Exploring the mechanical basis for acceleration: pelvic limb locomotor function during accelerations in racing greyhounds (Canis familiaris)

Abstract

SUMMARYAnimals in their natural environments are confronted with a regular need to perform rapid accelerations (for example when escaping from predators or chasing prey). Such acceleration requires net positive mechanical work to be performed on the centre of mass by skeletal muscle. Here we determined how pelvic limb joints contribute to the mechanical work and power that are required for acceleration in galloping quadrupeds. In addition, we considered what, if any, biomechanical strategies exist to enable effective acceleration to be achieved. Simultaneous kinematic and kinetic data were collected for racing greyhounds undergoing a range of low to high accelerations. From these data, joint moments and joint powers were calculated for individual hindlimb joints. In addition, the mean effective mechanical advantage (EMA) of the limb and the ʻgear ratioʼ of each joint throughout stance were calculated. Greatest increases in joint work and power with acceleration appeared at the hip and hock joints, particularly in the lead limb. Largest increases in absolute positive joint work occurred at the hip, consistent with the hypothesis that quadrupeds power locomotion by torque about the hip. In addition, hindlimb EMA decreased substantially with increased acceleration -a potential strategy to increase stance time and thus ground impulses for a given peak force. This mechanism may also increase the mechanical advantage for applying the horizontal forces necessary for acceleration.

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

“…These data from goats are consistent with the increased energy absorption at the MTP joint reported for accelerating wallabies (McGowan et al, 2005) and sprinting humans (Stefanyshyn and Nigg, 1997). Interestingly, net work at the MTP joint has been shown to be relatively independent of acceleration in running greyhounds (Williams et al, 2009) and wild turkeys (Roberts and Scales, 2004). Energy absorbed at the knee joint also increased with locomotor speed, particularly during downhill running.…”

“…This simpler approach is often justified by comparing the results with the net joint moments obtained using inverse dynamics, and noting that they match well (e.g. Williams et al, 2009). However, such comparisons are potentially problematic.…”

“…We hypothesized that goats modulate hindlimb joint work more at the hip than at distal joints based on the musculotendon architecture of the distal muscles (i.e. pennate muscles with long tendons) and on previous studies of accelerating dogs (Williams et al, 2009) and goats running over different grades (Lee et al, 2008;McGuigan et al, 2009). Notably, McGuigan and colleagues estimated that the gastrocnemius and superficial digital flexor muscles produce only about 3% of the work needed to raise the goat's center of mass when trotting uphill (McGuigan et al, 2009), while Lee and colleagues reported that the increase in net work at the ankle, from level to uphill running, is typically greater than the increase in work at the knee (Lee et al, 2008).…”

Kinematics and Ground Reaction Force Determination: A Demonstration Quantifying Locomotor Abilities of Young Adult, Middle-aged, and Geriatric Rats

“…In fact, kinematics, ground reaction force determination, or both have been used in a variety of species such as elephants [33][34][35] , cattle 36 , horses [37][38][39][40] , dogs 4,[41][42][43][44][45] , cats 21,[46][47][48][49] , various rodents 3,8,50,51 , birds 4,[52][53][54][55] , and fish 56,57 (this list is by no means exhaustive). In the authors' experience, however, the use of mice is problematic given that mice are not easy to operantly condition to travel along a runway.…”

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

“…Although its effect could be partially compensated for by altering musculoskeletal transmissions, this fundamental difference in muscle contractile mechanics has unavoidable consequences. As is typical of cursorial mammals, most of a dog's limb muscle is composed of its proximal retractors and, to a lesser extent, protractors (Pasi and Carrier, 2003;Williams et al, 2009a;Williams et al, 2009b) that actuate the limbs as levers. Hence, it is predicted that the limbs will function more as levers during uphill than downhill trotting (prediction 1).…”