Individual Muscle Force Differences During Loaded Hexbar Jumps: A Statistical Parametric Mapping Analysis.

Knowledge of individual muscle force during strength and conditioning exercises provides deeper understanding of how specific training decisions relate to desired training outcomes. The purpose of this study was to estimate individual muscle forces during hexbar jumps with 0%, 20%, 40%, and 60% of the hexbar deadlift 1-repetition maximum utilizing in vivo motion capture and computational modeling techniques of male participants. Muscle forces for the gluteus maximus, biceps femoris, rectus femoris, vastus intermedius, gastrocnemius, and soleus were estimated via static optimization. Changes in muscle forces over the concentric phase were analyzed across loading conditions using statistical parametric mapping, impulse, and peak values. Conclusions about the effects of load differ between the three analysis methods; therefore, careful selection of analysis method is essential. Peaks may be inadequate in assessing differences in muscle force during dynamic movements. If SPM, assessing point-by-point differences, is combined with impulse, where time of force application is considered, both timepoint and overall loading can be analyzed. The response of individual muscle forces to increases in external load, as assessed by impulse and SPM, includes increased total muscle output, proportionally highest at 20%1RM, and increased absolute force for the vasti and plantarflexors during the concentric phase of hexbar jumps.

The effect of load based on body mass percentage on peak power output in the hang power clean, hang high pull, and mid-thigh clean pull.

BACKGROUND: Prescribing load at the peak power output (PPO) is one of the strategies utilized to enhance lower-body muscle power. PPO of an exercise is determined based on a relative percentage of the one-repetition maximum test (1RM). However, 1RM tests may be impractical in some weightlifting derivatives. This study aimed to identify the PPO of the hang power clean (HPC), hang high pull (HHP), and mid-thigh clean pull (MTCP) based on a relative percentage of body mass (BM). METHODS: Fifteen males with weightlifting experience performed HPC, HHP, and MTCP at loads ranging from 30-90% BM. Kinematic data were collected through a 16-camera infrared motion capture system and processed based on a three-dimensional lower-extremity model. Ground reaction force (GRF) data were collected from two force plates. PPO was calculated as the product of model center of mass velocity and combined vertical GRF during the concentric phase. RESULTS: PPO occurred at 90% BM for the HPC. In addition, the PPO occurred at 90% BM for the HHP and it was not different than 70% and 80% BM. At last, the PPO for MTCP occurred at 80% BM and it was not different than 60% and 70% BM. CONCLUSIONS: Relative percentages of BM can be used to determine PPO in the HPC, HHP, and MTCP. PPO during HPC is achieved at 90% BM, while the PPO for HHP and MTCP is achieved between 70% to 90% BM and 60 to 80% BM, respectively.

Children Who Are Overweight Display Altered Vertical Jump Kinematics and Kinetics From Children Who Are Not Overweight.

PURPOSE: Children who are overweight typically do not perform motor skills as well as normal-weight peers. This study examined whether vertical jump kinetics and kinematics of children who are overweight differ from nonoverweight peers. METHODS: Thirty-nine children completed maximum-effort countermovement vertical jumps. Motion capture was used to complete lower extremity kinematic and kinetic analyses. RESULTS: The overweight group (body mass index ≥ 85th percentile; N = 11; age = 6.5 [1.6] y) jumped lower relative to their mass (0.381 cm/kg lower; P < .001) than normal-weight peers (N = 28; age = 6.4 [1.7] y). Compared with children who are normal weight, children who were overweight exhibited a shallower countermovement (knee: 12° less flexion, P = .02; hip: 10° less flexion, P = .045), lower hip torque (0.06 N·m/kg lower, P = .01) and hip work (40% less work, P = .01), and earlier peak joint angular velocities (knee: 9 ms earlier, P = .001; hip: 14 ms earlier, P = .004). CONCLUSION: Children who are overweight do not achieve optimal jumping mechanics and exhibit jumping characteristics of an earlier developmental stage compared with their peers. Interventions should help children who are overweight learn to execute a proper countermovement.

Effects of Anterior Knee Displacement During Squatting on Patellofemoral Joint Stress.

