October 25, 2015

Biomechanics: No force limit on greyhound sprint speed

The authors of this papers looked to explain why greyhounds do not need to slow down when racing round a tight bend, unlike human athletes. To test this, the scientists watched high speed video recordings of 17 different racing greyhounds both on straightaways and on bends. After observing the timing of the foot-ground contact in the dogs and calculating the peak force on the legs, it was determined that there were little no to changes in the time of the contact on the straightaways vs the bend. From this, they were able to conclude that peak force on the legs does not limit sprint speeds.

According to the study, maximum running speed is largely constrained by the speed that the limbs can be swung forwards and backwards at, as well as by the force they can handle while in contact with the ground. When humans sprint around banked bens, they change the amount of time that their feet are in contact with the ground to spread the amount of time over which the load is applied. This keeps the force on the legs constant. Greyhounds, upon entering a tight bend, do not change their foot-contact timings. They therefore have to undergo roughly a 65% increase in limb forces. This data agrees with the earlier idea that greyhounds power their motion with torque in the hips so that the the muscles that are providing their power are mechanically separated from the structures that support their weight.  Therefore, the difference in human and greyhound top speeds must be due to the fact that the two animals have different mechanisms for producing power and supporting weight.

Usherwood, J. and Wilson, A. (2018). No force limit on greyhound sprint speed. [online] Available at: http://rdcu.be/exZo [Accessed 29 Mar. 2018].