Strength training effects in prepubescent boys

Possible changes in muscle size and function due to resistance training were examined in prepubertal boys. Thirteen boys (9-11 yr) volunteered for each of the training and control groups. Progressive resistance training was performed three times weekly for 20 wk. Measurements consisted of the following: 1 repetition maximum (RM) bench press and leg press; maximal voluntary isometric and isokinetic elbow flexion and knee extension strength; evoked isometric contractile properties of the right elbow flexors and knee extensors; muscle cross-sectional area (CSA) by computerized tomography at the mid-right upper arm and thigh; and motor unit activation (MUA) by the interpolated twitch procedure. Training significantly increased 1 RM bench press (35%) and leg press (22%), isometric elbow flexion (37%) and knee extension strength (25% and 13% at 90 degrees and 120 degrees, respectively), isokinetic elbow flexion (26%) and knee extension (21%) strength, and evoked twitch torque of the elbow flexors (30%) and knee extensors (30%). There were no significant effects of training on the time-related contractile properties (time to peak torque, half-relaxation time), CSA, or %MUA of the elbow flexors or knee extensors. There was, however, a trend toward increased MUA for the elbow flexors and knee extensors in the trained group. Strength gains were independent of changes in muscle CSA, and the increases in twitch torque suggest possible adaptations in muscle excitation-contraction coupling. Improved motor skill coordination (especially during the early phase of training), a tendency toward increased MUA, and other undetermined neurological adaptations, including better coordination of the involved muscle groups, are likely the major determinants of the strength gains in this study.     

Relationship between cardiorespiratory fitness,body composition and blood pressure in school children

BACKGROUND: The purpose of this comparative and correlational cross-sectional study was to describe the associations between cardiorespiratory fitness, blood pressure and body composition in Portuguese school children. METHODS: The sample comprised 529 children (246 males and 283 females) aged 8-15 years-old. Body height and body mass were determined by standard anthropometric METHODS: Blood pressures were measured with children sitting after at least 5 min rest. The maximal multistage 20 m shuttle run test was carried-out to predict maximal aerobic power. RESULTS: The present study shows that boys were more fit (p= or <0.05) and less fat than girls (p= or <0.05). Multiple regression analysis reveals that weight and age explained significantly (p= or <0.01) the amounts of systolic blood pressure (SBP) and diastolic blood pressure (DBP). In girls, percentage of fat (%F) showed an influence on the variance in SBP (4.9%, p= or <0.05). In addition, weight (14.5%) and age (9.8%) account significantly (p= or <0.01) for the amount of variance to DBP in males. For girls, age (11.4%) and BMI (2.4%) account significantly to the variance found in DBP. However, the independent variables, for both sexes, account less than 50% of the overall variance found in blood pressures values. CONCLUSIONS: In conclusion, the present study shows that boys were more fit and had less fat than girls. The level of cardiorespiratory fitness does not seem to be an important correlate of blood pressure variation across age groups and gender.     

Relationship of body size, physique, and composition to physical performance in young boys and girls.

The present study examined the aerobic, anaerobic and strength performance characteristics of 52 young boys and girls (mean age 10.8 and 11.1 yrs, respectively) on selected laboratory measures. Anthropometrically, the boys and girls were similar, with the exception of measures of body fatness. The boys demonstrated greater values in maximal aerobic power, anaerobic performance, (especially related to body weight), and strength relative to lean body mass. Since body size measures, including height, were similar, the functional differences could not be attributed to such factors. The significant but low correlations between the performance variables failed to support the concept of children as "metabolic non-specialists" as proposed by previous authors. In fact, the large amount of variance not accounted for could be interpreted as supporting the unique contribution of genetic endowment of the effect of habitual activity patterns on the performance measures. Canonical correlations indicated a strong relationship between selected anthropometric and performance variables (rc = .94). For boys, height and weight were strongly related to anaerobic performance, whereas weight and thigh volume were strongly related to all performance measures for the girls.     

