PLoS One. 2014 Feb 4;9(2):e88105. doi: 10.1371/journal.pone.0088105. eCollection 2014.
Dose-response effect of isometric force production on the perception of pain.
Misra G, Paris TA, Archer DB, Coombes SA.

http://www.ncbi.nlm.nih.gov/pubmed/24505397

Isometric contractions can influence the way that we perceive pain, but conclusions on the dose-response effect of force amplitude on pain perception are limited because previous studies have not held the duration of force contractions constant while varying force amplitude. To address this issue we designed an experiment that allowed us to accurately guide the amplitude of an isometric pinch grip force contraction on a trial-by-trial basis, while a thermal pain eliciting stimulus was simultaneously delivered for the same duration to the non-contracting hand. Our results show that an increase in the amplitude of force produced by one hand corresponded with a decrease in pain perception in the opposite hand. Our observations provide novel evidence that the centralized inhibitory response that underlies analgesia is sensitive to and enhanced by stronger isometric contractions.