A STANDING LONG JUMP COMPARISON OF TWO-FOOT AND ONE-FOOT LANDING MECHANICS: A PILOT STUDY

Crickmore, KN, Connor, KR, Cogswell, TM, and Hegazy, MA

Department of Movement Sciences, University of Idaho, Moscow, Idaho email: mhegazy@uidaho.edu web: http://www.uidaho.edu/ed/movementsciences

INTRODUCTION Injuries to the Anterior Cruciate Ligament (ACL) are more commonly associated with non-contact mechanisms, like jump landings. One-foot landings are considered more dangerous than two-foot landings as the demand required to absorb the impact is placed on one lower limb [1]. Few studies compared one and two-foot landing mechanics [1,2] and those that have did so during vertical landings. However, comparing landing mechanics of two- and one-foot landings is warranted considering landing injuries do not occur only in vertical jump landings. Thus, the purpose of this pilot study was to investigate the difference in peak vertical and horizontal ground reaction force (GRF) as well as vertical and horizontal velocities and displacements during a series of submaximal long jumps. METHODS Five female active college students (20.6±0.89 years, 65.07±7.84 kg) volunteered for the study. Volunteers who had any musculoskeletal condition that may affect their jumping performance were excluded from the study. Participants were asks to complete three maximal effort standing long jumps to determine their maximal distance. Participants were then asked to complete two sets of nine submaximal jumps from 25%, 50%, and 75% (three times each, in a counterbalanced order) of the longest maximal effort jump. The first set were two-foot landings with each foot on separate force platforms (1000 Hz, AMTI, Watertown, MA) and the second set was dominant leg landings onto one force platform. Participants did not receive instructions regarding technique. Vertical and horizontal landing impulse was used to calculate vertical and horizontal velocities and displacements, respectively. A series of two-way ANOVA with repeated measures (landing type x horizontal distance) with both landing type (two-foot vs. one-foot) and horizontal distance (25%, 50%, 75% of maximal distance) as the within subjects factors were

conducted. The variables compared were vertical and horizontal GRF, velocity, and displacement. RESULTS AND DISCUSSION Results summary are presented in Table 1. Although participants jumped from the same point for both types of landings, they reduced their horizontal center of mass displacement during the one-foot landings for all horizontal distances. This was accomplished by lowering their vertical velocity and keeping their horizontal velocity constant for each horizontal displacement. Despite keeping horizontal velocity constant, there was a significant increase in peak horizontal GRF during one-foot landings (Figure 1). Peak vertical GRF showed a similar pattern despite the reduction in vertical velocity.

Figure 1: Peak horizontal GRF for landing type and horizontal distance Any questions about this abstract should be addressed to: mhegazy@uidaho.edu CONCLUSIONS During one-foot landings active college females tend to guard their landing by reducing vertical jump velocity. This was accompanied by an increase peak GRFs. Kinematic analysis is needed to get a better understanding of landing strategies. REFERENCES 1. Pappas, E, et al. Clin J Sport Med 17, 263-268, 2007 2. Yeow, CH, et al. Hum Movement Sci 30,624-635, 2011.

Table 1: Summary of two-way ANOVA results and mean and standard deviation for the different conditions

Landing Type Horizontal Distance Variable F Ratio One-foot Two-foot F Ratio 75 50 25

V Velocity (m·s-1) 21.97* 1.55±0.27 1.84±0.29 12.21* 1.89±0.31 1.72±0.24Y 1.78±0.25Z Jump Height (m) 31.42* 0.13±.0.04 0.18±0.05 12.93* 0.19±0.06 0.15±0.04 Y 0.11±0.36

H Velocity (m·s-1) 2.55 1.78±0.52 1.88±0.45 59.72* 2.34±0.29X 1.85±0.19 Y 1.29±0.17 Z H Distance (m) 16.58* 0.58±0.25 0.74±0.28 30.54* 0.92±0.22 X 0.66±0.14 Y 0.39±0.10 Z

V Peak Force (N) 53.89* 2092±460 1280±342 29.52* 2024±554 1692±549 Y 1341±440 Z H Peak Force (N) 132.84* 752±320 329±90 32.21* 750±398 X 537±235 Y 334±104 Z V = Vertical, H = Horizontal, * indicates a significant difference, Paired horizontal distance difference X = 75% vs. 50%, Y = 75% vs. 25%, Z =50% vs. 25%

0500

10001500

75% 50% 25%

Peak

Hor

izon

tal

GR

F (N

)

Horizontal Distance

One-footed Landings Two-footed Landings