Although previous studies have demonstrated neuromuscular and cardiovascular changes with slow inversion rates, emergencies, such as overturned vehicles and helicopters can occur rapidly. The purpose of this study was to investigate changes in neuromuscular and cardiovascular responses with rapid (1 s) and slower (3 s) transitions from upright to inverted seated positions. Twenty-two subjects performed separate and concurrent unilateral elbow flexion and leg extension maximal voluntary contractions (MVCs) for 6 s in an upright seated position and when inverted with 1 and 3 s rotations. Elbow flexion and leg extension force; biceps, triceps, quadriceps and hamstrings electromyographic (EMG) activity, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP) were measured. Whether the elbow flexion or leg extension contractions occurred concurrently or individually, significant (p < 0.05) decreases in MVC force and EMG activity were found when inverted within 1 and 3 s rotations as compared to upright. Triceps and hamstrings EMG activity (p < 0.05) decreased when inverted within 1 s rotation as compared to upright. Following rotation, the maintenance of the inverted position (3-6 s timepoint) resulted in a significant (p < 0.05) increase in leg extension MVC as compared to the initial second of rotation to inversion. HR, SBP and DBP demonstrated (p < 0.001) decreases when inverted within 1 and 3 s rotations as compared to upright. In conclusion, this is the first study to show that irrespective of rotation speed, inversion inhibited neuromuscular and cardiovascular responses, similar to the more deliberate, slower rotation of previous inversion studies.
Background: Seafaring workers must contend with motions that could impact their work performance and safety. Objective: To compare and analyze the neuromuscular responses to a stable immediate environment placed in a moving (simulated wave platform motions) extended environment. Methods: Isometric maximum voluntary contraction (MVC) forces of the elbow flexors and leg extensors as well as electromyography (EMG) of the biceps brachii and vastus lateralis were recorded. The EMG activity of the triceps brachii, semitendonosis, internal obliques, and lower lumbar erector spinae muscles were also monitored during the upper and lower limb MVCs. Three types of rotational motion (pitch, roll and mixed, all combined with a linear heave motion) created by a motion platform were randomly allocated for 1 minute each. While securely strapped and seated with the platform moving, two MVCs each were performed for the right elbow flexors and right knee extensors at the beginning and at the end of the one-minute wave motion protocol. Results: Platform motions impaired (p<0.0001) knee extension (pitch= −8%; roll=−13.4%; mixed=−13.5%) and elbow flexor MVC force (pitch=−21.1%; roll=−26.7%; mixed=−25.1%) compared to control conditions. Vastus lateralis EMG was reduced 13.3% with roll motions compared to control. Conclusions: Platform simulated wave motions can be detrimental to force production when the individual is strapped in a secure and stable seated position. Such impairments can impact the safety and work performance of employees on sea going vessels.
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