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The effect of gait and digital flexor muscle activation on limb compliance in the forelimb of the horse Equus caballus

M. Polly McGuigan^* and Alan M. Wilson

Structure and Motion Laboratory, Veterinary Basic Sciences, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Hertfordshire AL9 7TA, UK

View larger version (29K): [in a new window]   Fig. 1. (A) The equine forelimb, showing the muscles associated with weight bearing. (B) The limb can be conceptually divided into two springs, representing the proximal part of the limb (shoulder to elbow) and the distal part of the limb (elbow to digit). (C) The length of the springs during the stance phase can be calculated using Pythagarus theorem. MCP, metacarpo-phalangeal; DIP, distal interphalangeal; SDF, superficial digital flexor; DDF, deep digital flexor; AL, accessory ligament: SL, suspensory ligament; T, tendon.

View larger version (14K): [in a new window]   Fig. 6. A typical plot of the relationship between metacarpo-phalangeal (MCP) joint angle and vertical ground reaction force (GRF) during the stance phase of trot for one horse.

View larger version (12K): [in a new window]   Fig. 2. (A) Leg length (centre of rotation of the elbow joint to the hoof) and (B) metacarpo-phalangeal (MCP) joint angle—limb force relationship for an equine distal limb during in vitro loading. The solid lines are linear regression lines: (A) y=-0.2089x+132, r2=0.996 and (B) y=0.3821x+78.0, r2=0.994.

View larger version (20K): [in a new window]   Fig. 3. Linear regression lines of the metacarpo-phalangeal (MCP) joint angle—limb force relationship for nine distal limbs during in vitro loading. r2 values for these relationships were 0.983-0.996.

View larger version (15K): [in a new window]   Fig. 4. Metacarpo-phalangeal (MCP) joint angle—limb force relationship for an equine distal limb during unstimulated (blue) and stimulated (red) in vitro loading.

View larger version (31K): [in a new window]   Fig. 5. Mean vertical ground reaction force (GRF blue) and metacarpo-phalangeal (MCP) joint angle during forelimb stance of ridden walk (A), trot (B), lead canter (C), non-lead canter (D) and jump landing (E) on a soft riding surface for horse 1. The dotted lines represent ± 1 S.D. (N=4).

View larger version (19K): [in a new window]   Fig. 7. The relationship between metacarpo-phalangeal (MCP) joint angle and vertical ground reaction force (GRF) during the stance phase of walk (pink), trot (red), lead canter (blue dashed), non-lead canter (blue) and jump landing (green) for horse 1.

View larger version (18K): [in a new window]   Fig. 8. Peak metacarpo-phalangeal (MCP) joint angle versus peak vertical ground reaction force (GRF) for each gait of each horse. The different symbols represent the different horses. Linear regression lines are shown for each horse. The black broken line represents the relationship between MCP joint angle and vertical GRF for the population of horses; y=0.2113x-38.68, r2=0.70.

View larger version (28K): [in a new window]   Fig. 9. Mean vertical ground reaction force (GRF; blue) and metacarpo-phalangeal (MCP) joint angle (red) during forelimb stance of in-hand trot on a hard surface for one horse. The dotted lines represent ± 1 S.D. (N=4).