Clinical and physiological effects of high-intensity aerobic training on metabolic syndrome: understanding the individual exercise response variability

We analyzed the interindividual heterogeneity in health responses to a supervised high-intensity interval training (HIIT) program in individuals with metabolic syndrome (MetS). Two hundred and sixty-four adults with overweight/obesity (56.3 ± 7.3 yr, body mass index: 32.3 ± 4.7 kg/m²) and MetS were randomized to a standard health care nonexercise group (CONT group, <i>N</i> = 58) or standard health care plus HIIT (EXER group, <i>N</i> = 206). HIIT intervention was performed on a cycloergometer thrice a week (43 min/session). MetS components (i.e., MetS <i>z</i> score), cardiorespiratory fitness (V̇o_2peak), maximal cycling power (W_PEAK), and body weight/composition was assessed in both groups before (0 wk) and after the intervention (16 wk). Individual responses in the EXER group were considered attributable to HIIT when the improvements were larger than twice the typical error (>2TE). TE was calculated using pre- and postintervention data from the time-matched CONT group. The percentage of participants who improved MetS <i>z</i> score beyond 2TE was 51% driven by reductions in blood pressure (45%) and waist circumference (48%). Blood lipids and glucose response were only 21% and 16%, respectively (participants improving beyond 2TE). Sixty percent of individuals who improved MetS <i>z</i> score also improved V̇o_2peak (<i>r</i> = -0.013; <i>P</i> = 0.86), whereas 85% of individuals improving MetS <i>z</i> score also improved W_PEAK (<i>r</i> = 0.151; <i>P</i> = 0.03). In summary, health providers can expect that a 16-wk HIIT program would indisputably improve MetS in approximately 50% of individuals completing the program. Finally, W_PEAK better predicts which individuals would improve MetS than V̇o_2peak when the direct assessment of the five MetS factors is not feasible.<b>NEW & NOTEWORTHY</b> Our study offers healthcare providers the expected percentage of individuals who would improve their metabolic syndrome condition after completing a standardized HIIT program (16 wk, 43 min/session, 3 days/wk). Only half of the subjects achieved indisputable improvement in their MetS <i>z</i> score when we accounted for biological variability and instrument errors. Detection of individuals with a positive response in MetS <i>z</i> score could be inferred from gains in maximal cycling power (i.e., exercise functionality).