Exercise in Giraffes

Observation of giraffes reveal that they can run at very high speeds (~60 km h–1) for short periods (~5 minutes) but can also run at lower speeds (40 km h–1) for much longer periods. This combination of these two types of exercise capabilities is unusual. Their short periods of high speed running have the characteristics of anaerobic exercise. Analysis of the fiber types in their gastrocnemius muscle, and estimates of the available anaerobic energy sources support that conclusion. Longer periods depend on aerobic exercise and requires an adequate supply of oxygen to the lungs, adequate delivery of oxygen to muscles, and sufficient mitochondria to use oxygen. Despite the limitations of giraffe airway and lung anatomy the respiratory system of giraffes can supply sufficient oxygen. The volume of mitochondria in giraffe muscles far exceeds the volume required for maximum aerobic exercise. The cardiovascular system has evolved to generate high blood pressure rather than the circulation of high blood volumes, but if the maximum cardiac output is combined with an increase in the number of circulating erythrocytes, then oxygen delivery to muscles can match oxygen demand. Metabolic demand for oxygen can be reduced by an increase in running economy through storage of metabolic energy as elastic energy in tendons, and it is likely that because leg tendons of giraffes are long (~2 m) that the requirement for metabolic energy can be reduced by 30–40%.