Muscle power, locomotor performance and flexibility in aging mentally-retarded adults with and without Down's syndrome

Longer life expectancy is resulting in increasing numbers of elderly adults with mental retardation (MR). The objective of the study was to compare lower limb isokinetic muscle power, locomotor performance and flexibility of aged adult mentally-retarded individuals with and without Down's syndrome (DS). Nine subjects with MR and DS (mean age 61), and sixteen subjects with MR and without DS (mean age 63), performed leg power testing on a Biodex dynamometer. Parameters measured were dynamic torque, dynamic torque % body weight, and average power % body weight. Functional performance tests including "Timed Get-Up and Go" and flexibility were also analyzed and compared. Results indicate that in knee extension and flexion isokinetic power the MR group without DS showed significantly higher scores than the MR group with DS. The functional performance of elderly adults with MR and DS was significantly impaired compared with MR adults without DS, although no differences were observed between the two groups in the flexibility tests. It was concluded that muscle leg power, and gross motor performance of elderly mentally-retarded individuals without Down's syndrome is better than in those with Down's syndrome.     

Effect of training on the muscle strength and dynamic balance ability of adults with down syndrome

The purpose of this study was to evaluate the effect of training on the muscle strength and dynamic balance ability of adults with Down syndrome (DS). Twenty-five adults with DS were separated into 2 groups. Fifteen subjects (mean age, 24.5 years) constituted the experiment group, whereas 10 subjects (mean age, 24.7 years) were in the control group of the study. Parameters measured were peak torque, isokinetic muscle endurance, and dynamic balance ability. All subjects performed a leg strength test on a Cyber II isokinetic dynamometer. In addition, the subjects' dynamic balance ability was measured by means of a balance deck (Lafayette). The experimental group followed a 12-week training program. As the results indicated, the experimental group showed a statistically significant improvement in all measured values when compared with the control group. It is concluded that adults with DS can improve their physical and kinetic abilities with the application of a systematic and well-designed training program.     

CNTF genotype is associated with muscular strength and quality in humans across the adult age span.

The relationship between ciliary neurotrophic factor (CNTF) genotype and muscle strength was examined in 494 healthy men and women across the entire adult age span (20-90 yr). Concentric (Con) and eccentric (Ecc) peak torque were assessed using a Kin-Com isokinetic dynamometer for the knee extensors (KE) and knee flexors (KF) at slow (0.52 rad/s) and faster (3.14 rad/s) velocities. The results were covaried for age, gender, and body mass or fat-free mass (FFM). Individuals heterozygous for the CNTF null (A allele) mutation (G/A) exhibited significantly higher Con peak torque of the KE and KF at 3.14 rad/s than G/G homozygotes when age, gender, and body mass were covaried (P < 0.05). When the dominant leg FFM (estimated muscle mass) was used in place of body mass as a covariate, Con peak torque of the KE at 3.14 rad/s was also significantly greater in the G/A individuals (P < 0.05). In addition, muscle quality of the KE (peak torque at 3.14 rad x s(-1) x leg muscle mass(-1)) was significantly greater in the G/A heterozygotes (P < 0.05). Similar results were seen in a subanalysis of subjects 60 yr and older, as well as in Caucasian subjects. In contrast, A/A homozygotes demonstrated significantly lower Ecc peak torque at 0.52 rad/s for both KE and KF compared with G/G and G/A groups (P < 0.05). No significant relationships were observed at 0.52 rad/s between genotype and Con peak torque. These data indicate that individuals exhibiting the G/A genotype possess significantly greater muscular strength and muscle quality at relatively fast contraction speeds than do G/G individuals. Because of high positive correlations between fast-velocity peak torque and muscular power, these findings suggest that further investigations should address the relationship between CNTF genotype and muscular power.     

