M. Bedu

Muscle fat oxidative capacity is not impaired by age but by physical inactivity: association with insulin sensitivity

The study aimed at determining whether aging and/or sedentariness impairs muscle fat oxidative capacity (OXFA) and whether this was associated with increased risk to develop insulin resistance. We first examined muscle mitochondrial functions, OXFA and insulin sensitivity (ISI; evaluated during an oral glucose tolerance test) in a cross‐sectional study with 32 sedentary (S) and endurance‐trained (T), young (Y) and elderly (E) men (24.2±2.6 vs. 66.6±3.2 yr). As for mitochondrial functions, OXFA was higher in T than in S but similar between age groups (SY 41.8±11.3, TY 68.0±17.7, SE 40.1±14.1, TE 73.1±20.1 palmitate.min–1.g wet tissue–1; activity P<0.0001, age P=NS, activity × age P=NS). Similar results were obtained with ISI (SY 6.2±2.2, TY 11.4±4.4, SE 5.9±1.5, TE 11.0±3.5, activity P<0.001, age P=NS, activity × age P=NS). Stepwise regression showed that, among body composition, VO2max and muscle biochemical characteristics, OXFA was the main predictor of ISI (r=0.60, P<0.001). We subsequently showed in eight sedentary elderly subjects (63.5±3.3 yr) that OXFA and insulin sensitivity (measured using insulin clamp) improved in parallel after 8 weeks of endurance training (r=0.79, P<0.01). We concluded that mitochondrial functions, OXFA and ISI, are not impaired by age but by physical inactivity and are closely correlated.

Changes in Basal and Insulin and Amino Acid Response of Whole Body and Skeletal Muscle Proteins in Obese Men

CONTEXT Obesity-related insulin resistance of glucose and lipid metabolism may also affect protein kinetics, notably at the muscle level. OBJECTIVE We hypothesized that muscle protein response to insulin and amino acid is blunted during obesity. RESEARCH DESIGN AND METHODS Total (Tot) and mitochondrial (Mit) muscle proteins fractional synthesis rates (FSR) together with whole-body protein kinetics (WB) have been determined in postabsorptive state (PA) and during a hyperinsulinemic, hyperaminoacidemic, euglycemic clamp by using a continuous infusion of (13)C-leucine in six obese and eight nonobese subjects. RESULTS Responses of WB glucose disposal rate and protein breakdown to insulin and amino acid infusion were significantly lower in obese than in nonobese subjects (P < 0.05). In PA, Tot and Mit FSR were significantly lower (P < 0.05) in obese (Tot, 0.044 +/- 0.005% . h(-1); Mit, 0.064 +/- 0.008% . h(-1)) in comparison with nonobese subjects (Tot, 0.082 +/- 0.010% . h(-1); Mit, 0.140 +/- 0.006% . h(-1)). Tot FSR was similarly stimulated by insulin and amino acid in both groups (0.094 +/- 0.013 vs. 0.117 +/- 0.006% . h(-1), obese vs. nonobese; P < 0.05). Mit FSR was increased in nonobese subjects (0.179 +/- 0.007% . h(-1); P < 0.05) but not in obese subjects (0.078 +/- 0.012% . h(-1); P = not significant). CONCLUSIONS The obesity-related impairment of protein metabolism is characterized by 1) a reduced turnover rate of skeletal muscle proteins in PA; 2) a lack of stimulation of mitochondrial protein synthesis by insulin and amino acid; and 3) a lower inhibition of WB proteolysis by insulin and amino acid. Alterations of selective muscle protein kinetics may predispose obese subjects to muscle metabolic dysfunction leading to type 2 diabetes.

The importance of socioeconomic and nutritional conditions rather than altitude on the physical growth of prepubertal Andean highland boys.

The aim of this work was to study the effect of hypoxic stress on the physical growth of prepubertal Bolivian boys (10-11.5 years of age) of the same socioeconomic and nutritional conditions. The subjects consisted of 143 boys living in La Paz (altitude 3600 m, n = 67) and Santa Cruz de la Sierra (altitude 420 m, n = 76). Among the boys studied at high altitude, 23 were from a high socioeconomic background (HA1) and 44 from a low socioeconomic background (HA2). The group studied at low altitude consisted of 47 boys from a high socioeconomic background (LA1) and 29 from a low socioeconomic background (LA2). A scientific evaluation of the nutritional status of the boys was realized from specific anthropometric characteristics (height, body weight, upper arm muscle circumference, body fat mass and body mass index) and haematological (haematocrit, haemoglobin, serum iron, serum ferritin, red cell protoporphyrin, transferrin saturation) and biochemical (total serum protein, albumin and prealbumin) parameters. At high as at low altitudes, the biometric characteristics of boys from a low socioeconomic background were significantly lower than those of boys from a high socioeconomic background. The physical growth of HA2 and LA2 boys was delayed by approximately 2 years. All the boys had biochemical and haematological parameters within the normal range. Boys from a low socioeconomic background were considered as marginally undernourished and those from a high socioeconomic background as well-nourished. Within the same socioeconomic class there was no nutritional difference between highland and lowland boys. Similarly, and this is the most important feature of this study, there was no difference for the overall biometric characteristics between highland and lowland boys of the same socioeconomic and nutritional status. Therefore, it appears that when socioeconomic and nutritional conditions are taken into account, there is no effect of hypoxic stress on the physical growth of prepubertal Andean highland boys.

