“Precision Exercise Medicine: Understanding Exercise Response Variability”, Robert Ross, Bret H. Goodpaster, Lauren G. Koch, Mark A. Sarzynski, Wendy M. Kohrt, Neil M. Johannsen, James S. Skinner, Alex Castro, Brian A. Irving, Robert C. Noland, Lauren M. Sparks, Guillaume Spielmann, Andrew G. Day, Werner Pitsch, William G. Hopkins, Claude Bouchard2019-09 (; similar)⁠:

There is evidence from human twin and family studies as well as mouse and rat selection experiments that there are considerable interindividual differences in the response of cardiorespiratory fitness (CRF) and other cardiometabolic traits to a given exercise programme dose. We developed this consensus statement on exercise response variability following a symposium dedicated to this topic. There is strong evidence from both animal and human studies that exercise training doses lead to variable responses. A genetic component contributes to exercise training response variability.

In this consensus statement, we (1) briefly review the literature on exercise response variability and the various sources of variations in CRF response to an exercise programme, (2) introduce the key research designs and corresponding statistical models with an emphasis on randomized controlled designs with or without multiple pretests and post-tests, crossover designs and repeated measures designs, (3) discuss advantages and disadvantages of multiple methods of categorizing exercise response levels-a topic that is of particular interest for personalized exercise medicine and (4) outline approaches that may identify determinants and modifiers of CRF exercise response. We also summarise gaps in knowledge and recommend future research to better understand exercise response variability.

Figure 1: Preclinical animal model evidence for variation in training response: (A) frequency distribution for the change in running capacity (ΔDIST) for 152 genetically heterogeneous N/NIH rats shown in ascending order (males and females combined). The lowest and highest 10<sup>th</sup> percentile animals were used as founders to start low response trainer (LRT) and high response trainer (HRT) selected lines. Dotted line indicates the population mean change in running capacity with training. (B) Percentile rank score for the change in running capacity (ΔDIST) for LRT rats from generation 15 of selection arranged from lowest to highest. (C) Percentile rank score for the ΔDIST for HRT rats from generation 15 of selection arranged from lowest to highest. Dotted lines indicate the mean change in running capacity for the LRT and HRT selected lines. Adapted from Koch et al 2013.
Figure 1: Preclinical animal model evidence for variation in training response: (A) frequency distribution for the change in running capacity (ΔDIST) for 152 genetically heterogeneous N/NIH rats shown in ascending order (males and females combined). The lowest and highest 10th percentile animals were used as founders to start low response trainer (LRT) and high response trainer (HRT) selected lines. Dotted line indicates the population mean change in running capacity with training. (B) Percentile rank score for the change in running capacity (ΔDIST) for LRT rats from generation 15 of selection arranged from lowest to highest. (C) Percentile rank score for the ΔDIST for HRT rats from generation 15 of selection arranged from lowest to highest. Dotted lines indicate the mean change in running capacity for the LRT and HRT selected lines. Adapted from Koch et al 2013.

…Human studies designed to investigate CRF response variability: The vast majority of studies on the effects of chronic exercise on CRF focus on main effects and group differences and ignore interindividual CRF response variability. Studies specifically designed to determine the variability of response to exercise report an extraordinary heterogeneity in CRF response. There is variability in improvement to a standardized dose of exercise ranging from no gain in VO2max to about 1 L improvement of O2 uptake.

Here we summarise the findings of selected studies that examined individual variability in CRF (VO2max) response to endurance-type exercise training. The selection criteria used to identify suitable trials included: (1) recruitment of previously sedentary adults, (2) exercise interventions were standardized and supervised, (3) intervention duration was 12 weeks or greater, (4) study examined variability in CRF response and (5) included aerobic/endurance-type exercise. Combination (endurance and resistance) and resistance-only exercise were not considered. 8 studies met the inclusion criteria, with all but 2 having sample sizes of at least 30 participants (range 18–720). Table 1 provides a description of the study designs, exercise programmes, study population and mean change in CRF.