Circadian rhythms in blood lactate concentration during incremental ergometer rowing

Area of Science:

• Exercise Physiology
• Chronobiology

Background:

• Lactate threshold (Th(lac)) is a critical performance indicator in endurance sports.
• Understanding factors influencing Th(lac) variability is essential for precise athlete assessment.

Purpose of the Study:

• To investigate the influence of circadian rhythms on lactate threshold (Th(lac)) during rowing exercise.
• To determine optimal timing for Th(lac) assessment in endurance athletes.

Main Methods:

• Eleven male endurance-trained athletes performed incremental rowing tests at six different times of day (0200, 0600, 1000, 1400, 1800, 2200 hours).
• Lactate threshold was determined using the Dmax method, visual inspection (Th(lac-vis)), and a fixed blood lactate concentration of 4.0 mmol/L (Th(lac-4 mM)).
• Capillary blood lactate levels were measured, alongside oxygen consumption and heart rate.

Main Results:

• Circadian variations were observed in oxygen consumption and heart rate at Th(lac) when determined by the Dmax method (P=0.02 and P=0.04, respectively).
• The acrophases for these variables aligned with core body temperature rhythms, suggesting a circadian influence.
• No significant circadian effect was noted for Th(lac-vis) or Th(lac-4 mM).

Conclusions:

• Circadian rhythms demonstrably affect lactate threshold determination, particularly when using the Dmax method.
• To ensure accurate Th(lac) assessment, athletes should perform tests at the same time of day as their regular training sessions.
• Standardizing test timing is crucial for reliable performance monitoring in endurance athletes.