Background Previous studies of death during law enforcement restraint have focused on lying restraint positions; this study extends this work to seated restraint positions. Methods Lung function in a standing control position was compared with lung function in seated positions using 40 volunteers. Results No significant reduction in lung function was detected in an upright seated position. When participants were leant forward while seated, significant reductions in lung function occurred. The application of restraint holds in the seated, leant forward position resulted in a non-significant further reduction in lung function. Reductions in lung function were greater in those participants with higher body mass index (BMI). Conclusions Seated restraint positions with the person leant forward may increase the risk of harm or death during prolonged restraint. The risk will be further increased where the person exhibits higher BMI.