The relationship between physical activity and muscle strength in children who are obese
Aim: To investigate the relationship between peripheral muscle strength and physical activity levels with obesity.
Methods: The knee strength of subjects attending a paediatric outpatient weight management clinic was measured using the current gold-standard method for strength testing; isokinetic dynamometry. Peak torque was measured through range for three speeds (60°/s, 90°/s and 180°/s) of knee flexion and extension. Levels of physical activity were measured in MET hours/week using the Modifiable Activity Questionnaire for Adolescents. Inactivity was measured by hours of screen-time per day.
Results: Eighteen children (8 boys ang 11 girls, mean BMI=32.47±6.15 Kg/ m2, mean age=11.88±2.29 yrs) participated in the study. Mean peak torque to weight flexion values for gender were: 63.9±7.9 and 59.4 ±12.4 for boys and girls at 60°/s, 59.5±10 and 53.5 ±13.12 at 90°/s and 53.2±11.7 and 43.01±12 at 180°/s. Mean extension peak torque to weight values were: 119.90±17.77 and 139.0±30 at 60°/s; 117.7±23.2 and 119.69±25.6 at 90°/s; 95.19±21.96 and 87.74±19.96 at 180°/s for boys and girls respectively. Energy expenditure in regular activity as measured by MET hours/week (mean=17.66±12.5) was significantly correlated with knee flexion at 60°/s and 180°/s (r=0.645, p<0.05; r=0.571, p<0.05). Amount of time spent in sedentary activity (screen hours) was negatively correlated to knee flexion strength at 60°/s (r=−0.619, p<0.01), 90°/s (r=−0.567, p<0.05) and 180°/s (r=−0.506, p<0.05), and to knee extension strength at 90°/s (r=−0.617 p<0.01) and 180°/s (r=−0.578, p<0.05).
Conclusions: Lower limb muscle strength as measured by lower limb peak torque is significantly positively associated with physical activity and negatively associated with sedentary behaviour. As seen in previous studies, reduced peripheral muscle strength may impact on exercise capacity.