Physical fitness profiles of young men: associations between physical fitness, obesity and health

Obesity in youth has increased during the last 10 years in Western countries. Several studies have investigated physical activity and its effects on obesity and health, showing that regular physical activity combined with improved physical fitness reduces the risk of obesity and several metabolic problems (e.g. diabetes mellitus, metabolic syndrome, heart disease) and also improves overall health. However, there is only limited scientific information available concerning the changes in the physical fitness profiles of youth. It is obvious that only slight changes observed in endurance-type physical activity can also be observed in aerobic capacity. Today and in the future, a major public health concern for teenage and young adults is the combination of increasing body fatness together with decreasing physical fitness. In order to evaluate overall fitness level, it is particularly essential to examine both aerobic and neuromuscular fitness. Therefore, in clinical practice work and health behaviour education, a person's physical fitness should be measured more frequently with various measures. Furthermore, population-based surveys should be combined with regular measurement of physical fitness to study sedentary lifestyles, particularly in young people. This article presents a review of current physical fitness profiles of male children, adolescents and young adults, which hopefully initiates further studies in this relevant scientific field. In addition, the importance of physical fitness level is evaluated in relation to obesity and health. Collectively, studies examining physical fitness profiles of young men suggest a disturbing worldwide trend of decreased aerobic fitness and increased obesity. Continued efforts to foster improved physical fitness and healthy lifestyles should be encouraged to combat these trends. Such efforts should include frequent and objective assessment of physical fitness rather than solely relying on subjective assessment of physical activity.     

The influence of diabetes mellitus on cardiovascular function in children and adolescents.

Early manifestations of non-atherosclerotic cardiomyopathy, a recognized complication of diabetes in adults, have been suggested to contribute to depressed levels of aerobic fitness described in children and adolescents with this disease. This study measured components of aerobic fitness and cardiovascular function during maximal cycle ergometer exercise in 11 insulin-dependent diabetic boys aged 10.2-16.5 years. Mean duration of diabetes was 4.5 years. Eleven non-diabetic subjects matched for age, body size, and regular physical activity served as controls. No differences in maximal oxygen uptake or heart rate were observed between the two groups, nor were any significant differences recorded in submaximal stroke volume, cardiac output, heart rate, and pressure-rate product. This study failed to reveal any evidence of functional myocardial disease in children and young adolescents with diabetes, suggesting that manifestations of diabetic cardiomyopathy should not be expected during the pediatric years. Moreover, these findings indicating normal cardiovascular function in young diabetic subjects imply that regular levels of habitual physical activity are more likely to affect aerobic fitness in these patients rather than influences of the diabetic state itself.     

Myocardial and peripheral vascular functional adaptation to exercise training

Exercise training seems to restore impaired vascular function in both peripheral and myocardial vessels in patients with coronary artery and peripheral vascular disease or in patients with risk factors for these diseases. However, the results on the effects of exercise training on vascular function in apparently healthy subjects are controversial. We studied the effects of long-term volitionally increased physical activity on peripheral and myocardial vascular function in nine young healthy male monozygotic twin pairs discordant for physical activity and fitness. The brothers were divided into more (MAG) and less active groups according to physical activity and fitness. The difference between groups in VO(2max) was 18+/-10% (P<0.001). Myocardial perfusion at rest, during adenosine-induced vasodilatation and during cold-pressor test and myocardial oxygen consumption were measured with positron emission tomography. In addition, endothelial function was measured using ultrasound in brachial and left anterior descending coronary arteries, and standard echocardiographic measures were taken. No differences were observed in myocardial perfusion measurements between groups. MAG tended to have a lower oxygen extraction fraction (P=0.06), but oxygen consumption was similar between the groups. No differences were found in coronary artery, myocardial resistance vessel or peripheral endothelial function between groups. These results suggest that when the effects of heredity are controlled, myocardial perfusion reserve and endothelial function, both in peripheral arteries and myocardial vessels, are not enhanced by increased physical activity and fitness in young healthy adult men.     

