Physical activity of young people: the Amsterdam Longitudinal Growth and Health Study

PURPOSE: To describe the natural development of habitual physical activity behavior (HPA) of young Dutch male and female subjects between the ages of 13 and 27, using data from the Amsterdam Longitudinal Growth and Health Study. METHODS: HPA was measured by means of a structured interview at ages 13, 14, 15, 16, 21, and 27 and concerned all activities (at work, school, during leisure, organized and nonorganized sports, and active transportation) exceeding a level of intensity of 4 METs. Complete longitudinal data concern 98 female and 83 male subjects. MANOVA for repeated measurements were done for total HPA (expressed in min x wk(-1) and in METs x wk(-1)). Similar analyses were done for organized sports activities, leisure time activities, and all "other" activities separately (also min x wk(-1) and METs x wk(-1)), as well as for weekly time at three different levels of intensity of HPA, i.e. 4-7 MET (moderate), 7-10 MET (vigorous), and >10 MET (very vigorous). RESULTS: Our data showed regarding total HPA (min x wk(-1)) in male, but not in female, subjects a significant decrease in weekly time spent on HPA between the ages of 13 and 27. Regarding the three different levels of intensity in male and female subjects, a significant increase was found in time spent on moderate activities, where female subjects were spending significantly more time on moderate activities than male subjects; both in male and female subjects, a significant decrease was found in time spent on vigorous activities: in male subjects a significant decrease was found in time spent on very vigorous activities, whereas in female subjects time spent at this level of activity remained more or less stable. For the total weighted activity score (METs x wk(-1)), a significant decrease was found for both male (42%) and female subjects (17%). This decrease was significantly greater for male than for female subjects. Regarding more specific activities, it was found that in the course of time organized sports activities became relatively more important contributors to both weekly HPA time and energy expenditure, both in male and female subjects. CONCLUSIONS: Our data show a considerable decrease in HPA over a 15-yr period of time, both in male and female subjects. Differences between male and female subjects are predominantly caused by differences in time spent in moderate and very vigorous activities. In the course of time, organized sports activities became a relatively more important contributor of weekly HPA.     

Discrepancies between methods of identifying objectively determined physical activity

Current methods for validating physical activity (PA) questionnaires typically use accelerometers as objective measures for comparison with questionnaire responses and obtain low correlations or agreement. PURPOSE: We examined possible reasons for weak associations in validation studies by comparing published ActiGraph accelerometer intensity cut points with cut points based on intensity thresholds for heart rate response to PA. METHODS: Twelve adults (five men, seven women; age 31.0 +/- 14.3 yr) wore an ActiGraph accelerometer and a Polar Vantage NV heart watch simultaneously for seven consecutive days during their waking hours. We identified PA bouts from the minute-by-minute ActiGraph data using published accelerometer thresholds for defining moderate- and vigorous-intensity PA. We then compared PA bout intensities identified with these criteria with intensity classifications of the PA bouts using mean percent heart rate reserve (HRR). RESULTS: Most of the moderate-intensity PA bouts identified by the Freedson (78.3%), Swartz (88.0%), and Hendelman (94.7%) ActiGraph cut points were associated with a mean %HRR < 45% (very light and light intensities). The estimated mean frequency with which study participants engaged in moderate-intensity PA varied with the cut points and type of bouts used and ranged from 1.1 d.wk(-1) (45-60%HRR) to 7.0 d.wk(-1) (Hendelman cut points). The mean total duration on active days ranged from 17.9 min.d(-1)(45-60%HRR) to 139.2 min.d(-1) (Hendelman cut points). Fewer bouts of vigorous PA were found in the accelerometer data, and most were in the vigorous-intensity category of > or = 60%HRR. CONCLUSIONS: The method used for analyzing ActiGraph activity data can result in large differences in the summary measure of minutes of moderate- to vigorous-intensity activity.     

