The present study aimed to compare quadriceps femoris muscle strength and fatigue between obese (grade II and III) and nonobese adults. Ten obese (mean age: 25 years; mean BMI: 41 kg/m(2)) and ten lean (mean age: 27 years; mean BMI: 23 kg/m(2)) men were tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions at 180 degrees /s) and an electrostimulated (40 Hz) isometric protocol (5 min, 10% of the maximal torque). Maximal voluntary isometric and isokinetic torque and power were also measured. Voluntary torque loss was significantly higher (P < 0.05) in obese (-63.5%) than in lean subjects (-50.6%). Stimulated torque decreased significantly (P < 0.05) but equally in the two subject groups. Obese subjects displayed higher absolute (+20%; P < 0.01) but lower relative (i.e., normalized to body mass) (-32%; P < 0.001) muscle torque and power than their lean counterparts. Obese individuals demonstrated lower fatigue resistance during voluntary but not during stimulated knee extensions compared to their nonobese counterparts. Peripheral mechanisms of muscle fatigue -- at least those associated to the present stimulated test -- were not influenced by obesity. The observed quadriceps muscle function impairments (voluntary fatigue and relative strength) probably contribute to the reduced functional capacity of obese subjects during daily living activities.

IntroductIonThe increasing prevalence of obesity during the last decades (1) is ascribed mainly to a mismatch between energy intake and energy expenditure (EE) (2,3). The factors that influence this balance are numerous and complex, involving genes, environment, and their interaction. However, the rationale of weight management strategies is to identify and modify the amount of energy introduced and expended in order to regain normal body weight (BW) (1). EE is a major determinant of energy balance and body composition. According to an usually accepted scheme in human nutrition, daily EE (DEE) can be partitioned between basal metabolic rate (BMR) extrapolated to 24 h, which corresponds to the energy needed to sustain the body functions at rest and which accounts for ~65% of DEE in sedentary subjects (4); EE associated with physical activity (often referred to as the thermic effect of activity), which accounts for ~25% of DEE (5); and the thermic effect of food, which includes EE due to digestion, absorption, and metabolism of nutrients and which accounts for ~10% of DEE (5). Because of its large contribution to DEE, especially in obese subjects, BMR has frequently been the main focus of attention in the studies on the development and treatment of obesity.BMR can be considered as the sum of the EEs of tissues and organs in a fasting and resting state and in thermoneutral conditions. It depends on the mass and metabolic rate of tissues and organs (6). For instance, EE is ~10, 15, 20, 35, and 35 times higher in the digestive tract, liver, brain, heart, and kidney than in resting muscle, whereas it is only ~1/3 of resting muscle in white adipose tissues (7). Thus, although organs only account for ~7% of BW, they contribute ~60% of BMR. In comparison, skeletal and adipose tissues account for 35-40% of BW but only 18-22% and 3-4% of BMR, respectively (8). Generally, BMR depends on body composition as expressed by fat-free mass (FFM) and fat mass (FM) and on gender, age, physical activity, and nutritional status. The main determinant of BMR is FFM (6), whereas FM is significant only in obese subjects (9). Gender is also a significant determinant of BMR, with men having a greater BMR than females after adjustment for body composition (9,10). In addition, BMR markedly decreases with advancing age in sedentary populations (11) The objective of the present study was to explore the relationship between basal metabolic rate (BMR), gender, age, anthropometric characteristics, and body composition in severely obese white subjects. In total, 1,412 obese white children and adolescents (BMI > 97° percentile for gender and age) and 7,368 obese adults (BMI > 30 kg/m 2 ) from 7 to 74 years were enrolled in this study. BMR was measured using an indirect calorimeter equipped with a canopy and fat-free mass (FFM) were obtained using tetrapolar bioelectrical impedance analysis (BIA). Using analysis of covariance, we tested the effect of gender on the relationship between BMR, age, anthropometry, and body composition. In children and ad...

The purpose of this cross-sectional study was to compare quadriceps muscle strength and fatigue between severely obese (body mass index 34 kg/m2) and nonobese adolescents. Maximal isokinetic torque and angle of peak torque as well as isometric torque at short (40 degrees of knee flexion) and long (80 degrees of knee flexion) muscle length were measured using an isokinetic dynamometer. Muscle fatigue was quantified as the percent torque loss during an isokinetic voluntary protocol and an electrical stimulation isometric protocol. Obese adolescents produced greater absolute isokinetic (+16%; P < 0.05) and isometric torque at short (+25%; P < 0.01) but not at long muscle length (P > 0.05) compared to their lean counterparts. The angle of peak torque was significantly lower in obese than in nonobese subjects (-11%; P < 0.05), i.e., obese produced their maximal strength at shorter muscle length. Isokinetic and isometric torque normalized to the fat-free mass were not significantly different between the two groups. No significant difference in voluntary and stimulated torque loss was observed between groups. Muscle strength per unit of fat-free mass and muscle fatigue were similar in the obese and nonobese adolescents tested in this study, therefore suggesting that obesity has little or no effect on quadriceps muscle function characteristics. On the other hand, it remains to be confirmed whether the observed quadriceps muscle length specificity contributes to the reduced functional capacity of obese adolescents during complex motor tasks involving deep knee flexion (squatting, kneeling).