David N. Suprak

Shoulder joint position sense is not enhanced at end range in an unconstrained task

Shoulder joint position sense (JPS) is important for maintaining stability and contributing to coordinated movements. It is provided by afferent and centrally-derived signals interpreted and integrated by the central nervous system (CNS) for subsequent use. Shoulder JPS is enhanced as the joint approaches end range of motion (ROM) in studies involving internal and external rotation with the arm supported, but this finding has not been confirmed in unconstrained movements. To address this issue, the present study examined the effect of shoulder position in the horizontal plane on JPS at a constant elevation. Twenty-three healthy individuals were recruited from a university campus. Subjects attempted to actively replicate various target positions in both plane and elevation. Target positions consisted of five positions in the horizontal plane, normalized to individual horizontal abduction ROM, at 90° of arm elevation. All target positions were tested three times, and average absolute and variable errors were analyzed for each position. No differences in either absolute (p=.312) or variable (p=.185) errors were observed between positions. These results further support the contention that the muscle spindles are a dominant source of afferent feedback regarding shoulder JPS in unconstrained movements, even approaching end ROM, when the capsuloligamentous receptors are active.

Kinesio Tape and Shoulder-Joint Position Sense

CONTEXT Joint position sense (JPS) is a key neuromuscular factor for developing and maintaining control of muscles around a joint. It is important when performing specialized tasks, especially at the shoulder. No researchers have studied how Kinesio Tape (KT) application affects JPS. OBJECTIVE To investigate the effects of KT application and no tape on shoulder JPS at increasing shoulder elevations in athletes. DESIGN Cross-sectional study. SETTING University laboratory. PATIENTS OR OTHER PARTICIPANTS A total of 27 healthy athletes who did not participate in overhead sports (age = 20.44 ± 1.05 years, height = 175.02 ± 11.67 cm, mass = 70.74 ± 9.65 kg) with no previous pathologic shoulder conditions volunteered for the study. All participants were from 1 university. INTERVENTION(S) Shoulder JPS was assessed at increasing elevations with and without KT application. Participants attempted to actively replicate 3 target positions with and without the KT and without visual guidance. MAIN OUTCOME MEASURE(S) We examined absolute and variable repositioning errors at increasing shoulder-elevation levels with and without KT application. RESULTS Data revealed an interaction between tape and position for absolute error (F2,52 = 4.07, P = .02); simple effects revealed an increase in error, with KT demonstrating a 2.65° increase in error at 90° of elevation compared with no tape (t26 = 2.65, P = .01). The effect size was medium (ω(2) = .135). Variable error showed no interaction of tape and position (F2,52 = .709, P = .50). Further analysis of simple effects was not needed. However, we still calculated the effect size and observed small effect sizes for tape (ω(2) = .002), position (ω(2) = .072), and tape by position (ω(2) = .027). CONCLUSIONS At 90° of elevation, shoulder JPS was impaired by the application of KT.

The effects of exercise type and elbow angle on vertical ground reaction force and muscle activity during a push-up plus exercise

BackgroundProper alignment of the scapula during upper extremity motion is important in maintaining shoulder joint function and health. Push-up plus exercise is considered as one of the best exercise to strengthen the muscles that stabilize the scapula. The purpose of the study is to examine the effects of push-up plus variants and elbow position on vertical ground reaction force and electromyographical activity of four shoulder muscles during concentric contraction.MethodsA total of 22 healthy subjects volunteered for the study. Each of the subjects performed both modified and traditional push-up plus. Modified push-up plus was performed with both knees and hands touching the ground while the traditional push-up plus was executed with hands and feet contacting the ground. Electromyography (EMG) of the upper trapezius (UT), lower trapezius (LT), infraspinatus (INFRA), and serratus anterior (SA), and vertical ground reaction forces (vGRF) were collected.ResultsThe traditional push-up plus exhibited higher EMG activity in all muscles tested (P < .05) and vertical ground reaction force (P < .001) compared to modified push-up plus. The highest difference in EMG activity between the two exercises was observed with the Serratus Anterior muscle (22%). Additionally, the traditional push-up plus presented a higher vGRF compared to the modified push-up plus (P < .001) by 17%. The SA had the greatest EMG activity compared to the other muscles tested during the concentric phase of the traditional push-up plus, and this did not occur during the plus phase of the exercise.ConclusionThe highest activity of the serratus anterior occurred at 55° of elbow extension during the concentric phase of the traditional PUP and not at the plus phase of the exercise. This suggests that when prescribing an exercise to target the serratus anterior, a traditional push-up is adequate and the plus-phase is not necessary. However, for patients that cannot perform a traditional push-up, the modified push-up plus would be a great alternative to strengthen their serratus anterior.

Scapular kinematic is altered after electromyography biofeedback training.

Electromyography (EMG) biofeedback training affords patients a better sense of the different muscle activation patterns involved in the movement of the shoulder girdle. It is important to address scapular kinematics with labourers who have daily routines involving large amounts of lifting at shoulder level or higher. This population is at a heightened risk of developing subacromial impingement syndrome (SAIS). The purpose of this study was to investigate the acute effects of scapular stabilization exercises with EMG biofeedback training on scapular kinematics. Twenty-three healthy subjects volunteered for the study. Electrodes were placed on the upper and lower trapezius, serratus anterior, and lumbar paraspinals to measure EMG activity. Subjects underwent scapular kinematic testing, which consisted of humeral elevation in the scapular plane, before and after biofeedback training. The latter consisted of 10 repetitions of the I, W, T, and Y scapular stabilization exercises. Subjects were told to actively reduce the muscle activation shown on the screen for the upper trapezius during the exercises. The scapular external rotation had a statistically significant difference at all humeral elevation angles (p<0.004) after biofeedback was administered. After the exercises, the scapula was in a more externally rotated orientation with a mean difference of 6.5°. There were no significant differences found with scapular upward rotation, or posterior tilt at all humeral elevation angles following biofeedback. Scapular kinematics are altered by EMG biofeedback training utilizing scapular stabilization exercises. However, only scapular external rotation was affected by the exercises.

