(1) KINETICS AND LOWER EXTREMITY MUSCLE ACTIVATIONS DURING THE MAXIMUM ISOMETRIC MID-THIGH PULL AND BELT SQUAT

BACKGROUND: The isometric belt squat has grown in popularity as an alternative isometric testing option given its reduction of spinal loading. The isometric mid-thigh pull is a commonly used isometric performance test that has been heavily researched. Little research has been done to compare the kinetics or lower extremity muscle activations during these performance tests.

Purpose: To compare the kinetics and lower extremity muscle activations during maximum isometric mid-thigh pull and belt squat testing.

Methods: Seventeen participants (13 female, 4 male, age: 22.12 ± 1.36 years, height: 1.68 ± 0.10 m, mass: 71.98 ± 16.22 kg) completed one familiarization session and two experimental sessions. During the familiarization session, we explained the experimental setup and proper body positioning for competing each test, and participants completed two submaximal practice trials for both the isometric mid-thigh pull and belt squat. During separate experimental sessions for the isometric mid-thigh pull and belt squat, participants completed a warm-up, followed by two submaximal three second trials and four maximal five second trials. Participants rested for 30 seconds between practice trials and two-minutes between maximal effort trials. Experimental sessions were completed one-week apart and randomly ordered among participants. We used a custom Sorinex rack with separate AMTI force plates under each foot (1200 Hz sample rate) and 64-channel high-density electromyography arrays (2048 Hz sample rate) on the rectus femoris, biceps femoris, and lateral gastrocnemius muscles of the right leg. To analyze our EMG data, we applied a band pass filter (20-400 Hz cutoff) and used canonical correlation analysis for eliminating noise components from the signals. We then amplitude normalized the EMG activity to the peak activation during the isometric mid-thigh pull for each lower limb muscle and participant, respectively. We evaluated differences between the isometric mid-thigh pull and belt squat using paired samples t-tests for peak vertical force, time to peak force, and lower limb muscle activation amplitudes.

Results: Compared to the mid-thigh pull, during the belt squat we identified greater peak vertical forces per bodyweight (mean ± SD: mid-thigh pull: 3.40 ± 0.97 belt squat: 5.30 ± 2.35, t₃₂ = -3.1, p = 0.004, d = 1.06) and time to peak force (mean ± SD: mid-thigh pull: 3.06 ± 1.14s belt squat: 4.02 ± 1.17s, t₃₂ = -2.6, p = 0.013, d = 0.90). Lower limb muscle activation amplitudes did not differ between tests.

Conclusions: We identified greater peak vertical forces that occurred later, with equivalent lower limb electrical muscle activation dynamics during the maximum isometric belt squat compared to the mid-thigh pull. PRACTICAL APPLICATION: The maximum isometric belt squat provides an alternative, and possibly more effective, performance test for evaluating lower limb strength compared to the more commonly used mid-thigh pull.

Acknowledgements: None