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First published online September 19, 2006
Journal of Experimental Biology 209, 3742-3757 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02439

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Centre of mass movement and mechanical energy fluctuation during gallop locomotion in the Thoroughbred racehorse

Thilo Pfau^1,*, Thomas H. Witte^1, and Alan M. Wilson^1,2

¹ Structure and Motion Laboratory, The Royal Veterinary College, University of London, Hawkshead Lane, North Mymms, Hatfield, AL9 7TA, UK
² Structure and Motion Laboratory, University College London, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex, HA7 4LP, UK

View larger version (33K): [in a new window]   Fig. 1. Sum of potential and dorsoventral kinetic energy for the speed categories 12 m s-1 (11.5-12.5 m s-1; top plots) and 15 m s-1 (14.5-15.5 m s-1; bottom plots). Horses A-C are the three typical horses used in Figs 4, 5, 6 and 7, 10 and 11.

View larger version (22K): [in a new window]   Fig. 2. Positions used for the sensitivity analysis for the relative position of the centre of mass (CoM) of a standing horse relative to the position of the inertial sensor. The sensor (blue) was mounted over the dorsal spinous processes of the fourth to sixth thoracic vertebrae (withers). The red circle shows the estimate used in this study. Values indicate mm from the sensor.

View larger version (36K): [in a new window]   Fig. 3. Average external mechanical work per stride for different estimates of the position of the CoM relative to the position of the sensor on the horse. External mechanical work is calculated as the sum over all positive energy changes in total mechanical energy (sum of potential, and all linear kinetic energies).

View larger version (63K): [in a new window]   Fig. 4. Individual stride data of three typical horses for craniocaudal (x, blue), mediolateral (y, green) and dorsoventral (z, red) displacement (A), velocity (B) and acceleration (C) of the estimated CoM. Data presented are individual strides between 11.5 m s-1 and 12.5 m s-1 at gallop. The grey shaded area indicates the measured aerial time with the alignment being based on the assumption that vertical kinetic and potential energy is constant during the aerial phase (see Materials and methods; Fig. 1).

View larger version (75K): [in a new window]   Fig. 5. Individual stride data of three typical horses for craniocaudal (x, blue), mediolateral (y, green) and dorsoventral (z, red) displacement (A), velocity (B) and acceleration (C) of the estimated CoM. Data presented are individual strides between 14.5 m s-1 and 15.5 m s-1 at gallop. The grey shaded area indicates the measured aerial time with the alignment being based on the assumption that vertical kinetic and potential energy is constant during the aerial phase (see Materials and methods; Fig. 1).

View larger version (65K): [in a new window]   Fig. 6. Individual stride data of three typical horses for roll (blue), pitch (green) and heading (red) displacement (A), velocity (B) and acceleration (C) of the estimated CoM. Data presented are individual strides between 11.5 m s-1 and 12.5 m s-1 at gallop. The grey shaded area indicates the measured aerial time with the alignment being based on the assumption that vertical kinetic and potential energy is constant during the aerial phase (see Materials and methods; Fig. 1).

View larger version (73K): [in a new window]   Fig. 7. Individual stride data of three typical horses for roll (blue), pitch (green) and heading (red) displacement (A), velocity (B) and acceleration (C) of the estimated CoM. Data presented are individual strides between 14.5 m s-1 and 15.5 m s-1 at gallop. The grey shaded area indicates the measured aerial time with the alignment being based on the assumption that vertical kinetic and potential energy is constant during the aerial phase (see Materials and methods; Fig. 1).

View larger version (29K): [in a new window]   Fig. 8. Displacement range (A) and minimum and maximum velocity (B) and acceleration (C) from 7 m s-1 to 17 m s-1 for craniocaudal (left) and dorsoventral (right) movement. For each speed category mean and standard deviation (displacement) or median and interquartile range (velocity and acceleration) are given calculated from all strides falling into the respective category. In addition a quadratic function was fitted to the data and is shown as a dotted line.

View larger version (30K): [in a new window]   Fig. 9. Displacement range (A) and minimum and maximum velocity (B) and acceleration (C) from 7 m s-1 to 17 m s-1 for pitch (left) and heading (right) movement. For each speed category mean and standard deviation (displacement) or median and interquartile range (velocity and acceleration) are calculated from all strides falling into the respective category. In addition a quadratic function was fitted to the data and is shown as the dotted line.

View larger version (47K): [in a new window]   Fig. 10. Individual stride data of changes in external mechanical energy, potential energy and linear kinetic energy (A) and changes in potential, linear and rotational energy (B) as calculated from the movement of the estimated CoM. Data presented are individual strides of three typical horses recorded at speeds between 11.5 m s-1 and 12.5 m s-1 at gallop. (A) For illustrative purposes the minimum craniocaudal kinetic energy has been subtracted from forward kinetic and external mechanical energy. Ext, external energy (blue); CC, craniocaudal kinetic energy (green); ML, mediolateral kinetic energy (cyan); DV, dorsoventral kinetic energy (magenta); Pot, potential energy (red). Elast, elastic energy estimated from mean footfall pattern at this speed category (light green). (B) Pot, potential energy (red); Pitch, pitch kinetic energy (green); Heading, heading kinetic energy (cyan); ML, mediolateral kinetic energy (magenta); DV, dorsoventral kinetic energy (black). The grey shaded area indicates the measured aerial time with the alignment being based on the assumption that vertical kinetic and potential energy is constant during the aerial phase (see Materials and methods). (C) Stance phases of individual feet are presented as black bars: LF, lead front; NLF, nonlead front; LH, lead hind; NLH, nonlead hind.

View larger version (50K): [in a new window]   Fig. 11. Individual stride data of changes in external mechanical energy, potential energy and linear kinetic energy (A) and changes in potential, linear and rotational energy (B) as calculated from the movement of the estimated CoM. Data presented are individual strides of three typical horses recorded at speeds between 14.5 m s-1 and 15.5 m s-1 at gallop. (A) For illustrative purposes the minimum craniocaudal kinetic energy has been subtracted from forward kinetic and external mechanical energy. Ext, external energy (blue); CC, craniocaudal kinetic energy (green); ML, mediolateral kinetic energy (cyan); DV, dorsoventral kinetic energy (magenta); Pot, potential energy (red). Elast, elastic energy estimated from mean footfall pattern at this speed category (light green). (B) Pot, potential energy (red); Pitch, pitch kinetic energy (green); Heading, heading kinetic energy (cyan); ML, mediolateral kinetic energy (magenta); DV, dorsoventral kinetic energy (black). The grey shaded area indicates the measured aerial time with the alignment being based on the assumption that vertical kinetic and potential energy is constant during the aerial phase (see Materials and methods). (C) Stance phases of individual feet are presented as black bars: LF, lead front; NLF, nonlead front; LH, lead hind; NLH, nonlead hind.