CONTEXT: Squatting is a common rehabilitation training exercise for patellofemoral pain syndrome (PFPS). Patellofemoral joint stress (PFJS) during squatting with more anterior knee displacement has not been systematically investigated. OBJECTIVE: To compare PFJS during squatting using 2 techniques: squat while keeping the knees behind the toes (SBT) and squat while allowing the knees to go past the toes (SPT). SETTING: University research laboratory. PARTICIPANTS: Twenty-five healthy females (age: 22.69 (0.74) y; height: 169.39 (6.44) cm; mass: 61.55 (9.74) kg) participated. MAIN OUTCOME MEASURES: Three-dimensional kinematic and kinetic data were collected at 180 and 1800 Hz, respectively. A musculoskeletal model was used to calculate muscle forces through static optimization. These muscle forces were used in a patellofemoral joint model to estimate PFJS. RESULTS: The magnitudes of PFJS, reaction force, and quadriceps force were higher (P < .001) during SPT compared with the SBT technique. Knee flexion, hip flexion, and ankle dorsiflexion angles were reduced when using the SBT technique. CONCLUSIONS: Findings provide some general support for minimizing forward knee translation during squats for patients that may have patellofemoral pain syndrome.

Lower body predictors of glenohumeral compressive force in high school baseball pitchers.

The purpose of this study was to better understand how lower body kinematics relate to peak glenohumeral compressive force and develop a regression model accounting for variability in peak glenohumeral compressive force. Data were collected for 34 pitchers. Average peak glenohumeral compressive force was 1.72% ± 33% body weight (1334.9 N ± 257.5). Correlation coefficients revealed 5 kinematic variables correlated to peak glenohumeral compressive force (P < .01, α = .025). Regression models indicated 78.5% of the variance in peak glenohumeral compressive force (R2 = .785, P < .01) was explained by stride length, lateral pelvis flexion at maximum external rotation, and axial pelvis rotation velocity at release. These results indicate peak glenohumeral compressive force increases with a combination of decreased stride length, increased pelvic tilt at maximum external rotation toward the throwing arm side, and increased pelvis axial rotation velocity at release. Thus, it may be possible to decrease peak glenohumeral compressive force by optimizing the movements of the lower body while pitching. Focus should be on both training and conditioning the lower extremity in an effort to increase stride length, increase pelvis tilt toward the glove hand side at maximum external rotation, and decrease pelvis axial rotation at release.

Adductor longus activation during common hip exercises.

CONTEXT: Hip-adductor strains are among the most common lower-extremity injuries sustained in athletics. Treatment of these injuries involves a variety of exercises used to target the hip adductors. OBJECTIVE: To identify the varying activation levels of the adductor longus during common hip-adductor exercises. DESIGN: Descriptive study. SETTING: Laboratory. PARTICIPANTS: 24 physically active, college-age students. INTERVENTION: None. MAIN MEASUREMENT OUTCOMES: Peak and average electromyographic (EMG) activity of the adductor longus muscle during the following 6 hip-adductor rehabilitation exercises: side-lying hip adduction, ball squeezes, rotational squats, sumo squats, standing hip adduction on a Swiss ball, and side lunges. RESULTS: The side-lying hip-adduction exercise produced more peak and average activation than any other exercise (P < .001). Ball squeezes produced more peak and average activation than rotational squats, sumo squats, and standing adduction on a Swiss ball (P < .001). Ball squeezes had more average activation than side lunges (P = .001). All other variables for peak activation during the exercises were not statistically significant (P > .08). These results allowed the authors to provide an overall ranking system (highest to lowest muscle activation): side-lying hip adduction, ball squeezes, side lunges, standing adduction on a Swiss ball, rotational squats, and sumo squats. CONCLUSION: The study provides a ranking system on the activation levels of the adductor longus muscle for 6 common hip-adductor rehabilitation exercises, with the side-lying hip-adduction and ball-squeeze exercises displaying the highest overall activation.

Effect of plane of arm elevation on glenohumeral kinematics: a normative biplane fluoroscopy study.

