The effect of diurnal variation on the performance of exhaustive continuous and alternated-intensity cycling exercises

The purpose of this study was to explore the effect of time of day (TD) on two types of exercise protocols [continuous (CP) versus alternated (AP)]. Eleven physical education students (mean +/- SD: age = 24.4 +/- 1.2 years, aerobic peak power (APP) = 290 +/- 31.9 W) underwent four sessions. These sessions were performed at 08:00 (AM) and 18:00 (PM) and consisted of cycling exercises until voluntary exhaustion at 90% APP (CP) or 70%-105% APP (AP) with the order of testing randomly assigned. Time to exhaustion (time limit = Tlim) was measured from the start of the test to when voluntary exhaustion occurred. Heart rate (HR) was recorded at baseline (HRbaseline) and throughout the protocols to determine HR at exhaustion (HRpeak). Blood lactate ([La]) was measured at rest, immediately after exhaustion and at 2min30 post-exercise to determine [La]peak. A significantly higher means of Tlim (334 +/- 57 s; 272 +/- 59 s; p< 0.05), HRbaseline (72 +/- 5 beats/min; 67 +/- 5 beats/min; p< 0.01), HRpeak (186 +/- 8 beats/min; 178 +/- 9 beats/min; p< 0.01) and [La]peak (16.2 +/- 2.1 mmol/l; 13.9 +/- 1.9 mmol/l; p< 0.05) were observed in CP at the PM compared to the AM. In addition, a significant higher means of Tlim (380 +/- 54 s; 312 +/- 82 s; p< 0.05), HRbaseline (73.1 +/- 5.5 beats/min; 67 +/- 5.4 beats/min; p< 0.01), HRpeak (186 +/- 8 beats/min; 180 +/- 9 beats/min; p< 0.05) and [La]peak (17.9 +/- 1.8 mmol/l; 14.7 +/- 2.1 mmol/l; p< 0.01) were observed in AP at the PM compared to the AM. It is concluded that AP and CP are more appropriate in the late afternoon than in the morning for performing long-lasting exercises. The AP could be a novel strategy for increasing the engagement in physical activity.