Acute endocrine responses to plyometrics versus resistance exercise in children

The purpose of this study was to examine the acute hormonal responses to a bout of resistance versus plyometric exercise in young male athletes. Specifically, changes in salivary cortisol, testosterone and testosterone-to-cortisol ratio from pre- to post-exercise between the two different exercise protocols were examined. Twenty-six peri-pubertal active boys participated in this cross-over study, completing two exercise sessions. During each session, participants first completed a 30 min control period, which did not include any exercise, and then was randomly assigned to perform a 45 min of either a resistance exercise or a plyometric exercise protocol. All participants crossed over to perform the other exercise protocol during their second exercise session, a week later. Four saliva samples during each protocol were taken at: baseline, pre-exercise, 5 min post-exercise and 30 min post-exercise. Significant increases in testosterone values were reported 5 min post-exercise following the resistance protocol, but not the plyometric protocol. Both exercise protocols resulted in significant cortisol decreases overtime, as well as significant testosterone-to-cortisol ratio increases. The post-exercise increases in salivary testosterone and testosterone-to-cortisol ratio followed the typical exercise induced anabolic response seen in adults. However, the post-exercise decrease in salivary cortisol was different than the typical adult response indicating an insufficient stimulus for this age group maybe due to their stage of the biological development. Thus, in the adolescent boys, exercise appears to change the anabolic to catabolic balance in favor of anabolism.

What children value : a scale to guide health promotion programs

Objective. Physical activity is important for the health of all human beings. Although it is important to develop good health promotion programs for children to increase participation in physical activity, to date there appear to be no programs based on what kids value beyond health and physical activity itself. This study proposed to create a scale with strong content and face validity that could uncover what any given population of children value in life regardless of their participation in physical activity and that experts feel could be related to physical activity. These findings will allow the development of targeted health promotion programs to increase children's participation in regular physical activity. Method In this study, a combination of qualitative and quantitative approaches was used. Data were gathered from seven experts in the field, sixty-seven children in grades three to five, five parents, and three teachers. From these data response groupings were created and sent to four experts to be given single word names. The resulting nine theme names were re-worked into "child-friendly" language. Four children were then asked to discuss theme names to see if they liked and understood them. The next step involved asking children and experts to rank order the nine themes, the children in general and the experts in terms of relevance to physical activity. From these results, possible versions of the scale were then created using the combined expert/children rankings. Each version was examined for content validity. Two versions of a scale resulted. These were sent to experts, parents, teachers and children in order to determine which one they liked better and to suggest any foreseeable problems. Once this information was collected, a beta (final prototype) version of the scale was created. Results. Nine common theme names were created from the response groupings. All four children agreed that they did understand and like each of the nine theme names. Experts and teachers agreed that full coverage of the content had been achieved. Children suggested a single wording change from "Being Accepted" to "Being Included". Five themes were selected for inclusion. The beta version of the scale included 12 forced choice statements, the first ten comparing all themes against one another followed by two anchor statements. Conclusion. At the outset it was recognized that it is essential to know what children think is important in their lives in order to serve as potential benefits in the development of effective physical activity promotion programs. This study developed a scale which could be used to determine what a population of children feel is important in order to focus health promotion programs for physical activity. The scale has strong face and content validity.

The role of physical activity and perceived adequacy on cardiorespiratory fitness in children with developmental coordination disorder

Evidence suggests that children with developmental coordination disorder (DCD) have lower levels of cardiorespiratory fitness (CRF) compared to children without the condition. However, these studies were restricted to field-based methods in order to predict V02 peak in the determination of CRF. Such field tests have been criticised for their ability to provide a valid prediction of V02 peak and vulnerability to psychological aspects in children with DCD, such as low perceived adequacy toward physical activity. Moreover, the contribution of physical activity to the variance in V02 peak between the two groups is unknown. The purpose of our study was to determine the mediating role of physical activity and perceived adequacy towards physical activity on V02 peak in children with significant motor impairments. This prospective case-control design involved 122 (age 12-13 years) children with significant motor impairments (n=61) and healthy matched controls (n=61) based on age, gender and school location. Participants had been previously assessed for motor proficiency and classified as a probable DCD (p-DCD) or healthy control using the movement ABC test. V02 peak was measured by a progressive exercise test on a cycle ergometer. Perceived adequacy was measured using a 7 -item subscale from Children's Selfperception of Adequacy and Predilection for Physical Activity scale. Physical activity was monitored for seven days with the Actical® accelerometer. Children with p-DCD had significantly lower V02 peak (48.76±7.2 ml/ffm/min; p:50.05) compared to controls (53.12±8.2 ml/ffm/min), even after correcting for fat free mass. Regression analysis demonstrated that perceived adequacy and physical activity were significant mediators in the relationship between p-DCD and V02 peak. In conclusion, using a stringent laboratory assessment, the results of the current study verify the findings of earlier studies, adding low CRF to the list of health consequences associated with DCD. It seems that when testing for CRF in this population, there is a need to consider the psychological barriers associated with their condition. Moreover, strategies to increase physical activity in children with DCD may result in improvement in their CRF.

