Since skin displacement has a cyclic pattern, it has been possible to develop mathematical correction algorithms for many of the anatomical locations that are commonly used for marker placement (van Weeren et al., 1990a. The shoulder is a ball and socket joint (the type of joint that allows the greatest movement) between the humerus and the scapula. From the front, a plumb-line dropped from the point of shoulder should bisect the limb and hoof. Also on the human skeleton, the patella, also called the kneecap is visible. The measurement from the withers to the point of the elbow should be about the same as from the point of the elbow to the ground, ensuring adequate depth of chest. Energy absorption and generation on the extensor (cranial) aspect of the shoulder joint are similar in magnitude to those at the elbow joint but occur slightly later in the stance phase. Evaluation of the geometry and architecture of the musculotendinous units is helpful in understanding whether their function is to produce rapid movements or generate large forces to stabilize the joints. During galloping, the proximal limb from scapula to elbow shortens by about 12 mm, whereas the limb distal to the elbow shortens by around 127 mm. Discrete bursts of positive and negative work can be quantified as the areas under the positive and negative phases, respectively, of the power curve. During trotting, changes in potential and kinetic energy of the horse’s center of mass are in phase, which allows the distal limb to make substantial contributions to elastic energy storage (Biewener, 1998). In dogs, it has been suggested that the primary function of serratus ventralis cervicis is to stabilize the position of the fulcrum about which the forelimb rotates in a craniocaudal direction during active retraction of the forelimb, thus ensuring that the GRF vector passes close to the center of scapular rotation (Carrier et al., 2006). The CDE tendon has a stiffer matrix than the SDF tendon, which may be due to the smaller fibril diameters (Birch, 2007). Typical marker configurations involve either placing a marker over the center of rotation of each joint or aligning two markers along the long axis of each segment (Fig. Briefly, in a two-dimensional link segment model, each segment is represented as a solid bar and the location of its center of mass is known relative to the coordinates that define the segment. et al. The third interosseous muscle (suspensory ligament) acts as an energy-storing tendon and has an even lower modulus of elasticity than the SDF tendon (Birch, 2007). The input for the model comprises kinematic and force data that are synchronized in time and space, together with segment morphometric data (Fig. Draught horses have more ‘bone’: the circumference of the cannon bone just below the knee is greater than in lighter horses, this being associated with their superior weight-carrying capacity. The medial head, which has longer fibers (15–40 mm) and fewer slow-twitch fibers, may be more important in locomotion (Hermanson & Hurley, 1990). Pennation of the muscle fibers results in a larger PCSA than for equal-sized muscles with parallel fibers. 6.1). During trotting, the elbow has well-defined bursts of energy absorption on the extensor side of the joint in early stance followed by energy generation on the extensor aspect in midstance (Clayton et al., 1998). Reprinted from Willemen, M.A., Savelberg, H.H.C.M., Barneveld, A., 1997, The improvement of the gait quality of sound trotting warmblood horses by normal shoeing and its effect on the load on the lower forelimb, Livestock Production Science, 52 (2), 145–153, with permission from Elsevier. 6.5) (van Weeren et al., 1990a; Back et al., 1995a). A stride is regarded as the unit of measurement. It is divided into the thoracic and cervical parts and is attached to the bones by sheet-like tendons. They form a large, powerful muscle, with long fibers oriented parallel to the muscle belly (Payne et al., 2004). Reprinted from Brown, N.A.T., Kawcak, C.E., McIlwraith, W., Pandy, M.G., 2003, Architectural properties of distal forelimb muscles in horses, Equus caballus, Journal of Morphology, with permission from John Wiley and Sons. The vast majority (95%) of the muscle fibers are type I, and presumably slow-twitch (Wilson et al., 2001; Soffler & Hermanson, 2006). ), Architectural properties of the muscles of the equine antebrachium. Clue: Forelimb bones. The absence of a clavicle allows the scapula more freedom to rotate and translate relative to the ribcage, which may contribute to an increase in stride length. MFL, mean fiber length; PCSA, physiological cross-sectional area; force, maximal isometric force generation capacity estimated by multiplying muscle PCSA by the maximal isometric stress of skeletal muscle, taken as 0.3 MPa; power, maximal power output calculated as one-tenth of the product of force and maximal contraction velocity, which was estimated based on published values of equine muscle fiber-typing. When the DDF muscle becomes fatigued, the SDF tendon is over-loaded and predisposed to strain injury (, Sagittal plane analysis of forelimb kinematics and kinetics. There are related clues (shown below). In general, these are large muscles with long fibers arranged parallel with the long axis of the muscle belly (Table 6.2) that insert on the bones via short tendons or aponeurotic sheets (Payne et al., 2004). This is in contrast to brachialis, which acts as an elbow flexor in early swing (Tokuriki et al., 1989) and contributes to the flexor moment at the elbow at this time in walk (Clayton et al., 2000a, b) and trot (Lanovaz et al., 1999). In the canter, overall limb loading decreases with less elastic energy being stored in the SDF tendon, and the DDF tendon being more loaded (Butcher et al., 2007). At the elbow there are bursts of energy generation on the extensor