This paper describes a respiratory control system model
and the associated computer simulations for human
subjects during incremental exercise, involving work rates
from zero up to the highest level in the heavy exercise
domain. Modelling the respiratory control system for
conditions above lactate threshold has rarely been
attempted because many subsystems begin to lose
proportionality in their responses. Our model is built on
the basis of putative mechanisms and is based on
information identified from a large body of published
work. Simulation results are presented and validated using
experimental results from published sources. The model
confirms that the human body employs an open-loop
control strategy for ventilation during exercise, which
contrasts with the negative feedback control mode
employed for the rest condition. It is suggested that
control of ventilation simultaneously involves at least two
variables, one being proportional to the pulmonary CO2
output and another being proportional to blood acidity
