The mechanical properties of raw meat under tension were studied to characterise the factors responsible for tenderisation during storage. Extensibility and irreversible lengthening in the direction of muscle fibres was determined continuously from 2 h to 10 days after stunning by cycling the muscle between two applied forces. In post-rigor meat, extensibility increased slightly and the muscle lengthened by 40%. Lengthening occurred earlier at higher post-rigor temperatures and was more sensitive to changes in temperature than the changes in texture of cooked meat. Increasing the maximum applied stress also caused lengthening to occur earlier in post-rigor meat. No lengthening was detected pre-rigor. The relationship between the maximum applied stress and the rate of lengthening showed that lengthening would not have occurred with a stress of 0·07 Ncm(-2) or less. These findings suggest that weakening which occurs during conditioning commenced at rigor and that the component responsible for tenderising was about 30 times weaker than indicated using previous techniques. Histological sections showed regular cracks spaced at about 17 μm apart. This was believed to be indicative of the involvement of extracellular components in the texture of conditioned meat.