Lack of neuromuscular origins of adaptation after a long-term stretching program.

CONTEXT: Static stretching is commonly used during the treatment and rehabilitation of orthopedic injuries to increase joint range of motion (ROM) and muscle flexibility. Understanding the physiological adaptations that occur in the neuromuscular system as a result of long-term stretching may provide insight into the mechanisms responsible for changes in flexibility. OBJECTIVE: To examine possible neurological origins and adaptations in the Ia-reflex pathway that allow for increases in flexibility in ankle ROM, by evaluating the reduction in the synaptic transmission of Ia afferents to the motoneuron pool. DESIGN: Repeated-measures, case-controlled study. SETTING: Sports medicine research laboratory. PARTICIPANTS: 40 healthy volunteers with no history of cognitive impairment, neurological impairment, or lower extremity surgery or injury within the previous 12 mo. INTERVENTION: Presynaptic and postsynaptic mechanisms were evaluated with a chronic stretching pro- tocol. Twenty subjects stretched 5 times a wk for 6 wk. All subjects were measured at baseline, 3 wk, and 6 wk. MAIN OUTCOME MEASURES: Ankle-dorsiflexion ROM, Hmax:Mmax, presynaptic inhibition, and disynaptic reciprocal inhibition. RESULTS: Only ROM had a significant interaction between group and time, whereas the other dependent variables did not show significant differences. The experimental group had significantly improved ROM from baseline to 3 wk (mean 6.2 ± 0.9, P < .001), 3 wk to 6 wk (mean 5.0 ± 0.8, P < .001), and baseline to 6 wk (mean 11.2 ±0.9, P < .001). CONCLUSIONS: Ankle dorsiflexion increased by 42.25% after 6 wk of static stretching, but no significant neurological changes resulted at any point of the study, contrasting current literature. Significant neuromuscular origins of adaptation do not exist in the Ia-reflex-pathway components after a long-term stretching program as currently understood. Thus, any increases in flexibility are the result of other factors, potentially mechanical changes or stretch tolerance.

Dietary intake of adults with mental retardation who reside in community settings.

The dietary intake of adults with mental retardation among three different community residential settings was described and compared. Two dietary screeners were administered to 325 adults. The women's Fruit and Vegetable Screener scores from group homes were significantly higher than scores from those with family members and in semi-independent settings. No significant differences were found in dietary intake across residences for men. Overall, 0% to 6% of the participants consumed the recommended 5 or more fruits and vegetables per day, and 15% to 30% consumed the recommended

Development and reproducibility of the bone loading history questionnaire.

PURPOSE: To develop an historical bone loading questionnaire that assesses loads applied to the skeleton using bone loading units and to determine its reproducibility. Additional purposes were to correlate bone loading units with areal bone mineral density (aBMD) and to determine whether low levels of bone loading increase the odds for low aBMD in healthy premenopausal women. METHODS: Premenopausal women (N=80; age: 31+/-7.7 yr) completed the newly developed bone loading history questionnaire (BLHQ) twice within 4-6 wk to establish reproducibility. aBMD (g.cm) of the whole body, lumbar spine (L2-4), and right hip (proximal femur) were assessed with dual energy x-ray absorptiometry (DXA) in the women. RESULTS: The questionnaire demonstrated good test-retest reliability in premenopausal women using intraclass correlation coefficients (spine r=0.89, P<0.001; hip r=0.92, P<0.001). Total spine bone loading exposure (r=0.338; P=0.002) and hip bone loading exposure (r=0.317; P=0.004) were significantly and independently correlated with femoral neck aBMD, after adjusting for BMI. Logistic regression analyses revealed increased odds for low femoral neck aBMD among those in the lowest tertile for recent hip bone loading exposure after adjusting for older ages, oral contraceptive use, low calcium intake, and an overweight BMI (OR=3.62; CI=1.09-11.94; P=0.035). CONCLUSION: Historical bone loading activity can be reliably assessed and is moderately associated with femoral neck aBMD. This questionnaire could help to identify women with low femoral neck aBMD prior to menopause.

