John R. Harry • Leland A. Barker • John A. Mercer • Janet S. Dufek Differences in Vertical Impact Forces During Jump-Landings Among Soccer Players of Different Playing Positions John R. Harry • Leland A. Barker • John A. Mercer • Janet S. Dufek Department of Kinesiology & Nutrition Sciences, University of Nevada, Las Vegas, Las Vegas, NV ABSTRACT Background: Soccer is arguably the most popular and most participated sport in the world. Lower-extremity injuries often occur in soccer during non-contact landings. The greater frequency of observed lower-extremity injuries in defensive and attacking players may be related to a greater number of jumping and landing movements performed due to their direct involvement in set pieces and open-play airborne challenges and/or decreased landing abilities. However, the landing biomechanics of a position-based comparison of landing movements have yet to be investigation. Purpose: to examine vertical impact force parameters among Division 1 male soccer players of different playing positions during two vertical jump-landing tasks. The specific tasks examined were landings from a vertical jump (VJ) and landings from a vertical jump with a 180-degree airborne rotation (VJR). Methods: Twenty-four male Division 1 soccer players (179.6 ± 8.4 cm, 75.7 ± 10.1 kg, 19.9 ± 1.5 yrs) were divided into the following groups according to their primary playing positions: Goalkeepers (GK), defenders (DEF), midfielders (MID), and attackers (ATT). Participants performed three trials for the VJ landing and VJR landing tasks on a dual-force platform system (1000 Hz). Each trial was performed for maximum vertical height. Dependent variables of interest included jump height, the first (F1) and second (F2) peak vGRF magnitudes, time to F1 (tF1), time to F2 (tF2), landing impulse, and the duration of the impact phase. Kinetic limb asymmetry was examined by comparing the individual ground reaction force magnitudes of the left and right legs at the time of the F1 and F2 events. Results: Jump height was significantly greater during VJ landings. DEF players exhibited a significantly greater F1 magnitude and a longer tF1 during VJR landings. DEF players also demonstrated a significantly longer tF1 than MID players as well as generally longer tF1 than the GK and ATT position groups during VJR landings. The MID group had a significantly greater F2 during VJR landings compared to VJ landings. F2 was generally greater during VJR landings compared to VJ landings for the GK and ATT groups, though differences were not statistically significant. When collapsed across position groups, VJR landings produced a significantly more rapid tF2. No differences were found for impulse or the duration of the impact phase. Conclusion: These findings suggest that some differences in vertical impact force are present among playing positions during each landing task. METHODS Twenty-four male Division 1 soccer players (179.6 ± 8.4 cm, 75.7 ± 10.1 kg, 19.9 ± 1.5 yrs) participated Participants were divided into the following groups according to their primary playing positions: Goalkeepers (GK, n = 5), defenders (DEF, n = 6), midfielders (MID, n = 10), and attackers (ATT, n = 3) Participants performed three VJ landings and three VJR landings while vertical ground reaction forces (vGRF) were acquired using a dual-force platform system (1000 Hz; low pass filtered at 50 Hz)3 Group by task ANOVAs (α = 0.05) compared jump height, the first (F1) and second (F2) peak vGRF magnitudes (summation of the two force platforms), time to F1 (tF1), time to F2 (tF2), landing impulse, and the duration of the impact phase Independent t-tests (α = 0.05) examined kinetic limb asymmetry by comparing the individual vGRF magnitudes of the left and right legs at the time of the F1 and F2 events Figure 3. F2 (Top) and tF2 (Bottom) during VJ and VJR Landings. Note: * = significantly greater than VJ/VJR for the respective group (p < 0.05). CONCLUSION The greater frequency of lower-extremity injuries observed in DEF and ATT players2 does not appear related to impact force characteristics during vertical landings Due to the more rapid tF2, VJR landings may present a greater risk for overuse injuries in comparison to VJ landings, which warrants further investigations specific to rate of loading variables during ballistic movements Training programs might benefit from including additional VJR landings to address the more rapid loading time and reduced jump height compared to VJ landings Emphasizing eccentric strength of the lower-extremity muscles could improve the ability to attenuate vGRF and absorb elastic energy4 during a jump-landing Soccer athletes who include a combination of VJ and VJR landings may experience improved jumping and landing performance, while concurrently improving the ability to reduce impact forces during simple and complex landing tasks RESULTS No significant interactions or group main effects were detected for jump height, F1 asymmetry, F2 asymmetry, tF2, or the duration of the impact phase (p > 0.05) Significant task main effects detected differences in jump height regardless of position group (p < 0.05; Figure 1) Significant interactions revealed DEF exhibited a greater F1 and a longer tF1 during VJR landings versus VJ landings (p < 0.05; Figure 2) as well as a longer tF1 than MID (p < 0.05) A significant interaction detected different F2 magnitudes between tasks for MID (p < 0.05; Figure 3) Significant task main effects detected a more rapid tF2 during VJR landings regardless of position group (p < 0.05; Figure 3) BACKGROUND The vertical jump (VJ) landing is one of the more essential explosive movements performed in soccer Landings can result in non-contact injuries due to the high demand on the body1 to rapidly decelerate the center of mass before a subsequent movement can be initiated A greater frequency of lower-extremity injuries was observed in players of defensive and attacking positions compared to goalkeeping and midfield positions2 Defensive and attacking players may at greater risk due to their direct involvement in set pieces and open-play airborne challenges that require jump-landings with and without rotation about the vertical axis The greater frequency of injury might also be related to decreased landing abilities in defensive and attacking players compared to other playing positions The purpose of this investigation was to examine vertical impact force parameters among Division 1 male soccer players of different playing positions during landings from a vertical jump (VJ) and landings from a vertical jump with a 180-degree airborne rotation (VJR) ACKNOWLEDGEMENT The authors would like to acknowledge the Graduate & Professional Student Association (GPSA) at UNLV for their assistance with the presentation of this project REFERENCES Zhang, S. N., Bates, B. T., & Dufek, J. S. (2000). Contributions of lower extremity joints to energy dissipation during landings. Medicine and Science in Sports and Exercise, 32(4), 812-819 Mallo, J., & Dellal, A. (2012). Injury risk in professional football players with special reference to the playing position and training periodization. The Journal of Sports Medicine and Physical Fitness, 52(6), 631-638 Harry, J. R., Paquette, M. R., Caia, J., Townsend, R. J., Weiss, L. W., & Schilling, B. K. (2015). Effects of footwear condition on maximal jumping performance. Journal of Strength and Conditioning Research / National Strength & Conditioning Association, 29(6), 1657-1665 Baechle, T. R., & Earle, R. W. (2008). Essentials of Strength Training and Conditioning. Champaign, Ill: Human Kinetics Figure 1. Vertical Jump Height During VJ and VJR landings Note: * = significantly greater than VJR landings (p < 0.05). Figure 2. F1 (Top) and tF1 (Bottom) during VJ and VJR Landings. Note: * = significantly greater than MID; ** = significantly greater than VJ for the respective group (p < 0.05).