Persistent muscle weakness after anterior cruciate ligament (ACL) reconstruction may be due to underlying activation failure and arthrogenic muscle inhibition (AMI). Knee-joint cryotherapy has been shown to improve quadriceps function transiently in those with AMI, thereby providing an opportunity to improve quadriceps muscle activation and strength in patients with a reconstructed ACL.
To compare quadriceps muscle function in patients with a reconstructed ACL who completed a 2-week intervention including daily cryotherapy (ice bag), daily exercises, or both.
Patients or Other Participants:
A total of 30 patients with reconstructed ACLs who were at least 6 months post-index surgery and had measurable quadriceps AMI.
The patients attended 4 supervised visits over a 2-week period. They were randomly assigned to receive 20 minutes of knee-joint cryotherapy, 1 hour of therapeutic rehabilitation exercises, or cryotherapy followed by exercises.
Main Outcome Measure(s):
We measured quadriceps Hoffmann reflex, normalized maximal voluntary isometric contraction torque, central activation ratio using the superimposed-burst technique, and patient-reported outcomes before and after the intervention period.
After the 2-week intervention period, patients who performed rehabilitation exercises immediately after cryotherapy had higher normalized maximal voluntary isometric contraction torques (P = .002, Cohen d effect size = 1.4) compared with those who received cryotherapy alone (P = .16, d = 0.58) or performed exercise alone (P = .16, d = 0.30).
After ACL reconstruction, patients with AMI who performed rehabilitation exercises immediately after cryotherapy experienced greater strength gains than those who performed cryotherapy or exercises alone.
knee; arthrogenic muscle inhibition; disinhibition; therapeutic exercises
Although ankle braces supposedly protect the ankle by providing mechanical support of the joint and enhancing proprioceptive input, their proprioceptive effects are unclear. Measuring the center of pressure during posture provides a reasonably well-controlled evaluation of proprioceptive input at the ankle. We, therefore, compared the changes in the center of pressure resulting from wearing ankle braces and wearing no brace (control).
Design and Setting:
Center-of-pressure variables were measured during a one-legged modified Romberg test with six variations. The six test conditions systematically altered the three sensory modalities that control posture: visual input, vestibular input, and proprioceptive input. Subjects performed three 16-second trials of each Romberg variation for each brace condition.
Twenty-four male volunteers (age = 18 to 26 yr) with no history of ankle injuries in the past 5 years and no difficulty with balance.
Center of pressure, transmitted through the bottom of the foot, was monitored during each trial and transformed into total distance traveled, anterior-posterior (AP) position, and medial-lateral (ML) position.
Average AP and ML center-of-pressure positions were increased only during brace wearing when all sensory modalities were functioning normally (control condition). Total center-of-pressure distance was the same for all three brace conditions.
Our results do not support or refute the concept that bracing enhances proprioception. The fact that subjects relocated their center of pressure only during the control condition is perplexing. If braces were to enhance proprioception, one would expect to see lower average ML and average AP center-of-pressure values when comparing the braced with the unbraced conditions. Alternatively, the relocated position may represent a more stable position resulting from enhanced proprioception.
ankle braces; balance; center of pressure; proprioception
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The effect of cooling on proprioception of the knee has not been studied extensively. In this study, we investigated the movement reproduction (timing and accuracy) aspect of proprioception. Subjects were tested under two conditions: a 20-minute application of ice and control. Proprioceptive accuracy and timing were measured by passively moving the knee, then comparing the subject's active reproduction of the passive movement. Subjects were blindfolded, then tested in three sectors of the knee's range of motion: 90° to 60°, 60° to 30°, and 30° to full extension. Ice application had no apparent effect on the subject's ability to perform accurate movement reproductions in the sectors tested. However, accuracy of the subject's final angle reproduction varied between the sectors as did the total time of the movement. One possible explanation for the difference between sectors is that different receptors are active at different points in the knee's range of motion. We conclude that cooling the knee joint for 20 minutes does not have an adverse effect on proprioception.
