Chemical Control of Breathing in Identical Twin Athletes

The contribution of genetic and environmental factors to physiological variables has always been difficult to quantitate. Studies of identical twins have shown a close correlation between twins in vital capacity (Arkinstall, Nirmel, Klissouras and Milic-Emili, 1974) and maximal oxygen uptake (Klissouras, Pirnay and Petit, 1973). No such correlation was found for measurements of the ventilatory response to carbon dioxide (Arkinstall et al., 1974) and the ventilatory response to hypoxia has never been reported in identical twin subjects.