Ignacio Ara

Regular participation in sports is associated with enhanced physical fitness and lower fat mass in prepubertal boys

OBJECTIVE: To study the effect of physical activity on whole body fat (BF), its regional deposition and the influence of body fatness on physical performance in prepubertal children.DESSIGN: Cross-sectional study.SUBJECTS: A total of 114 boys (9.4±1.5 y, Tanner I–II), randomly sampled from the population of Gran Canaria (Spain), 63 of them physically active (PA, at least 3 h per week during the previous year) and 51 nonphysically active (non-PA).MEASUREMENTS: Body composition (DXA), anthropometric variables (body circumferences and skinfolds) and physical fitness were determined in all subjects.RESULTS: The PA obtained better results in maximal oxygen uptake, isometric leg extension force, vertical jump (muscular power), and 300 m (anaerobic capacity) and 30 m running tests (speed) than the non-PA. A lower percentage of body fat (% BF) (4 U less, P<0.05), whole BF mass (36% less, P<0.05) and regional fat mass (28, 25, and 30% less in the trunk, legs and arms, respectively, all P<0.05) was observed in the PA compared to the non-PA. The waist and hip circumferences correlated more closely with both the fat mass accumulated in the trunk region and the % BF (r=0.81–0.95, P<0.001) than the waist-to-hip ratio (WHR). The WHR correlated with the percentage of the whole fat mass accumulated in the trunk (PFT) (r=0.52–0.53, P<0.001). In both groups, the PFT increased curvilinearly with the % BF, regardless of the level of physical activity. ANCOVA analysis revealed that total and regional fat masses explained less than 40% of the difference in performance between the PA and non-PA group. The mean speed in the 30 m running test (V30), combined with the height and whole body mass, has predictive value for the BF mass (R=0.98, P<0.001). The % BF may be estimated from the body mass index (BMI) and V30 (% BF=8.09+2.44·BMI (kg m−2)–5.8·V30 (m s−1), R=0.94, P<0.001) in prepubertal boys.CONCLUSIONS: Regular participation in at least 3 h per week of sports activities and competitions on top of the compulsory physical education program is associated with increased physical fitness, lower whole body and trunkal fat mass in prepubertal boys.

Influence of extracurricular sport activities on body composition and physical fitness in boys: a 3-year longitudinal study.

Objective:To analyse the effect of extracurricular physical activities on fat mass accumulation and physical fitness during growth in early pubertal males.Design:Longitudinal study.Subjects:A total of 42 male children (9.4±1.4 years, Tanner I–II and 12.7±1.5 years, Tanner III–IV, before and after the 3.3 years follow-up, respectively), randomly sampled from the population of Gran Canaria (Spain), 26 of them physically active (PA, at least 3 h per week during 3 years) and 16 non-physically active (non-PA).Measurements:Body composition (dual-energy X-ray absorptiometry), anthropometrics (body circumferences and skinfolds) and physical fitness variables (dynamic and isometric force, anaerobic capacity and maximal aerobic power) were determined in all subjects.Results:Both groups had comparable body sizes at the start and the end of the study. Body mass index increased with growth more in the PA than in the non-PA group (P<0.05). However, fat mass accumulation with growth was lower in the PA than in the non-PA (P<0.05). There was a positive relationship between the increment of total and trunkal fat mass, especially in non-active children (r 2=0.93). In contrast, there was an inverse relationship between the total lean mass growth and the accumulation of total and regional fat mass (r=−0.37 to −0.41, all P<0.05). Physical fitness was maintained in the PA, while it worsened in the non-PA children.Conclusions:Without any dietary intervention, children who regularly participate in at least 3 h per week of sports activities are more protected against total and regional fat mass accumulation. They also increase their total lean and bone mass to a greater extent than children who do not participate in extracurricular sport activities. In addition, PA children maintain their physical fitness during growth, while it deteriorates in the non-PA children.

Muscular development and physical activity as major determinants of femoral bone mass acquisition during growth

Objectives: To investigate to what extent bone mass accrual is determined by physical activity and changes in lean, fat, and total body mass during growth. Methods: Twenty six physically active and 16 age matched control boys were followed up for three years. All subjects were prepubertal at the start of the survey (mean (SEM) age 9.4 (0.3) years). The weekly physical activity of the active boys included compulsory physical education sessions (80–90 minutes a week), three hours a week of extracurricular sports participation, and occasional sports competitions at weekends. The physical activity of the control group was limited to the compulsory physical education curriculum. Bone mineral content (BMC) and areal density (BMD), lean mass, and fat mass were measured by dual energy x ray absorptiometry. Results: The effect of sports participation on femoral bone mass accrual was remarkable. Femoral BMC and BMD increased twice as much in the active group as in the controls over the three year period (p<0.05). The greatest correlation was found between the increment in femoral bone mass and the increment in lean mass (BMC r  =  0.67 and BMD r  =  0.69, both p<0.001). Multiple regression analysis revealed enhancement in lean mass as the best predictor of the increment in femoral bone BMC (R  =  0.65) and BMD (R  =  0.69). Conclusions: Long term sports participation during early adolescence results in greater accrual of bone mass. Enhancement of lean mass seems to be the best predictor of this bone mass accumulation. However, for a given muscle mass, a greater level of physical activity is associated with greater bone mass and density in peripubertal boys.

