Kathleen A. Swanik, Kellie Huxel Bliven, and Charles Buz Swanik
There are contradictory data on optimal muscle-activation strategies for restoring shoulder stability. Further investigation of neuromuscular-control strategies for glenohumeral-joint stability will guide clinicians in decisions regarding appropriate rehabilitation exercises.
To determine whether subscapularis, infraspinatus, and teres minor (anteroposterior force couple) muscle activation differ between 4 shoulder exercises and describe coactivation ratios and individual muscle-recruitment characteristics of rotator-cuff muscles throughout each shoulder exercise.
healthy, physically active men, age 20.55 ± 2.0 y.
4 rehabilitation exercises: pitchback, PNF D2 pattern with tubing, push-up plus, and slide board.
Main Outcomes Measures:
Mean coactivation level, coactivation-ratio patterns, and level (area) of muscle-activation patterns of the subscapularis, infraspinatus, and teres minor throughout each exercise.
Coactivation levels varied throughout each exercise. Subscapularis activity was consistently higher than that of the infraspinatus and teres minor combined at the start of each exercise and in end ranges of motion. Individual muscle-recruitment levels in the subscapularis were also different between exercises.
Results provide descriptive data for determining normative coactivation-ratio values for muscle recruitment for the functional exercises studied. Differences in subscapularis activation suggest a reliance to resist anteriorly directed forces.
Stephen J. Thomas, Kathleen A. Swanik, Charles “Buz” Swanik, Kellie C. Huxel, and John D. Kelly IV
Pathologies such as anterior instability and impingement are common in baseball and have been linked to decreases in internal rotation (IR) and concurrent increases in external rotation (ER). In addition, alterations to scapular position have been identified in this population, but the chronology of these adaptations is uncertain.
To determine whether there is a change in range of motion and scapular position after a single baseball season.
19 high school baseball players (age 16.6 ± 0.8 y, mass 78.6 ± 12.0 kg, height 180.3 ± 6.2 cm).
Subjects were measured for all dependent variables at preseason and postseason.
Main Outcome Measures:
Participants were measured for glenohumeral (GH) IR and ER with the scapula stabilized. Total GH range of motion was calculated as the sum of IR and ER. Scapular upward rotation was measured at 0°, 60°, 90°, and 120° of GH abduction in the scapular plane, and scapular protraction, at 0°, hands on hips, and 90° of GH abduction.
Overall, the dominant arm had significantly less GH IR (11.4°, P = .005) and significantly more ER (4.7°, P = .001) than the nondominant arm. Total motion in the dominant arm was significantly less than in the nondominant arm (6.7°, P = .001). Scapular upward rotation in the dominant arm significantly increased at 0° (2.4°, P = .002) and significantly decreased at 90° (3.2°, P = .001) and 120° (3.2°, P < .001) of abduction from preseason to postseason. Scapular protraction in the nondominant arm significantly decreased at 45° (0.32 cm, P = .017) and 90° (0.33 cm, P = .006) from preseason to postseason.
These data suggest that scapular adaptations may be acquired over a relatively short period (12 wk) in a competitive baseball season. Competitive high school baseball players also presented with significant GH motion differences between their dominant and nondominant arms. Total motion was also significantly less in the dominant arm than in the nondominant arm.
Martin Ramsi, Kathleen A. Swanik, Charles “Buz” Swanik, Steve Straub, and Carl Mattacola
Changes in strength over the course of a swim season could predispose the shoulder to strength imbalances and lead to injury.
To examine isometric shoulder internal- (IR) and external-rotator (ER) strength in high school swimmers over a 12-week competitive season.
Three 3 × 2 × 2 ANOVAs with repeated measures were used to determine significant main effects for IR, ER, and IR:ER strength ratio.
27 (14 female, 13 male) high school varsity swimmers.
Main Outcome Measures:
IR and ER strength during preseason, midseason, and postseason.
Significant increases in IR strength in both groups were revealed for all test sessions. ER strength significantly improved in both males and females from preseason to midseason and from preseason to postseason. IR:ER ratio revealed a significant increase from preseason to postseason.
Increases in IR strength without equal gains in ER strength were revealed and could contribute to future shoulder pathologies in competitive swimmers
Stephen John Thomas, Charles Buz Swanik, Thomas W. Kaminski, Jill S. Higginson, Kathleen A. Swanik, and Levon N. Nazarian
Subacromial impingement is a common injury in baseball players and has been linked to a reduction in the subacromial space. In addition, it has been suggested that decreases in scapular upward rotation will lead to decreases in the subacromial space and ultimately impingement syndrome.
The objective of this study was to evaluate the relationship between acromiohumeral distance and scapular upward rotation in healthy college baseball players.
Posttest-only study design.
Controlled laboratory setting.
24 healthy college baseball players.
Participants were measured for all dependent variables at preseason.
Main Outcome Measures:
Acromiohumeral distance at rest and 90° of abduction was measured with a diagnostic ultrasound unit. Scapular upward rotation at rest and 90° of abduction was measured with a digital inclinometer.
Dominant-arm acromiohumeral distance at rest and 90° of abduction (P = .694, P = .840) was not significantly different than in the nondominant arm. In addition, there was not a significant correlation between acromiohumeral distance and scapular upward rotation at rest and 90° of abduction for either the dominant or the nondominant arm.
These results indicate that the acromiohumeral distance is not adapting in the dominant arm in healthy throwing athletes. In addition, a relationship was not identified between acromiohumeral distance and scapular upward rotation, which was previously suggested. These results may suggest that changes that are typically seen in an injured population may be occurring due to the injury and are not preexisting. In addition, scapular upward rotation may not be the only contributing factor to acromiohumeral distance.