Timothy L. Uhl

Differences in Kinematics and Electromyographic Activity Between Men and Women during the Single-Legged Squat*

Background Numerous factors have been identified as potentially increasing the risk of anterior cruciate ligament injury in the female athlete. However, differences between the sexes in lower extremity coordination, particularly hip control, are only minimally understood. Hypothesis There is no difference in kinematic or electromyographic data during the single-legged squat between men and women. Study Design Descriptive comparison study. Methods We kinematically and electromyographically analyzed the single-legged squat in 18 intercollegiate athletes (9 male, 9 female). Subjects performed five single-legged squats on their dominant leg, lowering themselves as far as possible and then returning to a standing position without losing balance. Results Women demonstrated significantly more ankle dorsiflexion, ankle pronation, hip adduction, hip flexion, hip external rotation, and less trunk lateral flexion than men. These factors were associated with a decreased ability of the women to maintain a varus knee position during the squat as compared with the men. Analysis of all eight tested muscles demonstrated that women had greater muscle activation compared with men. When each muscle was analyzed separately, the rectus femoris muscle activation was found to be statistically greater in women in both the area under the linear envelope and maximal activation data. Conclusions Under a physiologic load in a position commonly assumed in sports, women tend to position their entire lower extremity and activate muscles in a manner that could increase strain on the anterior cruciate ligament.

Hip Strength and Hip and Knee Kinematics During Stair Descent in Females With and Without Patellofemoral Pain Syndrome

STUDY DESIGN Cross-sectional. OBJECTIVE To determine if females presenting with patellofemoral pain syndrome (PFPS) from no discernable cause other than overuse demonstrate hip weakness and increased hip internal rotation, hip adduction, and knee valgus during stair descent. BACKGROUND Historically, PFPS has been viewed exclusively as a knee problem. Recent findings have indicated an association between hip weakness and PFPS. Researchers have hypothesized that patients who demonstrate hip weakness would exhibit increased hip internal rotation, hip adduction, and knee valgus during functional activities. To date, researchers have not simultaneously examined hip and knee strength and kinematics in subjects with PFPS to make this determination. METHODS AND MEASURES Eighteen females diagnosed with PFPS and 18 matched controls participated. Strength measures were taken for the hip external rotators and hip abductors. Hip and knee kinematics were collected as subjects completed a standardized stair-stepping task. Independent t tests were used to determine between-group differences in strength and kinematics during stair descent. RESULTS Subjects with PFPS generated 24% less hip external rotator (P = .002) and 26% less hip abductor (P =. 006) torque. No between-group differences (P > .05) were found for average hip and knee transverse and frontal plane angles during stair descent. CONCLUSION Subjects with PFPS had significant hip weakness but did not demonstrate altered hip and knee kinematics as previously theorized. Additional investigations are needed to better understand the association between hip weakness and PFPS etiology.

Electromyographic Analysis of Specific Exercises for Scapular Control in Early Phases of Shoulder Rehabilitation

Background Restoration of control of dynamic scapular motion by specific activation of the serratus anterior and lower trapezius muscles is an important part of functional rehabilitation. This study evaluated activation of those muscles in specific exercises. Hypothesis Specific exercises will activate key scapular-stabilizing muscles in clinically significant amplitudes and patterns. Study Design Controlled laboratory study. Methods Muscle activation amplitudes and patterns were evaluated in the serratus anterior, upper trapezius, lower trapezius, anterior deltoid, and posterior deltoid muscles with electromyography in symptomatic (n = 18) and asymptomatic (n = 21) subjects as they executed the low row, inferior glide, lawnmower, and robbery exercises. Results There were no significant differences in muscle activation amplitude between groups. Muscle activation was moderate across all of the exercises and varied slightly with the specific exercise. The serratus anterior and lower trapezius were activated between 15% and 30% in all exercises. Upper trapezius activation was high (21%-36%) in the dynamic exercises (lawnmower and robbery). Serratus anterior was activated first in the low row and last in the lawnmower and robbery. The upper trapezius and lower trapezius were activated first in the lawnmower and robbery. Conclusion These specific exercises activate key scapular-stabilizing muscles at amplitudes that are known to increase muscle strength. Clinical Relevance These exercises can be used as part of a comprehensive rehabilitation program for restoration of shoulder function. They activate the serratus anterior and lower trapezius—key muscles in dynamic shoulder control—while variably activating the upper trapezius. Activation patterns depended on scapular position resulting in variability of amplitude and activation sequencing between exercises. Inferior glide and low row can be performed early in rehabilitation because of their limited range of motion, while lawnmower and robbery, which require larger movements, can be instituted later in the sequence.