Relationship between %HRmax, %HR reserve, %VO2max, and %VO2 reserve in elite cyclists

PURPOSE: To evaluate the relations between %HRmax, %HRR, %VO2max, and %VO2R in elite cyclists and to check whether the intensity scale recommended by ACSM in its 1998 position stand is also applicable to this specific population. METHODS: Twenty-six male elite road cyclists (25.1 +/- 0.7 yr, 71.0 +/- 1.2 kg, 70.9 +/- 1.2 mL x kg(-1) x min(-1), 433.9 +/- 9.8 W) performed an incremental maximal exercise test (50 W x 3 min(-1)). Individual linear regressions based on HR and VO2 values measured at rest, end of each stage, and maximum, were used to calculate slopes and intercepts, and to predict %HRmax, %HRR, %VO2max, or %VO2R for a given exercise intensity. RESULTS: Below 85% VO2max or VO2R, predicted %HRmax values were significantly higher (P < 0.001) than the ACSM intensity scale (58, 65, 73, and 87% vs 55, 62, 70, and 85% HRmax at 40, 50, 60, and 80% VO2max, and 48, 61, 74% vs 35, 55, and 70% HRmax at 20, 40, and 60% VO2R). The %HRR versus %VO2max regression mean slope (1.069 +/- 0.01) and intercept (-5.747 +/- 0.80) were significantly different (P < 0.0001) from 1 and 0, respectively. Conversely, the %HRR versus %VO2R regression was indistinguishable from the line of identity (mean slope = 1.003 +/- 0.01; mean intercept = 0.756 +/- 0.7). Predicted %VO2R values were equivalent to %HRR in the 35-95%HRR range. %VO2max was equivalent to %HRR at and above 75%HRR, and it was significantly higher at (P < 0.05) and below 65%HRR (P < 0.001). CONCLUSION: The intensity scale recommended by ACSM underestimates exercise intensity in elite cyclists. Prediction of %HRR by %VO2R is better than by %VO2max. Thus, elite cyclists should use %HRR in relation to %VO2R rather than in relation to %VO2max.     

Assessment of physical activity by telephone interview versus objective monitoring

PURPOSE: To compare different methods of quantifying time in physical activity (PA). METHODS: Twenty-five participants (12 male, 13 female) volunteered to be monitored for seven consecutive days, during which different PA patterns were measured by the simultaneous heart-rate motion sensor technique (HR+M). At the end of the 7th day, participants completed questions taken from the 2001 Behavioral Risk Factor Surveillance System (BRFSS) PA module telephone survey, in which they recalled the amount of time spent walking, and in moderate and vigorous activities. The results of the BRFSS PA module were then compared with those of the HR+M. RESULTS: No significant group differences were found in the amount of time spent in moderate and vigorous activities between methods. However, individual differences were greater for time spent in moderate activities (SE +/- 7.36 min x d(-1); range -70 to 77 min x d(-1)) than for time spent in vigorous activities (SE +/- 3.57 min x d(-1); range -39 to 33 min x d(-1). Spearman correlation coefficients between the HR+M and the BRFSS were significant for vigorous activities (r = 0.54, P < 0.01). There was 80% agreement between the two methods of classifying individuals who either: (a) met the recommendations (through moderate and/or vigorous PA) or (b) did not meet the recommendations. CONCLUSION: The BRFSS and HR+M methods yielded similar group estimates of PA, but individual assessments of moderate activity differed more than those of vigorous activity. BRFSS estimations of group compliance with national PA recommendations were similar to those of the HR+M.     

Physical activity and active commuting to elementary school

PURPOSE: This study was conducted to determine if fifth-grade students who walked or bicycled to school on a regular basis were more physically active than those that did not. METHODS: The sample consists of 219 fifth-grade students (10.3 +/- 0.6 yr, 44% male, 58% minority) from eight randomly selected urban and suburban elementary schools. Students wore an Acti-Graph physical activity monitor during the same week that they completed a daily survey to report their mode of transportation to and from school. Students were categorized on the number of reported active commuting trips, to and from school, per week (regular;>or=5 (N=11), irregular; 1-4 (N=25), nonactive; 0 (N=183)). RESULTS: Compared with both other groups, regular active commuters accumulated 3% more minutes of moderate-to-vigorous physical activity (MVPA; P=0.04) during weekdays. This weekday difference was because of regular active commuters accumulating 8.5% more minutes of MVPA both before and after school (P 相似文献   

Habitual physical activity levels in childhood and adolescence assessed with accelerometry

AIM: The purposes of this study were: 1) to evaluate age and gender differences in physical activity (PA) of children and adolescents; 2) to find out if children and adolescents fulfill the PA recommendations of 60 min x day(-1) of moderate (MPA) to vigorous PA (VPA). METHODS: PA was assessed in 265 female and 238 male subjects, ranging from 6 to 18 years of age, grouped in 4 age groups, with MTI ActiGraph model 7164, during 7 consecutive days. The MTI actigraph data was reduced to bouts (30-, 20-, 10-, and 5-min) and minutes spent in MPA, VPA, and very VPA (VVPA). RESULTS: The oldest boys and girls revealed a lower number of PA bouts than the younger ones. Significant gender differences were found in daily VPA, F(1, 492)=37.67, P<0.001; and VVPA F(1, 494)=24.11, P<0.001. Boys were more active than girls. Significant age group differences were also found in MPA, F(3, 494)=87.4, P<0.001; VPA, F(3, 492)=78.15, P<0.001; and VVPA, F(3, 454)=54.89, P<0.001. In both genders MPA, VPA and VVPA decreased with age. Till the age of 14, children had means between 79.6+/-30.6 and 144.1+/-76.9 min*day(-1) of PA. After this age, there was a decrease to 44.1+/-19.9 min*day(-1) in girls and to 56.3+/-31.9 min*day(-1) in boys. CONCLUSION: Boys had more minutes a day of VPA and VVPA than girls. PA decreased with age. The subjects of this study, aged 6 to 15, fulfilled the recommendations of 60 min x day(-1) of MPA to VPA.     

Vasomotor sympathetic nerve activity in men during bed rest and on orthostasis after bed rest

BACKGROUND: Alterations in autonomic function are commonly seen during and after spaceflight, and its ground-based analog, 6 degrees head-down bed rest (HDBR). They may include peripheral vascular regulation, but vasomotor sympathetic efferent nerve discharges to peripheral vasculatures have not been examined. The aim of our study was to examine changes in vasomotor sympathetic nerve activity during HDBR and under orthostasis after HDBR. METHODS: We performed 6 d of HDBR on six male subjects, and measured muscle sympathetic nerve activity (MSNA) together with plasma norepinephrine concentrations in the supine position before HDBR and in 6 degrees head-down position on the sixth day (HDBR6) of HDBR. We also measured MSNA in head-up tilt (HUT) test before and after HDBR. RESULTS: On HDBR6, MSNA burst rate was the same (17+/-4 bursts x min(-1)) as that in supine position before HDBR (15+/-2 bursts min(-1)), but plasma norepinephrine concentrations were decreased to 1.14+/-0.10 pmol x ml(-1) compared with the supine value before HDBR (1.56+/-0.20 pmol x ml(-1), p<0.05). After HDBR, supine MSNA burst rate significantly increased by 58% to 24+/-4 bursts x min(-1). MSNA increment in response to HUT was similar between before (34+/-3 bursts min(-1) x sin HUT(-1)) and after (40+/-6 bursts x min(-1) x sin HUT(-1)) HDBR. CONCLUSIONS: Our findings suggest that: a) the relationship between MSNA and plasma norepinephrine concentrations was altered on the sixth day during HDBR; b) the vasomotor sympathetic nerve activity was enhanced after HDBR; and c) the augmentation of vasomotor sympathetic outflow to muscles under orthostasis was preserved after HDBR.     

