Knee extensor fatigue developed during high-intensity exercise limits lower-limb power production.

Area of Science:

• Sports Science
• Exercise Physiology
• Biomechanics

Background:

• Muscle fatigue significantly impacts athletic performance, particularly in high-intensity cycling.
• Understanding the relationship between muscle activation patterns and fatigue is crucial for optimizing training and performance.

Purpose of the Study:

• To investigate the association between vastii electromyography (EMG) changes and knee extensor fatigue during high-intensity cycling.
• To determine the effect of this fatigue on lower-limb power and intermuscular coordination during subsequent all-out cycling.

Main Methods:

• Participants underwent high-intensity cycling protocols followed by all-out cycling tests.
• Electromyography (EMG) of major leg muscles (gluteus maximus, rectus femoris, vastii, hamstrings, gastrocnemius) was recorded.
• Isometric maximal voluntary force (IMVF) and resting twitch of knee extensors were measured, alongside muscle co-activation patterns.

Main Results:

• Increases in vastii EMG during high-intensity cycling correlated negatively with knee extensor force loss.
• Decreased knee extensor force was positively correlated with reduced all-out cycling power.
• Vastii and gastrocnemius EMG decreased during all-out cycling, while their co-activation remained stable.

Conclusions:

• Greater vastii EMG increase during high-intensity cycling is linked to more significant knee extensor fatigue and power reduction.
• High vastii/gastrocnemius co-activation may play a protective role, limiting power loss during intense cycling efforts despite knee extensor fatigue.