Receiver operating characteristic analysis of body mass index, triceps skinfold thickness, and arm girth for obesity screening in children and adolescents.
BACKGROUND: Valid and practical methods based on health-related criteria for obesity screening in children and adolescents are not available. Arbitrarily defined body mass index (BMI) cutoffs have been proposed to select adolescents at high risk of developing obesity in adulthood. OBJECTIVE: We assessed the usefulness of BMI, triceps skinfold thickness, and upper arm girth for screening for obesity by using a health-related definition of obesity (> or = 25% body fat in boys and > or = 30% body fat in girls) and a criterion method (dual-energy X-ray absorptiometry) that estimates percentage fat without the potential bias associated with other methods in adolescents. DESIGN: This was a cross-sectional study of Portuguese boys (n = 165) and girls (n = 163) aged 10-15 y. Nonparametric receiver operating characteristic (ROC) analysis was used to define the best tradeoff between true-positive and false-positive rates. RESULTS: True-positive rates ranged from 67% to 87% and from 50% to 100% in girls and boys, respectively, and false-positive rates ranged from 0% to 19% and from 5% to 26%, respectively. For children aged 10-11 y, the areas under the curves (AUCs) for ROCs, an index of diagnostic accuracy, were close to 1.0, suggesting very good accuracy. For older boys and girls, AUCs for triceps skinfold thickness were similar to or greater than AUCs for BMI and upper arm girth. CONCLUSIONS: The results suggest that triceps skinfold thickness gives the best results for obesity screening in adolescents aged 10-15 y. BMI and upper arm girth were reasonable alternatives, except in 14-15-y-old boys, in whom both indexes were only marginally able to discriminate obesity. (+info)
Group selection, altruism, reinforcement, and throwing in human evolution.
Evolution of altruism by group selection involves sacrifice of some individuals, not to the "group as a whole," but to other individuals in the group. Deme-group selection may establish strictly altruistic genes in a population, but only under limited conditions, and perhaps never among vertebrates, among which apparently altruistic behaviors may always potentially benefit the altruists. Responsive-group selection is a more effective mode of evolution of altruism, conspicuous in man. Evolutionary reinforcement increases the force of selection of advantageous behaviors, including altruistic ones, by making them pleasant or rewarding. It is probably involved also in ecological habitat selection, and may be the source of many human emotions, including esthetic ones. Throwing (of stones and weapons) exemplifies both the possible importance of a difficult-to-measure evolutionary factor and the role of reinforcement; in human evolution throwing may have been decisive in food-getting and fighting, in shifting emphasis from brute force to skill, and in inducing evolution of a brain able to handle three-body geometric problems precisely and thus preadapted for more complex functions. (+info)
Pixel T2 distribution in functional magnetic resonance images of muscle.
Increases in skeletal muscle (1)H-NMR transverse relaxation time (T2) observed by magnetic resonance imaging have been used to map whole muscle activity during exercise. Some studies further suggest that intramuscular variations in T2 after exercise can be used to map activity on a pixel-by-pixel basis by defining an active T2 threshold and counting pixels that exceed the threshold as "active muscle." This implies that motor units are nonrandomly distributed across the muscle and, therefore, that the distribution of pixel T2 values ought to be substantially broader after moderate exercise than at rest or after more intense exercise, since moderate-intensity exercise should recruit some motor units, and hence some pixels, but not others. This study examined the distribution of pixel T2 values in three muscles (quadriceps, anterior tibialis, and biceps/brachialis) of healthy subjects (5 men and 2 women, 18-46 yr old) at rest, after exercise to fatigue (50% 1 repetition maximum at 20/min to failure = Max), and at 1/2Max (25% 1 repetition maximum, same number of repetitions as Max). Although for each muscle there was a linear relationship between exercise intensity and mean pixel T2, there was no significant difference in the variance of pixel T2 between 1/2Max and Max exercise. There was a modest (10-43%) increase in variance of pixel T2 after both exercises compared with rest, but this was consistent with a Monte Carlo simulation of muscle activity that assumed a random distribution of motor unit territories across the muscle and a random distribution of muscle cells within each motor unit's territory. In addition, 40% of the pixel-to-pixel muscle T2 variations were shown to be due to imaging noise. The results indicate that magnetic resonance imaging T2 cannot reliably map active muscle on a pixel-by-pixel basis in normal subjects. (+info)
MR measurements of muscle damage and adaptation after eccentric exercise.
The purposes of this study were, first, to clarify the long-term pattern of T2 relaxation times and muscle volume changes in human skeletal muscle after intense eccentric exercise and, second, to determine whether the T2 response exhibits an adaptation to repeated bouts. Six young adult men performed two bouts of eccentric biceps curls (5 sets of 10 at 110% of the 1-repetition concentric maximum) separated by 8 wk. Blood samples, soreness ratings, and T2-weighted axial fast spin-echo magnetic resonance images of the upper arm were obtained immediately before and after each bout; at 1, 2, 4, 7, 14, 21, and 56 days after bout 1; and at 2, 4, 7 and 14 days after bout 2. Resting muscle T2 [27.6 +/- 0.2 (SE) ms] increased immediately postexercise by 8 +/- 1 ms after both bouts. T2 peaked 7 days after bout 1 at 47 +/- 4 ms and remained elevated by 2.5 ms at 56 days. T2 peaked lower (37 +/- 4 ms) and earlier (2-4 days) after bout 2, suggesting an adaptation of the T2 response. Peak serum creatine kinase values, pain ratings, and flexor muscle swelling were also significantly lower after the second bout (P < 0.05). Total volume of the imaged arm region increased transiently after bout 1 but returned to preexercise values within 2 wk. The exercised flexor compartment swelled by over 40%, but after 2 wk it reverted to a volume 10% smaller than that before exercise and maintained this volume loss through 8 wk, consistent with partial or total destruction of a small subpopulation of muscle fibers. (+info)
Haptic stabilization of posture: changes in arm proprioception and cutaneous feedback for different arm orientations.
