G-Force Exposure In Contact Sport
Malachy P. McHugh, FACSM, Marcus P. Hannon.
PURPOSE:GPS-based analyses of movement patterns are inadequate for quantifying the physical stress imposed on athletes in contact sports. Accelerometers may be useful for monitoring such athletes. The purpose of this study was to: (1) document G-force exposure for Gaelic football players, (2) determine if accelerometer analysis could detect position- dependent differences, and (3) compare G-force exposure in games versus practice.
METHODS:A small triaxial accelerometer (mass 5 g) with a flash memory chip data logger (Axivity, Newcastle, UK) was fitted to the center-rear of the waistband of players’ shorts. Data was acquired at 100 Hz (scale ±16G). Game data were recorded from 19 club level players (age 22±7 yr). Training data were recorded from 8 players. Accelerometer data was rectified, summed for the 3 planes of motion, and expressed as G-force (baseline: vertical=1, frontal and sagittal=0). For the summed data, time spent at less than 2G, 2-3G and greater than 3G was categorized as low, moderate, and high G-force exposure, respectively. Player positions were categorized as central (half backs/half forwards/midfield) and peripheral (full back/full forward) with central players typically more involved in continuous running. ANOVA with Bonferroni corrections was used to compare G-force exposure in games vs. practice and between central vs. peripheral players (practice not position dependent).
RESULTS:Overall 7.0% of game time was spent at high G-force, with 11.7% at moderate and 81.3% at low. High G-force exposure was greater for central vs. peripheral players (7.7% vs. 6.1%, P<0.05) and for practice vs. games (9.1% vs. 7.1%, P<0.001). Position-dependent effects were evident in the vertical plane (P<0.001) but not the frontal (P=0.27) or sagittal (P=0.65) planes. Differences between practice and games were evident in all 3 planes (P<0.01).
CONCLUSIONS:Accelerometry analysis was effective in distinguishing position-dependent physical demands in contact sport athletes. The differences in vertical G-force exposure may reflect greater running and jumping demands on central players. The absence of position-dependent effects in horizontal planes indicates that cutting, pivoting and physical contact (accelerations in the horizontal planes) were not different positions.
Nicholas Institute of Sports Medicine and Athletic Trauma, Lenox Hill Hospital, New York, NY.