Self-paced exercise is less physically challenging than enforced constant pace exercise of the same intensity: influence of complex central metabolic control.

OBJECTIVE: To examine whether self-pacing reduces the physiological challenge of performing 5000 m rowing ergometry exercise in comparison with a matched-intensity exercise condition in which a constant effort pacing strategy is enforced. METHODS: Nine healthy well-trained male participants volunteered to participate in three 5000 m rowing conditions (two submaximal and one maximal conditions) in an individualised order. In the submaximal conditions, participants were required to (1) perform 5000 m at a constant rating of perceived exertion (RPE 15-Hard) (SubRPE) or (2) perform 5000 m at an enforced constant pace equivalent to the mean power output (PO) of the SubRPE condition (SubEXT). A maximal condition (MaxTT) was included to disguise the purpose of the study and to facilitate an element of randomisation in the test sequence. Dynamic intratest responses were assessed every 30 s: PO, VO2, iEMG, core (Tc) and skin temperatures (Tsk). RESULTS: There was no difference between performance times of the two submaximal trials. The mean PO represented 83.83 (SD 8.88)% (SubRPE) and 83.40 (8.84)% (SubEXT) of the mean MaxTT power output. Tc (SubRPE:38.46 (0.23) degrees C, SubEXT:38.72 (0.36) degrees C; p<0.01), post-test BLa (SubRPE:5.24 (2.18), SubEXT:6.19 (2.51) mmol/l; p<0.05) and iEMG (p<0.05) were significantly elevated in SubEXT compared with SubRPE. There were no differences in the dynamics of HR or VO2 between SubEXT and SubRPE. The intratest stroke-to-stroke variability of power output was significantly greater in the SubRPE condition compared with SubEXT (p<0.01). CONCLUSIONS: Enforced constant paced exercise presents a significantly greater physiological challenge than self-paced exercise. The ability to dynamically self-pace effort via manipulations of power output during exercise is an important behavioural response to homeostatic challenges and thus forms an integral part of a complex central regulatory process.

Associations of leisure-time physical activity and obesity with atherogenic lipoprotein-lipid markers among non-smoking middle-aged men.

The association of both leisure-time physical activity and obesity with lipoprotein-lipids and composite atherogenic markers were examined within a cross-sectional study of middle-aged men of higher socioeconomic status. Analyses were performed on a subsample (n=629) of non-smoking, non-diabetic men (46.7+/-7.8 years) who completed a preventive medical assessment between 1992 and 1996. Mean adjusted (age, body mass index (BMI), sum of skinfolds, fasting glucose, and logarithmic alcohol consumption) levels of high-density lipoprotein-cholesterol (HDL-C) were significantly higher, and logarithmic triglycerides significantly lower, with higher physical activity index (PAI) categories (both P<0.0001). Significantly lower adjusted mean ratios of both total cholesterol to HDL-C (TC:HDL-C), and logarithmic triglycerides to HDL-C (TG:HDL-C) with higher PAI were evident following adjustment for the above covariates (P=0.005 and P<0.0001). Age-adjusted non-HDL-C (total cholesterol minus HDL-C) decreased significantly with higher PAI categories, but was not significantly lower following covariate adjustment (P=0.150). On stepwise multiple regression, logarithmic physical activity score and BMI explained 9.5-14% of the variance in the TC:HDL-C and TG:HDL-C ratios in models including age, body mass, sum of skinfolds, fasting glucose and logarithmic alcohol consumption. Age, sum of skinfolds and logarithmic alcohol consumption were significant predictors of non-HDL-C (r2=8.0%). These findings emphasise the importance of both physical activity and obesity in predicting lipoprotein-lipid risk markers.

Metabolic clustering, physical activity and fitness in nonsmoking, middle-aged men.

PURPOSE: The relationship of both physical activity and predicted maximum oxygen consumption (VO2max) with the clustering of metabolic risk factors associated with the metabolic syndrome (MS) was examined within 711 employed middle-aged (46.9 +/- 7.8 yr) men. METHODS: Metabolic markers included fasting glucose, triglycerides, high-density lipoprotein cholesterol, blood pressure, and BMI, defined by highest risk quintiles or clinically relevant risk thresholds. RESULTS: The prevalence and age-adjusted odds ratios of all MS clusters were inversely graded across both higher physical activity index (PAI) and cardiorespiratory fitness (CRF) categories. The age-adjusted odds ratio for the clustering of clinically relevant metabolic markers was 0.60 (95% CI 0.22-1.22) for subjects in the occasional/light PAI, 0.32 (95% CI 0.12-0.82) for the moderate/moderately vigorous PAI, and 0.13 (95% CI 0.02-1.02) for the vigorous PAI when compared with subjects in the sedentary PAI (P < 0.05 for trend). The corresponding age-adjusted odds ratio was 0.28 (95% CI 0.14-0.57) for subjects in the moderate fitness category and 0.12 (95% CI 0.05-0.32) for the highest fitness category compared with those in the lowest fitness category (P < 0.001 for trend). Higher levels of physical activity or CRF were also associated with significantly lower age-adjusted odds ratios for the MS after exclusion of obesity in the MS definition. CONCLUSION: Overall, these cross-sectional results suggest that higher physical activity and predicted VO2max levels are associated with a decreased clustering of risk factors associated with the MS in middle-aged men of higher social class.