Controversy still exists regarding the use of isokinetic and isotonic exercise in rehabilitation. Many authors have compared these two types of training methods on various strength measures and functional activity, but have used open kinetic chain training. The purposes of this investigation were to determine: 1) which form of closed kinetic chain training, isokinetic or isotonic, would produce the greatest increase in one-legged jump reaction force, and 2) which training method most accurately predicts peak force produced during a one-legged jump. Forty-two legs from 21 female volunteer subjects were used. Each subject had her dominant and nondominant extremities identified, and then each extremity was randomly assigned to either isokinetic training, isotonic training, or control. Both training groups trained using a leg press exercise 3 days a week for 5 weeks, while the control extremities did not train. The isokinetic extremities were trained using a velocity spectrum (two sets of 10 repetitions at each speed: 60°, 180° and 240°/sec) and the isotonic extremities trained using the DAPRE technique. Data were analyzed with an analysis of variance (ANOVA). There was no difference between the three groups for change in one-legged jump force. Both isokinetic and isotonic groups increased strength after training, but these changes did not correlate with changes in one-legged jump reaction force. These results suggest that changes in neither isokinetic force nor isotonic weight lifted developed in a nonweight-bearing closed kinetic chain, directly translate into increased force production during a functional activity.
Specific terms are often used to describe the pain athletes typically experience during cold treatments. It is not clear whether providing athletes with such descriptive sensory information will decrease their perceived pain during treatments. The purpose of this study was to determine if subjects' perceptions of cold-induced pain could be influenced by the type of information provided before treatment, such as “pain will be cursing” or “pain will be flickering.” Ninety Division I intercollegiate athletes were randomly assigned to one of five groups: traditional terms (cold, burning, aching, numbness), high-level terms (freezing, crushing, pounding, heavy), moderate-level terms (cold, gnawing, pulsing, aching), or low-level terms (cool, pinching, flickering, dull) from the McGill Pain Questionnaire, or no terms at all (control). The four groups that received a set of terms were told that those terms described the sensations they would feel during cold immersion of the ankle. Pain was measured with the McGill Pain Questionnaire every 3 minutes during a 21-minute immersion (1°C) of the foot and ankle. Sensory, affective, evaluative, and miscellaneous pain measures were derived. The control group experienced greater sensory and affective pain than did any of the other groups and experienced greater evaluative pain than did the groups receiving low-level or traditional terms. We conclude that providing athletes with some type of sensory information to describe their cold-pain experience will decrease their perceived pain during cold immersion, although it does not seem to matter what terms are used.
Manual therapies, directed to the knee and lumbopelvic region, have demonstrated the ability to improve neuromuscular quadriceps function in individuals with knee pathology. It remains unknown if manual therapies may alter impaired spinal reflex excitability, thus identifying a potential mechanism in which manual therapy may improve neuromuscular function following knee injury.
To determine the effect of local and distant mobilisation/manipulation interventions on quadriceps spinal reflex excitability.
Seventy-five individuals with a history of knee joint injury and current quadriceps inhibition volunteered for this study. Participants were randomised to one of five intervention groups: lumbopelvic manipulation (grade V), lumbopelvic manipulation positioning (no thrust), grade IV patellar mobilisation, grade I patellar mobilisation, and control (no treatment). Changes in spinal reflex excitability were quantified by assessing the Hoffmann reflex (H-reflex), presynaptic, and postsynaptic excitability. A hierarchical linear-mixed model for repeated measures was performed to compare changes in outcome variables between groups over time (pre, post 0, 30, 60, 90 min).
There were no significant differences in H-reflex, presynaptic, or postsynaptic excitability between groups across time.
Manual therapies directed to the knee or lumbopelvic region did not acutely change quadriceps spinal reflex excitability. Although manual therapies may improve impairments and functional outcomes the underlying mechanism does not appear to be related to changes in spinal reflex excitability.
H-reflex; knee pain; mobilization; manipulation
Analyzing ligament stiffness between males and females at 3 maturational stages across the lifespan may provide insight into whether changes in ligament behavior with aging may contribute to joint laxity.
To compare the stiffness of the medial structures of the tibiofemoral joint and the medial collateral ligament to determine if there are differences at 3 distinct ages and between the sexes.
Patients or Other Participants:
A total of 108 healthy and physically active volunteers with no previous knee surgery, no acute knee injury, and no use of exogenous hormones in the past 6 months participated. They were divided into 6 groups based on sex and age (8–10, 18–40, 50–75 years).
