard et al, 1999)
Estimating interindividual variability requires partitioning the variability in outcome measurements caused by exercise training per se, referred to as interindividual differences in trainability, from the variability caused by random measurement error and within-subject variability (Bonafiglia et al, 2019a)
Most included studies had an unclear-high risk of bias
Summary
In 1999, the seminal Health, Risk Factors, Exercise Training, and Genetics (HERITAGE) Family Study reported individual cardiorespiratory fitness responses ranging from approximately −100 to +1,000 ml/min following 20 weeks of supervised and standardized aerobic exercise training (Bouchard et al, 1999). In 2015, biostatisticians recommended statistical approaches that estimate interindividual differences in trainability by partitioning error or within-subject variability (Atkinson and Batterham, 2015; Hecksteden et al, 2015; Hopkins, 2015). Many reviews have used data simulations or theoretical arguments to emphasize the importance of partitioning error or within-subject variability to encourage researchers to adopt these statistical approaches (Williamson et al, 2017; Swinton et al, 2018; Atkinson et al, 2019; Bonafiglia et al., 2019a; Ross R. et al, 2019; Voisin et al, 2019; ChrzanowskiSmith et al, 2020; Dankel and Loenneke, 2020). 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
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