Plasma viscosity and its biochemical predictors: associations with lifestyle factors in healthy middle-aged men.

The association of lifestyle factors and biochemical variables with plasma viscosity was examined in a sample of middle-aged males of high social status. Analyses were performed on a subsample of men that had relevant rheological and biochemical variables determined during a preventive medical assessment conducted between 1992 and 1996. Among 622 subjects (64 smokers), measures of physical activity or predicted VO2max and adiposity (sum of subcutaneous skinfolds) were the lifestyle factors significantly associated with plasma viscosity (both P < 0.001). Among the biochemical variables, serum total protein and plasma fibrinogen concentrations accounted for most of the explained variability in plasma viscosity within subjects (combined adjusted r2 = 65.5%). Logarithm-transformed triglyceride, leukocyte count and serum globulin together contributed an additional 3.0% of the variance in plasma viscosity. Serum total protein, In triglycerides and leukocyte count decreased significantly across higher quartiles of predicted VO2max (all P < 0.0001), with trends towards lower fibrinogen and globulin concentrations (P = 0.054 and P = 0.050, respectively). Higher levels of adiposity were also significantly associated with higher levels of serum total protein (P < 0.0001), globulin (P < 0.0001), fibrinogen (P < 0.01), leukocyte count (P < 0.05), and triglycerides (P < 0.0001). The association of lifestyle factors with the biochemical predictors of plasma viscosity may result directly from a pro-inflammatory state of adipose tissue origin and/or a larger plasma volume related to higher levels of cardiorespiratory fitness. Randomised controlled trials of the effects of regular physical activity of different intensities on plasma viscosity, with reference to body composition, are now required.

Leisure time physical activity, cardiorespiratory fitness, and plasma fibrinogen concentrations in nonsmoking middle-aged men.

PURPOSE: The relationship of both leisure time physical activity and predicted maximum oxygen consumption (VO2max) with plasma fibrinogen concentration was examined within a cohort of employed middle-aged men. METHODS: Analyses were performed on a subsample of 635 nonsmoking men (46.7 +/- 7.7 yr) who completed a preventive medical assessment between 1992 and 1996. RESULTS: Among nonsmokers, mean age-adjusted fibrinogen concentration decreased significantly with higher physical activity index (PAL) categories and quartiles of predicted VO2max (mL x kg(-1) x min(-1)) (both P = 0.001). Mean age-adjusted plasma fibrinogen concentrations were significantly different (P < 0.05) between inactive and vigorous PAI groups and extreme quartiles of predicted VO2max (mL x kg(-1) x min(-1)). These relationships were no longer significant after adjustment for the confounding effect of other ischemic heart disease risk factors. Stepwise multiple regression analyses showed that age, sum of skinfolds, and blood leukocyte count were the strongest predictors of plasma fibrinogen concentration. CONCLUSION: These data do not confirm a significant independent association of both physical activity and predicted VO2max (mL x kg(-1) x min(-1)) with fibrinogen concentrations among nonsmoking middle-aged men of similar high social class.

Plasma viscosity, fibrinogen and the metabolic syndrome: effect of obesity and cardiorespiratory fitness.

