Oxygen consumption and heart rate responses during and after constant load and alternating intensity exercise at 105% of lactate threshold

The purpose of this study was a secondary-analysis of previously published data, in order to compare the acute VO2 responses, the time spent at high percentage of VO2max and total VO2 consumed (TVO2) between constant and alternating intensity exercise of the same intensity and duration. This study also aimed to examine VO2 and heart rate (HR) responses one hour after both exercises. Ten recreationally trained men (24.7±4.7 years) completed the following two exercise tests lasting an hour each and having the same mean intensity at 105% of lactate threshold (70% VO2max): 1) constant load cycling (CON), and 2) alternating intensity exercise (ALT), during which 40 seconds of light exercise (47% VO2max) were alternated with 20 seconds of supramaximal intensity at 120% of VO2max. TVO2 (69.89±7.02 vs. 58.22±9.13 mL/kg/min, P=0.03) and HR (142±16, 128±12, P=0.04) was higher in CON exercise compared to ALT. All participants reached 70% and 80% of VO2max irrespective of the exercise protocol. In ALT exercise the time spent at 90% was higher compared to CON exercise (70.81±21.37 vs. 36.88±11.88 seconds). Also, TVO2 recovery values after ALT exercise was higher compared to CON (11.1 ±2.93 vs. 9.94±3.54 mL/kg/min). ALT exercise allowed participants to spend longer time at 90% of VO2max, even if TVO2 in CON exercise was higher, suggesting that in ALT exercise greater aerobic stress (as based on exercise intensity) is imposed on the athletes. While VO2 recovery values were higher in ALT compared to CON, indicating different substrate utilization during and after exercise.