Resistance and aerobic exercise have similar effects on 24-h nutrient oxidation

BACKGROUND: Whether resistance exercise is as effective as aerobic exercise for body-weight management is debated. PURPOSE: To compare 24-h energy expenditure (EE) and macronutrient oxidation elicited by comparable bouts of stationary cycling (BK) and weightlifting (WTS). METHODS: 24-h EE and macronutrient oxidation were measured in 10 nonobese male subjects on three occasions using whole-room indirect calorimetry. BK and WTS days were compared with a nonexercise control day (Con). RESULTS: During BK, subjects exercised for 49 +/- 7 min (mean +/- SEM) at 70% of OV(2max) and expended 546 +/- 16 kcal. During WTS, subjects performed a 70-min circuit consisting of four sets of 10 different exercises at 70% of exercise-specific 1-repetition maximum and expended 448 +/- 21 kcal (P < 0.001 vs BK). 24-h EE on BK and WTS days (2,787 +/- 76 kcal x d(-1), 2,730 +/- 106 kcal x d(-1), respectively, P > 0.05) was elevated compared with Con (2,260 +/- 96 kcal x d(-1), P < 0.001), but 24-h respiratory exchange ratio (RER) was not different. 24-h carbohydrate oxidation was significantly elevated on the exercise days (BK = 370 +/- 18 g x d(-1), WTS = 349 +/- 23 g x d(-1), P > 0.05) compared with Con (249 +/- 29 g x d(-1), P = 0.04). 24-h fat and protein oxidation were the same on BK, WTS, and Con days. EE and macronutrient oxidation in the periods after exercise also did not differ across conditions. CONCLUSION: In men, resistance exercise has a similar effect on 24-h EE and macronutrient oxidation as a comparable bout of aerobic exercise. Neither exercise produced an increase in 24-h fat oxidation above that observed on a nonexercise control day.     

Comparison of pedometer and accelerometer measures of free-living physical activity

PURPOSE: The purpose of this investigation was 1) to evaluate agreement between dual-mode CSA accelerometer outputs and Yamax pedometer outputs assessed concurrently under free-living conditions; 2) to determine the relationship between pedometer-steps per day and CSA-time spent in inactivity and in light-, moderate-, and vigorous-intensity activities; and 3) to identify a value of pedometer-steps per day that corresponds with a minimum of 30 CSA-min x d(-1) of moderate ambulatory activity. METHODS: Data were analyzed from 52 participants (27 men, 25 women; mean age = 38.2 +/- 12.0 yr; mean BMI = 26.4 +/- 4.5 kg x m(-2)) who were enrolled in the International Physical Activity Questionnaire study and wore both motion sensors during waking hours for 7 consecutive days. RESULTS: Participants averaged 415.0+/-159.5 CSA-counts x min(-1) x d(-1), 357,601 +/- 138,425 CSA-counts x d(-1), 11,483 +/- 3,856 CSA-steps x d(-1), and 9,638 +/- 4,030 pedometer-steps x d(-1). There was a strong relationship between all CSA outputs and pedometer outputs (r = 0.74-0.86). The mean difference in steps detected between instruments was 1845+/-2116 steps x d(-1) (CSA > pedometer; t = 6.29, P < 0.0001). There were distinct differences (effect sizes >0.80) in mean CSA-time (min x d(-1)) in moderate and vigorous activity with increasing pedometer-determined activity quartiles; no differences were noted for inactivity or light activity. Approximately 33 CSA-min x d(-1) of moderate activity corresponded with 8000 pedometer-steps x d(-1).CONCLUSION: Differences in mean steps per day detected may be due to differences in set instrument sensitivity thresholds and/or attachment. Additional studies with different populations are needed to confirm a recommended number of steps per day associated with the duration and intensity of public health recommendations for ambulatory activity.     

