Physical activity in relation to aerobic fitness and body fat in 14- to 15-year-old boys and girls

The purpose of this study was to examine the strength of the relationship between different variables of physical activity and aerobic fitness and body fat in adolescent boys and girls. Activity energy expenditure (AEE), time spent in a sedentary state, and time spent engaged in moderate and vigorous physical activity (MVPA, ≥50% peak oxygen uptake, ) were assessed by the minute-by-minute heart rate monitoring method in 82 randomly selected 14- to 15-year olds (42 boys, 40 girls). Body fat was determined by measuring skinfold thicknesses. was measured by indirect calorimetry. Somatic maturity level was determined by percentages of adult (i.e. 18 years) height attained at examination. AEE was related to aerobic fitness for both genders (boys, r=0.30, P=0.056; girls, r=0.45, P=0.003). For boys, there was a significant relationship between maturity level and (r=0.48, P<0.001). For both genders, body fat was significantly and negatively related to (r=–0.48 and r=–0.43, P<0.01). Body fat and maturity explained 47% of the variation in in boys, whereas AEE and body fat explained 22% of the variation in in girls. No significant associations between physical activity variables and the data on body fat were observed. The total amount of physical activity (AEE) was related to , at least in adolescent girls. Although seems to be influenced by the maturity level in adolescent boys, the data support the promotion of a daily active lifestyle among young people. Electronic Publication     

Lean soft tissue contributes more to bone health than fat mass independent of physical activity in women across the lifespan

ObjectivesTo investigate the association between lean soft tissue (LST) and fat mass (FM) on bone health variables in women across the lifespan, while taking into account the influence of objectively measured habitual physical activity (PA).Study designA total of 104 women, 37 young (23.3 ± 2.6 years), 28 middle-age (49.2 ± 5.4 years), and 39 old (68.3 ± 6.4 years) participated in this cross-sectional study. All underwent a DXA scan and wore a pedometer for 7 days.Main outcome measuresBone mineral content (BMC) and BMD of the whole body (WB), lumbar spine (LS) and proximal femur (PF), and body composition (FM and LST) were assessed with DXA and PA (steps/day) was assessed from 7 day pedometer counts.ResultsLST was significantly and positively associated with PF and LS BMD (r = 0.34; 0.67, p < 0.05), and WB, PF and LS BMC (r range = 0.41–0.59, p < 0.05) in all age groups and WB BMD in the middle-age group (r = 0.72, p < 0.05) independent of PA, FM, and hormonal status. FM was not positively associated with any bone variable in any age group when adjusted for PA, LST, and hormonal status. PA was significantly associated with WB BMD in the middle-age group (r = 0.60, p < 0.05), independent of LST, FM, and hormonal status.ConclusionsLST contributes more to bone health in women across the lifespan than FM, independent of PA and hormonal status.     

Fatigue resistance during high-intensity intermittent exercise from childhood to adulthood in males and females

This study examined the maturation pattern of fatigue resistance (FR) from childhood to adulthood in females and males during high-intensity intermittent exercise and compared FR between females and males in childhood and adolescence. Thirty males (boys 11.3 ± 0.5 years, teen-males 14.7 ± 0.3 years, men 24.0 ± 2.1 years) and 30 females (girls 10.9 ± 0.6 years, teen-females 14.4 ± 0.7 years, women 25.2 ± 1.4) participated in this study. They performed high-intensity intermittent exercise (4 × 18 maximal knee flexions and extensions with 1-min rest) on an isokinetic dynamometer at 120°s⁻¹. Peak torque of flexors (PTFL) and extensors (PTEX), and total work (TW) were measured. FR was calculated as % of PTEX, PTFL, and TW in 4th versus 1st set. FR was greater (P < 0.05) in boys versus teen-males and men, and in teen-males versus men. In females, FR was greater (P < 0.05) in girls versus teen-females and women, but not different between teen-females and women. FR was not different in boys versus girls and in teen-males versus teen-females. FR for PTFL, PTEX, and TW correlated negatively (P < 0.001) with the respective peak values (r = −0.68 to −0.84), and FR for TW with peak lactate (r = −0.58 to −0.69). In addition, age correlated (P < 0.01) with FR for males (r = −0.75) and females (r = −0.55). In conclusion, FR during high-intensity intermittent exercise undergoes a gradual decline from childhood to adulthood in males, while in females the adult profile establishes at mid-puberty (14–15 years). The maturation profile of FR in males and females during development appears to reflect the maturation profiles of peak torque, short-term muscle power, and lactate concentration after exercise. T. Tsirini and A. Zafeiridis contributed equally to this work.     

