Total Work Output Research Articles

Muscle fatigue and efficiency in relation to interval duration of successive contractions

The work output, energy consumption and efficiency during repetitive dynamic contractions were calculated for rat extensor digitorum longus muscle. The muscles performed 40 successive dynamic contractions at 37 degrees C (with occluded bloodflow) with interval durations of either 500, 250 or 167 ms. The muscle-tendon complexes were allowed to shorten at the velocity at which they could exert their highest power output (50 mm.s-1). Work output in the first contraction was the same among the three groups with different interval durations. The reduction in work output during the series of contractions differed among the groups, mainly in the last part of the exercise period. In the group with the longest interval duration, work output steadily decreased over the whole contraction period and at the end was approximately 72% of the output in the first contraction. In contrast, after the 30th contraction, work output decreased at a significantly higher rate of approximately 3% of each contraction in the groups with the intermediate and the shortest interval duration. After the last contraction, work output in these groups was approximately 52% of the work output in the first contraction. These differences in fatigue coincided with differences in the reduction in adenosine 5'-triphosphate and the production of inosine-5'-monophosphate. Total work output was not significantly different among the three groups with different interval durations, indicating that the different reductions in work output in the last contractions only had a minor influence on total work output of all 40 contractions. Also high-energy phosphate consumption and efficiency were not significantly different over these three exercise periods. Thus with the protocol used no interval dependent pattern of efficiency could be detected.

Aerobic and Anaerobic Energy Contribution during Maximal Work Output in 90 s Determined with Various Ergocycle Workloads

The aim of this experiment was to evaluate the effect of different workloads on the relative contribution of the various energy delivery systems during a 90-s ergocycle test. Nine male subjects, 22 +/- 1 (mean +/- SD) years of age and weighing 71.4 +/- 6.8 kg, were submitted to a VO2max test, as 10-s test (0.1 kp/kg) and three 90-s tests at different loads (LO: 0.05, ME: 0.075 and HI: 0.1 kp/kg) on an ergocycle. No difference was found between peak power output during the 10-s and HI tests. No differences were observed in the total work output performed during 90 s at different workloads (between 481 and 495 J/kg) as well as in the contribution of aerobic and anaerobic pathways to total energy production. However, VO2max was reached earlier during the ME and HI tests than during the LO test. These results indicate that variation in workload did not influence the total work output and the total contribution of aerobic and anaerobic systems during maximal 90-s ergocycle performances. However, variation in workload had an impact on the relative aerobic and anaerobic contribution at various time points. It is concluded that a 90-s ergocycle test with a resistance of at least 0.1 kp/kg is required to appropriately assess maximal anaerobic power while anaerobic capacity might be measured with workloads as low as 0.05 kp/kg.

Effect of shortening velocity on work output and energy cost during repeated contractions of the rat EDL muscle

The effect of shortening velocity on the reduction in work output, energy consumption and efficiency during repetitive contractions has been determined in rat extensor digitorum longus muscle. Muscles in situ (with occluded blood flow, 37 degrees C) were stimulated to perform 40 successive contractions (at 4 Hz) with a total duration of the exercise period of 10 s and shortening velocities of either 25, 50 or 75 mm.s-1 (whole muscle-tendon complex). Care was taken that work output during the shortening phase of the first contraction was the same for the different velocities used. Total work output of the 40 contractions was not significantly different between the three groups with different shortening velocities; nor was there a significant difference in the high-energy phosphate consumption over this 10-s exercise period. However, when the ratio of total work output and total energy consumption was calculated a significantly higher efficiency (25-30% in comparison with the efficiency of the other two velocities) was found with the shortening velocity of 50 mm.s-1. There was no significant difference in efficiency between shortening velocities of 25 and 75 mm.s-1. This suggests that with this protocol efficiency showed a velocity-dependent pattern that may have the same shape as the power/velocity curve. Whereas total work output during the 10-s exercise period was not significantly different between the velocities studied, the time course of the changes in work output was quite different. With shortening velocities of 50 and 75 mm.s-1 work output initially increased by maximally 6% and 12% respectively in contrast to a steady level in the contractions with a velocity of 25 mm.s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobic performances in Black and White subjects