Total daily energy expenditure and patterns of physical activity in adolescents assessed by two different methods

Minute-by-minute heart rate monitoring and an activity diary were used simultaneously during three days in 30 randomly selected adolescents (16 boys, 14 girls; mean age 15.0+/-1.0). Total daily energy expenditure (TDEE) and its components (energy expenditure during sleep, during rest and in physical activity) and times spent at different intensity levels (sedentary, light, moderate physical activity and vigorous physical activity) were compared. TDEE from heart rate monitoring averaged 10.9+/-2.7 MJ x d(-1) compared to 11.3+/-2.3 MJ x d(-1) from the activity diary (NS). The limits of agreement (mean+/-2 SD) were -3.54 MJ x d(-1) and 2.74 MJ x d(-1). There was no significant difference for any of the TDEE components between the methods (MANOVA). A significant method effect (P<0.001) was observed for time spent in sedentary and light physical activity (MANOVA). No significant difference was observed for time spent in moderate and vigorous physical activity. According to this, heart rate monitoring and activity diary are comparable for group assessment of TDEE and its components, and for estimating time spent in moderate and vigorous physical activity. The activity diary underestimated time spent in moderate and vigorous physical activity for inactive subjects and consequently overestimated highly active subjects.     

Thermoregulatory responses to exercise in the heat: chronic caffeine intake has no effect

INTRODUCTION: Authorities advise individuals to refrain from caffeine intake before or during exercise, especially when performed in the heat, due to potential fluid-electrolyte imbalances that exaggerate physiological strain. Yet, military personnel are often deployed to hot environments and must perform under sleep-deprived conditions where caffeine would be an ideal intervention strategy to enhance physical and cognitive performance. PURPOSE: To assess the effects of controlled chronic and acute caffeine ingestion on fluid-electrolyte, physiological and thermoregulatory responses during an exercise heat tolerance test (EHT). METHODS: Subjects were 59 active, college-aged males (mean +/- SE 21.6 +/- 0.4 yr, 177.9 +/- 0.8 cm, 75.4 +/- 1.0 kg, 11.1 +/- 0.7% body fat) who were randomized and stratified by age, bodyweight, and body composition into three groups. All subjects equilibrated caffeine intake at 3 mg x kg(-1) x d(-1) for days 1-6. On days 7-12, they consumed a treatment dose of either 0 (G0), 3 (G3), or 6 (G6) mg x kg(-1) x d(-1). Fluid-electrolyte and physiological measures were made on day 12, 1 h after caffeine intake, during the EHT (90 min walking, 1.56 m x s(-1), 5% grade; dry bulb temperature, 37.7 +/- 0.1 degree C; relative humidity, 56.3 -1.5%). RESULTS: There were no between-group differences (p > 0.05) in plasma, urinary, thermoregulatory, cardiovascular, and perceptual variables across time (pre- vs. post-EHT), although some of these variables increased significantly over time (p < 0.05). EHT time was significantly greater in G3 (86 +/- 2.0 min) vs. GO (75 +/- 3.3 min, p < 0.05). DISCUSSION: Acute caffeine ingestion, in chronically consuming subjects (3 and 6 mg x kg(-1) x d(-1)) did not alter fluid-electrolyte, exercise endurance or thermoregulatory responses during EHT when compared with G0.     

Adaptations to short-term high-fat diet persist during exercise despite high carbohydrate availability.

PURPOSE: Five days of a high-fat diet produce metabolic adaptations that increase the rate of fat oxidation during prolonged exercise. We investigated whether enhanced rates of fat oxidation during submaximal exercise after 5 d of a high-fat diet would persist in the face of increased carbohydrate (CHO) availability before and during exercise. METHODS: Eight well-trained subjects consumed either a high-CHO (9.3 g x kg(-1) x d(-1) CHO, 1.1 g x kg(-1) x d(-1) fat; HCHO) or an isoenergetic high-fat diet (2.5 g x kg(-1) x d(-1) CHO, 4.3 g x kg(-1) x d(-1) fat; FAT-adapt) for 5 d followed by a high-CHO diet and rest on day 6. On day 7, performance testing (2 h steady-state (SS) cycling at 70% peak O(2) uptake [VO(2peak)] + time trial [TT]) of 7 kJ x kg(-1)) was undertaken after a CHO breakfast (CHO 2 g x kg(-1)) and intake of CHO during cycling (0.8 g x kg(-1) x h(-1)). RESULTS: FAT-adapt reduced respiratory exchange ratio (RER) values before and during cycling at 70% VO(2peak); RER was restored by 1 d CHO and CHO intake during cycling (0.90 +/- 0.01, 0.80 +/- 0.01, 0.91 +/- 0.01, for days 1, 6, and 7, respectively). RER values were higher with HCHO (0.90 +/- 0.01, 0.88 +/- 0.01 (HCHO > FAT-adapt, P < 0.05), 0.95 +/- 0.01 (HCHO > FAT-adapt, P < 0.05)). On day 7, fat oxidation remained elevated (73 +/- 4 g vs 45 +/- 3 g, P < 0.05), whereas CHO oxidation was reduced (354 +/- 11 g vs 419 +/- 13 g, P < 0.05) throughout SS in FAT-adapt versus HCHO. TT performance was similar for both trials (25.53 +/- 0.67 min vs 25.45 +/- 0.96 min, NS). CONCLUSION: Adaptations to a short-term high-fat diet persisted in the face of high CHO availability before and during exercise, but failed to confer a performance advantage during a TT lasting approximately 25 min undertaken after 2 h of submaximal cycling.     

