Descending bilateral control of external oblique (EO) and latissimus dorsi (LD) was investigated using transcranial magnetic stimulation. Contralateral (CL) motor evoked potential (MEP) thresholds were lower and latencies were shorter than for ipsilateral (IL) MEPs. Hotspots for EO were symmetrical; this was not the case for LD. The volumes of drive to the left and right muscles were not different. The laterality index was not different between the left and right muscles. The average index for the EO muscles was closer to zero than that for LD, suggesting a stronger IL drive to EO. The symmetry of drive to each muscle did not differ; however, the symmetry of drive varies within a subject for different muscles and between subjects for the same muscle. The findings may be useful in understanding a number of clinical conditions relating to the trunk and also for predicting the outcome of rehabilitative strategies.
Wightman and Delves are with the Department of Physiology, University College London, London, UK. Alexander is with Department of Physiotherapy, Imperial College Healthcare NHS Trust, Charing Cross Hospital, London, UK. Strutton is with the Nick Davey Laboratory, Human Performance Group, Division of Surgery, Department of Surgery and Cancer, Faculty of Medicine, Imperial College London, Charing Cross Hospital, London, UK.