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The aim of this study was to compare the effects of time-efficient, low-volume interval exercises on cardiorespiratory capacity and left ventricular (LV) mass with traditional continuous exercise in sedentary adults.Forty-two healthy but sedentary male subjects (age 26.5 ± 6.2 yr) participated in an 8-wk, five times per week, supervised exercise intervention. They were randomly assigned to one of three exercise protocols: sprint interval training (SIT, 5 min, 100 kcal), high-intensity interval aerobic training (HIAT, 13 min, 180 kcal), and continuous aerobic training (CAT, 40 min, 360 kcal). Cardiorespiratory capacity (V˙O2max) and LV mass (3T-MRI) were measured preintervention and postintervention.We observed significant (P < 0.01) increases in V˙O2max in all three groups, and the effect of the HIAT was the greatest of the three (SIT, 16.7% ± 11.6%; HIAT, 22.5% ± 12.2%; CAT, 10.0% ± 8.9%; P = 0.01). There were significant changes in LV mass, stroke volume (SV), and resting HR in both the SIT (LV mass, 6.5% ± 8.3%; SV, 5.3% ± 8.3%; HR, −7.3% ± 11.1%; all P < 0.05) and HIAT (LV mass, 8.0% ± 8.3%; SV, 12.1% ± 9.8%; HR, −12.7% ± 12.2%; all P < 0.01) but not in the CAT (LV mass, 2.5% ± 10.1%; SV, 3.6% ± 6.6%; HR, −2.2% ± 13.3%; all P > 0.05).Our study revealed that V˙O2max improvement with the HIAT was greater than with the CAT despite the HIAT being performed with a far lower volume and in far less time than the CAT. This suggests that the HIAT has potential as a time-efficient training mode to improve V˙O2max in sedentary adults.