BACKGROUND: Understanding glenohumeral motion in normal and pathologic states requires the precise measurement of shoulder kinematics. The effect of the plane of arm elevation on glenohumeral translations and rotations remains largely unknown. The purpose of this study was to measure the three-dimensional glenohumeral translations and rotations during arm elevation in healthy subjects. METHODS: Eight male subjects performed scaption and forward flexion, and five subjects (three men and two women) performed abduction, inside a dynamic biplane fluoroscopy system. Bone geometries were extracted from computed tomography images and used to determine the three-dimensional position and orientation of the humerus and scapula in individual frames. Descriptive statistics were determined for glenohumeral joint rotations and translations, and linear regressions were performed to calculate the scapulohumeral rhythm ratio. RESULTS: The scapulohumeral rhythm ratio was 2.0 ± 0.4:1 for abduction, 1.6 ± 0.5:1 for scaption, and 1.1 ± 0.3:1 for forward flexion, with the ratio for forward flexion being significantly lower than that for abduction (p = 0.002). Humeral head excursion was largest in abduction (5.1 ± 1.1 mm) and smallest in scaption (2.4 ± 0.6 mm) (p < 0.001). The direction of translation, as determined by the linear regression slope, was more inferior during abduction (-2.1 ± 1.8 mm/90°) compared with forward flexion (0.1 ± 10.9 mm/90°) (p = 0.024). CONCLUSIONS: Scapulohumeral rhythm significantly decreased as the plane of arm elevation moved in an anterior arc from abduction to forward flexion. The amount of physiologic glenohumeral excursion varied significantly with the plane of elevation, was smallest for scaption, and showed inconsistent patterns across subjects with the exception of consistent inferior translation during abduction.

Filtering ground reaction force data affects the calculation and interpretation of joint kinetics and energetics during drop landings.

An inverse dynamic analysis and subsequent calculation of joint kinetic and energetic measures is widely used to study the mechanics of the lower extremity. Filtering the kinematic and kinetic data input to the inverse dynamics equations affects the calculated joint moment of force (JMF). Our purpose was to compare selected integral values of sagittal plane ankle, knee, and hip joint kinetics and energetics when filtered and unfiltered GRF data are input to inverse dynamics calculations. Six healthy, active, injury-free university student (5 female, 1 male) volunteers performed 10 two-legged landings. JMFs were calculated after two methods of data filtering. Unfiltered: marker data were filtered at 10 Hz, GRF data unfiltered. Filtered: both GRF and marker data filtered at 10 Hz. The filtering of the GRF data affected the shape of the knee and hip joint moment-time curves, and the ankle, knee and hip joint mechanical power-time curves. We concluded that although the contributions of individual joints to the support moment and to total energy absorption were not affected, the attenuation of high-frequency oscillations in both JMF and JMP time curves will influence interpretation of CNS strategies during landing.

High knee valgus in female subjects does not yield higher knee translations during drop landings: a biplane fluoroscopic study.

The goal of this study was to determine the effects of peak knee valgus angle and peak knee abductor moment on the anterior, medial, and lateral tibial translations (ATT, MTT, LTT) in the "at risk" female knee during drop landing. Fifteen female subjects performed drop landings from 40 cm. Three-dimension knee motion was simultaneously recorded using a high speed, biplane fluoroscopy system, and a video-based motion analysis system. Valgus knee angles and knee abduction moments were stratified into low, intermediate, and high groups and peak ATT, MTT, and LTT were compared between these groups with ANOVA (α = 0.05). Significant differences were observed between stratified groups in peak knee valgus angle (p < 0.0001) and peak knee abduction moment (p < 0.0001). However, no corresponding differences in peak ATT, LTT, and MTT between groups exhibiting low to high-peak knee valgus angles (ATT: p = 0.80; LTT: p = 0.25; MTT: p = 0.72); or, in peak ATT (p = 0.61), LTT (p = 0.26) and MTT (p = 0.96) translations when stratified according to low to high knee abduction moments, were found. We conclude that the healthy female knee is tightly regulated with regard to translations even when motion analysis derived knee valgus angles and abduction moments are high.

The long head of the biceps tendon has minimal effect on in vivo glenohumeral kinematics: a biplane fluoroscopy study.

