Characteristics of upper limb mass, muscle CSA and stiffness in adolescent baseball players with and without elbow injury

Since elbow injuries are common in adolescent baseball players, this study aimed to determine the relationship between musculoskeletal status and elbow injuries in 47 baseball players aged 12-14 years. Participants answered a questionnaire and had their general body measurements taken. Magnetic resonance imaging was used to evaluate muscle cross sectional areas (CSA) of the upper arm flexor and extensor muscles, and x-ray absorptiometry was used to determine the mass of the upper arm and the total mass of the forearm and hand. Shear wave elastography was used to determine muscle stiffness of the biceps brachii, brachialis, pronator teres, and brachioradialis. An orthopedic surgeon performed a clinical assessment and elbow ultrasonography for each participant to diagnose elbow injuries. The measured values were compared between the elbow injury and control groups using two-sample t-tests. The elbow injury group had significantly higher muscle stiffness in the brachialis (p < 0.001) and brachioradialis (p = 0.004) muscles and greater elbow flexor CSA of the distal upper arm (p = 0.004) than the control group. The total mass of the forearm and hand and the mass ratio of the forearm and hand to the upper arm were significantly greater in the elbow injury group than in the control group (p = 0.002 and p < 0.001). Thus, it may be necessary to increase flexibility of the brachialis and brachioradialis flexible by stretching and massaging in addition to evaluating the mass distal to the elbow and the elbow flexor muscle size of the distal upper arm to manage elbow injury in youth baseball players. Characteristics of Upper Limb Mass, Muscle Cross-Sectional Area and Stiffness in Adolescent Baseball Players with and without Elbow Injury.

Gender differences in relationship between fat-free mass index and fat mass index among Korean children using body composition chart

PURPOSE

This study aimed to investigate gender differences in the relationship between fat-free mass index (FFMI) and fat mass index (FMI) by applying body composition chart on Korean elementary students.

MATERIALS AND METHODS

Data from 965 healthy Korean children of 8 to 12 years of age (501 boys, 464 girls) were obtained. FFMI and FMI were plotted on the body composition chart, and the differences in the relationships between FFMI and FMI were separately evaluated by gender or grade.

RESULTS

Weight was heavier and BMI was higher in 3rd and 4th grade boys compare to girls. The value of FFM was higher in boys, but FM was not different. In subgroup analysis by grade, significant gender by FFMI interaction (p=0.015) was found, indicating that the slope of the lines for FMI vs. FFMI was different between boys and girls (Figure was not shown). In subgroup analysis by gender, grade by FFMI interaction was significant in boys, indicating that FMI vs. FFMI relationship differed according to grade only in boys.

CONCLUSION

Boys are leaner than girls, despite having similar BMI. Gender difference in the direction of the change of the FFMI and FMI relationship is evident in children.

The effect of type of physical activity measure on the relationship between body fatness and habitual physical activity in children: a meta-analysis

BACKGROUND

The relationship between activity levels and body fat in children is unclear, despite a large number of studies. The issue is clouded by the wide variety of methods used to assess children's activity levels. It is important to assess whether the type of activity measure influences the fatness-activity relationship. This is a first step to uncovering the role of modifying variables such as gender, age, maturity, etc.

PRIMARY OBJECTIVE

This study uses meta-analytic procedures to synthesize the results of such studies and to assess whether the type of activity measure used has an effect on the strength of the relationship observed.

METHODS AND PROCEDURES

Fifty studies were located that satisfied the inclusion criteria. Seventy-eight per cent of the studies showed a negative relationship, 18% no relationship and 4% a positive relationship between physical activity and body fatness. Data were analysed using the meta-analytic procedures described by Rosenthal (Meta-analytic Procedures for Social Research, Sage, 1991).

MAIN OUTCOMES AND RESULTS

The mean effect size indicated a small to moderate, inverse relationship (r = -0.16). Mean effect sizes differed significantly (F(3,52) = 8.04, p < 0.001) according to the activity measure used: questionnaire, r = -0.14; motion counters, r = -0.18; observation, r = -0.39; heart rate (HR), r = 0.00. Observation measures elicited a significantly stronger relationship with body fat than did questionnaire or heart rate measures (p < 0.05). However, there was no significant difference between the effect sizes elicited by observation and motion counters. Correlational analyses revealed no effect of age group or gender on the strength of the relationship between fatness and activity.

CONCLUSIONS

This meta-analysis suggests there is a small to moderate relationship between body fat and activity in children. It is important to note, however, that the size of the relationship depends on the activity measure used. It is therefore recommended that direct measures of movement, such as observation or motion counter methods, are used to assess the relationship of activity levels with health.