Main Outcome Measure(s):
Ligament stiffness of the tibiofemoral joint was measured with an arthrometer in 0° and 20° of tibiofemoral-joint flexion. The slope values of the force-strain line that represents stiffness of the medial tibiofemoral joint at 0° and the medial collateral ligament at 20° of flexion were obtained.
When height and mass were controlled, we found a main effect (P < .001) for age group: the 8- to 10-year olds were less stiff than both the 18- to 40- and the 50- to 75-year-old groups. No effects of sex or tibiofemoral-joint position on stiffness measures were noted when height and mass were included as covariates.
Prepubescent medial tibiofemoral-joint stiffness was less than postpubescent knee stiffness. Medial tibiofemoral-joint stiffness was related to height and mass after puberty in men and women.
medial collateral ligament; arthrometry; hormones; sex differences
Objective: Wound care is a part of daily activity for many athletic trainers. Knowing which cleansers are effective against the bacteria that most commonly cause infection and whether they are toxic to healthy cells enables athletic trainers to make educated decisions on which cleanser to use. We compared the bactericidal effectiveness and cytotoxicity to human fibroblast cells of 4 cleansers at various dilutions.
Design and Setting: A 4 × 4 factorial design was used for the cytotoxicity testing. The independent variables were type and dilution of cleanser. The dependent variable was cell viability of the human fibroblast cells. We used a 2 × 3 × 4 × 4 factorial design for the bacterial testing. The independent variables were type and dilution of bacteria and type and dilution of cleanser. The dependent variable was the bactericidal action of the cleanser on the bacteria.
Subjects: Human foreskin samples were used to obtain a line of fibroblast cells. Bacterial samples were obtained from an athletic training clinic, isolated from swabs of a whirlpool water supply valve (Pseudomonas aeruginosa) or skin surface (Staphylococcus aureus).
Measurements: We obtained bactericidal measurements by testing isolated Gram-negative (Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. Minimum and maximum concentrations were identified according to bactericidal effectiveness. Cytotoxicity measurements were obtained from spectrophotometer readings of a neutral red assay for fibroblast cell viability. Final dilutions tested were determined by pilot testing.
Results: At the 1:5 dilution of product in sterile 0.9% saline, both Cinder Suds and Nitrotan and hydrogen peroxide were different from the control with regard to Pseudomonas aeruginosa. At the 1:10 dilution, both Betadine and hydrogen peroxide were different from the control with regard to Pseudomonas aeruginosa. These 2 cleansers were also different from each other. At the 1:10 dilution, only Betadine was not different from the control for the cytotoxicity testing.
Conclusions: Betadine was both effective against bacteria and not harmful to human fibroblast cells at a 1:10 dilution of a commercially purchased solution.
wound cleansers; cytotoxicity; bactericidal; antimicrobial
Anterior cruciate ligament (ACL) injuries are common in female athletes and are related to poor neuromuscular control. Comprehensive neuromuscular training has been shown to improve biomechanics; however, we do not know which component of neuromuscular training is most responsible for the changes.
To assess the efficacy of either a 4-week core stability program or plyometric program in altering lower extremity and trunk biomechanics during a drop vertical jump (DVJ).
High school athletic fields and motion analysis laboratory.
Patients or Other Participants:
Twenty-three high school female athletes (age = 14.8 ± 0.8 years, height = 1.7 ± 0.07 m, mass = 57.7 ± 8.5 kg).
Independent variables were group (core stability, plyometric, control) and time (pretest, posttest). Participants performed 5 DVJs at pretest and posttest. Intervention participants engaged in a 4-week core stability or plyometric program.
Main Outcome Measure(s):
Dependent variables were 3-dimensional hip, knee, and trunk kinetics and kinematics during the landing phase of a DVJ. We calculated the group means and associated 95% confidence intervals for the first 25% of landing. Cohen d effect sizes with 95% confidence intervals were calculated for all differences.
We found within-group differences for lower extremity biomechanics for both intervention groups (P ≤ .05). The plyometric group decreased the knee-flexion and knee internal-rotation angles and the knee-flexion and knee-abduction moments. The core stability group decreased the knee-flexion and knee internal-rotation angles and the hip-flexion and hip internal-rotation moments. The control group decreased the knee external-rotation moment. All kinetic changes had a strong effect size (Cohen d > 0.80).