The chemoreflex in young boys and girls

In order to determine the influence of the chemoreflex on the cardiovascular system of young children, 35 boys and 35 girls (all 7 - 9 years old) performed three minutes of 30 % maximal voluntary contraction (MVC) static handgrip (SHG) exercise followed by four minutes of blood flow occlusion in the previously exercised arm, and then six minutes of passive recovery. Heart rate (HR) and blood pressure (BP) were measured each minute. Twenty girls performed a second occlusion trial to determine reliability. Reliability coefficients for HR (R = 0.51 - 0.78), diastolic (R = 0.46 - 0.81) and systolic (R = 0.57 - 0.78) BP throughout the occlusion trial were moderately high. There was a similar increase in HR (19 +/- 8 vs. 16 +/- 10 %), diastolic (34 +/- 12 vs. 34 +/- 16 %) and systolic (18 +/- 9 vs. 15 +/- 7 %) BP in boys and girls, respectively, during three minutes 30 % MVC exercise. During the occlusion period, diastolic (43 +/- 31 vs. 47 +/- 26 %) and systolic (51 +/- 25 vs. 54 +/- 32 %) BP dropped similarly during minute one but remained elevated significantly above baseline in both boys and girls the entire four-minute period. During the recovery period, minute one SBP and DBP dropped similarly in boys (23 +/- 37, 20 +/- 37 %) and girls (20 +/- 38, 12 +/- 38 %), respectively. In boys and girls DBP remained significantly above baseline the entire recovery period. HR in boys and girls returned to baseline immediately following SHG exercise and remained there through recovery. In conclusion, as reported in adults, the drop in HR to baseline during post-exercise ischemia with a concomitant maintenance of BP significantly above baseline indicates that at least two separate mechanisms, with varying influence, are responsible for HR and BP control in young children. Further, the chemoreflex operates similarly in young boys and girls.     

Physical efficiency tests in Indian urban adolescent boys and girls.

Simple anthropometric measurements and physical efficiency tests were performed on adolescent Indian urban boys between 10-14 years and girls between 11-14 years of age. The similar height and weight of the subjects of both sexes were observed and was suggestive of higher growth rate in girls than the boys during only the initial phase of adolescent growth spurt. The vital capacity (total, ml/cm of height, l/m2 of surface area), Peak Expiratory Flow Rate (total, l/cm of height, l/kg of weight, l/m2 of surface area, l/year of age) and grip strength were observed to be insignificantly different between the sexes.     

Characterizing body composition,cardiorespiratory fitness,and physical activity in women with anterior cruciate ligament reconstruction

ObjectivesThe purpose was to compare body composition, cardiorespiratory fitness, and physical activity (PA) engagement between women with ACLR and healthy controls.DesignCross-sectional study.SettingUniversity laboratory.ParticipantsTen women with ACLR (time since surgery = 33.0 ± 18.3 months; age = 21.4 ± 3.8 years) and 10 healthy women (age = 21.9 ± 3.1 years) matched based on age (±2 years) and Tegner Activity Level (±2) participated.Main outcome measuresBody fat percentage (%BF) was estimated using air displacement plethysmography, cardiorespiratory fitness was assessed via a graded cycle test, and PA was assessed using accelerometers worn for 7 days. Groups were compared using Mann-Whitney U tests. Time (minutes/week) spent in moderate-to-vigorous PA and step count (steps/day) were compared between groups using a one-way ANCOVA with 7-day total wear time as the only covariate. Statistical significance was established a priori as α ≤ 0.05.ResultsWomen with ACLR had significantly higher %BF than controls (ACLR = 32.7 ± 6.7%, healthy = 22.6 ± 4.9%; p < 0.01) and participated in less steps per day (ACLR = 6650 ± 3227 steps/day, healthy = 9361 ± 2626 steps/day; p = 0.02).ConclusionsThere may be persistent negative effects on body composition and PA engagement for women following ACLR. Low PA and high %BF have adverse consequences for premature mortality and morbidity; therefore, it is crucial to assess these characteristics and determine interventions to maintain PA and healthy body composition following ACLR.     

