Biological Maturation and Physical Activity in South Korean Adolescent Girls.

INTRODUCTION/PURPOSE: To examine whether body fatness (i.e., body mass index and percent body fat) and psychosocial correlates of physical activity (PA) mediate the relationships between pubertal status and PA and sedentary behavior (SB) among South Korean adolescent girls. METHODS: Pubertal status, body fatness, sport competence, perceived barriers to PA, self-efficacy, parental support for PA, self-reported and step-determined PA, and self-reported SB were assessed among 236 South Korean adolescent girls (mean age = 13.56 ± 1.2 yr). RESULTS: A direct association was identified between pubertal status and PA in all models; more advanced pubertal status predicted lower PA among South Korean adolescents (b = -0.51 to -0.57; P < 0.001). Indirect effects on the pubertal status-PA relationship were also found: body fatness, perceived barriers to PA, and self-efficacy mediated the relationship between pubertal status and PA. Parental support for PA did not moderate the relationship between maturation and PA. SB was not associated with pubertal status. CONCLUSIONS: This study found mediated effects of body fatness, and psychosocial correlates (i.e., perceived barriers to PA, self-efficacy) on the relationship between maturity and PA among South Korean adolescent girls. Efforts to promote PA among South Korean adolescent girls should focus on reducing perceived barriers to PA, and increasing self-efficacy by providing more opportunities to have positive, and enjoyable experiences in PA among early-maturing girls.

Physical activity and sedentary behaviour of toddlers and preschoolers in child care centres in Alberta, Canada.

OBJECTIVE: To describe duration of physical activity and duration and bouts of sedentary behaviour during child care in a sample of toddlers and preschoolers (19-60 months) from Alberta, Canada, and to examine whether duration and bouts differed among sex, age and parental immigration status groups. METHODS: One hundred and fourteen children aged 19-60 months from eight child care centres throughout Alberta participated. Data were collected at baseline of a study examining revised Alberta Child Care Accreditation Standards. Duration of physical activity (light (LPA), moderate-to-vigorous (MVPA)) and duration and bouts (1-4, 5-9, 10-14, and ≥15 minutes) of sedentary behaviour during child care were accelerometer-derived using 15-second epochs during October/November, 2013. Median [Interquartile ranges] and ANOVAs, accounting for the clustered nature of the data, were calculated. RESULTS: Minutes/hour spent in sedentary behaviour, LPA and MVPA were 36.9 [32.9, 40.7], 18.4 [16.0, 20.9] and 4.2 [2.5, 5.6] respectively. Frequency/hour of sedentary bouts lasting 1-4, 5-9, 10-14 and ≥15 mins were 6.7 [6.1, 7.6], 0.9 [0.6, 1.1], 0.4 [0.2, 0.5] and 0.3 [0.2, 0.4] respectively. Preschoolers participated in less sedentary behaviour and more LPA and MVPA, and had fewer sedentary bouts lasting 10-14 and ≥15 mins compared to toddlers (p < 0.05). CONCLUSION: This is the first Canadian study to report on the duration of physical activity and duration and bouts of sedentary behaviour among both toddlers and preschoolers attending child care centres. These findings suggest child care interventions are needed to increase MVPA and decrease total sedentary behaviour while continuing to promote short sedentary bouts.

Assessment of Pre-Pregnancy Dietary Intake with a Food Frequency Questionnaire in Alberta Women.

