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Effect of Long-Term Vigorous Physical Activity on Healthy Adult Knee Cartilage
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Introduction: Whether participation in long-term vigorous physical activity affects knee cartilage is unclear and may depend on the state of knee health. We examined the association between vigorous physical activity during a decade and the subsequent changes in knee cartilage among healthy adults. We then examined whether this effect differed in those with and without bone marrow lesions (BMLs), as an indicator of preclinical joint damage. Methods: A total of 297 healthy adults age 50–79 yr were recruited. Physical activity was assessed via questionnaire at baseline (1990–1994) and at follow-up (2003–2004), and a score for persistence of vigorous physical activity score was determined. Each subject underwent knee magnetic resonance imaging in 2003–2004 and in 2006–2007. Cartilage volume, defects, and BMLs were measured using validated methods. Results: Persistent participation in vigorous physical activity was associated with worsening of medial knee cartilage defects (odds ratio (OR) = 1.5, 95% confidence interval (CI) = 1.0–2.3). In the subgroup with BMLs, but not in those without BML, persistent vigorous physical activity was associated with a significant worsening of medial knee cartilage defects (OR = 3.4, 95% CI = 1.0–16.5) and a trend toward an increased rate of loss of medial knee cartilage volume (21.6 mm3·yr−1, 95% CI = −0.4 to 43.6). Conclusions: In knees with BMLs, persistent participation in vigorous physical activity was associated with adverse cartilage changes in the medial compartment. This suggests that the long-term effects of vigorous physical activity may depend on the preexisting health of the joint.
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Is High-Impact Sports Participation Associated with Bowlegs in Adolescent Boys?
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The purpose of this study was to investigate whether the participation in load bearing sports is associated with significant knee alignment adaptations in adolescent boys, which might cause a higher risk for the development of knee osteoarthritis in later life. Methods: Five hundred twenty-one healthy boys (from 7 to 18 yr), selected from local primary and secondary schools, participated in the study. Two hundred sixty-five of them practiced competitive sports (track and field, field hockey, basketball, volleyball, tennis, badminton, and squash) for at least 3 h·wk−1. The other remaining 256 boys did not practice any kind of sports. Genu varum/valgum was determined by measuring the intercondylar (IC) and intermalleolar (IM) distance with the subjects in a relaxed erect standing position. The IC and/or IM distance was measured using a caliper. Both measurements were combined to one parameter: the IC–IM distance. A one-way ANOVA was performed to analyze differences between the different age groups within the sporting and nonsporting boys separately. For each age group, the IC–IM distances of the sporting and nonsporting boys were compared by ANOVA with post hoc Bonferroni corrections. Results: A comparison between the sporting and nonsporting boys showed that the sporting boys had a significantly higher degree of genu varum from 13 to 15 yr or older (P = 0.01). Conclusions: From the results of this study, it can be concluded that practicing load bearing sports in general is associated with the same knee varus alignment in adolescent boys as previously has been indicated in intense soccer-playing adolescents.
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Prevalence of Allergy and Upper Respiratory Tract Symptoms in Runners of the London Marathon
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Background: The prevalence of self-reported upper respiratory tract (URT) symptoms in athletes has been traditionally associated with opportunistic infection during the temporal suppression of immune function after prolonged exercise. There is little evidence for this, and a competing noninfectious hypothesis has been proposed, whereby the exercise-induced immune system modulations favor the development of atopy and allergic disease, which manifests as URT symptoms. The aim of this study was to examine the association between allergy and URT symptoms in runners after an endurance running event. Methods: Two hundred eight runners from the 2010 London Marathon completed the validated Allergy Questionnaire for Athletes (AQUA) and had serum analyzed for total and specific immunoglobulin E response to common inhalant allergens. Participants who completed the marathon and nonrunning controls who lived in the same household were asked to complete a diary on URT symptoms. Results: Forty percent of runners had allergy as defined by both a positive AQUA and elevated specific immunoglobulin E. Forty-seven percent of runners experienced URT symptoms after the marathon. A positive AQUA was a significant predictor of postmarathon URT symptoms in runners. Only 19% of nonrunning controls reported symptoms. Conclusions: The prevalence of allergy in recreational marathon runners was similar to that in elite athletes and higher than that in the general population. There was a strong association between a positive AQUA and URT symptoms. The low proportion of households in which both runners and nonrunners were symptomatic suggests that the nature of symptoms may be allergic or inflammatory based rather than infectious. Allergy is a treatable condition, and its potential effect on performance and health may be avoided by accurate clinical diagnosis and management. Both athletes’ and coaches’ awareness of the potential implications of poorly managed allergy needs to be raised.