The effect of backward locomotion training on the body composition and cardiorespiratory fitness of young women

This study investigated the effect of a backward training program on the physical and fitness condition of young women. Twenty-six healthy female university students (aged 18 - 23 years) took part in three different baseline tests: body composition, a submaximal treadmill test, and a 20-m shuttle run test. Subjects were divided into a training group (n = 13) and a control group (n = 13). The training group completed a six-week backward run/walk training program. The control group was restricted to their daily activities similar to the four weeks prior to the onset of the baseline tests. The training group showed a significant (p = 0.01) decrease in O(2) consumption during both submaximal forward and backward exercise on the treadmill (32 % decrease during backward and 30 % decrease during forward exercise). A significant (p = 0.01) decrease in percentage body fat (2.4 %), a 19.7 % decrease in the sum of skinfolds (p = 0.001) and significantly (p = 0.013) improved predicted VO(2max) values from the forward 20-m shuttle run test (5.2 %) were also found in the case of the training group. The findings suggest that backward walk/run training improves cardiorespiratory fitness for both forward and backward exercise and causes significant changes in body composition in young women.     

Interhemispheric asymmetry of regional cerebral blood flow in prepubescent boys with attention deficit hyperactivity disorder.

The prefrontal cortex is asymmetric in both structure and function. In normal subjects, the right prefrontal cortex is activated more than the left during response inhibition. Patients with attention deficit hyperactivity disorder (ADHD) have impaired response inhibition and altered structural interhemispheric asymmetry. This study was conducted to examine the functional interhemispheric asymmetry during response inhibition in children with ADHD. Subjects were divided into three groups according to the level of motor hyperactivity. Blood flow tracer (99m)Tc-ethyl cysteinate dimer was injected while subjects were performing a response inhibition task (RIT), followed by single photon emission computerized tomography (SPECT). After three-dimensional reconstruction, filtering and smoothing, individual scans were morphed to a template. Three average group images were created from individual scans. Each average group image was subtracted voxel-by-voxel from its mirror image to compare the regional cerebral blood flow (rCBF) in the right and left cerebral hemispheres, yielding images of significant interhemispheric rCBF asymmetry. The severe hyperactivity group exhibited most prefrontal left>right rCBF asymmetry and left>right occipitoparietal asymmetry. Reversal of functional prefrontal asymmetry in boys with severe motor hyperactivity supports the hypothesis of right prefrontal cortex dysfunction in ADHD.     

Contribution of muscular strength in cardiorespiratory fitness tests

AIM: Reports from laboratory-based studies have revealed a relationship between resistance training and endurance performance in both trained and untrained individuals. The purpose of the present study was to investigate the contribution of lower extremity muscular strength levels in performing cardiorespiratory fitness tests in laboratory, as well as field-based settings. METHODS: Within 2 weeks 38 healthy males (age 21.6+/-2.5 years, body mass index--BMI--24.4+/-2.2) performed three maximal oxygen uptake (VO(2max)) assessments using the 20 m multistage shuttle run test (MSR), the 20 m square shuttle run test (SSR), and a maximal treadmill test (MT) to exhaustion. Data were also obtained from knee flexion and extension isokinetic dynamometry at 60 degrees xs(-1). RESULTS: MSR performance correlated with the peak torque generated from both legs at r=0.63 (P<0.001). The equivalent for SSR was significant at r=0.44 (P<0.05), while MT demonstrated a non-significant positive correlation coefficient (r=0.34, P>0.05). Stepwise regression analyses revealed that the inclusion of leg strength parameters increased the coefficient of determination by 9% (P<0.001) and 4% (P<0.05) in the MSR and SSR, respectively. The MT model was not significantly associated with any of the isokinetic indices studied. CONCLUSIONS: Although moderately significant, the present coefficients suggest that performance in the present field-based cardiorespiratory fitness tasks is affected to a certain extent by lower extremity muscular strength. The latter also demonstrates a positive relationship with laboratory-based performance.     

