Comparing continuous and intermittent exercise: an "isoeffort" and "isotime" approach

Area of Science:

• Exercise Physiology
• Sports Science

Background:

• Traditional methods for comparing continuous and intermittent exercise often lack control for overall effort and duration.
• This limitation can confound the interpretation of physiological responses and performance outcomes.

Purpose of the Study:

• To propose and validate an alternative method for comparing continuous and intermittent exercise.
• To ensure similar between-protocol overall effort (isoeffort) and total exercise duration (isotime).
• To investigate the effects of different work-to-rest ratios on physiological responses in competitive cyclists.

Main Methods:

• Fourteen competitive cyclists performed four 30-minute self-paced protocols: one continuous and three intermittent (40:20s, 30:30s, 20:40s work-to-rest ratios).
• A maximal session effort prescription was used, with isoeffort and isotime conditions maintained.
• Physiological responses including oxygen uptake, heart rate, blood lactate, and respiratory frequency were measured.

Main Results:

• Continuous exercise resulted in higher total work, oxygen uptake, and heart rate, but lower lactate levels compared to intermittent exercise.
• Decreasing the work-to-rest ratio in intermittent exercise led to reduced total work, oxygen uptake, and heart rate, with increased lactate.
• Ventilatory responses were similar across protocols, with a strong correlation between respiratory frequency and perceived exertion.

Conclusions:

• Controlling for both isoeffort and isotime is crucial for accurately comparing continuous and intermittent exercise protocols.
• Work-to-rest ratio manipulation in intermittent exercise elicits different physiological responses than previously reported using traditional comparison methods.
• Respiratory frequency may serve as a more reliable indicator of physiological strain during intermittent exercise than oxygen uptake, heart rate, or blood lactate.