An examination of the effects on learning seen in children afforded the opportunity to control the order of repetitions for three novel spatiotemporal sequences

Children were afforded the opportunity to control the order of repetitions for three novel spatiotemporal sequences. The following was predicted: a) children and adults in the self-regulated (SELF) groups would produce faster movement (MT) and reaction times (R T) and greater recall success (RS) during retention compared to the age-matched yoked (YOKE) groups; b) children would choose to switch sequences less often than adults; c) adults would produce faster MT and RT and greater RS than the children during acquisition and retention, independent of experimental group. During acquisition, no effects were seen for RS, however for MT and RT there was a main effect for age as well as block. During retention a main effect for practice condition was seen for RS and failed to reach statistical significance for MT and RT, thus partially supporting our first and second hypotheses. The third hypothesis was not supported.

Comparison of strength gains over 13 and 26-weeks of resistance training in children

The primary aim of this study was to determine if there were significant strength gains achieved by children participating in the Hamilton Wentworth District School Board Sport Academy Program. The secondary aim was to determine if the children participating in the 26-week program achieved greater gains or if a plateau in strength adaptations occurred following the 13-week session. The tertiary aim was to determine if there were varying levels of response to the training stimulus between grade 7, grade 8 and grade 9 subjects. Ninety-eight (98) subjects completed a13-week RT program. 6RM strength testing of the chest press, seated row and leg press were conducted prior to the program. Subjects were tested following the 13-week training stimulus to determine if strength gains were achieved and to assess the variation in strength adaptations between the groups. Forty seven (47) subjects completed 26 weeks ofRT. Subjects' strength was tested prior to starting the program, at week 13 of the program and at week 26 of the program to determine the variation in adaptation over a 13 week program versus a 26- week RT program. There were significant (pexercises while grade 9 subjects showed significant gains across the 6RM seated row, chest press, and leg press measures.

Bone speed of sound, biochemical markers of bone turnover and IGF-1 in competetive synchronized swimmers

The purpose of this study was to compare bone speed of sound (SOS) measured by quantitative ultrasound, circulating levels of IGF- 1 and biochemical markers of bone turnover in pre- (Pr) and post-menarcheal (Po) synchronized swimmers (SS) and controls (NS). Seventy participants were recruited: 8 PrSS, 22 PoSS, 20 PrNS, and 20 PoNS. Anthropometric measures of height, weight, skeletal maturity and percent body fat were taken, and dietary intake evaluated using 24-hour recall. Bone SOS was measured at the distal radius and mid-tibia and blood samples analyzed for IGF-1, osteocalcin, NTx, and 25-OH vitamin D. Results demonstrated maturational effects on bone SOS, IGF-1 and bone turnover (p<0.05), with no differences observed between SS and NS. Main effects were observed for a reduced caloric intake in SS compared to NS (p<0.05). Therefore, SS does not offer additive affects on bone strength but imparts no adverse affects to skeletal health in these athletes.

Exploring Chinese-Canadians' perspectives on health : a quantitative study

Chinese have unique perspectives on health and illness, which is mostly umecognized by western medicine. Immigration may contribute to problems with health consultations, inconvenience, and dissatisfaction. As the largest visible minority in Canada, Chinese- Canadians' perspectives on health should be studied in order to help Chinese immigrants adapt to a new health-care and health-promotion system, and keep them healthy. A quantitative questionnaire was designed based on the findings from a pilot study and previous literature. A hundred participants were recruited from Toronto, Vancouver, Halifax, and St. Catharines. Descriptive analysis and correlation analysis were used to investigate the structure of the variables. Findings indicated that most oftheir attitudes and corresponding practices to the different health aspects were positive. The relation between dietary practices and attitude was only found in small cities. Their attitudes were impacted by their length of stay in Canada. Their attitudes to regularly timed meals and psychological consultation were related to their acculturation level, as was the regularity of their practice of dental flossing. Their self-evaluated general health levels were also found to be affected by their medical history, education level, feeling to talk about • sexual health, and smoking, particularly in the male subjects of the study. In conclusion, they realized that each health aspect w~s important to their health. However, their practices did not bear a strong relation to their beliefs. Traditional thoughts about health reseeded with time. Acculturation level did not affect most of their attitudes or practices. Under pressure, the priority of the daily health practices decreased. Older persons, those with low incomes, lower education levels or families under stress need to pay more attention to their health level. In-depth future research was recommended.