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Exercise Training Post-MI Favorably Modifies Heart Extracellular Matrix in the Rat
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: In order to assess the effect of daily exercise on extracellular matrix remodeling in the heart after myocardial infarction (MI), we measured collagen concentration (%COL) and nonreducible collagen cross-linking (hydroxylysylpyridinoline, HP) in the right ventricle (RV), and regionally within the infarcted (INF) and viable left ventricular free wall (LVF) and septum (LVS), using a rodent MI training model. Methods: Infarcts (19%–24% of LV) were surgically induced in adult rats that were assigned to either trained (MI-TR) or sedentary (MI-SED) groups and compared to sham–surgery sedentary controls (SHAM). Results: In LVF, 10 wk of treadmill running had no effect on the increase (P < 0.001) in %COL seen with MI (MI-SED = 7.14% ± 0.15%, MI-TR = 7.61% ± 0.19%, SHAM = 3.55% ± 0.19%). However, it normalized the increase (P < 0.05) in HP cross-linking (MI-SED = 0.43 ± 0.02, MI-TR = 0.27 ± 0.03, SHAM = 0.30 ± 0.04 mol HP·mol−1 collagen). The INF scar in MI-SED rats showed a sevenfold increase in %COL (P < 0.001) compared to SHAM LVF myocardium, an increase that was attenuated by training (MI-SED = 26% ± 1% vs MI-TR = 21% ± 2%; P < 0.05). However, training had no effect on MI-induced increases in cross-linking in the INF scar (1.01 ± 0.22 vs 0.84 ± 0.14 mol HP·mol−1 collagen). In LVS, although a small but significant increase in %COL was seen in both MI groups, HP cross-linking was unaltered compared to SHAM rats. Training also normalized the increase observed in cross-linking in RV after MI. Conclusions: Because increased HP cross-linking in the heart is associated with decreased chamber compliance, these findings may help to explain the improved heart function seen after daily exercise in cardiac rehabilitation patients.
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Effects of Hypoxic Living and Training on Gene Expression in an Obese Rat Model
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The study’s purpose was to determine in a rat obesity model the effects of normoxic training, sedentary hypoxic living, or hypoxic living plus training on the skeletal muscle messenger RNA (mRNA) levels of 14 genes involved in oxygen sensing (hypoxia-inducible factor 1α, vascular endothelial growth factor, myoglobin), glucose metabolism (glucose transporter 4, muscle phosphofructokinase), mitochondrial biogenesis (peroxisome proliferator–activated receptor γ coactivator 1-α, nuclear respiratory factor 1) and function (citrate synthase, mitochondrial-encoded cytochrome oxidase subunit 1), pH regulation (monocarboxylate transporter 1, carbonic anhydrase 3), and antioxidant defense (manganese superoxide dismutase, copper/zinc superoxide dismutase, glutathione S-transferase pi). Methods: One hundred thirty male 3-wk-old Sprague–Dawley rats were fed a high-fat diet (4100 kcal·kg−1) for 3 months (all reaching a final weight >415 g) and then randomly assigned to the following groups (n = 10 per group): C (control, 2 d of sedentary living in normoxic conditions), TN1–TN4 (1–4 wk of normoxic treadmill training), SH1–SH4 (1–4 wk of sedentary hypoxic living (13.6% O2)), or TH1–TH4 (1–4 wk of hypoxic living (13.6% O2) + hypoxic treadmill training). Individual mRNA levels recorded for TN1–TN4, SH1–SH4, and TH1–TH4 were expressed relative to the mean obtained in C for each gene. Results: Through a two-way ANOVA, a significant interaction (treatment × treatment duration) effect was detected on expression levels of mRNAs for hypoxia-inducible factor 1α, vascular endothelial growth factor, myoglobin, nuclear respiratory factor 1, citrate synthase, carbonic anhydrase 3, monocarboxylate transporter 1, copper/zinc superoxide dismutase, glutathione S-transferase pi, and manganese superoxide dismutase. Expression levels were overall highest when training and living under hypoxia, usually after 3 wk (TH3), i.e., 79%–99% higher than the lowest values (usually corresponding to TN2) and 15.5%–53.9% higher than the second highest values (usually TH4). Normoxic training elicited no greater response than hypoxic sedentary living. Conclusions: In our obese rat model, hypoxic living conditions, especially if accompanied by hypoxic exercise training, can lead to health-related molecular adaptations at the skeletal muscle level.
