Benjamin M. Goerger

Influence of humeral torsion on interpretation of posterior shoulder tightness measures in overhead athletes

Objective:To measure the influence of humeral torsion on interpretation of clinical indicators of posterior shoulder tightness in overhead athletes. Design:Cross-sectional control group comparison. Setting:A university-based sports medicine research laboratory. Participants:Twenty-nine healthy intercollegiate baseball players and 25 college-aged control individuals with no history of participation in overhead athletics were enrolled. Intervention:In all participants, bilateral humeral rotation and humeral horizontal adduction variables were measured with a digital inclinometry. Bilateral humeral torsion was measured with ultrasonography. Main Outcome Measures:Group and limb comparisons were made for clinical indicators of posterior shoulder tightness (humeral rotation and horizontal adduction variables) and humeral torsion variables. The relationship between humeral torsion and clinical indicators of posterior shoulder tightness were established. Results:The dominant limb of the baseball players demonstrated greater humeral torsion, and less internal rotation and total rotation range of motion, compared with control participants and the nondominant limb in both groups. Once corrected for torsion, no group or limb differences in internal rotation were present. Statistically significant relationships existed between the amount of humeral torsion and measures of posterior shoulder tightness. Conclusions:Although limb differences in clinical indicators of posterior tightness exist in healthy overhead athletes, these measures appear to be influenced by humeral torsion rather than soft tissue tightness. Once torsion is accounted for, the limb differences observed clinically were minimal in healthy overhead athletes. When possible, accounting for humeral torsion when interpreting clinical measures of posterior shoulder tightness may aid in treatment decisions.

The association between lower extremity energy absorption and biomechanical factors related to anterior cruciate ligament injury

BACKGROUND Greater total energy absorption by the lower extremity musculature during landing may reduce stresses placed on capsuloligamentous tissues with differences in joint contributions to energy absorption potentially affecting anterior cruciate ligament injury risk. However, the relationships between energy absorption and prospectively identified biomechanical factors associated with non-contact anterior cruciate ligament injury have yet to be demonstrated. METHODS Sagittal plane total, hip, knee and ankle energy absorption, and peak vertical ground reaction force, anterior tibial shear force, knee flexion and knee valgus angles, and internal hip extension and knee varus moments were measured in 27 individuals (14 females, 13 males) performing double leg jump landings. Correlation coefficients assessed the relationships between energy absorption during three time intervals (initial impact phase, terminal phase, and total landing) and biomechanical factors related to anterior cruciate ligament injury. FINDINGS More favorable values of biomechanical factors related to non-contact anterior cruciate ligament injury were associated with: 1) Lesser total (R(2)=0.178-0.558), hip (R(2)=0.229-0.651) and ankle (R(2)=0.280), but greater knee (R(2)=0.147) energy absorption during the initial impact phase; 2) Greater total (R(2)=0.170-0.845), hip (R(2)=0.599), knee (R(2)=0.236-0.834), and ankle (R(2)=0.276) energy absorption during the terminal phase of landing; and 3) Greater knee (R(2)=0.158-0.709), but lesser hip (R(2)=0.309) and ankle (R(2)=0.210-0.319) energy absorption during the total landing period. INTERPRETATION These results suggest that biomechanical factors related to anterior cruciate ligament injury are influenced by both the magnitude and timing of lower extremity energy absorption during landing.

Reliability and interpretation of single leg stance and maximum voluntary isometric contraction methods of electromyography normalization.

Normalization of electromyographic (EMG) amplitudes is necessary in the study of human motion. However, there is a lack of agreement on the most reliable and appropriate normalization method. This study evaluated the reliability of single leg stance (SLS) and maximal voluntary isometric contraction (MVIC) normalization methods and the relationship between these measures for the gluteus maximus (GMax), gluteus medius (GMed), rectus femoris (RF), vastus lateralis (VL), hip adductor group (ADD), and biceps femoris (BF). Surface EMG was recorded in 20 subjects during three 5s trials of SLS and MVIC. SLS and MVIC methods both demonstrated good-to-excellent reliability in all muscles (ICCs>0.80). Intrasubject coefficients of variation were lower for the MVIC method (9-36%) than for the SLS method (20-59%). EMG amplitudes during MVIC and SLS were significantly correlated for all muscles (Pearson rs=0.604-0.905, p<0.005) except GMax (r=0.250, p=0.288). Use of SLS normalization for the RF, VL, and BF is not recommended due to a lack of measurement precision. However, this method is justified in the GMax, GMed, and ADD and may provide a better representation of coordinated muscle function during a functional task.

The influence of hip strength on gluteal activity and lower extremity kinematics

The effects of hip muscle strength and activation on anterior cruciate ligament injury biomechanics, particularly knee valgus loading, have been reported in isolation and with equivocal results. However, the combination of these factors influences joint biomechanics. This investigation evaluated the influence of hip strength on gluteal activation and knee valgus motion. Maximal isometric hip abduction (ABD) and external rotation (ER) contractions were used to define High and Low strength groups. Knee kinematics and gluteus maximus (GMax) and medius (GMed) EMG amplitudes obtained during landing were compared between High and Low strength groups after controlling for the potential confounding influence of sex. Knee valgus motion did not differ between the High and Low hip ABD and ER strength groups. However, the Low ABD and ER strength groups displayed greater GMed and GMax EMG amplitudes, respectively, compared to the High strength groups. These findings suggest that weaker individuals compensate for a lack of force production via heightened neural drive. As such, hip muscle strength influences knee valgus motion indirectly by determining neural drive requirements.

Effects of Non-Assisted Posterior Shoulder Stretches on Shoulder Range of Motion Among Collegiate Baseball Pitchers

Maintenance of the posterior shoulder flexibility has implica tions for prevention of upper extremity injuries in athletes who use overhead throwing. Therefore, determination of stretching techniques that can be performed easily by these athletes and are most effective in improving flexibility is of great clinical interest. The purpose of this study was to evaluate the acute changes in glenohumeral internal rotation, external rotation, and horizontal adduction range of motion (ROM) after 3 onthe-field posterior shoulder stretches in 15 collegiate baseball pitchers. All stretches resulted in significant acute improvement in internal rotation and horizontal adduction ROM. However, there were no differences in improvements among the stretch es. This study demonstrated that the acute increase in internal rotation and horizontal adduction ROM could be achieved by the non-assisted stretches. Non-assisted stretches can be performed without the aid from a clinician or a treatment table, and therefore can be used readily and frequently by baseball players of all levels.