Muscular strength, aerobic fitness, and metabolic syndrome risk in Flemish adults

PURPOSE: To investigate the association of muscular strength and aerobic fitness with a continuous metabolic syndrome risk score in male and female adults. METHODS: This cross-sectional study included 1019 (571 men) Flemish adults, aged 18-75. Muscular strength was evaluated by measuring isometric knee extension and flexion peak torque, using a Biodex System Pro 3 dynamometer. Aerobic fitness was quantified as VO2peak and was determined during a maximal cycle ergometer exercise test. Both strength and aerobic fitness were scaled for differences in FFM, using allometric analyses. A validated metabolic syndrome risk score that was based on waist circumference, triglycerides, blood pressure, fasting plasma glucose, and HDL cholesterol was used. Metabolic syndrome risk score, strength, and aerobic fitness were analyzed as continuous variables using multiple linear regression. RESULTS: Metabolic syndrome risk was inversely associated with strength, independently of aerobic fitness, and after adjustment for age, height, education level, smoking status, and dietary intake in women (beta = -0.172, P < 0.001). In men, however, adjustment for aerobic fitness attenuated the inverse association between strength and metabolic syndrome risk (beta = -0.044, P > 0.05). Independently of strength, aerobic fitness was inversely associated with metabolic syndrome risk (men: beta = -0.309, P < 0.001; women: beta = -0.208, P < 0.001). Furthermore, independent associations were found for strength and aerobic fitness with several individual metabolic syndrome risk factors in women, and most of these associations were only partially mediated by central and general adiposity indicators. CONCLUSION: Although cross-sectional, the present results support inclusion of strength training in addition to aerobic exercise in physical activity recommendations for women, because both types of activity might show additional effects in reducing the risk of the metabolic syndrome.     

Fluid shifts with successive running and bicycling performance

Seven men and five women triathletes ran 10 km and bicycled 40 km at race pace for the purpose of studying changes in plasma, blood, and red blood cell volumes. A second trial followed 1 wk later with the order of exercise counterbalanced (running first-cycling second; cycling first-running second). Water consumption was measured by providing water bottles on the bike phase, at 3.2 and 6.7 km on the run phase, and at the transition area. Body weight was obtained at the start and end of each phase. A 10-ml blood sample was obtained just before starting and immediately upon finishing each phase. Changes in plasma volume, blood volume, and red cell volume were calculated from hematocrit and hemoglobin values. Changes in blood volume, plasma volume, and red cell volume did not differ between the sexes; therefore, results were combined. Sequential cycling and running caused significant hemoconcentration (-6 to -8% blood volume; -8 to -10% plasma volume) with moderate dehydration (-3 to -4% body weight) despite ad libitum fluid replacement. More severe fluid compartment shifts occurred on the initial phase regardless of exercise mode. Blood volume and plasma volume changes during the second mode of exercise were minor in extent with the major differences occurring in red cell volume. When fluid changes were calculated on a per hour basis, shifts were greater during running than during cycling.     

Body composition and aerobic capacity in young and middle-aged endurance-trained men

Aging is associated with increased body fat, decreased muscle mass, lower maximal O2 uptake, and lower energy intake. It has been asserted that these changes are caused in part by decreased activity. In order to determine the effects of aging in men who are habitually active, 6 young men (26.8 +/- 1.2 yr) and 6 middle-aged men (52.0 +/- 1.9 yr) who had been running, cycling, and/or rowing for at least 2 yr were studied in a metabolic ward. The men consumed a diet to maintain constant body weight while keeping to their usual exercise schedule and intensity. Both groups had a similar body mass index and muscle mass, but the middle-aged men had a 77% greater fat mass (P = 0.028). Daily energy requirement was 17% lower in the middle-aged men (P = 0.029) although basal metabolic rate was similar in both groups. Aerobic capacity was 15% lower in the middle-aged men per unit body weight (P = 0.048) but not per unit of lean body mass. The young men exercised for an average 12.3 hr.wk-1 and the middle-aged men for 7.5 hr.wk-1 (P = 0.018). For both young and middle-aged men, weekly hours of exercise were negatively correlated with fat mass, and positively correlated with daily energy requirements and maximal O2 uptake. These findings show that in both young and middle-aged men who habitually exercise aerobically at 65 to 80% maximal O2 uptake, the time spent training was associated with body composition, energy requirements, and aerobic capacity.     