Effects of combination oral contraceptives on strength development in women athletes

This study was designed to investigate the effects of combination oral contraceptive agents (OCAs) on strength and torque production in collegiate women softball and water polo athletes who participated in a 12-week strength development program. A double-blind research design was used to mask subjects to the main outcome of interest. Thirty-one women collegiate softball and water polo players were divided into experimental (OCA users, n = 13), and control (non-OCA users, n = 18) groups. All subjects participated in the same supervised 12-week preseason strength development program. One-repetition maximum bench press (1RMBP), 10-repetition maximum leg extension (10RMLE), isokinetic peak torque bench press (IKBP), and isokinetic peak torque leg extension (IKLE) data were collected at weeks 0 (pre-test), 4, 8, and 12 (post-test). Significant increases in strength and torque production over time were identified regardless of group for 1RMBP, 10RMLE, and IKLE. No significant differences in IKBP torque production occurred during the 12-week strength training program. No significant differences in 1RMBP, 10RMLE, IKBP, or IKLE occurred between the OCA users and the non-OCA users groups. It was concluded that, within the limitations of the study, the use of combination OCAs did not provide sufficient androgenic effect to increase strength gains beyond the stimulus of the training protocol.     

Hypertrophic response to unilateral concentric isokinetic resistance training.

The purposes of this study were to 1) determine the effect of concentric isokinetic training on strength and cross-sectional area (CSA) of selected extensor and flexor muscles of the forearm and leg, 2) examine the potential for preferential hypertrophy of individual muscles within a muscle group, 3) identify the location (proximal, middle, or distal level) of hypertrophy within an individual muscle, and 4) determine the effect of unilateral concentric isokinetic training on strength and hypertrophy of the contralateral limbs. Thirteen untrained male college students [mean age 25.1 +/- 6.1 (SD) yr] volunteered to perform six sets of 10 repetitions of extension and flexion of the nondominant limbs three times per week for 8 wk, using a Cybex II isokinetic dynamometer. Pretraining and posttraining peak torque and muscle CSA measurements for both the dominant and nondominant limbs were determined utilizing a Cybex II isokinetic dynamometer and magnetic resonance imaging scanner, respectively. The results indicated significant (P less than 0.0008) hypertrophy in all trained muscle groups as well as preferential hypertrophy of individual muscles and at specific levels. None of the muscles of the contralateral limbs increased significantly in CSA. In addition, significant (P less than 0.0008) increases in peak torque occurred for trained forearm extension and flexion as well as trained leg flexion. There were no significant increases in peak torque, however, for trained leg extension or for any movement in the contralateral limbs. These data suggest that concentric isokinetic training results in significant strength and hypertrophic responses in the trained limbs.     

The effects of diverting activities on recovery from fatiguing concentric isokinetic muscle actions

The purpose of this study was to examine the effects of diverting activities on recovery from fatiguing concentric isokinetic muscle actions. On 3 separate occasions, 11 men (mean ± SD age = 22.2 ± 1.5 years) and 8 women (mean ± SD age = 22.2 ± 2.1 years) performed 2 bouts of 50 consecutive maximal concentric isokinetic muscle actions of the dominant leg extensors. Between these bouts, the subjects either performed math problems (mental diverting activity), contralateral dynamic constant external resistance (DCER) leg extensions (physical diverting activity), or rested quietly (control). For each trial, the peak torque data from the first and second bouts of 50 muscle actions served as the pretest (Pre) and posttest (Post) data, respectively. The results indicated that when the subjects rested quietly or performed contralateral DCER leg extensions between the fatiguing bouts, the initial peak torque values observed for Post were significantly less than those for Pre. When the subjects performed math problems, however, no decline in the initial peak torque values was observed, thus indicating better recovery. In addition, a decline in the average torque values was observed from Pre to Post for the control trial but not for the math problem or contralateral exercise trials. No differences were observed among the trials for final peak torque, percent decline, or the linear slope of the decline in peak torque. These findings demonstrated that performing either mental or physical diverting activities after fatiguing isokinetic muscle actions enhanced recovery.     

