Physiological responses to "all-out" and even-paced cycling intervals

Emma Zadow

Background: Endurance cyclists typically devote ~20% of their training regimens to performing low-volume high-intensity interval training which is associated with large physiological and performance benefits. The relationship between intensity and duration is important during high-intensity interval training as both can profoundly influence metabolic energy expenditure, fatigue development and subsequent adaptations. Purpose: Within the literature, most interval training is delivered using either an "all-out" or even-paced approach; however, to the author’s knowledge no study has yet compared the metabolic stress, perceived exertion and fatigue resulting from such intervals. Therefore, this study compared the physiological and perceptual responses to matched mechanical work interval bouts using “all-out” and two different even-paced methodologies (i.e. computer- and athlete-controlled). Methods: In a randomised design, 15 male trained cyclists (age: 39 ± 8 years, body mass: 79.4 ± 8.2kg, VO2max: 59.8 ± 6.5 ml•kg-1•min-1, peak power: 436 ± 27 W) performed one incremental maximal exercise test, one familiarisation session and three experimental high-intensity interval sessions implementing one of three pacing strategies; (i) “all-out”, (ii) computer-controlled and (iii) athlete-controlled. All experimental sessions were work- matched and consisted of three 3-minute intervals with three minutes of recovery. A 4 km time trial was completed twenty minutes following each experimental interval session to assess measured levels of latent fatigue. Oxygen consumption, heart rate and perceived exertion, pain and effort were recorded throughout the high-intensity interval sessions with average power output and heart rate measured throughout the 4 km time trial. Results: Overall greater (p<0.001) oxygen consumption was observed in the “all-out” condition (54.1 ± 6.6 ml.kg-1.min-1) compared with the computer- (51.5 ± 5.7 ml.kg-1.min-1) and athlete-controlled conditions (53.0 ± 5.8 ml.kg-1.min-1). Furthermore, the time spent at 85% VO2max was greater (p<0.001) during the “all-out” trial when compared with computer- and athlete-controlled trials. Sessional perceived exertion was greater in the “all-out” trial when compared with the computer- (p<0.001) and athlete-controlled (p<0.05) conditions. Average power output measured during the 4 km time trial was lower (p<0.001) after the “all-out” session compared with both even-pacing strategies. Conclusion: Our findings indicate irrespective of work completed, greater physiological stress was observed within an “all-out” interval training approach when compared with both athlete- and computer- controlled conditions, resulting in greater latent fatigue as measured by 4 km time trial performance. The selections of pacing strategies are likely to play a key role in interval training and should be acknowledged throughout exercise prescription.

Physiological responses to "all-out" and even-paced cycling intervals

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