Atrioventricular plane displacement in untrained and trained females

PURPOSE: Female athletes often demonstrate changes in cardiac dimensions that are less prominent than in male athletes, and results from longitudinal studies are conflicting. The atrioventricular plane displacement (AVPD) in the heart is used as an index of left ventricular systolic function with the assumption that it is a more sensitive method for measuring myocardial contractility compared with left ventricular ejection fraction. The aim of the present study was to determine the effect of a short period of endurance training on cardiac dimensions in sedentary female subjects and to measure the AVPD at rest and during submaximal workload. METHODS: Twelve sedentary female subjects (21.9 +/- 1.3 yr, 168.8 +/- 3.5 cm, 64.0 +/- 6.6 kg, and 42.6 +/- 2.9 mL x kg(-1) x min(-1) in maximal oxygen uptake) were examined with echocardiography before and after a period of interval training (varying from 2 to 5 min at 90-95% of maximal heart rate, 3 d x wk(-1), 8 wk). RESULTS: Maximal oxygen uptake increased by 18% to 50.4 +/- 3.1 mL x kg(-1) x min(-1) (P < 0.001). Left ventricular mass increased from 123.9 to 139.2 g (P = 0.007). There was a significant increase in posterior wall thickness but no change in cavity size. The AVPD did not change at rest but increased significantly from 15.6 to 17.6 mm (P < 0.001) during exercise at 85-90% of maximal heart rate. CONCLUSION: This study shows that a short period of aerobic endurance training induces changes in the female heart, both in cardiac dimensions at rest and in left ventricular systolic function at submaximal workload. AVPD during submaximal exercise discriminate well between the untrained and trained healthy heart.     

Children's pedometer-determined physical activity during the segmented school day

PURPOSE: To describe the sex-specific patterns of school children's daily pedometer-determined physical (PA) during physical education (PE), recess and lunchtime, and before and after school. METHODS: Eighty-one sixth-grade students (28 boys, age = 11.9 +/- 0.4 yr, BMI = 18.8 +/- 4.1 kg x m(-2); 53 girls, 11.8 +/- 0.5 yr, BMI = 20.2 +/- 4.6 kg x m(-2)) wore pedometers for four school days and were prompted to record steps accumulated at arrival and departure from school and during pre- and postrecess, lunchtime, and PE class. RESULTS: Boys took significantly (P < 0.001) more steps per day than girls: 16,421 +/- 5,444 vs 12,332 +/- 3,056 steps per day, and more steps during release time (e.g., before-school Delta = 1289 steps, recess Delta = 479 steps, lunchtime Delta = 608 steps, and after-school Delta = 1872 steps) but the same number of steps during structured PE classes (1429 +/- 567 vs 1410 +/- 445 steps; P = 0.87). Lunchtime PA represented the most important source of daily PA (15-16%) obtained during school hours for both boys and girls, whereas recess accounted for 8-9% and PE class accounted for 8-11% of total steps per day. Regardless, almost half of daily steps taken are attributable to after-school activities. CONCLUSION: These data provide greater understanding of sex-specific PA patterns and the relative contribution of distinct segments of the school day to school children's total PA.     