Muscle mitochondrial capacity exceeds maximal oxygen delivery in humans

Across a wide range of species and body mass a close matching exists between maximal conductive oxygen delivery and mitochondrial respiratory rate. In this study we investigated in humans how closely in-vivo maximal oxygen consumption (VO(2) max) is matched to state 3 muscle mitochondrial respiration. High resolution respirometry was used to quantify mitochondrial respiration from the biopsies of arm and leg muscles while in-vivo arm and leg VO(2) were determined by the Fick method during leg cycling and arm cranking. We hypothesized that muscle mitochondrial respiratory rate exceeds that of systemic oxygen delivery. The state 3 mitochondrial respiration of the deltoid muscle (4.3±0.4 mmol o(2)kg(-1) min(-1)) was similar to the in-vivo VO(2) during maximal arm cranking (4.7±0.5 mmol O(2) kg(-1) min(-1)) with 6 kg muscle. In contrast, the mitochondrial state 3 of the quadriceps was 6.9±0.5 mmol O(2) kg(-1) min(-1), exceeding the in-vivo leg VO(2) max (5.0±0.2 mmol O(2) kg(-1) min(-1)) during leg cycling with 20 kg muscle (P<0.05). Thus, when half or more of the body muscle mass is engaged during exercise, muscle mitochondrial respiratory capacity surpasses in-vivo VO(2) max. The findings reveal an excess capacity of muscle mitochondrial respiratory rate over O(2) delivery by the circulation in the cascade defining maximal oxidative rate in humans.

Normal mitochondrial function and increased fat oxidation capacity in leg and arm muscles in obese humans

Aim/hypothesis:The aim of this study was to investigate mitochondrial function, fibre-type distribution and substrate oxidation during exercise in arm and leg muscles in male postobese (PO), obese (O) and age- and body mass index (BMI)-matched control (C) subjects. The hypothesis of the study was that fat oxidation during exercise might be differentially preserved in leg and arm muscles after weight loss.Methods:Indirect calorimetry was used to calculate fat and carbohydrate oxidation during both progressive arm-cranking and leg-cycling exercises. Muscle biopsy samples were obtained from musculus deltoideus (m. deltoideus) and m. vastus lateralis muscles. Fibre-type composition, enzyme activity and O2 flux capacity of saponin-permeabilized muscle fibres were measured, the latter by high-resolution respirometry.Results:During the graded exercise tests, peak fat oxidation during leg cycling and the relative workload at which it occurred (FatMax) were higher in PO and O than in C. During arm cranking, peak fat oxidation was higher in O than in C, and FatMax was higher in O than in PO and C. Similar fibre-type composition was found between groups. Plasma adiponectin was higher in PO than in C and O, and plasma leptin was higher in O than in PO and C.Conclusions:In O subjects, maximal fat oxidation during exercise and the eliciting relative exercise intensity are increased. This is associated with higher intramuscular triglyceride levels and higher resting non esterified fatty acid (NEFA) concentrations, but not with differences in fibre-type composition, mitochondrial function or muscle enzyme levels compared with Cs. In PO subjects, the changes in fat oxidation are preserved during leg, but not during arm, exercise.

Leptin receptor 170 kDa (OB-R170) protein expression is reduced in obese human skeletal muscle: a potential mechanism of leptin resistance

To examine whether obesity‐associated leptin resistance could be due to down‐regulation of leptin receptors (OB‐Rs) and/or up‐regulation of suppressor of cytokine signalling 3 (SOCS3) and protein tyrosine phosphatase 1B (PTP1B) in skeletal muscle, which blunt janus kinase 2‐dependent leptin signalling and signal transducer and activator of transcription 3 (STAT3) phosphorylation and reduce AMP‐activated protein kinase (AMPK) and acetyl‐coenzyme A carboxylase (ACC) phosphorylation. Deltoid and vastus lateralis muscle biopsies were obtained from 20 men: 10 non‐obese control subjects (mean ±s.d. age, 31 ± 5 years; height, 184 ± 9 cm; weight, 91 ± 13 kg; and percentage body fat, 24.8 ± 5.8%) and 10 obese (age, 30 ± 7 years; height, 184 ± 8 cm; weight, 115 ± 8 kg; and percentage body fat, 34.9 ± 5.1%). Skeletal muscle OB‐R170 (OB‐R long isoform) protein expression was 28 and 25% lower (both P < 0.05) in arm and leg muscles, respectively, of obese men compared with control subjects. In normal‐weight subjects, SOCS3 protein expression, and STAT3, AMPKα and ACCβ phosphorylation, were similar in the deltoid and vastus lateralis muscles. In obese subjects, the deltoid muscle had a greater amount of leptin receptors than the vastus lateralis, whilst SOCS3 protein expression was increased and basal STAT3, AMPKα and ACCβ phosphorylation levels were reduced in the vastus lateralis compared with the deltoid muscle (all P < 0.05). In summary, skeletal muscle leptin receptors and leptin signalling are reduced in obesity, particularly in the leg muscles.

