title: Postural effects on intra-abdominal pressure during Valsalva maneuver.
abstract: When lifting heavy loads, trunk muscle contraction converts the abdominal and thoracic cavities into a nearly rigid-walled cylinder that provides increased extrinsic stability and allows partial transfer of load away from the spine. Because twisting is a common mechanism of low-back injuries, this study was undertaken to determine if trunk rotation results in a decrease in the extrinsic stability of the spine. We studied the effects of changes in trunk posture on intra-abdominal pressure generated during a maximum effort Valsalva's maneuver (IAP max) in eight healthy volunteers. IAP max during standing combined with trunk rotation was found to be significantly lower than IAP max during standing straight (p < 0.05). IAP max during forward flexion combined with trunk rotation was significantly lower than during forward flexion (p < 0.01). The results of our study indicate that trunk rotation adversely effects the ability to perform a Valsalva's maneuver. We conclude that extrinsic stability of the spine is at a biomechanical disadvantage when the trunk is rotated and thus may be a contributing factor to twisting-type back injuries.
authors.affiliation: Department of Physical Medicine and Rehabilitation, Veterans Administration Medical Center, Minneapolis, MN 55417.
authors.forename: G D
authors.initials: GD
authors.lastname: Goldish
authors.forename: J E
authors.initials: JE
authors.lastname: Quast
authors.forename: J J
authors.initials: JJ
authors.lastname: Blow
authors.forename: M A
authors.initials: MA
authors.lastname: Kuskowski
mesh_terms: D000005:Abdomen / Q000502:physiology*; D000009:Abdominal Muscles / Q000502:physiology; D000328:Adult; D001416:Back Pain / Q000209:etiology; D001696:Biomechanical Phenomena; D004576:Electromyography; D005069:Evaluation Studies as Topic; D006801:Humans; D017770:Lifting / Q000009:adverse effects; D008875:Middle Aged; D011187:Posture; D011312:Pressure; D012399:Rotation; D013131:Spine / Q000502:physiology*; D014102:Torsion Abnormality; D014636:Valsalva Maneuver / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology