Physiological differences between a noncontinuous and a continuous endurance training protocol in recreational runners and metabolic demand prediction

This study investigated the physiological difference in recreational runners between a noncontinuous and a continuous endurance training protocol. It also aimed to determine physiological surrogate that could monitor metabolic demand of prolonged running in real-time. For data collection, a total of 18 active male recreational runners were recruited. Physiological (HR, RR, RER, ṼO2, BLa), and overall perceptual (RPEO) responses were recorded against three designed test sessions. Session 1 included ṼO2submax test to determine critical speed (CS) at anaerobic threshold (AT). Session 2 was the noncontinuous CS test until exhaustion, having 4:1 min work-to-rest ratio at CS, whereas session 3 was the continuous CS test till exhaustion. As 1-min recovery during session 2 may change fatigue behavior, it was hypothesized that it will significantly change the physiological stress and hence endurance outcomes. Results reported average time to exhaustion (TTE) was 37.33(9.8) mins for session 2 and 23.28(9.87) mins for session 3. Participants experienced relatively higher metabolic demand (BLa) 6.78(1.43) mmol.l-1 in session 3 as compared to session 2 (5.52(0.93) mmol.l-1). RER was observed to increase in session 3 and decrease in session 2. Student's paired t-test only reported a significant difference in TTE, ṼO2, RER, RPEO, and BLa at "End" between session 2 and 3. Reported difference in RPEO and %HRmax at "AT" were 5 (2.2) and 89.8 (2.60)% during session 2 and 6 (2.5) and 89.8 (2.59)% during session 3, respectively. Regression analysis reported strong correlation of %HRmax (adj. R-square = 0.588) with BLa than RPEO (adj. R-square = 0.541). The summary of findings suggests that decreasing RER increased TTE and reduced BLa toward "End" during session 2 which might have helped to have better endurance. The %HRmax was identified to be used as a better noninvasive surrogate of endurance intensity estimator.