Strength and cross-sectional area of knee extensor muscles in children

Iksokinetic strength and cross-sectional area (CSA) of knee extensor muscles were examined in 60 boys and girls, aged 6–9 years, and in 71 young adult men and women to investigate the influences of age and gender on the strength capabilities in relation to muscle size. A single anatomical CSA of quadriceps femoris at the right mid-thigh was measured by using a B-mode ultrasonic apparatus. Isokinetic strength produced at three kinds of constant velocity, 1.05, 3.14, and 5.24 rad · s^–1, was significantly correlated to the product of CSA and thigh length (TL) in separate samples by age and gender. In both genders, however, young adults had significantly higher ratios of strength to CSA · TL (ST · CSA^–1 · TL^–1) than children at all measurement velocities. Relative differences in ST · CSA^–1 · TL^–1 between children and young adults became larger with increasing test velocity. Within the same generation, men had significantly higher ST · CSA^–1 · TL^–1 than women at all measurement velocities except for the ratio in children at 1.05 rad · s^–1. These results indicate that the ability to produce strength proportional to muscle size is lower in children than in young adults, regardless of gender, and lower in women than in men within the same generation.     

Exercise ventilatory kinematics in endurance trained and untrained men and women

To determine how increased ventilatory demand impacts ventilatory kinematics, we compared the total chest wall volume variations (V(CW)) of male and female endurance-trained athletes (ET) to untrained individuals (UT) during exercise. We hypothesized that training and gender would have an effect on V(CW) and kinematics at maximal exercise. Gender and training significantly influenced chest wall kinematics. Female ET did not change chest wall end-expiratory volume (V(CW,ee)) or pulmonary ribcage (V(RCp,ee)) with exercise, while female UT significantly decreased V(CW,ee) and V(RCp,ee) with exercise (p<0.05). Female ET significantly increased pulmonary ribcage end-inspiratory volume (V(RCp,ei)) with exercise (p<0.05), while female UT did not change V(RCp,ei) with exercise. Male ET significantly increased V(RCp,ei) with exercise (p<0.05); male UT did not. Men and women had significantly different variation of V(CW) (p<0.05). Women demonstrated the greatest variation of V(CW) in the pulmonary ribcage compartment (V(RCp)). Men had even volumes variation of the V(RCp) and the abdomen (V(Ab)). In conclusion, gender and training had a significant impact on ventilatory kinematics.     

Interplay among the changes of muscle strength,cross-sectional area and maximal explosive power: theory and facts

A model has recently been proposed to predict the changes of mechanical power ( ) during a maximal explosive effort (such as a standing high jump off both feet) following an adaptation (e.g. training/de-training). The model is based on the assumption that, all other things being equal (ceteris paribus), the predicted changes in depend on the measured changes of muscle force (F) or cross-sectional area (CSA) only. It follows that, if the measured changes in are not equal to those predicted by the model, factors other than a change in F (or CSA) must be responsible for this difference. The model does not allow the determination of factors specifically involved in the adaptation process but it helps in discriminating whether an adaptation has taken place at a local level (when the observed changes in F would be attributed to factors other than the observed changes in CSA, e.g. co-contractions, fibre type modifications...), or at a central level (when the observed changes in would be attributed to other factors than the observed changes in F, e.g. co-ordination of multiple joints and muscle groups...), or in both regions. In this paper the model has been applied to data reported in the literature on disuse (BR, bed rest), de-conditioning (SF, space flight), strength training (ST) and de-training (DT). The results of these calculations have confirmed previous observations on the determinants of the adaptation process and further suggest: (1) that training for one specific motor task (e.g. ST) could affect the performance of a second task (e.g. a maximal explosive jump) but that, as soon as the trained motor task is terminated (DT), this ability is re-gained; and (2) that neuromuscular impairment in disuse (BR) is closer to de-training than to the de-conditioning brought about by weightlessness (SF). Electronic Publication     

Elbow flexion strength curves in untrained men and women and male bodybuilders

Summary The influence of elbow joint angle on voluntary isometric elbow flexion strength was assessed in 15 young women (F), 18 young men (M) and 11 male body-builders (BB). Measurements were made at elbow joint angles of 1.31, 1.57, 1.83, 2.09, 2.36, 2.62 and 2.88 rad (3.14 rad = 180° = full extension). The peak voluntary strength [mean (SE), N.m] in M [69.5 (4.3)] and BB [93.3 (4.8)] occurred at 2.09 rad (120°), but occurred at 1.57 rad (90°) in F [35.4 (2.4)]. Peak torque at 1.31 rad was 20% and 25% lower than at 2.09 rad in M and BB, respectively, but did not differ between these two angles in F. The larger elbow flexor muscle and fibre size in M and BB may have been responsible for their impaired torque production at joint angles corresponding to the shortest muscle lengths.     