Exercise training preserves endothelium-dependent relaxation in brachial arteries from hyperlipidemic pigs.

We tested the hypothesis that exercise training (Ex) attenuates the effects of hyperlipidemia on endothelial function by enhancing NO-mediated vasorelaxation in porcine brachial (Br) arteries. Adult female pigs were fed a normal-fat (NF) or high-fat (HF) diet for 20 wk. Four weeks after initiation of the diet, pigs underwent Ex or remained sedentary (Sed) for 16 wk. Relaxation to ACh was impaired by HF (P = 0.03). The combination of HF and Sed impaired ACh-induced relaxation more than HF or Sed alone (P = 0.0002). Relaxation to high doses of bradykinin (BK) was impaired by HF (P = 0.0002). Ex significantly improved ACh-induced relaxation (P = 0.01) and tended to improve relaxation to BK (P = 0.38). To determine the mechanism(s) by which HF and Ex affected relaxation to ACh and BK, relaxation was assessed in the presence of N(G)-nitro-l-arginine methyl ester (l-NAME; to inhibit NO synthase), indomethacin (Indo; to inhibit cyclooxygenase), or l-NAME + Indo. In the presence of l-NAME, Indo, or l-NAME + Indo, ACh-induced relaxation was no longer different between HF and NF arteries; however, relaxation remained greater in Ex than in Sed arteries. In the presence of l-NAME or Indo, BK-induced relaxation was no longer altered by HF but was enhanced by Ex. In the presence of l-NAME + Indo, BK-induced relaxation was enhanced by HF and Ex. These data indicate that hyperlipidemia impairs ACh- and BK-induced relaxation by impairing NO- and PGI(2)-mediated relaxation. Ex attenuates the effects of HF by enhancing a vasodilator mechanism independent of NO and PGI(2).

Estimation of body fat from skinfold thicknesses in middle-aged and older men and women: A multiple component approach.

The relationship of skinfold thicknesses and body density to body fatness was assessed, and skinfold prediction equations were developed for the estimation of body fatness determined from measures of body density, total body water, and bone mineral in a sample of 91 males and 116 females aged 34-84 years. For a given skinfold thickness, adjustment for individual deviations in the water and bone mineral fractions of the fat-free body assumed constant by traditional body composition models resulted in absolute reductions in overstimates of body fatness from 4.5 to 1.9% in females and from 2.8 to 1.7% in males for every 15 year increase in age. Percentage fat from density, water, and bone was estimated from skinfold thicknesses with SEEs of 2.9% in males and 3.8% in females. When compared to percentage fat from our multicomponent-derived criterion, percentage fat from body density and a two-component model resulted in individual errors ranging from underestimates of 5.6% fat to overestimates of 14.0% fat. The multicomponent prediction equations presented herein should produce more valid estimates of body composition in middle-aged and older men and women than equations based on two-component models. © 1992 Wiley-Liss, Inc.

Differences in cardiovascular disease risk between nondiabetic adults with mental retardation with and without Down syndrome.

A reduced expression of the insulin resistance syndrome, a common neuroendocrine disorder underlying atherosclerosis, may play a role in reduced atherosclerosis in adults with Down syndrome. We compared selected components of the insulin resistance syndrome between 75 adults with Down syndrome and 70 with mental retardation due to other causes. After adjusting for age differences, residence, cigarette smoking, and medication use, women with Down syndrome had lower fasting plasma glucose and lower systolic blood pressure than comparison women. Men with Down syndrome had lower systolic and diastolic blood pressure than comparison men. Results suggest that women with Down syndrome may be less likely to express the insulin resistance syndrome, and men and women with Down syndrome may possess fewer atherosclerotic risk factors than the comparison groups.

Physical activity, dietary intake, and the insulin resistance syndrome in nondiabetic adults with mental retardation.

