Highly Athletic Terrestrial Mammals: Horses and Dogs

Abstract

Evolutionary forces drive beneficial adaptations in response to a complex array of environmental conditions. In contrast, over several millennia, humans have been so enamored by the running/athletic prowess of horses and dogs that they have sculpted their anatomy and physiology based solely upon running speed. Thus, through hundreds of generations, those structural and functional traits crucial for running fast have been optimized. Central among these traits is the capacity to uptake, transport and utilize oxygen at spectacular rates. Moreover, the coupling of the key systems--pulmonary-cardiovascular-muscular is so exquisitely tuned in horses and dogs that oxygen uptake response kinetics evidence little inertia as the animal transitions from rest to exercise. These fast oxygen uptake kinetics minimize Intramyocyte perturbations that can limit exercise tolerance. For the physiologist, study of horses and dogs allows investigation not only of a broader range of oxidative function than available in humans, but explores the very limits of mammalian biological adaptability. Specifically, the unparalleled equine cardiovascular and muscular systems can transport and utilize more oxygen than the lungs can supply. Two consequences of this situation, particularly in the horse, are profound exercise-induced arterial hypoxemia and hypercapnia as well as structural failure of the delicate blood-gas barrier causing pulmonary hemorrhage and, in the extreme, overt epistaxis. This chapter compares and contrasts horses and dogs with humans with respect to the structural and functional features that enable these extraordinary mammals to support their prodigious oxidative and therefore athletic capabilities.

Assessment of protein synthesis in highly aerobic canine species at the onset and during exercise training

“…One interpretation of the data is that the rested Alaskan Huskies keep a proportionally faster Mito protein synthesis, relative to the other two fractions, during the untrained state. This interpretation implies that the Alaskan Huskies maintain a relatively greater (as compared with Laboratory Retrievers) aerobic phenotype, which would be commensurate with the known highly aerobic nature of the breed (17), even in the untrained state (1). A second interpretation is that rather than the exercised Labrador Retrievers being in a negative energy balance, the sedentary Labrador Retrievers were actually in a positive energy balance and the greater synthesis rates of Mixed and Cyto fractions were from weight gain.…”

“…(V O 2max ) of 145.8 ml·kg Ϫ1 ·min Ϫ1 recorded in Labrador Retrievers (18) and 240 ml·kg Ϫ1 ·min Ϫ1 in one greyhound (17).…”

Integrative Biology of Exercise

“…With respect to speed, the cheetah (Acinonyx jubatus) reigns supreme among terrestrial mammals, achieving maximum velocities of 113 km/hr (Sharp, 1997), making the world's fastest human (with a top speed of 48 km/hr) seem rather pedestrian. The pronghorn antelope (Antilocapra Americana) can sustain speeds of >80 km/hr for 4-5 km, and the Greyhound and sled dog are similarly capable of extraordinary bursts of speed (Poole and Erickson, 2011). Notwithstanding such comparisons, research into the ''limits'' of athletic capacity provides insight into the roles of various organ systems involved in maximizing human performance (Joyner and Coyle, 2008).…”

Regulation of Increased Blood Flow (Hyperemia) to Muscles During Exercise: A Hierarchy of Competing Physiological Needs

“…It is also important to note that in certain "athletic" species including dogs and ponies, V O 2max values in excess of 120 ml·kg Ϫ1 ·min Ϫ1 are seen with values of 140 -150 ml·kg Ϫ1 ·min Ϫ1 reported in both foxhounds and thoroughbred horses (30,332,364). Incredibly, pronghorn antelopes are thought to have V O 2max s in excess of 200 ml·kg Ϫ1 ·min Ϫ1 based on the fact that they can run 11 km in 10 min (282).…”