PURPOSE: Pre-pregnancy is an under-examined and potentially important time to optimize dietary intake to support fetal growth and development as well as maternal health. The purpose of the study was to determine the extent to which dietary intake reported by non-pregnant women is similar to pre-pregnancy dietary intake reported by pregnant women using the same assessment tool. METHODS: The self-administered, semi-quantitative food frequency questionnaire (FFQ) was adapted from the Canadian version of the Diet History Questionnaire, originally developed by the National Cancer Institute in the United States. Pregnant women (n = 98) completed the FFQ which assessed dietary intake for the year prior to pregnancy. Non-pregnant women (n = 103) completed the same FFQ which assessed dietary intake for the previous year. Energy, macronutrients, and key micronutrients: long-chain omega-3 fatty acids, folate, vitamin B6, vitamin B12, calcium, vitamin D and iron were examined. RESULTS: Dietary intake between groups; reported with the FFQ; was similar except for saturated fat; trans fat; calcium; and alcohol. Pregnant women reported significantly higher intakes of saturated fat; trans fat; and calcium and lower intake of alcohol in the year prior to pregnancy compared to non-pregnant women who reported intake in the previous year. CONCLUSIONS: Despite limitations; a FFQ may be used to assist with retrospective assessment of pre-pregnancy dietary intake.

Oral L-arginine before resistance exercise blunts growth hormone in strength trained males.

Acute resistance exercise and L-arginine have both been shown to independently elevate plasma growth hormone (GH) concentrations; however, their combined effect is controversial. The purpose was to investigate the combined effects of resistance exercise and L-arginine supplementation on plasma L-arginine, GH, GH secretagogues, and IGF-1 in strength trained participants. Fourteen strength trained males (age: 25 ± 4 y; body mass: 81.4 ± 9.0 kg; height: 179.4 ± 6.9 cm; and training experience: 6.3 ± 3.4 y) participated in a randomized double-blind crossover design (separated by ~7 days). Subjects reported to the laboratory at 08:00 in a fasted state, consumed L-arginine (ARG; 0.075 g·kg-1 body mass) or a placebo (PLA) before performing an acute bout of resistance exercise (3 sets of 8 exercises, 10 repetitions at ~75% 1RM). Blood samples were collected at rest, before exercise, and at 0, 15, 30, and 60 min of rest-recovery. The ARG condition significantly increased plasma L-arginine concentrations (~120%) while no change was detected in the PLA condition. There were no differences between conditions for GH, GH-releasing hormone, ghrelin, or IGF-1 at any time point. GH-inhibiting hormone was significantly lower in the ARG condition. However, integrated area under the curve for GH was blunted in the ARG condition (L-arginine = 288.4 ± 368.7 vs. placebo = 487.9± 482.0 min·ng·mL1, p < .05). L-arginine ingested before resistance exercise significantly elevated plasma L-arginine concentration but attenuated plasma GH in strength trained individuals despite a lower GHIH. Furthermore our data shows that the GH suppression was not due to a GH or IGF-1 induced autonegative feedback loop.

The acute effects of L-arginine on hormonal and metabolic responses during submaximal exercise in trained cyclists.

L-arginine may enhance endurance performance mediated by two primary mechanisms including enhanced secretion of endogenous growth hormone (GH) and as a precursor of nitric oxide (NO); however, research in trained participants has been equivocal. The purpose was to investigate the effect of acute L-arginine ingestion on the hormonal and metabolic response during submaximal exercise in trained cyclists. Fifteen aerobically trained men (age: 28 ± 5 y; body mass: 77.4 ± 9.5 kg; height: 180.9 ± 7.9 cm; VO2max: 59.6 ± 5.9 ml·kg- 1·min-1) participated in a randomized, double-blind, crossover study. Subjects consumed L-arginine (ARG; 0. 075 g·kg-1 body mass) or a placebo (PLA) before performing an acute bout of submaximal exercise (60 min at 80% of power output achieved at ventilatory threshold). The ARG condition significantly increased plasma L-arginine concentrations (~146%), while no change was detected in the PLA condition. There were no differences between conditions for GH, nonesterified fatty acids (NEFA), lactate, glucose, VO2, VCO2, RER, CHO oxidation, and NOx. There was reduced fat oxidation at the start of exercise (ARG: 0.36 ± 0.25 vs. PLA: 0.42 ± 0.23 g·min-1, p < .05) and an elevated plasma glycerol concentrations at the 45-min time point (ARG: 340.3 vs. PLA: 288.5 µmol·L-1, p < .05) after L-arginine consumption. In conclusion, the acute ingestion of L-arginine did not alter any hormonal, metabolic, or cardio-respiratory responses during submaximal exercise except for a small but significant increase in glycerol at the 45-min time point and a reduction in fat oxidation at the start of exercise.