Comparison of the isometric cervical extension strength and a cross-sectional area of neck extensor muscles in college wrestlers and judo athletes

Increasing neck muscle strength can play an important role in preventing neck injuries in contact sports. The purpose of this study was to examine the actual conditions of the isometric cervical extension strength (ICES) and the cross-sectional area (CSA) of neck extensor muscles in male athletes participating in college wrestling and judo. The subjects comprised 18 wrestlers and 37 judo athletes from Nippon Sports Science University in Japan. The ICES was measured at eight angles (126°, 108°, 90°, 72°, 54°, 36°, 18°, 0°). Transverse slices of 10 mm thickness were obtained at the position of each intervertebral disc between C2 and C3, C3 and C4, C4 and C5 and C5 and C6 using magnetic resonance imaging. The ICES of the wrestlers were significantly higher than those of the judo athletes. The ICES curve against the angle in wrestlers tended to differ from that of judo athletes. The CSA of neck extensor muscles in the wrestlers was significantly larger at all intervertebral levels examined than those of the judo athletes. A significant difference was observed in the CSA of the deepest area of neck extensor muscles between the groups although the difference was not significant in the superficial area. In this study, the ICES and the CSA in wrestlers were shown to be significantly higher and larger respectively than in the judo athletes, indicating a significant difference between these two sports. Electronic Publication     

Reproducibility of isokinetic leg strength and endurance characteristics of adult men and women

Summary Day-to-day variability and single-measurement reliability of selected isokinetic knee extension-flexion strength and endurance indices were assessed in 10 adult men and 8 adult women. On three occasions separated by at least 5 days, the subjects completed 4 reciprocal maximal voluntary contractions (MVC) at different angular velocities (1.05 rad · s^–1 and 3.14 rad · s^–1). The men also completed a muscular endurance test consisting of 30 reciprocal, MVC at 3.14 rad ·^–1. Coefficient of variation, intra-class correlation coefficient and standard error of single-measurement scores support the continued use of gravity corrected peak torque (PT) and average peak torque (APT) as indices of isokinetic leg strength. Similarly, gravity corrected APT and total work should be the recommended indices of isokinetic leg muscular endurance in men. The results suggest that these isokinetic indices must be assessed using multiple day-to-day trial protocols adequately to describe performance capacity. Composite indices such as the ratio of Knee flexion to extension PT and fatigue measurements offer considerably reduced reliability and a greater potential for misinterpretation. The reliability of knee extension indices generally exceeds that of flexion indices. Similar variability and reproducibility of responses were observed between men and women and between reciprocal contractions performed at angular velocities of 1.05 rad · s^–1 and 3.14 rad · s^–1.     

Muscle strength and functional capacity in 78–81-year-old men and women

Summary Muscle strength was measured in 23 men and 29 women regarded as representative of the healthy urban population of about 80 years of age. Isometric and isokinetic strengths of right knee-extension, plantar, and dorsal flexion, and the isometric strength of some upper extremity functions were measured. For knee-extension there was a decrease in strength of about 30% from the values in a population study of 70-year-old subjects (Aniansson et al. 1980). Muscle strength was significantly lower in women than in men in all muscle groups except for plantar and dorsal flexion of the foot. Body cell mass was reduced compared to younger age groups by about the same extent as muscle strength, and correlated to knee-extension and hand grip strengths.Functional examinations such as step tests and walking tests were performed. A correlation between the results of these tests and muscle strength was not found except for knee-extension at 60 degrees/s in men. The rather low speed in comfortable walking (men 1.0 m·s^–1, women 0.9 m·s^–1) and the reduced capacity for step climbing diminish the possibility of using public transport and pedestrian street intersections in relatively healthy old people.     