Work capacity during 30 days of bed rest with isotonic and isokinetic exercise training

The purpose was to test the hypothesis that twice daily, short-term, variable intensity isotonic and intermittent high-intensity isokinetic leg exercise would maintain peak O2 uptake (VO2) and muscular strength and endurance, respectively, at or near ambulatory control levels during 30 days of -6 degrees head-down bed rest (BR) deconditioning. Nineteen men (aged 32-42 yr) were divided into no exercise control (peak VO2 once/wk, n = 5), isokinetic (Lido ergometer, n = 7), and isotonic (Quinton ergometer, n = 7) groups. Exercise training was conducted in the supine position for two 30-min periods/day for 5 days/wk. Isotonic training was at 60-90% of peak VO2, and isokinetic training (knee flexion-extension) was at 100 degrees/s. Mean (+/- SE) changes (P less than 0.05) in peak VO2 (ml.m-1.kg-1) from ambulatory control to BR day 28 were 44 +/- 4 to 36 +/- 3, -18.2% (3.27-2.60 l/m) for no exercise, 39 +/- 4 to 40 +/- 3, +2.6% (3.13-3.14 l/min) for isotonic, and 44 +/- 3 to 40 +/- 2, -9.1% (3.24-2.90 l/min) for isokinetic. There were no significant changes in any groups in leg peak torque (right knee flexion or extension), leg mean total work, arm total peak torque, or arm mean total work. Mean energy costs for the isotonic and isokinetic exercise training were 446 kcal/h (18.8 +/- 1.6 ml.min-1.kg-1) and 214 kcal/h (8.9 +/- 0.5 ml.m-1.kg-1), respectively. Thus near-peak, variable intensity, isotonic leg exercise maintains peak VO2 during 30 days of BR, while this peak, intermittent, isokinetic leg exercise protocol does not.     

Muscular strength and power are correlated with motor unit action potential amplitudes,but not myosin heavy chain isoforms in sedentary males and females

It remains unclear if the sizes of higher-threshold motor units (MU) are associated with muscular strength and power. Therefore, the purpose of this study was to examine sex-related differences in muscle cross-sectional area (mCSA), percent myosin heavy chain (%MHC) isoform expression, and the MU action potential amplitudes (MUAP_AMPS)-recruitment threshold (RT) relationships of the vastus lateralis and isometric peak torque, isokinetic peak torque and mean power at 1.05 rad·s⁻¹ of the leg extensors. Surface electromyographic decomposition techniques were used to quantify MUAP_AMPS recorded during isometric muscle actions at 70% of maximal voluntary contractions and regressed against RTs with the slopes calculated. Ultrasound images were used to measure mCSA. Males had greater slopes from the MUAP_AMP-RT relationship than the females (P < 0.05). The greater slopes likely reflected larger higher-threshold MUs for the males. The mCSAs and slopes from the relationships were strongly correlated with isometric and isokinetic peak torque and isokinetic mean power (r = 0.78–0.82), however, type I %MHC isoform was only moderately correlated with isometric peak torque (r = −0.54). The results indicated that sex-related differences in muscular strength and power were associated more so with the sizes of the higher-threshold MUs (slopes) and mCSA than MHC isoforms. The amount of cross-bridge activity within muscle fibers that comprise higher-threshold MUs may be the primary contributor to muscular strength and power rather than the contractile properties of the muscle.     

Relationship between hip and knee strength and knee valgus during a single leg squat

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2=0.13), knee flexion (r2=0.18), and knee extension (r2=0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r=-0.37), knee flexion (r=-0.43), and knee extension (r=-0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.     