Reduced plasma glucose and leptin after 12 weeks of functional electrical stimulation-rowing exercise training in spinal cord injury patients.

OBJECTIVE: To investigate the effects of exercise training with a functional electrical stimulation (FES) rowing machine on insulin resistance, plasma leptin levels, and body composition in people with spinal cord injury (SCI). DESIGN: Experimental study. SETTING: A fitness and research center for people with disabilities. PARTICIPANTS: Healthy male participants with paraplegia (N=6) participated in the study (mean age, 48.6±6y; mean weight, 70.06±3.28kg; injury levels between T4-5 and T10). INTERVENTIONS: Twelve weeks of FES-rowing exercise training 3 to 4 times a week (600-800kcal). MAIN OUTCOME MEASURES: Peak oxygen consumption, plasma leptin, insulin, and glucose levels, insulin sensitivity, body composition. RESULTS: Twelve weeks of FES-rowing training improved aerobic fitness significantly (P=.048). In addition, plasma glucose and leptin levels were significantly decreased after exercise training by 10% and 28% (P<.028), respectively. A trend toward fat mass reduction was seen in 4 of the 6 subjects; this change did not reach statistical significance (P=.08). CONCLUSION: A 12-week training program that included FES rowing improved aerobic fitness and fasting glucose and leptin levels in the absence of significant change to body composition, fasting insulin levels, or calculated insulin sensitivity in people with SCI.

A comparison of fitness training to a pedometer-based walking program matched for total energy cost.

BACKGROUND: Fitness and health variables were measured in 128 sedentary men and women randomly assigned to 6 months of fitness training (F), a walking program (W), or a control (C) group. METHODS: The F program gradually increased volume and intensity until 4 d/wk of training, at 70% of peak VO2 for 43 min/session was prescribed while the W group performed daily walking monitored with pedometers and increased until 10,000 steps x d-1 were prescribed. Total weekly energy expenditure was matched between the activity groups. The control group was asked to maintain their usual activity. RESULTS: Body mass, waist circumference, waist/hip ratio, resting HR were reduced in all groups after 6 months (P < .05). Fasting glucose, glucose tolerance, and total cholesterol were similarly improved in all groups (P < .05). Blood pressure and HR decreased during submaximal exercise in all groups (P < .05) but rating of perceived exertion (RPE) was decreased only in the F group (P < .05). Only the F participants showed a significant increase in ventilatory threshold (VT; ~15%) and peak VO2 (~9%) after 6 months. CONCLUSIONS: Supervised fitness training in previously sedentary adults produced greater improvements in submaximal RPE, BP(sys), VT, and peak VO2 but not other fitness and health-related variables compared with a pedometer-based walking program matched for total energy cost.

A randomized controlled crossover trial of the effect of ginseng consumption on the immune response to moderate exercise in healthy sedentary men.

Ginseng is a popular herbal remedy that is reputed to increase resistance to stress and improve immune function. Regular exercise results in acute physiologic stress that affects the immune response. This study was conducted to investigate the effects of daily consumption of a standardized ginsenoside-containing North American ginseng (Panax quinquefolius) extract on immune function before, during, and after a moderate-exercise protocol in healthy sedentary men. Ten healthy males were randomized to receive either ginseng (1125 mg.d-1) or placebo for 35 days. After a 3 month washout period, subjects received the opposite treatment for another 35 days. An exercise test and blood collection were performed at the end of each treatment period. Immune parameters and blood hormone levels were measured before, during, and after the exercise stress protocol. Ginseng treatment reduced the peripheral blood concentration of CD8+ T cells and increased mitogen-stimulated T cell production of interleukin-2 ex vivo. Ginseng had no effect on total white blood cell counts; on concentrations of neutrophils, monocytes, or lymphocytes (CD3+, CD4+, CD16+, CD20+); on lymphocyte proliferation; or on neutrophil oxidative burst. Ginseng did not significantly affect exercise-induced changes in plasma concentrations of lactate, insulin, cortisol, or growth hormone. The consumption of ginseng for 5 weeks had a limited effect on the immune response to an acute exercise protocol.

