Thermal and electromyographic correlates of shivering thermogenesis in the pigeon.

1. Electromyographic, thermal and metabolic measurements were made on pigeons subjected to stepwise ambient cooling. Subsequent signal analysis of the EMG-recordings from the pectoral muscle showed that the mean rectified value (Umrv) is the most reliable EMG-based indicator of metabolic heat production (M). 2. The muscle-abdomen temperature difference was linearly related to M, and correlated strongly with Umrv. 3. The long-term and short-term fluctuations of shivering intensity (Umrv) were highly synchronous in the two main muscles, m. pectoralis and m. supracoracoideus. 4. The EMG-signal approached a Gaussian process at high shivering intensities. Evaluation of the changes in EMG median frequency suggested a size-dependent recruitment of motor units for shivering. 5. It is pointed out that Umrv and the integrated value of EMG are interconvertible and that Umrv should be preferred, because it has more physiological relevance.