Both programs resulted in biomechanical changes, suggesting that both types of exercises are warranted for ACL injury prevention and should be implemented by trained professionals.
anterior cruciate ligament; plyometrics; core stability
Isolated lumbar paraspinal muscle fatigue causes lower extremity and postural control deficits.
To describe the change in body position during gait after fatiguing lumbar extension exercises in persons with recurrent episodes of low back pain compared with healthy controls.
Motion analysis laboratory.
Patients or Other Participants:
Twenty-five recreationally active participants with a history of recurrent episodes of low back pain, matched by sex, height, and mass with 25 healthy controls.
We measured 3-dimensional lower extremity and trunk kinematics before and after fatiguing isometric lumbar paraspinal exercise.
Main Outcome Measure(s):
Measurements were taken while participants jogged on a custom-built treadmill surrounded by a 10-camera motion analysis system.
Group-by-time interactions were observed for lumbar lordosis and trunk angles (P < .05). A reduced lumbar spine extension angle was noted, reflecting a loss of lordosis and an increase in trunk flexion angle, indicating increased forward trunk lean, in healthy controls after fatiguing lumbar extension exercise. In contrast, persons with a history of recurrent low back pain exhibited a slight increase in spine extension, indicating a slightly more lordotic position of the lumbar spine, and a decrease in trunk flexion angles after fatiguing exercise. Regardless of group, participants experienced, on average, greater peak hip extension after lumbar paraspinal fatigue.
Small differences in response may represent a necessary adaptation used by persons with recurrent low back pain to preserve gait function by stabilizing the spine and preventing inappropriate trunk and lumbar spine positioning.
gait analysis; spine
Physical inactivity is common in patients with knee osteoarthritis (OA) and has been linked to serious comorbidities such as cardiovascular disease, obesity, and diabetes. The purpose of this study was to examine the association between quadriceps strength and self‐reported physical activity in patients with radiographically confirmed knee OA. Secondarily, the authors' sought to determine if there were differences in quadriceps strength between knee OA patients with low physical activity (LPA) and knee OA patients with higher physical activity (HPA). A tertiary aim of this study was to examine the effect of gender on physical activity and quadriceps strength in patients with knee OA.
Thirty‐six patients with radiographically diagnosed tibiofemoral knee OA participated (15 males, 21 females; age = 59.9±11.6 yrs; height = 171.2±9.2 cm; mass = 84.3±18.9 kg; body mass index (BMI)= 28.9±6.9;Godin Leisure‐Time questionnaire =32.5±25.01). Maximal isometric knee extensor strength was assessed with a Isokinetic dynamometer in 70° of knee flexion. Knee extension torque values were normalized to body mass (Nm*kg−1). Physical activity was evaluated using the Godin Leisure‐Time questionnaire. A Godin‐Leisure time score of 32.5, which was the mean score in the current dataset, was what was used to categorize subjects into LPA and HPA subgroups. Independent t‐tests were used to determine differences in strength between HPA and LPA subgroups, as well as differences in strength and physical activity between genders. Pearson Product Moment and Spearman rank correlations were used to analyze associations between normally and non‐normally distributed variables.
Quadriceps strength was positively correlated with physical activity (r=0.44, r2=0.18, p=0.01). The HPA subgroup had significantly greater quadriceps strength (n=15, 2.01±0.84) compared to the LPA subgroup (n=21, 1.5±0.59, p=0.04). Strength was significantly correlated with physical activity in the HPA subgroup (ρ=0.53, p=0.04), but not in the LPA subgroup (ρ=−0.21,p=0.35). Males reported significantly more physical activity (43.0±28.5 vs 25.1±19.64; p=0.03) and greater strength than females in the entire cohort (2.15±0.73 Nm*kg−1 vs 1.40±0.57 Nm*kg−1; p= 0.002), and the HPA subgroup (2.4±0.65 Nm*kg−1 vs 1.4± 0.68 Nm*kg−1; P=0.02). There were no gender differences for strength in the LPA subgroup.
Higher levels of quadriceps strength correlate with higher physical activity in knee OA patients. The association between higher strength and increased physical activity is stronger in the HPA subgroup compared to the entire sample. Additionally, the HPA subgroup demonstrated greater quadriceps strength compared to the LPA subgroup.
Level of Evidence:
Inactivity; maximum voluntary isometric contraction; physical function; quadriceps
The valgus stress test is used clinically to assess injury to the medial knee structures in 2 positions: full extension and some degree of flexion. The amount of flexion used to “isolate” the medial collateral ligament is not consistent in the literature, but most studies have shown that stiffness of the ligaments was consistent between the limbs.