BACKGROUND: The in vivo stabilizing role of the long head of the biceps tendon (LHB) is poorly understood. While cadaveric studies report that the loaded LHB constrains translations in all directions, clinical data suggest that there is no clinically demonstrable alteration in glenohumeral position after LHB tenodesis or tenotomy. The purpose of this study was to investigate potential alterations in glenohumeral kinematics after LHB tenodesis during 3 dynamic in vivo motions using a biplane fluoroscopy system. HYPOTHESIS: Our hypothesis was that there would be no difference in glenohumeral translations greater than 1.0 mm between shoulders after biceps tenodesis and healthy contralateral shoulders. STUDY DESIGN: Controlled laboratory study. METHODS: Five patients who underwent unilateral, open subpectoral tenodesis performed abduction, a simulated late cocking phase of a throw, and simulated lifting with both their tenodesed shoulder and their contralateral healthy shoulder inside a biplane fluoroscopy system. Dynamic 3-dimensional glenohumeral positions and electromyography activity of the biceps brachii muscle were determined and compared. RESULTS: Significant glenohumeral translations occurred in both shoulders for abduction (3.4 mm inferiorly; P < .01) and simulated late cocking (2.6 mm anteriorly; P < .01). The mean difference for each motion in glenohumeral position between the tenodesed and the contralateral healthy shoulders was always less than 1.0 mm. The tenodesed shoulders were more anterior (centered) during abduction (0.7 mm; P < .01) and for the eccentric phase of the simulated late cocking motion (0.9 mm; P < .02). No significant differences were found during the simulated lifting motion and in the superior-inferior direction. CONCLUSION: The effect of biceps tenodesis on glenohumeral position during the motions studied in vivo was minimal compared with physiological translations and interpatient variability. CLINICAL RELEVANCE: Our findings demonstrated that LHB tenodesis does not dramatically alter glenohumeral position during dynamic motions, suggesting the risk for clinically significant alterations in glenohumeral kinematics after tenodesis is low in otherwise intact shoulders.

In vivo tibiofemoral kinematics during 4 functional tasks of increasing demand using biplane fluoroscopy.

BACKGROUND: The anterior cruciate ligament (ACL) has been well defined as the main passive restraint to anterior tibial translation (ATT) in the knee and plays an important role in rotational stability. However, it is unknown how closely the ACL and other passive and active structures of the knee constrain translations and rotations across a set of functional activities of increasing demand on the quadriceps. HYPOTHESIS: Anterior tibial translation and internal rotation of the tibia relative to the femur would increase as the demand on the quadriceps increased. STUDY DESIGN: Controlled laboratory study. METHODS: The in vivo 3-dimensional knee kinematics of 10 adult female patients (height, 167.8 ± 7.1 cm; body mass, 57 ± 4 kg; body mass index [BMI], 24.8 ± 1.7 kg/m(2); age, 29.7 ± 7.9 years) was measured using biplane fluoroscopy while patients completed 4 functional tasks. The tasks included an unloaded knee extension in which the patient slowly extended the knee from 90° to 0° of flexion in 2 seconds; walking at a constant pace of 90 steps per minute; a maximum effort isometric knee extension with the knee at 70° of flexion; and landing from a height of 40 cm in which the patient stepped off a box, landed, and immediately performed a maximum effort vertical jump. RESULTS: Landing (5.6 ± 1.9 mm) produced significantly greater peak ATT than walking (3.1 ± 2.2 mm) and unweighted full extension (2.6 ± 2.1 mm) (P < .01), but there was no difference between landing and a maximum isometric contraction (5.0 ± 1.9 mm). While there was no significant difference in peak internal rotation between landing (19.4° ± 5.7°), maximum isometric contraction (15.9° ± 6.7°), and unweighted full knee extension (14.5° ± 7.7°), each produced significantly greater internal rotation than walking (3.9° ± 4.2°) (P < .001). Knee extension torque significantly increased for each task (P < .01): unweighted knee extension (4.7 ± 1.2 N·m), walking (36.5 ± 7.9 N·m), maximum isometric knee extension (105.1 ± 8.2 N·m), and landing (140.2 ± 26.2 N·m). CONCLUSION: Anterior tibial translations significantly increased as demand on the quadriceps and external loading increased. Internal rotation was not significantly different between landing, isometric contraction, and unweighted knee extension. Additionally, ATT and internal rotation from each motion were within the normal range, and no excessive amounts of translation or rotation were observed. CLINICAL RELEVANCE: This study demonstrated that while ATT will increase as demand on the quadriceps and external loading increases, the knee is able to effectively constrain ATT and internal rotation. This suggests that the healthy knee has a safe envelope of function that is tightly controlled even though task demand is elevated.

Relationship of knee shear force and extensor moment on knee translations in females performing drop landings: a biplane fluoroscopy study.

