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(12) GROUND REACTION FORCE AND ELECTROMYOGRAPHIC DETERMINANTS OF THE JAB IN BOXERS


Authors:

Jonathan G. Neville – Research Fellow, Auckland University of Technology

Matt R. Cross – PhD Student, Univ Savoie Mont Blanc

Anna V. Lorimer – Assistant Professor, Bond University

Matt Brughelli – Senior Lecturer, Auckland University of Technology

Roy J. Nates – Associate Professor, Auckland University of Technology

Kristin J. Heumann, PhD, CSCS, c-EP – Associate Professor , Colorado Mesa University

Seth M. Lenetsky, PhD – Research Associate, Auckland University of Technology

Abstract:

INTRODUCTION: Effective mass (EM), an athlete’s inertial contribution to a strike, has been identified as a key impact kinetic in punching. While double peak muscle activation (DPMA) has been theorised as vital to the development of EM, no studies have empirically identified its determinants. PURPOSE: To investigate the relationship between ground reaction forces (GRF) and electromyographic (EMG) to EM in the jab of a cohort of experienced boxers. METHODS: 10 experienced and competitive male boxers (age = 25.6 years ± 5.97, height = 179.5 cm ± 7.72, mass = 95.66 kg ± 21.82, and years training = 10.3 years ± 5.97) participated in this study. The following muscles were prepared for EMG data collection: triceps brachii (LTB and RTB), latissimus dorsi (LLD and RLD), rectus abdominis (LRA and RRA), and rectus femoris (LRF and RRF) of the lead and rear sides. After preparation, participants performed a standardised warm-up, maximal voluntary isometric contractions for EMG normalization, and familiarisation. Five maximal punches against an instrumented bag were used for analysis. Trials were recorded with an EMG system, 2 force plates (1 plate under each leg), 2D high speed video (HSV), and an instrumented bag to measure impact kinetics; all devices sampled at 1000 Hz, were time synchronised to impact. 2D HSV was used to determine pre-impact punch velocity of the jabs which was used to calculate EM with impulse measured through the instrumented bag. A hierarchical regression using magnitude-based inference was employed to identify the determinants of EM. Pearson correlation coefficient (r) and co-efficient of determination () were calculated for each model. Inferences based on the square-root of the  were used to describe the magnitude of the observed relationship. A 5:1 ratio of boxers to independent variables (10 boxers = maximum of 2 independent variables) was used to account for shrinkage and inflated error rates due to the study’s relatively small sample size. RESULTS: EM was determined by the GRF variables of minimal lead leg X axis value during the impact phase (force applied towards the boxer’s mid-line) and max GRF development in the lead leg (Y axis) during the execution phase. Both variables had negative relationships with EM. RTB results were the final EMG determinants of EM in the jab. RTB duration of activation had a negative relationship (r = -0.51) and the phase of activation start had a positive relationship (r = 0.41) with EM. The key determinants of EM in the jab were minimal lead leg GRF (X axis) and the duration of activation of the RTB. CONCLUSION: These findings contrast with the theory of optimizing EM. Instead of DPMA being a primary determinant of EM, two variables which optimize the rotation of the torso were key to the development of EM in the jab. PRACTICAL APPLICATION: These results indicate that to improve EM in the jab of boxers, practitioners should focus on improving rotational performance over methods thought to improve DPMA.

 

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