To determine (1) if the stiffness of the medial knee structures was the same bilaterally, and (2) if the stiffness was different in full extension compared with 20° of knee flexion.
Criterion standard, before-after design.
University research laboratory.
Patients or Other Participants:
Both knees of 45 healthy and active volunteers (26 females, 19 males; age = 23.2 ± 3.96 years, height = 170.6 ± 7.75 cm, mass = 74.2 ± 15.14 kg) were studied.
A valgus force of 60 N was applied to the lateral aspect of both knees in full extension and in 20° of flexion.
Main Outcome Measure(s):
The slope of the force-strain line of the medial knee during a valgus force was calculated using the LigMaster arthrometer.
Slope means in full extension were 16.1 ± 3.3 (right knee) and 15.8 ± 3.1(left knee). Means for 20° of flexion were 12.2 ± 3.1 (right) and 11.7 ± 2.8 (left). Stiffness was greater when the knee was in full extension versus 20° of flexion (t44 = 12.04, P < .001). No difference was noted between the slopes of the 2 knees in extension (t44 = 0.74, P = .46) or in flexion (t44 = 1.2, P = .27).
These findings support the use of the contralateral knee as a control. Further, the valgus stress test should be performed in full extension and in some degree of flexion to assess the different restraining structures of the medial tibiofemoral joint.
arthrometry; leg dominance; valgus stress
Context: An arthrogenic muscle response (AMR) of the soleus and peroneal muscles has been previously demonstrated in individuals with chronic ankle instability (CAI), but the presence of AMR in muscles acting on joints proximal to unstable ankles has not been previously explored.
Objective: To determine if AMR is present in the quadriceps and hamstrings muscles of those with and without unilateral CAI.
Design: Case control.
Setting: University research laboratory.
Patients or Other Participants: Twenty subjects with unilateral CAI (12 males, 8 females: age = 19.9 ± 3.7 years; height = 170.3 ± 15.6 cm; mass = 78.0 ± 23.1 kg) and 21 controls (16 males, 5 females: age = 23.2 ± 5.4 years; height = 173.9 ± 12.7 cm; mass = 87.2 ± 24.6 kg) with no previous ankle injuries.
Main Outcome Measure(s): The central activation ratio (CAR), a measure of motoneuron pool excitability during maximal voluntary isometric contraction, for the hamstrings and quadriceps muscles was measured in both limbs using the superimposed burst technique.
Results: The CAI group demonstrated quadriceps CARs that were significantly larger in their involved limbs (.87 ± .09), as compared with their uninvolved limbs (.84 ± .08), whereas no significant side-to-side difference was seen in the control group (sham involved = .80 ± .11, sham uninvolved = .81 ± .11). When values from both the involved and uninvolved limbs were averaged, the hamstrings CAR was significantly lower for the CAI group (.94 ± .03) than for the control group (.96 ± .03).
Conclusions: Arthrogenic inhibition of the hamstrings muscles bilaterally and facilitation of the quadriceps muscle ipsilateral to the involved limb were noted in subjects with unilateral CAI. Motoneuron pool excitability appears to be altered in muscles that act on joints proximal to the ankle in those with unilateral CAI.
ankle sprain; functional ankle instability; muscle inhibition
Context: Clinicians should consider multiple factors when estimating tissue-heating rates.
Objective: To report 3 separate occurrences of blisters during an ultrasound treatment experiment.
Background: While we were conducting a research experiment comparing the measurement capabilities of 2 different intramuscular temperature devices, 3 female participants (age = 26.33 ± 3.79 years, height = 169.34 ± 3.89 cm, mass = 63.39 ± 3.81 kg) out of 16 healthy volunteers (7 men: age = 22.83 ± 1.17 years, height = 170.61 ± 7.77 cm, mass = 74.62 ± 19.24 kg; 9 women: age = 24.22 ± 2.73 years, height = 171.88 ± 6.35 cm, mass = 73.99 ± 18.55 kg) developed blisters on the anterior shin after a 1-MHz, 1.5-W/cm
2 continuous ultrasound treatment delivered to the triceps surae muscle.
