Directions for Exercise Treatment Response Heterogeneity and Individual Response Research

Abstract

Treatment response heterogeneity and individual responses following exercise training are topics of interest for personalized medicine. Proposed methods to determine the contribution of exercise to the magnitude of treatment response heterogeneity and categorizing participants have expanded and evolved. Setting clear research objectives and having a comprehensive understanding of the strengths and weaknesses of the available methods are vital to ensure the correct study design and analytical approach are used. Doing so will ensure contributions to the field are conducted as rigorously as possible. Nonetheless, concerns have emerged regarding the ability to truly isolate the impact of exercise training, and the nature of individual responses in relation to mean group changes. The purpose of this review is threefold. First, the strengths and limitations associated with current methods for quantifying the contribution of exercise to observed treatment response heterogeneity will be discussed. Second, current methods used to categorize participants based on their response to exercise will be outlined, as well as proposed mechanisms for factors that contribute to response variation. Finally, this review will provide an overview of some current issues at the forefront of individual response research.

Resistance training and inter-interindividual response differences on cardiorespiratory fitness in older adults: An ancillary meta-analysis of randomized controlled trials

“…However, selection of a lower or higher MCID would have yielded different results for both IIRD and treatment effect analyses. Fourth, while the standard deviation of individual response approach has been recommended for examining IIRD, 54 , 55 a limitation of this method, despite random assignment, is that it is based on the assumption that random and within-subject variation is the same between an intervention and control group. 80 Fifth, while 95% PI's have been suggested to provide more accurate information regarding how much effect sizes vary across studies, 49 they are negatively affected when sample sizes are small and the data in a meta-analysis are not normally distributed.…”

“…53 IIRD meta-analysis. Based on previous recommendations, 54,55 the standard deviation of individual response approach (SD ir ), an absolute difference method, was chosen over others for the primary aim of this study, i.e. an IIRD meta-analysis for changes in VO 2max in ml .…”

Evidence-based yet still challenging! Research on physical activity in old age

“…Compared to other age groups, old age is typified by increased heterogeneity, which complicates research [14] and renders practice harder to conduct [15]. This heterogeneity is typical of physical performance (e.g., [16]), as well as cognitive (e.g., [17]) and behavioral (e.g., [18]) performance.…”

“…Yet even more complex for research and practice are the intra-individual variations [20], which are associated with the measuring of a single person in either multiple tasks (dispersion) or in a single task yet on multiple occasions (inconsistency) [17]. Such inter-and intra-individual differences have also been reported in response to PA, yet scientific understanding is still limited with regards to the characteristics that could help identify responders and nonresponders [15,22,23]. Identifying principal biological and behavioral markers of responsiveness to PA interventions could significantly enhance clinicians' ability to prescribe PA in a more individualized and effective manner [15].…”

“…Such inter-and intra-individual differences have also been reported in response to PA, yet scientific understanding is still limited with regards to the characteristics that could help identify responders and nonresponders [15,22,23]. Identifying principal biological and behavioral markers of responsiveness to PA interventions could significantly enhance clinicians' ability to prescribe PA in a more individualized and effective manner [15].…”