Effect of hydration status on high-intensity rowing performance and immune function.

PURPOSE: This study determined the effect of dehydration and rehydration (DR) on performance, immune cell response, and tympanic temperature after high-intensity rowing exercise. METHODS: Seven oarswomen completed two simulated 2000-m rowing race trials separated by 72 h in a random, cross-over design. One trial was completed in a euhydrated (E) condition and the other using a DR protocol. RESULTS: The DR condition resulted in a 3.33+/-0.14% reduction in body mass (P<.05) over a 24-h period followed by a 2-h rehydration period immediately before the simulated rowing race. There was a greater change in tympanic temperature observed in the DR trial (P<.05). There were increases in the blood concentration of leukocytes, lymphocytes, lymphocyte subsets (CD3+, CD3+/4+, CD3+/8+, CD3-/16+, CD4+/25+; P<.05) and decreases in lymphocyte proliferation and neutrophil oxidative burst activity immediately following the simulated race (P<.05) in both trials. Blood leukocyte and neutrophil concentrations were greater after exercise in the DR trial (P<.05). Whereas most immune measures returned to resting values after 60 min of recovery in both trials, lymphocyte proliferation and the concentrations of CD3+/4+ and CD4+/25+ cells were significantly lower than before exercise. Blood leukocyte and neutrophil concentrations were significantly higher before and after exercise in the E trial. CONCLUSION: The effects of dehydration/rehydration did not negatively influence simulated 2000-m rowing race performance in lightweight oarswomen but did produce a higher tympanic temperature and had a differential effect on blood leukocyte, neutrophil, and natural killer (CD3-/16+) cell concentrations after exercise compared with the euhydrated state.

Effects of aerobic exercise training on estrogen metabolism in premenopausal women: a randomized controlled trial.

BACKGROUND: Regular physical activity may alter estrogen metabolism, a proposed biomarker of breast cancer risk, by shifting metabolism to favor production of 2-hydroxyestrone (2-OHE1). Few studies, however, have examined this question using a randomized controlled trial. PURPOSE: To examine the effects of 12 weeks of aerobic exercise training on 2-OHE1 and 16alpha-hydroxyestrone (16alpha-OHE1) in premenopausal women. METHODS: Participants were healthy, regularly menstruating, Caucasian women, 20 to 35 years, body mass index of 18 to 29.9, not using pharmacologic contraceptives, with average or below average fitness [maximal oxygen consumption (VO(2max)), <40 mL/kg/min]. Following a baseline menstrual cycle, participants (N = 32) were randomly assigned to a 12-week aerobic exercise training intervention (n = 17) or usual lifestyle (n = 15). Height, body mass, body composition by dual-energy X-ray absorptiometry, and VO(2max) were measured at baseline and following the intervention. Urine samples were collected in the luteal phase of four consecutive menstrual cycles. RESULTS: The exercise group increased VO(2max) by 14% and had significant, although modest, improvements in fat and lean body mass. No significant between-group differences were observed, however, for the changes in 2-OHE1 (P = 0.944), 16alpha-OHE1 (P = 0.411), or the ratio of 2-OHE1 to 16alpha-OHE1 (P = 0.317). At baseline, there was an inverse association between body fat and 2-OHE1 to 16alpha-OHE1 ratio (r = -0.40; P = 0.044); however, it was the change in lean body mass over the intervention that was positively associated with a change in 2-OHE1 to 16alpha-OHE1 ratio (r = 0.43; P = 0.015). CONCLUSIONS: A 12-week aerobic exercise training intervention significantly improved aerobic fitness and body composition but did not alter estrogen metabolism in premenopausal women. Interestingly, an increase in lean body mass was associated with a favorable change in 2-OHE1 to 16alpha-OHE1 ratio.