Oxidative stress, inflammation, and muscle soreness in an 894-km relay trail run

We describe the effects of multi-day relay trail running on muscle soreness and damage, and systemic immune, inflammatory, and oxidative responses. 16 male and 4 female athletes ran 894 km in 47 stages over 95 h, with mean (SD) 6.4 (1.0) stages per athlete and 19.0 (1.7) km per stage. We observed post–pre run increases in serum creatine kinase (qualified effect size extremely large, p = 0.002), IL-6 (extremely large, p < 0.001), urinary 8–isoprostane/creatinine (extremely large, p = 0.04), TNF-α (large, p = 0.002), leukocyte count (very large, p < 0.0001) and neutrophil fraction (very large, p < 0.001); and reductions in hemoglobin (moderate, p < 0.001), hematocrit (moderate, p < 0.001), and lymphocyte fraction (trivial, p < 0.001). An increase in ORAC total antioxidant capacity (TAC, small, p = 0.3) and decrease in urinary 8-OHdG/creatinine (small, p = 0.1) were not statistically significant. During the run, muscle soreness was most frequent in the quadriceps. The threshold for muscle pain (pain-pressure algometry) in the vastus lateralis and gastrocnemius was lower post-run (small, p = 0.04 and 0.03). Average running speed was correlated with algometer pain and leukocyte count (large, r = 0.52), and TAC was correlated with IL-6 (very large, r = 0.76) and 8-isoprostane/creatinine (very large, r = −0.72). Multi-day stage-racing increases inflammation, lipid peroxidation, muscle damage and soreness without oxidative DNA damage. High TAC is associated with reduced exercise-induced lipid peroxidation, but is not related to immune response or muscle damage.     

Aerobic fitness testing in 6- to 9-year-old children: reliability and validity of a modified Yo–Yo IR1 test and the Andersen test

This study analysed the reliability and validity of two intermittent running tests (the Yo–Yo IR1 test and the Andersen test) as tools for estimating VO_2max in children under the age of 10. Two groups, aged 6–7 years (grade 0, n = 18) and 8–9 years (grade 2, n = 16), carried out two repetitions of a modified Yo–Yo IR1 test (2 × 16 m) and the Andersen test, as well as an incremental treadmill test, to directly determine the VO_2max. No significant differences were observed in test–retest performance of the Yo–Yo IR1 test [693 ± 418 (±SD) and 670 ± 328 m, r ² = 0.79, CV = 19%, p > 0.05, n = 32) and the Andersen test (988 ± 77 and 989 ± 87 m, r ² = 0.86, CV = 3%, p > 0.05, n = 31). The Yo–Yo IR1 (r ² = 0.47, n = 31, p < 0.002) and Andersen test performance (r ² = 0.53, n = 32, p < 0.001) correlated with the VO_2max. Yo–Yo IR1 performance correlated with Andersen test performance (r ² = 0.74, n = 32, p < 0.0001). In conclusion, the Yo–Yo IR1 and the Andersen tests are reproducible and can be used as an indicator of aerobic fitness for 6- to 9-year-old children.     