Low-intensity training increases peak arm VO2 by enhancing both convective and diffusive O2 delivery

It is an ongoing discussion the extent to which oxygen delivery and oxygen extraction contribute to an increased muscle oxygen uptake during dynamic exercise. It has been proposed that local muscle factors including the capillary bed and mitochondrial oxidative capacity play a large role in prolonged low‐intensity training of a small muscle group when the cardiac output capacity is not directly limiting. The purpose of this study was to investigate the relative roles of circulatory and muscle metabolic mechanisms by which prolonged low‐intensity exercise training alters regional muscle VO2.

Feasibility of resistance training in adult McArdle patients: clinical outcomes and muscle strength and mass benefits

We analyzed the effects of a 4-month resistance (weight lifting) training program followed by a 2-month detraining period in 7 adult McArdle patients (5 female) on: muscle mass (assessed by DXA), strength, serum creatine kinase (CK) activity and clinical severity. Adherence to training was ≥84% in all patients and no major contraindication or side effect was noted during the training or strength assessment sessions. The training program had a significant impact on total and lower extremities’ lean mass (P < 0.05 for the time effect), with mean values increasing with training by +855 g (95% confidence interval (CI): 30, 1679) and +547 g (95%CI: 116, 978), respectively, and significantly decreasing with detraining. Body fat showed no significant changes over the study period. Bench press and half-squat performance, expressed as the highest value of average muscle power (W) or force (N) in the concentric-repetition phase of both tests showed a consistent increase over the 4-month training period, and decreased with detraining. Yet muscle strength and power detraining values were significantly higher than pre-training values, indicating that a training effect was still present after detraining. Importantly, all the participants, with no exception, showed a clear gain in muscle strength after the 4-month training period, e.g., bench press: +52 W (95% CI: 13, 91); half-squat: +173 W (95% CI: 96, 251). No significant time effect (P > 0.05) was noted for baseline or post strength assessment values of serum CK activity, which remained essentially within the range reported in our laboratory for McArdle patients. All the patients changed to a lower severity class with training, such that none of them were in the highest disease severity class (3) after the intervention and, as such, they did not have fixed muscle weakness after training. Clinical improvements were retained, in all but one patient, after detraining, such that after detraining all patients were classed as class 1 for disease severity.

Load‐controlled moderate and high‐intensity resistance training programs provoke similar strength gains in young women

Introduction: While current exercise guidelines recommend progressive, high‐intensity resistance training (RT) to promote muscle hypertrophy and strength gains, controversy exists regarding the efficacy of lighter‐load RT. We compared 2 work‐matched RT interventions that differed in training intensity. Methods: Fifteen women underwent 10 weeks of unilateral knee extensor RT. One leg was trained at increasing intensity (intensity leg, InL, 50–80% 1‐repetition maximum [1‐RM]), and training progression in the contralateral leg (volume leg, VoL, 50% 1‐RM) was based on increasing training volumes. Quadriceps muscle size (ultrasound, dual energy X‐ray absorptiometry) and strength (isokinetic dynamometry) were assessed on 4 occasions. Results: Both training programs induced significant, yet comparable increases in muscle size (InL: +4.6–12%, VoL: +3.1–11%) and strength (InL: +10–16%, VoL: +10–14%). Conclusions: Training at lower than commonly suggested intensities may be an equally effective alternative form of RT. Factors other than training intensity, such as the total mechanical work during training, may strongly affect the training response. Muscle Nerve 51: 92–101, 2015

Physical activity during leisure time and quality of life in a Spanish cohort: SUN (Seguimiento Universidad de Navarra) Project

Background Leisure-time physical activity (LTPA) has been associated with better mental and physical health particularly in cross-sectional studies. Purpose To longitudinally assess the association between LTPA, changes in LTPA and health-related quality of life (HRQL). Methods Cross-sectional and prospective analysis of the Seguimiento Universidad de Navarra Project, a dynamic cohort study. Information is gathered through mailed questionnaires biannually since 1999. A validated LTPA questionnaire was used to assess LTPA level at baseline. Changes in LTPA were ascertained at 2 and 4 years of follow-up. HRQL was assessed at 4 and 8 years of follow-up with a validated Spanish version of the SF-36 Health Survey. Multivariate regression coefficients, means and their 95% CIs for each of the eight domains of the SF-36 according to quintiles of baseline LTPA and changes in LTPA over time were calculated using generalised linear models. Results At 4 years of follow-up, mean scores for upper quintiles of LTPA (second to highest quintile) of physical functioning, general health, vitality, social functioning and mental health were significantly higher than the mean score obtained for participants with the lowest level of LTPA (first quintile). In general, and independent of previous scores in SF-36 survey, the maintenance or the increase in LTPA levels during follow-up was associated with better scores in HRQL after 8 years of follow-up, especially for mental domains. Conclusion These findings provide support for an association between LTPA, long-term changes in LTPA and several aspects of HRQL (especially in relation to mental domains) extending previous cross-sectional findings.