The muscle activity paradox during circular rhythmic leg movements

Area of Science:

• Biomechanics
• Sports Science
• Human Physiology

Background:

• Cycling involves complex lower limb movements combining joint rotation and upper body translation.
• Electromyography (EMG) readings during pedaling suggest an 'anatomical paradox' with flexor muscle activity during the leg extension phase.
• This apparent paradox requires further investigation to understand muscle activation patterns in cycling.

Purpose of the Study:

• To verify the anatomical paradox observed in cyclist's muscle activity during pedaling.
• To investigate the timing of flexor and extensor muscle activation in relation to joint torques.
• To analyze muscle activity patterns under both submaximal and maximal cycling efforts.

Main Methods:

• Measured the electromyography (EMG) activity of six lower limb muscles in nine elite cyclists.
• Utilized a portable EMG data acquisition system with active surface electrodes for remote monitoring.
• Collected data during a 1000 m submaximal constant effort and a 200 m sprint.

Main Results:

• Confirmed the anatomical paradox, showing high flexor muscle activity during the leg extension (propulsion) phase (0-90 degrees).
• Observed zero knee torque at 135 degrees, coinciding with the end of extensor activity in one leg and the start in the other.
• Demonstrated that flexor muscles activate before extensor activity fully ceases to ensure continuous circular motion past the bottom dead center.

Conclusions:

• The study confirms the existence of an anatomical paradox in elite cyclists' pedaling biomechanics.
• Flexor muscle activation is crucial before extensor activity concludes to maintain the continuous circular motion of the pedal stroke.
• Understanding these complex muscle activation patterns can inform training and performance optimization in cycling.