The anaerobic performance characteristics of 15 Black males of African ancestry (25 +/- 2 yr; mean +/- SD) and 17 White males of French Canadian ancestry (22 +/- 2 yr) were compared. All subjects were sedentary. Morphological characteristics and body composition were similar in both groups. They were tested for maximal force during voluntary isometric contraction of the knee extensors and for total work output during 10 s, 30 s, and 90 s of maximal and repetitive knee extensions. Results indicated no significant differences between Blacks and Whites in maximal force of the knee extensors (736 +/- 78 N vs 722 +/- 11 N, respectively) and in total work output during the 10-s (1134 +/- 246 J vs 1124 +/- 207 J) and 30-s (2735 +/- 519 J vs 2779 +/- 647 J) tests. There was a difference of about 400 J between Blacks and Whites in the total work output during the 90-s test, but this difference was not statistically significant. However, significant differences were found between Blacks and Whites in the peak power output decrement during the last 60 s of the 90-s anaerobic test. These differences in peak power output between the two groups ranged between 7 and 10 W during the last 30 s of the 90-s test. The results indicate that knee extensor muscles of sedentary Black and White males have similar anaerobic performance power and capacities. However, the results reveal that sedentary Black subjects experience a greater degree of fatigue than sedentary Whites during an anaerobic exercise lasting longer than 30 s.

31P NMR spectroscopy of hypertrophied rat heart: Effect of graded global ischemia

To investigate the cause for the greater susceptibility of hypertrophied hearts to ischemic injury, we determined the interrelations of total work output, contractile function and energy metabolism in isolated, perfused normal and hypertrophied rat hearts subjected to graded global ischemia. Cardiac hypertrophy was induced by giving rats seven daily injections of either triiodothyronine (0.2 mg/kg) or isoproterenol (5 mg/kg). All hearts were perfused at an aortic pressure of 100 mmHg in the isovolumic mode in an NMR spectrometer (7.05 Tesla). Heart rate, developed pressure, and coronary flow were monitored simultaneously with changes in pH, creatine phosphate, ATP and inorganic phosphate. During pre-ischemic perfusion, the total work output (rate-pressure product) of hyperthyroid hearts was 28% higher than that of control hearts, whereas hearts from isoproterenol-treated animals showed no difference. However, when related to unit muscle mass, work was normal in hyperthyroid hearts and 26% lower after isoproterenol. Contractile function per unit myocardium (developed pressure/g wet weight) was lower in the hypertrophied hearts. ATP content was the same in all groups. Creatine phosphate decreased 41% after triiodothyronine and 25% after isoproterenol. Inorganic phosphate levels and intracellular pH were similar in control and isoproterenol-treated rat hearts, but were higher in the hyperthyroid rat hearts. The phosphorylation potential and the free energy change of ATP hydrolysis were lowered by hypertrophy, the levels correlating with the depressed contractile function. At each ischemic flow rate, both work and contractile function per unit myocardium were the same for all hearts, but the relations between flow and phosphorylation potential were different for each type of heart. Thus, at low flow rates, hypertrophied hearts perform the same amount of work and have the same contractile function as control hearts, but with abnormal changes in energy metabolism, indicating that the relations of energy status to coronary flow, total work output and contractile function are altered during the process of hypertrophy.

Effect of thyroid dysfunction on thigh muscle efficiency.

To establish whether muscle weakness in thyroid dysfunction can be attributed solely to muscle atrophy (i.e. reduction in the total muscle cross-section) or whether the intrinsic contractile strength of the muscle is reduced per unit cross-sectional area, the ratio between thigh muscle strength and thigh muscle area was determined before and after treatment of hyper- and hypothyroidism. Midthigh muscle areas, assessed by computer tomography, increased in all seven hyperthyroid and decreased in three of four hypothyroid patients investigated after treatment of the thyroid disease. Peak torque and total work output, assessed by an isokinetic dynamometer (Cybex II), increased in both groups of patients. The muscle efficiency (total work output per cm2 muscle) increased in all patients after therapy [mean +/- SD values before vs. after therapy in hyperthyroid patients, 17.6 +/- 5.3 vs. 30.5 +/- 3.7 joules (J)/cm2 (P less than 0.001); in hypothyroid patients, 12.8 +/- 6.1 J/cm2 vs. 25.8 +/- 8.6 J/cm2 (P less than 0.05)]. Thus, the present study demonstrates that patients with thyroid dysfunction have altered muscle mass and diminished muscle efficiency.

Beneficial effects of erythropoietin on haematological parameters, aerobic capacity, and body fluid composition in patients on haemodialysis.