The 6-minute walk test as a predictor of objectively measured aerobic fitness in healthy working-aged adults

There is a paucity of research examining the 6-minute walk test (6MWT) in young to middle-aged healthy individuals, and little is known about the utility of the 6MWT for predicting aerobic fitness. Purpose: 1) To characterize the aerobic demand of the 6MWT in a group of healthy working-aged adults; 2) to examine the ability of the 6MWT to objectively differentiate the fitness level between participants; and 3) to create prediction equations for 6MWT distance and maximal oxygen consumption (VO2 max) using the 6MWT results in combination with easily measured anthropometric and demographic variables. Methods: Participants (N = 44; men, 23; women, 21) completed the 6MWT, VO2 max, and a battery of simple fitness measures. Results: The aerobic demand of the 6MWT was 28.7 ± 5.7 mL·kg(-1)·min(-1) (72.7% ± 11.6% of VO2 max). Rank order correlation revealed a moderate strength association between 6MWT distance and VO2 max (r = 0.49; P = 0.001). Using stepwise multiple linear regression, we were able to account for 72.4% of the variance in VO2 max using the 6MWT when combined with participant body weight, sex, resting heart rate (HR), and age according to the following equation: VO2 max (mL·kg(-1)·min(-1)) = 70.161 + (0.023 × 6MWT [m]) - (0.276 × weight [kg]) - (6.79 × sex, where m = 0, f = 1) - (0.193 × resting HR [beats per minute]) - (0.191 × age [y]). Conclusion: The 6MWT is of moderate-to-vigorous intensity, and may be useful in the classification of aerobic fitness, which is associated with health outcomes. Inclusion of further patient characteristics greatly increases the predictive value of the 6MWT for estimating VO2 max, which has important implications for those seeking a noninvasive and simple-to-use determinant of maximal aerobic power.     

Exercise training in obesity lowers blood pressure independent of weight change

PURPOSE: We used the rabbit model of obesity and exercise training to determine effects of exercise training during the development of obesity on resting blood pressure and heart rate, ventricular hypertrophy, blood volume, and hormonal profile. METHODS: Female New Zealand white rabbits were assigned to one of four groups: lean sedentary (L-S, N = 17), lean exercise-trained (L-EX, N = 16), obese sedentary (O-S, N = 18), and obese exercise-trained (O-EX, N = 15). Lean rabbits were fed a maintenance diet whereas obese rabbits were fed an ad libitum high fat (10% added fat) diet. Simultaneously, exercise-trained animals underwent a progressive treadmill exercise training protocol for 12 wk. After 12 wk of diet and exercise regimens, resting blood pressure and heart rate were measured from a central ear artery catheter. Ventricular hypertrophy was evaluated using wet ventricular weights. Blood volume was measured using the Evans blue dye procedure; hormonal profile was evaluated from arterial plasma/serum samples. RESULTS: After 12 wk, O-S and O-EX had similar body weights and similar percentage increases in body weight. Despite similar body weights, O-EX had an approximate 6-mm Hg lower mean blood pressure compared with the elevated pressure seen in O-S (P < or = 0.05). Obese rabbits had greater resting heart rate, plasma cholesterol and triglycerides, and plasma renin activity compared with lean rabbits, and these values were unaffected by exercise training. Plasma and blood volumes, as well as plasma insulin, cortisol, and aldosterone were unaffected by exercise training. CONCLUSION: These data suggest that exercise training, in the absence of differences in body weight, may be useful in the reduction of obesity-induced hypertension but that other therapies may be needed in order to control other cardiovascular risk factors.     

A survey of aerobic fitness levels in a Canadian military population.

Aerobic fitness was assessed for 3171 men aged 17-55 years and for 610 women aged 17-29 years serving in almost every segment of the Canadian Forces (CF). Maximal oxygen uptake (Vo2 max) was predicted from heart rate measured during submaximal exercise. The survey showed that recruit training markedly improved Vo2 max for both men and women but that, after graduates were assigned to their trades and classifications and fitness training was no longer compulsory, fitness returned to pre-training levels. The relationship between daily activity and aerobic fitness was further demonstrated by comparing land, air, and sea elements in the CF. The active life of the young infantry soldiers is reflected in their relatively high Vo2 max. The available evidence indicates that, unless their duties involve compulsory fitness training (recruits) or hard physical work (infantry soldiers), the military in Canada have aerobic fitness levels which are not markedly higher than their civilian counterparts.     