The association between physical activity, dietary behaviors, and elevated cardiovascular disease risk factor components of the insulin resistance syndrome in adults with mental retardation was identified. Established clinical cutoff points were used to identify 145 participants with mild mental retardation and hyperinsulinemia, borderline high triglycerides, low high-density lipoprotein cholesterol, hypertension, and abdominal obesity. Odds ratios were calculated from logistic regression analysis. Those who participated in more frequent bouts of physical activity or who consumed lower dietary fat intakes were approximately one third as likely to have hyperinsulinemia and abdominal obesity compared to those who participated in less frequent physical activity or who consumed higher fat intakes, suggesting that these behaviors are protective against elevated components of the insulin resistance syndrome.

Physical activity differences by birthplace and sex in youth of Mexican heritage.

BACKGROUND: One of the goals of Healthy People 2020 is to increase physical activity (PA) and reduce health disparities among different racial and ethnic segments of the U.S. population. Few studies have been conducted to examine PA differences by birthplace and sex in youth of Mexican heritage. METHODS: Participants were 101 youth (43 boys, 58 girls, 59% U.S.-born, 41% Mexico-born) who wore a sealed New Lifestyles NL-1000 pedometer for 7 consecutive days. RESULTS: Mexico-born youth took more steps, on average, than their U.S.-born counterparts (P = .038). However, moderate-to-vigorous intensity (MVI) time did not differ between Mexico- and U.S.-born youth (P = .146). By contrast to birthplace, sex-related differences were more consistent, as boys took more steps (P = .005) and accumulated more MVI time (P = .043) than girls. Only 4% of our sample met either one or both of the PA recommendations. CONCLUSIONS: We conclude that PA may differ by birthplace and by sex in youth of Mexican heritage, as U.S.-born girls were the least active segment of our sample. Culturally sensitive interventions to increase daily PA must become a higher public health priority for youth of Mexican heritage, in particular, for U.S.-born girls of Mexican heritage.

Percent body fat and chronic disease risk factors in U.S. children and youth.

BACKGROUND: The dramatic increase in pediatric obesity has renewed interest in accurate methods and screening indexes for identifying at-risk children and youth. Whether age-specific standards are needed is a factor that remains uncertain. PURPOSE: This study was designed to describe the age-specific fatness-risk factor relationship in boys and girls across a wide age range. METHODS: Data were from 12,279 white, black, and Mexican-American children and adolescents from the National Health and Nutritional Examination Surveys (NHANES) III (1998-1994) and IV (1999-2004). Children were grouped based on percent fat, estimated from subscapular and triceps skinfolds, and the age-specific relationships between percent fat and chronic disease risk factors (e.g., blood pressure, lipids and lipoprotein levels, glucose, insulin, and circulating C-reactive protein levels) were described in boys and girls, aged 6-18 years. RESULTS: Percent fat was significantly related to risk factor levels. At higher levels of percent fat, the prevalence of adverse cardiovascular disease risk factors was higher, particularly above 20% fat in boys and above 30% fat in girls. In boys and girls, the interaction term age by percent fat was a significant predictor of risk factors, whereas the percent fat by race interaction term was nonsignificant. CONCLUSIONS: The results demonstrate a strong relationship between chronic disease risk factors and percent fat in children and youth that varies by age in boys and girls.

Waist circumference, pedometer placement, and step-counting accuracy in youth.

This study examined whether differences in waist circumference (WC) and pedometer placement (anterior vs. midaxillary vs. posterior) affect the agreement between pedometer and observed steps during treadmill and self-paced walking. Participants included 19 pairs of youth (9- 15-years-old) who were matched for sex, race, and height and stratified by WC (high WC: HWC; low WC: LWC). Participants performed 3-min treadmill-walking trials at speeds of 59, 72, and 86 m x min(-1) and a 400-m self-paced walking trial on level ground. Bland-Altman plots were used to assess the agreement between pedometer and observed steps of spring-levered pedometers by WC, pedometer placement, and walking speed. In the HWC group, the posterior pedometer placement consistently agreed most closely with observed steps at all treadmill speeds and during self-paced walking. In the LWC group, no single pedometer placement consistently agreed most closely with observed steps at all treadmill speeds and during self-paced walking. We conclude that a posterior pedometer placement improves step-count accuracy in most youth with an HWC at a range of walking speeds on level ground.