Measurement error in short-term power testing in young people

The aim of this study was to examine the consistency or reproducibility of measuring cycling peak power in children and adults. Twenty-seven pre-pubertal girls and boys and 27 female and male physical education students (age 9.8±0.5 and 24.4±4.3 years, respectively; mean±s) participated in the study. All participants performed five tests over 15 days and underwent a habituation session before the study. Each test included four sprints against four different braking forces. We found that braking forces of 7.5% of body weight in children and 10% of body weight in adults were too high for most of the participants to elicit maximal cycling power. Unlike the children, the physical education students improved their performance between session 1 and session 2 (1025±219 vs 1069±243 W; P<0.001). Therefore, to obtain reproducible measures of cycling peak power, a habituation session including a complete test protocol (i.e. warm-up plus three sprints) is highly recommended. When the protocol included three sprints in children and at least two sprints in adults, measurement of cycling peak power was found to be highly reliable (test-retest coefficient of variation ∼3%). Finally, to avoid performance fluctuations, especially over several consecutive evaluations (e.g. longitudinal studies), it is necessary to maintain high motivation in children.

Enzymatic and hormonal responses following a 24 h endurance run and a 10 h triathlon race

SummaryMuscle cell leakage and hormonal changes were compared immediately after and during the 3 days following a 24 h endurance run (R24 h) in 8 subjects, and a 10 h triathlon non-competitive race (T10 h) in 6 subjects. The study showed three main differences: 1) plasma enzyme increases were considerably more significant in R24 h than in T10 h: compared with resting levels, creatine kinase increased ×120 after R24 h but only ×2 after T10 h; lactic dehydrogenase ×4, as opposed to ×1.5; and transaminases only showed an increase after R24 h. The plasma myoglobin increase after R24 h was double that found after T10 h; 2) for the same magnitude of plasma aldosterone and cortisol after R24 h and T10 h (3 times the resting levels), a highly significant decrease in urinary Na+ (p<0.001) and an increase in urinary K+ (p<0.01) were found only after R24 h; and 3) the plasma free noradrenaline level increased significantly after R24 h (×2.6) whereas it was unchanged after T10 h. In contrast, the plasma level of conjugated dopamine increased only after T10 h (×3.7, p<0.05). These results suggest that long-distance running causes more muscular lesions than the triathlon, and that important factors other than aldosterone are probably involved in the regulation of urinary electrolyte excretions during T10 h.

Serum insulin-like growth factor I and physical performance in prepubertal Bolivian girls of a high and low socio-economic status

Abstract The aim of the study was to determine if a decrease in serum insulin-like growth factor I (Igf-I) levels under marginal malnutrition is responsible for the lower physical performance of girls of a low socio-economic status (LSES). Girls were selected after physical examination (Tanners stage 1) and anthropometric measurements (height, body mass or mb, body mass index or BMI = mb height2). Lean body mass mb,l was measured after skinfold thickness determination; serum IGF-I, by radioimmunoassay; maximal O2 consumption, (V˙O2max), directly during incremental exercise up to exhaustion; and maximal aerobic power (W˙max), using the force-velocity test. LSES girls (n = 31) had been malnourished in the past and, currently, were suffering from marginal malnutrition: they were smaller (135.2 ± 5.5 vs 146.1 ± 4.3 cm), lighter (31.7 ± 3.9 vs 37.6 ± 5.0 kg), exhibited a lower mb,l (24.2 ± 2.5 vs 27.5 ± 3.0 kg) but same BMI compared with HSES (high socio-economic status) girls (n = 32). Igf-I levels (27.7 ± 7.9 vs 34.1 ± 6.5 nmol · l−1), V˙O2max (45.26 ± 4.72 vs 50.74 ± 6.02 ml · min−1 · kg−1 LBM) and W˙max (6.00 ± 1.15 vs 8.70 ± 1.53 W · kg−1mb,l were lower in LSES girls. Moreover, the differences in every parameter were not the consequence of the younger age (10.8 ± 0.9 vs 11.2 ± 0.6 years) of the LSES girls. Our results provide evidence that the lower W˙max of undernourished prepubertal girls was partly the consequence of alterations in muscle function at the qualitative level, as a result of a decrease in Igf-I levels. Conversely, under normal nutritional conditions, anthropometric characteristics only are explicatory factors for physical performances.

Evaluation of physical fitness from field tests at high altitude in circumpubertal boys: comparison with laboratory data.

AbstractField tests of running and laboratory tests were performed in La Paz [high altitude (HA), 3700 m] and in Clermont-Ferrand [low altitude (LA), 300 m] to investigate their validity at HA. Prepubertal boys of mean ages 10.6 years (HA1,n = 16; LA1,n = 28) and pubertal boys of 13.7 years (HA2,n = 12; LA2,n = 41) took part in the study. All the boys performed a 30-m sprint (v30m), a 30-s shuttle run (v3os) and a progressive shuttle run test until their maximal aerobic velocity (vmaxsRT). Maximal oxygen consumption was extrapolated from the last test.

Acid-base balance during repeated cycling sprints in boys and men

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