Effect of high-volume and -intensity endurance training in heart transplant recipients

BACKGROUND: A recommended component of heart transplant recipients (HTR) is endurance-oriented exercise therapy. However, the trainability of HTR after transplantation is vague. We examined the effect of high-volume and -intensity exercise training on exercise performance in HTR, compared with HTR undergoing regular rehabilitation training, and sedentary healthy subjects (SHS). METHODS: We studied four groups of individuals; of those, three groups were HTR. Subjects were a regularly trained HTR group of denervated (HTR-D; N = 15), reinnervated (HTR-R; N = 26) hearts, a high-volume and -intensity endurance-training group (training time 7-20 h.wk(-1); HTR-ET; N = 12), and a group of sedentary healthy subjects (SHS; N = 21). All participants performed cardiopulmonary exercise testing. RESULTS: The HTR-ET achieved a significantly higher performance (255 +/- 47 W, VO(2max) of 45.2 +/- 6.9 mL.kg(-1).min(-1)) in contrast to all other groups (HTR-D: 119 +/- 17 W, VO(2max) of 17.4 +/- 4.5 mL.kg(-1).min(-1); HTR-R: 119 +/- 17 W, VO(2max) of 16.9 +/- 3.7 mL.kg(-1).min(-1); SHS: 184 +/- 19 W, VO(2max) of 35.0 +/- 6.9 mL.kg(-1).min(-1)). The HR at maximal power output in the HTR-ET was 169 +/- 17 bpm and similar to SHS (164 +/- 17 bpm), but significantly higher than HTR-D (125 +/- 16) and HTR-R (142 +/- 10). Maximal lactate concentration (LAmax) of HTR-ET was 9.9 +/- 2.2 mmol.L(-1), comparable to SHS (9.2 +/- 2.1 mmol.L(-1)), and significantly higher than HTR-D (5.5 +/- 1.5 mmol.L(-1)) and HTR-R (5.1 +/- 1.0 mmol.L(-1)). CONCLUSIONS: Data suggest that HTR can perform high-volume and -intensity exercise training, reaching exercise performance comparable to or even exceeding values of sedentary or moderately trained healthy subjects.     

Plasma nitrite/nitrate and erythropoietin levels in cross-country skiers during altitude training

BACKGROUND: The aim of this study was to evaluate the effects of training at altitude on plasma nitrite/nitrate and erythropoietin levels since previously it has been reported an interaction of the NO/cGMP system in erythropoietin production. METHODS: Nine physically trained cross-country male skiers, usually living at 800-1200 m altitude, underwent 6 days of intensive training at a moderate altitude of 3100 m preceeded by 2 days of acclimatisation. Six team-managers, selected as controls, did not undergo any regular physical activity in the last 5 years and during the altitude period. Haematological parameters, erythropoietin and nitrite/nitrate were measured prior to reach the place at altitude, at the end of the period at moderate altitude and 7 days after returning at home. RESULTS: Haematocrit significantly increased in controls after 8 days at altitude. Erythropoietin levels significantly increased after the intensive altitude training only in trained subjects (13.1+/-1.7 vs 6.7+/-1.7 mU x ml-1, p<0.001). Nitrite/nitrate baseline values were significantly higher in trained subjects compared to untrained (49.9+/-17.9 vs 25.4+/-2.8 micromol x l(-1), p<0.01); the altitude period significantly increased nitrite/nitrate levels, in untrained subjects, to the same values observed in trained subjects under control conditions (47.0+/-10.3 micromol x l(-1)). CONCLUSIONS: In our experimental conditions we demonstrated the influence of hypoxia on Epo levels in athletes sustaining a short-term training and the role of a regular physical activity (partly independent from altitude hypoxia) on NO production.     