Shoulder elevation affects joint position sense and muscle activation differently in upright and supine body orientations.

OBJECTIVE Investigate the effects of shoulder elevation on repositioning errors in upright and supine body orientations, and examine these effects on anterior and posterior deltoid muscle activation. We hypothesized decreased errors, and altered anterior and posterior deltoid activation with increasing elevation, in both orientations. DESIGN Crossover trial. SETTING University laboratory. PARTICIPANTS Thirty-five college-aged participants. INTERVENTION Subjects attempted to replicate target positions of various elevation angles in upright and supine body orientations. Also, anterior and posterior deltoid activation was recorded in each shoulder position and body orientation. MAIN OUTCOME MEASURES Vector and variable repositioning errors, anterior and posterior deltoid percentage of maximal contraction. RESULTS Vector error was greater in supine compared to upright at 90° and 110°, but not at 70°. Variable error was larger in supine than upright, but was unaffected by elevation. Anterior deltoid activation increased with elevation in the upright posture only. Posterior deltoid activation increased with elevation across postures. CONCLUSIONS Muscle activation, external torque, and cutaneous sensations may combine to provide afferent feedback, and be used with centrally-generated signals to interpret the state of the limb during movement. Clinicians may prescribe open kinetic chain exercises in the upright posture with the shoulder elevated approximately 90-100°.

Acute Effects of Two Hip Flexor Stretching Techniques on Knee Joint Position Sense and Balance: 1671 Board #6 May 31 3

Background Tightness of hip flexor muscles has been recognized as a risk factor for various musculoskeletal injuries in the lower extremities. Purpose The purpose of this study was to examine the acute effects of two hip flexor stretching techniques (dynamic and hold-relax proprioceptive neuromuscular facilitation, HR-PNF) on hip extension (ROM), knee joint position sense (JPS) and balance in healthy college age students who exhibit tightness in hip flexor muscles. Study Design Pretest-posttest randomized experimental groups. Methods Thirty-six healthy college age students (mean = 22.37 years) with tight hip flexors participated in this study. Hip extension ROM, knee joint position sense and dynamic balance were tested pre- and post-stretching using a digital inclinometer, an iPod touch and the Y-Balance test, respectively. Subjects were randomly divided into dynamic and HR-PNF stretching groups. Three-way mixed analysis of variance was utilized to explore if an interaction existed between the groups in tested variables. Results There was a significant effect of time on hip extension ROM in both groups (p < 0.001). There was also a significant effect of stretch type on hip extension ROM (p = 0.004) favoring hold-relax over dynamic stretching group. There was a non-significant effect of time on mean knee joint position replication error in both groups. There was a significant main effect of time on the Y-Balance tests mean distance of reach to posteromedial and posterolateral directions (p < 0.001). There was also a significant main effect of directions of reach on distances achieved (p < 0.001) favoring posterolateral over posteromedial, and the latter over anterior direction. Conclusions The results of this study demonstrated the effectiveness of both HR-PNF and dynamic stretching techniques which resulted in a significant acute improvement in hip extension ROM and dynamic balance measures, with HR-PNF being more effective than dynamic stretch. However, there were no significant improvements in knee joint position replication over time in either stretching group. Level of Evidence 2b.

Lower Extremity Strength and Range of Motion in High School Cross-Country Runners

Cross-country running is becoming an increasingly popular sport, with a significant participation noted at the high school level. The aim of this study was to compare gender and bilateral hip extension range of motion and hip and knee extension strength of high school cross-country runners. 31 participants volunteered from a local high school cross-country team (16 males and 15 females). The modified Thomas test was utilized to measure hip extension range of motion bilaterally using a digital inclinometer. In order to measure hip and knee isometric strengths, an isokinetic dynamometer was employed. A mixed model approach revealed a statistically significant difference in peak hip extension strength between genders but not the side. Male athletes demonstrated a 29.2 Nm/kg (P < 0.05) greater force production than females during isometric hip extension strength testing. There were no significant differences in peak knee extension isometric strength, hip extension range of motion, and the ratio of peak hip and knee strength between genders and the dominant and nondominant leg. Female cross-country runners should focus on increasing hip extension strength to help maintain hip stability during running. This may be beneficial in decreasing the chances of experiencing patellofemoral pain in long-distance runners.

Eccentric, Concentric, And Isometric Strength In Trained And Untrained Older Adults: 153 Board #4 May 27, 9

The process of aging includes changes in muscle and connective tissue architecture and function, increased stiffness, loss of strength and functionality. Nonetheless, older adults are able to maintain eccentric (ECC) strength levels in a greater proportion, when compared to maintaining isometric (ISO) strength and concentric (CON) strength. The purpose of this study was to compare CON, ECC and ISO leg extension torque between trained (T) and untrained (U) older adults. Twenty older adults (60 years and older) who had no knee pathologies were recruited. A Biodex dynamometer was used to measure leg extensor torque for ISO, CON and ECC, in T and U subjects. Torque values relative to body weight (relative torques) were determined for each subject and compared between groups. The ratio of ECC: ISO was calculated and compared across groups. The T group were significantly stronger for ISO (p = 0.009). No significant differences were found for CON (p = 0.088) and ECC (p = 0.220). In addition, the U group registered a significantly higher ratio of ECC: ISO (p = 0.029), when compared to the T group. The findings in this study demonstrate older adults are able to maintain ECC, regardless of training status.