电影磁共振图像评定运动员心脏形态与功能

本文对瑞典10名耐力运动员(耐力组,长跑7人,游泳3人),10名举重运动员(力量组)及10名健康无训练者(对照组)进行了心脏电影磁共振图像与最大吸氧量的测试。结果表明:1)从左室舒末容量、左室编末容量、心搏量、左室心肌重量、最大吸氧量、最大通气量等指标来看,无论是其绝对实测值,还是其按体表面积或体重校正计算的相对值,耐力组均非常显著地大于其它二组。力量组除了左室心肌重量及左室心肌重量/左室舒末容量比值略有增高外(P<0.05),其余各指标与对照组比较均无显著性差异。2)左室舒末容量、心搏量、左室心肌重量及最大通气量四指标均与最大吸氧量呈高度正相关关系,相关系数依次为0.88,0.85,0.81,0.76,各相关系数均有高度显著性(P<0.001)。3)本文各组的左室心肌重量的电影磁共振图像测定值低于以往多数类似研究对象的超声心动图测定值。文章指出,电影磁共振图像技术是评定左室心肌重量与左室容量十分准确可靠的无创性检查新方法。本文首先报道了运动员心脏电影磁共振部分指标正常测量值。     

Heart size and function of soldiers, athletes, and sedentary men

This study compares the heart sizes and left ventricular masses of soldiers (n = 11) with age- and body size-matched groups of sedentary men (n = 10) and accomplished athletes (n = 11). Echocardiography revealed that active duty soldiers (A) who met minimal fitness standards and pentathletes (P) had greater average left ventricular (LV) end-diastolic volumes (A = 10%, NS; P = 28%, p less than 0.05), stroke volumes (A = 29%, NS; P = 44%, p less than 0.01), and LV masses (A = 22%, NS; P = 76%, p less than 0.01) than sedentary subjects. Athletes had an average LV wall thickness which was 23% (p less than 0.05) greater than that of soldiers and 32% (p less than 0.01) greater than that of sedentary men. The LV wall thickness to radius ratio (h/r) was similar between soldiers and sedentary men, but in athletes the h/r was greater (p less than 0.01) than in the less conditioned subjects. These data suggest that soldiers who meet minimal standards of fitness exhibit cardiac morphometric features consistent with endurance conditioning. However, the soldiers studied were significantly less (p less than 0.001) conditioned than the competitive athletes. These data suggest that improvements in aerobic and cardiac conditioning could be achieved through a greater emphasis on physical training.     

Aerobic fitness does not contribute to prediction of orthostatic intolerance

Several investigations have suggested that orthostatic tolerance may be inversely related to aerobic fitness (VO2max). To test this hypothesis, 18 males (age 29 to 51 yr) underwent both treadmill VO2max determination and graded lower body negative pressures (LBNP) exposure to tolerance. VO2max was measured during the last minute of a Bruce treadmill protocol. LBNP was terminated based on pre-syncopal symptoms, and LBNP tolerance (peak LBNP) was expressed as the cumulative product of LBNP and time (torr-min). Changes in heart rate, stroke volume, cardiac output, blood pressure, and impedance rheographic indices of mid-thigh-leg fluid accumulation were measured at rest and during the final minute of LBNP. For all 18 subjects, mean (+/- SE) fluid accumulation index and leg venous compliance index at peak LBNP were 139 +/- 22 ml and 3.9 +/- 0.4 ml . 100 ml . torr-min-2 x 10(3), respectively. Pearson product-moment correlations and step-wise linear regression were used to investigate relationships with peak LBNP. Variables associated with endurance training, such as VO2max and percent body fat, were not found to correlate significantly (P less than 0.05) with peak LBNP and did not add sufficiently to the prediction of peak LBNP to be included in the step-wise regression model. The step-wise regression model included only fluid accumulation index, leg venous compliance index, and blood volume, and resulted in a squared multiple correlation coefficient of 0.978. These data do not support the hypothesis that orthostatic tolerance as measured by LBNP is lower in individuals with high aerobic fitness.     