Eleven patients on haemodialysis were treated with erythropoietin (EPO), 50-200 U kg-1 once to three times a week, for up to 1 year. After outset of EPO all patients became transfusion-independent. Four patients did not reach the target haemoglobin (Hb) level 100 g l-1 in 5 months. These patients had higher serum concentrations of aluminium (225 +/- 87 micrograms l-1, mean +/- SD) than the responding patients (55 +/- 56 micrograms l-1). Addition of desferrioxamine to treatment with EPO resulted in a rapid rise in Hb values in these patients. Thus, aluminium may inhibit EPO responsiveness. All patients were iron overloaded. Serum ferritin levels declined in all but one patient with secondary haemochromatosis. In exercise tests the aerobic capacity and oxygen uptake increased during EPO therapy. Peak oxygen consumption (Vo2 peak), oxygen pulse, oxygen uptake at anaerobic threshold (AT) and total work output (W max) increased 19%, 36%, 26% and 24%, respectively. Lean body mass (LBM) increased by 8%. Taken together, all clinical EPO effects measured appeared clinically favourable.

Influence of carbohydrate dosage on exercise performance and glycogen metabolism.

This study was undertaken to examine the effects of ingestion of carbohydrate (CHO) solutions of 0 (WP), 6 (CHO-6), 12 (CHO-12), and 18 g CHO/100 ml (CHO-18) on performance and muscle glycogen use. Ten trained cyclists performed five 120-min cycling trials. The first 105 min of each trial was at 70% of maximal O2 consumption (VO2max), and the final 15 min was an all-out performance ride on an isokinetic cycle ergometer equipped to measure total work output. In one of the trials (CHO-12I) the submaximal portion of the ride consisted of seven 15-min rides at 70% of VO2max with a 3-min rest between each ride. Every 15 min the men consumed 8.5 ml.kg-1.h-1 (approximately 150 ml) of one of the four test solutions. Venous blood samples were obtained every 15 min for glucose and insulin. Muscle biopsies were obtained from the vastus lateralis at 0 and 105 min in the WP and the CHO-12 continuous and intermittent trials. Biopsy samples were assayed for glycogen and sectioned and stained for myosin adenosinetriphosphatase and glycogen for single fiber depletion measurements. There were no differences in glycogen use (86.7 +/- 6.0, 75.5 +/- 7.9, and 83.5 +/- 5.5 mmol/kg for the WP, CHO-12C, and CHO-12I, respectively) or depletion patterns between the WP and the two CHO-12 trials. Blood glucose was significantly elevated in both the CHO-12 trials and in the CHO-18 trial compared with the WP trial.(ABSTRACT TRUNCATED AT 250 WORDS)

The size, operation, and technical capabilities of protein and nucleic acid core facilities.

A survey of 40 protein and nucleic acid chemistry facilities has provided data about the capabilities of core facilities and the cost of the services they provide. Approximately 43% of the +158,000 average annual operating budget for a typical university facility is derived from service charges. After correcting for the various degrees of subsidization of the different facilities, it was found that it costs a typical university facility +65 to carry out an acid hydrolysis and amino acid analysis on a protein. A 25-residue peptide can be synthesized and cleaved for +2078, whereas sequencing the same peptide costs +874. A 25-residue oligonucleotide can be synthesized for +258. The total work output per month of an average facility corresponds to 65 amino acid analyses, 15 amino acid sequencing runs, three peptide syntheses, and 16 oligonucleotide syntheses. Depending on the approach used, from 85 to nearly 200 pmol of protein are required to obtain an accurate amino acid composition. To sequence the first 15 amino acids in a protein typically requires 150 pmol compared with 1.2 nmol of protein required to first carry out a tryptic digest and then isolate and sequence the first 15 residues in one of the resulting tryptic peptides.

A cost-benefit analysis of demand for food.

Laboratory studies of consumer demand theory require assumptions regarding the definition of price in the absence of a medium of exchange (money). In this study we test the proposition that the fundamental dimension of price is a cost-benefit ratio expressed as the effort expended per unit of food value consumed. Using rats as subjects, we tested the generality of this "unit price" concept by varying four dimensions of price: fixed-ratio schedule, number of food pellets per fixed-ratio completion, probability of reinforcement, and response lever weight or effort. Two levels of the last three factors were combined in a 2 x 2 x 2 design giving eight groups. Each group was studied under a series of six FR schedules. Using the nominal values of all factors to determine unit price, we found that grams of food consumed plotted as a function of unit price followed a single demand curve. Similarly, total work output (responses x effort) conformed to a single function when plotted in terms of unit price. These observations provided a template for interpreting the effects of biological factors, such as brain lesions or drugs, that might alter the cost-benefit ratio.