Exercise training effects on serum lipids of prepubescent boys and adult men

The effects of 10 wk of exercise training at low (40% VO2max) or high (75% VO2max) intensity on serum lipids and lipoproteins were compared in prepubescent boys and adult men. The final sample size consisted of: 8 boys (mean +/- SE age = 8.5 +/- 1.96 yr) and 8 men (36.6 +/- 3.18 yr) in low; 12 boys (8.0 +/- 1.40 yr) and 12 men (36.6 +/- 4.09 yr) in high; and 10 boys (9.0 +/- 2.08 yr) and 10 men (36.7 +/- 4.82 yr) in control. Training involved walking/jogging/running 3 d X wk-1 at a distance which progressed from 2.4 km X d-1 in the first week to 4.8 km X d-1 from the fifth week. Fasting blood samples, collected on 2 d during both pre- and post-training, were assayed for triglycerides, total cholesterol (CHOL), and high density lipoprotein cholesterol (HDL-C). Maximum aerobic power (VO2max) was determined from a treadmill test. Additionally, dietary intake was assessed from a 3-d dietary record and body composition from the sum of 6 skinfolds. The only statistically significant (P less than 0.05) changes occurred in HDL-C and CHOL for the high groups. HDL-C decreased following training. CHOL was lower for high than the other groups for the first day post-training only. There were no differences in the changes in HDL-C/CHOL ratio among the groups. VO2max only increased in the high groups. Dietary intake and body weight did not change. Further statistical adjustment in lipids for changes in sum of 6 skinfolds did not alter the results.(ABSTRACT TRUNCATED AT 250 WORDS)     

Occupational demand and human rights. Public safety officers and cardiorespiratory fitness

The issue of discrimination in physically demanding employment, such as police, firefighters, prison guards and military personnel, is contentious. In terms of oxygen transport, the 'action limit' (calling for personnel selection or task redesign) is a steady oxygen consumption of 0.7 L/min, while the maximum permissible limit is 2.1 L/min. Note is taken of the commonly expressed belief that public safety duties are physically demanding, calling for personnel with an aerobic power of at least 3 L/min, or 42 to 45 ml/kg/min. The actual demands of such work can be assessed on small samples by physiological measurements (using heart rate or oxygen consumption meters), but the periods sampled may not be typical of a normal day. A Gestalt can also be formed as to the heaviness of a given job, or a detailed task analysis can be performed; most such analyses of public safety work list distance running and other aerobic activities infrequently. An arbitrary requirement of 'above average fitness' is no longer accepted by courts, but a further approach is to examine the characteristics of those currently meeting the demands of public safety jobs satisfactorily. Young men commonly satisfy the 3 L/min standard, but this is not usually the case for women or older men; in the case of female employees, it also seems unreasonable that they should be expected to satisfy the same standards as men, since a lower body mass reduces the energy cost of most of the tasks that they must perform. A second criterion sometimes applied to physically demanding work (a low vulnerability to heart attacks) is examined critically. It is concluded that the chances that a symptom-free public safety officer will develop a heart attack during a critical solo mission are so low that cardiac risk should not be a condition of employment. Arbitrary age- and sex-related employment criteria are plainly discriminatory, since some women and 65-year-old men have higher levels of physical fitness than the average young man of 25 years. Neither laboratory nor field tests offer a satisfactory means of distinguishing such individuals, and the only equitable basis of selecting personnel for physically demanding work seems a probationary period of employment.     

Childhood cardiorespiratory fitness,muscular fitness and adult measures of glucose homeostasis

Objectives

To assess whether childhood cardiorespiratory fitness (CRF) and muscular fitness phenotypes (strength, power, endurance) predict adult glucose homeostasis measures.

Effects of methylphenidate discontinuation on cerebral blood flow in prepubescent boys with attention deficit hyperactivity disorder.

Methylphenidate (MPH) is an effective symptomatic treatment of attention deficit hyperactivity disorder (ADHD), but the mechanisms of its therapeutic action have not been fully elucidated. To address this issue, we assessed the effects of discontinuation of chronic MPH treatment on regional cerebral blood flow (rCBF) in ADHD patients. METHODS: Twenty-two prepubescent boys with ADHD (age range, 8.2-11.5 y) and 7 healthy volunteers were studied with SPECT on and off MPH. Their rCBF data were automatically normalized to whole-brain counts and coregistered with standard anatomic space. rCBF changes were evaluated with statistical parametric mapping based on voxel-by-voxel ANOVA. RESULTS: When the subjects were not taking MPH, rCBF was higher in the motor, premotor, and the anterior cingulate cortices (Brodmann's areas 4, 6, and 32). CONCLUSION: Brief discontinuation of MPH treatment is associated with increased motor and anterior cingulate cortical activity. Our findings suggest that MPH treatment modulates motor and anterior cingulate cortical activity directly or indirectly. Alternatively, our findings may be related to MPH withdrawal. These data provide novel information on the potential mechanisms of the therapeutic action of MPH. Furthermore, they are clinically relevant to the commonly occurring brief interruptions in MPH treatment.