Assessment of Select Lower Extremity Muscle Firing Patterns during the Baseball Pitch

Abstract

Successful baseball pitching requires coordination of the upper extremity, trunk and lower extremity. A relative lack of research regarding lower extremity muscle activity during pitching exists. PURPOSE: To investigate the muscle firing patterns of select lower extremity muscles during the pitching motion. METHODS: Eleven injury free college aged males with previous pitching experience performed 10 baseball pitches (5 with EMG electrodes on stride leg and 5 with EMG electrodes on trail leg) at a minimum required velocity of 70 mph off of a standard indoor pitching mound. Pitch velocity was monitored and controlled using a JUGS radar gun. Pitch trials that did not meet the minimal required 70 mph velocity were not used. Bilateral surface electromyography (Noraxon USA, Inc. Scottsdale, AZ) recorded muscle activity at 1000Hz during the pitching trials from the biceps femoris (BF), rectus femoris (RF), and vastus medialis (VM). Electromyography signals were rectified and smoothed (50ms RMS method). The pitch was divided into three phases (P1 - initiation of pitch to stride foot contact (SFC), P2 - SFC to ball release and P3 - ball release to opposite foot contact). Mean EMG values for each of the three phases for the BF, RF, and VM were averaged and then normalized as a percentage of a standardized maximal isometric exercise (MVC). RESULTS: The trail leg elicited muscle activity of 29%, 14%, and 46% of the standard MVC for the VM, RF and BF respectively during P1. In P2 the trail leg elicited muscle activity of 138%, 28% and 152% of the standard MVC for the VM, RF and BF respectively. In P3 the trail leg elicited muscle activity of 60%, 14% and 68% of the standard MVC for the VM, RF and BF respectively. The stride leg elicited muscle activity of 32%, 25%, and 33% of the standard MVC for the VM, RF and BF respectively during P1. In P2 the stride leg elicited muscle activity of 164%, 150% and 90% of the standard MVC for the VM, RF and BF respectively. In P3 the stride leg elicited muscle activity of 75%, 33% and 93% of the standard MVC for the VM, RF and BF respectively. CONCLUSIONS: During P2, the stride leg is snapping into extension therefore the large activation levels are elicited by the two quadriceps muscles tested while the trail leg is being using to push off the mound with the use of the VM and BF to extend the knee and hip respectively.