Biomedical subjects

Jean L McCrory

Publications and source records attributed to Jean L McCrory.

6 recordsLinked to original sources

PubMed2006

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.

Adult↗

PubMed2004

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.

Adult↗

PubMed2004

Locomotion in simulated zero gravity: ground reaction forces.

BACKGROUND: Exercise is likely to be an important countermeasure to bone demineralization, which remains a concern for astronauts during long-duration spaceflight. However, loads on the feet during exercise with 1 G equivalent gravity replacement are not known. The purpose of this study was to compare ground reaction forces (GRFs) during over-ground and simulated zero gravity (0 G) locomotion. HYPOTHESIS: It was hypothesized that sufficient gravity replacement loading could be applied to the subjects such that GRF profiles similar to those seen in 1 G would occur during locomotion in a zero-gravity locomotion simulator (ZLS). METHODS: GRFs were measured during overground walking and running, and during locomotion in two restraint harness designs in the ZLS with an initial loading of 1 body weight. Load cells measured the gravity replacement load (GRL) in the ZLS. Joint angles at the hip and knee were also measured by goniometers. RESULTS: Peak forces were greater in overground locomotion than in the ZLS; however, loading rates were greater in the ZLS running conditions than in overground running. The knee joint was more flexed at key times in the support phase during running in the ZLS compared with overground. CONCLUSIONS: Large loads and loading rates can be generated at the feet during simulated 0 G exercise although peak forces during running in the ZLS are less than overground running at the same speed. The refinement of the gravity replacement system to provide a constant 1 G load should be considered.

Adult↗

PubMed2002

Locomotion in simulated microgravity: gravity replacement loads.

BACKGROUND: When an astronaut walks or runs on a treadmill in microgravity, a subject load device (SLD) is used to return him or her back to the treadmill belt. The gravity replacement load (GRL) in the SLD is transferred, via a harness, to the pelvis and/or the shoulders. This research compared comfort and ground reaction forces during treadmill running in a microgravity locomotion simulator at GRLs of 60%, 80%, and 100% of body weight (BW). Two harness designs (shoulder springs only (SSO) and waist and shoulder springs (WSS)) were used. HYPOTHESES: 1) The 100% BW gravity replacement load conditions would be comfortably tolerated and would result in larger ground reaction forces and loading rates than the lower load conditions, and 2) the WSS harness would be more comfortable than the SSO harness. METHODS: Using the Penn State Zero Gravity Locomotion Simulator (ZLS), 8 subjects ran at 2.0 m x s(-1) (4.5 mph) for 3 min at each GRL setting in each harness. Subjective ratings of harness comfort, ground reaction forces, and GRL data were collected during the final minute of exercise. RESULTS: The 100% BW loading conditions were comfortably tolerated (2.3 on a scale of 0-10), although discomfort increased as the GRL increased. There were no overall differences in perceived comfort between the two harnesses. The loading rates (27.1, 33.8, 39.1 BW x s(-1)) and the magnitudes of the first (1.0, 1.4, 1.6 BW) and second (1.3, 1.7, 1.9 BW) peaks of the ground reaction force increased with increasing levels (60, 80, 100% BW respectively) of GRL. CONCLUSIONS: Subjects were able to tolerate a GRL of 100% BW well. The magnitude of the ground reaction force peaks and the loading rate is directly related to the magnitude of the GRL.

Adult↗

PubMedDate not supplied

Differences in kinematics and electromyographic activity between men and women during the single-legged squat.

BACKGROUND: Numerous factors have been identified as potentially increasing the risk of anterior cruciate ligament injury in the female athlete. However, differences between the sexes in lower extremity coordination, particularly hip control, are only minimally understood. HYPOTHESIS: There is no difference in kinematic or electromyographic data during the single-legged squat between men and women. STUDY DESIGN: Descriptive comparison study. METHODS: We kinematically and electromyographically analyzed the single-legged squat in 18 intercollegiate athletes (9 male, 9 female). Subjects performed five single-legged squats on their dominant leg, lowering themselves as far as possible and then returning to a standing position without losing balance. RESULTS: Women demonstrated significantly more ankle dorsiflexion, ankle pronation, hip adduction, hip flexion, hip external rotation, and less trunk lateral flexion than men. These factors were associated with a decreased ability of the women to maintain a varus knee position during the squat as compared with the men. Analysis of all eight tested muscles demonstrated that women had greater muscle activation compared with men. When each muscle was analyzed separately, the rectus femoris muscle activation was found to be statistically greater in women in both the area under the linear envelope and maximal activation data. CONCLUSIONS: Under a physiologic load in a position commonly assumed in sports, women tend to position their entire lower extremity and activate muscles in a manner that could increase strain on the anterior cruciate ligament.

Adult↗

PubMedDate not supplied

Effects of 2 ankle fatigue models on the duration of postural stability dysfunction.

CONTEXT: Muscle fatigue is generally categorized in 2 ways: that caused by peripheral weakness (peripheral fatigue) and that caused by a progressive failure of voluntary neural drive (central fatigue). Numerous variables have been studied in conjunction with fatigue protocols, including postural stability, maximum voluntary contraction force, and reaction time. When torque recordings fall below 50% of a maximum voluntary contraction, the muscle is described as fatigued, but whether this value is a good indicator of fatigue has not been studied. OBJECTIVE: To compare the effects of 2 ankle musculature fatigue protocols (30% and 50%) on the duration of postural stability dysfunction. DESIGN: To assess differences between the 30% and 50% fatigue protocols, we calculated a 1 between-groups factor (subjects) and 2 within-groups factors (fatigue, test) analysis of variance. SETTING: E.J. Nutter Athletic Training Facility. PATIENTS OR OTHER PARTICIPANTS: Twenty subjects (10 men, 10 women; age = 21.15 +/- 2.23 years; height = 172.97 +/- 9.86 cm; mass = 70.62 +/- 14.60 kg) volunteered for this study. Subjects had no history of lower extremity injury, vestibular or balance disorders, functional ankle instability, or head injury in the past 6 months. INTERVENTION(S): On separate days, subjects performed isokinetic fatiguing contractions of the plantar flexors and dorsiflexors in a 30% protocol (70% decrease in strength) and a 50% protocol (50% decrease in strength). MAIN OUTCOME MEASURE(S): Baseline and postfatigue postural stability scores were determined before and after the isokinetic fatiguing contractions. Plantar-flexion peak-torque measurements were obtained for the 2 fatiguing protocols. Three prefatigue and 12 postfatigue postural stability trials were recorded. Velocities for testing were 60 degrees /s for plantar flexion and 120 degrees /s for dorsiflexion. RESULTS: Sway velocity was significantly greater when the ankle was fatigued to 30% (1.56 degrees /s) than in the 50% condition (1.36 degrees /s). For the 30% protocol, sway was significantly impaired when the pretest condition (1.19 degrees /s) was compared with posttest trial 1 (2.34 degrees /s), trial 2 (2.37 degrees /s), and trial 3 (1.71 degrees /s). For the 50% protocol, sway was significantly impaired when the pretest condition (1.27 degrees /s) was compared with posttest trial 1 (2.02 degrees /s). CONCLUSIONS: The 30% fatigue protocol resulted in significantly longer impairment of postural stability than the 50% protocol. Because the 30% protocol resulted in a greater effect but was relatively short-lived (approximately 75 to 90 s), it is more useful for research purposes.

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