Effects of grade and mass distribution on the mechanics of trotting in dogs

Abstract

SUMMARYQuadrupedal running on grades requires balancing of pitch moments about the center of mass (COM) while supplying sufficient impulse to maintain a steady uphill or downhill velocity. Here, trotting mechanics on a 15deg grade were characterized by the distribution of impulse between the limbs and the angle of resultant impulse at each limb. Anterior-posterior manipulation of COM position has previously been shown to influence limb mechanics during level trotting of dogs; hence, the combined effects of grade and COM manipulations were explored by adding 10% body mass at the COM, shoulder or pelvis. Whole body and individual limb ground reaction forces, as well as spatiotemporal step parameters, were measured during downhill and uphill trotting. Deviations from steady-speed locomotion were determined by the net impulse angle and accounted for in the statistical model. The limbs exerted only propulsive force during uphill trotting and, with the exception of slight hindlimb propulsion in late stance, only braking force during downhill trotting. Ratios of forelimb impulse to total impulse were computed for normal and shear components. Normal impulse ratios were more different from level values during uphill than downhill trotting, indicating that the limbs act more as levers on the incline. Differential limb function was evident in the extreme divergence of forelimb and hindlimb impulse angles, amplifying forelimb braking and hindlimb propulsive biases observed during level trotting. In both downhill and uphill trotting, added mass at the up-slope limb resulted in fore-hind distributions of normal impulse more similar to those of level trotting and more equal fore-hind distributions of shear impulse. The latter result suggests a functional trade-off in quadruped design: a COM closer to the hindlimbs would distribute downhill braking more equally, whereas a COM closer to the forelimbs would distribute uphill propulsion more equally. Because muscles exert less force when actively shortening than when lengthening, it would be advantageous for the forelimb and hindlimb muscles to share the propulsive burden more equally during uphill trotting. This functional advantage is consistent with the anterior COM position of most terrestrial quadrupeds. Supplementary material available online at

Modulation of joint moments and work in the goat hindlimb with locomotor speed and surface grade

“…This result is consistent with the heightened role of the hindlimbs in providing support and propulsion on inclined terrain (e.g. Lee, 2011).…”

“…These studies have confirmed, for example, that ground reaction forces (GRFs) are re-distributed between the forelimbs and hindlimbs with changes in surface grade; the forelimbs typically provide increased support and braking on a downslope, while the hindlimbs provide increased support and propulsion on an upslope (e.g. Dutto et al, 2004;Gregor et al, 2006;Lammers et al, 2006;Lee, 2011). Cats have been shown to generate increased extension moments at the hip, knee and ankle when walking on an upslope and decreased moments at the hip and ankle when walking on a downslope (Gregor et al, 2006), which is consistent with re-distribution of the GRFs and reorientation of the resultant force vectors.…”

“…A few biomechanical studies of cats (e.g. Gregor et al, 2006), dogs (Lee, 2011), goats (Lee et al, 2008) and other animals (e.g. Dutto et al, 2004;Lammers et al, 2006) on sloped surfaces have been reported.…”

The metabolic cost of incline locomotion in the Svalbard rock ptarmigan (Lagopus muta hyperborea): the effects of incline grade and seasonal fluctuations in body mass

“…In addition to the elevated incline cost imposed by changes in muscle contractile behaviour, there may be a reduction in the force-generating capacity of the locomotor muscles as a result of altered limb posture (Higham and Biewener, 2008). Such changes have been observed in a number of quadrupedal species (Carlson-Kuhta et al, 1998;Lammers et al, 2006;Lee, 2011;Vilensky et al, 1994). Although posture was not quantified in the present study, the intercepts of the lines relating P met to U have been postulated to represent a 'postural cost' separate from the cost of moving and that of resting metabolism.…”

How forelimb and hindlimb function changes with incline and perch diameter in the green anole,Anolis carolinensis

“…Although the hindlimbs are the key propulsors in terrestrial vertebrates, with the forelimbs absorbing collisional energy and acting primarily as brakes (Lammers and Biknevicius, 2004;Autumn et al, 2006;Lee, 2010;Deban et al, 2012), the coordinated function of the forelimbs and the hindlimbs is poorly understood in arboreal vertebrates. Structural differences between the forelimbs and the hindlimbs have been well documented among vertebrates; the pectoral girdle is generally more mobile than the pelvic girdle and structural differences between the glenoid cavity and the acetabulum lead to the potential for a greater range of motion in the forelimb than in the hindlimb (Haines, 1952;Snyder, 1954;Peterson, 1971;Peterson, 1973;Peterson, 1974;Jenkins and Goslow, 1983;Peterson, 1984;Reynolds, 1985;Schmitt, 1994;Larson et al, 2001;Lammers, 2007;Zihlman et al, 2011).…”