The Effect of Shoulder Plyometric Training on Amortization Time and Upper-Extremity Kinematics

Context: Plyometric training is credited with providing benefits in performance and dynamic restraint. However, limited prospective data exist quantifying kinematic adaptations such as amortization time, glenohumeral rotation, and scapulothoracic position, which may underlie the efficacy of plyometric training for upper-extremity rehabilitation or performance enhancement. Objective: To measure upper-extremity kinematics and plyometric phase times before and after an 8-wk upper-extremity strength- and plyometric-training program. Design: Randomized pretest-posttest design. Setting: Research laboratory. Participants: 40 recreationally active men (plyometric group, age 20.43 +/- 1.40 y, height 180.00 +/- 8.80 cm, weight 73.07 +/- 7.21 kg; strength group, age 21.95 +/- 3.40 y, height 173.98 +/- 11.91 cm, weight 74.79 +/- 13.55 kg). Intervention: Participants were randomly assigned to either a strength-training group or a strength- and plyometric-training group. Each participant performed the assigned training for 8 wk. Main Outcome Measures: Dynamic and static glenohumeral and scapular-rotation measurements were taken before and after the training programs. Dynamic measurement of scapular rotation and time spent in each plyometric phase (concentric, eccentric, and amortization) during a ball-toss exercise were recorded while the subjects were fitted with an electromagnetic tracking system. Static measures included scapular upward rotation at 3 different glenohumeral-abduction angles, glenohumeral internal rotation, and glenohumeral external rotation. Results: Posttesting showed that both groups significantly decreased the time spent in the amortization, concentric, and eccentric phases of a ball-toss exercise (P < .01). Both groups also exhibited significantly decreased static external rotation and increased dynamic scapular upward rotation after the training period (P < .01). The only difference between the training protocols was that the plyometric-training group exhibited an increase in internal rotation that was not present in the strength-training group (P < .01). Conclusion: These findings support the use of both upper-extremity plyometrics and strength training for reducing commonly identified upper-extremity-injury risk factors and improving upper-extremity performance.