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Voluntary and electrically evoked strength characteristics of obese and nonobese preadolescent boys
Insights
Obese children show weaker strength performance due to excess fat, not reduced muscle strength. Their muscle size and intrinsic strength are similar to non-obese peers, indicating body weight is the primary factor.
Area of Science:
- Pediatric Physiology
- Sports Science
- Human Movement Studies
Background:
- Overweight and obese children often exhibit poorer motor skills, particularly in strength- and power-dependent activities.
- Previous research suggests a potential link between excess body fat and reduced functional strength in pediatric populations.
Purpose of the Study:
- To investigate if the inferior motor performance in obese children is due to a lower strength-to-muscle-area ratio.
- To compare the intrinsic muscle strength and contractile properties between obese and non-obese pre-adolescent boys.
Main Methods:
- Recruited 11 non-obese and 13 obese boys (ages 9-13).
- Measured peak torque during isometric and isokinetic elbow flexion and knee extension.
- Determined muscle cross-sectional areas (CSA) using computed axial tomography.
- Assessed muscle contractile properties via percutaneous stimulation.
Main Results:
- Non-obese boys had significantly higher body weight-normalized strength.
- No significant differences were found in muscle CSA between obese and non-obese groups.
- Absolute and relative muscle strength, as well as contractile properties, were comparable between groups when normalized for muscle size.
Conclusions:
- Obese and non-obese pre-adolescent boys possess similar intrinsic muscle strength and contractile properties.
- The reduced motor performance in obese children is likely attributable to the mechanical disadvantage of carrying excess fat mass, not inherent muscle weakness.
Abstract:
Overweight and obese children demonstrate inferior motor performance for strength- and power-related activities requiring support or lifting of body weight. Our purpose here was to determine whether the inferior performance could be attributed to a lower strength to muscle area ratio in the obese. Eleven nonobese (16.6% fat) and 13 obese (35.5% fat) boys (9-13 years old) volunteered for the study. Peak torque was measured during voluntary isometric and isokinetic elbow flexion and knee extension at four joint angles and four velocities, respectively. The contractile properties, twitch torque, time to peak torque, and half-relaxation time were evoked for the elbow flexors by percutaneous stimulation. Elbow flexor and knee extensor cross-sectional areas (CSA) were determined by computed axial tomography taken at the mid-upper arm and mid-thigh, respectively. Isometric and isokinetic elbow flexion and knee extension strength normalized for body weight were significantly (p less than 0.05) higher in the nonobese compared to the obese boys. There were no significant (p greater than 0.05) differences, however, between groups for elbow flexor and knee extensor CSA or for absolute and relative (normalized for muscle CSA or the product of muscle CSA and height, the latter accounting for differences in moment arm length) isometric, isokinetic, or evoked twitch torque for elbow flexion or knee extension. Likewise, there were no differences between groups for the time-related contractile properties, time to peak torque, or half-relaxation time. These findings suggest that there is no difference in the intrinsic strength or contractile properties of the elbow flexor and knee extensor muscles between obese and nonobese pre-adolescent boys and that other factors, such as the handicapping effect of excess fat mass, probably account for the reduced motor performance of the obese child.