Toward Personalized Exercise Medicine: A Cautionary Tale.

Purpose: This study aimed to examine individual exercise response rates across a range of cardiometabolic variables, cardiorespiratory fitness, and body composition in adults.
Methods: A retrospective analysis of data from three randomized controlled trials was used in this study. Participants include those who completed the given trial (control, n = 87; intervention, n = 251). Anthropometric (weight, body mass index, waist circumference), cardiorespiratory fitness (V̇O 2peak ), MRI-measured total adipose tissue (AT), abdominal subcutaneous AT, and visceral AT and common cardiometabolic variables were assessed pre- and postintervention using standard methodologies. The technical error (TE), which includes both the day-to-day variability and instrument error, was calculated using pre- and postintervention data from the time-matched control group.
Results: On average, all anthropometric, MRI, and V̇O 2peak variables improved significantly after intervention compared with the control group ( P < 0.05). With the exception of glucose disposal rate (37%), after intervention less than 13% of participants improved cardiometabolic outcome measures beyond the day-to-day variability of measurement. In other words, the individual response for 63%-96% of participants fell within the uncertain range (2 TE). Similarly, for absolute V̇O 2peak (L·min -1 ), only 45% of participants improved beyond 2 TE. By comparison, for MRI-derived variables, the majority of participants (77%, 58%, and 51% for total AT, abdominal subcutaneous AT, and visceral AT, respectively) improved beyond 2 TE. The observed reductions beyond 2 TE for WC and body weight were 53% and 63%, respectively.
Conclusions: The findings suggest extreme caution when inferring that the cardiometabolic and cardiorespiratory fitness response for a given individual is attributable to the exercise dose prescribed.
(Copyright © 2022 by the American College of Sports Medicine.)