Peak Torque and Total Work Relationship in the Thigh Muscles After Anterior Cruciate Ligament Injury

The purpose of the present study was to 1) assess the relationship between the isometric and isokinetic peak torques (speed of movement 0, 60, 180 degrees /sec) and the total work output of multiple contractions (180 degrees /sec) of the quadriceps and hamstrings in 36 patients having a chronic anterior cruciate ligament (ACL) insufficient knee joint, and 2) determine the possible association of these muscle function parameters with the subjective and functional outcome of the ACL insufficient knees. At every test speed the Pearson product moment (r) and the Spearman rank (r,) correlation coefficients between the peak torque and the total work were highly significant for the quadriceps and hamstrings in the uninjured (r = 0.71-0.93, rs = 0.70-0.90) as well as in the anteriorly unstable (r = 0.82-0.89, rs = 0.79-0.86) knees. All correlation coefficients were higher at the highest speed (180 degrees /sec) of the isokinetic test (r = 0.85-0.93, rs = 0.85-0.90) than at the other speeds (0 and 60 degrees /sec) (r = 0.71 -0.90, rs = 0.70-0.85) obviously since the total work was registered at that speed. Both the peak torque and total work parameters of quadriceps as well as hamstrings correlated significantly with the subjective and functional outcome of the ACL insufficient knees (r = 0.75-0.84, rs = 0.76-0.85): the better the muscular function the better the outcome. In conclusion, in anteriorly unstable knees the total work analysis offers little additional information to that attained by the peak torque measurements. J Orthop Sports Phys Ther 1988;10(3):97-101.

Relationship between peak torque and total work in an isokinetic contraction of the medial collateral ligament insufficient knee.

The aim of this study was to assess the relationship between the isometric and isokinetic peak torques (speed of movement 0, 60, and 180 degrees/s) and the total work output of multiple contractions (180 degrees/s) of the quadriceps and hamstrings in 25 subjects having a chronic, complete insufficiency of the medial collateral ligament of the knee. At every test speed the Pearson product moment (r) and the Spearman rank (rs) correlation coefficients between the peak torque and total work were highly significant for both muscle groups in the uninjured (r = 0.75-0.96, rs = 0.72-0.95) as well as in the medially unstable (r = 0.79-0.93, rs = 0.76-0.92) knees. In both knees and in both muscle groups, the correlation coefficients increased toward the highest speed of the isokinetic movement, obviously since the total work was registered at that speed. The author concludes that in the medial collateral ligament insufficient knees the total work analysis offers little additional information to that attained by more simple measurement, the peak torque analysis.

Differential effects of exercise intensity on serum uric acid concentration.

To investigate the effects of exercise intensity and short-term training on alterations in plasma uric acid, two series of experiments were performed using untrained male subjects. In series 1, 6 subjects (age 19 to 23 yr) cycled at 120% VO2max for 1 min followed by 4 min recovery until fatigue or until 24 repetitions had been completed. In series 2, 7 subjects (age 19 to 25 yr) cycled continuously at 65% VO2max for 2 h. In both experiments, short-term training was performed by repeating the exercise protocol for three consecutive days. In series 1, a progressive increase of 40% (P less than 0.05) was observed on day 1 in plasma uric acid concentration over the duration of the exercise. On day 2, pre-exercise values remained elevated over day 1 (mean +/- SD, 476 +/- 77 vs 352 +/- 30 mumol.l-1) and showed a further 23% increase (P less than 0.05) with exercise. Although resting uric acid concentrations on day 3 were elevated (P less than 0.05) over day 1, the exercise levels between day 1 and day 3 were not different (P greater than 0.05). In contrast, in series 2, prolonged sub-maximal exercise failed to stimulate increases in uric acid concentration either between days or within days. It is concluded that exercise intensity rather than total work output is a critical factor mediating increases in blood uric acid concentration. These results are consistent with the interpretation that uric acid formation may arise from purine nucleotide degradation and fast-twitch fiber utilization during conditions of high energy utilization.

