Is parasternal intercostal EMG an accurate surrogate of respiratory neural drive and biomarker of dyspnea during cycle exercise testing?

Recent evidence suggests that surface electromyography of the parasternal intercostals (EMGpara) can be a non-invasive alternative to diaphragmatic EMG (EMGdi) for estimating neural respiratory drive (NRD) during cardiopulmonary exercise testing (CPET). The purpose of this study was to determine if non-respiratory muscles influence EMGpara by having subjects place their hands on (Hon) and off (Hoff) the handlebars during cycling-based CPET. Ten healthy adults performed an incremental cycling test until volitional exhaustion. Participants were instrumented with an esophageal electrode catheter to measure EMGdi, and surface electrodes on the 2nd intercostal space to measure EMGpara. Subjects alternated between 30 s of Hon and 30 s Hoff during each exercise stage. There were no differences in EMGdi across all exercise intensities. However, EMGpara was significantly greater during the Hon vs. Hoff condition at all exercise intensities (p < 0.05). These results suggest that EMGpara may not be an appropriate surrogate of NRD during cycle exercise testing due to co-activation of adjacent skeletal muscles.