Quadriceps fatigue alters human muscle performance during a novel weight bearing task.

UNLABELLED: Limited information is currently available regarding muscle synergistic patterns and triggered reflex responses during dynamic weight-bearing activities in the presence of muscle fatigue. PURPOSE: The purpose of this study was to examine the effects of quadriceps muscle fatigue on patterns of muscle activation and performance in response to sudden, unexpected perturbations during a weight-bearing task. METHODS: Motion of the knee was measured as subjects were asked to track a visual target as accurately as possible while performing a resisted single leg squat task. Random perturbations were delivered in 20% of the trials by unexpectedly releasing the resistance during the flexion phase of the exercise. Absolute and constant errors were calculated to evaluate target tracking performance. Quadriceps and hamstring muscle activity was recorded during both perturbed and unperturbed trials. Twelve healthy women were tested before and after completing a repetitive submaximal eccentric quadriceps fatigue protocol. A second group of 12 women served as controls. Unexpected perturbations elicited long-latency responses characterized by facilitation of the quadriceps and inhibition of the hamstrings. RESULTS: Muscle fatigue increased the amplitude of the long-latency response in vastus lateralis by 4.3% maximum voluntary isometric contraction (P = 0.004). Changes in tracking error occurred in response to perturbations after fatigue in spite of significantly increased quadriceps muscle activity, especially during the extension phase of the exercise. CONCLUSION: Quadriceps muscle fatigue alters the patterns of coordinated muscle activity and may render subjects less able to cope with unexpected perturbations during weight-bearing tasks.

The effect of a single treatment of the Protonics system on lower extremity kinematics during gait and the lateral step up exercise.

INTRODUCTION: Patellofemoral pain (PFP) is often attributed to abnormal patellar tracking. The Protonics knee orthosis was developed to reduce femoral internal rotation by altering pelvic alignment via hamstring activation. The purpose of this research was to determine if a single treatment with the orthosis improved lower extremity alignment during gait and the lateral step up exercise. We hypothesized that anterior pelvic tilt, hip internal rotation and adduction, and external rotation of the tibia with respect to the femur would decrease after use of the brace. METHODS: Nineteen females (23.4+/-3.1 year, 1.66+/-0.05 m, 65.3+/-20.4 kg) with chronic PFP participated. Three-dimensional kinematic data were collected for each subject at 60 Hz during pre-treatment (PRE), after a placebo condition with the orthosis set at zero resistance (PLAC), and post-treatment (POST). Treatment consisted of having the subject perform the rehabilitation exercises recommended by the Protonics manufacturer. A repeated measures ANOVA was performed on each dependent variable (alpha=0.05). RESULTS: This investigation did not verify the changes in alignment proposed by the manufacturer as a result of acute application of the Protonics system. However, after the use of the brace, pelvic rotation and hip hike were decreased during the lateral step up exercise. CONCLUSION: Based on the results of this study, it was concluded that a single application of the Protonics system did not alter anterior pelvic tilt, hip internal rotation and adduction, or tibial external rotation during the lateral step up and gait.

The addition of the Protonics brace system to a rehabilitation protocol to address patellofemoral joint syndrome.