Differential Diagnosis: Allergies; chemical reaction with cleaning agents; sunburn; negative interaction between the temperature measurement instruments and the ultrasound field; the ultrasound transducer not being calibrated properly, producing a nonuniform field and creating a hot spot or heating differently when compared with other ultrasound devices; the smaller anatomy of our female subjects; or a confounding interaction among these factors.
Treatment: Participants were given standard minor burn care by a physician.
Uniqueness: (1) The development of blisters on the anterior aspect of the shin as a result of an ultrasound treatment to the posterior aspect of the triceps surae muscle and (2) muscle tissue heating rates ranging from 0.19°C to 1.1°C/min, when ultrasound researchers have suggested tissue heating in the range of 0.3°C/min with these settings.
Conclusions: These adverse events raise important questions regarding treatment application and potential differences in heating and quality control among different ultrasound devices from different manufacturers.
muscle heating; burn; spatial average intensity; beam nonuniformity ratio; therapeutic modalities
The purpose of this study was to determine the contribution of hamstrings and quadriceps fatigue to quadriceps inhibition following lumbar extension exercise. Regression models were calculated consisting of the outcome variable: quadriceps inhibition and predictor variables: change in EMG median frequency in the quadriceps and hamstrings during lumbar fatiguing exercise. Twenty-five subjects with a history of low back pain were matched by gender, height and mass to 25 healthy controls. Subjects performed two sets of fatiguing isometric lumbar extension exercise until mild (set 1) and moderate (set 2) fatigue of the lumbar paraspinals. Quadriceps and hamstring EMG median frequency were measured while subjects performed fatiguing exercise. A burst of electrical stimuli was superimposed while subjects performed an isometric maximal quadriceps contraction to estimate quadriceps inhibition after each exercise set. Results indicate the change in hamstring median frequency explained variance in quadriceps inhibition following the exercise sets in the history of low back pain group only. Change in quadriceps median frequency explained variance in quadriceps inhibition following the first exercise set in the control group only. In conclusion, persons with a history of low back pain whose quadriceps become inhibited following lumbar paraspinal exercise may be adapting to the fatigue by using their hamstring muscles more than controls.
Key PointsA neuromuscular relationship between the lumbar paraspinals and quadriceps while performing lumbar extension exercise may be influenced by hamstring muscle fatigue.QI following lumbar extension exercise in persons with a history of LBP group may involve significant contribution from the hamstring muscle group.More hamstring muscle contribution may be a necessary adaptation in the history of LBP group due to weaker and more fatigable lumbar extensors.
Superimposed burst technique; electromyography; spectral median frequency; correlation and regression; low back pain
Context: Exposure of the human body to cold is perceived as a stressor and results in a sympathetic response geared at maintaining core temperature. Application of ice to the periphery may lead to a decrease in core temperature, which may counteract the therapeutic effects of cryotherapy.
Objective: To determine if core temperature is lowered by the application of an ice bag to the ankle joint complex.
Design: A within-subjects, repeated-measures design.
Setting: The University of Virginia General Clinical Research Center.
Patients or Other Participants: Twenty-three healthy adults aged 19 to 39 years.
Intervention(s): Subjects were admitted to the hospital on 2 separate occasions. During one admission, subjects had a 20-minute ice treatment applied to their ankles; in the other admission, a bag of marbles was applied. Temperature measurements were recorded at 6 time intervals: baseline (before ice application), immediately after ice application, 10 and 20 minutes after ice application, and 10 and 20 minutes after ice removal.
Main Outcome Measure(s): We measured core temperature and ankle and soleus muscle surface temperatures. A mixed-effects model analysis of variance with repeated measures was used to determine if differences existed in core temperature and ankle and soleus surface temperatures between conditions (cryotherapy and control) and over time.
Results: Core temperature did not change after ice application or ice removal (
P > 0.05). The average core temperatures during the cryotherapy and control conditions were 36.72°C ± 0.42°C and 36.45°C ± 1.23°C, respectively.
Conclusions: A 20-minute cryotherapy treatment applied to the ankle did not alter core temperature.
cryotherapy; cold; ice; temperature
Context: Sex differences in lower extremity landing mechanics and muscle activation have been identified as potential causative factors leading to the increased incidence of anterior cruciate ligament injuries in female athletes. Valgus knee alignment places greater strain on the anterior cruciate ligament than a more neutral alignment. Gluteus medius (GM) activation may stabilize the leg and pelvis during landing, limiting valgus knee motion and potentially preventing anterior cruciate ligament injury.