Lower excess postexercise oxygen consumption and altered growth hormone and cortisol responses to exercise in obese men.

CONTEXT: Obesity is associated with altered patterns of substrate utilization at rest and during exercise. OBJECTIVE: The relationship between obesity and fat oxidation during recovery from exercise was examined. HYPOTHESIS: The postexercise shift toward fat oxidation is blunted in the obese state, reflected by higher respiratory exchange ratio (RER), blunted GH, and increased cortisol values compared with lean controls. DESIGN: Each subject completed two 160-min protocols (baseline and exercise). During baseline, subjects rested for 160 min; during exercise, they completed 30 min of cycling at ventilatory threshold, followed by 130 min of rest. SETTING: This study was performed at the University of Alberta. SUBJECTS: Healthy untrained (maximal oxygen consumption, <45 ml/kg.min or <3.35 liter/min) lean (<16% body fat; n = 6) and obese (>25% body fat; n = 7) men, aged 30-39 yr, were studied. MAIN OUTCOME MEASURES: RER, GH, cortisol, oxygen consumption, heart rate, tympanic temperature, and lactate were obtained during both protocols at matched time intervals and analyzed by repeated measures ANOVA. RESULTS: During baseline, there were no differences detected between lean and obese groups for any of the measured variables. In contrast, during exercise, peak GH levels were blunted (P < 0.05) and cortisol levels were elevated (P < 0.05) in the obese compared with the lean subjects, but RER values were similar in the two groups. The differences in GH and cortisol persisted during the postexercise period accompanied by higher RER values (P < 0.05) and reduced total oxygen consumption (P < 0.05) in the obese group. CONCLUSION: These findings indicate that exercise-induced fat oxidation is diminished in obese men.

Effect of elk velvet antler supplementation on the hormonal response to acute and chronic exercise in male and female rowers.

To examine the effects of elk velvet antler supplementation (EVA) combined with training on resting and exercise-stimulated hormonal response, male (n = 25) and female (n = 21) rowers ingested either EVA (560 mg/d) or placebo (PL) during 10 wk of training. VO(2max), 2000 m rowing time, leg and bench press strength were determined before and after 5 and 10 wk of training. Serum hormone levels were measured prior to and 5 and 60 min after a simulated 2000 m rowing race. VO(2max)and strength increased and 2000 m times decreased similarly (P < 0.05) with training. There was no significant difference between the EVA and PL group for any hormonal response. Testosterone (males only) and growth hormone (both genders) were higher 5 min after the simulated race (P < 0.05) but returned to baseline at 60 min. Cortisol was higher 5 and 60 min compared to rest (both genders) (P < 0.05) and was higher 60 min post-exercise following 5 and 10 wk of training. It appears that 10 wk of EVA supplementation does not significantly improve rowing performance nor alter hormonal responses at rest or after acute exercise than training alone.

Associations between aerobic fitness and estrogen metabolites in premenopausal women.

UNLABELLED: Chronic physical activity may alter estrogen metabolism, a proposed biomarker of breast cancer risk, by causing a shift toward higher 2-OHE1 and lower 16alpha-OHE1 levels. PURPOSE: To investigate the association between an objective indicator of chronic exercise, aerobic fitness, and 2-OHE1 and 16alpha-OHE1 in premenopausal women. METHODS: Women with high aerobic fitness (N=17; VO2max>or=48 mL.kg.min-1) were compared with women with average aerobic fitness (N=13; VO2max

Energy balance and reproductive function in active women.

