In order to interpret data describing segment and joint angles, it is important to know where the angles were measured. Since biceps brachii and the long head of triceps brachii are biarticular, their interaction affects motion and stability of both shoulder and elbow joints. The lateral head, with a mass of 171–343 g, is composed of short (5–8 mm), pennate fibers (Watson & Wilson, 2007), a large percentage of which are slow-twitch and well suited to postural control. 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). Log In or. 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). The forelimb (pectoral flipper) of the harbor seal has five digits of comparable length. Studies of three-dimensional forelimb kinematics, which will be described at the end of this chapter, have confirmed that flexion/extension is the dominant rotation at the carpal, metacarpophalangeal, proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints (Chateau et al., 2004, 2006; Clayton et al., 2004, 2007a, b; Hobbs et al., 2006). The Forelimb; Humerus (pl. The vast majority (95%) of the muscle fibers are type I, and presumably slow-twitch (Wilson et al., 2001; Soffler & Hermanson, 2006). At faster speeds, vertical excursions of the center of mass are reduced and the limb sweeps through a larger angle during its stance phase causing the horse to bounce off the ground more quickly (Farley et al., 1993). In a catapult, a large force is applied to store energy, which is then released rapidly to accelerate a small mass. 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). Humans have bipedal locomotion whereas cows are quadrupeds and therefore the major differences is adaptation of human forelimbs to lift the things and use their fingers (phalanges are the bones supporting fingers), there are wrist bones as well. 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. A ‘tied-in’ elbow limits stride length. Spectra Staffing Services . This muscle is more variable in its mass than the other extrinsic muscles, which may reflect adaptation in response to the amount and type of training. This work is very difficult and time consuming, but it can help biologists determine the evolution-ary ancestry of a species. The functions of the musculotendinous system of the equine forelimb include connecting the forelimb to the trunk; supporting the body mass; stabilizing the joints in opposition to the force of gravity during the stance phase; generating forces that are used for propulsion, braking and turning; and flexing the joints to lift the hoof clear of the ground during the swing phase. (1995a) How the horse moves: significance of graphical representations of equine forelimb kinematics. The architectural properties of these muscles have been described (Hermanson, 1997; Hagen et al., 2002; Brown et al., 2003; Zarucco et al., 2004) and are summarized in Table 6.3. The tree shrew is small bodied, moves easily on the ground or in the trees, and has a flexible forelimb for these functions. Discrete bursts of positive and negative work can be quantified as the areas under the positive and negative phases, respectively, of the power curve. An inverse dynamic solution is used to compute net joint moments and net joint powers (Colborne et al., 1997a,b). Compared with the primary limb protractors, brachiocephalicus and omotransversarius, latissimus dorsi develops similar amounts of force but less than half as much power. Electromyographic activity in extensor carpi radialis is concentrated at the beginning of swing (Jansen et al., 1992) when the elbow and carpus are flexing. The digits include a medial thumb (when viewed with the palm down), containing two phalanges, and four fingers, each containing three phalanges. Bones in the human arm, the forelimbs of horses and dogs, a bat’s wing, and a penguin’s flipper all share a similarity in basic structural pattern called homology. This confers the ability to resist elongation of the muscle (isometric contraction) as the limb is loaded, so elongation of the musculotendinous unit is due to stretching of the tendon that acts in series with the muscle. Forelimb segmental masses, densities, reference lines for division of segments (see Fig. There is a printable worksheet available for download here so you can take the quiz with pen and paper.. Extensive research has been done to find similarities and differences in the DNA sequences of different an-imals. Fiber lengths in Table 6.2 represent a mean of the two muscles, though brachiocephalicus has longer fibers than omotransversarius. The functions of the DDF are to flex the digital joints during the swing phase and to generate a propulsive force during the second half of stance. These qualities suggest a role in initiating and controlling carpal flexion/extension during the swing phase. 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). Subclavius (Table 6.2) has long fibers (519 mm) that allow generation of large forces to assist in adduction and retraction of the forelimb or stabilization of the scapula (Payne et al., 2004). This fiber composition is well suited for its support role as part of the stay apparatus (Swanstrom et al., 2005), and for attenuating high-frequency forces associated with impact (Wilson et al., 2001). The superficial digital flexor (SDF) muscle has a much smaller volume than the DDF muscle. The upper jaw of the human, and the upper beak of the bird is composed of a bone … There is an additional burst of energy generation on the extensor aspect of the shoulder in late stance (Clayton et al., 1998) corresponding with activity in biceps brachii (Tokuriki et al., 1989). The pectoral girdles are to the upper limbs as the pelvic girdle is to the lower limbs; the … This chapter describes the structure of the forelimb musculature, the movements of the forelimb and the role of specific muscle groups in causing and controlling those movements. In order to interpret data describing segment and joint angles, it is important to know where the angles were measured. The stance phase starts at the moment of initial ground contact, after which the hoof is decelerated during the impact phase. 