Relationship between the level of plasma insulin and lipid profile in Iranian fat-tailed sheep

Insulin is an important hormone in regulating lipid metabolism in a variety of animal tissues; it can both decrease lipolysis and cause an increase in triglyceride synthesis of adipose tissue in ruminants. In this study, variations in the plasma concentration of insulin and its correlation with the plasma cholesterol, triglyceride, high-density lipoprotein (HDL cholesterol), low-density lipoprotein (LDL cholesterol), and very-low-density lipoprotein (VLDL) concentrations were investigated. Blood samples were collected from the jugular vein of 96 clinically healthy, non-pregnant ewes (grouped according to their age 1–3, 3–6, 6–12, 12–24, 24–48, and >48 months) in the autumn months. The level of plasma insulin was determined by chemiluminescence and other parameters were measured by spectrophotometry using commercial kits. According to our data from Iranian fat-tailed sheep, increasing age results in significant decrease in the plasma concentration of insulin (p < 0.05, r = −0.278), cholesterol (p < 0.05, r = −0.249), and HDL (p < 0.01, r = −0.299), there was also a significant correlation between plasma insulin and LDL concentration (p < 0.05, r = 0.268). In addition, we found significant differences between age groups for cholesterol and HDL concentrations (p < 0.05).     

Relationships between bioelectric impedance and subcutaneous adipose tissue thickness measured by LIPOMETER and skinfold calipers in children

The aim of this study was to compare the relationships between bioelectrical impedance and thicknesses of adipose tissue measured by traditional skinfold caliper (double thickness) or a LIPOMETER device (single non-compressed thickness) in 9- to 12-year-old boys (n=52) and girls (n=44). In total, nine skinfolds (triceps, subscapular, biceps, iliac crest, supraspinale, abdominal, front thigh, medial calf, mid-axilla) were measured. Measurement for the thickness of subcutaneous adipose tissue layers (SAT-layers) by LIPOMETER were performed at 15 body sites (neck, triceps, biceps, upper back, front chest, lateral chest, upper abdomen, lower abdomen, lower back, hip, front thigh, lateral thigh, rear thigh, inner thigh, calf). Body bioelectrical impedance was measured with a multiple-frequency impedance device Multiscan-5000 (Bodystat, UK). Impedance at 50 kHz highly correlated with body mass (r=–0.47 in boys, r=–0.46 in girls, r=–0.47 in total group). The relationship with body height was significant only in girls (r=–0.42). Skinfold thicknesses measured by caliper did not correlate significantly with body impedance at 50 kHz. SAT-layers measured by LIPOMETER at triceps, front thigh, lateral thigh and rear thigh sites in boys and at the lateral thigh site in girls correlated significantly with body impedance measured at 50 kHz. Stepwise multiple regression analysis indicated that the iliac crest and front thigh skinfold thicknesses measured by caliper characterized only 5.7–12.0% of the impedance at 50 kHz in the total group (n=96). From the measured 15 SAT-layers, the most significant was the lateral thigh layer which characterized 20.0%, 11.9% and 13.6% of the impedance at 50 kHz in boys, girls and the total group, respectively. It was concluded that the influence of subcutaneous adipose tissue on body impedance is relatively low in children. However, SAT-layers have a slightly higher influence on body impedance than skinfold thicknesses measured by caliper. The sum of skinfolds or SAT-layers did not correlate significantly with body impedance in any group.     

Bone mineral density in older non-Hispanic Caucasian and Mexican-American women: relationship to lean and fat mass

Primary objective: The prevalence of osteoporotic fracture is higher in non-Hispanic Caucasian (NHC) than Mexican-American (MA) women in the USA. The present study examined bone mineral density (BMD) in these two ethnic groups and the association between BMD and body composition.

Research design: Cross-sectional.

Subjects: Sixty-two NHC and 54 MA women, aged 60-86 years, with a body mass index (kgm^-2) of &lt; 30.

Methods: BMD (gcm^-2) of the spine (L_2-4), hip (femoral neck, trochanter, Ward's triangle) and whole body was determined by dual-energy X-ray absorptiometry (DXA). Bone mineral-free lean mass (LM) and fat mass (FM) and several ratios of body fat distribution were also assessed by DXA.

Results: There was no difference in age (NHC, 69.5 ± 0.7; MA 69.5 ± 0.9 years; mean ± SEM) or body mass, but MA women were shorter with a higher truncal adiposity (p < 0.001). There was no significant difference in BMD between groups, however, adjusting for height resulted in higher hip and whole body BMD in MA women (p < 0.01). When volumetric bone density was calculated (bone mineral apparent density; BMAD, g cm^?3), a trend for higher values in MA women was observed at the femoral neck (p = 0.018). LM contributed independently to BMD at the spine and hip in NHC women, with FM also contributing at the femoral neck. In MA women, LM was an independent contributor to lumbar spine and trochanter BMD, and both LM and FM contributed to whole body BMD. However, the effects of LM and FM were removed in both groups when BMD was adjusted for body or bone size, the only exception being at the trochanter in NHC women.