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Differential Effects of Acute and Chronic Exercise on Human Neutrophil Functions
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Exercise effects on immunity are highly dependent on exercise intensity, duration, and frequency. Purpose: Because neutrophils play an essential role in innate immunity, we investigated whether acute severe exercise (ASE) and chronic moderate exercise (CME) differentially regulate human neutrophil functions. Methods: Thirteen sedentary young males underwent an initial ASE (pedaling on a bicycle ergometer with increasing loads until exhaustion), and they were subsequently divided into exercise (n = 8) and control groups (n = 5). The exercise group underwent 2 months of CME (pedaling on the ergometer at a moderate intensity for 30 min each day) followed by 2 months of detraining. The control group was abstained from regular exercise during these 4 months. Additional ASE paradigms were performed every month (in the exercise group) or every 2 months (in the control group). Neutrophils were isolated from blood specimens drawn at rest and immediately after each ASE for assaying chemotaxis, phagocytosis, citrate synthase activity, and mitochondrial membrane potential (ΔΨm). Additional blood specimens were drawn from the exercise group before and immediately after the first bout of CME to determine the acute moderate exercise (AME) effects on neutrophil functions. Results: The study’s results are the following: 1) the initial ASE enhanced chemotaxis and induced ΔΨm depolarization; 2) AME did not influence any measured parameter in neutrophils; 3) CME increased chemotaxis, phagocytosis, citrate synthase activity, and ΔΨm; 4) the CME effects remained after detraining except phagocytosis; and 5) the ASE effects disappeared after CME and were partially restored after detraining. Conclusions: ASE and CME differentially affected neutrophil functions, whereas AME was ineffective. Moreover, the fact that CME improves neutrophil functions may partially explain why physically active subjects have a low risk of infection.
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Effect of Exercise Training Modality on C-Reactive Protein in Type 2 Diabetes
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: Type 2 diabetes is associated with increased risk of cardiovascular disease and elevated C-reactive protein (CRP) levels. Aerobic exercise training has been shown to improve CRP; however, there are limited data evaluating the effect of other exercise training modalities (aerobic, resistance, or combination training) in individuals with type 2 diabetes. Methods: Participants (n = 204) were randomized to an aerobic exercise (aerobic), resistance exercise (resistance), or a combination of both (combination) for 9 months. CRP was evaluated at baseline and at follow-up. Results: Baseline CRP was correlated with fat mass, waist circumference, body mass index, and V˙O2peak (P < 0.05). CRP was not reduced after aerobic (0.16 mg·L−1, 95% confidence interval (CI) = −1.0 to 1.3 mg·L−1), resistance (−0.03 mg·L−1, 95% CI = −1.1 to 1.0 mg·L−1), or combination (−0.49 mg·L−1, 95% CI = −1.5 to 0.6 mg·L−1) training compared to control (0.35 mg·L−1, 95% CI = −1.0 to 1.7 mg·L−1). Changes in fasting glucose (r = 0.20, P = 0.009), glycated hemoglobin (HbA1c) (r = 0.21, P = 0.005), and fat mass (r = 0.19, P = 0.016) were associated with reductions in CRP but not with change in fitness or weight (P > 0.05). There were significant trends observed for CRP among tertiles of change in HbA1c (P = 0.009) and body fat (P = 0.040). Conclusions: Aerobic, resistance, or a combination of both did not reduce CRP levels in individuals with type 2 diabetes. However, exercise-related improvements in HbA1c, fasting glucose, and fat mass were associated with reductions in CRP.