BACKGROUND: Research has linked knee extensor moment and knee shear force to the non-contact anterior cruciate ligament injury during the landing motion. However, how these biomechanical performance factors relate to knee translations in vivo is not known as knee translations cannot be obtained with traditional motion capture techniques. The purpose of this study was to combine traditional motion capture with high-speed, biplane fluoroscopy imaging to determine relationships between knee extensor moment and knee shear force profiles with anterior and lateral tibial translations occurring during drop landing in female athletes. METHODS: 15 females performed drop landings from a height of 40 cm while being recorded using a high speed, biplane fluoroscopy system and simultaneously being recorded using surface marker motion capture techniques to estimate knee joint angle, reaction force and moment profiles. FINDINGS: No significant statistical relationships were observed between peak anterior or posterior knee shear force and peak anterior and lateral tibial translations; or, between peak knee extensor moment and peak anterior and lateral tibial translations. Although differences were noted in peak shear force (P=0.02) and peak knee extensor moment (P<0.001) after stratification into low and high shear force and moment cohorts, no differences were noted in anterior and lateral tibial translations (all P ≥ 0.18). INTERPRETATION: Females exhibiting high knee extensor moment and knee shear force during drop landings do not yield correspondingly high anterior and lateral tibial translations.

A comparison of calibration methods for stereo fluoroscopic imaging systems.

Stereo (biplane) fluoroscopic imaging systems are considered the most accurate and precise systems to study joint kinematics in vivo. Calibration of a biplane fluoroscopy system consists of three steps: (1) correction for spatial image distortion; (2) calculation of the focus position; and (3) calculation of the relative position and orientation of the two fluoroscopy systems with respect to each other. In this study we compared 6 methods for calibrating a biplane fluoroscopy system including a new method using a novel nested-optimization technique. To quantify bias and precision, an electronic digital caliper instrumented with two tantalum markers on radiolucent posts was imaged in three configurations, and for each configuration placed in ten static poses distributed throughout the viewing volume. Bias and precision were calculated as the mean and standard deviation of the displacement of the markers measured between the three caliper configurations. The data demonstrated that it is essential to correct for image distortion when sub-millimeter accuracy is required. We recommend calibrating a stereo fluoroscopic imaging system using an accurately machined plate and a calibration cube, which improved accuracy 2-3 times compared to the other calibration methods. Once image distortion is properly corrected, the focus position should be determined using the Direct Linear Transformation (DLT) method for its increased speed and equivalent accuracy compared to the novel nested-optimization method. The DLT method also automatically provides the 3D fluoroscopy configuration. Using the recommended calibration methodology, bias and precision of 0.09 and 0.05 mm or better can be expected for measuring inter-marker distances.

Defining a safety margin for labral suture anchor insertion using the acetabular rim angle.

BACKGROUND: Suture anchors are commonly used to reattach a torn labrum to the acetabular rim. The acetabular rim anatomy is not uniform, and the safety margin for inserting suture anchors is unknown. The acetabular rim angle is an anatomic measurement that is indicative of the safety margin for inserting suture anchors. PURPOSE: To investigate the acetabular rim angle as a function of clock position, to evaluate the effect of drill depth on the acetabular rim angle, and to evaluate the effect of rim trimming on the acetabular rim angle. STUDY DESIGN: Descriptive laboratory study. METHODS: Three-dimensional acetabular models were reconstructed from computed tomography scans of 20 nonpaired cadaveric hip specimens, and the acetabular rim angle, which quantifies the angle between the subchondral margin and the outer cortex of the acetabulum, was measured from the 8- to 4-o'clock positions. At each position, the acetabular rim angle was measured for 5 drill depths (10, 12.5, 15, 20, and 25 mm) to simulate different lengths of suture anchors or drill bit depths on the acetabular rim angle. To simulate rim trimming, the acetabular rim angle was measured at the points that would become the suture anchor insertion points after 2.5- and 5-mm rim trimming. RESULTS: Clock position, drill depth, and rim trimming all had significant effects on the acetabular rim angle (P < .0001). The acetabular rim angle was largest at the 2-o'clock and smallest at the 3-o'clock position. Greater drill depths provided smaller acetabular rim angles, whereas rim trimming provided larger acetabular rim angles. CONCLUSION: The acetabular rim angle varied significantly as a function of the location on the acetabular rim. A shorter drill depth and a greater amount of rim trimming provided a larger acetabular rim angle. CLINICAL RELEVANCE: Surgeons should be aware of the acetabular rim variations, especially in the anterosuperior quadrant, as well as the effects of drill depth and rim trimming, when selecting the optimal insertion angle for suture anchor placement to avoid articular cartilage penetration. The acetabular safety angle was smallest at the 3-o'clock position. Therefore, extra care must be taken when drilling or inserting anchors around the 3-o'clock position.

