ABSTRACT
The bulk of the information regarding the control of physiological function relies in its transient, or non-steady state, response to a particular forcing regime. In the steady state of dynamic muscular exercise, for example, the oxygen uptake ( https://www.w3.org/1998/Math/MathML"> V ˙ O 2 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315025001/ca0a1b50-16e7-4532-9e85-fe2cd38f2327/content/inline-eqn468_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> ) response as a function of work rate is largely independent of physical “fitness” or training status, at least over the work-rate range within which there is not a sustained metabolic acidaemia (i.e. below the lactate threshold). The transient behaviour, however, is often appreciably different. In response to a square-wave or constant-load exercise bout, https://www.w3.org/1998/Math/MathML"> V ˙ O 2 https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315025001/ca0a1b50-16e7-4532-9e85-fe2cd38f2327/content/inline-eqn469_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> increases faster in “fit” or endurance-trained subjects, whereas the transient response is slower in sedentary subjects. Even at this simplified level, this response behaviour provokes two important questions:
What are the physiological control mechanisms which produce the pattern of response in the non-steady state and which account for it varying with sedentarity or training?
What are the consequences of the different response profiles for the demands on the energy stores which supplement the aerobic energy yield?
