Muscle activation patterns of the upper and lower extremity during the windmill softball pitch

Oliver G.D., Plummer H.P., & Keeley D.W. (2011) Muscle activation patterns of the upper and lower extremity during the windmill softball pitch. Journal of Strength and Conditioning Research, 25(6),1653-1658.

A total of 7 pitchers were recruited with average age, height and weight 17.7 years, 1.69 m, and 69.1 kg, respectively. EMG readings were taken from the Biceps and Triceps Brachii, Rhomboids, Gluteus Maximus and Medius. Each threw 5 strikes, the fastest of which was used for analysis.

Gluteus Maximus activity was most intense during the wind-up, with the pivot foot leg extension (196.3%), and at stride foot contact, in the stride leg (180.1%). Gluteus Medius activity peaked during hip rotation/stabilization in phases 3 and 4 starting at 101.2% and moving to 93.2% through release. Biceps activity peaked through release at 73.2%. The triceps were actively firing the entire motion under 150% and the rhomboids peaked during the middle of the windmill for scapular retraction.

Biceps activity in this study was similar to Rojas, et al. (2009), which is interesting, but previously discussed. The triceps activity was curious in that it constantly fired. However, I would be interested in further studies that involved a discussion of the importance of this finding and why it’s happening. I find the research on the rhomboids to be interesting. Scapular stabilization has been studied over and over in baseball pitching. Due to the intense forces that the overhand motion creates, the scapula must elevate to avoid impingement, while also providing a solid base for the rotator cuff muscles to properly hold the arm in place. The scapular movement has been discussed, but never truly studied in the sense of proper movement, risk factors, etc. Until then, drawing conclusions on what rhomboid activity is meant for is dangerous. However, it does appear to have some activity in retracting the shoulder during arm elevation.

The glute activity in this study is the most intriguing to me. The Gluteus Maximus, the main hip extensor, fires during phase one for the push off. This is consistent with jumping research that has overwhelmingly concluded that hip extension is the main mover in all jumps, particularly horizontal jumping. Then the same muscle in the other leg works eccentrically to decelerate the body during the landing, and maybe extending a little bit as well during pelvic stabilization. The author states that the Gluteus Maximus is most used for weight shifting, but being a pitcher and after reviewing the literature on jumping, I think I can conclude with confidence that the 196.3% activation is a little more than just a weight shift.

Another interesting anecdote is that the author in concluded that the pivot foot gluteus maximus and medius was more active than the stride leg. This is tough to comprehend knowing that during stride foot plant, almost no forces are working on the pivot foot leg, meaning that everything should be loaded on the stride leg. I am curious to see more research looking at leg muscle firing to determine what is really happening. More subjects and better pitchers would be ideal to study.