The relationship between isometric contraction durations and improvement in shoulder joint range of motion

Proprioceptive Neuromuscular Facilitation (PNF) flexibility techniques are now being used in health and sports related activities, yet it is unclear as to the relationship between various isometric contraction time increments and joint range of motion. The purpose of this study, therefore, was to determine the relationship between a three-second, six-second, and ten-second maximum voluntary isometric contraction (MVIC). A modified PNF procedure referred to as the slow-reversal-hold-relax (SRHR) flexibility technique was employed in the investigation. It was hypothesized that longer MVIC time increments used with the SRHR flexibility technique would provide greater range of motion (ROM). Specifically, the ten-second MVIC was believed to be superior to the six-second and three-second MVIC. Furthermore, it was hypothesized that the six-second MVIC was superior to the three-second MVIC. Sixty subjects, ages 14-57 were randomly assigned to one of three treatment groups. Using a Leighton Flexometer, acute internal rotation of the shoulder joint was measured in degrees for six trials. Three passive stretch trials served as the baseline measurement for each subject (trials 1-3). The SRHR flexibility technique was used as the treatment for trials 4-6. A sixty-second rest interval common to clinical settings was integrated between each trial. The hypothesis was not accepted that a positive correlation existed between increased MVIC time and greater ROM.