Susceptibility to Exercise-Induced Muscle Damage: a Cluster Analysis with a Large Sample.

Area of Science:

• Exercise physiology
• Muscle damage research
• Biomarker validation

Background:

• Exercise-induced muscle damage (EIMD) is commonly assessed using indirect markers.
• Maximal voluntary contraction torque (MVC) is a direct measure of muscle function.
• Individual responses to eccentric exercise vary significantly.

Purpose of the Study:

• To investigate the relationship between MVC decrease and indirect EIMD markers.
• To determine if stratifying individuals by MVC response improves marker precision.
• To validate indirect markers of EIMD in relation to MVC decline.

Main Methods:

• 286 young men performed maximal eccentric elbow flexion exercise.
• Participants were clustered into low, moderate, and high MVC decrease groups (LR, MR, HR).
• Changes in MVC, muscle soreness (SOR), creatine kinase (CK), range of motion (ROM), and upper-arm circumference (CIR) were measured post-exercise.

Main Results:

• Cluster centers for MVC decrease were 82% (LR), 61% (MR), and 42% (HR) of baseline.
• All indirect markers (SOR, CK, ROM, CIR) showed significant differences between clusters.
• The magnitude of change in indirect markers followed the pattern: LR < MR < HR.

Conclusions:

• Stratifying individuals by MVC decrease magnitude significantly increases the precision of indirect EIMD markers.
• Commonly used indirect markers (SOR, CK, ROM, CIR) are valid for assessing EIMD.
• MVC decline orchestrates the response of indirect markers, confirming MVC as the primary EIMD indicator.