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Monday, January 3, 2011

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

  1. 1 Departments of Medicine and
  2. 3 Pediatrics, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick 08903; and
  3. 2 Department of Biomedical Engineering, Rutgers University, Piscataway, New Jersey 08554 Journal of Applied
Physiology May 2000 vol. 88 no. 5 1678-1684. 

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 determineL o. L o was also obtained by using submaximal efforts while simultaneously recording electromyographic activity of the genioglossus, withL 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 atL o and fell to 47.5% at L o + 1 cm, 53.8% at L o − 1 cm, and 47.4% atL o − 1.5 cm. We conclude thatL 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.