[AusRace] Moderating influences in the running of racehorses - pt 4

[Tony Moffat]

All the words and numbers are here

https://www.physiology.org/doi/full/10.1152/japplphysiol.00560.2011

If you knew, or had an oversight of the topography of todays course, this would be important. The 'stitch' at Randwick (old) for instance was often cited as a cruelling climb for tiring horses. It is (was) obvious, a view downslope almost but horses overcame it to win running away, or Bernboroughlike.  


DISCUSSION: 
The aim of this study was to explore whether a constant metabolic power limit accounts for the speed of racehorses during racing. If predominantly limited by power, racehorse maximum speed would be lower on an incline and greater on a decline. Results show that highest speeds were in fact achieved on a level gradient and horses were slower on both incline and decline slopes.

Incline data were consistent with a simple metabolic power limit. As gradient is increased, there is an increased power requirement to raise the COM against gravity, increasing the COM potential energy. This can be demonstrated as an energy constraint as work of forward locomotion is offset against potential energy work, as reflected in data by Eaton et al. (4). This, in turn, reflects the metabolic capacity of the animal through its ability to maintain speed on an incline. This can be utilized in the racing industry, in that, if horse speed decreases on an incline, those with the metabolic capacity to cope with the additional cost and maintain speed will take advantage over hilly races.

Comparison of the cost of horizontal movement with vertical work in humans and horses can give insight into power constraints on running. Snyder and Carello (26) combined data from a number of studies to examine the additional metabolic cost of incline running in a range of bipeds and quadrupeds of different sizes. They concluded that, although there is a substantial difference between small and large animals in the size range we are discussing here, the efficiency of generating potential energy work from metabolic work (over and above horizontal running) is approximately constant. This means that differences in body mass do not confound conclusions about the effect of incline, for these animals. From the data in Fig. 4, horses gallop 0.5 m/s slower for each 1% increment in uphill gradient. From these data a horse ascending at 1 m/s vertically will gallop 3 m/s slower than on the flat (18 m/s on the flat vs. 15 m/s on a 6% slope). This equates to a trade-off of 1 vertical meter to 3 horizontal meters. Davies (2) gives a slowing of 3.3% for each 1% increase in gradient for elite human runners, a figure that is often quoted in the athletics performance literature with some anecdotal validation. At a workload equivalent to 4-min mile pace (6.7 m/s) a runner on a 6% slope will slow by 19.8%, i.e., by 0.198·6.7 = 1.33 m/s and have a vertical velocity of 0.06·(6.7–1.33) = 0.32 m/s. So for each 1 m of vertical ascent they will travel 1.33/0.32 = 4.2 m less horizontal distance. This relationship is predicted from limited data for human running, which may affect accuracy. This is interesting because published data indicate that COT (energy to move 1 kg 1 m) is almost speed independent. Furthermore the COT is about twice as high in humans [5 J·kg−1·m−1(30), 4.25 J·kg−1·m−1 (6)] than horses [2.4 J·kg−1·m−1 (14), 2.44–2.48 J·kg−1·m−1 (31)]. If the cost of doing potential energy work is similar in both then the horse should slow by twice as much as the human, because this additional cost is a much larger fraction of the total cost of transport. To the contrary, we find that the horse actually slows slightly less than the human. There are a number of potential explanations for this, including the gradients used, the accuracy of the various datasets (particularly the effect of gradient on human running speed), and differences between overground and treadmill locomotion. If horses are more efficient at performing potential energy work this may reflect an effect of the greater aerodynamic drag losses at their higher speeds, an inherent difference in their muscle efficiency or a locomotor mechanics effect.

There are more paragraphs, sorry - follow link for the whole article. The topography of the course, essentially the slopes and declines of the run, would seem to be important. 

Conclusion
During moderate duration races, horses show a speed detriment on inclines that corresponds to trading off the metabolic cost of height gain with the metabolic cost of horizontal galloping. This is consistent with existing data for human runners. From the literature, humans run faster on a decline, explained by the energy gained by the COM from height loss, but this study has shown that horses go slower, which may be attributable to the anatomical simplicity of their front legs, limiting weight support and stability. Humans appear to be power limited with an optimum gradient of 0.1–0.2 decline for maximum speed running (15, 16). During racing, horse maximum speed is less on both inclines and declines, with top speeds being achieved during level running.


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