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Hypoxia Augments Oscillatory Blood Flow in Brachial Artery during Leg Cycling
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The purpose of the present study was to elucidate changes in mean blood flow and oscillatory blood flow patterns to the inactive limb during leg cycle exercise in hypoxia. We hypothesized that oscillatory antegrade and retrograde blood flows to the nonworking limb would increase during incremental cycle exercise under hypoxic condition. Methods: Eight males participated in this study. Two maximal exercise tests were conducted on a semirecumbent cycle ergometer while subjects inhaled a normoxic (inspired oxygen fraction [FIO2] = 0.21) or hypoxic gas mixture (FIO2 = 0.12). The exercise began at an initial power output of 30 W, and workload was increased by 30 W every 2 min until exhaustion. Brachial artery blood velocity and diameter were simultaneously recorded during exercise using Doppler ultrasonography. Blood flow was calculated using the cross-sectional area of the brachial artery and time-averaged mean blood velocity. Results: Mean blood flow decreased until 120 W in both trials (P < 0.05), and the magnitude of the reduction in mean blood flow was not different between two trials. However, the extent of changes in antegrade and retrograde blood flows during submaximal exercise in hypoxia was greater than that in normoxia (normoxia vs hypoxia: antegrade blood flow at 120 W = 145.4 ± 10.3 vs 172.4 ± 9.0 mL·min−1 and retrograde blood flow at 120 W = −89.1 ± 4.9 vs −118.1 ± 6.2 mL·min−1, P < 0.05). Conclusions: These results indicate that hypoxia has a significant effect on oscillatory antegrade/retrograde blood flow patterns in nonworking limb during cycling exercise.
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Oxygen Cost of Breathing and Breathlessness during Exercise in Nonobese Women and Men
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Introduction: Although it has been reported that the work of breathing may be higher in women, inconsistencies among studies leaves this important question unresolved. Also, the association between the oxygen cost of breathing and rating of perceived breathlessness (RPB) during exercise has not been examined between women and men. Purpose: This study aimed to measure oxygen cost of breathing during eucapnic voluntary hyperpnea and RPB (Borg 0–10 scale) during 6 min of constant work rate cycling at 60 and 90 W, respectively, in healthy, nonobese women and men. Methods: A total of 9 women (27 yr, body mass index = 21 kg·m−2) and 10 men (29 yr, body mass index = 25 kg·m−2) participated. All subjects underwent pulmonary function testing, exercise cycling, and determination of oxygen cost of breathing during eucapnic voluntary hyperpnea. Oxygen cost of breathing was obtained from the slope of the oxygen uptake (mL·min−1) and ventilation (L·min−1) relationship. RPB and cardiorespiratory measures were collected during minute 6 of the exercise. Data were analyzed by independent t-test and regression analysis. Results: Age and pulmonary function were similar between the nonobese women and men. Oxygen cost of breathing was similar between the nonobese women (1.17 ± 0.26 mL·L−1) and men (1.21 ± 0.42 mL·L−1). RPB during exercise was similar between the women (2.1 ± 1.3) and men (2.6 ± 1.2) and was correlated (P < 0.05) with relative oxygen uptake (r = 0.55) but not the oxygen cost of breathing. Conclusions: In nonobese women and men, oxygen cost of breathing is not different over the ventilatory ranges studied and RPB is similar at the same relative exercise intensity. In addition, the oxygen cost of breathing was not associated with RPB during constant work rate exercise.