Measurements of tibiofemoral kinematics during soft and stiff drop landings using biplane fluoroscopy.

BACKGROUND: Previous laboratory studies of landing have defined landing techniques in terms of soft or stiff landings according to the degree of maximal knee flexion angle attained during the landing phase and the relative magnitude of the ground-reaction force. Current anterior cruciate ligament injury prevention programs are instructing athletes to land softly to avoid excessive strain on the anterior cruciate ligament. PURPOSE: This study was undertaken to measure, describe, and compare tibiofemoral rotations and translations of soft and stiff landings in healthy individuals using biplane fluoroscopy. STUDY DESIGN: Controlled laboratory study. METHODS: The in vivo, lower extremity, 3-dimensional knee kinematics of 16 healthy adults (6 male and 10 female) instructed to land softly and stiffly in different trials were collected in biplane fluoroscopy as they performed the landing from a height of 40 cm. RESULTS: Average and maximum relative anterior tibial translation (average, 2.8 ± 1.2 mm vs 3.0 ± 1.4 mm; maximum, 4.7 ± 1.6 mm vs 4.4 ± 0.8 mm), internal/external rotation (average, 3.7° ± 5.1° vs 2.7° ± 4.3°; maximum, 5.6° ± 5.5° vs 4.9° ± 4.7°), and varus/valgus (average, 0.2° ± 1.2° vs 0.2° ± 1.0°; maximum, 1.7° ± 1.2° vs 1.6° ± 0.9°) were all similar between soft and stiff landings, respectively. The peak vertical ground-reaction force was significantly larger for stiff landings than for soft landings (2.60 ± 1.32 body weight vs 1.63 ± 0.73; P < .001). The knee flexion angle total range of motion from the minimum angle at contact to the maximum angle at peak knee flexion was significantly greater for soft landings than for stiff (55.4° ± 8.8° vs 36.8° ± 11.1°; P < .01). CONCLUSION: Stiff landings, as defined by significantly lower knee flexion angles and significantly greater peak ground-reaction forces, do not result in larger amounts of anterior tibial translation or knee rotation in either varus/valgus or internal/external rotation in healthy individuals. CLINICAL RELEVANCE: In healthy knees, the musculature and soft tissues of the knee are able to maintain translations and rotations within a small, safe range during controlled landing tasks of differing demand. The knee kinematics of this healthy population will serve as a comparison for injured knees in future studies. It should be stressed that because the authors did not compare how the loads were distributed over the soft tissues of the knee between the 2 landing styles, the larger ground-reaction forces and more extended knee position observed during stiff landings should still be considered dangerous to the anterior cruciate ligament and other structures of the lower extremities, particularly in competitive settings where movements are often unanticipated.

Rehabilitation exercise progression for the gluteus medius muscle with consideration for iliopsoas tendinitis: an in vivo electromyography study.

