Muscle Glycogen Content during Endurance Training under Low Energy Availability

Area of Science:

• Sports Medicine
• Exercise Physiology
• Nutritional Science

Background:

• Understanding the physiological impact of energy availability is crucial for optimizing athletic performance and health.
• Low energy availability (LEA) is a condition where energy intake is insufficient to meet the energy demands of the body, potentially affecting training adaptations.
• Endurance training requires adequate energy stores, particularly muscle glycogen, for sustained performance.

Purpose of the Study:

• To investigate the effects of three consecutive days of endurance training under low energy availability (LEA) on male runners.
• To assess changes in muscle glycogen content, muscle damage markers, endocrine regulation, and endurance capacity.
• To compare the outcomes of LEA with normal energy availability (NEA) conditions.

Main Methods:

• Seven male long-distance runners participated in a randomized crossover trial.
• Participants completed three consecutive days of 75-minute treadmill running at 70% of maximal oxygen uptake (V˙O2max) under either LEA (18.9 kcal·kg FFM·d) or NEA (52.9 kcal·kg FFM·d).
• Measurements included body weight, fat-free mass, skeletal muscle volume, muscle glycogen content, and time to exhaustion on day 4.

Main Results:

• Three days of LEA significantly reduced body weight, fat-free mass, and skeletal muscle volume.
• Muscle glycogen content was significantly decreased by approximately 30% under LEA compared to NEA.
• Despite reduced glycogen stores, time to exhaustion was not significantly different between LEA and NEA conditions.

Conclusions:

• Three consecutive days of endurance training under LEA leads to decreased muscle glycogen content and body weight.
• Endurance capacity, as measured by time to exhaustion, was not significantly impaired by LEA in this study.
• Further research is needed to understand the long-term implications and adaptive mechanisms related to LEA in endurance athletes.