Adjustments of prehension synergies in response to self-triggered and experimenter-triggered load and torque perturbations. (1/157)

Humans are known to show anticipatory adjustments in the grip force prior to a self-generated or predictable action or perturbation applied to a hand-held object. We investigated whether humans can also adjust covariation of individual finger forces (multi-finger synergies) prior to self-triggered perturbations. To address this issue, we studied adjustments in multi-digit synergies associated with applied load/torque perturbations while the subjects held a customized handle steadily. The main hypothesis was that the subjects would be able to demonstrate the phenomenon of anticipatory covariation, that is changes in covariation patterns among digit forces and moments of force in anticipation of a perturbation, but only when the perturbation was triggered by the subjects themselves. Based on the principle of superposition (decoupled grasping force and resultant torque control), we also expected to see different adjustments in indices of multi-digit synergies stabilizing the total gripping force and the total moment of force. The task for the subjects (n = 8) was to return the initial handle position as quickly as possible after a perturbation, which consisted of removing one of three loads hanging from the handle. There were six experimental conditions: two types of perturbations (self-triggered and experimenter-triggered) by three positions of the load (left, center, and right). Three-dimensional forces and moments of force recorded from each digit contact were used for the analysis. Indices of covariation among digit forces and among moments of force, previously employed for studying motor synergies, were computed across trials. Positive values of the indices reflected negative covariations of individual digit forces and moments of force (their inter-compensatory changes) to stabilize the total force and moment acting on the handle. In steady-state conditions, subjects showed strong positive indices for both digit forces and digit moments. Under the self-triggered conditions, changes in the indices of digit force and moment covariation were seen about 150 ms prior to the perturbation, while such changes were observed only after the perturbation under the experimenter-triggered conditions. Immediately following a perturbation, the indices of force and moment covariation rapidly changed to negative revealing the lack of inter-compensation among the individual digit forces and moments. Later, both indices showed a recovery to positive values; the recovery was faster in the self-triggered conditions than in the experimenter-triggered ones. During the steady-state phase after the perturbation, the indices of force and moment covariation decreased and increased, respectively, as compared to their values during the steady-state phase prior to the perturbation. We conclude that humans are able to adjust multi-digit synergies involved in prehensile tasks in anticipation of a self-triggered perturbation. These conclusions speak against hypotheses on the organization of multi-element actions based on optimal control principles. Different changes in the indices of force and moment covariation after a perturbation corroborate the principle of superposition. We discuss relations of anticipatory covariation to anticipatory postural adjustments.  (+info)

A comparison of different balance tests in the prediction of falls in older women with vertebral fractures: a cohort study. (2/157)

BACKGROUND: people with vertebral fractures are at high risk of developing hip fractures. Falls risk is important in the pathogenesis of hip fractures. AIM: to investigate if balance tests, in conjunction with a falls history, can predict falls in older women with vertebral fractures. METHODS: a cohort study of community-dwelling women aged over 60 years, with vertebral fractures. Balance tests investigated were: 5 m-timed-up-and-go-test (5 m-TUG), timed 10 m walk, TURN180 test (number of steps to turn 180 degrees ), tandem walk, ability to stand from chair with arms folded. Leg extensor power was also measured. OUTCOME MEASURE: fallers (at least one fall in a 12 month follow-up period) versus non-fallers. RESULTS: one hundred and four women aged 63-91 years [mean=78 +/- 7], were recruited. Eighty-six (83%) completed the study. Four variables were significantly associated with fallers: previous recurrent faller (2+ falls) [OR=6.52; 95% CI=1.69-25.22], 5 m-TUG test [OR=1.03; 1.00-1.06], timed 10 m walk [OR=1.07; 1.01-1.13] and the TURN180 test [OR=1.22; 1.00-1.49] [P <0.05]. Multi-variable analysis showed that only two variables, previous recurrent faller [OR=5.60; 1.40-22.45] and the 5 m-TUG test [OR=1.04; 1.00-1.08], were independently significantly associated with fallers. The optimal cut-off time for performing the 5 m-TUG test in predicting fallers was 30 s (area under ROC=60%). Combining previous recurrent faller with the 5 m-TUG improved prediction of fallers [OR=16.79, specificity=100%, sensitivity=13%]. CONCLUSIONS: a previous history of recurrent falls and the inability to perform the 5 m-TUG test within 30 s predicted falls in older women with vertebral fractures. Combining these two measures can predict fallers with a high degree of specificity (although a low sensitivity), allowing the identification of a group of patients suitable for fall and fracture prevention measures.  (+info)