Conclusions: These results indicate that MA women have higher bone density at the proximal femur than NHC women, which may partially account for their lower rate of hip fracture. Further, differences in bone density between the two ethnic groups do not appear to be dependent on soft-tissue composition.     

Daily physical activity and its relation to aerobic fitness in children aged 8–11 years

A positive relationship between daily physical activity and aerobic fitness exists in adults. Studies in children have given conflicting results, possibly because of differences in methods used to assess daily physical activity and fitness. No study regarding daily physical activity and fitness in children has been published, where fitness has been assessed by direct measurement of maximum oxygen uptake and related to daily physical activity intensities by accelerometers. We examined 248 children (140 boys and 108 girls), aged 7.9–11.1 years. Maximum workload and maximal oxygen uptake (VO_2PEAK) by indirect calorimetry were measured during a maximum bicycle ergometer exercise test. Exercise capacity was adjusted for body mass and (body mass)^2/3. Daily physical activity was evaluated by accelerometers, worn around the waist for 4 days. Mean accelerometer counts and time spent in vigorous physical activity were calculated. VO_2PEAK was correlated with mean accelerometer counts (r=0.23 for boys and r=0.23 for girls, both P<0.05), but somewhat better with time spent in vigorous activity (r=0.32 for boys, r=0.30 for girls, both P<0.05). All results remained virtually the same regardless of the method used to adjust for differences in body size.     

Subacute Inflammatory Activation in Subjects with Acute Coronary Syndrome and Left Ventricular Dysfunction

Several lines of evidence indicate that increased inflammatory cytokine levels can be used for risk prediction in patients with acute coronary syndrome (ACS). This study therefore aimed to evaluate correlations between levels of soluble interleukin (IL)-2 receptor (sIL-2r), IL-6, and IL-8 and in-hospital incidence of acute heart failure (AHF) and left ventricular (LV) systolic dysfunction in the subacute phase of ACS. In 48 consecutive patients with ACS, circulating levels of sIL-2r, IL-6, and IL-8 were ascertained 72–96 h after onset of symptoms. Clinical data, LV function, and in-hospital incidence of AHF were also evaluated. IL-8 levels were significantly higher in patients with pulmonary edema (1,829 ± 2,496 vs 456 ± 624 pg/ml, p < 0.05); sIL-2r, IL-6, and IL-8 levels were increased proportionally to Killip class (r = 0.35, p < 0.05; r = 0.48, r = 0.47, p < 0.01) and in patients with LV ejection fraction (LVEF) < 30%. Levels of sIL-2r were inversely related to LVEF in subjects with acute myocardial infarction (r = −0.51, p < 0.05). Soluble IL-2r and IL-8 levels were related to mitral regurgitation severity (r = 0.34, p < 0.05; r = 0.37, p < 0.05). Levels of sIL-2 were proportional to LV end-diastolic diameter (r = 0.49, p < 0.001) and LV end-systolic diameter (r = 0.58, p < 0.001). Number of cytokines with circulating values above upper level of normal was significantly correlated with Killip class and LVEF (r = 0.40, r = −0.38, p < 0.05). sIL-2r, IL-6, and IL-8 are increased in patients with ACS and systolic dysfunction or AHF. These data suggest that inflammatory cytokine activity detectable in peripheral blood may be useful in identifying subjects with a worse clinical course.     