A comparison of strength and muscle endurance in strength-trained and untrained women

Summary Muscular strength and fatigability of strength-trained (ST) and untrained (UT) women were compared during a 6-min bout of maximal rhythmic exercise involving the elbow flexor muscles given at a rate of 30 contractions · min^–1. Fifteen ST and 15 UT subjects, aged 18–34 years and pair-matched for body size, were tested for differences in initial strength, final strength, absolute endurance, relative endurance, and rate of fatigue. Results revealed a significant difference in initial strength, final strength, and absolute endurance in favor of ST subjects. No significant difference was found for relative endurance, and rates of fatigue were similar for both groups. It is concluded that muscular strength and endurance are enhanced in women engaged in a training program designed primarily to increase muscular strength and hypertrophy, but fatigability is not affected.     

Plasma FFA responses to prolonged walking in untrained men and women

Summary Gender differences in plasma FFA responses to 90 min of treadmill walking at 35% were investigated in six men and six women following an overnight fast. The subjects represented average values for maximal oxygen uptake and body fat percentage for age and gender. Mean plasma FFA concentration at 45 and 90 min of exercise were significantly (P<0.05) higher for women (0.82 mmol·l^–01, 0.88 mmol·l^–01) than men (0.42 mmol·l^–01, 0.59 mmol·l^–1). Lower R values for women throughout the exercise period indicated a greater percentage fat in total metabolism than for men while the FFA/glycerol results supported greater lipolytic activity for women. The uniformity of percent fat in metabolism for women from rest to exercise showed that FFA release from adipose tissue increased rapidly with the onset of exercise which was not the case for men. Comparison of metabolic data as well as a statistical analysis (ANCOVA) controlling for the influence of and percentage body fat on FFA plasma concentration suggested that gender differences in FFA responses to prolonged submaximal exercise can be expected to occur in untrained subjects.     

Force generation capacity of knee extensor muscles in speed skaters

The force generation capacities during a single as well as repetitive maximal knee extensions were investigated in speed skaters in relation to the cross-sectional area (CSA) of quadriceps femoris muscles. The subjects were 15 male and 12 female speed skaters, and an age-matched untrained group (20 men and 21 women). An isokinetic dynamometer was used to determine force output at three constant velocities of 1.05, 3.14 and 5.24 rad · s^–1 and to perform 50 repetitive maximal contractions at 3.14 rad · s^–1. The CSA was measured by using a B-mode ultrasound technique at the midpoint of the thigh length. The isokinetic force produced at each test velocity was significantly correlated to CSA in all the subjects (r = 0.867–0.920, P < 0.05). There was no significant difference in force (F) per unit CSA (F · CSA^–1) at the three test velocities between the speed skaters and untrained subjects within the same sex. In both the speed skaters and untrained subjects, the women showed significantly lower F · CSA^–1 at 3.14 and 5.24 rad · s^–1 than the men. The means of force output ( ) of every five consecutive and all trials during the repetitive maximal bout were significantly correlated to CSA in all the subjects (r = 0.889–0.934, P < 0.05). Compared to the untrained subjects, the speed skaters showed significantly higher ( ) for every five consecutive contractions even when calculated per unit of CSA ( · CSA^–1), and had lower percentage of decline of F during a trial span between the 6th–10th and 41th–45th trials. For the untrained subjects, · CSA^–1 for every five consecutive contractions was significantly lower in the women than in the men. For the speed skaters, the men showed significantly higher · CSA^–1 than the women during a trial span from the 1st–5th trial to the 31th–35th trial, although there was no significant sex difference in the ratio on and after the 36th–40th trial. From these results, it is concluded that the speed skaters show a higher muscle performance in a repetitive maximal contraction task rather than in a single contraction compared to the untrained subjects. In addition, judging from the results for the speed skaters, the women might be less trainable than the men in the · CSA^–1 during a single contraction at a fast velocity as well as repetitive maximal contractions.     

