Running endurance in 27-h-fasted humans

Area of Science:

• Exercise Physiology
• Sports Nutrition
• Human Performance

Background:

• Understanding the impact of fasting on endurance exercise is crucial for athletes.
• Previous research suggests metabolic and hormonal shifts occur during fasting.

Purpose of the Study:

• To investigate the effects of a 27-hour fast on endurance performance in male marathon runners.
• To identify the physiological, metabolic, and psychological factors contributing to performance decrements.

Main Methods:

• Nine male marathon runners completed two treadmill tests at 70% maximal oxygen uptake (VO2max).
• Tests were conducted in a randomized order: one after a 27-hour fast, and one after a pre-exercise meal.
• Data collected included oxygen uptake, heart rate, respiratory exchange ratio, blood metabolites (glucose, lactate, fatty acids, insulin, epinephrine, norepinephrine), muscle glycogen, and psychological fatigue ratings.

Main Results:

• Fasting decreased endurance performance by 44.7% (P < 0.01).
• Fasted state showed increased oxygen uptake, heart rate, perceived exertion, ventilation, and psychological fatigue within 60 minutes.
• Muscle glycogen degradation rates were similar, but fasted state had lower respiratory exchange ratio and higher free fatty acids.
• Increased norepinephrine, type I muscle fiber diameter, and ending insulin levels correlated with reduced endurance time in the fasted state.

Conclusions:

• A 27-hour fast significantly impairs endurance running performance.
• Performance decline is multifactorial, involving physiological, psychological, metabolic, and hormonal alterations.
• Norepinephrine, muscle fiber characteristics, and insulin levels are key correlates of fatigue during prolonged fasting and exercise.