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Dyspnea, Chest Wall Hyperinflation, and Rib Cage Distortion in Exercising Patients with Chronic Obstructive Pulmonary Disease
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: Whether dyspnea, chest wall dynamic hyperinflation, and abnormalities of rib cage motion are interrelated phenomena has not been systematically evaluated in patients with chronic obstructive pulmonary disease (COPD). Our hypothesis that they are not interrelated was based on the following observations: (i) externally imposed expiratory flow limitation is associated with no rib cage distortion during strenuous incremental exercise, with indexes of hyperinflation not being correlated with dyspnea, and (ii) end-expiratory chest wall volume may either increase or decrease during exercise in patients with COPD, with those who hyperinflate being as breathless as those who do not. Methods: Sixteen patients breathed either room air or 50% supplemental O2 at 75% of peak exercise in randomized order. We evaluated the volume of chest wall (Vcw) and its compartments: the upper rib cage (Vrcp), lower rib cage (Vrca), and abdomen (Vab) using optoelectronic plethysmography; rib cage distortion was assessed by measuring the phase angle shift between Vrcp and Vrca. Results: Ten patients increased end-expiratory Vcw (Vcw,ee) on air. In seven hyperinflators and three non-hyperinflators, the lower rib cage paradoxed inward during inspiration with a phase angle of 63.4° ± 30.7° compared with a normal phase angle of 16.1° ± 2.3° recorded in patients without rib cage distortion. Dyspnea (by Borg scale) averaged 8.2 and 9 at the end of exercise on air in patients with and without rib cage distortion, respectively. At iso-time during exercise with oxygen, decreased dyspnea was associated with a decrease in ventilation regardless of whether patients distorted the rib cage, dynamically hyperinflated, or deflated the chest wall. Conclusions: Dyspnea, chest wall dynamic hyperinflation, and rib cage distortion are not interrelated phenomena.
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Neural Correlates of Attentional and Executive Processing in Middle-Age Fencers
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: Open-skill sports require high levels of visual attention and fast and flexible decision making and action execution. We evaluated whether these sports may counteract the well-known age-related declines in executive processing. Methods: Young and middle-age fencers and nonathletes were studied. Participants (N = 40) performed visual motor tasks while reaction times (RTs) and event-related potentials were recorded. Results: RTs were slower for the older subjects, but accuracy was not impaired. At event-related potential level, the late P3 component was delayed in older subjects, but those who participated in sports showed less delay. The RTs of middle-age and young fencers were comparable; the P1 latency of middle-age fencers was similar to that of the younger subjects; the N1 was enhanced in older, as well as younger, fencers; the N2 component of fencers had shorter latencies and larger amplitudes than nonathletes; and in no-go trials, the P3 component was enhanced in fencers independent of age. Conclusions: Overall, the practice of open-skill sports was associated with improvement of the executive functions that are already degraded at middle age.
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Exercise during Pregnancy and the Gestational Age Distribution: A Cohort Study
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The study’s purpose was to examine the associations between exercise performed at different time points during pregnancy and gestational age (GA) in a population-based cohort study. Methods: Data included 61,098 singleton pregnancies enrolled between 2000 and 2006 in the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health. Self-reported exercise was collected from two questionnaires in pregnancy weeks 17 and 30. GA was determined on the basis of the expected date of delivery according to ultrasound, as registered in the Medical Birth Registry of Norway. We used logistic regression to analyze preterm (<37 completed weeks) and postterm births (≥42 wk). Comparison of mean GA by exercise levels was estimated by a general linear model. Results: Mean GA for women exercising three to five times a week in week 17 was 39.51 (95% confidence interval [CI] = 39.48–39.54) compared with 39.34 (95% CI = 39.30–39.37) completed weeks for nonexercisers (P < 0.001). Mean differences remained for all categories of exercise after adjusting for confounding with the greatest mean difference between exercising three to five times per week in week 17 and nonexercisers (equals 1 d). Similar mean differences in GA were observed by exercise levels in week 30. The greatest protective effect on risk of preterm birth was observed for women exercising three to five times a week in week 17 or 30 (adjusted odds ratio (aOR) = 0.82, 95% CI = 0.73–0.91 and aOR = 0.74, 95% CI = 0.65–0.83, respectively) compared with nonexercisers. On the other hand, women exercising one to two or three to five times per week in week 17 were slightly more likely to have a postterm birth (aOR = 1.14, 95% CI = 1.04–1.24 and aOR = 1.15, 95% CI = 1.04–1.26, respectively). Mean GA did not differ by type of exercise performed during pregnancy. Conclusions: Exercise performed during pregnancy shifted the GA distribution slightly upward resulting in reduced preterm births and slightly increased postterm births.