Muscle strength and activation characteristics of power- trained and non-athlete boys and men

During maturation, muscle strength is enhanced through muscle growth, although neuro-muscular factors are also believed to be involved. In adults, training for power sports has been shown to enhance muscle strength and activation. The purpose of this study was to examine muscle strength and activation in power-trained athletes (POW) compared with non-athletes (CON), in boys and in adults. After familiarization subjects performed ten 5-s explosive maximal voluntary contractions for elbow and knee flexion and extension. The adults were stronger then the boys and the adult POW were stronger then the adult CON, even after correction for muscle size. Normalized rate of torque development was higher in the adults then in the boys and higher in the POW then CON boys. The rate of muscle activation was higher in the adults and POW groups. The results suggest that maturation and power-training have an additive effect on muscle activation.

Electrophysiological correlates of performance monitoring in middle and late adolescence

The ability to monitor and evaluate the consequences of ongoing behaviors and coordinate behavioral adjustments seems to rely on networks including the anterior cingulate cortex (ACC) and phasic changes in dopamine activity. Activity (and presumably functional maturation) of the ACC may be indirectly measured using the error-related negativity (ERN), an event-related potential (ERP) component that is hypothesized to reflect activity of the automatic response monitoring system. To date, no studies have examined the measurement reliability of the ERN as a trait-like measure of response monitoring, its development in mid- and late- adolescence as well as its relation to risk-taking and empathic ability, two traits linked to dopaminergic and ACC activity. Utilizing a large sample of 15- and 18-year-old males, the present study examined the test-retest reliability of the ERN, age-related changes in the ERN and other components of the ERP associated with error monitoring (the Pe and CRN), and the relations of the error-related ERP components to personality traits of risk propensity and empathy. Results indicated good test-retest reliability of the ERN providing important validation of the ERN as a stable and possibly trait-like electrophysiological correlate of performance monitoring. Ofthe three components, only the ERN was of greater amplitude for the older adolescents suggesting that its ACC network is functionally late to mature, due to either structural or neurochemical changes with age. Finally, the ERN was smaller for those with high risk propensity and low empathy, while other components associated with error monitoring were not, which suggests that poor ACe function may be associated with the desire to engage in risky behaviors and the ERN may be influenced by the extent of individuals' concern with the outcome of events.

Asymmetrical balance of power in preadolescents' mutual friendships

Dyadic friendShip' asymmetry was examined in relation to gender, friendship quality, and friendship status. Sixty-nine grade five children and their mutual, same-sex, friends participated in a laboratory session comprised ofvarious activities and completed questionnaires to identify mutual friends and evaluate friendship quality. Asymmetry of power was assessed observationally during an origami task. Variations in balance of power were evident in children's friendships. Boys' dyads had significantly greater levels of asymmetry than girls' dyads. Regardless of gender, asymmetry was associated with lower friendship quality, particularly as indexed by validation and caring and conflict resolution. Asymmetry was unrelated to differences in friendship status. Furthermore, relative individual power within the friendship was not related to individual perceptions offriendship quality. The implications ofthese findings in the theoretical and empirical literature were considered and suggestions for future research were made.

Attenuation of skeletal muscle FFA-induced insulin resistance by the polyphenol resveratrol. Elucidation of the mechanisms involved

Excess plasma free fatty acids (FFA) are correlated with insulin resistance and are a risk factor for the development of type 2 diabetes. In this study we examined the effect of the polyphenol resveratrol on FF A-induced insulin resistance in skeletal muscle cells and the mechanisms involved. Incubation of L6 myotubes with the FF A palmitate significantly decreased the insulin-stimulated glucqse uptake. Importantly, the effect of palmitate was ameliorated by resveratrol. Palmitate significantly increased serine phosphorylation of IRS..; 1 and reduced insulin-stimulated Akt phosphorylation, an effect that was abolished by resveratrol. We then investigated the effect of palmitate and resveratrol on the expression and phosphorylation of JNK, mTOR, p70-S6K, and AMPK kinases. The results demonstrated that our treatments had no effect on the expression of these proteins. However, palmitate increased the phosphorylation of mTOR and p70- S6K, whereas resveratrol abolished this effect and increased the phosphorylation of AMPK. Furthermore, all effects of resveratrol were abolished with sirtuin inhibitors, sirtinol and nicotinamide. These results indicate that resveratrol ameliorated FF A-induced insulin resistance by regulating mTOR and p70-S6K phosphorylation in skeletal muscle cells, through a mechanism involving sirtuins.