Physical fitness and physical activity during adolescence as predictors of cardiovascular disease risk in young adulthood. Danish Youth and Sports Study. An eight-year follow-up study

The purpose of this study was to determine if physical activity, aerobic fitness and isometric strength during adolescence were predictors of cardiovascular risk factor levels in young adulthood. The following measurements were carried out: maximal oxygen uptake (VO(2)max), maximal voluntary contraction (MVC) in four muscle groups, physical activity (questionnaire), blood pressure (BP), total cholesterol, high density lipoprotein cholesterol (HDL-C), triglycerides, anthropometric variables and body fat % (sum of four skinfolds). The data were collected from the Danish Youth and Sports study, an observational longitudinal study in which two measurements were carried out over an eight-year period. The findings in this study indicated that the relationships between the absolute levels of physical fitness and activity in adolescence and the subsequent level of CVD risk factors are weak. However, the changes in physical fitness and physical activity were related to the absolute levels of CVD risk factors in young adulthood, especially in men. Weak relationships were found between the changes in physical fitness/activity and changes in CVD risk factor levels in both sexes. In conclusion, many subjects changed their levels of physical activity and physical fitness between adolescence and young adulthood and the changes, especially in aerobic fitness, seemed to be the best predictor of CVD risk factor levels in young adulthood.     

Relationships between left ventricular morphology, diastolic function and oxygen carrying capacity and maximal oxygen uptake in children

Little attention has been paid to children with respect to factors controlling maximal oxygen uptake (V.O (2max)). This study was therefore specifically designed to examine the potential relationships between cardiac size, diastolic function and O (2) carrying capacity with maximal aerobic capacity. Specifically, body size indices (body surface area, lean body mass), resting left ventricular dimensions and filling characteristics, blood haemoglobin concentration as well as V.O (2max) established during a maximal cycle exercise test were assessed in a large cohort (n = 142) of healthy 10 - 11 year old boys and girls. Results were compared between groups of low (< 50, L), moderate (50 - 60, M) and high (> 60, H) V.O (2max) (ml . min (-1) . kg (-1) of lean body mass). Moreover, potential contributors to V.O (2max) variance were investigated using univariate and multivariate regression analyses over the overall population. The major results show no differences between the 3 groups for all diastolic and systolic function indices as well as blood haemoglobin and systemic vascular resistances (used as an index of afterload). None of these variables emerged from regression analyses as potential predictors of V.O (2max.) After accounting for body size variation, heart dimensions, and especially left ventricular internal dimensions, differed between H and M and L and were associated with higher cardiac filling and subsequently stroke volume. Strong relationships between V.O (2max) and heart dimensions were noticed, due primarily but not exclusively to the influence of body size. After adjusting for lean body mass, end-diastolic diameter contributed modestly (8 %) but significantly to V.O (2max) variance, which is biologically meaningful.     

Maximal oxygen uptake in trained and untrained 15-year-old boys.

The purpose of this study was to assess maximal aerobic power (VO2max) in trained and untrained 15-year-old boys. The trained subjects (18) were junior swimmers from a Belgrade swimming team, and the untrained ones (12) were from a Belgrade high school. VO2max was directly measured during progressive cycle ergometer exercise using open circuit spirometry. No significant differences in height, mass, percentage fat and vital capacity were noted between the trained and untrained groups. Maximal aerobic power (overall, relative and in relation to lean body mass) in absolute values, and expressed per kilogram of body mass and lean body mass, was 31.5%, 21.2% and 20.6%, respectively, higher in the trained than in the untrained group (P less than 0.05). These data suggest that physical training significantly increases maximal aerobic power in young subjects.     

Blood volume: importance and adaptations to exercise training, environmental stresses, and trauma/sickness

This paper reviews the influence of several perturbations (physical exercise, heat stress, terrestrial altitude, microgravity, and trauma/sickness) on adaptations of blood volume (BV), erythrocyte volume (EV), and plasma volume (PV). Exercise training can induce BV expansion: PV expansion usually occurs immediately, but EV expansion takes weeks. EV and PV expansion contribute to aerobic power improvements associated with exercise training. Repeated heat exposure induces PV expansion but does not alter EV. PV expansion does not improve thermoregulation, but EV expansion improves thermoregulation during exercise in the heat. Dehydration decreases PV (and increases plasma tonicity) which elevates heat strain and reduces exercise performance. High altitude exposure causes rapid (hours) plasma loss. During initial weeks at altitude, EV is unaffected, but a gradual expansion occurs with extended acclimatization. BV adjustments contribute, but are not key, to altitude acclimatization. Microgravity decreases PV and EV which contribute to orthostatic intolerance and decreased exercise capacity in astronauts. PV decreases may result from lower set points for total body water and central venous pressure, while EV decreases may result from increased erythrocyte destruction. Trauma, renal disease, and chronic diseases cause anemia from hemorrhage and immune activation which suppresses erythropoiesis. The re-establishment of EV is associated with healing, improved life quality, and exercise capabilities for these injured/sick persons.     

