Reliability of leg muscle electromyography in vertical jumping

Area of Science:

• Biomechanics
• Exercise Physiology
• Sports Science

Background:

• Assessing the reliability of biomechanical and neuromuscular measures is crucial for understanding athletic performance.
• Surface electromyography (EMG) is commonly used to evaluate muscle activity during dynamic movements like vertical jumps.
• Previous research has not consistently established the test-retest reliability of EMG during vertical jumping.

Purpose of the Study:

• To determine the reliability of surface electromyography (EMG) of leg muscles during vertical jumping.
• To compare the reliability of EMG signals with kinematic variables during vertical jumps.
• To identify factors influencing the reliability of EMG measurements in this context.

Main Methods:

• Fifteen females performed three maximal vertical jumps with countermovement.
• Kinematic variables (body centre of mass displacement, propulsion phase duration, range of motion, knee angular velocity) and surface EMG of four leg muscles were recorded.
• Intraclass correlation coefficients (ICC) were calculated to assess test-retest reliability over two sessions, 2 weeks apart.

Main Results:

• Kinematic variables (BCM, ROM, time) demonstrated high reliability (ICC > 0.90).
• Knee angular velocity showed moderate reliability (ICC = 0.75).
• EMG reliability varied greatly by muscle: rectus femoris (ICC=0.88), vastus medialis (ICC=0.70), biceps femoris (ICC=0.24), and gastrocnemius (ICC=0.01).
• Interactions between EMG and kinematic variables were generally poor (ICC < 0.50).

Conclusions:

• Kinematic variables during vertical jumps exhibit high reproducibility.
• The reliability of surface EMG signals during vertical jumps is muscle-dependent.
• Factors such as electrode placement, skin resistance, and muscle cross-talk may impact EMG reliability.