Relative importance of body composition, osteoporosis- related behaviours and socioeconomic status on bone SOS in adolescent females

The purpose of this study was to examine the associations between bone speed of sound (SOS) and body composition, osteoporosis-related health behaviours, and socioeconomic status (SES) in adolescent females. A total of 442 adolescent females in grades 9-11 participated. Anthropometric measures of height, body mass, and percent body fat were taken, and osteo-protective behaviours such as oral contraceptive use (OC), physical activity and daily calcium intake were evaluated using self-report questionnaires. Bone SOS was measured by transaxial quantitative ultrasound (QUS) at the distal radius and mid-tibia. The results suggest that fat mass is a significant negative predictor of tibial SOS, while lean mass is positively associated with radial SOS scores and calcium intake was positively associated with tibial SOS scores (p

The relationship between body mass index and breast cancer recurrence/progression and breast cancer-specific death

The aim of this study was to describe the nonlinear association between body mass index (BMI) and breast cancer outcomes and to determine whether BMI improves prediction of outcomes. A cohort of906 breast cancer patients diagnosed at Henry Ford Health System, Detroit (1985-1990) were studied. The median follow-up was 10 years. Multivariate logistic regression was used to model breast cancer recurrence/progression and breast cancer-specific death. Restricted cubic splines were used to model nonlinear effects. Receiver operator characteristic areas under the curves (ROC AUC) were used to evaluate prediction. BMI was nonlinearly associated with recurrence/progression and death (p= 0.0230 and 0.0101). Probability of outcomes increased with increase or decrease ofBMI away from 25. BMI splines were suggestive of improved prediction of death. The ROC AUCs for nested models with and without BMI were 0.8424 and 0.8331 (p= 0.08). I f causally associated, modifying patients BMI towards 25 may improve outcomes.

The effects of an acute bout of whole-body vibration on pulse wave velocity in individuals with SCI

Cardiovascular disease is a leading cause of mortality in the spinal cord injured (SCI) population. Reduced arterial compliance is a cardiovascular risk factor and whole body vibration (WBV) has be en shown to improve arterial compliance in able-bodied individuals. The study investigated the effect of an acute session ofWBV on arterial compliance as measured by pulse wave velocity (PWV). On separate days, arm, leg and aortic PWV were measured pre- and post- a 45 minute session of passive stance (PS) and WBV. The WBV was intermittent with a set frequency of 45Hz and amplitude of O.6mm. There was no condition by time effect when comparing PWV after WBV and PS. Following WBV, aortic (928.6±127.7 vs. 901.1±96.6cm/sec), leg (1035.2±113.8 vs.l099.8±114.2cm/sec) and arm PWV (1118.9±119.8 vs. 1181.1±124.4cm/s) did not change. As such, WBV did not reduce arterial compliance, however future research with protocol modifications is recommended.

Canadian Society for Exercise Physiology Position Paper: Resistance Training in Children and Adolescents

Many position stands and review papers have refuted the myths associated with resistance training (RT) in children and adolescents. With proper training methods, RT for children and adolescents can be relatively safe and improve overall health. The objective of this position paper and review is to highlight research and provide recommendations in aspects of RT that have not been extensively reported in the pediatric literature. In addition to the well-documented increases in muscular strength and endurance, RT has been used to improve function in pediatric patients with cystic fibrosis, cerebral palsy and burn victims. Increases in children’s muscular strength have been attributed primarily to neurological adaptations due to the disproportionately higher increase in muscle strength than in muscle size. Although most studies using anthropometric measures have not shown significant muscle hypertrophy in children, more sensitive measures such as magnetic resonance imaging and ultrasound have suggested hypertrophy may occur. There is no minimum age for RT for children. However the training and instruction must be appropriate for children and adolescents involving a proper warm-up, cool-down and an appropriate choice of exercises. It is recommended that low-to-moderate intensity resistance should be utilized 2-3 times per week on non-consecutive days, with 1-2 sets initially, progressing to 4 sets of 8-15 repetitions for 8-12 exercises. These exercises can include more advanced movements such as Olympic style lifting, plyometrics and balance training, which can enhance strength, power, co-ordination and balance. However specific guidelines for these more advanced techniques need to be established for youth. In conclusion, a RT program that is within a child’s or adolescent’s capacity, involves gradual progression under qualified instruction and supervision with appropriately sized equipment can involve more advanced or intense RT exercises which can lead to functional (i.e. muscular strength, endurance, power, balance and co-ordination) and health benefits.