In the last 25 years, techniques utilising muscle flaps to perform mechanical work have become part of the reconstructive surgeon's repertoire. In this paper, these techniques and the particular physiological challenges faced by active flaps are discussed and a sub-classification of muscle flaps into passive and active is proposed. A series of experiments are described that were designed to compare local pO(2) and gaseous perfusion, at multiple sites in pedicled tibialis anterior muscle flaps and controls, using specially developed dual amperometric microelectrodes, in an in vivo rabbit model. No significant difference in perfusion was found comparing flaps and controls until the flap's vascular pedicles were divided and ligated, and then flap perfusion fell to zero. Flap and control oxygenation varied significantly only during mobilisation and again, after pedicle division and ligation (F[13,55] = 12.3; P < 0.001)]. This absence of functional ischaemia as a consequence of mobilisation in the model used suggests the practice of delaying electrical conditioning of muscle flaps in dynamic cardiomyoplasty and neoanal sphincteroplasty might be unnecessary if these data are reproduced in human latissimus dorsi muscle. The relevance of these findings to free flap oxygen consumption and to the delay phenomenon is discussed.