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Breaks in Sedentary Time during Childhood and Adolescence: Iowa Bone Development Study
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The frequency of interruptions in sedentary time (sedentary breaks) is an aspect of sedentary behaviors that may be associated with metabolic health outcomes. The aim of this study was to describe the change in the frequency of sedentary breaks during a 10-yr period from ages 5 to 15 yr. Methods: The longitudinal Iowa Bone Development Study has collected accelerometry data at approximately 5, 8, 11, 13, and 15 yr. Data from participants who wore an accelerometer at least 10 h·d−1 and 3 d per data collection episode were used (423 children at age 5 yr, 550 children at age 8 yr, 520 children at age 11 yr, 454 children at age 13 yr, and 344 children at age 15 yr). The frequency of sedentary breaks was determined based on accelerometry data and compared by weekday/weekend, period during the day, gender, and data collection episode. Results: The frequency of sedentary breaks decreased by >200 times per day during a 10-yr period from ages 5 to 15 yr. Linear regression models estimated a 1.84-times-per-hour decrease per year for boys and a 2.04-times-per-hour decrease per year for girls (P values < 0.0001). Both boys and girls showed significantly fewer breaks on weekdays from morning to 3:00 p.m. than on weekends from morning to 3:00 p.m. (P values < 0.0001). The frequency of sedentary breaks was slightly higher among boys than among girls (gender difference ≤2 times per hour; P values < 0.01 at ages 11, 13, and 15 yr). Conclusions: Breaks in sedentary time notably decrease during childhood and adolescence. During school hours, boys and girls have fewer breaks in sedentary time than during any other period of weekday or weekend day.
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A Prospective Study of Sedentary Behavior in a Large Cohort of Youth
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The study’s purpose was to describe longitudinal patterns of objectively measured sedentary behavior from age 12 to 16. Methods: Children participating in the Avon Longitudinal Study of Parents and Children wore accelerometers for 1 wk at ages 12, 14, and 16. Participants included boys (n = 2591) and girls (n = 2845) living in a single geographic location in the United Kingdom (Bristol). Total minutes per day spent in sedentary behavior and time spent in blocks of sedentary behavior lasting 10–19, 20–29, and ≥30 min are described. Growth curve models were used to determine the rate of change in sedentary behavior from age 12 to 16. Results: At age 12, the boys and girls, on average, were sedentary for 418.0 ± 67.7 and 436.6 ± 64.0 min·d−1, respectively, and sedentary behavior increased over time to 468.0 ± 74.3 and 495.6 ± 68.9 min·d−1 at age 14 and to 510.4 ± 76.6 and 525.4 ± 67.4 min·d−1 at age 16. Growth curve analyses found that total sedentary behavior increased at a rate of 19.5 ± 0.7 and 22.8 ± 0.7 min·d−1·yr−1 for the boys and girls, respectively. The absolute mean increase in total sedentary behavior (+92.4 and +88.8 min·d−1 for the boys and girls, respectively) closely matched the mean decrease in light physical activity (−82.2 and −82.9 min·d−1 for the boys and girls, respectively) from age 12 to 16. Time spent in continuous sedentary behavior lasting ≥30 min increased by 121% from age 12 to 16. Conclusions: Sedentary behavior increased with age, at the expense of light physical activity. The increase in sedentary behavior lasting ≥30 min in duration contributed greatly to the increase in total sedentary behavior.
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Physical Activity and Inflammation in a Multiethnic Cohort of Women
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: Many cross-sectional studies using data from a single time point have reported that higher levels of physical activity or fitness are associated with lower levels of inflammatory markers, but data examining change are limited, as are race/ethnicity-specific data. The purpose of this study was to examine the associations between physical activity and inflammation assessed at two time points among women of different race/ethnicities. Methods: A total of 1355 postmenopausal women (301 whites, 300 blacks, 300 Hispanics, 300 Asians/Pacific Islanders, and 154 American Indians) age 50–79 yr were studied. Participants were from 40 US cities and were free of cardiovascular disease and cancer. At baseline and year 3, women reported their recreational physical activities and provided blood samples, which were analyzed for several inflammatory markers. Results: In cross-sectional analyses, after adjusting for several potential confounders including body mass index, higher physical activity levels were generally related to lower inflammatory marker concentrations. For example, P values for a linear trend of lower C-reactive protein levels across physical activity tertiles at baseline were <0.0001 in all women and 0.94, 0.09, 0.002, 0.20, and 0.10, respectively, for the five race/ethnic groups listed above. For interleukin 6, the corresponding P values were <0.0001, 0.0007, 0.01, 0.03, 0.37, and 0.004, respectively, at baseline. Relationships at year 3 were similar to baseline. However, there was no relation between changes in physical activity and changes in inflammatory markers during the 3-yr period. Conclusions: Among middle-age and older women overall, there were strong, inverse, cross-sectional associations between physical activity level and inflammatory markers. However, changes in inflammatory markers were unrelated to changes in physical activity. These data suggest a noncausal association between physical activity and inflammatory markers.