Fitness, inflammation, and the metabolic syndrome in men with paraplegia.

OBJECTIVE: To determine the relations among peak aerobic capacity, physical activity, functional ability, components of the metabolic syndrome (high-density lipoprotein cholesterol [HDL-C], triglycerides [TG], glucose, insulin, abdominal obesity, high blood pressure), and inflammatory factors (interleukin-6 [IL-6], C-reactive protein [CRP]) in men with paraplegia. DESIGN: Cross-sectional exploratory design. SETTING: University research laboratory. PARTICIPANTS: Twenty-two men (age, 39+/-9y; duration of injury, 17+/-9y; level of injury, T2-L2) with functionally complete paraplegia volunteered to participate. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Peak aerobic capacity was measured using a graded peak exercise test with an arm ergometer, and physical activity was assessed by the Physical Activity and Disability Scale. Functional ability was assessed by the Self-Report Functional Measure. Circulating glucose, insulin, HDL-C, TG, total cholesterol, IL-6, and CRP levels were determined by specific enzyme or immunologic assays. Body fat was determined by dual-energy x-ray absorptiometry, and central obesity was estimated from abdominal sagittal diameters. RESULTS: Lower peak aerobic capacities were associated with lower HDL-C and lower physical activity levels ( P <.014). Lower physical activity levels were associated with higher fasting glucose, lower HDL-C level, and larger abdominal sagittal diameters ( P <.036). Larger abdominal sagittal diameters were associated with higher fasting glucose, higher fasting and postload insulin, lower HDL-C, higher TG, and higher CRP levels ( P <.05). CONCLUSIONS: Diet and exercise trials are needed to determine the efficacy and effectiveness of lifestyle interventions aimed at slowing the progression of the metabolic syndrome in people with spinal cord injury.

Prevalence of physical inactivity and recommended physical activity in community-based adults with mental retardation.

Little information has been reported on the leisure time physical activity (LTPA) habits of adults with mental retardation. Prevalence of physical inactivity and recommended LTPA of adults with mild to moderate mental retardation who live in community settings was described. Adults with mental retardation (76 men, 74 women) reported their physical activity habits. Overall, men and women who resided in community settings were similarly inactive, with 47% to 51% of individuals participating in little to no LTPA. Forty-two to 47% of them reported participation in moderate to vigorous LTPA five or more times per week. Limitations to quantifying physical activity through questionnaire process is discussed and development and implementation of programs designed to increase physical activity levels recommended.

Physical activity, body fat, and serum C-reactive protein in postmenopausal women with and without hormone replacement.

The objective was to determine whether higher physical activity is associated with lower serum C-reactive protein (CRP), independent of oral hormone replacement therapy (HRT) status and body fatness, in 133 postmenopausal women using a cross-sectional exploratory design at a university research laboratory. The subjects were 133 postmenopausal women, age 50-73 years, with no evidence of coronary artery disease or diabetes. The main outcome measures were: serum CRP, physical activity as measured by Stanford 7-day activity recall, body fat (both total and regional) as measured by dual energy X-ray absorptiometry (DXA), and anthropometry (waist and hip circumference). Secondary outcome measures included fasting plasma glucose and insulin as well as fasting serum triglycerides, total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol. Higher physical activity energy expenditures were significantly associated with lower serum CRP levels (r = -0.18, P = 0.041), independent of oral HRT use, age, smoking behavior, alcohol consumption, aspirin use, and statin use. However, in the complete multivariate model, which included body fat, older ages (P = 0.047), greater trunk fat masses (P < 0.001), any oral HRT use (P < 0.001), and unopposed oral estrogen use (P = 0.012) were the sole independent predictors of higher serum CRP levels. The complete multivariate model accounted for 58% of the variance in serum CRP. We conclude that the association between higher physical activity and lower serum CRP levels is dependent on the lower body fat of the more active women, yet independent of oral HRT use. Future intervention trials should determine whether diet- and exercise-related reductions in body fat may be effective ways to diminish the proinflammatory effects of oral HRT in postmenopausal women.