Muscle mass and strength, body composition and dietary intake in master strength athletes vs untrained men of different ages

AIM: The aim of this study was to compare muscle strength and thickness, body composition and dietary intake between master strength athletes and controls. METHODS: Cross-sectional comparison between: 1) young control men (25.7+/-3.4 y; n=10); 2) middle-aged master athletes (52.1+/-4.7 y; n=9); 3) middle-aged control men (51.9+/-3.1 y; n=11); 4) older master athletes (71.8+/-3.8 y; n=8); and 5) older control men (70.6+/-3.3 y; n=10). Athletes had been strength trained for 22.8+/-14.9 y. Maximal isometric strength of the leg extensors was measured with a leg dynamometer, body composition by skin folds, muscle thickness of the vastus lateralis with an ultrasound scanner and dietary intake by food diaries for 4 days. RESULTS: Athletes had more lean body mass than age-matched controls (P<0.001-0.05) and young controls more than older controls (P<0.01). No group differences were observed in the thickness of vastus lateralis. Athletes showed higher absolute strength and strength per vastus lateralis thickness ratio than all control groups (P<0.01-0.001). Body mass adjusted dietary intake did not differ between the strength trained and control men. Dietary intake did not correlate with strength, muscle thickness and lean body mass. CONCLUSION: The present older men with a long-term history of strength training showed greater muscle strength and strength per muscle thickness ratio than the untrained controls. The data support the usefulness of continuous strength training to preserve muscle strength in older men.     

Aerobic fitness in women and responses to lower body negative pressure

High aerobic fitness may be associated with impaired responsiveness to orthostatic challenge. This could be detrimental to astronauts returning from spaceflight. Thus, we examined the cardiovascular responses of a group of 45 healthy women to graded lower body negative pressure (LBNP) through 5 min at -50 mm Hg or until they become presyncopal. The ages (range = 23-43 years, mean = 30.4) and peak aerobic capacities (range = 23.0-55.3 ml.kg-1.min-1, mean = 37.8) of these subjects paralleled those of the women astronauts. We monitored heart rate, stroke volume, cardiac output, Heather index of contractility, arterial pressure, peripheral resistance, change in calf circumference, and thoracic impedance (ZO)--a measure of fluid in the chest. The women in this study exhibited the same response pattern to LBNP as previously reported for male subjects. VO2peak of the six subjects who became presyncopal was not different from VO2peak of the tolerant subjects. At rest, only systolic and mean arterial pressures were significantly correlated with VO2peak. Percent changes in calf circumference (i.e. fluid accumulation in the legs) at -30 and -40 mm Hg were the only responses to LBNP significantly related to VO2peak. The greater pooling of blood in the legs during LBNP by women with higher aerobic fitness, and lower percent body fat may be related to more muscle tissue and vasculature in the legs of the more fit subjects. These data indicated that orthostatic tolerance is not related to aerobic capacity in women, and orthostatic tolerance need not be a concern to aerobically fit women astronauts.     

Effects of exercise in the heat on body fluid distribution.

Experimental findings as to body fluid shifts during exercise appear to be greatly influenced by the mode of exercise (bicycle ergometer, treadmill, etc) and by the state of subject hydration. Endurance training has been shown to increase resting plasma (blood) volume. Also, endurance training results in modification of vascular volume dynamics during exercise, i.e. for a set task, plasma volume becomes stabilized. In the untrained individual, heat exposure exaggerates body fluid shifts during exercise. With training, stability of vascular volume is attained during heat exposure, but maximum protective responses towards exercise in heat is only gained upon heat acclimatization. Two items benefit the individual: an increase in the capacity of the sweat mechanism and an expansion of plasma volume. Benefits of training as to body fluid shifts are probably a result of metabolic changes within the active muscle mass.