The effect of sex on the cardiopulmonary and neuromuscular response to high-intensity interval exercise

Sex differences exist in the integrative response to exercise; however, these are typically researched during incremental and constant-load exercise. Interval exercise involves high-intensity efforts interspersed with recovery periods to repeatedly stress physiological systems, and it is currently unknown whether the response to this form of exercise differs between sexes. Ten males and 10 females (age: 25 ± 3 yr) completed two experimental visits. First, an incremental treadmill exercise test was performed to obtain submaximal (lactate threshold) and maximal (V̇o_2peak) data. Thereafter, visit two involved 4 × 3-min running intervals at 90% of the final incremental test velocity (vV̇o_2peak), with 90-s rest between intervals. Before exercise and after each interval, maximal voluntary contraction (MVC), quadriceps potentiated twitch (<i>Q</i>_tw.pot), and voluntary activation (VA) were recorded. The rates of oxygen uptake (V̇o₂), carbon dioxide production (V̇co₂), and ventilation (V̇e) were continuously recorded throughout. There was no sex difference in relative V̇o_2peak (males: 47.2 ± 6.0 vs. females: 44.4 ± 5.8 mL·kg^-1·min^-1, <i>P</i> = 0.292). When expressed relative to peak values, there were no sex differences in the V̇o₂ or V̇co₂ response to the interval task (<i>P</i> ≥ 0.781). Females had greater V̇e/V̇o₂, and V̇e/V̇co₂ values during the first (<i>P</i> ≤ 0.034) and second (V̇e/V̇co₂, <i>P</i> = 0.006) intervals, with a sex × time interaction effect (<i>P</i> ≤ 0.046). There were no sex differences in the reductions in MVC, <i>Q</i>_tw.pot, and VA during the interval task (<i>P</i> ≥ 0.150); however, females had lesser reductions in <i>Q</i>_tw.pot values postexercise (-24 ± 9 vs. -15 ± 8%, <i>P</i> = 0.044). Sex differences exist in the physiological response to interval exercise. Compared with males, females experienced greater hyperpnea during the initial stages, and had lesser decreases in contractile function postexercise.<b>NEW & NOTEWORTHY</b> This study determined that males and females differ in the physiological response to high-intensity interval exercise. Specifically, females had poorer ventilatory efficiency during the first half of the task, but greater knee-extensor fatigue resistance following the task. These data build upon previous observations from constant-load exercise, demonstrating that physiological sex differences are observed during an ecologically valid exercise task commonly prescribed by practitioners in clinical and athletic populations.