STUDY DESIGN: Randomized clinical trial. OBJECTIVES: To investigate the clinical efficacy of the addition of the Protonics system to a standard exercise-based patellofemoral rehabilitation protocol. BACKGROUND: The Protonics system has been suggested as an intervention for patients with patellofemoral pain syndrome (PFPS). However, the effects of this system have not been compared to the effects associated with traditional exercise-based rehabilitation alone. METHODS AND MEASURES: Seventeen of 34 females (mean age, 28 years; range, 13-55 years) diagnosed with PFPS were randomly assigned to wear the Protonics system while participating in a conventional exercise-based rehabilitation program. Functional and patient-reported outcome measures were evaluated, including Kujala score and the lateral step-up test. In addition, measurements of hip internal and external rotation, hip extension, and iliotibial band muscle length were compared between groups. RESULTS: Patients in both groups demonstrated improvement in Kujala score (P<.001), performance on the lateral step-up test (P<.001), and pain during the step-up test (P<.001) at the conclusion of the study. However, there was no difference between groups with respect to improvement in Kujala score (P = .33), step-up test performance (P = .47), or pain during the step-up test (P = .24). Patients using the Protonics system demonstrated greater gain in passive hip extension (P = .023) and increased hip external rotation motion (P = .017) at discharge versus patients treated with exercise alone. However, there was no difference in iliotibial band flexibility (P = .80) or hip internal rotation motion (P = .09) between groups. A greater proportion of patients in the Protonics group reported no pain with step-up testing at each 2-week interval. However, the 2.2 fewer visits required by patients in the Protonics group to meet discharge criteria did not achieve statistical significance (P = .08). CONCLUSIONS: Patients using the Protonics system demonstrated a shift in available hip rotation and increased passive hip extension flexibility. However, these changes were not outside the bounds of potential measurement error and did not translate into significant functional differences from a similar group treated with exercise alone. The economic implications of an average 2.2-visit decrease in treatment sessions per patient using the Protonics system are uncertain.

Core stability measures as risk factors for lower extremity injury in athletes.

INTRODUCTION/PURPOSE: Decreased lumbo-pelvic (or core) stability has been suggested to contribute to the etiology of lower extremity injuries, particularly in females. This prospective study compares core stability measures between genders and between athletes who reported an injury during their season versus those who did not. Finally, we looked for one or a combination of these strength measures that could be used to identify athletes at risk for lower extremity injury. METHODS: Before their season, 80 female (mean age = 19.1 +/- 1.37 yr, mean weight 65.1 +/- 10.0 kg) and 60 male (mean age = 19.0 +/- 0.90 yr, mean weight 78.8 +/- 13.3 kg) intercollegiate basketball and track athletes were studied. Hip abduction and external rotation strength, abdominal muscle function, and back extensor and quadratus lumborum endurance was tested for each athlete. RESULTS: Males produced greater hip abduction (males = 32.6 +/- 7.3%BW, females = 29.2 +/- 6.1%BW), hip external rotation (males = 21.6 +/- 4.3%BW, females = 18.4 +/- 4.1%BW), and quadratus lumborum measures (males = 84.3 +/- 32.5 s, females = 58.9 +/- 26.0 s). Athletes who did not sustain an injury were significantly stronger in hip abduction (males = 31.6 +/- 7.1%BW, females = 28.6 +/- 5.5%BW) and external rotation (males = 20.6 +/- 4.2%BW, females = 17.9 +/- 4.4%BW). Logistic regression analysis revealed that hip external rotation strength was the only useful predictor of injury status (OR = 0.86, 95% CI = 0.77, 0.097). CONCLUSION: Core stability has an important role in injury prevention. Future study may reveal that differences in postural stability partially explain the gender bias among female athletes.

The effect of a single treatment of the Protonics system on biceps femoris and gluteus medius activation during gait and the lateral step up exercise.

INTRODUCTION: Patellofemoral pain, a frequent complaint among women, is attributed in part to excessive femoral internal rotation, leading to patellofemoral malalignment. The Protonics resistive dynamic knee orthosis was designed to facilitate hamstring activation, leading to a less anteriorly tilted pelvis and less femoral internal rotation. This decrease in femoral internal rotation is thought to improve patellofemoral joint alignment, thereby reducing knee pain. In this position, the gluteus medius (GM) would be more effective against the force of gravity. Therefore, this study's purpose was to determine the effects of a single application of the Protonics orthosis on knee pain and biceps femoris (BF) and GM activation. METHODS: 21 females (23.4+/-3.1 years, 1.66+/-0.05 m, 65.3+/-20.4 kg) with a history of chronic PFP participated in the study. Data were collected during level walking and a lateral-step up exercise in three conditions: pre-treatment (PRE), a placebo condition collected after the orthosis was set at zero resistance (PLAC), and post-treatment (POST). PLAC and POST were performed after the orthosis had been removed from the subject's leg. Percent of gait cycle activated, integrated EMG (IEMG), and level of pain (VAS scale) were measured in each condition. An ANOVA was used to determine significance between conditions (alpha=0.05). RESULTS: Use of the Protonics orthosis did not result in any change in the level of knee pain, IEMG or duration of activation for the BF or GM. SUMMARY: Our results do not support an increase in hamstring activation or decrease in GM activation following a single treatment with the Protonics orthosis.

