“In comparison to exercise on land, respiratory work during underwater exercise is increased due to the hydrostatic pressure differences across the chest as well as increased flow resistive respiratory work.”
“It has recently been shown in healthy individuals that ventilatory limitations may cause a reduction of maximal exercise performance on land. The weakened exercise capacity has been attributed to a reduction in locomotor muscle oxygen transport secondary to diminished locomotor muscle blood flow. In several studies on land, respiratory muscle fatigue has been reported as a contributing factor to reduced maximal and endurance exercise performance. These same factors may also limit exercise performance in divers.
“The major findings of the present study were that 30 minutes of resistance respiratory muscle training carried out three or five days per week for four weeks substantially improved fin swimming endurance (at 70-75%V. O ) and that similar improvements in respiratory muscle performance were obtained.”