Calculating the standard deviation of individual responses (SD IR ) is recommended for estimating the magnitude of individual differences in training responsiveness in parallel‐arm exercise randomized controlled trials (RCTs). The purpose of this review article is to discuss potential limitations of parallel‐arm exercise RCTs that may confound/complicate the interpretation of the SD IR . To provide context for this discussion, we define the sources of variation that contribute to variability in the observed responses to exercise training and review the assumptions that underlie the interpretation of SD IR as a reflection of true individual differences in training responsiveness. This review also contains two novel analyses: (1) we demonstrate differences in variability in changes in diet and physical activity habits across an intervention period in both exercise and control groups, and (2) we examined participant dropout data from six RCTs and found that significantly ( P < 0.001) more participants in control groups (12.8%) dropped out due to dissatisfaction with group assignment compared to exercise groups (3.4%). These novel analyses raise the possibility that the magnitude of within‐subject variability may not be equal between exercise and control groups. Overall, this review highlights that potential limitations of parallel‐arm exercise RCTs can violate the underlying assumptions of the SD IR and suggests that these limitations should be considered when interpreting the SD IR as an estimate of true individual differences in training responsiveness.

Objective To determine the effects of exercise amount (kilocalories per session) and intensity (percent of maximal oxygen consumption [% VO2peak]) on adipose tissue (AT) and skeletal muscle (SM) in adults with abdominal obesity. Methods Participants (n = 103; 52.7 ± 7.6 years) were randomized to the following groups: control; low‐amount, low‐intensity exercise (180 kcal/session [women] and 300 kcal/session [men] at 50% VO2peak); high‐amount, low‐intensity exercise (HALI; 360 kcal/session [women] and 600 kcal/session [men] at 50% VO2peak); or high‐amount, high‐intensity exercise (HAHI; 360 kcal/session [women] and 600 kcal/session [men] at 75% VO2peak) for 24 weeks. Activities of daily living were measured by accelerometry. Magnetic resonance imaging was used to measure tissue mass. Results Reduction in all AT depots was greater in the exercise groups compared with control (P < 0.002); however, there were no differences between exercise groups (P > 0.05). Visceral and abdominal subcutaneous AT reduction was uniform across the abdomen. Total SM mass did not change with exercise compared with control (P = 0.32). However, while lower‐body SM mass was maintained (P = 0.32), upper‐body SM mass in the high‐amount, high‐intensity and the high‐amount, low‐intensity groups was reduced compared with controls (P < 0.008). Conclusions In adults with abdominal obesity, substantial reductions in total, abdominal subcutaneous, and visceral AT with a preservation of total SM mass were observed independent of exercise amount or intensity.

Purpose High throughput profiling of metabolic status (metabolomics) allows for the assessment of small-molecule metabolites that may participate in exercise-induced biochemical pathways and corresponding cardiometabolic risk modification. We sought to describe the changes in a diverse set of plasma metabolite profiles in patients undergoing chronic exercise training and assess the relationship between metabolites and cardiometabolic response to exercise. Methods secondary analysis was performed in 216 middle-aged abdominally obese men and women ([mean (SD)], 52.4 (8.0) years) randomized into one of four groups varying in exercise amount and intensity for 6 months duration: high amount high intensity, high amount low intensity, low amount low intensity, and control. 147 metabolites were profiled by liquid chromatography-tandem mass spectrometry. Results No significant differences in metabolite changes between specific exercise groups were observed; therefore, subsequent analyses were collapsed across exercise groups. There were no significant differences in metabolite changes between the exercise and control groups after 24 weeks at a Bonferroni-adjusted statistical significance (p < 3.0 × 10-4). Seven metabolites changed in the exercise group compared to the control group at p < 0.05. Changes in several metabolites from distinct metabolic pathways were associated with change in cardiometabolic risk traits, and three baseline metabolite levels predicted changes in cardiometabolic risk traits. Conclusion Metabolomic profiling revealed no significant plasma metabolite changes between exercise compared to control after 24-weeks at Bonferroni significance. However, we identified circulating biomarkers that were predictive or reflective of improvements in cardiometabolic traits in the exercise group.

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