Relationships between muscle strength and muscle cross-sectional area in male sprinters and endurance runners

Summary The relationship between the cross-sectional area (CSA) and maximum voluntary isometric strength of the knee extensor muscles was measured in a group of untrained subjects (control group, n=30), a group of successful marathon runners (n=6) and a group of successful sprinters (n=6). All subjects were male, aged between 20 and 41 years. In the control group muscle strength was found to be positively correlated with lean body mass (p<0.01) and with muscle CSA as determined by computed tomography scanning of the leg at mid-thigh level (p<0.001). However, in spite of these significant relationships, there was considerable variability between subjects. The sprinters were significantly stronger than the endurance runners (p<0.01), but neither of the athletic groups differed significantly from the control group. Muscle CSA was greater in the sprinters than in the marathon runners but this difference was not significant. The ratio of muscle strength to CSA in the control group varied from 7.07 to 13.57. All the trained subjects fell within this normal range, but the sprinters' muscles were stronger per unit CSA than the muscles of the marathon runners (p<0.05). Since it is well established that the leg muscles of sprinters contain a high proportion of fast twitch (FT) muscle fibres whereas endurance runners have a high proportion of slow twitch (ST) fibres, these results suggest that the strength which can be produced by a muscle may depend on its fibre composition. Variation in the distribution of the different fibre types in the untrained population may therefore account at least in part for the wide variability observed in this group.Supported by a grant from Lipha Pharmaceuticals Ltd     

Physiological and biomechanical analysis of treadmill walking up various gradients in men and women

This investigation was undertaken to examine the physiological and biomechanical responses during treadmill walking up various gradients in men and women. Groups of 11 men and 11 women took part in four experiments consisting of 8 min treadmill walks at 1.3 m·s^–1 up gradients of 0%, 5%, 10% and 15%. The subjects also underwent an anthropometric assessment during which their height, body mass (BM), percentage (%) body fat, lean body mass (LBM), and waist-to-hip ratio (WHR) were obtained. During exercise, each subject was videotaped during three walking cycles so that sagittal kinematics including stride length (SL) and frequency (SF) and ranges of motion achieved at the shoulder, hip and knee during a walking cycle could be determined using a motion analysis system. The motion capture was followed by a measurement of steady-state oxygen uptake (VO₂) and heart rate (HR) using indirect calorimetry and a HR monitor. Compared to men, women were higher in % body fat, but lower in height, BM, LBM, and WHR. The VO₂ in millilitres per kilogram per minute and HR were similar between men and women at 0% and 5%, but greater in women than men at 10% and 15%. The SL and SF were greater and smaller, respectively, in men than women up all gradients. Shoulder extension was greater up gradients of 10% and 15% in women than men, whereas no sex difference in shoulder flexion was noted. Hip extension and flexion as well as knee flexion remained the same between men and women up all gradients. An inverse relationship was observed between VO₂ in millilitres per kilogram per minute and BM, LBM, and WHR when men and women were combined. In conclusion, the mass-specific metabolic cost of treadmill walking up high gradients is greater in women than men. Such an increase in relative metabolic cost may be attributable to the fact that women are smaller in size, and/or have relatively more BM distributed peripherally. This sex difference may also be due to a greater movement of the upper limbs in women during walking uphill, although direct evidence is needed to support this contention. Electronic Publication     

Relationship between in vivo muscle force at different speeds of isokinetic movements and myosin isoform expression in men and women

In an attempt to explore the relationship between force production during voluntary contractions at different speeds of isokinetic movement and the myofibrillar protein isoform expression in humans, an improved isokinetic dynamometer that corrects for gravitation, controls for acceleration and deceleration, and identifies a maximum voluntary activation was used. Muscle torque recordings were compared at the same muscle length (knee angle) and the torque was calculated as the average torque at each angle over a large knee angle range (75°–25°) to reduce the influence of small torque oscillation on the calculated torque. Muscle torque at fast (240° s⁻¹) versus slow (30° s⁻¹) speeds of movement, torque normalized to muscle cross-sectional area (specific tension), and absolute torque at fast speeds of movement were measured in 34 young healthy male and female short-, middle-, and long-distance runners. The relationship between the different measures of muscle function and the expression of myosin heavy chain (MyHC) isoforms using enzyme–histochemical and electrophoretic protein separation techniques were investigated. A significant correlation between the 240° s⁻¹ vs 30° s⁻¹ torque ratio and the relative area of the type II fibers and type II MyHC isoforms were observed in both the men (r=0.74;P<0.001) and the women (r=0.81; P<0.05). Thus, the present results confirm a significant relationship between in vivo human muscle function and the MyHC isoform expression in the contracting muscle. Electronic Publication     