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Presence and Duration of Reactivity to Pedometers in Adults
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: This study aimed to examine the presence and duration of reactivity to wearing a pedometer and recording daily step counts in free-living adults. Methods: On the first visit to the laboratory, 90 participants (69% were females, age = 26.8 ± 13.0 yr, body mass index = 23.4 ± 4.0 kg·m−2), blinded to the study aim, were provided with a sealed pedometer (New Lifestyles NL-800) and informed that it was a “body posture monitor” (covert condition). Participants wore the pedometer throughout waking hours for 1 wk. On their return to the laboratory, stored step counts were recorded, and participants were informed that the device was a pedometer. Participants wore the pedometer unsealed (no restriction on viewing the step count display) for 2 wk, during which they recorded their daily step count in a diary (diary condition). Mean daily step counts recorded during the covert condition and during weeks 1 and 2 of the diary condition were compared using a repeated-measures ANOVA. Results: There was a significant overall effect of study condition (P < 0.001), with post hoc analyses revealing that mean daily step counts reported during the first week of the diary condition (9898 ± 3002 steps per day) were significantly higher than those reported during the covert condition (8331 ± 3010 steps per day) and during the second week of the diary condition (8226 ± 3170 steps per day, P < 0.001). Conclusions: Reactivity to wearing unsealed pedometers and step count recording seems to last for 1 wk. In the absence of any intervention material, step counts return to normal levels during the second week of monitoring and therefore represent a more accurate estimate of habitual activity. These findings have important implications to both researchers and practitioners interested in the use of pedometers for physical activity surveillance and promotion.
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Real-Time Head Acceleration Measurement in Girls’ Youth Soccer
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: The purpose of the current study was to collect real-time head acceleration data for soccer impacts during girls’ youth (U14) soccer play. Methods: Linear and angular head accelerations were collected during girls’ youth soccer scrimmages using a wireless head acceleration measurement device (the Head Impact Telemetry System). After field data collection, each individual impact was analyzed. The type of impact, header or nonheader, was determined, and nonheader impacts were further assessed by the category of impact. The head injury criterion and resultant linear and angular accelerations were analyzed and compared with current injury tolerance values for all impacts. Results: A total of 47 header and 20 nonheader impacts were observed during the study. The front of the head experienced more headers than the other locations (n = 17). Header impacts ranged in peak linear acceleration from 4.5g to 62.9g and in peak angular head acceleration from 444.8 to 8869.1 rad·s−2. The majority of the nonheader impacts (40%) were player collisions with other players. Only one goalpost collision occurred, but it resulted in the highest peak angular acceleration (5179.5 rad·s−2) and was the only nonheader impact to exceed any of the tolerance levels. Conclusions: Head accelerations were found to exceed the majority of previous laboratory studies. None of the impacts exceeded linear acceleration tolerance values for concussion, but angular accelerations did exceed the suggested limits. Three angular acceleration measurements for heading events (4509.8, 5298.3, and 8869.1 rad·s−2) exceeded the concussion tolerance values, but no concussions were diagnosed during the study.
