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The authors of this review are to be congratulated on an interesting synopsis of the evidence for either peripheral or central fatigue which occurs during different types of exercise. However, they appear to have used it to criticise the model that we developed in five consecutive articles published recently in this journal. 1–5 For some reason, they have focused on one of these five articles, 2 which in particular outlines the problems with the peripheral model of fatigue and introduces the concept of dynamic, active, central regulation of exercise. They appear to have ignored the further development of the complete central governor model as described in the later papers, 34 in which a complex system model of fatigue was systemically developed, and summarised in the fifth and final paper of the series. 5 Indeed, the title of the fourth paper 4 was ‘‘Complex systems model of fatigue: integrative homoeostatic control of peripheral physiological systems during exercise in humans’’. We therefore draw the attention of the readers of this review to the fact that the complete central governor model is not merely a reworking of the old debate of central versus peripheral fatigue. In the later papers in the above series, the concepts of complex systems and non-linear control during exercise are introduced, feedforward and feedback control mechanisms during exercise are described, a number of different candidates (signallers) in peripheral systems that may regulate the fatiguing process are suggested, system redundancy and hierarchical control mechanisms during exercise are proposed, and the relation between these multiple regulatory systems and the perception of effort are described. It is not clear therefore why the authors of this review have not acknowledged the central governor model in its entirety, as outlined and developed in all five of our papers, and have rather attempted to reduce the model to a central versus peripheral debate. Therefore we suggest that the authors of this review read all five papers more carefully, and they will see that their ‘‘alternative’’ concept of task dependency is one of several of the key components discussed. In the short space available, it is not possible to rebut each of the concerns described in this review, and indeed we do not feel it is necessary to do so, as a number of these points raised would support hypotheses described by us as part of the complete central governor model in the five papers. We suggest that the authors, and readers, of this review ponder the following question: what organ or control processes would decide which physiological system is used for a specific task in the ‘‘task dependency’’ model described here as an alternative model to the central governor model? Finally, for readers who have not yet read our five articles outlining the complete central governor model, we draw attention to a section of the final paragraphs of the series: ‘‘The challenge to exercise physiologists therefore is to examine changes in pacing strategy (and exercise) from a complex system process, rather than concentrating on any single physiological system or metabolic process when researching the causes of ‘fatigue’. Perhaps it is now finally time to replace the concept of catastrophe with that of complexity in our future studies of human exercise physiology.’’ The central governor model is a complex model of fatigue, and is not a reworking of the old central versus peripheral debate, to which the authors of this review appear to have attempted to reduce our model. T D Noakes, A St Clair Gibson, E V Lambert University of Cape Town, Cape Town, South Africa; tdnoakes@sports.uct.ac.za REFERENCES 1 Noakes TD, St Clair Gibson A, Lambert EV. From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans. Br J Sports Med 2004;38:511–14. 2 Noakes TD, St Clair Gibson A. Logical limitations to the ‘‘catastrophe’’ models of fatigue during exercise in humans. Br J Sports Med 2004;38:648–9. 3 St Clair Gibson A, Noakes TD. Evidence for complex system integration and dynamic neural regulation of skeletal muscle recruitment during exercise in humans. Br J Sports Med 2004;38:797–806. 4 Lambert EV, St Clair Gibson A, Noakes TD. Complex systems model of fatigue: integrative homoeostatic control of peripheral physiological systems during exercise in humans. Br J Sports Med 2005;39:52–62. 5 Noakes TD, St Clair Gibson A, Lambert EV. From catastrophe to complexity: a novel model of integrative central neural regulation of effort and fatigue during exercise in humans: summary and conclusions. Br J Sports Med 2005;39:120–4. 586 Weir, Beck, Cramer, et al www.bjsportmed.com