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. 27, 31–38, with permission from the Equine Veterinary Journal. The knee should be flat and broad at the front with good depth. 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. It is a two-beat gait with the limbs coordinated by diagonal pairs. 6.3) and rhomboideus are the smallest extrinsic muscles of the forelimb and have medium-length fibers (Table 6.2) (Payne et al., 2004). The exception is serratus ventralis thoracis, which has short, pennate fibers and is encased in a strong aponeurotic sheath. Fig 6.2 Skin markers used to locate the centers of mass of the forelimb segments in Table 6.1, which are separated according to the incision lines shown in red. Lower row – first, second, third and fourth carpals. 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. This shows that the bones are arranged in a column, directly on top of each other, giving strength and ensuring that concussive forces spread evenly up the limb. There are related clues (shown below). Both muscles insert on the dorsal scapula and have fiber orientations ranging from vertical in the middle of the muscle to almost longitudinal towards the extremities. When the carpus buckles, the forearm is released allowing the biceps tendon to recoil. Over at the knee – the knee appears to be slightly flexed, Back at the knee – the front of the leg appears concave, Tied in below the knee – there is less bone below the knee than there is lower down the leg. The bulk of the musculature is in the proximal limb, which reduces the moment of inertia of the limb as a whole. Ventral. 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). 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). 6.3, Table 6.2) is a moderately large and powerful muscle with fairly long fibers (Payne et al., 2004). It is active through most of the stance phase when it may assist in moving the trunk forward over the grounded limb. Left: markers placed over centers of joint rotation with limb segments being represented by lines joining the markers. A strong internal tendon (mass, 122–260 g; fiber length, 9–17 cm) runs through the muscle belly of biceps brachii uniting the tendons of origin and insertion. As a consequence of the large pennation angle, the SDF is capable of minimal shortening and only about 71% of the total muscle force is transmitted to the tendon. 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. 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). The horse should have a good sloping shoulder so that there is ‘plenty in front of the rider’ and the saddle sits in a comfortable position. Part of the internal tendon of biceps brachii emerges from the muscle and continues distally as the lacertus fibrosus, a tendinous band that blends with the epimysium of extensor carpi radialis. These characteristics, which confer an increase in passive stiffness to the muscle, are typical of the anti-gravity muscles that support the body during the stance phase. Pennation of the muscle fibers results in a larger PCSA than for equal-sized muscles with parallel fibers. Serratus ventralis cervicis (Fig. Discrete bursts of positive and negative work can be quantified as the areas under the positive and negative phases, respectively, of the power curve. Latissimus dorsi (Fig. The joint angle–time diagrams were analyzed simultaneously with corresponding stick figures and marker diagrams to create a complete picture of equine forelimb motion at the trot that could be related to limb function (Back et al., 1995a). 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. The trot is the most important gait for evaluation of the quality of a horse’s movement and for detection of lameness. A long, correctly angulated scapula will also allow for a longer stride length. 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. 3.4 Skeleton of the forelimb – rear view. Furthermore, the angle may be expressed in absolute terms or it may be normalized to the standing angle, the angle at ground contact or the average angle during the stride (. 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 (+). 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). Biceps brachii has tonic activity during standing (Tokuriki et al., 1989), which supports the suggestion that the lateral part of the muscle, with its high proportion of type I muscle fibers, acts in series with lacertus fibrosus and extensor carpi radialis to stabilize the shoulder as part of the passive stay apparatus (Hermanson, 1997). In humerus. Both of these muscles insert on the accessory carpal bone, which increases their moment arm and facilitates their ability to stabilize the carpus during stance. Reprinted from Payne, R.C., Veenman, P., Wilson, A.M., 2004, The role of the extrinsic thoracic limb muscles in equine locomotion, Journal of Anatomy, with permission from John Wiley and Sons. 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 (, In the equine distal limb, the suspensory ligament and SDF tendon are primarily responsible for storing and releasing elastic energy. Biceps brachii has tonic activity during standing (Tokuriki et al., 1989), which supports the suggestion that the lateral part of the muscle, with its high proportion of type I muscle fibers, acts in series with lacertus fibrosus and extensor carpi radialis to stabilize the shoulder as part of the passive stay apparatus (Hermanson, 1997). It is a broad flat muscle covered medially and laterally by broad aponeurotic sheets. 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