EMG recordings of the respiratory muscles during unilateral and bilateral chest expansion.

Respiratory muscle (RM) EMG was recorded in 10 healthy adults during bilateral and voluntary unilateral inspiration. Each performed bilateral and unilateral inspiration at 50, 75 and 100 per cent of maximal inspiration (PI max) measured with a mouth pressure gauge. The obliquus externus abdominus (EAO) EMG was also recorded in five subjects. Results showed that RM and EAO activity on the expanding side was similar during all levels of effort. The RM activity on the non-contracting side during most submaximal efforts was higher than that on the same side during bilateral efforts but not during maximal effort. The increase in EMG could be due to cross-talk from EAO and latissimus dorsi, or co-activation of the internal intercostal muscles. Because RM activity at PI max was similar for unilateral and bilateral efforts, it was concluded that voluntary unilateral RM inhibition may not be possible during maximal effort.