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Context: Isolated infraspinatus muscle atrophy (IIMA) affects only the hitting shoulder of overhead-activity athletes and is caused by suprascapular nerve neuropathy. No study has assessed the static and dynamic stability of the shoulder in overhead professional athletes with IIMA to reveal possible shoulder sensorimotor alterations. Objective: To assess the shoulder static stability, dynamic stability, and strength in professional volleyball players with IIMA and in healthy control players. Design: Cross-sectional study. Setting: Research lab. Patients or Other Participants: A total of 24 male professional volleyball players (12 players with diagnosed IIMA and 12 healthy players) recruited from local volleyball teams. Intervention(s): Static stability was evaluated with 2 independent force platforms, and dynamic stability was assessed with the “Upper Quarter Y Balance Test.” Main Outcome Measure(s): The static stability assessment was conducted in different support (single hand and both hands) and vision (open and closed eyes) conditions. Data from each test were analyzed with analysis of variance and paired t-test models to highlight statistical differences within and between groups. Results: In addition to reduced abduction and external rotation strength, athletes with IIMA consistently demonstrated significant less static (P <.001) and dynamic stability (P <.001), compared with the contralateral shoulder and with healthy athletes. Closed eyes condition significantly enhanced the static stability deficit of the shoulder with IIMA (P =.04 and P =.03 for both hand and single hand support, respectively) but had no effect on healthy contralateral and healthy players’ shoulders. Conclusions: This study highlights an impairment of the sensorimotor control system of the shoulder with IIMA, which likely results from both proprioceptive and strength deficits. This condition could yield subtle alteration in the functional use of the shoulder and predispose it to acute or overuse injuries. The results of this study may help athletic trainers and physical/physiotherapists to prevent shoulder injuries and create to specific proprioceptive and neuromuscular training programs. [ABSTRACT FROM AUTHOR]

We developed a biomechanical model to determine the joint torques and loadings during squatting with a backward/forward-inclined Smith machine. The Smith squat allows a large variety of body positioning (trunk tilt, foot placement, combinations of joint angles) and easy control of weight distribution between forefoot and heel. These distinctive aspects of the exercise can be managed concurrently with the equipment inclination selected to unload specific joint structures while activating specific muscle groups. A backward (forward) equipment inclination decreases (increases) knee torque, and compressive tibiofemoral and patellofemoral forces, while enhances (depresses) hip and lumbosacral torques. For small knee flexion angles, the strain-force on the posterior cruciate ligament increases (decreases) with a backward (forward) equipment inclination, whereas for large knee flexion angles, this behavior is reversed. In the 0 to 60 degree range of knee flexion angles, loads on both cruciate ligaments may be simultaneously suppressed by a 30 degree backward equipment inclination and selecting, for each value of the knee angle, specific pairs of ankle and hip angles. The anterior cruciate ligament is safely maintained unloaded by squatting with backward equipment inclination and uniform/forward foot weight distribution. The conditions for the development of anterior cruciate ligament strain forces are clearly explained. [ABSTRACT FROM AUTHOR]

We developed a biomechanical model to determine the joint torques and loadings during squatting with a backward/forward-inclined Smith machine. The Smith squat allows a large variety of body positioning (trunk tilt, foot placement, combinations of joint angles) and easy control of weight distribution between forefoot and heel. These distinctive aspects of the exercise can be managed concurrently with the equipment inclination selected to unload specific joint structures while activating specific muscle groups. A backward (forward) equipment inclination decreases (increases) knee torque, and compressive tibiofemoral and patellofemoral forces, while enhances (depresses) hip and lumbosacral torques. For small knee flexion angles, the strain-force on the posterior cruciate ligament increases (decreases) with a backward (forward) equipment inclination, whereas for large knee flexion angles, this behavior is reversed. In the 0 to 60 degree range of knee flexion angles, loads on both cruciate ligaments may be simultaneously suppressed by a 30 degree backward equipment inclination and selecting, for each value of the knee angle, specific pairs of ankle and hip angles. The anterior cruciate ligament is safely maintained unloaded by squatting with backward equipment inclination and uniform/forward foot weight distribution. The conditions for the development of anterior cruciate ligament strain forces are clearly explained. [ABSTRACT FROM AUTHOR]

Abstract: This study is devoted to characterizing the operation of the entire photovoltaic system installed in one of the Auger Muons and Infill for the Ground Array (AMIGA) stations, a complimentary detector for the Pierre Auger Observatory, the largest cosmic‐ray air shower array in the world, 3000 km2, powered exclusively by solar energy. To understand charge and discharge cycles, the whole system behavior under different climatic conditions and to determine its limitations, the design of a new prototype for monitoring the whole system online is a fundamental part of this contribution. Also, it is demonstrated that the configuration of solar charge controllers in parallel is able to manage panels of different powers and brands and that the monitoring system allows analyzing periods with adverse weather conditions. [ABSTRACT FROM AUTHOR]