The association between both plasma viscosity and fibrinogen concentration with clustering of metabolic risk markers was examined within a cross-sectional study of employed middle-aged men. Analyses were performed on a subsample of 629 non-smokers (46.7+/-7.8 years) without diabetes. The effect of obesity and cardiorespiratory fitness on these haemorheological parameters and their association with the metabolic syndrome was also investigated. The cohort was grouped by the number of metabolic markers present. Metabolic markers included high-density lipoprotein-cholesterol (<1.13 mmol/l), triglycerides (> or =1.805 mmol/l), glucose (> or =5.5 mmol/l) and diastolic blood pressure (> or =90 mm Hg). The age-adjusted odds ratio for hyperviscosity (> or =1.67 mPa/s) was 2.08 [95% confidence interval (CI), 1.06-4.05; P = 0.031] for the subjects with the metabolic syndrome (three or more metabolic markers) when compared with those with no metabolic abnormalities. The comparable age-adjusted odds ratio for hyperfibrinogenaemia (> or = 3.47 g/l) was non-significantly higher at 1.69 (95% CI, 0.87-3.27; P = 0.119). The mean age-adjusted plasma viscosity level and the prevalence of hyperviscosity increased significantly from 1.629 to 1.692 mPa/s (P = 0.0005) and from 21.0 to 36.0% with accumulating metabolic markers (P = 0.006). Plasma viscosity and fibrinogen concentration both increased with higher quartiles of skinfolds (P = 0.003 and P = 0.01, respectively) following adjustment for age, lipids and leucocyte count. Plasma viscosity was also significantly lower with higher levels of predicted maximum oxygen consumption (VO2max) (P = 0.0005). The odds ratio for hyperviscosity in subjects with the metabolic syndrome as compared with those with no metabolic markers was attenuated following adjustment for age, sum of skinfolds and predicted maximum oxygen consumption (VO2max) (1.44; 95% CI, 0.72-2.90; P = 0.307). These cross-sectional results suggest that plasma viscosity is associated with increased clustering of metabolic markers in middle-aged men of high socio-economic status. Obesity and poor cardiorespiratory fitness may be important in the development of haemorheological abnormalities associated with the metabolic syndrome.

Physical activity, cardiorespiratory fitness, and the primary components of blood viscosity.

PURPOSE: The relationship of both self-reported leisure time physical activity (LTPA) and predicted maximum oxygen consumption (VO2max) with plasma viscosity and hematocrit (Hct) concentration was examined within a cross-sectional sample of employed middle-aged men. METHODS: Analyses were performed on a subsample of nonsmoking men who completed a preventive medical assessment between 1992-1996. RESULTS: Among nonsmokers the mean age-adjusted levels of plasma viscosity (N = 590) and Hct concentration (N = 632) were significantly lower with higher Physical Activity Index (PAI) categories (P = 0.001 and P = 0.01, respectively). Following adjustment for conventional IHD risk factors and blood leukocyte count, a significant inverse relationship remained for Hct (P = 0.044) but not plasma viscosity. Mean age-adjusted plasma viscosity and Hct concentration also showed a significant decrease with higher quartiles of predicted VO2max (mL x kg(-1) x min(-1))(P = < 0.00005 and P = 0.0004, respectively). Following adjustment for all confounding variables mean plasma viscosity and Hct concentration remained significantly lower with higher quartiles of predicted VO2max (mL x kg(-1) x min(-1))(P = < 0.00005 and P = 0.047). CONCLUSIONS: These data confirm the inverse relationship between LTPA and/or predicted VO2max with plasma viscosity and Hct concentration within nonsmoking middle-aged men of high socioeconomic status.

The effects of a children's summer camp programme on weight loss, with a 10 month follow-up.

OBJECTIVE: To assess the long-term effects of a multidisciplinary approach involving structured fun-type skill learning physical activities in the treatment of obese and overweight children. DESIGN: A longitudinal investigation incorporating repeated measurements before and after the 8 week intervention and after the 44 week follow-up period. METHODS: The camp programme (Massachusetts, USA) utilised structured fun-based skill learning physical activities, moderate dietary restriction and behaviour modification. The primary aims of the intervention were to reduce body mass and promote the maintenance of the reduction in body mass using an alternative to standard exercise prescription. SUBJECTS: One-hundred and ninety-four children (64 boys and 130 girls, aged 12.6+/-2.5y) enrolled at a summer weight loss camp, of which 102 children (38 boys and 64 girls aged 13.6+/-2.4y) returned 1 y later. MEASUREMENTS: On commencement of the programme all children were assessed for body mass and stature. At follow-up, data was available on 102 subjects for body mass and stature. RESULTS: Over the 8 week intervention significant reductions (P= 0.00) in body mass were obtained. During the 44 week follow-up significant increases (P= 0.00) were noted in body mass, body mass index (BMI) and stature, but as expected there were large variations in the responses. One year after the initial measures had been taken mean body mass and BMI were lower than at the start of the intervention, BMI significantly so (week 0, 32.9 +/- 7.4 kg/m2; week 8 29.1 +/- 6.5 kg/m2; week 52, 30.05 +/- 7.04 kg/m2); (P= 0.00). Stature increased significantly (week 0, 1.58 +/- 0.12 m; week 52, 1.64 0.11 m) (P= 0.00) during this period, demonstrating a reduction in mean body mass over a 1 y period whilst subjects continued to increase in stature. When changes in BMI are analysed with the use of standard scores, there is a non-significant increase (P=0.07) in BMI during the follow-up phase and 89% of children had a lower BMI than at week 0. CONCLUSIONS: These findings suggest that the use of a structured fun-based skill learning programme may provide an alternative method of exercise prescription to help children prolong the effects of the 8 week intervention. Further investigations will help identify the key factors that are necessary for long-term lifestyle modification.