BACKGROUND: It is common for hip arthroscopy patients to demonstrate significant gluteus medius muscle weakness and concurrent iliopsoas tendinitis. Restoration of gluteus medius muscle function is essential for normal hip function. HYPOTHESIS: A progression of hip rehabilitation exercises to strengthen the gluteus medius muscle could be identified that minimize concurrent iliopsoas muscle activation to reduce the risk of developing or aggravating hip flexor tendinitis STUDY DESIGN: Descriptive laboratory study. METHODS: Electromyography (EMG) signals of the gluteus medius and iliopsoas muscles were recorded from 10 healthy participants during 13 hip rehabilitation exercises. The indwelling fine-wire EMG electrodes were inserted under ultrasound guidance. The average and peak EMG amplitudes, normalized by the peak EMG amplitude elicited during maximum voluntary contractions, were determined and rank-ordered from low to high. The ratio of iliopsoas to gluteus medius muscle activity was calculated for each exercise. Exercises were placed into respective time phases based on average gluteus medius EMG amplitude, except that exercises involving hip rotation were avoided in phase I (phase I, initial 4 or 8 weeks; phase II, subsequent 4 weeks; phase III, final 4 weeks). RESULTS: A continuum of hip rehabilitation exercises was identified. Resisted terminal knee extension, resisted knee flexion, and double-leg bridges were identified as appropriate for phase I and resisted hip extension, stool hip rotations, and side-lying hip abduction with wall-sliding for phase II. Hip clam exercises with neutral hips may be used with caution in patients with hip flexor tendinitis. Prone heel squeezes, side-lying hip abduction with internal hip rotation, and single-leg bridges were identified for phase III. CONCLUSION/CLINICAL RELEVANCE: This study identified the most appropriate hip rehabilitation exercises for each phase to strengthen the gluteus medius muscle after hip arthroscopy and those to avoid when iliopsoas pain or tendinitis is a concern.

The influence of arm and shoulder position on the bear-hug, belly-press, and lift-off tests: an electromyographic study.

BACKGROUND: Clinical testing for the integrity of the subscapularis muscle includes the belly-press, lift-off, and bear-hug examinations. While these tests have been widely applied in clinical practice, there is considerable variation in arm positioning within each clinical examination. HYPOTHESIS: To determine the ideal arm and shoulder positions for isolating the subscapularis muscle while performing the bear-hug, belly-press, and lift-off tests. STUDY DESIGN: Controlled laboratory study. METHODS: The activity of 7 muscles was monitored in 20 healthy participants: upper and lower divisions of the subscapularis, supraspinatus, infraspinatus, latissimus dorsi, teres major, triceps, pectoralis major. Electromyogram data were collected and compared across each clinical test at varying arm positions: bear-hug (ideal position, 10° superior, 10° inferior to the shoulder line), belly-press (ideal position, maximum shoulder external rotation, and maximal shoulder internal rotation), and lift-off (ideal position, hand position 5 in. [12.7 cm] superior and 5 in. [12.7 cm] inferior to the midlumbar spine). RESULTS: Regardless of arm and shoulder position, the upper and lower subscapularis muscle activities were significantly greater than all other muscles while performing each test. No significant differences were observed between the upper and lower subscapularis divisions at any position within and across the 3 tests. There were no significant differences in subscapularis electromyogram activities across the 3 tests. CONCLUSION: The level of subscapularis muscle activation was similar among the bear-hug, belly-press, and lift-off tests. The 3 tests activated the subscapularis significantly more than all other muscles tested but were not different from one another when compared across tests and positions. Although the bear-hug and lift-off tests have been described to activate differential portions of the subscapularis, the findings of this study do not support the preferential testing of a specific subscapular division across the 3 tests. As such, all 3 tests are effective in testing the integrity of the entire subscapularis muscle, although there does not appear to be an ideal position for selectively testing its divisions. CLINICAL RELEVANCE: Clinicians may feel comfortable in using any of the 3 tests, depending on the patient, to isolate the function of the subscapularis as a single muscle. Furthermore, clinicians should not solely focus on a patient's arm position when administering an examination but also compare the affected arm to the contralateral shoulder when appropriate.

A comparison of forearm supination and elbow flexion strength in patients with long head of the biceps tenotomy or tenodesis.

PURPOSE: The purpose of this study was to compare the forearm supination and elbow flexion strength of the upper extremity in patients who have had an arthroscopic long head of the biceps tendon (LHBT) release with patients who have had an LHBT tenodesis. METHODS: Cybex isokinetic strength testing (Cybex Division of Lumex, Ronkonkoma, NY) was performed on 17 patients who underwent arthroscopic LHBT tenotomy, 19 patients who underwent arthroscopic LHBT tenodesis, and 31 age-, gender-, and body mass index-matched control subjects. Subjects were considered fully recovered from shoulder surgery, were released for unrestricted activities, and were at least 6 months after surgery before testing. Subjects were tested for forearm supination and elbow flexion strength of both arms by use of a Cybex II NORM isokinetic dynamometer at 60°/s and 120°/s. Testing was performed on injured and uninjured arms as well as dominant and nondominant arms in control subjects. Both forearm supination and elbow flexion strength values were recorded. RESULTS: Comparison between the involved and uninvolved upper extremities within each group by use of a paired t test showed a 7% increase in elbow flexion strength when the dominant and nondominant arms were compared at 60°/s. Neither the tenotomy nor tenodesis groups exhibited elbow flexion strength differences at 120°/s (all P ≥ .147). Comparison between groups by use of 2 × 3 analysis of variance (speed × group) showed no statistical difference in either forearm supination or elbow flexion strength when we compared the tenotomy, tenodesis, and control groups. CONCLUSIONS: In asymptomatic patients who have had biceps tenotomy or tenodesis, no statistically significant forearm supination or elbow flexion strength differences existed in the involved extremity between the 2 study groups. LEVEL OF EVIDENCE: Level III, case-control study.