Improving the Q:H strength ratio in women using plyometric exercises

Plyometric training programs have been implemented in anterior cruciate ligament injury prevention programs. Plyometric exercises are designed to aid in the improvement of muscle strength and neuromuscular control. Our purpose was to examine the effects of plyometric training on lower leg strength in women. Thirty (age = 20.3 ± 1.9 years) recreationally active women were divided into control and experimental groups. The experimental group performed a plyometric training program for 6 weeks, 3 d·wk(-1). All subjects attended 4 testing sessions: before the start of the training program and after weeks 2, 4, and 6. Concentric quadriceps and hamstring strength (dominant leg) was assessed using an isokinetic dynamometer at speeds of 60 and 120°·s(-1). Peak torque, average peak torque, and average power (AvgPower) were measured. The results revealed a significant (p < 0.05) interaction between time and group for flexion PkTq and AvgPower at 120°·s(-1). Post hoc analysis further revealed that PkTq at 120°·s(-1) was greater in the plyometric group than in the control group at testing session 4 and that AvgPower was greater in the plyometric group than in the control group in testing sessions 2-4. Our results indicate that the plyometric training program increased hamstring strength while maintaining quadriceps strength, thereby improving the Q:H strength ratio.     

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

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.s-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.     

Force-velocity relations and fiber composition in human knee extensor muscles.

Standardized measurements of dynamic strength of the kneee extensor muscles were performed in 25 healthy male subjects (17-37 yr) by means of isokinetic contractions, i.e., knee extensions with constant angular velocities. Overall variation between double determinations of maximal torque throughout the 90 degrees arc of motion (0 degrees = fully extended leg) averaged 10% for the different constant velocities chosen. At any given angle of the knee the torque produced was higher for isometric than for dynamic contractions. Dynamic torque decreased gradually with increased speed of shortening. Peak dynamic torque was reached at knee angles in the range: 55-66 degrees, with a displacement toward smaller knee angles with higher angular velocities. Correlations were demonstrated between peak torque produced at the highest speed of muscle shortening and percent as well as relative area of fast twitch fibers in the contracting muscle. In addition muscles with a high percentage of fast twitch fibers had the highest maximal contraction speeds. These observations on intact human skeletal muscle are consistent with earlier findings in animal skeletal muscle preparations.     

Allometric scaling of isokinetic peak torque: the Nebraska Wrestling Study

Allometric scaling has been used increasingly in the exercise sciences to control statistically for body size differences in physical performance variables. The purpose of this study was to use multivariate allometric scaling to examine the influence of fat-free mass (FFM) on age-related differences in strength in young club (8-13 years) and high-school (14-18 years) wrestlers. The dependent variables were log-transformed values of isokinetic peak torque for leg extension and flexion at 0.52, 3.14, and 5.24 rad x s(-1)(30, 180, and 300 x s(-1)). The independent variables used in the multiple regression analyses were log-transformed values for FFM, age, and the FFM versus age interaction. The resulting regression equations were of the form: log Y = log a + b1 log X1 + b2 log X2 + bn log Xn. The initial multiple regression analyses showed significant interaction effects (P < 0.05) for all dependent variables, therefore separate regression analyses were performed for the younger and older groups of wrestlers. The results indicate that for the younger wrestlers there were increases in isokinetic peak torque at all velocities across age after controlling for FFM. The FFM scaling exponents ranged from 0.94 to 1.31. All exponents included 1.0 in the 95% confidence interval, except for extension at 3.14 rad x s(-1). For the high-school wrestlers, both FFM and age were significant for the extension data, but only FFM was significant for the flexion data. All FFM exponents included 1.0 in the 95% confidence interval. These results indicate that the relationship between FFM and peak torque differed across age. In addition, with the exception of the flexion data for the high-school wrestlers, within each group increases in isokinetic peak torque occurred across age, independent of increases in FFM. The causes of the age effect for strength are speculative, but it may be due to developmental changes in neuromuscular function, alterations in the distribution of muscle mass as a percentage of FFM and/or the distribution of FFM across body segments.     