Influence of age, sex, and aerobic capacity on forearm and skin blood flow and vascular conductance

This study investigated the influence of age, sex, and aerobic capacity on resting and peak forearm and cutaneous blood flow (FBF, CBF). We recruited 93 female and 129 male subjects (age range 16–76 years). FBF and CBF were assessed by plethysmography and laser-Doppler flowmetry, respectively. Peak FBF was obtained following 5 min forearm vascular occlusion and peak CBF in response to local skin heating of 42°C. Blood pressure was measured manually and by Finapres. Maximal oxygen uptake (VO_2max) was obtained from a treadmill exercise stress test. Age was associated with declines in resting FBF (y = −1.176 ln(x) + 6.6899, r ² = 0.45) and peak FBF (y = −17.21 ln(x) + 93.843, r ² = 0.53) (both p < 0.05). Peak CBF decreased with increasing age (y = −223.6 ln(x) + 1,102.9, r ² = 0.34) (p < 0.05), but resting CBF was unchanged (p > 0.05). Males had higher resting and peak FBF than females (p < 0.05) and these variables were related to ageing better in males (y = −1.245 ln(x) + 7.188, r ² = 0.71 and y = −18.53 ln(x) + 102.82, r ² = 0.69) than in females (y = −1.149 ln(x) + 6.4307, r ² = 0.38 and y = −16.59 ln(x) + 88.872, r ² = 0.55). There were no sex differences in resting CBF (p > 0.05). Peak CBF was much better related to ageing in males than females (y = −276.1 ln(x) + 1,365.4, r ² = 0.53 vs. y = −183.1 ln(x) + 907.86, r ² = 0.28). VO_2max decreased with advancing age and this decline was associated with the decline in peak FBF (y = −0.5933x + 10.91, r ² = 0.36, p < 0.05) but not with peak CBF (p > 0.05). These results suggest that healthy ageing is associated with a curvilinear decline in resting and peak forearm and peak cutaneous vasodilator capacity, with males more severely affected than females. The data indicate that peak FBF is influenced by VO_2max but peak CBF is not.     

Plasma TNF-α and IL-10 Level-Based Prognostic Model Predicts Outcome of Patients with Diffuse Large B-Cell Lymphoma in Different Risk Groups Defined by the International Prognostic Index

Tumor necrosis factor (TNF)-α and interleukin (IL)-10 are key cytokines involved in lymphoma development. Their pretreatment plasma levels were reported to influence the clinical course of non-Hodgkin’s lymphoma. In this study the impact of combined elevation of TNF-α and IL-10 on disease features and outcome of patients with diffuse large B-cell lymphoma (DLBCL) were investigated. Plasma TNF-α and IL-10 levels were determined at the time of diagnosis in a group of 106 DLBCL patients uniformly treated with anthracycline-based regimens. Three risk groups depending on the pretreatment levels of the cytokines were identified: low-, intermediate-, and high-risk groups. In univariate analysis, the cytokine intermediate- and high-risk groups were associated with lower probability of achieving a complete remission (odds ratio [OR] = 0.2, 95% confidence interval [CI] 0.06–0.6, p = 0.006 and OR = 0.05, 95% CI 0.01–0.2, p < 0.0001, respectively) and shorter progression-free survival (PFS) (OR = 4.4, 95% CI 1.9–10.2, p < 0.001 and OR = 9.7, 95% CI 4.1–23.0, p < 0.0001, respectively) and overall survival (OS) (OR = 4.2, 95% CI 1.7–10.1, p = 0.002 and OR = 11.2, 95% CI 4.4–28.4, p < 0.0001, respectively) in comparison with the cytokine low-risk group. In multivariate analysis, the cytokine intermediate- and high-risk groups also correlated with shorter PFS (relative risk [RR] = 4.5, 95% CI 1.9–10.9, p = 0.001 and RR = 5.8, 95% CI 2.2–15.3, p < 0.0001, respectively) and OS (RR = 4.6, 95% CI 1.8–12.0, p = 0.001 and RR = 7.5, 95% CI 2.7–20.9, p < 0.0001, respectively) regardless of the International Prognostic Index (IPI) scoring system. The TNF-α and IL-10 level-based index may work as an additional model to the IPI for predicting the survival of DLBCL patients. This model may help to identify patients in a given IPI risk group for whom more accurate and risk-adapted treatment could be advised.     

