Contribution of central and reflex nervous activity to the rapid increase in pulmonary ventilation at the start of muscular exercise in man

The role of central command in ventilatory control during static exercise

The role of central command in the respiratory response to 15 min of rhythmic-static (isometric) exercise was studied in humans. Voluntary exercise (VE) was compared with electrically induced exercise (EE) at three different work intensities, i.e. 5%, 15% and 25% of maximal voluntary contraction. A group of 12 volunteers participated in the study and each of them performed six sessions. A session consisted of at least 5 min rest, 15 min rhythmic-static single leg exercise (4 s contraction/12 s relaxation) and at least 5 min recovery. Force, minute ventilation (VE) and oxygen uptake (VO2) were measured. In EE, both VE and VO2 increased continuously during the entire exercise period after an initial rapid increase at all three work intensities. Correlation between VE and VO2 was highly significant during EE. During all three work intensities of VE, VE and VO2 achieved a steady-state after the initial increase. During VE, VE did not correlate as closely with VO2 as during EE. All these findings indicate that central command was not imperative for an adequate ventilatory response to exercise within all three work intensities investigated. Without the influence of central command, correlation between VE and VO2 was even better than during VE.