Accessory muscle activation during the superimposed burst technique

Area of Science:

• Biomechanics
• Exercise Physiology
• Muscle Physiology

Background:

• The superimposed burst technique is commonly used to assess quadriceps muscle activation during maximal isometric knee extension.
• Accessory muscle activation during this test may confound the accurate estimation of quadriceps activation.
• The influence of specific instructions on minimizing accessory muscle activity is not well understood.

Purpose of the Study:

• To compare accessory muscle activation during the superimposed burst technique under two conditions: constrained system (CS) with investigator verbal instruction and participant preferred (PP) technique.
• To determine if verbal instructions to isolate quadriceps activation affect knee extension torque and muscle activation patterns.

Main Methods:

• Twenty-five healthy, active individuals participated in the study.
• Participants performed maximal isometric knee extension with superimposed burst testing under both CS and PP conditions.
• Knee extension torque, quadriceps central activation ratio (CAR), and electromyography (EMG) of vastus lateralis, biceps femoris, and lumbar paraspinal muscles were measured.

Main Results:

• Significant differences were observed in knee extension torque, superimposed burst torque, and quadriceps CAR between the CS and PP techniques (p<0.001 for torque and CAR).
• Lumbar paraspinal muscle EMG was significantly lower in the CS condition compared to the PP condition (p=0.043).
• Vastus lateralis EMG did not show significant differences between the two techniques.

Conclusions:

• Investigator-delivered verbal instructions to constrain the system (encourage isolated quadriceps activation) significantly improve quadriceps central activation ratio and reduce confounding accessory muscle activation, specifically in the lumbar paraspinals.
• This controlled approach enhances the reliability of the superimposed burst technique for accurately assessing quadriceps muscle activation during maximal isometric knee extension.
• Utilizing verbal cues to minimize proximal muscle recruitment is a practical method to improve the validity of muscle activation assessments in clinical and research settings.