Validity of newly-developed BMI and waist cut-off values for Sri Lankan children

Background: Excess body fat leads to obesity-related morbidity and population/ethnicity-specific cut-off values of anthropometric measures are useful for better diagnosis. This study assesses the suitability of newly-developed Sri Lankan anthropometric cut-off values in the diagnosis of obesity in Sri Lankan children.

Methods: A cross-sectional study was conducted at University of Colombo, Sri Lanka involving 5–15 year old children. Height, weight, waist (WC), and hip (HC) circumferences were measured. Total body fat (FM) was measured using whole body BIA. WHR and WHtR were calculated. Validity of anthropometric measures in detecting childhood obesity (Sri Lankan BMI/WC; IOTF, WHO, British and CDC BMI and British WC cut-off values) were evaluated.

Results: Nine hundred and twenty children were assessed. FM showed significant associations with BMI (r = 0.92, p < 0.001), WC (r = 0.90, p < 0.001) and HC (r = 0.85, p < 0.001), but poor association with WHR (r = 0.17, p < 0.001). However, WHtR had a high association with FM (r = 0.75, p < 0.001) and %FM (r = 0.78, p < 0.001). Based on %FM cut-offs, 85 (22.8%) girls and 101 (18.5%) boys were obese. All international anthropometric cut-off values under-estimated obesity. Sri Lankan WC and BMI cut-off values over-estimated obesity. International BMI based cut-off values had high specificity (>99%) but a low sensitivity (～12–33%), while Sri Lankan BMI cut-off values had high sensitivity (>93.1) but low specificity (>79.7).

Conclusions: Internationally available BMI cut-off values are poor in diagnosing obesity in Sri Lankan children. Newly developed Sri Lankan BMI cut-off values for children improved the diagnosis. WC can be used successfully as an alternative diagnostic tool of obesity.     

Bone cross-sectional geometry in male runners,gymnasts, swimmers and non-athletic controls: a hip-structural analysis study

Loading of the skeleton is important for the development of a functionally and mechanically appropriate bone structure, and can be achieved through impact exercise. Proximal femur cross-sectional geometry was assessed in the male athletes (n = 55) representing gymnastics, endurance running and swimming, and non-athletic controls (n = 22). Dual energy X-ray absorptiometry (iDXA, GE Healthcare, UK) measurements of the total body (for body composition) and the left proximal femur were obtained. Advanced hip structural analysis (AHA) was utilised to determine the areal bone mineral density (aBMD), hip axis length (HAL), cross-sectional area (CSA), cross-sectional moment of inertia (CSMI) and the femoral strength index (FSI). Gymnasts and runners had greater age, height and weight adjusted aBMD than in swimmers and controls (p < 0.05). Gymnasts and runners had greater resistance to axial loads (CSA) and the runners had increased resistance against bending forces (CSMI) compared to swimmers and controls (p < 0.01). Controls had a lower FSI compared to gymnasts and runners (1.4 vs. 1.8 and 2.1, respectively, p < 0.005). Lean mass correlated with aBMD, CSA and FSI (r = 0.365–0.457, p < 0.01), particularly in controls (r = 0.657–0.759, p < 0.005). Skeletal loading through the gymnastics and running appears to confer a superior bone geometrical advantage in the young adult men. The importance of lean body mass appears to be of particular significance for non-athletes. Further characterisation of the bone structural advantages associated with different sports would be of value to inform the strategies directed at maximising bone strength and thus, preventing fracture.     

Depressive Symptoms and Alcohol Use are Genetically and Environmentally Correlated Across Adolescence

Depressive symptoms and alcohol use are frequently positively associated during adolescence. This study aimed to assess the heritability of each phenotype across adolescence; to assess potential shared liabilities; to examine changes in the nature of shared liabilities across adolescence; and to investigate potential causal relationships between depressive symptoms and alcohol use. We studied a longitudinally assessed sample of adolescent Finnish twins (N = 1,282) to test hypotheses about genetic and environmental influences on these phenotypes within and across ages, using data from assessments at ages 12, 14, and 17.5 years. The heritability of depressive symptoms is consistent across adolescence (~40–50%), with contributions from common and unique environmental factors. The heritability of alcohol use varies across time (a² = .25–.44), and age 14 alcohol use is heavily influenced by shared environmental factors. Genetic attenuation and innovation were observed across waves. Modest to moderate genetic (r_A = .26–.59) and environmental (r_C = .30–.63) correlations between phenotypes exist at all ages, but decrease over time. Tests for causal relationships between traits differed across ages and sexes. Intrapair MZ difference tests provided evidence for reciprocal causation in girls at ages 14 and 17.5. Formal causal models suggested significant causal relationships between the variables in both boys and girls. The association between depressive symptoms and alcohol use during adolescence is likely due to a combination of shared genetic and environmental influences and causal influences. These influences are also temporally dynamic, complicating efforts to understand factors contributing to the relationship between these outcomes.     

