Jean L. McCrory

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.

Vertical ground reaction forces: objective measures of gait following hip arthroplasty.

After hip arthroplasty, many patients continue to exhibit abnormal gait patterns. The purpose of this study was to compare the vertical ground reaction forces of a group of 27 individuals who have undergone hip arthroplasty with a group of 35 normal control subjects. Specific force measures were determined from vertical ground reaction forces collected on a treadmill instrumented with two force plates. Symmetry indices were calculated on both groups of subjects. First and second peak forces, loading rate, impulse, and stance time were significantly less, while time to first peak force was significantly greater on the affected leg of the hip arthroplasty subjects when compared to their unaffected leg, or to the control group. The hip arthroplasty group showed greater asymmetry of ground reaction forces than the control group did. Bilateral asymmetric limb loading persists well after unilateral hip replacement surgery. Ground reaction force measures have been shown to be an effective means of quantifying the antalgic gait of hip arthroplasty patients.

Etiologic factors associated with Achilles tendinitis in runners

PURPOSE The purpose of this study was to determine whether relationships exist between selected training, anthropometric, isokinetic muscular strength, and endurance, ground reaction force, and rearfoot movement variables in runners afflicted with Achilles tendinitis. METHODS Specifically, we examined differences in selected measures between a noninjured cohort of runners (N = 58) and a cohort of injured runners with Achilles tendinitis (N = 31). Isokinetic, kinetic, and kinematic measures were collected using a Cybex II+ isokinetic dynamometer (Medway, MA), AMTI force plate (500 Hz), and Motion Analysis high-speed videography (200 Hz), respectively. Separate discriminant function analyses were performed on each of the five sets of variables to identify the factors that best discriminate between the injured and control groups. RESULTS Years running, training pace, stretching habits (injured runners were less likely to incorporate stretching into their training routine), touchdown angle, plantar flexion peak torque at 180 degrees x s(-1) and arch index were found to be significant discriminators. CONCLUSION A combined discriminant analysis using the above mentioned significant variables revealed that plantar flexion peak torque, touchdown angle, and years running were the strongest discriminators between runners afflicted with Achilles tendinitis and runners who had no history of overuse injury.

Arch index as a predictor of arch height

Abstract A number of indirect methods of estimating the height of the medial longitudinal arch of the foot have been devised.1 The efficacy of the arch index as a valid and convenient predictor of arch height has been questioned.2 In this study, arch index was measured in 45 elderly subjects and navicular height was measured from weight bearing radiographs. Normalized navicular height was determined by dividing navicular height by foot length as measured from radiographs. A correlation coefficient of r=0.67 was found between navicular height and arch index. The correlation coefficient between arch index and normalized navicular height was found to be r=0.71. Arch index thus provides a simple quantitative means of assessing the height of the medial longitudinal arch with the limitation that only half of the variance in arch height can be explained.

Dynamic postural stability during advancing pregnancy.

UNLABELLED Pregnant women are at an increased risk of experiencing a fall. Numerous anatomical, physiological, and hormonal alterations occur during pregnancy, but the influence of these factors on dynamic postural stability has not been explored. The purpose of this study was to examine dynamic postural stability in pregnant women during their second and third trimesters as well as in a group of non-pregnant control women. METHODS Eighty-one women (41 pregnant, 40 controls) participated stood on a force plate that translated anteroposteriorly at small, medium, and large magnitudes. Reaction time and center of pressure (COP) movement during the translations were analyzed. Trimester, perturbation direction, and perturbation magnitude were the independent variables in a mixed-model analysis of variance on each of the following dependent variables: reaction time, initial sway, total sway, and sway velocity. RESULTS Reaction time to the perturbation was not significantly different between the groups. Initial sway, total sway, and sway velocity were significantly less during the third trimester than during the second trimester and when compared to the non-pregnant controls (P<0.05). No differences were found in any of the measures between the pregnant women in their second trimesters and the control group. CONCLUSION Alterations in sway responses to perturbations are seen in the third trimester in healthy women with uncomplicated pregnancies. Further study is needed to examine the biomechanical and physiological reasons behind this altered dynamic postural stability.

Does a single control mechanism exist for both forward and backward walking

It has been proposed that the highly reproducible forward walking (FW) locomotor pattern is generated by a central neuronal program or central pattern generator (CPG) which provides the underlying mechanism which produces the coordinated walking movement. The purpose of this study was to quantify the differences in the muscular activation patterns during FW and backward walking (BW) at a constant step frequency and to determine if common features exist across both locomotor conditions. The hypothesis was that FW and BW are both mediated by the same CPG; therefore, only small modifications in the CPG are required in order to produce the different characteristics of each walking mode. The results noted kinematically reversed patterns at the hip and ankle joints between FW and BW. The knee joint movement pattern was similar between conditions, however, a phase shift of 14.3% of the gait cycle occurred. An approximately 25% phase shift in the muscle activation patterns existed between FW and BW in four of the six muscles studied. Additionally, a pattern recognition technique was applied to the combined EMG signals to determine the minimum number of features required to generate the measured muscular output. Only two main features were necessary to produce the EMG patterns for both the FW and BW condition. The main features in FW were more consistent than noted in BW. The results support the notion that a single spinal mechanism such as a CPG with two main features appears to be in control during both FW and BW. Copyright 1998 Elsevier Science B.V. All rights reserved