Hip strength in females with and without patellofemoral pain.

STUDY DESIGN: Cross-sectional. OBJECTIVES: To determine if females with anterior knee pain are more likely to demonstrate hip abduction or external rotation weakness than a similar, asymptomatic, age-matched control group. BACKGROUND: Diminished hip strength has been implicated as being contributory to lower-extremity malalignment and patellofemoral pain. The identification of reliable and consistent patterns of weakness in this population may assist health care professionals establish a more effective treatment plan. METHODS AND MEASURES: Hip abduction and external rotation isometric strength measurements were recorded for the injured side of 15 female subjects with patellofemoral joint pain (mean +/- SD age, 15.7 +/- 2.7 years; age range, 12-21 years). These were compared with strength measurements from the corresponding hip of 15 age-matched female control subjects (mean +/- SD age, 15.7 +/- 2.7 years; age range, 12-21 years). All strength measurements were made using hand-held dynamometers. RESULTS: Subjects with patellofemoral pain demonstrated 26% less hip abduction strength (P<.001) and 36% less hip external rotation strength (P<.001) than similar age-matched controls. CONCLUSIONS: The results indicate that young women with patellofemoral pain are more likely to demonstrate weakness in hip abduction as well as external rotation than age-matched women who are not symptomatic.

Comparison of outcomes between males and females after anterior cruciate ligament reconstruction.

Few studies have specifically addressed the potential differences in outcome from ACL reconstruction between males and females. The present study compared patient-reported outcomes between the sexes after a minimum of 2 years following arthroscopic ACL reconstruction using bone-patellar tendon-bone autograft. Patients were also categorized as acute or chronic based on the time from injury to surgery. Outcome questionnaires were mailed to 638 patients, resulting in 151 eligible respondents included in the analysis. The outcome instruments used were the Cincinnati scale, the ACL-Quality of Life scale, and the Tegner activity rating scale. At an average of 5 years following ACL reconstruction no differences were found between males (n=74) and females (n=77) on the ACL-QOL scale. Females perceived a significantly higher activity level prior to surgery according to the Tegner scale. However, no other differences were identified by gender or stage based on prior, highest, or current Tegner activity levels. Results of the Cincinnati scale for the entire sample showed that females scored an average of 5.7 points lower than males. Analysis of this difference by patient age indicates a trend toward lower scores in females between 12-18 and over 24 years old. Chronicity was not a factor that affected outcome in either males or females. No differences were found in the number of patients who complained of anterior knee pain. We conclude that autogenous bone-patella tendon-bone ACL reconstruction is equally successful in well-matched populations of males and females.

Acute effects of the Protonics system on patellofemoral alignment: an MRI study.

This study used magnetic resonance imaging (MRI) to determine whether changes in patellofemoral alignment occur after initial treatment with the Protonics exercise device. The first scan was obtained before the device was used. After performing a set of exercises with no resistance on the device the device was removed, and a second scan was obtained. The same set of exercises was again performed with resistance on the device set at the appropriate level, and a final scan was obtained with the device removed. An isometric leg press was maintained as each image was obtained to simulate more closely a functional weight-bearing activity. Subjects were 26 women with complaints of patellofemoral pain. The main outcome measures were: patellar tilt angle, bisect offset, and lateral facet angle. Nonparametric repeated measures analysis of variance tests showed no differences between test conditions for any of the three measures of patellofemoral alignment. We conclude that after an initial treatment session using the Protonics system there is no change in patellofemoral alignment as determined by MRI.