Differential neuromuscular adaptations following multi-joint vs single-joint resistance exercise training

Area of Science:

• Biomechanics
• Exercise Physiology
• Muscle Adaptations

Background:

• Resistance training elicits neuromechanical adaptations, but the influence of exercise type (multi-joint vs. single-joint) on these adaptations is debated.
• Understanding differences in muscle architecture and strength gains between squat and leg extension training is crucial for optimizing exercise prescriptions.

Purpose of the Study:

• To compare neuromechanical adaptations between a multi-joint (squat) and a single-joint (leg extension) resistance training program of equal volume.
• To investigate changes in muscle architecture, maximal isometric torque (Tmax), and electromyography (EMG) activity.

Main Methods:

• Twenty-four participants were assigned to either a squat group (SQG) or a leg extension group (LEG) for 10 weeks.
• Ultrasound, EMG, and dynamometry were used to measure muscle thickness, vastus lateralis (VL) fascicle length, pennation angle, and Tmax before and after training.
• One-repetition maximum (1RM) was assessed for both squat and leg extension exercises.

Main Results:

• Both groups showed significant increases in 1RM and muscle thickness, with greater increases in the SQG.
• The SQG exhibited a larger improvement in Tmax (+14%) compared to the LEG group (+10%).
• Post-training increases in pennation angle, fascicle length, and optimal VL fascicle length (L0) were observed only in the SQG.

Conclusions:

• Squat training appears more effective than leg extension training in promoting greater muscle hypertrophy and strength gains.
• Multi-joint squat exercise may elicit superior neuromuscular adaptations, potentially due to higher knee torque requirements.
• These findings suggest that exercise selection significantly impacts training outcomes in resistance exercise programs.