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Abstract Background Static stretching may result in various strength and power deficiencies. Prior research has not determined, however, if static stretching causes a change in muscle activation during a functional task requiring dynamic stability. The purpose of this study was to determine if static stretching has an effect on mean pre and postlanding muscle (vastus medialis VM, vastus lateralis VL, medial hamstring MH, and biceps femoris BF) activity. Methods 26 healthy, physically active subjects were recruited, from which 13 completed a 14-day static stretching regimen for the quadriceps and hamstrings. Using the data from the force plate and EMG readings, a mean of EMG amplitude was calculated for 150 msec before and after landing. Each trial was normalized to an isometric reference position. Means were calculated for the VM, VL, MH, and BF from 5 trials in each session. Measures were collected pre, immediately following the 1st stretching session, and following 2 weeks of stretching. Results A 14-day static stretching regimen resulted in no significant differences in pre or postlanding mean EMG amplitude during a drop landing either acutely or over a 14-day period. Conclusions Static stretching, done acutely or over a 14-day period does not result in measurable differences of mean EMG amplitude during a drop landing. Static stretching may not impede dynamic stability of joints about which stretched muscles cross.

Individuals with chronic ankle instability (CAI) demonstrate altered movement patterns when their vision is disturbed during simple tasks, such as single-legged standing and walking. However, it remains unclear whether visual disruption by stroboscopic glasses alters movement patterns during landing-cutting movements, considered highly demanding sport maneuvers that mimic a typical athletic movement. To identify altered lower extremity kinematics and muscle activation when vision is disrupted by stroboscopic glasses during landing-cutting tasks in individuals with CAI. Case-control study. Laboratory. A total of 18 individuals with CAI (age = 22.3 ± 2.3 years, height = 1.75 ± 0.1 m, mass = 72.5 ± 9.8 kg) and 18 matched healthy controls (age = 21.7 ± 2.3 years, height = 1.75 ± 0.1 m, mass = 71.9 ± 10.3 kg). All participants performed 5 trials of a landing-cutting task with (SV) and without (NSV) stroboscopic glasses. Frontal- and sagittal-plane lower extremity kinematics and 6 lower extremity muscle activations during the stance phase of a landing-cutting task in the SV and NSV conditions. Individuals with CAI demonstrated more ankle-inversion angle from 18% to 22% and from 60% to 100% of the stance phase and more peroneus longus activation from initial contact to 18% of the stance phase under the SV condition than under the NSV condition. We observed no differences in knee- and hip-joint angles between the visual conditions for both groups. When wearing stroboscopic glasses, individuals with CAI showed altered movement patterns, including increased ankle-inversion angle and peroneus longus activation during the stance phase of a landing-cutting task. The results suggest that they may lack the ability to reweight sensory information to adapt their movement to visual disruption. [ABSTRACT FROM AUTHOR]

Therapeutic interventions for individuals with chronic ankle instability (CAI) are recommended to improve muscle strength, postural control, and range of motion. However, their effects on neuromechanics during a drop landing remain unclear. In addition, even though therapeutic interventions with stroboscopic glasses appear to effectively improve postural control, how they affect landing neuromechanics remains unclear. To identify the effect of balance training with stroboscopic glasses on neuromechanics during a single-legged drop landing in patients with CAI. Randomized controlled clinical trial. Laboratory. A total of 50 participants with CAI were randomly assigned to 1 of 2 groups: strobe (n = 25; age = 22 ± 3 years, height = 174.7 ± 8.2 cm, mass = 71.8 ± 12.2 kg) or control (n = 25; age = 21 ± 2 years, height = 173.1 ± 8.3 cm, mass = 71.1 ± 13.5 kg). The 4-week rehabilitation (3 sessions per week) included hop-based tasks and single-legged stance. The strobe group wore stroboscopic glasses during the training, whereas the control group did not. Ankle-, knee-, and hip-joint kinematics and 4 lower extremity muscle activations 150 milliseconds before and after initial contact during a single-legged drop landing in the 2 groups. The strobe group showed greater eversion (from 150 milliseconds before to 30 milliseconds after initial contact) and dorsiflexion (from 30 to 96 milliseconds after initial contact) angles and peroneal longus (from 35 milliseconds before to 5 milliseconds after initial contact) and tibialis anterior (from 0 to 120 milliseconds after initial contact) activation in the posttest than the pretest. Patients with CAI who underwent a 4-week rehabilitation with stroboscopic glasses demonstrated changes in neuromechanics, including increased ankle-dorsiflexion and -eversion angles and tibialis anterior and peroneus longus activation, during a single-legged drop landing. This finding suggests that use of stroboscopic glasses during rehabilitation could help patients with CAI develop safe landing mechanics. [ABSTRACT FROM AUTHOR]

