Abstract 10704: Myocardial Mass Increases with both Sprint- and Aerobic-type Interval Exercise but not with a Traditional, Continuous Aerobic Exercise in Sedentary Adults: An 8-week Randomized Intervention Study

Abstract

Introduction: Modern, time-pressed, sedentary adults require a time-efficient exercise protocol. Previous studies indicate that sprint interval training (SIT) improves maximal oxygen consumption (VO_2max) mainly through increased oxidative capacity in peripheral muscles, whereas, high-intensity interval aerobic training (HIAT) improves VO_2max mainly through improved cardiac function. We tested the hypotheses that (1) SIT and HIAT had greater effects on VO_2max than did traditional continuous aerobic training (CAT), and that (2) left ventricular myocardial mass (LVM) increased only through HIAT.

Methods: Forty-two healthy but sedentary male subjects (age, 26.5 ± 6.2 years; BMI, 21.3 ± 1.9 kg·m^-2; VO_2max, 42.6 ± 6.3 ml·kg^-1·min^-1; LVM, 105.0 ± 15.7 g) participated in an 8-week, 5 times/wk, supervised exercise intervention study. They were randomly assigned to each (n = 14) of the 3 exercise protocols: SIT (total 5 min) consisting of 7 sets of 30-s cycling at 110∼120% VO_2max with a 15-s rest between sets; HIAT (total 13 min) consisting of 3 sets of 3-min cycling at 80∼90% VO_2max with a 2-min active rest at 50% VO_2max between sets; and CAT consisting of 40 min of cycling at 60∼65% VO_2max. We originally developed both the SIT and HIAT protocols for sedentary individuals in our laboratory. We measured VO_2max by indirect calorimeter and LVM by 3T-MRI before and after the intervention.

Results: No differences were observed at baseline across the three groups in any of the measures. All subjects completed the 8-week exercise training. There was a significant (P = 0.01) difference between the groups in increased VO_2max (SIT, 16.7 ± 11.6%; HIAT, 22.5 ± 12.2%; CAT, 10.0 ± 8.9%). Whereas, we observed significant changes in LVM and resting heart rate (HR) in both the SIT (LVM, +6.5 ± 8.3%; HR, -7.3 ± 11.1%, both P = 0.02) and HIAT (LVM, +8.0 ± 8.3%; HR, -12.7 ± 12.2%, both P < 0.01) groups, but not in the CAT group (LVM, +2.5 ± 10.1%; HR, -2.2 ± 13.3%).

Conclusions: HIAT had the greatest effect on VO_2max of the three protocols, but the LVM increased significantly with both the HIAT and the SIT. Both our SIT and HIAT may be useful, time-efficient exercise protocols to improve cardiac activity for sedentary adults.