Background: A number of research studies provide evidence that hamstring cocontraction during open kinetic chain knee extension exercises enhances tibiofemoral (TF) stability and reduces the strain on the anterior cruciate ligament. Purpose: To determine the possible increase in hamstring muscle coactivation caused by a voluntary cocontraction effort during open kinetic chain leg-extension exercises, and to assess whether an intentional hamstring cocontraction can completely suppress the anterior TF shear force during these exercises. Study Design: Descriptive laboratory study. Methods: Knee kinematics as well as electromyographic activity in the semitendinosus (ST), semimembranosus (SM), biceps femoris (BF), and quadriceps femoris muscles were measured in 20 healthy men during isotonic leg extension exercises with resistance (R) ranging from 10% to 80% of the 1-repetition maximum (1RM). The same exercises were also performed while the participants attempted to enhance hamstring coactivation through a voluntary cocontraction effort. The data served as input parameters for a model to calculate the shear and compressive TF forces in leg extension exercises for any set of coactivation patterns of the different hamstring muscles. Results: For R ≤ 40% 1RM, the peak coactivation levels obtained with intentional cocontraction (l) were significantly higher (P< 10–3) than those obtained without intentional cocontraction (l0). For each hamstring muscle, maximum level l was reached at R = 30% 1RM, corresponding to 9.2%, 10.5%, and 24.5% maximum voluntary isometric contraction (MVIC) for the BF, ST, and SM, respectively, whereas the ratio l/l0 reached its maximum at R = 20% 1RM and was approximately 2, 3, and 4 for the BF, SM, and ST, respectively. The voluntary enhanced coactivation level l obtained for R ≤ 30% 1RM completely suppressed the anterior TF shear force developed by the quadriceps during the exercise. Conclusion: In leg extension exercises with resistance R ≤ 40% 1RM, coactivation of the BF, SM, and ST can be significantly enhanced (up to 2, 3, and 4 times, respectively) by a voluntary hamstring cocontraction effort. The enhanced coactivation levels obtained for R ≤ 30% 1RM can completely suppress the anterior TF shear force developed by the quadriceps during the exercise. Clinical Relevance: This laboratory study suggests that leg extension exercise with intentional hamstring cocontraction may have the potential to be a safe and effective quadriceps-strengthening intervention in the early stages of rehabilitation programs for anterior cruciate ligament injury or reconstruction recovery. Further studies, including clinical trials, are needed to investigate the relevance of this therapeutic exercise in clinical practice. [ABSTRACT FROM AUTHOR]

Key points The semicircular canals of the labyrinths are a source of information for self-motion perception and reflex eye movements., Prolonged vestibular asymmetric stimulation of standing humans about the earth-vertical axis, made of fast body rotation to one side and slow rotation to the other side, induced different adaptive mechanisms in the perception of body motion and in the vestibulo-ocular reflex (VOR)., Motion perception became progressively more asymmetric, increasing gradually in response to the fast body rotation and decreasing in response to the slow rotation. VOR became gradually more symmetric, decreasing for fast body movement and increasing for slow movement., These oppositely directed adaptive effects in motion perception and VOR persisted for at least 30 min., Long-lasting asymmetric stimulation discloses independent brain mechanisms for perception of body motion and eye movement control., These adaptive mechanisms may enhance awareness toward the side where the body is moving faster, while improving eye stabilizing properties of the VOR., Abstract Self-motion perception and the vestibulo-ocular reflex (VOR) were investigated in healthy subjects during asymmetric whole body yaw plane oscillations while standing on a platform in the dark. Platform oscillation consisted of two half-sinusoidal cycles of the same amplitude (40°) but different duration, featuring a fast (FHC) and a slow half-cycle (SHC). Rotation consisted of four or 20 consecutive cycles to probe adaptation further with the longer duration protocol. Self-motion perception was estimated by subjects tracking with a pointer the remembered position of an earth-fixed visual target. VOR was measured by electro-oculography. The asymmetric stimulation pattern consistently induced a progressive increase of asymmetry in motion perception, whereby the gain of the tracking response gradually increased during FHCs and decreased during SHCs. The effect was observed already during the first few cycles and further increased during 20 cycles, leading to a totally distorted location of the initial straight-ahead. In contrast, after some initial interindividual variability, the gain of the slow phase VOR became symmetric, decreasing for FHCs and increasing for SHCs. These oppositely directed adaptive effects in motion perception and VOR persisted for nearly an hour. Control conditions using prolonged but symmetrical stimuli produced no adaptive effects on either motion perception or VOR. These findings show that prolonged asymmetric activation of the vestibular system leads to opposite patterns of adaptation of self-motion perception and VOR. The results provide strong evidence that semicircular canal inputs are processed centrally by independent mechanisms for perception of body motion and eye movement control. These divergent adaptation mechanisms enhance awareness of movement toward the faster body rotation, while improving the eye stabilizing properties of the VOR. [ABSTRACT FROM AUTHOR]

Objective To investigate the influence of gaze eccentricity on movement perception during asymmetric vestibular stimulation. Material and Methods Subjects ( n =10) were placed on a rotating platform and oscillated asymmetrically in the dark. Subjects were asked to reproduce with a pointer the location in space of a light spot that was turned off at the beginning of the oscillation. The target was presented in centric and eccentric (0°, 20° and 40°) positions. Results In the centric position a large shift from the real position of the target was observed in the opposite direction to that of the faster vestibular stimulation. The shift increased when the target was placed eccentrically toward the slower vestibular stimulation side and decreased when it was placed in the opposite direction. Conclusion The dependence of rotation perception on the target position suggests that the eye deviation, imposed by the eccentricity of the target, is able to influence the perception of body movement and may modulate the internal reference frame. [ABSTRACT FROM AUTHOR]