The authors comment on the article by B. Sonnery-Cottet and colleagues related to the incidence of and risk factors for arthrogenic muscle inhibition (AMI) following acute anterior cruciate ligament injuries. Topics covered include how the clinical assessment and intervention approaches suggested by the authors fail, the concern with the reliance on the Sonnery-Cottet classification for the purpose of diagnosing AMI, and the goal of AMI-based treatments.

Context: Knee injury and disease are common, debilitating, and expensive. Pain is a chief symptom of knee injury and disease and likely contributes to arthrogenic muscle inhibition. Joint pain alters isolated motor function, muscular strength, and movement biomechanics. Because knee pain influences biomechanics, it likely also influences long-term knee joint health. Objective: The purpose of this article is 2-fold: (1) review effects of knee pain on lower-extremity muscular activation and corresponding biomechanics and (2) consider potential implications of neuromechanical alterations associated with knee pain for long-term knee joint health. Experimental knee pain is emphasized because it has been used to mimic clinical knee pain and clarify independent effects of knee pain. Three common sources of clinical knee pain are also discussed: patellofemoral pain, anterior cruciate ligament injury and reconstruction, and knee osteoarthritis. Data Sources: The PubMed, Web of Science, and SPORTDiscus databases were searched for articles relating to the purpose of this article. Conclusion: Researchers have consistently reported that knee pain alters neuromuscular activation, often in the form of inhibition that likely occurs via voluntary and involuntary neural pathways. The effects of knee pain on quadriceps activation have been studied extensively. Knee pain decreases voluntary and involuntary quadriceps activation and strength and alters the biomechanics of various movement tasks. If allowed to persist, these neuromechanical alterations might change the response of articular cartilage to joint loads during movement and detrimentally affect long-term knee joint health. Physical rehabilitation professionals should consider neuromechanical effects of knee pain when treating knee injury and disease. Resolution of joint pain can likely help to restore normal movement neuromechanics and potentially improve long-term knee joint health and should be a top priority. [ABSTRACT FROM AUTHOR]

Objectives: Patients with chronic ankle instability (CAI) tend to increase their reliance on visual information, perhaps to compensate for proprioceptive deficits which appear after lateral ankle sprains. However, little is known about how limited visual feedback would alter static postural control in patients with CAI compared with copers and controls. The purpose of this study was to identify the effects of reduced visual feedback via stroboscopic glasses on static balance among CAI, coper, and uninjured control participants. Design: Controlled trial in a laboratory setting. Methods: Nineteen patients with CAI, 19 copers, and 19 controls participated in this study. Each participant performed a single-leg balance test with eyes open, stroboscopic vision, and eyes closed. Two-way analysis of variance (group x condition) was used to examine the differences between condition (eyes open, stroboscopic vision, and eyes closed) and group (CAI, coper, and control). Results: There were no significant interactions for static balance. Although there were no group effects among 3 groups for all static postural control measures, visual condition main effects were present (P < .01) for each dependent variable. Across all groups, anterior-posterior and mediolateral center of pressure path length and center of pressure velocity with stroboscopic vision were greater than the condition with eyes open (P < .01) and less than with eyes closed (P < .01). Conclusions: Stroboscopic glasses could be cost effective visual disruption equipment during static postural control regardless of ankle injury history. However, incorporating static balance with limited visual information via stroboscopic glasses could not display the differences in visual reliance in individuals with and without CAI. [ABSTRACT FROM AUTHOR]

