Studies link hip, shoulder function
By Chris Klingenberg
Kids grow up thinking that throwing a baseball hard is all about strength in the arm and shoulder, but new evidence suggests that muscle strength and range of motion in the hip affect shoulder function during throwing in youth baseball players.
Gretchen Oliver, PhD, FACSM, ATC, an assistant professor in the School of Kinesiology at Auburn University in Alabama, and colleagues found that rotational passive range of motion (PROM) in the throwing shoulder was significantly correlated with hip PROM in 26 youth baseball pitchers with no history of injury.
“A pitcher needs adequate stance leg internal rotation for the windup, then as they drive off the rubber they need stance hip external rotation. Just as the stride hip needs adequate external rotation to get the best foot contact, once the ball is released, they need to have adequate stride hip internal rotation for the body and arm to decelerate around the stride hip,” Oliver said.
A single examiner measured bilateral hip and throwing shoulder rotational PROM in the youth pitchers using an inclinometer. The players averaged 31.3° of internal rotation and 35° of external rotation in the stance hip and 28.5° of internal rotation and 37.2° of external rotation in the lead hip. In the throwing shoulder, mean internal rotation was 34.5° and external rotation was 110.5°. The differences between internal and external rotation were statistically significant for the shoulder and lead hip, but total PROM did not differ significantly between the stance and lead hips. The findings were epublished in December by the Journal of Strength and Conditioning Research.
“Internal and external rotation of the hips should average forty-five degrees. Deviations from that are going to ultimately result in problems,” Oliver said.
Michael Hannon, MD, an orthopedic surgeon at the Kerlan-Jobe Orthopedic Clinic in Los Angeles, and his colleagues have also assessed both upper and lower extremity function in preadolescent and adolescent baseball players.
“Ultimately, the most important thing with younger kids is that people focus so much on arm strength when it is really the lower extremity that we should be focusing on,” Hannon said.
— Michael Hannon, MD
The Kerlan-Jobe study analyzed 54 preadolescents (mean age 9.9 years, 38 pitchers) and 54 adolescents (mean age 15.1 years; 34 pitchers) with regard to hip ROM, hip abduction strength, scapular dyskinesis, coracoid distance, and single-leg squat testing. All players were male. There was a clear difference in the number of years pitched: a mean of 2.9 years in the preadolescent group compared with 8.9 in the adolescent group. The adolescent pitchers were throwing an average of 9.2 months per year, whereas the preadolescents averaged only 5.7 months per year.
There was a significant difference in hip internal rotation between the preadolescent group and the adolescent group for the dominant or stance leg (40.81° vs 33.09°) and the nondominant or stride leg (38.37° vs 34.35°). External rotation did not differ significantly between the two age groups for either leg. There was a significant difference in dominant hip ROM (78.46° vs 71.63°) between the preadolescent and adolescent groups. No difference was seen when considering the total hip ROM of the nondominant hip. The findings were published in August 2014 by the American Journal of Sports Medicine.
For the single-leg squat test, participants were first asked to stand on one leg and establish single-leg balance, then squat to at least 60° and return to the baseline position. The test was considered positive if the player was unable to maintain single-leg balance, was unable to maintain level hips, or exhibited significant hip adduction or internal rotation during squatting. None of the 54 preadolescents could complete the single-leg squat test on either leg; in the adolescent group, 13% performed the test successfully on the stance leg and 9% were successful on the stride leg.
“It is important that coaches are informed that the core and lower extremity are critical to avoid arm problems,” Hannon said. “If the core and lower extremities are weak, there is a better chance of throwing out your arm.”
Oliver underscored the benefits of the single-leg squat test for examining balance and pelvic stability.
“Can they balance on one leg and, if they can, do they have the gluteus medius strength to stabilize their pelvis to perform the squat? Usually after a few tries, they get the balance down, and then we see a corkscrew from the hip down as they do not have the glute-med strength to stabilize the pelvis, which then results in knee valgus,” she said.
Chris Klingenberg is a freelance writer based in Massachusetts.
Oliver GD, Weimar WH. Hip and shoulder range of motion in youth baseball players. J Strength Cond Res 2014 Dec 5. [Epub ahead of print]
Beckett M, Hannon M, Ropiak C, et al. Clinical assessment of scapula and hip joint function in preadolescent and adolescent baseball players. Am J Sports Med 2014;42(10):2502-2509