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Aerodynamic Drag Modeling of Alpine Skiers Performing Giant Slalom Turns
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: Aerodynamic drag plays an important role in performance for athletes practicing sports that involve high-velocity motions. In giant slalom, the skier is continuously changing his/her body posture, and this affects the energy dissipated in aerodynamic drag. It is therefore important to quantify this energy to understand the dynamic behavior of the skier. The aims of this study were to model the aerodynamic drag of alpine skiers in giant slalom simulated conditions and to apply these models in a field experiment to estimate energy dissipated through aerodynamic drag. Methods: The aerodynamic characteristics of 15 recreational male and female skiers were measured in a wind tunnel while holding nine different skiing-specific postures. The drag and the frontal area were recorded simultaneously for each posture. Four generalized and two individualized models of the drag coefficient were built, using different sets of parameters. These models were subsequently applied in a field study designed to compare the aerodynamic energy losses between a dynamic and a compact skiing technique. Results: The generalized models estimated aerodynamic drag with an accuracy of between 11.00% and 14.28%, and the individualized models estimated aerodynamic drag with an accuracy between 4.52% and 5.30%. The individualized model used for the field study showed that using a dynamic technique led to 10% more aerodynamic drag energy loss than using a compact technique. Discussion: The individualized models were capable of discriminating different techniques performed by advanced skiers and seemed more accurate than the generalized models. The models presented here offer a simple yet accurate method to estimate the aerodynamic drag acting upon alpine skiers while rapidly moving through the range of positions typical to turning technique.
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Effect of Ankle Braces on Lower Extremity Joint Energetics in Single-Leg Landings
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: Ankle sprains are one of the most common injuries in competitive and recreational athletics. Studies have shown that the use of prophylactic ankle braces effectively reduces the frequency of ankle sprains in athletes. However, although it is generally accepted that the ankle braces are effective at reducing frontal plane motion, some researchers report that the design of the brace may also reduce ankle sagittal plane motion. The purpose of this study was to quantify lower extremity joint contributions to energy absorption during single-legged drop landings in three ankle brace conditions (no brace, boot brace, and hinged brace). Methods: Eleven physically active females experienced in landing and free of lower extremity injury (age = 22.3 ± 1.7 yr, height = 1.66 ± 0.04 m, mass = 58.43 ± 5.83 kg) performed 10 single-leg drop landings in three conditions (one unbraced, two braced) from a 0.33-m height. Measurements taken were hip, knee, and ankle joint impulse; hip, knee, ankle, and total work; and hip, knee, and ankle joint relative work. Results: Total energy absorption remained consistent across the braced conditions (P = 0.057). Wearing the boot brace reduced relative ankle work (P = 0.04, Cohen d = 0.43) but did not change relative knee (P = 0.08, Cohen d = 0.32) or hip (P = 0.14, Cohen d = 0.20) work compared with the no-brace condition. Conclusions: In an ankle-braced condition, ankle, knee, and hip energetics may be altered depending on the design of the brace.
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Lower Limb Movement Symmetry Cannot Be Assumed When Investigating the Stop–Jump Landing
Medicine and Science in Sports and Exercise - Fri, 06/01/2012 - 05:00
Purpose: When investigating lower limb landing biomechanics, researchers often assume movement symmetry between a participant’s right and left lower limbs for the simplicity of data collection and analysis, although landing tasks often involve dual-limb motion. However, whether lower limb symmetry can be assumed when investigating dynamic, sport-specific movements such as the stop–jump has not been investigated. Therefore, this study aimed to determine whether there were any significant differences in selected kinetic, kinematic, and muscle activation patterns characterizing lower limb biomechanics displayed by the dominant limb compared with the nondominant limb of participants during a stop–jump task. Methods: Sixteen male athletes with normal patellar tendons on diagnostic imaging performed five successful stop–jump trials. Patellar tendon forces (FPT), ground reaction forces, three-dimensional kinematics, and EMG activity of seven lower limb muscles were recorded for the dominant and nondominant lower limbs during each trial. Results: During the horizontal landing phase, the dominant lower limb sustained a significantly higher FPT and peak net knee joint extension moment compared with the nondominant lower limb. Furthermore, during the vertical landing phase, the dominant lower limb sustained significantly lower vertical but higher posterior ground reaction forces compared with the nondominant lower limb. Other variables did not significantly vary as a function of lower limb dominance. Conclusions: It is recommended that researchers clearly identify their primary outcome variables and ensure that their experimental design, particularly in terms of lower limb dominance, provides an appropriate framework to investigate possible mechanics underlying unilateral and bilateral knee joint injuries during dual-limb movements such as the stop–jump task.
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