Muscle Activity Characteristics of the Pronator Teres during Throwing in Baseball Pitchers: A Pilot Study

Abstract

The pronator teres muscle is a major dynamic stabilizer of elbow valgus stress during throwing. This study aims to investigate pronator teres muscle activation during breaking ball pitching in baseball pitchers. Twelve male college baseball players with more than eight years of baseball experience were included in this study. A wireless surface electromyography (EMG) system was used to measure the activation of the forearm muscles and record EMG data during fastball and curveball pitching. Peak pronator teres muscle activation during curveball pitching was greater than that during fastball pitching (p = 0.03). There was no difference in the muscle activation of the other forearm muscles (p > 0.05). These results indicate that increased muscle activity in the pronator teres may contribute to stiffness and induce pronator teres syndrome or medial elbow injuries related to the overuse of the pronator teres, especially during curveball pitching. Controlling curveball throws contributes to player coaching and conditioning for the prevention of elbow joint disorders and pronator teres syndrome.

Keywords: elbow joint; electromyography; forearm; injury prevention.

Figure 1

Surface electrodes placement. (A,B) represent the dorsal (posterior) and palmar (anterior) views of the right forearm, respectively: (a) brachioradialis muscle, (b) pronator teres muscle, (c) flexor carpi radialis, (d) flexor carpi ulnaris, (e) extensor carpi ulnaris, (f) extensor carpi radialis.

Figure 2

Comparison of EMG average values (%MVC) in forearm muscles during fastball and curveball pitching Horizontal black lines represent median values within each box. Boxes extend from the lower quartile to the upper quartile of the distribution of values during fastball and curveball pitching, respectively. The whiskers indicate the minimum value to the lower quartile and then the upper quartile to the maximum value. EMG data (%MVC) are presented on the y-axis. BRD: brachioradialis muscle; PT: pronator teres muscle; FCR: flexor carpi radialis; FCU: flexor carpi ulnaris; ECU: extensor carpi ulnaris; ECR: extensor carpi radialis.

Figure 3

Comparison of EMG peak values (%MVC) in forearm muscles during fastball and curveball pitching. Horizontal black lines represent median values within each box. Boxes extend from the lower quartile to the upper quartile of the distribution of values during fastball and curveball pitching, respectively. The whiskers indicate the minimum value to the lower quartile and then the upper quartile to the maximum value. EMG data (%MVC) are presented on the y-axis. *: statistical significance (p < 0.05); BRD: brachioradialis muscle; PT: pronator teres muscle; FCR: flexor carpi radialis; FCU: flexor carpi ulnaris; ECU: extensor carpi ulnaris; ECR: extensor carpi radialis.

Figure 4

Time-series data of muscle activations during fastball and curveball pitching. Mean values of EMG data (%MVC) during fastball (black lines) and curveball (dotted gray lines). The normalized time (%) was defined as duration from the late cocking phase to the follow-through phase, with 0% representing the maximum shoulder external rotation and 100% representing the end of the follow-through phase and is presented on the x-axis. EMG data (%MVC) are presented on the y-axis.