1,721,087 research outputs found
Physical rehabilitation and the challenge of anterior cruciate ligament injury in the physically active female
Full text linkRehabilitation professionals facilitate healthy movement and mobility in individuals seeking to engage in physically active lifestyles. The disparate rate of injury to the anterior cruciate ligament of the knee in physically active females in comparison to males serves as an excellent example of the challenges faced by rehabilitation professionals. The surgical reconstruction of the ligament and post-surgical rehabilitation has received a great deal of attention, but far less emphasis has been placed on the etiology and prevention of this disabling injury. This article addresses the impact of increased physical activity among females on ACL injury incidence, what is known and unknown about injury risk, and the importance of identifying strategies for prevention of injury to the ACL. One example of a research program that is exploring the potential risk factors for ACL injury in the physically active female is discussed
Using Surface Electromyography To Assess Sex Differences in Neuromuscular Response Characteristics
Full text linkObjective: To provide an overview of the continuum of muscular responses that typically occur with joint perturbation. The applications and limitations of surface electromyography (sEMG) in evaluating these responses are also addressed. Research applications assessing sex differences in these neuromuscular response characteristics are discussed along with suggestions for future research.
Data Sources: MEDLINE was searched from 1969 through 1998. Sport DISCUS was searched from 1975 through 1998. Terms searched included "anterior cruciate ligament," "epidemiology," "neuromuscular control," "neuromuscular performance," "electromyography," "latency," "reflex," "electromechanical delay," "dynamic stability," "intrinsic stiffness," "short-range stiffness," "muscle," "mechanoreceptors," and "reaction time."
Data Synthesis: It is widely accepted that efficient neuromuscular control is essential to dynamic joint stability and protection. Many studies have established the significant role of the muscles, and particularly the hamstrings, in providing knee stability. By observing the timing, phasing, and recruitment of reflexive muscular activation after a loading stress to the knee, we can better understand the coordinative mechanisms necessary to protect the joint and prevent ligament injury. A number of research models have employed the use of sEMG to evaluate neuromuscular responses at the knee after joint loading or perturbation. However, very few studies have specifically addressed potential sex differences in these response characteristics.
Conclusions/Recommendations: From the limited research available, it appears that a sex difference may exist in some aspects of neuromuscular responses. However, further research is needed to explore these differences at the knee and their potential role as predisposing factors to the higher incidence of anterior cruciate ligament injuries in females. Future studies should examine sex differences in neuromuscular response characteristics at the knee under functional, weight-bearing conditions while controlling for training and other confounding variables. The limitations of sEMG should be considered when interpreting neuromuscular response studies
Relationship between sex hormones and anterior knee laxity across the menstrual cycle
Full text linkPurpose: To comprehensively quantify through daily, serial measures changes in knee laxity as a function of changing sex-hormone levels across one complete menstrual cycle.
Methods: Twenty-five females, 18–30 yr, body mass index <= 30, who reported normal menstrual cycles (28–32 d) over the past 6 months participated. Participants were tested daily across one complete menstrual cycle; 5–7 cc of venous blood were withdrawn to assay serum levels of estradiol, progesterone, and testosterone. Knee laxity was measured as the amount of anterior tibial displacement at 133 N, using a standard knee arthrometer. To evaluate the relationship of knee laxity to changes in sex hormone concentrations, a multiple linear regression model with the possibility of a time delay was performed on each individual subject and the group as a whole.
Results: Individual regression equations revealed an average of 63% of the variance in knee laxity was explained by the three hormones and their interactions. All three hormones significantly contributed to the prediction equation, and the amount of variance explained was substantially greater when a time delay was considered. On average, knee laxity changed approximately 3, 4, and 4.5 d after changes in estradiol, progesterone, and testosterone, respectively. When females were analyzed as a group, only 8% of the variance in knee laxity was explained by sex-hormones levels.
Conclusion: Changes in sex hormones mediate changes in knee laxity across the menstrual cycle. However, the strength of this relationship, the relative contribution of each hormone, and the associated time delay are highly variable between women. This individual variability is consistent with the variability in menstrual cycle characteristics among women
Assessment of neuromuscular response characteristics at the knee following a functional perturbation
Full text linkPrevious research indicates that both the extent and timing of muscular activation at the knee can be influenced by muscle activity state, joint angle, weight-bearing status and trunk position. However, little research to date has evaluated protective neuromuscular response times and activation patterns to an imposed perturbation with the knee joint in a functional, weight-bearing stance. Hence, we designed a lower extremity perturbation device to produce a sudden, forward and either internal or external rotation moment of the trunk and femur relative to the weight-bearing tibia. Surface electromyography (EMG) recorded long latency reflex times of the medial and lateral quadriceps, hamstring and gastrocnemius muscles in 64 intercollegiate lacrosse and soccer players in response to both internal and external rotation perturbation. We found the gastrocnemius fired significantly faster that the hamstring, which in turn fired significantly faster than the quadriceps. There was also a significant difference in activation times of the medial and lateral hamstring not found for the quadriceps or gastrocnemius muscles. Our findings confirmed that reactive neuromuscular responses following this functional perturbation differ markedly from those previously reported using seated, partial weight-bearing and/or uni-planar models under relaxed conditions
Knee joint laxity affects muscle activation patterns in the healthy knee
