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First published online February 29, 2008
Journal of Experimental Biology 211, 935-944 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.006650

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High-speed gallop locomotion in the Thoroughbred racehorse. I. The effect of incline on stride parameters

K. J. Parsons^*, T. Pfau and A. M. Wilson

Structure and Motion Laboratory, The Royal Veterinary College, University of London, North Mymms, Hatfield, Hertfordshire AL9 7TA, UK

View larger version (6K): [in this window] [in a new window]   Fig. 1. Track survey showing elevation of the track from start to finish. Overall length of the track was 1077 m with an elevation of 50.5 m. The areas of the track that fell within the selected level (0–2%) and incline (8–12%) categories are indicated.

View larger version (21K): [in this window] [in a new window]   Fig. 2. Scatter plot showing speed against percentage incline for strides included in the analysis. Points are coloured according the horse number. The shaded areas represent the two incline categories that were used for the general linear model (GLM) analysis: 0–2% incline category (classified as level, A) and 8–12% incline category (classified as incline, B). NB Many of the points represent multiple numbers of strides due to superimposition.

View larger version (8K): [in this window] [in a new window]   Fig. 3. Stance duration as a function of speed. Values are means + s.e.m. for hindlimbs and means – s.e.m. for forelimbs (for clarity; N=6 throughout) of individual horse mean data (indicated by different symbols) during level (0–2%) and incline (8–12%) galloping for the six horses. Quadratic lines of best fit (P<0.001) are shown. These were estimated for the population using mean data. Coefficients: forelimb level b0=289.1, b1=–17.59, b2=0.34, r2=0.75; forelimb incline b0=377.7, b1=–33.58, b2=1.06, r2=0.915; hindlimb level b0=392.0.1, b1=–34.32, b2=1.06, r2=0.75; hindlimb incline b0=377.2, b1=–32.22, b2=0.99, r2=0.82.

View larger version (8K): [in this window] [in a new window]   Fig. 4. Protraction duration as a function of speed. Values are means + s.e.m. for forelimb level and hindlimb level and means – s.e.m. for forelimb incline and hindlimb incline (for clarity; N=6 throughout) of individual horse mean data for fore- and hindlimbs (indicated by different symbols) during level (0–2%) and incline (8–12%) galloping for the six horses. Quadratic lines of best fit (P<0.001) are shown. These were estimated for the population using mean data. Coefficients: forelimb level b0=86.7, b1=50.37, b2=–2.38, r2=0.11; forelimb incline b0=89.13, b1=48.60, b2=–2.38, r2=0.17; hindlimb level b0=4.02, b1=66.39, b2=–3.19, r2=0.19; hindlimb incline b0=233.59, b1=19.81, b2=–1.00, r2=0.06.

View larger version (6K): [in this window] [in a new window]   Fig. 5. Stride frequency as a function of speed. Values are means – s.e.m. for level and means + s.e.m. for incline (for clarity; N=6 throughout) of individual horse mean data for fore- and hindlimbs (indicated by different symbols) during level (0–2%) and incline (8–12%) galloping for the six horses. Quadratic lines of best fit (P<0.001) are shown. These were estimated for the population using mean data. Coefficients: level b0=2.88, b1=–0.202, b2=0.012, r2=0.44; incline b0=2.70, b1=–0.158, b2=0.010, r2=0.454.

View larger version (9K): [in this window] [in a new window]   Fig. 6. Duty factor as a function of speed. Values are means + s.e.m. for forelimb level and hindlimb level and means – s.e.m. for forelimb incline and hindlimb incline (for clarity; N=6 throughout; indicated by different symbols) during level (0–2%) and incline (8–12%) galloping for the six horses. Quadratic lines of best fit (P<0.001) are shown. These were estimated for the population using mean data. Coefficients: forelimb level b0=0.525, b1=–0.031, b2=0.001, r2=0.53; forelimb incline b0=0.727, b1=–0.066, b2=0.002, r2=0.71; hindlimb level b0=0.718, b1=–0.063, b2=0.002, r2=0.54; hindlimb incline b0=0.667, b1=–0.052, b2=0.002, r2=0.69.

View larger version (9K): [in this window] [in a new window]   Fig. 7. Calculated peak vertical force, normalised to total mass of the subject (including mass of horse, riding tack and rider) as a function of speed assuming a shift in forelimb to hindlimb force distribution on inclined surfaces. Values are means + s.e.m. for forelimbs and means – s.e.m. (N=6 throughout) for hindlimbs (for clarity; indicated by different symbols) during level (0–2%) and incline (8–12%) galloping for the six horses. Peak forces were calculated from duty factor and Eqn 1 assuming a shift in forelimb to hindlimb impulse distribution from 57:43 on the level to 52:48 on a 10% incline (Dutto et al., 2004). Quadratic lines of best fit (P<0.001) are shown. These were estimated for the population using mean data. Coefficients: forelimb level b0=2.40, b1=1.578, b2=–0.034, r2=0.51; forelimb incline b0=–7.68, b1=3.100, b2=–0.104, r2=0.72; hindlimb level b0=–1.73, b1=1.846, b2=–0.057, r2=0.53; hindlimb incline b0=0.870, b1=1.617, b2=–0.052, r2=0.61.

View larger version (9K): [in this window] [in a new window]   Fig. 8. Calculated peak vertical force, normalised to total mass of the subject (including mass of horse, riding tack and rider) as a function of speed – assuming no shift in forelimb to hindlimb force distribution. Values are means + s.e.m. for forelimbs and means – s.e.m. (N=6 throughout) for hindlimbs (for clarity; indicated by different symbols) during level (0–2%) and incline (8–12%) galloping for the six horses. Peak forces were calculated from duty factor and Eqn 1 assuming no shift in forelimb to hindlimb impulse distribution from 57:43 on the level and incline. Quadratic lines of best fit (P<0.001) are shown. These were estimated for the population using mean data. Coefficients: forelimb level b0=3.358, b1=1.436, b2=–0.028, r2=0.51; forelimb incline b0=–7.271, b2=3.355, b2=–0.119, r2=0.70; hindlimb level b0=–2.615, b1=1.978, b2=–0.063, r2=0.53; hindlimb incline b0=–1.077, b1=1.668, b2=–0.052, r2=0.686.

View larger version (10K): [in this window] [in a new window]   Fig. 9. Stride frequency vs mass-specific work per stride (Wc) for galloping horses (coloured lines). Data were categorised into 1 m s–1 speed bins, and linear regression lines (solid lines) and 95% confidence intervals (broken lines) have been plotted. Each colour represents data from a 1 m s–1 speed bin. Calculated work per stride and stride frequency from figures and data from Wickler et al. (Wickler et al., 2005) measured from trotting horses are also presented (black data points). As data are categorised into speed bins, moving from left to right represents an increase in incline.

View larger version (11K): [in this window] [in a new window]   Fig. 10. Stride frequency vs mean stance climbing power (Pc) per stride cycle for galloping horses (coloured lines). Pc was calculated assuming the work was performed during the hindlimb stance period. Data were categorised into 1 m s–1 speed bins and linear regression lines (solid lines) and 95% confidence intervals (broken lines) have been plotted. Each colour represents data from a 1 m s–1 speed bin. Calculated Pc and stride frequency from figures and data of Wickler et al. (Wickler et al., 2005) measured from trotting horses are also presented (black data points). As data are categorised into speed bins, moving from left to right represents an increase in incline.

View larger version (125K): [in this window] [in a new window]   Fig. 11. A fully instrumented galloping horse. At gallop the jockey stands and their centre of mass is positioned over the estimated position of the horse's centre of mass.

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