Force production of the genioglossus as a function of muscle length in normal humans

Abstract

Resting muscle length affects both maximum force production and force maintenance. The strength and force maintenance characteristics of the genioglossus as a function of resting muscle length have not been described. We hypothesized that genioglossus optimum length ( L o) could be defined in vivo and that the ability of the genioglossus to sustain a given workload would decrease as resting length deviated from L o. To test this, 11 normal men repeated maximal isometric genioglossus protrusions at different muscle lengths to determine L o. L o was also obtained by using submaximal efforts while simultaneously recording electromyographic activity of the genioglossus, with L o defined as the length at which the force-to-genioglossus electromyographic activity ratio was maximum. Both methods provided similar results. Force maintenance was measured at four muscle lengths on separate days. Target efforts representing 60% of each subject's maximum at L o and lasting 5 s were performed at 12-s intervals. Time limit of endurance of the genioglossus was defined as the time from trial onset at which 90% of the target could not be maintained for three consecutive efforts. Time limit of endurance was greatest at L o and fell to 47.5% at L o + 1 cm, 53.8% at L o − 1 cm, and 47.4% at L o − 1.5 cm. We conclude that L o of the genioglossus can be determined in vivo and that force maintenance of the genioglossus is decreased when operating length deviates from L o.