Bone mineral density and leg muscle strength in young Caucasian, Hispanic, and Asian women. (3/157)

Differences in bone mineral density (BMD) of ethnically diverse populations are usually attributed to anthropometric characteristics, but may also be due to life style or diet. We studied healthy young sedentary women with Asian (ASN, n=40), Hispanic (HIS, n=39), or Caucasian (CAU, n=36) backgrounds. Body composition and regional BMD were measured by dual-energy X-ray absorptiometry (Hologic) or PIXI (Lunar GE) for the heel and wrist). Leg strength was quantified with a leg press and dietary calcium was estimated with 3-d diet records. CAU were taller than HIS and ASN (p<0.01). ASN had lower body weights, fat mass, lean body mass, and leg strength than HIS or CAU (p<0.01). Differences in BMD among groups were not eliminated by adjusting for body weight and height at the arm, trochanter, femoral neck, and total hip where BMD values remained lower in the ASN than in HIS or CAU (p<0.01). Conversely, adjusted BMD at the wrist was 7.3% higher in ASN and 8.3% higher in HIS and at the heel, 7.3% higher in ASN and 7.0% higher in HIS than in CAU (p<0.05). Leg strength was a significant predictor of BMD in the hip in CAU (R=0.53, p=0.004), in the hip with dietary calcium in ASN (R=0.65, p=0.02), and in the heel with height in HIS (R=0.57, p=0.03). We conclude that significant factors underlying BMD in ethnically diverse young women vary as a function of ethnicity and include leg strength and dietary calcium as well as anthropometric characteristics.  (+info)

Mathematical model that predicts the force-intensity and force-frequency relationships after spinal cord injuries. (4/157)

We have previously developed and tested a muscle model that predicts the effect of stimulation frequency on muscle force responses. The aim of this study was to enhance our isometric mathematical model to predict muscle forces in response to stimulation trains with a wide range of frequencies and intensities for the quadriceps femoris muscles of individuals with spinal cord injuries. Isometric forces were obtained experimentally from 10 individuals with spinal cord injuries (time after injury, 1.5-8 years) and then compared to forces predicted by the model. Our model predicted accurately the force-time integrals (FTI) and peak forces (PF) for stimulation trains of a wide range of frequencies (12.5-80 HZ) and intensities (150-600-mus pulse duration), and two different stimulation patterns (constant-frequency trains and doublet-frequency trains). The accurate predictions of our model indicate that our model, which now incorporates the effects of stimulation frequency, intensity, and pattern on muscle forces, can be used to design optimal customized stimulation strategies for spinal cord-injured patients.  (+info)

Isometric measurement of wrist-extensor power following surgical treatment of displaced lateral condylar fracture of the humerus in children. (5/157)

Muscle disability is a common sequel after fracture management. Previous research has shown divergent results concerning muscle-power recovery after bone healing. This study has investigated the muscle function of wrist extensors after lateral condylar fracture in children, as evaluated by a hand-held dynamometer and compared with sex- and age-matched children. From 1999 to 2004, 20 patients (13 boys and seven girls; mean age: 9 years and 4 months) with displaced lateral condylar fracture of the humerus were treated by open reduction and internal fixation with Kirschner wires (K-wire). The duration of K-wire fixation was 35 days and the mean follow-up time was 50 months. A total of 180 healthy age-, sex- and weight-matched children were used as control groups. A paired Student's test was applied for the analysis of statistical significance. The range of motion of the elbow and radiographic findings were not significantly different between the injured limb and normal control groups. The maximum isometric power of wrist-extensor muscles after surgical treatment of lateral condylar fracture of the humerus in final follow-up was not statistically different from that in the normal control children. Muscle power therefore recovers to its normal status after the healing of lateral condylar fracture of the humerus in children.  (+info)

Dynamometry testing in spinal cord injury. (6/157)

Persons with a spinal cord injury (SCI) demonstrate strength deficits that can limit their functional ability to perform activities of daily living. For a specific lesion level, performance of functional activities is related to the level of muscle strength. Consequently, in clinical practice, we need reliable measures of muscle strength to determine mobility and self-care ability. Muscle-strength testing is used to document recovery or loss of motor function early in SCI, as well as measure improvements in strength in chronic SCI. We also need such measures for research purposes to determine the efficacy of clinical trials. Several methods are available for testing muscle strength of persons with SCI, such as handheld, handgrip, and isokinetic dynamometers. This article provides an overview of muscle-contraction definitions and testing methodologies and discusses the reliability of these testing methods and dynamometry devices.  (+info)