Development and testing of a cross-sectional area measurement tool for evaluating vein size

This paper describes a software system for measuring cross-sectional area in reconstructed elliptical tubular structures. A measurement tool was developed using the freely available, cross-platform, open-source three-dimensional (3-D) Slicer environment. The software is easy to operate and allows the user to make multiple measurements on the fly. Results can be displayed to the screen, output to the system printer, and written to a user-specified data file for later analysis in commercial spreadsheet software. Measuring a known cross-sectional area tested the software. Phantoms of known physical dimensions were imaged using both CT and MR. The measured cross-sectional areas reported by the software were compared to each other, and the cross-sectional areas calculated from the known physical dimensions of the phantoms. The measurement errors were negligible. The results of this study indicate that the cross-sectional area measurement tool described provides reliable measurements and is an inexpensive and versatile alternative to high-end 3-D modeling software.     

Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women

Twelve middle-aged men and 12 middle-aged women in the 50-year-old age group (M50; range 44–57 years; W50; 43–57), and 12 elderly men and 12 elderly women in the 70-year-old age group (M70; 59–75; W70; 62–75) volunteered as subjects in order to examine effects of 12-week progressive heavy resistance strength training on electromyographic activity (EMG), muscle cross-sectional area (CSA) of the quadriceps femoris and maximal concentric force in a one repetition maximum (1 RM) test of the knee extensor muscles. One half of the subjects in each group performed the knee extension (and flexion) exercises only bilaterally (BIL), while another half performed the exercises only unilaterally (UNIL). None of the subject groups demonstrated statistically significant changes in any of the 1 RM values during the 2 week control period with no training (between week -2 and 0) preceding the actual experimental training. However, the 12-week training resulted in increases (P<0.05–0.001) in 1 RM values in each group so that the average relative increase of 19±12% (P<0.001) in bilateral 1 RM in all BIL trained subjects was greater (P<0.05) than that of 13±8% (P<0.001) recorded for all UNIL trained subjects. The average relative increases of 17±11% (P<0.001) and 14±14% (P<0.001) in unilateral 1 RM values of the right and left leg in all UNIL trained subjects were greater (P<0.05) than those of 10±18% (P<0.001) and 11±11% (P<0.001) recorded for all BIL trained subjects, respectively. The relative average increase of 19±19% (P<0.001) observed in the maximum averaged IEMG of both legs during the bilateral actions in all BIL trained subjects was greater (P<0.05) than that of 10±17% (P<0.05) recorded for all UNIL trained subjects. The relative increases of 14±12% (P<0.001) and 11±6% (P<0.001) recorded for the CSA in all BIL and UNIL trained subjects did not differ significantly from each others. The present findings suggest that progressive heavy resistance strength training leads to great increases in maximal dynamic strength of the trained subjects accompanied by both considerable neural adaptations and muscular hypertrophy not only in middle-aged but also in elderly men and women. Both bilateral and unilateral exercises are effective to produce functional and structural adaptations in the neuromuscular system, although the magnitude of functional strength increase seems to be specific to the type of exercise used, further supporting the principle of specificity in the design of strength programmes.     

Muscle cross-sectional area,force production and relaxation characteristics in women at different ages

Summary Thirty women, divided among three different age groups, i.e. 30 years (range 26–35;n = 10), 50 years (range 46–55;n = 10) and 70 years (range 66–75;n = 10) volunteered as subjects for examination of the characteristics of the muscle cross-sectional area (CSA), maximal voluntary isometric force, isometric force-time and relaxation-time of their leg extensor muscles. The CSA of the quadriceps femoris muscle in the youngest age group was slightly larger (NS) than in the middle-aged group and much larger (P<0.41) than in the oldest age group whose CSA was markedly smaller (P<0.01) than the middle-aged group. Maximal force in the youngest group was slightly greater (NS) than in the middle-aged group and much greater (P<0.01) than in the oldest group whose values were markedly smaller (P<0.05) than the middle-aged group. The individual values in CSA correlated with maximal force both in the total subject sample (r=0.82;P<0.001) and in the three age groups separately (r=0.72;P<0.01;r=0.86;P<0.01 andr=0.67;P<0.05, respectively). When the force values were related to the CSA of the muscle, the mean values of 45.4N·cm^–2, SD 5.6, 47.6 N·cm^–2, SD 5.0 and 46.8 N· cm^–2, SD 7.0 for the three groups did not differ significantly from each other. The isometric force-time curves differed among the groups, so that the times to produce the same absolute as well as relative force levels were shorter in the 30-year age group (P<0.05) than in the 70-year age group. The times of relaxation did not differ significantly among the groups. The present results suggested that the decline in maximal force in females with age could well be related to the decline in the cross-sectional area of the muscle. However, the time taken in the production of explosive force may worsen even more than maximal strength especially at older ages. This indicated that atrophying effects of aging may be greater on fast than on slow twitch muscle fibres and/or that the rate of neural activation of the muscles could also be influenced by aging.     