Prehabilitation before total knee arthroplasty increases strength and function in older adults with severe osteoarthritis

Preparing for the stress of total knee arthroplasty (TKA) surgery by exercise training (prehabilitation) may improve strength and function before surgery and, if effective, has the potential to contribute to postoperative recovery. Subjects with severe osteoarthritis (OA), pain intractable to medicine and scheduled for TKA were randomized into a usual care (UC) group (n = 36) or usual care and exercise (UC + EX) group (n = 35). The UC group maintained normal daily activities before their TKA. The UC + EX group performed a comprehensive prehabilitation program that included resistance training using bands, flexibility, and step training at least 3 times per week for 4-8 weeks before their TKA in addition to UC. Leg strength (isokinetic peak torque for knee extension and flexion) and ability to perform functional tasks (6-minute walk, 30 second sit-to-stand repetitions, and the time to ascend and descend 2 flights of stairs) were assessed before randomization at baseline (T1) and 1 week before the subject's TKA (T2). Repeated-measures analysis of variance indicated a significant group by time interaction (p < 0.05) for the 30-second sit-to-stand repetitions, time to ascend the first flight of stairs, and peak torque for knee extension in the surgical knee. Prehabilitation increased leg strength and the ability to perform functional tasks for UC + EX when compared to UC before TKA. Short term (4-8 weeks) of prehabilitation was effective for increasing strength and function for individuals with severe OA. The program studied is easily transferred to a home environment, and clinicians working with this population should consider prehabilitation before TKA.     

The effect of a competitive wrestling season on body weight, hydration, and muscular performance in collegiate wrestlers

The purpose of the present investigation was to examine the effects of a collegiate wrestling season on body weight, hydration, and muscular performance. Twelve Division I collegiate wrestlers (mean +/- SE; 20.75 +/- 0.41 year) volunteered to participate in testing sessions during midseason and 3 weeks following the season. Testing consisted of weigh-in, providing a urine sample for hydration analysis, and a measure of isometric leg extension peak torque. Weight significantly increased (p < 0.05) following the completion of the competitive season. No significant change in urine specific gravity (p > 0.05) was observed. Muscular performance was affected by the season as peak torque (PT) and PT-to-body weight ratio increased significantly (p < 0.05). Following the collegiate wrestling season, augmentation in body weight and muscular performance of the wrestlers occurs without alterations in hydration status. Further research is warranted on what type of strength training program would most effectively reduce the decrements in strength associated with weight loss and the strain of a competitive season.     

The duration of the inhibitory effects with static stretching on quadriceps peak torque production

Although several studies have investigated the acute effect of static stretching exercises, the duration of exercises that negatively affects performance has not been ascertained. This study was conducted to determine the acute effect of different static stretching durations on quadriceps isometric and isokinetic peak torque production. The 50 participants were randomly allocated into five equivalent sized groups and were asked to perform a stretching exercise of different duration (no stretch, 10-second stretch, 20-second stretch, 30-second stretch, and 60-second stretch). The knee flexion range of motion and the isometric and concentric isokinetic peak torques of the quadriceps were measured before and after a static stretching exercise in the four experimental groups. The same parameters were examined in the control group (no stretch) without stretching, before and after a 5-minute passive rest. There were no significant differences among groups before the experimentation regarding their physical characteristics and performances (P > 0.05). These results reflect the different groups' homogeneity. Significant knee joint flexibility increases (P < 0.001) and significant isometric and isokinetic peak torque reductions (P < 0.05-0.001) have been shown to occur only after 30 and 60 seconds of quadriceps static stretching. Stretching reduced isometric peak torque by 8.5% and 16.0%, respectively. Concerning isokinetic peak torque after 30 and 60 seconds of stretching, it was reduced by 5.5% vs. 11.6% at 60 degrees/s and by 5.8% vs. 10.0% at 180 degrees/s. We suggest that torque decrements are related to changes of muscle neuromechanical properties. It is recommended that static stretching exercises of a muscle group for more than 30 seconds of duration be avoided before performances requiring maximal strength.     