Relationship of anterior knee laxity to knee translations during drop landings: a bi-plane fluoroscopy study.

PURPOSE: Passive anterior knee laxity has been linked to non-contact ACL injury risk. High deceleration movements have been implicated in the non-contact ACL injury mechanism, and evidence suggests that greater anterior tibial translations (ATT) may occur in healthy knees that are lax compared to a tight knee. The purpose of this study was to determine the relationship between anterior knee laxity scores and ATT during drop landings using biplane fluoroscopy. METHODS: Sixteen healthy adults (10 women; 6 men) performed stiff drop landings (40 cm) while being filmed using a high-speed, biplane fluoroscopy system. Initial, peak and excursions for rotations and translations were calculated and regression analysis used to determine the 6DoF kinematic relationships with KT1000 scores with peak ATT occurring during the landing. RESULTS: KT1000 values were (+) correlated with peak ATT values for group (r = 0.89; P < 0.0001) and both genders (males, r = 0.97; P = 0.0003; females, r = 0.93; P = < 0.0001). Regression analysis yielded a significant linear fit for the group (r (2) = 0.80; Y (ATT-group) = - 0.516 + 1.2 × X (KT1000-group)) and for each gender (females: r(2) = 0.86; Y (ATT-females) = 0.074 + 1.2 × X (KT1000-females) and males: r (2) = 0.94; Y (ATT-males) = - 0.79 + 1.2 × X (KT1000-males)). CONCLUSION: A strong relationship was observed between passive anterior knee laxity measured via KT1000 and peak ATT experienced during dynamic activity in otherwise healthy persons performing a stiff drop-landing motion.

Knee kinematic profiles during drop landings: a biplane fluoroscopy study.

INTRODUCTION: The six degrees of freedom knee motion during dynamic activities is not well understood. PURPOSE: Biplane fluoroscopy was used to measure the three-dimensional rotations and translations of healthy knees during stiff drop landings and to determine the relationships between three-dimensional rotations and anterior (ATT) and lateral tibial translations (LTT). METHODS: Six males performed stiff drop landings from 40 cm while being filmed using a high-speed, biplane fluoroscopy system. Initial, peak, and excursions for rotations and translations were calculated, and relationships and changes in these variables were assessed (α = 0.05). RESULTS: Knee flexion at contact was 13.9° ± 9.2° (mean ± SD) and increased to a peak of 44.0° ± 17.2° with an excursion of 31.5° ± 14.1°. Knee varus/valgus angle at contact was -0.3° ± 1.8° varus; subjects progressed into a mean peak valgus position of 1.5° ± 0.9° with total excursion of 2.5° ± 0.9°. Four of six subjects landed externally rotated (2.5° ± 3.0°); two landed internally rotated (-4.9° ± 1.5°), yielding a contact angle of -2.4° ± 3.0° of internal rotation, a peak internal rotation of -5.5° ± 6.0°, and excursion of 3.1° ± 5.5°. Peak ATT were 4.3 ± 0.7 mm (excursion = 2.1 ± 0.9 mm), occurring within 50 ms after contact. Peak LTT were 1.5 ± 1.4 mm (excursion = 2.6 ± 1.6 mm). Significant regressions were found between ATT and knee valgus angle (r2 = 0.39, P = 0.006), between LTT and internal rotation (r2 = 0.96, P < 0.0001), and between LTT and knee valgus angle (quadratic, r2 = 0.90, P < 0.0001). CONCLUSION: This study provides a direct correlation between knee valgus angle with knee ATT and LTT during drop landings.