News & Views from the Editor-in-Chief: Andrew M. Jones
From this month’s issue of MSSE, I have chosen to highlight two studies which emphasize the importance of physical activity on health outcomes and the necessity of accounting for measurement variability when assessing individual responses to an exercise intervention.
While cardiorespiratory fitness (CRF) is inversely associated with all-cause mortality in women, less is known regarding the gradient of mortality risk in women, particularly at the lower end of the CRF continuum. In their article, ‘Examining the Gradient of All-Cause Mortality Risk in Women across the Cardiorespiratory Fitness Continuum’, Farrell et al. followed a sample of 17901 women (mean age of 46 years) who underwent a maximal treadmill test to measure fitness. A total of 1198 deaths occurred during the 18-year follow-up period. Beginning at the lowest point on the fitness continuum (4.5 METs), they observed a 10% decreased adjusted mortality risk per 1 MET increment, up to ~11 METs. At that point, women were about 50% less likely to die during follow-up compared to the least fit women. Beyond 11 METs, mortality risk essentially leveled off. Thus, small increments in CRF were associated with significant mortality risk reduction among low fit women, a finding that is very important from a public health perspective.
The extent to which individual variability in response to a standardized exercise dose is a consequence of differences in genotype or random day-to-day variability is the subject of considerable debate. In their article, ‘Towards Personalized Exercise Medicine: A Cautionary Tale’, Brennan et al. examined individual response to exercise in 338 adults across a range of cardiometabolic, body composition, and cardiorespiratory fitness outcomes. Individual response was interpreted using the technical error of measurement which includes both the day-to-day variability and instrument error calculated from a time-matched control group. Following intervention, less than 13% and 45% of adults improved cardiometabolic or cardiorespiratory fitness, respectively, beyond the day-to-day variability of measurement. The authors’ findings suggest caution when inferring that the cardiometabolic and cardiorespiratory fitness response for a given individual is attributable to the exercise dose prescribed. The authors call for improvements in trial design and assessment methodology to help reduce variability and improve the ability to determine an individual’s response to exercise alone.
Andrew M. Jones
University of Exeter