Fat mass and fat-free mass as indicators of body composition among Bengalee Muslim children

Background: The composition of fat mass (FM) and fat-free mass (FFM) are now considered to be important indicators of body composition.

Aim: This cross-sectional study determines the body composition using FM and FFM among children.

Subjects and methods: The study was conducted among 1248 children (619 boys; 629 girls) aged 5–12 years and belonging to the Bengalee Muslim population of West Bengal, India. Anthropometric measurements of height, weight, triceps and sub-scapular skin-folds were recorded and body mass index (BMI) calculated. Body composition was assessed using FM and FFM.

Results: The age-specific mean values of FM and FFM ranged from 1.93–3.07 kg (boys) and 1.91–3.62 kg (girls) and from 14.69–23.44 kg (boys) and 14.18–22.87 kg (girls), respectively. Statistically significant sex differences were observed in FM and FFM (p < 0.05). Age- and sex-specific smooth percentile curves were derived for BMI, FM and FFM using the L, M and S modelling approach for further evaluation of body composition.

Conclusion: These findings are important for future investigations in the field and in epidemiological and clinical settings so as to accurately identify risk of lower or higher adiposity and body composition using FM and FFM.     

Relevance of individual characteristics for thermoregulation during exercise in a hot-dry environment

The aim of this study was to investigate the relevance of individual characteristics for thermoregulation during prolonged cycling in the heat. For this purpose, 28 subjects cycled for 60 min at 60% VO_2peak in a hot-dry environment (36 ± 1°C; 25 ± 2% relative humidity, airflow 2.5 m/s). Subjects had a wide range of body mass (99–43 kg), body surface area (2.2–1.4 m²), body fatness (28–5%) and aerobic fitness level (VO_2peak = 5.0–2.1 L/min). At rest and during exercise, rectal and mean skin temperatures were measured to calculate the increase in body temperature (ΔT _body) during the trial. Net metabolic heat production (M _NET) and potential heat loss (by means of evaporation, radiation and convection) were calculated. Although subjects exercised at the same relative intensity, ΔT _body presented high between-subjects variability (range from 0.44 to 1.65°C). ΔT _body correlated negatively with body mass (r = −0.49; P < 0.01), body surface area (r = −0.47; P < 0.01) and T_body at rest (r = −0.37; P < 0.05), but it did not significantly correlate with body fatness (r = 0.12; P > 0.05). ΔT _body positively correlated with the body surface area/mass ratio (r = 0.46; P < 0.01) and the difference between M _NET and potential heat loss (r = 0.56; P < 0.01). In conclusion, a large body size (mass and body surface area) is beneficial to reduce ΔT _body during cycling exercise in the heat. However, subjects with higher absolute heat production (more aerobically fit) accumulate more heat because heat production may exceed potential heat loss (uncompensability).     

Higher prevalence of exercise-associated hyponatremia in female than in male open-water ultra-endurance swimmers: the 'Marathon-Swim' in Lake Zurich