Objective: To determine if frontal-plane knee angle and GM activation differ between the sexes at initial contact and maximal knee flexion during a single-leg drop landing.
Design: Between-groups design.
Setting: Motion analysis laboratory.
Patients or Other Participants: Thirty-two healthy subjects between the ages of 18 and 30 years.
Intervention(s): The independent variables were sex (male or female) and position (initial contact or maximal knee flexion).
Main Outcome Measure(s): Frontal-plane knee angle and GM average root mean square (aRMS) amplitude.
Results: At initial contact, women landed in knee valgus and men landed in knee varus (
P < .025). At maximal knee flexion, both men and women were in a position of knee varus, but the magnitude of varus was less in women than in men (
P < .025). The GM aRMS amplitude was greater at maximal knee flexion than at initial contact (
P < .025); however, male GM aRMS did not differ from female GM aRMS amplitude at either position (
P > .025).
Conclusions: Women tended to land in more knee valgus before and at impact than men. The GM muscle activation did not differ between the sexes and, thus, does not appear to be responsible for the sex differences in knee valgus. The excessive valgus knee angles displayed in women may help to explain the sex disparity in anterior cruciate ligament injury.
biomechanics; kinematics; landing; electromyography; anterior cruciate ligament
Context: Although poor paraspinal muscle endurance has been associated with less quadriceps activation (QA) in persons with a history of low back pain, no authors have addressed the acute neuromuscular response after lumbar paraspinal fatiguing exercise.
Objective: To compare QA after lumbar paraspinal fatiguing exercise in healthy individuals and those with a history of low back pain.
Design: A 2 × 4 repeated-measures, time-series design.
Setting: Exercise and Sport Injury Laboratory.
Patients or Other Participants: Sixteen volunteers participated (9 males, 7 females; 8 controls and 8 with a history of low back pain; age = 24.1 ± 3.1 years, height = 173.4 ± 7.1 cm, mass = 72.4 ± 12.1 kg).
Intervention(s): Subjects performed 3 sets of isometric lumbar paraspinal fatiguing muscle contractions. Exercise sets continued until the desired shift in lumbar paraspinal electromyographic median power frequency was observed. Baseline QA was compared with QA after each exercise set.
Main Outcome Measure(s): An electric burst was superimposed while subjects performed a maximal quadriceps contraction. We used the central activation ratio to calculate QA = (FMVIC/[FMVIC + FBurst])* 100, where F = force and MVIC = maximal voluntary isometric contractions. Quadriceps electromyographic activity was collected at the same time as QA measurements to permit calculation of median frequency during MVIC.
Results: Average QA decreased from baseline (87.4% ± 8.2%) after the first (84.5% ± 10.5%), second (81.4% ± 11.0%), and third (78.2% ± 12.7%) fatiguing exercise sets. On average, the group with a history of low back pain showed significantly more QA than controls. No significant change in quadriceps median frequency was noted during the quadriceps MVICs.
Conclusions: The quadriceps muscle group was inhibited after lumbar paraspinal fatiguing exercise in the absence of quadriceps fatigue. This effect may be different for people with a history of low back pain compared with healthy controls.
superimposed burst technique; quadriceps muscle inhibition; low back pain
Context: A neuromuscular relationship exists between the lumbar extensor and quadriceps muscles during fatiguing exercise. However, this relationship may be different for persons with low back pain (LBP).
Objective: To compare quadriceps inhibition after isometric, fatiguing lumbar extension exercise between persons with a history of LBP and control subjects.
Design: A 2 × 3 factorial, repeated-measures, time-series design with independent variables of group (persons with a history of LBP, controls) and time (baseline, postexercise set 1, postexercise set 2).
Setting: University research laboratory.
Patients or Other Participants: Twenty-five subjects with a history of LBP were matched by sex, height, and mass to 25 healthy control subjects.
Intervention(s): Electromyography median frequency indexed lumbar paraspinal muscular fatigue while subjects performed 2 sets of isometric lumbar extension exercise. Subjects exercised until a 15% downward shift in median frequency for the first set and a 25% shift for the second set were demonstrated.
