Increased Morning Heart Rate in Runners: A Valid Sign of Overtraining?

Area of Science:

• Sports Medicine
• Exercise Physiology
• Endurance Sports

Background:

• Elevated resting pulse rate is a recognized indicator of overtraining in endurance athletes.
• Athletes often increase training volume significantly, particularly during ultramarathon events.

Purpose of the Study:

• To investigate the relationship between extreme endurance running and resting heart rate.
• To determine if increased training mileage during a 500km road race impacts morning heart rate.

Main Methods:

• 12 male athletes participated in a 20-day, 500km road race.
• Morning heart rates were monitored throughout the event.
• Physiological markers including blood pressure, temperature, body weight, and blood analytes were assessed.

Main Results:

• Morning heart rates initially decreased slightly in the first week.
• Subsequently, heart rates progressively increased, reaching 10 beats min(-1) higher by the race's end (p <.01).
• No significant correlations were found between heart rate changes and blood pressure, temperature, body weight, sweat loss, or blood markers (glucose, lactate, insulin, cortisol).

Conclusions:

• The study supports the assumption that elevated resting heart rate is a marker of overtraining in endurance athletes.
• Significant increases in morning heart rate during prolonged high-mileage running indicate physiological stress.
• Further research may explore specific physiological mechanisms beyond the measured parameters.