Aerobic fitness and upper extremity strength in patients aged 11 to 21 years with spinal cord dysfunction as compared to ideal weight and overweight controls. (7/157)

OBJECTIVE: To determine whether the aerobic fitness, upper extremity strength, and body composition in groups of adolescents with mobility impairment due to thoracic and upper lumbar spinal cord injury (SCI) or spina bifida (SB) are significantly different from those in groups of adolescents without mobility impairment who are of normal weight (CTRL) or overweight (OW). SUBJECTS: One hundred fifteen total subjects were evaluated including 59 female (19 SB, 9 SCI, 17 OW, and 14 CTRL) and 56 male (18 SB, 10 SCI, 8 OW, and 20 CTRL) participants aged 11 to 21 years. METHODS: Aerobic fitness was assessed using a ramp protocol with a magnetically braked arm ergometer. Heart rate and oxygen uptake (VO2) were recorded. Peak isokinetic upper arm and shoulder strength values were determined with a dynamometer. Body composition was estimated using dual energy x-ray absorptiometry (DEXA). Male and female subjects were categorized as overweight if their percent body fat by DEXA exceeded 25% and 30%, respectively. Results were analyzed with an ANOVA using the Bonferroni correction. Significance was accepted at P < 0.05. RESULTS: The percent body fat of both the male and female SB and SCI subjects was significantly higher than CTRL but was not different than OW. In general, the shoulder extension and flexion strength in both the SB and SCI males and females was significantly lower than that of the CTRL and OW. The SCI and SB subjects had significantly reduced aerobic capacity (VO2/kg) compared to the CTRL subjects but were not different than the OW subjects. During the maximal exercise test, the SB and SCI subjects reached exhaustion at significantly lower workloads than the CTRL and OW subjects. CONCLUSIONS: Patients age 11 to 21 years with SB and SCI had reduced aerobic capacity that was associated with being overweight and having reduced upper extremity strength. These data suggest that interventions to increase strength and fitness and to manage weight should be recommended in this population.  (+info)

Behavioral intervention, exercise, and nutrition education to improve health and fitness (BENEfit) in adolescents with mobility impairment due to spinal cord dysfunction. (8/157)

BACKGROUND/OBJECTIVE: Determine the effects of a nutrition education and exercise intervention on the health and fitness of adolescents with mobility impairment due to spinal cord dysfunction from myelomeningocele and spinal cord injury. Subjects participated in a 16-week intervention consisting of a behavioral approach to lifestyle change, exercise, and nutrition education to improve fitness (BENEfit) program. Participants were given a schedule of aerobic and strengthening exercises and attended nutrition education and behavior modification sessions every other week along with their parent(s). SUBJECTS: Twenty adolescents (aged 11-18 years, mean 15.4 +/- 2.2 years) with spinal cord dysfunction. METHODS: Subjects were tested immediately prior to starting and upon completion of the program. Aerobic fitness was measured using a ramp protocol with an arm ergometer. Heart rate and oxygen uptake were measured. Values at anaerobic threshold and maximum oxygen uptake were recorded. Peak isokinetic arm and shoulder strength were determined with a dynamometer. Body composition was estimated with dual-energy x-ray absorptiometry. Serum chemistry included measures of cholesterol, high-density lipoprotein, low-density lipoprotein, and triglycerides. RESULTS: Fourteen individuals completed all testing sessions. There was no significant overall change in weight, body mass index, body mass index z-scores, or serum chemistry. Overall, there was a significant increase in whole body lean tissue without a concomitant increase in whole body fat. Fitness measures revealed a significant increase in maximum power output, work efficiency as measured by the amount of power output produced aerobically, and resting oxygen uptake. Strength measurements revealed a significant increase in shoulder extension strength and a trend towards increased shoulder flexion strength. There were no significant changes in high-density lipoprotein, low-density lipoprotein, total cholesterol, or triglycerides. CONCLUSIONS: The BENEfit program shows promise as a method for improving the health and fitness of adolescents with mobility impairments who are at high risk for obesity and obesity-related health conditions.  (+info)