Modulation of the ventilatory increase at the onset of exercise in humans

The fast initial increase in ventilation at the start of exercise is generally assumed to be of reflex origin (exercising limbs) and/or caused by a 'feedforward' mechanism increasing breathing via brainstem respiratory centres or cortical areas controlling respiratory muscles. We wanted to test whether this ventilatory increase is in part a learned response which can be modified. Eleven subjects did two 20 min low-intensity arm-cranking exercise bouts on eight different days. Seven subjects were assigned to the experimental group which performed exercise paired with an 1.5 L external dead space. Before and after their eight exercise 'training'-days, these subjects did the same exercise without dead space. At the beginning of the first post-training exercise test (without dead space), the ventilatory increase at the start of exercise (sum of the first four breaths) was significantly increased (31.1 +/- 4.1 L . min-1) compared to the pre-training test session (24.4 +/- 3.9 L . min-1). No significant change was observed in the control group. We conclude that part of the ventilatory increase at the start of exercise can be modulated and might possibly be a learned response.