Breath holding at beginning of exercise.

Abstract

Men stood astride a moving treadmill belt and at a verbal signal held their breath, jumped on the treadmill belt, and walked or ran at a series of speeds up to 9 mph until the breaking point was reached. Breath-holding time decreased sharply with increasing exercise rates, but began to level off at approximately 30 sec between 6 and 9 mph. Breaking-point alveolar Po2 decreased and Pco2 increased with increasing treadmill speeds. When these two factors were applied in the Otis, Fenn, and Rahn ventilation equation to describe ventilation at the breaking point, the ventilation ratio increased, and it was observed that the men withstood a stronger stimulus to breathe as the work rate increased, even though the breath-holding time remained fairly constant at higher work levels. Apparently at the beginning of work the stimulus to breathe is the combination of a relatively weak neurogenic stimulus and an accumulating chemical stimulus. It is postulated that the constancy of beginning breath-holding times at high work rates may reflect a transport time for the chemical stimulus to reach the receptor area from working muscles via the circulation. Submitted on September 25, 1961