Effects of high volume upper extremity plyometric training on throwing velocity and functional strength ratios of the shoulder rotators in collegiate baseball players

To achieve maximal force output, clinicians and coaches have been experimenting with upper extremity plyometric exercises for years, without sufficient scientific validation of this training method. The goal of this study was to examine the effects of an 8-week course of high volume upper extremity plyometric training on the isokinetic strength and throwing velocity of a group of intercollegiate baseball players. Twenty-four Division I collegiate baseball players (age: 19.7 +/- 1.3 years; height: 183.9 +/- 5.9 cm; mass: 90.7 +/- 10.5 kg) were recruited to participate in this study. Throwing velocity, isokinetic peak torque, isokinetic functional strength ratios, and time to peak torque were measured pre- and posttraining. Subjects were rank-ordered according to concentric internal rotation (IR) strength and were assigned randomly to either the plyometric training group (PLY) or the control group (CON). Training consisted of 6 upper extremity plyometric exercises ("Ballistic Six") performed twice per week for 8 weeks. Subjects assigned to CON performed regular off-season strength and conditioning activities, but did not perform plyometric activities. PLY demonstrated significant increases (p < 0.05) in throwing velocity following 8 weeks of training when compared with CON (83.15 mph [pre] vs. 85.15 mph [post]). There were no statistically significant differences in any of the isokinetic strength measurements between PLY and CON groups pre- to posttraining. Statistically significant differences were seen within PLY for concentric IR and eccentric external rotation (ER) isokinetic strength at 180 degrees x s(-1) and 300 degrees x s(-1); and within CON for eccentric ER isokinetic strength at 300 degrees x s(-1) and concentric IR isokinetic strength at 180 degrees x s(-1). The Ballistic Six training protocol can be a beneficial supplement to a baseball athlete's off-season conditioning by improving functional performance and strengthening the rotator cuff musculature.     

Effects of unilateral isometric strength training on joint angle specificity and cross-training

The purpose of this study was to examine the effects of unilateral isometric leg extension strength training on the strength and integrated electromyogram (IEMG) of both the trained and untrained limbs at multiple joint angles. A training (TRN) group [nine women; mean (SD) age, 20(1) years] exercised for 6 weeks with isometric leg extensions at 80% of maximal isometric torque. A control (CTL) group [eight women; 21(1) years] did not exercise. The training was performed three times per week on a Cybex II isokinetic dynamometer at a joint angle where the lever arm was 0.79 rad below the horizontal plane. The subjects were tested pre- and posttraining for maximal unilateral isometric torque in both limbs at joint angles of zero, 0.26, 0.79,1.31, and 1.57 rad below the horizontal plane. Bipolar surface electrodes were used to record the IEMG of the vastus lateralis (VL) and vastus medialis (VM) during the isometric tests. Three univariate (torque, IEMG-VL, and IEMG-VM) four-way (group x time x limb x angle) mixed factorial ANOVAs were used to analyze the data. The results indicated joint angle specificity for isometric torque in the TRN group only, with significant increases in torque at 0.79 (P = 0.0004) and 1.31 (P = 0.0039) rad. No significant increases in torque were found in the untrained limb of the TRN group or in either limb of the CTL group. Similarly, there were no significant changes in IEMG as a result of the training for the VL or VM. The joint-angle-specific strength increases without concomitant increases in IEMG were hypothesized to result from joint-angle-specific decreases in antagonistic co-contraction and/or preferential hypertropy of the quadriceps femoris at specific levels of the muscle group.     

Voluntary and electrically evoked strength characteristics of obese and nonobese preadolescent boys

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.     

Isometric and isokinetic muscle strength, anthropometry and physical activity in 8 and 13 year old Swedish children

Isometric muscle strength of the hand-grip and of trunk flexion and extension, and isokinetic torque of elbow and knee flexion and knee extension were assessed in a random sample of 8 and 13 year old Swedish children. The results were compared with respect to sex and age in absolute terms and relative to weight, height2 and estimates of lean body mass and cross-sectional muscle area. Daily physical activity was also estimated. The muscle strength variables were in general found to be very similar in the 8 year old boys and girls. In the 13 year old group the boys were generally stronger than the girls, in both absolute and relative terms, except for similar torque values during knee extension. The absolute and relative muscle strength and torque values were higher in the older than in the younger children, with the exception of trunk strength per unit of body weight and of lean body mass, which were similar in boys of both ages and significantly lower in the older than in the younger girls. No significant correlation was found between the estimates of physical activity and isometric and isokinetic muscle strength and torque.