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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 protocol. 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.

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.

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.

(2006). Agreement in Body Fat Estimates Between a Hand-Held Bioelectrical Impedance Analyzer and Skinfold Thicknesses in African American and Caucasian Adolescents. Research Quarterly for Exercise and Sport: Vol. 77, No. 4, pp. 519-526.

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[middle dot]cm-2) 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.

The purpose of this study was to compare the relationships of anthropometric, bioelectrical impedance analysis (BIA), and near infrared interactance (NIR) measurements with a multiple-component (MC) criterion estimate of body composition derived from body density (D), body water (W), and bone mineral (B) in 48 white adults aged 49-80 yr. Relative errors of predicting the MC criterion from the practical measurements were determined by simple regressions within gender and calculated as the SEE divided by the criterion mean and expressed as a percentage. Relative errors were lowest for the BIA variable, height2/resistance (4.8-5.0%), higher for body mass index and the sum of 10 skinfold thicknesses (7.0-14.5%), and highest for NIR-derived optical density readings at the biceps and the sum of 10 sites (10.8-15.8%). Due to the low relative prediction error for height2/resistance, sex-specific BIA formulas for estimating fat-free mass from D, W, and B (FFM-DWB) were developed. The SEEs for predicting FFM-DWB from BIA, weight, and age were both 1.5 kg in women and men. Because BIA is not limited to ambulatory subjects, it is concluded that BIA may be a particularly useful, practical technique for estimating body composition in older adults.