The effect of obesity and gender on body segment parameters in older adults

BACKGROUND Anthropometry is a necessary aspect of aging-related research, especially in biomechanics and injury prevention. Little information is available on inertial parameters in the geriatric population that account for gender and obesity effects. The goal of this study was to report body segment parameters in adults aged 65 years and older, and to investigate the impact of aging, gender and obesity. METHODS Eighty-three healthy old (65-75 years) and elderly (>75 years) adults were recruited to represent a range of body types. Participants underwent a whole body dual energy X-ray absorptiometry scan. Analysis was limited to segment mass, length, longitudinal center of mass position, and frontal plane radius of gyration. A mixed-linear regression model was performed using gender, obesity, age group and two-way and three-way interactions (alpha=0.05). FINDINGS Mass distribution varied with obesity and gender. Males had greater trunk and upper extremity mass while females had a higher lower extremity mass. In general, obese elderly adults had significantly greater trunk segment mass with less thigh and shank segment mass than all others. Gender and obesity effects were found in center of mass and radius of gyration. Non-obese individuals possessed a more distal thigh and shank center of mass than obese. Interestingly, females had more distal trunk center of mass than males. INTERPRETATION Age, obesity and gender have a significant impact on segment mass, center of mass and radius of gyration in old and elderly adults. This study underlines the need to consider age, obesity and gender when utilizing anthropometric data sets.

Dynamic postural stability in pregnant fallers and non-fallers

Please cite this paper as: McCrory J, Chambers A, Daftary A, Redfern M. Dynamic postural stability in pregnant fallers and non‐fallers. BJOG 2010;117:954–962.

Healing of Charcot fractures: skin temperature and radiographic correlates

Abstract We explored whether skin temperature, measured with an infrared thermometer, is useful in managing Charcot fractures. Seventy patients with active Charcot fractures were enrolled. Of these, 64 were excluded from further analysis because of factors deemed likely to confound skin temperature measurement, i.e. most skin lesions. Radiographs were obtained using a standardized weight bearing protocol and interpreted by formal criteria. Patients were treated with a walking total contact cast for approximately 6 months and PTB bracing thereafter. The temperature of the affected feet was elevated compared to the contralateral feet at presentation (difference of 4.25±1.63°C). This decreased on average at 0.022°C/day ( r =0.5), giving an intercept of 0°C difference at 147±75 days. However, there was too much variability in the individual data even in these highly selected patients to give any correlation between skin temperature and radiographs in individuals. Radiographic worsening ended by 3–6 months. Radiographic healing began by 3–6 months and continued after the change from casting to bracing. We conclude that skin cooling occurs with treatment of active Charcot fractures, but many patients have other events that confound skin temperature measurement, and even in patients without such confounding factors individual skin temperatures are too variable to be clinically useful.

Thigh Muscle Strength in Senior Athletes and Healthy Controls

McCrory, JL, Salacinski, AJ, Hunt, SE, and Greenspan, SL. Thigh muscle strength in senior athletes and healthy controls. J Strength Cond Res 23(9): 2430-2436, 2009-Exercise is commonly recommended to counteract aging-related muscle weakness. While numerous exercise intervention studies on the elderly have been performed, few have included elite senior athletes, such as those who participate in the National Senior Games. The extent to which participation in highly competitive exercise affects muscle strength is unknown, as well as the extent to which such participation mitigates any aging-related strength losses. The purpose of this study was to examine isometric thigh muscle strength in selected athletes of the National Senior Games and healthy noncompetitive controls of similar age, as well as to investigate strength changes with aging in both groups. In all, 95 athletes of the Games and 72 healthy controls participated. Of the senior athletes, 43 were runners, 12 cyclists, and 40 swimmers. Three trials of isometric knee flexion and extension strength were collected using a load cell affixed to a custom-designed chair. Strength data were normalized to dual-energy x-ray absorptiometry-obtained lean mass of the leg. A 3-factor multivariate analysis of variance (group × gender × age group) was performed, which included both the extension and flexion variables (α = 0.05). Athletes exhibited 38% more extension strength and 66% more flexion strength than the controls (p < 0.001). Strength did not decrease with advancing age in either the athletes or the controls (p = 0.345). In conclusion, senior athletes who participate in highly competitive exercise have greater strength than healthy aged-matched individuals who do not. Neither group displayed the expected strength losses with aging. Our subject cohorts, however, were not typical of those over age 65 years because individuals with existing health conditions were excluded from the study.