Main Outcome Measure(s): Knee extension force was measured while subjects performed an isometric maximal quadriceps contraction. During this maximal effort, a percutaneous electric stimulus was applied to the quadriceps, causing a transient, supramaximal increase in force output. We used the ratio between the 2 forces to estimate quadriceps inhibition. Quadriceps electromyographic activity was recorded during the maximal contractions to compare median frequencies over time.
Results: Both groups exhibited significantly increased quadriceps inhibition after the first (12.6% ± 10.0%,
P < .001) and second (15.2% ± 9.7%,
P < .001) exercise sets compared with baseline (9.6% ± 9.3%). However, quadriceps inhibition was not different between groups.
Conclusions: Persons with a history of LBP do not appear to be any more or less vulnerable to quadriceps inhibition after fatiguing lumbar extension exercise.
superimposed burst technique; neuromuscular activity; knee
Context: Muscular fatigue impedes sensorimotor function and may increase the risk of shoulder injury during activity. The effects of fatigue on the sensorimotor system of the shoulder have been studied with various results. Deceleration times have been used to study neuromuscular control of the shoulder; however, no studies involving the effects of fatigue on deceleration times have been reported.
Objective: To compare shoulder deceleration times after a shoulder internal rotation perturbation before and after a repetitive throwing exercise protocol.
Design: A 2 × 2 repeated-measures design.
Setting: Exercise and sport injury laboratory.
Patients or Other Participants: Twenty healthy, recreationally active men (age = 24.76 ± 4.03 years, height = 178.41 ± 8.36 cm, mass = 80.16 ± 15.20 kg) volunteered to participate in the study. To ensure familiarity with the overhead motion, all subjects chosen had previously participated in an overhead throwing sport.
Intervention(s): The independent variables were time (preintervention and postintervention) and session (experimental and control). The intervention consisted of continuous overhead throwing. The subjects were considered fatigued when a 10% decrease in velocity was noted on 3 consecutive pitches.
Main Outcome Measure(s): Time necessary to decelerate from an internal rotation perturbation.
Results: Deceleration time was significantly increased by the fatiguing intervention (
P = .001).
Conclusions: The decreased ability to decelerate may be an adaptive response by the subjects to dissipate a lower percentage of force per second.
shoulder fatigue; shoulder neuromuscular control; throwing fatigue protocol
To discuss the proper methods used to elicit the Hoffmann reflex (H-reflex) and to present different situations in which this tool can be used in sports medicine research.
We searched MEDLINE and SPORT Discus from 1960 to 2004 using the key words Hoffmann reflex, H-reflex, and methodology. The remaining citations were collected from references of similar papers.
Numerous authors have used the H-reflex as a tool to examine neurologic conditions. However, few have used the H-reflex to examine neuromuscular impairments after sport injuries. Several studies were available describing the appropriate methods to elicit the H-reflex and examining the reliability of this measurement in different muscles.
The H-reflex is a valuable tool to evaluate neurologic function in various populations. However, because of the sensitivity of this measurement to extraneous factors, care must be taken when eliciting the H-reflex. We discuss recommendations on how to elicit the H-reflex and how to appropriately present methods in a manuscript.
H-reflex; neuromuscular system; motor neuron; injury; muscle
Objective: To determine if the spectral qualities of medial-lateral (ML) and anterior-posterior (AP) center of pressure during a 1-legged stance are affected by 4 days of ankle-brace application.
Design and Setting: The study, which consisted of a pretest-posttest randomized group design, took place in the Sports Injury Research Laboratory at Indiana State University.
Subjects: Twenty-eight Indiana State University students, who had not suffered from any ankle injuries within the past 2 years and were free of any neurologic or vestibular disorders, participated in the study.
Measurements: The effects of 3 independent variables on mean frequency amplitude for both ML and AP center of pressure were examined: (1) treatment (brace, control), (2) frequency bin (0%–20%, 20%–40%, 40%–60%, 60%–80%, and 80%–100% of area), and (3) time (pretest, immediately after brace application, and after 1, 2, 3, or 4 days of brace wear).
Results: We detected no difference (P > .05) for the ML or AP mean frequency when comparing the brace and control groups.
Conclusions: Application of an ankle brace may not require modifications in the postural-control strategies during a 1-legged stance in subjects with healthy ankles.
fast Fourier transformation; somatosensation; frequency analysis; balance