Exercise metabolism in human skeletal muscle exposed to prior eccentric exercise

Area of Science:

• Exercise Physiology
• Muscle Metabolism
• Sports Science

Background:

• Eccentric exercise, characterized by muscle lengthening under tension, can induce muscle damage and alter metabolic responses.
• Understanding the metabolic consequences of unaccustomed eccentric exercise is crucial for optimizing training and recovery strategies.

Purpose of the Study:

• To investigate the metabolic effects of unaccustomed eccentric exercise on subsequent concentric exercise performance and substrate utilization.
• To determine how prior eccentric contractions influence muscle glycogen and glucose metabolism during dynamic exercise.

Main Methods:

• Seven healthy males underwent unilateral eccentric exercise, followed 2 days later by bilateral concentric knee-extensor exercise.
• Blood samples and muscle biopsies were collected to analyze substrate levels, glucose uptake, and transporter expression.
• Maximal exercise capacity was assessed in both the previously exercised and control limbs.

Main Results:

• Maximal concentric exercise capacity was reduced by 23% in the eccentric thigh.
• Resting muscle glycogen was lower in the eccentric thigh and depleted more significantly after exercise.
• Impaired triacylglycerol breakdown and altered lactate release were observed in the eccentric thigh, despite similar glucose transporter (GLUT4) expression and transport capacity.

Conclusions:

• Prior unaccustomed eccentric exercise leads to reduced muscle glycogen availability and impaired fat metabolism.
• The increased relative workload on damaged muscle accelerates glycogen utilization, contributing to diminished endurance capacity.
• Muscle glucose uptake and GLUT4 transporter function remain largely unaffected during subsequent concentric exercise.