We investigated the prevalence of exercise-associated hyponatremia (EAH) in 25 male and 11 female open-water ultra-endurance swimmers participating in the ‘Marathon-Swim’ in Lake Zurich, Switzerland, covering a distance of 26.4 km. Changes in body mass, fat mass, skeletal muscle mass, total body water, urine specific gravity, plasma sodium concentration [Na⁺] and haematocrit were determined. Two males (8%) and four females (36%) developed EAH where one female was symptomatic with plasma sodium [Na⁺] of 127 mmol/L. Body mass and plasma [Na⁺] decreased (p < 0.05). The changes in body mass correlated in both male and female swimmers to post-race plasma [Na⁺] (r = −0.67, p = 0.0002 and r = −0.80, p = 0.0034, respectively) and changes in plasma [Na⁺] (r = −0.68, p = 0.0002 and r = −0.79, p = 0.0039, respectively). Fluid intake was neither associated with changes in body mass, post-race plasma [Na⁺] or the change in plasma [Na⁺]. Sodium intake showed no association with either the changes in plasma [Na⁺] or post-race plasma [Na⁺]. We concluded that the prevalence of EAH was greater in female than in male open-water ultra-endurance swimmers.     

The effects of agonist and antagonist muscle activation on the knee extension moment–angle relationship in adults and children

The present study examined the effect of agonist activation and antagonist co-activation on the shape of the knee extension moment–angle relationship in adults and children. Isometric knee extension maximum voluntary contractions (MVCs) were performed at every 5° of knee flexion between 55° and 90° (full extension = 0°) by ten men, ten women, ten boys and ten girls. For each trial, the knee extensors’ voluntary activation level was quantified using magnetic stimulation and the level of antagonist co-activation was quantified from their electromyographical activity. Peak MVC moment was greater for men (264 ± 63 N m) than women (177 ± 60 N m), and greater for adults than children (boys 78 ± 17 N m, girls 91 ± 28 N m) (p < 0.01). The agonistic activation level was greater for adults (~85%) than children (~70%). Similarly, antagonist co-activation was greater for adults than children, but relative to the agonist moment there were no differences between groups (all groups 7–8%). Correcting the peak moment for agonist and antagonist activation levels resulted in moments produced by fully activated agonist muscles of 334 ± 83, 229 ± 70, 114.2 ± 32 and 147 ± 46 N m, for men, women, boys and girls, respectively. Although correcting for shifts in joint angle during contraction altered the angle of peak moment by ~10° (p < 0.01), the peak moment occurred at ~60° for all groups. Changes in tendon stiffness, muscle size and architecture, and the pattern of the moment arm–angle relationship may in combination occur so that as children develop and mature into adults the shape of the moment–angle relationship is not altered.     

Characterizing near-infrared spectroscopy responses to forearm post-occlusive reactive hyperemia in healthy subjects

During post-occlusive reactive hyperemia (PORH) there is a temporary increase in the total hemoglobin + myoglobin (T[Hb+Mb]) signal as measured by near-infrared spectroscopy (NIRS). This transient increase predicts differences in the kinetic responses of deoxy[Hb+Mb] and oxy[Hb+Mb] during PORH. The purpose of this study was to determine whether sigmoidal (Gompertz or logistic) or exponential functions better describe these response curves during PORH. The fit of the three functions (exponential, Gompertz and logistic) to the NIRS responses, as determined from residual sum of squares, was compared using repeated measures ANOVA on Ranks. The Gompertz function provided a better fit to the oxy[Hb+Mb] response curve than did either the exponential or logistic function (χ ² = 21.7, df = 2, p < 0.001). The logistic function provided a better fit for the deoxy[Hb+Mb] response (χ ² = 22.9, df = 2, p < 0.001) than did either the Gompertz or exponential functions. For both NIRS signals, the better fitting sigmoidal functions fit the data well, with an average r value of 0.99 or greater. Adipose tissue thickness was correlated with parameters related to signal strength (amplitude, r = 0.86–0.89; baseline, r = 0.67–0.75; all p < 0.001) but was not related to kinetic parameters (time constant and inflection point; p > 0.05 for all comparisons). These results suggest that during PORH distinct sigmoidal mathematical functions best describe the responses of the oxy[Hb+Mb] (Gompertz) and deoxy[Hb+Mb] (logistic) as measured by NIRS. Further, differences in both the kinetic and amplitude aspects for the responses of oxy[Hb+Mb] and deoxy[Hb+Mb] predict the observed transient change in T[Hb+Mb]. Our methods provide a technique to evaluate and quantify NIRS responses during PORH, which may have clinical utility.