Differences in activation patterns of knee flexor muscles during concentric and eccentric exercises

Area of Science:

• Biomechanics
• Sports Medicine
• Musculoskeletal Imaging

Background:

• Understanding knee flexor muscle activation is crucial for optimizing training and rehabilitation.
• Electromyography (EMG) and muscle functional magnetic resonance imaging (mfMRI) are key tools for assessing muscle function.

Purpose of the Study:

• To elucidate the activation patterns of knee flexor muscles during knee flexion exercises.
• To compare muscle activation using EMG and muscle physiological changes using mfMRI.

Main Methods:

• Seven male volunteers performed knee flexion exercises at 120% and 50% of 1 repetition maximum (1RM).
• EMG activity of biceps femoris long head, semitendinosus, semimembranosus, and gracilis was recorded.
• mfMRI T2 values of these muscles were measured at rest and post-exercise.

Main Results:

• Semitendinosus (ST) and gracilis (G) exhibited significantly higher EMG activity than semimembranosus (SM) at 120% 1RM.
• ST and G showed significantly greater mfMRI T2 value changes compared to biceps femoris long head (BFlh) and SM in both exercise intensities.
• Muscle activation patterns were nonuniform across the investigated knee flexor muscles.

Conclusions:

• Knee flexor muscle activation is not uniform during knee flexion exercises.
• The semitendinosus and gracilis muscles are more involved in knee flexion compared to the semimembranosus and biceps femoris long head under tested conditions.