Urinary profile of androgen metabolites in a population of sportswomen during the menstrual cycle

The aim of this investigation was to evaluate the urinary profile of androgen metabolites during menstrual cycle in both young-trained female athletes, and young sedentary women, not presenting any pathological signs. Urines were collected for 24 hours (08 : 00 a. m. the first day to 08 : 00 a. m. the second day) from all sportive and sedentary subjects. All steroids were measured by specific radioimmunological analysis, and the implications of these results in terms of concentrations and modifications by exercise will be discussed. During follicular phase, control values were respectively, testosterone glucuronide (TG): 1.67 +/- 0.70 nmol x mmol C -1; epitestosterone glucuronide (ETG): 2.51 +/- 0.88 nmol x mmol C -1; TG/ETG ratio: 0.72 +/- 0.26 and cortisol (FLU): 10.02 +/- 0.79 nmol x mmol C -1. No significant modifications were observed during luteal phase (respectively: TG: 1.48 +/- 0.50 nmol x mmol C -1; ETG: 2.65 +/- 0.93 nmol x mmol C -1; TG/ETG ratio: 0.67 +/- 0.31 and FLU: 9.29 +/- 3.37 nmol x mmol C -1. Similarly, no significant effect of physical training was observed on studied parameters between these two groups during either follicular phase (TG: 1.96 +/- 1.00 nmol x mmol C -1; ETG: 1.97 +/- 0.70 nmol x mmol C -1; TG/ETG ratio: 0.66 +/- 0.05 and FLU: 11.31 +/- 3.73 nmol x mmol C -1) or luteal phase (TG: 1.93 +/- 0.86 nmol x mmol C -1; ETG: 3.19 +/- 1.23 nmol x mmol C -1; TG/ETG ratio: 0.69 +/- 0.33 and FLU: 9.52 +/- 3.86 nmol x mmol C -1). It is concluded that although physical training could play a role in androgen metabolism, it has no significant incidence on urinary TG/ETG ratio. This study thus confirms that sportswomen can also be considered as normal subjects when they do not present any obvious endocrine disorder induced by physical activity.     

Seasonal variation in adult leisure-time physical activity

PURPOSE: To determine the effect of season on self-reported leisure-time physical activity (LTPA) behaviors of Michigan adults. METHODS: Data were obtained from the 1996 Michigan Behavioral Risk Factor Survey conducted throughout the year. Survey respondents were considered active if they reported participating in at least one LTPA during the past month. Complete information regarding type, frequency, and duration of up to two LTPA was available on 2843 adults (1635 women and 1208 men). Four seasons were defined as winter (January-March; N = 677), spring (April-June; N = 759), summer (July-September; N = 760), and fall (October-December; N = 647). Total weekly leisure-time energy expenditure was quantified (kcal x kg-1 x wk-1) from MET intensities, duration, and frequency of activity sessions per week. Seasonal differences were identified using ANOVA. RESULTS: Average (+/-SEM) weekly leisure time energy expenditure was significantly greater (P < 0.001) during spring (17.5 +/- 0.8 kcal x kg-1 x wk-1) and summer (17.5 +/- 0.7 kcal.kg-1.wk-1) compared with winter (14.8 +/- 0.7 kcal x kg-1 x wk-1) and fall (15.0 +/- 0.7 kcal x kg-1 x wk-1). Duration of the first activity was significantly greater (P < 0.05) in summer (58.6 +/- 1.6 min) compared with winter (53.4 +/- 1.8 min). However, intensity (4.6 +/- 0.1 METs) and frequency (3.1 +/- 0.1 sessions per week) of the first activity did not differ among seasons. A second activity was performed by 1319 (46.4%) of active individuals and was more common in the spring (46.8%) and summer (54.5%) compared with fall (42.6%) and winter (39.4%) (chi2 = 31.0; P < 0.01). When both active and inactive subjects are considered, the Healthy People 2010 recommendation for moderate physical activity was met only during spring and summer. CONCLUSION: Weekly leisure-time energy expenditure averaged approximately 15-20% higher during spring and summer. Much of this difference was due to active respondents participating in a second activity during these seasons.