Energy cost of running in similarly trained men and women

Summary The energy demand of running on a treadmill was studied in different groups of trained athletes of both sexes. We have not found any significant differences in the net energy cost (C) during running (expressed in J·kg⁻¹·m⁻¹) between similarly trained groups of men and women. For men and women respectively in adult middle distance runnersC=3.57±0.15 and 3.65±0.20, in adult long-distance runnersC=3.63±0.18 and 3.70±0.21, in adult canoeistsC=3.82±0.34 and 3.80±0.24, in young middle-distance runnersC=3.84±0.18 and 3.78±0.26 and in young long-distance runnersC=3.85±0.12 and 3.80±0.24. This similarity may be explained by the similar training states of both sexes, resulting from the intense training which did not differ in its relative intensity and frequency between the groups of men and women. A negative relationship was found between the energy cost of running and maximal oxygen uptake expressed relative to body weight (for menr=−0.471,p<0.001; for womenr=−0.589,p<0.001). In contrast, no significant relationship was found in either sex between the energy cost of running and . We conclude therefore that differences in sports performance between similarly trained men and women are related to differences in . The evaluation ofC as an additional characteristic during laboratory tests may help us to ascertain, along with other parameters, not only the effectiveness of the training procedure, but also to evaluate the technique performed.     

Computer-assisted determination of muscle fiber cross-sectional areas

A computer-assisted technique for the calculation of individual muscle fiber cross-sectional areas is described. This system employs the use of an electronic digitizer to describe the boundary of the selected area. Green's theorem in the plane (Kreysizig, Advanced Engineering Mathematics, Wiley, New York), A=1/2 ∫(xdy-ydx), was selected to mathematically determine the area of a plane region as a line integral over the boundary. This procedure may be easily modified to allow for the area measurement of any single plane figure. This technique may improve the accuracy as well as shorten the time involved when compared to some other applications of conventional methods of planimetry.     

Shoulder muscle strength in paraplegics before and after kayak ergometer training

The purpose was to investigate if shoulder muscle strength in post-rehabilitated persons with spinal cord injury (SCI) was affected by kayak ergometer training and to compare shoulder strength in persons with SCI and able-bodied persons. Ten persons with SCI (7 males and 3 females, injury levels T3–T12) performed 60 min kayak ergometer training three times a week for 10 weeks with progressively increased intensity. Maximal voluntary concentric contractions were performed during six shoulder movements: flexion and extension (range of motion 65°), abduction and adduction (65°), and external and internal rotation (60°), with an angular velocity of 30° s⁻¹. Position specific strength was assessed at three shoulder angles (at the beginning, middle and end of the range of motion) in the respective movements. Test–retests were performed for all measurements before the training and the mean intraclass correlation coefficient was 0.941 (95% CI 0.928–0.954). There was a main effect of kayak ergometer training with increased shoulder muscle strength after training in persons with SCI. The improvements were independent of shoulder movement, and occurred in the beginning and middle positions. A tendency towards lower shoulder muscle strength was observed in the SCI group compared to a matched reference group of able-bodied persons. Thus, it appears that post-rehabilitated persons with SCI have not managed to fully regain/maintain their shoulder muscle strength on a similar level as that of able-bodied persons, and are able to improve their shoulder muscle strength after a period of kayak ergometer training.     

Differences in quadriceps muscle strength and fatigue between lean and obese subjects

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/m2) and ten lean (mean age: 27 years; mean BMI: 23 kg/m2) men were tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions at 180°/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.