Effect of preload on lumbar muscle contraction during co-activation of trunk muscles in young males simulating anti-G straining maneuver.

ObjectPreload is known to improve spinal stability; however, its effect on the voluntary contraction of lumbar muscles needs investigation. This study aimed to investigate the role of preload in enhancing the voluntary contraction of lumbar muscles in a group of young men.MethodsTwenty healthy participants successively participated in experiments with the following preload conditions arranged in random order: no preload, forward preload, backward preload, or right-hand-pull preload. Preload intensity was set to 20% and 40% of the maximum load forces, and the participants voluntarily co-activated their trunk muscles while seated. Surface electromyography signals were recorded for analysis.ResultsForward preload was able to increase the maximal voluntary contraction strength of lumbar muscles, an effect enhanced with greater preload intensity. Backward preload reduced the maximal voluntary contraction strength of lumbar muscles as preload intensity increased. Right-hand-pull preload exhibited some asymmetrical characteristics.DiscussionDuring co-activation of the trunk muscles, preload demonstrated different effects on the voluntary contraction strength of lumbar muscles in a group of young men. As forward preload enhanced the voluntary contraction of lumbar muscles, it may play a significant role in stabilising the spine. Backward preload may also have a stabilising effect on the spine, but more research is required.