In April-July 2008, intensive measurements were made of atmospheric composition and chemistry in Sabah, Malaysia, as part of the "Oxidant and particle photochemical processes above a South-East Asian tropical rainforest" (OP3) project. Fluxes and concentrations of trace gases and particles were made from and above the rainforest canopy at the Bukit Atur Global Atmosphere Watch station and at the nearby Sabahmas oil palm plantation, using both ground-based and airborne measurements. Here, the measurement and modelling strategies used, the characteristics of the sites and an overview of data obtained are described. Composition measurements show that the rainforest site was not significantly impacted by anthropogenic pollution, and this is confirmed by satellite retrievals of NO2 and HCHO. The dominant modulators of atmospheric chemistry at the rainforest site were therefore emissions of BVOCs and soil emissions of reactive nitrogen oxides. At the observed BVOC:NOx volume mixing ratio (∼100 pptv/pptv), current chemical models suggest that daytime maximum OH concentrations should be ca. 105 radicals cm-3, but observed OH concentrations were an order of magnitude greater than this. We confirm, therefore, previous measurements that suggest that an unexplained source of OH must exist above tropical rainforest and we continue to interrogate the data to find explanations for this.

This paper is based on alkyl nitrate measurements made over the North Atlantic as part of the International Consortium for Research on Atmospheric Transport and Transformation (ICARTT). The focus is on the analysis of air samples collected on the UK BAe-146 aircraft during the Intercontinental Transport of Ozone and Precursors (ITOP) project, but air samples collected on board the NASA DC-8 and NOAA WP-3D aircraft as part of a Lagrangian experiment are also used. The ratios between the alkyl nitrates and their parent hydrocarbons are compared with those expected from chemical theory. Further, a box model is run to investigate the temporal evolution of the alkyl. nitrates in three Lagrangian case studies and compared to observations. The air samples collected during ITOP do not appear to be strongly influenced by oceanic sources, but rather are influenced by emissions from the N.E. United States and from Alaskan fires. There also appears to be a widespread common source of ethyl nitrate and 1-propyl nitrate other than from their parent hydrocarbons. The general agreement between the alkyl nitrate data and photochemical theory suggests that during the first few days of transport from the source region, photochemical production of alkyl nitrates, and thus ozone, had taken place. The observations in the more photochemically processed air masses are consistent with the alkyl nitrate production reactions no longer dominating the peroxy radical self/cross reactions. Further, the results also suggest that the rates of photochemical processing in the Alaskan smoke plumes were small. Copyright 2007 by the American Geophysical Union.

Patients with chronic ankle instability (CAI) consistently display postural control alterations, which may result from sensorimotor dysfunction. This study aimed to compare muscle activity in the lower extremity and postural control among individuals with CAI, copers and uninjured controls during a static balance test. A total of 57 physically active participants were categorized into three groups (CAI, copers and controls) and performed a single-leg balance test with two visual conditions: eyes open and eyes closed. Muscle activity in six lower extremity muscles and center of pressure (CoP) variables were recorded and analyzed. Patients with CAI exhibited greater muscle activity in the medial gastrocnemius and gluteus maximus compared to controls or copers, regardless of the visual condition. Copers displayed increased gluteus medius activity compared to controls. Additionally, all groups demonstrated increased muscle activity and CoP variables when visual feedback was disrupted. These findings suggest that patients with CAI may have less effective recruitment of motor units during static balance. On the other hand, greater muscle activity in the gluteus medius in copers may represent a coping mechanism to avoid further ankle injuries. Further research on muscle activity during dynamic postural control is warranted to explore sensorimotor alterations in patients with CAI. [ABSTRACT FROM AUTHOR]