Vol. 88, Issue 5, 1678-1684, May 2000
Force production of the genioglossus as a function of muscle
length in normal humans
B. F. Bu
Sha1,2,
S. J.
England2,3,
R. A.
Parisi1, and
R. J.
Strobel1
Departments of 1 Medicine and
3 Pediatrics, University of Medicine and
Dentistry of New Jersey-Robert Wood Johnson Medical School, New
Brunswick 08903; and 2 Department of
Biomedical Engineering, Rutgers University, Piscataway, New Jersey
08554
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 (Lo) could be defined in vivo and
that the ability of the genioglossus to sustain a given workload would
decrease as resting length deviated from Lo. To
test this, 11 normal men repeated maximal isometric genioglossus
protrusions at different muscle lengths to determine
Lo. Lo was also obtained by
using submaximal efforts while simultaneously recording
electromyographic activity of the genioglossus, with
Lo 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 Lo 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
Lo and fell to 47.5% at Lo + 1 cm, 53.8% at Lo 
1 cm, and 47.4% at
Lo 1.5 cm. We conclude that Lo of the genioglossus can be determined in vivo
and that force maintenance of the genioglossus is decreased when
operating length deviates from Lo.
upper airway mechanics; optimum length; length-tension relationship
