A laboratory experiment was conducted to determine whether grip force capabilities are lower when the wrist is moved than in a static position. The purpose was to determine the wrist velocity levels and wrist postures that had the most significant effect on grip force. Maximum grip forces of five male and five female subjects were determined under both static and dynamic conditions. The dominant wrist of each subject was secured to a CYBEX II dynamometer and grip force was collected during isokinetic wrist deviations for four directions of motion (flexion to extension, extension to flexion, radial to ulnar, and ulnar to radial). Six different velocity levels were analyzed and grip forces were recorded at specific wrist positions throughout each range of movement. For flexion-extension motions, wrist positions from 45 degrees flexion to 45 degrees extension were analyzed whereas positions from 20 degrees radial deviation to 20 degrees ulnar deviation were studied for radial-ulnar activity. Isometric exertions were also performed at each desired wrist position. Results showed that, for all directions of motion, grip forces for all isokinetic conditions were significantly lower than for the isometric exertions. Lower grip forces were exhibited at extreme wrist flexion and extreme radial and ulnar positions for both static and dynamic conditions. The direction of motion was also found to affect grip strength; extension to flexion exertions produced larger grip forces than flexion to extension exertions and radial to ulnar motion showed larger grip forces than ulnar to radial deviation. Although, males produced larger grip forces than females in all exertions, significant interactions between gender and velocity were noted.

No abstract

Low back disorders have been a major concern for both industries and the public in general. Diurnal variation in trunk flexibility has been previously observed and quantified in terms of range of motion. It was hypothesized that decreased disc height as the day progresses allows the spinal ligaments to slacken, resulting in an increase in the range of motion (flexibility) and possible reduction in risk of injury. Evidence suggests that this risk may be accentuated under dynamic motions of the spine. This experiment focused on observing the change in dynamic components of trunk flexibility (trunk mobility) as a function of time of the day. Trunk motions of twenty-one male participants were obtained at three specific times of the day using a tri-axial electrogoniometer. No variation in trunk range of motion in any of the cardinal planes was observed. However, velocity and acceleration in the sagittal plane showed significant variations, suggesting the re-examination of the “slack ligaments” hypothesis. This study asserts that identifying flexibility by only its static component, range of motion, gives only partial information. Industrial injuries occurring in the early morning hours may be a result of insufficient trunk mobility. The relation between trunk mobility and back injury incidence rates should be further investigated.