Flexibility comparisons of junior elite tennis players to other athletes

Flexibility measurements were obtained in 86 junior elite tennis players and compared to the flexibility meas urements of 139 athletes involved in other sports. The measurements obtained included sit and reach flexibil ity, quadricep flexibility, hamstring flexibility, gastroc nemius flexibility, shoulder internal rotation, and shoul der external rotation. All measurements except sit and reach flexibility were obtained goniometrically. Tennis players were significantly tighter in sit and reach flexi bility, dominant shoulder internal rotation, and nondom inant shoulder internal rotation. They were significantly more flexible in dominant shoulder external rotation and nondominant shoulder external rotation. The flexibility differences found in tennis players suggest adaptations to the musculoskeletal demands of their sport. These results suggest that a sport-specific flexibility program may be necessary for junior elite tennis players in order to promote maximum performance and help prevent flexibility-related injuries.

Hip Strengthening Prior to Functional Exercises Reduces Pain Sooner Than Quadriceps Strengthening in Females With Patellofemoral Pain Syndrome: A Randomized Clinical Trial

STUDY DESIGN Randomized clinical trial. OBJECTIVES To determine if females with patellofemoral pain syndrome (PFPS) who perform hip strengthening prior to functional exercises demonstrate greater improvements than females who perform quadriceps strengthening prior to the same functional exercises. BACKGROUND Although PFPS has previously been attributed to quadriceps dysfunction, more recent research has linked this condition to impairment of the hip musculature. Lower extremity strengthening has been deemed an effective intervention. However, research has often examined weight-bearing exercises, making it unclear if increased strength in the hip, quadriceps, or both is beneficial. METHODS Thirty-three females with PFPS performed either initial hip strengthening (hip group) or initial quadriceps strengthening (quad group) for 4 weeks, prior to 4 weeks of a similar program of functional weight-bearing exercises. Self-reported pain, function, and functional strength were measured. Isometric strength was assessed for hip abductors, external rotators, and knee extensors. A mixed-model analysis of variance was used to determine group differences over time. RESULTS After 4 weeks, there was less mean ± SD pain in the hip group (2.4 ± 2.0) than in the quad group (4.1 ± 2.5) (P = .035). From baseline to 8 weeks, the hip group demonstrated a 21% increase (P<.001) in hip abductor strength, while that remained unchanged in the quad group. All participants demonstrated improved subjective function (P<.006), objective function (P<.001), and hip external rotator strength (P = .004) from baseline to testing at 8 weeks. CONCLUSION Both rehabilitation approaches improved function and reduced pain. For patients with PFPS, initial hip strengthening may allow an earlier dissipation of pain than exercises focused on the quadriceps.

The effects of fish oil and isoflavones on delayed onset muscle soreness.

INTRODUCTION/PURPOSE Fish oils (FO) have been shown to modulate the inflammatory response through alteration of the eicosanoid pathway. Isoflavones (ISO) appear to reduce the inflammatory pathway through their role as a tyrosine kinase inhibitor. Delayed onset muscle soreness (DOMS) develops after intense exercise and has been associated with an inflammatory response. Therefore, we hypothesized that physical parameters associated with DOMS could be decreased via the modulation of the inflammatory response by supplementing subjects with either FO or ISO. METHODS 22 subjects were recruited and randomly assigned to one of three treatment groups: FO (1.8 g of omega-3 fatty acids x d(-1)), ISO (120 mg soy isolate x d(-1)), or placebo (PL) (Western fat blend and/or wheat flour). All treatment groups received 100-IU vitamin E x d(-1) to minimize lipid peroxidation of more highly unsaturated fatty acids. Subjects were supplemented 30 d before the exercise and during the week of testing and were instructed to refrain from unusual exercise. DOMS was induced by 50 maximal isokinetic eccentric elbow flexion contractions. Strength parameters, pain, arm circumference, and relaxed arm angle (RANG) were measured at 48, 72, and 168 h post exercise. Cortisol, creatine kinase (CK), interleukin-6 (IL-6), tumor necrosis factor (TNFalpha), malondialdehyde (MDA), and serum iron were measured before supplementation, after supplementation, and post exercise. RESULTS Significant decreases were observed in RANG and strength 48 h postexercise among all groups, and there were significant increases in pain and arm circumference. There were no significant changes among all groups from baseline at 168 h (7 d) post exercise. There were no significant treatment effects between groups for the physical parameters or for cortisol, CK, IL-6, TNFalpha, MDA, or serum iron. CONCLUSION These data indicate FO or ISO, at the doses supplemented, were not effective in ameliorating DOMS with the above-cited protocol.

A musculoskeletal approach to the preparticipation physical examination Preventing injury and improving performance

Preparticipation physical examinations provide infor mation concerning an athletes ability to participate safely in sports. By collecting information specific to the musculoskeletal system in addition to that from a general medical examination, information can be gained that may improve performance and help prevent certain injuries. Two thousand one hundred seven athletes from a variety of sports from the junior high to the college level were examined using specific tests for flexibility, strength, and endurance. Females were sig nificantly more flexible than were males on all flexibility measurements, and males were significantly stronger than were females on all strength measurements. Up per-body athletes were tighter in dominant side internal rotation and significantly looser in dominant side exter nal rotation. Lower-body athletes, especially females, were significantly tighter in the leg muscles. These results indicate that the adaptations of the musculo skeletal system are sport specific and depend on the body area that is placed under stress.

