Effect of airway control by glottal structures on postural stability.

Maintenance of upright posture involves complex neuromotor processes that include control of thoracic and abdominal pressures. Control of airflow by glottal structures is a primary determinant of thoracic pressure and may have a role in control of postural stability. This study aimed to investigate the effect of modulation of airway control on upright postural stability during postural perturbations. Standing balance was gently perturbed in the sagittal plane during 7 breathing/voicing tasks that ranged from completely closed (breath-hold), to partially opened (voicing) or completely open (sigh) glottal conditions in 11 healthy adults. Dependent measures were peak amplitude of displacement of the thorax and center of pressure (CoP). When the glottis was completely open during sigh, thoracic displacement in response to the perturbation was greater than in all other conditions, regardless of direction of perturbation (post hoc, all P < 0.002). The absolute amplitude of CoP displacement was greater with backward perturbation (main effect, Direction P = 0.001) and was greater at both extremes of glottal modulation (glottis closed and completely open) than when the glottis was partially opened during counting out loud (post hoc, all P < 0.04). These results show that airway modulation affects postural control during upright perturbations. The thorax was more stable when the glottis was engaged than when it was required to remain open, whereas control of CoP displacement appeared more optimal during the natural dynamic mid-range airway modulation of voicing. These data suggest that glottal control influences balance, and that glottal control strategies may be an important consideration for patients with breathing and/or balance disorders.

Effects of practice on the ability to perform lumbar stabilization exercises.

STUDY DESIGN: Randomized pretest-posttest control group design. OBJECTIVES: To determine the intratester and intertester reliability of a modified isometric stability test and to use this test to evaluate the effects of practice following a 4-week stabilization exercise program with weekly reinstruction. BACKGROUND: Although "stabilization" exercise programs are commonplace in the clinic, the reliability to a tool capable of measuring changes in the ability to perform increasingly difficult stabilization exercises has not, to our knowledge, been reported. In addition, it is not clear if practice improves the ability to perform stabilization exercises. METHODS AND MEASURES: A convenience sample of 44 asymptomatic subjects was pretested using a pressure transducer placed beneath the lumbar spine to detect motion (+/- 4 mm Hg). A series of 7 exercises was attempted, which required increasing levels of muscular control of the lumbar spine for stability. Subjects received a pass or fail for each exercise level based on the pressure gauge readings and the absence of movement compensations. Subjects were assigned randomly to exercise and nonexercise groups, and posttest measurements were taken after 4 weeks. The control group did not receive additional instruction. RESULTS: The weighted kappa coefficient of 0.61 for intratester and 0.62 for intertester represents good agreement. The median level of exercise attainment increased for the exercise group but not for the nonexercise group. CONCLUSION: These results suggest that the modified isometric stability test was reliable and that a 4-week lumbar stabilization exercise program, with weekly intervals of reinstruction and testing, improves the ability to perform progressively difficult lumbar stabilization exercises.