Postural sway during quiet stance is attenuated by actively maintained contact of the index finger with a stationary surface, even if the level of applied force (<1 N) cannot provide mechanical stabilization. In this situation, changes in force level at the fingertip lead changes in center of foot pressure by approximately 250 ms. These and related findings indicate that stimulation of the fingertip combined with proprioceptive information about the hand and arm can serve as an active sensor of body position relative to the point of contact. A geometric analysis of the relationship between hand and torso displacement during body sway led to the prediction that arm and hand proprioceptive and finger somatosensory information about body sway would be maximized with finger contact in the plane of body sway. Therefore, the most postural stabilization should be possible with such contact. To test this analysis, subjects touched a laterally versus anteriorly placed surface while in each of two stances: the heel-to-toe tandem Romberg stance that reduces medial-lateral stability and the heel-to-heel, toes-outward, knees-bent, "duck stance" that reduces fore-aft stability. Postural sway was always least with finger contact in the unstable plane: for the tandem stance, lateral fingertip contact was significantly more effective than frontal contact, and, for the duck stance, frontal contact was more effective than lateral fingertip contact. Force changes at the fingertip led changes in center of pressure of the feet by approximately 250 ms for both fingertip contact locations for both test stances. These results support the geometric analysis, which showed that 1) arm joint angles change by the largest amount when fingertip contact is maintained in the plane of greatest sway, and 2) the somatosensory cues at the fingertip provide both direction and amplitude information about sway when the finger is contacting a surface in the unstable plane. (+info)
The normal range for inter-arm differences in blood pressure.
OBJECTIVE: to establish the mean and normal range for the difference in simultaneous systolic and diastolic blood pressure measurements between the right and left arm. SUBJECTS: 462 subjects, age range 20-89 years, in sinus rhythm and with no history of stroke, 98 of whom had a history of cardiovascular disease or were taking vasoactive medication. METHODS: four simultaneous recordings of blood pressure in both arms were made using two automated sphygmomanometers with the subject supine after resting for 10 min. RESULTS: inter-arm systolic and diastolic blood pressure differences show a near normal distribution of values. Some individuals had clinically important differences in systolic and diastolic blood pressure between their arms. The magnitude of these differences was not related to the mean baseline blood pressure. Linear regression analysis did not demonstrate any significant relationship between inter-arm systolic or diastolic blood pressure difference and age in patients of either sex. For systolic blood pressure the mean difference between the right and left arm was 1.1 mmHg and the normal range was -9 mmHg to 11 mmHg. For diastolic blood pressure the mean difference was 0 mmHg and the normal range -10 mmHg to 10 mmHg. CONCLUSION: the frequency of significant inter-arm systolic and diastolic blood pressure differences suggests that the blood pressure should be taken in both arms at the initial consultation. At subsequent visits, the arm in which measurements are taken should be recorded in the case notes. The higher of the two readings should be used to guide further management decisions. (+info)
Technical note: the humeral canal approach to the brachial plexus.
Many variations to the axillary approach to the brachial plexus have been described. However, the success rate varies depending on the approach used and on the definition of success. Recent work describes a new approach to regional anaesthesia of the upper limb at the humeral/brachial canal using selective stimulation of the major nerves. This report outlines initial experience with this block, describing the technique and results in 50 patients undergoing hand and forearm surgery. All patients were assessed for completeness of motor and sensory block. The overall success rate was 90 percent. Motor block was present in 80 percent of patients. Completion of the block was necessary in 5 patients. Two patients required general anaesthesia. The preponderance of ulnar deficiencies agrees with previously published data on this technique. No complications were described. Initial experience confirms the high success rate described using the Dupre technique. This technically straightforward approach with minimal complications can be recommended for regional anaesthesia of the upper limb. (+info)
Abnormal central integration of a dual somatosensory input in dystonia. Evidence for sensory overflow.
Several observations suggest impaired central sensory integration in dystonia. We studied median and ulnar nerve somatosensory evoked potentials (SEPs) in 10 patients who had dystonia involving at least one upper limb (six had generalized, two had segmental and two had focal dystonia) and in 10 normal subjects. We compared the amplitude of spinal N13, brainstem P14, parietal N20 and P27 and frontal N30 SEPs obtained by stimulating the median and ulnar nerves simultaneously (MU), the amplitude value being obtained from the arithmetic sum of the SEPs elicited by stimulating the same nerves separately (M + U). Throughout the somatosensory system, the MU : (M + U) ratio indicates the interaction between afferent inputs from the two peripheral nerves. No significant difference was found between SEP amplitudes and latencies for individually stimulated median and ulnar nerves in dystonic patients and normal subjects, but recordings in patients yielded a significantly higher percentage ratio [MU : (M + U)x100] for spinal N13 brainstem P14 and cortical N20, P27 and N30 components. The SEP ratio of central components obtained in response to stimulation of the digital nerves of the third and fifth fingers was also higher in patients than in controls but the difference did not reach a significant level. The possible contribution of subliminal activation was ruled out by recording the ratio of SEPs in six normal subjects during voluntary contraction. This voluntary contraction did not change the ratio of SEP suppression. These findings suggest that the inhibitory integration of afferent inputs, mainly proprioceptive inputs, coming from adjacent body parts is abnormal in dystonia. This inefficient integration, which is probably due to altered surrounding inhibition, could give rise to an abnormal motor output and might therefore contribute to the motor impairment present in dystonia. (+info)