Scapular Summit 2009, July 16, 2009, Lexington, Kentucky

This was the third research meeting focused on scapular function and dysfunction, following similar meetings in 2003 and 2006. The purpose of this meeting, hosted by the Shoulder Center of Kentucky, was to continue to examine the biomechanical and clinical factors thought to be associated with the role of the scapula in shoulder function and dysfunction. Since the last Summit, much more information has been created in this area, and it was thought that enough progress had been made that an organized overview of current knowledge could provide some consensus statements to guide further research and provide assessment and treatment guidelines. A call for abstracts was extended to researchers with proven interest and published research on the scapula. The meeting was organized around 3 primary categories of information: scapular kinematics and dysfunction, clinical evaluation of the scapula, and interventions. The last session of the meeting involved development of consensus statements for each category. This document represents the current state of knowledge concerning the aspects of scapular function and dysfunction discussed at the Summit. It is expected that, as more knowledge is developed, the gaps will be filled in and a clearer understanding of the roles of the scapula in shoulder function will emerge. This issue includes the consensus statements and abstracts from the Summit.

Comparison of Lower Extremity Kinematics and Hip Muscle Activation During Rehabilitation Tasks Between Sexes

CONTEXT Closed kinetic chain exercises are an integral part of rehabilitation programs after lower extremity injury. Sex differences in lower extremity kinematics have been reported during landing and cutting; however, less is known about sex differences in movement patterns and activation of the hip musculature during common lower extremity rehabilitation exercises. OBJECTIVE To determine whether lower extremity kinematics and muscle activation levels differ between sexes during closed kinetic chain rehabilitation exercises. DESIGN Cross-sectional with 1 between-subjects factor (sex) and 1 within-subjects factor (exercise). SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Participants included 21 women (age = 23 +/- 5.8 years, height = 167.6 +/- 5.1 cm, mass = 63.7 +/- 5.9 kg) and 21 men (age = 23 +/- 4.0 years, height = 181.4 +/- 7.4 cm, mass = 85.6 +/- 16.5 kg). INTERVENTION(S) In 1 testing session, participants performed 3 trials each of single-leg squat, lunge, and step-up-and-over exercises. MAIN OUTCOME MEASURE(S) We recorded the peak joint angles (degrees) of knee flexion and valgus and hip flexion, extension, adduction, and external rotation for each exercise. We also recorded the electromyographic activity of the gluteus maximus, rectus femoris, adductor longus, and bilateral gluteus medius muscles for the concentric and eccentric phases of each exercise. RESULTS Peak knee flexion angles were smaller and peak hip extension angles were larger for women than for men across all tasks. Peak hip flexion angles during the single-leg squat were smaller for women than for men. Mean root-mean-square amplitudes for the gluteus maximus and rectus femoris muscles in both the concentric and eccentric phases of the 3 exercises were greater for women than for men. CONCLUSIONS Sex differences were observed in sagittal-plane movement patterns during the rehabilitation exercises. Because of the sex differences observed in our study, future researchers need to compare the findings for injured participants by sex to garner a better representation of altered kinematic angles and muscle activation levels due to injury.

Reliability of electromyographic methods used for assessing hip and knee neuromuscular activity in females diagnosed with patellofemoral pain syndrome

Patellofemoral pain syndrome (PFPS) is one of the most common, yet misunderstood, knee pathologies. PFPS is thought to result from abnormal patella tracking caused from altered neuromuscular control. Researchers have investigated neuromuscular influences from the gluteus medius (GM), vastus medialis (VM), and vastus lateralis (VL) but with inconsistent findings. A reason for these discrepancies may be from varying methodology. The purpose of this study was to determine the reliability of electromyographic (EMG) methods used to assess amplitudes and timing differences of the GM, VM, and VL in subjects with PFPS. Seven females with PFPS participated. GM, VM, and VL activity was assessed during the stance phase of a stair descent task on two separate occasions. Amplitudes during the different intervals of stance were recorded and expressed as a percent of each muscles maximum voluntary isometric contraction. Muscle onsets at the beginning of stair descent were also determined. VM-GM, VL-GM, and VL-VM onset timing differences were quantified. Intraclass correlation coefficients (ICCs) and standard errors of measurement (SEMs) were calculated to assess between-day reliability. Most EMG measures had acceptable reliability (ICC(3,5)>or=0.70). Although some measures had moderate reliability (ICC<0.70), they had low SEMs, which suggested high measurement precision. These findings support using these methods for examining neuromuscular activity in subjects with PFPS.