Factors that influence vertical velocity during take-off over a water jump

Horses competing in the team competition at the 1992 Olympic games were videotaped as they attempted to jump a 4.5 m wide water jump. The video images were digitised to provide kinematic and centre of gravity (CG) data from 18 horses: 12 horses that cleared the water jump (Group 1) and 6 horses that failed to clear the tape on the landing side (Group 2). Univariate ANOVA revealed significant between-group differences in horizontal distance jumped (Group 1: 5.79 m ± 0.37, Group 2: 5.03 m ± 0.34; F=0.001), inclination of the trunk segment to the horizontal at lift off of the leading hindlimb (Group 1: 21.4° ± 2.5, Group 2: 16.9° ± 4.1; F=0.011) and horizontal distance of the leading hind hoof from the horse's CG at lift off (Group 1:1.11 m ± 0.12, Group 2: 1.30 m ± 0.06; F=0.004). Pearson correlation coefficients revealed that 3 variables were highly correlated with vertical velocity at lift off: distance of the leading hind hoof from the CG at impact (r=-0.53, P<0.05) and lift off (r=-0.76, P<0.001) and trunk angle at lift off (r=0.70, P<0.001). Distance of the leading hind hoof from the CG at lift off and trunk angle at lift off were also significantly correlated with horizontal distance jumped (r=-0.56, P<0.01; r/0.67, P<0.01 respectively). Stepwise multiple linear regression with vertical velocity as the dependent variable selected 3 of the 7 investigated independent variables: trunk angle, distance of the leading hindlimb from CG at lift off and distance of the leading hind hoof from the approach side of the water (r²=0.799). The position of the hindlimbs through their take off phase relative to the CG of the horse and the trunk angle at lift off are important variables in the take off over a water jump.