Athletes engaged in rigorous training programs expend large amounts of energy and require appropriate energetic compensation to maintain or improve performance. If these exercise regimens are not fueled sufficiently, a negative energy balance will likely emerge and lead to a broad spectrum of menstrual cycle disturbances and less than optimal performance. This review examines the theory and evidence surrounding energy availability and reproductive function. Implications for performance and treatment strategies are also addressed.

Intact sympathetic nervous system is required for leptin effects on resting metabolic rate in people with spinal cord injury.

Compared with able-bodied (AB), people with spinal cord injury (SCI) have a 3- to 5-fold higher risk of developing type 2 diabetes mellitus, which may be associated with increased fat mass. Evidence suggests that leptin regulates body adiposity through the sympathetic nervous system, which is impaired in people with high lesion SCI. The purpose of this study was to determine the relationship among leptin levels, body composition, and resting metabolic rate (RMR) in people with high lesion SCI and body mass index-, weight-, height-, and waist circumference-matched AB subjects. Fourteen subjects (seven SCI and seven AB) participated in the study. After an overnight fast, various hormones, glucose, and RMR were measured. There was no significant difference in plasma glucose, insulin, GH, cortisol, and glucagon levels between the two groups. The SCI group had 105% higher plasma leptin levels than the AB group (P < 0.05). Plasma leptin levels correlated with body mass index (SCI: r = 0.80; P = 0.028; AB: r = 0.79; P = 0.035) and fat mass (SCI: r = 0.95; P = 0.001; AB: r = 78; P = 0.038) in both groups. The plasma leptin level correlated with the absolute RMR (SCI: r = 0.15; P = 0.75; AB: r = 0.99; P < 0.006) and the RMR per unit fat-free mass (SCI: r = -0.70; P < 0.08; AB: r = 0.845; P < 0.017) in the AB group, but not in the SCI group. The absolute RMR was significantly reduced in the SCI group compared with the AB group, but there was no difference in the relative RMR between the groups. In conclusion, the SCI group has a significantly higher plasma leptin level than the AB group. The absolute and relative RMR correlated with leptin only in the AB group.

Leptin response to short-term fasting in sympathectomized men: role of the SNS.

We studied plasma leptin levels in six people with high-lesion spinal cord injury [SCI; body mass index (BMI) 25.9 +/- 1.5 kg/m(2), age 37 +/- 3.0 yr] and six able-bodied (AB) controls (BMI 29.1 +/- 1.9 kg/m(2), age 35 +/- 3.5 yr) before and after 12, 24, and 36 h of fasting. The plasma leptin levels significantly decreased during 36 h fasting by 48.8 +/- 4.5% (pre: 11.3 +/- 2.3, post: 6.2 +/- 1.5 ng/ml) and 38.6 +/- 7.9% (pre: 7.6 +/- 5.0, post: 4.2 +/- 1.0 ng/ml) in SCI and AB, respectively. Plasma leptin started to decrease at 24 h of fasting in the SCI group, whereas plasma leptin started to decrease at 12 h of fasting in the AB group. The current study demonstrated that plasma leptin decreased with fasting in both SCI and AB groups, with the leptin decrease being delayed in the SCI group. The delayed leptin response to fasting in the SCI group may be because of increased fat mass (%body fat, SCI: 33.8 +/- 3.0, AB: 24.1 +/- 2.9) and sympathetic nervous system dysfunction.

Energy balance and luteal phase progesterone levels in elite adolescent aesthetic athletes.

Menstrual abnormalities are associated with negative energy balance and reduced energy expenditure (REE). To examine this relationship in elite adolescent aesthetic athletes, 3 groups of females (aged 15-18 years) were studied: 10 oligo/amenorrheic athletes (OA), 11 eumenorrheic athletes (EA), and 8 non-athlete controls (C). Components of energy balance, body composition, dietary restraint, pubertal maturation, and luteal phase salivary progesterone were assessed in all groups. Both groups of athletes had a later age of menarche and lower pubertal development score compared to the non-athletes (p < or = .05). With the exception of salivary progesterone (ng/ml; OA = 0. 15 +/- 0.01