aspect in early stance, which is thought to be due to concentric action of triceps brachii, and on the flexor aspect in late stance, which coincides with electrical activity in biceps brachii (Tokuriki et al., 1989). As the name suggests, it has three heads. The joints of the horse’s forelimb from the elbow distally are more or less constrained to move in a sagittal plane with relatively small amounts of abduction/adduction and internal/external rotation (Thompson et al., 1992; Degueurce et al., 1996). For example, joint angles may be measured between the proximal and distal segments on the anatomical flexor aspect or as the angle by which the distal segment deviates from alignment with the proximal segment, or some combination of these methods (Fig. The common digital extensor (CDE) (Table 6.3) and lateral digital extensor muscles have long fibers, small PCSA and long tendons (Brown et al., 2003). Color the patella (S) green. 6.3, Table 6.2) is the largest extrinsic muscle of the forelimb both in mass and volume and has the shortest mean fiber length. For instance, Humans, Cows and Whales are all mammals but their forelimbs vary. Today, muscle fibers comprise about 10% of the suspensory ligament. Flexor carpi radialis and extensor carpi radialis (Table 6.3) have long muscle fibers with small pennation angles (less than 20°), a small PCSA, and short tendons (Brown et al., 2003). They are subject to high tendon strains as the limb is loaded during stance, especially at the trot. However, the fibers are very short (2–10 mm) and highly pennate (pennation angle up to 60°) (Grandage, 1981; Dimery et al., 1986; Hermanson & Cobb, 1992; Biewener, 1998; Wilson et al., 2001; Brown et al., 2003; Zarucco et al., 2004), resulting in the largest cross-sectional area of the antebrachial muscles and endowing a large force-generating capacity (Hagen et al., 2002; Brown et al., 2003). Breakover is the terminal part of stance when the heels leave the ground and rotate around the toe, which is still in ground contact. In general, these are large muscles with long fibers arranged parallel with the long axis of the muscle belly (Table 6.2) that insert on the bones via short tendons or aponeurotic sheets (Payne et al., 2004). Supraspinatus and infraspinatus are active during early and midstance in walk, trot and canter (Aoki et al., 1984; Robert et al., 1998), when the primary action of supraspinatus appears to be stabilization of the shoulder joint. In the horse’s forelimb, the biceps tendon is stretched by forward movement of the trunk and the changing orientation of the ground reaction force vector relative to the shoulder and elbow joints during the stance phase. The DDF is also compartmentalized morphologically into regions with different lengths of fibers in the range 5–117 mm (Hagen et al., 2002; Brown et al., 2003; Zarucco et al., 2004). Net joint power, calculated as the product of the joint moment and that joint’s angular velocity, measures the rate of mechanical energy generation and absorption across a joint. As a consequence of this translational motion, the instantaneous center of rotation of the scapulothoracic joint changes throughout the stride. The force of contraction of a muscle can be estimated in a Hill-type model based on four parameters: fiber length, maximal fiber shortening velocity, pennation angle, and peak isometric muscle force (Zajac, 1989). The fatigue-resistant, slow-twitch fibers of the SDF tendon act eccentrically or isometrically during stance with changes in length of the musculotendinous unit being due almost entirely to stretching of the elastic tendon (Butcher et al., 2007). Thus biceps brachii appears to be responsible for a net extensor moment at the shoulder through most of stance, while triceps brachii is generating an extensor moment at the elbow. Energy absorption and generation on the extensor (cranial) aspect of the shoulder joint are similar in magnitude to those at the elbow joint but occur slightly later in the stance phase. When fibers insert into the tendon at an angle (pennation angle), the amount of force transmitted to the tendon is determined as force developed in the fiber multiplied by the cosine of the pennation angle. It has been speculated that reduction in the muscular function of the equine interosseus began about 15 million years ago, when ancestral horses were increasing in size and moving to the grasslands where efficient overground locomotion was required (Camp & Smith, 1942). These organisms share the same forearm bones because they all evolved from a common ancestor. It supports the metacarpophalangeal (MCP) joint during the stance phase, which is critical to the function of the equine limb. Right: measurement of the angle by which the distal segment differs from alignment with the proximal segment; deviation toward the flexor aspect is negative (−), deviation toward the extensor aspect is positive (+). Left: measurement of the angle between the proximal and distal segments on the anatomical flexor aspect. The "funny bone" (technically the olecranon process) is the backwards-pointing projection of the ulna. When the carpus buckles, the forearm is released allowing the biceps tendon to recoil. These features suggest that serratus ventralis thoracis bears primary responsibility for anti-gravitational support of the trunk, whereas the other extrinsic muscles move the forelimb relative to the trunk during the swing phase or advance the trunk over the grounded limb during the stance phase. This clue was last seen on December 8 2017 on New York Times’s Crossword. Compared with supraspinatus, biceps brachii has a larger force generating capacity and a larger moment arm at the shoulder joint, which suggests that it may be a more effective extensor of the shoulder (Watson & Wilson, 2007). The SDF muscle has a high percentage of slow-twitch muscle fibers (Butcher et al., 2007) that are resistant to fatigue. These qualities suggest a role in initiating and controlling carpal flexion/extension during the swing phase. The point of the elbow should be in the same plane as the point of the shoulder, so that it does not turn in or out. Tags: Equine Locomotion Flexor carpi ulnaris and ulnaris lateralis have short, highly pennated fibers (pennation angle close to 30o), which results in a large PCSA (Brown et al., 2003). Left: measurement of the angle between the proximal and distal segments on the anatomical flexor aspect. The rhomboideus lies underneath the trapezius and ties the scapula into the sides of the spinous processes of the thoracic vertebrae and the nuchal ligament. The concept of the forelimb acting as a spring implies that changes in joint angles as the limb accepts weight result in shortening of the bony column and stretching of the musculotendinous units. For muscles with equal volumes, PCSA is larger in muscles with short, pennated fibers because a larger number of fibers can be contained within the volume. Read More. Read This! Distances are expressed as percentage segment length between the two reference markers. The muscles of the forearm move and stabilize the carpal and digital joints. toward or near the belly (front of a primate or lower surface of a lower … The hoof may be represented by different combinations of markers with radiographic identification of the center of rotation of the DIP joint relative to the hoof markers. The humerus is very strong and its angulation, which should be about 60° to the horizontal, allows for shock absorption. Muscles in the proximal forelimb tend to be large and powerful with long fibers arranged parallel to the muscle belly to move the joints through a large range of motion. The diagonal support phases are usually separated by aerial or suspension phases in which all feet are off the ground (Alexander & Jayes, 1978). Evaluation of the geometry and architecture of the musculotendinous units is helpful in understanding whether their function is to produce rapid movements or generate large forces to stabilize the joints. Within a stride, each limb has a stance phase when the hoof is in contact with the ground, and a swing phase when the hoof is swinging through the air. A vertical axis drawn through the centre of the cannon bone should bisect the hoof into two equal halves, A line running across the top of the coronary band should be horizontal, showing that the hoof wall is at the same angle on both sides, The wall should not flare out or run under, The hoof should be the same shape and size on either side of the frog, The hoof–pastern axis (HPA) should be in alignment. During standing, the suspensory ligament is fully capable of supporting the horse’s weight passively (, The common digital extensor (CDE) (Table 6.3) and lateral digital extensor muscles have long fibers, small PCSA and long tendons (, As horses bounce over the ground in the trot, canter and gallop, the forelimbs have been estimated to contribute one-third of the energy storage compared with two-thirds in the hind limbs (Biewener, 1998). GRF data can be combined with kinematic data using a link segment model to calculate internal forces within the limb that cannot be measured directly (see Chapter 19 for details). Seen from the side, a line dropped from the midpoint of the scapula should run down in front of the forelimb and pass down through the middle of the hoof. Serratus ventralis thoracis is the primary muscular component of the thoracic sling, which suspends the trunk between the forelimbs and controls the position of the thorax and withers relative to the scapulae when the forelimbs are weight-bearing. Serratus ventralis thoracis (Fig. In the equine forelimb, artifacts due to skin displacement may be small enough to be negligible on the antebrachial and metacarpal segments, but are large enough to alter sagittal plane kinematics significantly on the scapular, brachial, and pastern segments. In small, non-cursorial mammals, the forelimb is attached to the trunk via a shoulder girdle, in which the clavicle articulates with the sternum and scapula, imposing some constraints on forelimb motion. It is estimated to withstand forces of 3.2 × 104 − 5.4 × 104 N when stretched as the forelimb is retracted in late stance with the shoulder and elbow in extension (Watson & Wilson, 2007). Serratus ventralis thoracis (Fig. The effect is rapid extension of the shoulder, flexion of the elbow and forward acceleration of the distal limb. Horses do not have a clavicle or shoulder girdle. The hoof should land level and slightly heel first. Muscle density, calculated as mass divided by volume, has been determined to be 1.075 g/cm3 over a range of muscles, with different muscles varying by only a small amount (Brown et al., 2003). An inverse dynamic solution is used to compute net joint moments and net joint powers (Colborne et al., 1997a,b). Left: markers placed over centers of joint rotation with limb segments being represented by lines joining the markers. The medial and lateral heads of the biarticular biceps brachii span the extensor aspect of the shoulder and the flexor aspect of the elbow. Negative work is done when the net joint moment acts in the opposite direction to the angular velocity of the joint, so the muscle lengthens as it generates tension (eccentric contraction) and acts to restrain joint movement in opposition to gravity or some other external force. By comparison, muscles in the distal limb are smaller and less powerful with short, pennate fibers that are not capable of a large amount of shortening but are well suited to contract isometrically. During standing, the suspensory ligament is fully capable of supporting the horse’s weight passively (Dyce et al., 1996). 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