Full text linkThis study investigated the effects of anterior knee joint laxity on muscle activation patterns prior to and following a lower extremity perturbation. Participants were subjected to a forward and either internal (IR) or external (ER) rotation perturbation of the trunk and thigh on the weight-bearing shank. Pre-activity (%MVIC) before the perturbation, and reflex time (ms) and mean reflex amplitude (%MVIC) following the perturbation were recorded via surface electromyography (sEMG) in the medial and lateral gastrocnemius, hamstring and quadriceps muscles. Twenty-one NCAA DI intercollegiate female athletes with below average anterior knee laxity (3–5 mm) were compared to 21 with above average anterior knee laxity (7–14 mm) as measured by a standard knee arthrometer. Groups differed in reflex timing by muscle (P= 0.013), with females with above average knee laxity (KT(>7mm)) demonstrating a 16 ms greater delay in biceps femoris reflex timing compared to females with below average knee laxity (KT(15mm)). Groups also differed in muscle activation amplitude by response, muscle and direction of rotation (i.e. a 4-way interaction; P= 0.027). The magnitude of change from pre to post perturbation was significantly less in KT(>7mm) vs. KT(15mm) for the medial (MG) and lateral (LG) gastrocnemius muscles, primarily due to higher levels of muscle preactivity while awaiting the perturbation (MG = 20% vs. 12% MVIC, P= 0.05; LG = 33% vs. 21% MVIC, P= 0.11). Further, KT(>7mm) demonstrated higher activation levels in the biceps femoris than KT(15mm) (47% vs. 27% MVIC; P= 0.025) regardless of response (pre vs. post perturbation) or direction of rotation. These findings suggest females with increased knee laxity may be less sensitive to joint dis-placement or loading (delayed reflex), and are more reliant on active control of the gastrocnemius and biceps femoris muscles to potentially compensate for reduced passive joint stability
Knee ligament behavior following a controlled loading protocol does not differ by menstrual cycle day
Full text linkBackground. Females experience a disproportionate number of anterior cruciate ligament injuries compared to males. Increased estradiol concentration has been suggested to alter ligament properties and strength. Determining whether the knee responds differently to an external load at various hormonal levels may be helpful in further explaining the gender disparity. Methods. Estradiol, progesterone and testosterone were quantified at menses, near ovulation and at the mid-luteal phase. With one knee serving as the control limb and the other as the experimental limb, displacement at 134N and stiffness between 90 and 134N were recorded with a knee ligament arthrometer on both knees before and after a loading protocol. The protocol consisted of three, 3-min, posterior to anterior normalized loads directed to the posterior calf with a ligament testing device. Findings. The loading protocol produced a measurable increase in displacement but not stiffness. Neither displacement nor stiffness measures however were affected by day of the menstrual cycle. No consistent relationships between hormonal concentrations and displacement or stiffness were evident.
Interpretation. Following a controlled, static external load, displacement and stiffness were not affected differently by day of the menstrual cycle
Serial administration of clinical concussion assessments and learning effects in healthy young athletes
Full text linkObjective: To determine if serial administration of the Standardized Assessment of Concussion (SAC) and Balance Error Scoring System (BESS) would elicit a learning effect in young athletes and to determine the intratester reliability of scoring the BESS.
Design: A prospective study of 50 healthy young athletes who were assigned to either the control or practice group. All subjects were administered the assessments on 2 occasions, 60 days apart. In addition, subjects in the practice group received serial administration of the assessments on 3 occasions in the week following the initial assessment.
Setting: University Sports Medicine/Athletic Training Research Laboratory.
Subjects: Fifty uninjured young athletes between 9 and 14 years of age.
Main Outcome Measured: Scores on 2 clinical concussion assessments, the SAC and the BESS.
Results: We found a significant learning effect upon serial BESS testing in the practice group. BESS error scores were significantly lower than baseline (15.0 ± 4.6) on days 5 (11.3 ± 5.33), 7 (12.4 ± 6.2), and 60 (12.6 ± 6.2). We also found a significant learning effect upon the day 60 BESS administration across all subjects. We did not find a practice or learning effect with serial SAC test administration. The intratester reliability of the investigator’s ability to score repeated observations of the same BESS test ranged from 0.87 to 0.98.
Conclusions: Our results demonstrated that serial administration of the BESS elicited a learning effect, which was more prominent during the tandem conditions. Clinicians utilizing the BESS as a measure of postural stability should be aware of the potential for improvement with repeated testing. Clinicians should not expect improvement with the SAC, as scores remained relatively stable across all trials
Females recruit quadriceps faster than males at multiple knee flexion angles following a weight-bearing rotary perturbation
Full text linkObjective: To compare the effect of knee angle on muscle response times and neuromuscular recruitment patterns between sexes following a perturbation in single leg stance at 10°, 20°, and 30°. We hypothesized that response times would be faster at lesser knee flexion angles and that females would recruit their quadriceps faster than males at all angles.
Design: A repeated-measures design.
Setting: Motion analysis laboratory.
Participants: Twenty (10 female; 10 male) healthy, recreationally active volunteers.
Interventions: A rotary perturbation in single leg stance.
Outcome Measurements: Response times of the medial and lateral quadriceps, hamstrings, and gastrocnemius.
Results: There was a trend toward faster response times for all muscles closer toward extension. A consistent neuromuscular recruitment pattern for both males and females was evident for each knee angle tested. Females, however, contracted their quadriceps faster than males at all knee flexion angles.
Conclusions: Small changes in knee angle near extension do not alter muscle response times and hence neuromuscular recruitment patterns in males and females. Regardless of knee flexion angle, following a perturbation in single leg stance, females contract their quadriceps faster than males.
Clinical Relevance: Earlier contraction of the quadriceps in females may increase anterior tibial translation and hence anterior cruciate ligament strain, thereby heightening injury risk
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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