Heredity and muscle adaptation to endurance training

To determine whether sensitivity of muscle characteristics and aerobic performances to endurance training was genotype-dependent, 6 pairs of monozygotic (MZ) twins, 21 +/- 4 yr of age (mean +/- SD), took part in a 15-wk ergocycle endurance training program. Tests were performed before and after 7 and 15 weeks of training. A biopsy of the vastus lateralis muscle was obtained for the determination of fiber type composition and activities of creatine kinase, hexokinase, phosphofructokinase, lactate dehydrogenase, malate dehydrogenase, 3-hydroxyacyl CoA dehydrogenase, and oxoglutarate dehydrogenase. Maximal oxygen uptake was measured with a progressive maximal ergocycle test, while endurance performance was determined as the total work output during a 90-min maximal ergocycle test. Results indicated that maximal oxygen uptake X kg-1 and endurance performance X kg-1 increased significantly (14 and 31%, respectively) with training, and intra-pair resemblance (intra-class) in response to 15 wk of training ranged from 0.65 to 0.83. Hexokinase (31%), phosphofructokinase (37%), lactate dehydrogenase (21%), malate dehydrogenase (31%), and 3-hydroxyacyl CoA dehydrogenase (60%) were significantly increased with training whereas no mean change in fiber-type proportions, oxoglutarate dehydrogenase and creatine kinase activities and the phosphofructokinase/oxoglutarate dehydrogenase ratio was observed. Similarity within twin pairs in the response to enzyme activities was mainly detected in the second half of the training program. The present results confirm, therefore, that both maximal oxygen uptake and endurance performance responses to training are largely genotype-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobic performance in brothers, dizygotic and monozygotic twins

Forty-two brothers, 66 dizygotic twins of both sexes and 106 monozygotic twins of both sexes, 16 to 34 yr of age, took part in this study that was designed to investigate the effect of heredity in aerobic performance. Maximal oxygen uptake (VO2 max), maximal heart rate (HR max), maximal ventilation, and maximal oxygen pulse were obtained from a progressive ergocycle test to exhaustion. Total work output in a 90-min maximal ergocycle test was also determined in the twins. Fat-free weight was estimated from body density measurements obtained through underwater weighing. Aerobic performance scores were adjusted for age (brothers), and age and sex (dizygotic and monozygotic twins) by regression procedures. Dizygotic twins and brothers of same sibship exhibited about the same level of resemblance for all variables or were only slightly different, with the exception of HR max. Monozygotic pairs were generally more alike than the other sibs, as suggested by the intra-class coefficients. Twin data were used to compute the genetic effects. The within-pair estimate of genetic variance revealed that it was significant (P less than or equal to 0.05) for all variables except VO2 max X kg-1 fat-free weight X min-1. In the case of HR max, the among-pairs component estimate had to be used, and it also proved significant (P less than or equal to 0.01). The size of the genetic effect was computed from three different methods, and it reached about 40% for VO2 max X kg-1 X min-1, 50% for HR max, 60% for maximal oxygen pulse and maximal ventilation, and 70% for 90-min work output X kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

In Vivo Approximations of the Classic In Vitro Length-Tension Relationship: An Isokinetic Evaluation

Several biarticular muscles of the human lower extremity were placed in various positions of stretch, using a hinged board to alter trunk-thigh relationships in 59 young adult volunteers of both sexes. Prior measurement, by direct x-ray of one subject on the test apparatus and by use of an articulated skeleton placed in the same pelvofemoral orientations as seen on the x-rays, supports the conclusion that the test positions of these 59 subjects were such that the biarticular extensor (rectus femoris) and flexors, (biceps femoris, semimembranosus and semitendinosus) were in fact being shortened or lengthened as desired under the prescribed positioning protocol. Isokinetic torques, total work output,; and average power production were obtained for maximal knee extensions and flexions through the full anatomical range of motion. The results support an assertion of close in vivo approximation to the classic in vitro length-tension relationship. J Orthop Sports Phys Ther 1986;7(5):222-231.

Specificity of aerobic and anaerobic work capacities and powers.

Thirty-three untrained subjects of both sexes, 18-31 years of age, performed several tests on cycle ergometers. Maximal aerobic power (MAP) was obtained in a progressive work test. Maximal aerobic capacity (MAC) was measured in a 90-min maximal test and was computed as the total work output during that period. Two all-out cycle ergometer work tests lasting 10 s and 90 s were used to estimate the anaerobic alactic capacity (AAC) and lactic capacity (ALC). Anaerobic alactic power (AAP) was computed as the highest output in 1 s in the AAC test and anaerobic lactic power (ALP) was obtained as the mean output during the last 5 s in an all-out test of 30 s. Correlation coefficients were computed between all measurements of capacity and power expressed per kg of body weight as well as with scores adjusted for sex differences. Common variances (r2 X 100) between measurements of power were either low (MAP-AAP, 40%) or moderate (MAP-ALP, 61%; AAP-ALP, 62%) while common variances between measurements of capacity were sometimes low (MAC-AAC, 49%) or higher (MAC-ALC, 76%; AAC-ALC, 77%). The common variances between tests of power and capacity reached high values when calculated with metabolic criteria of the same class (MAP-MAC, 81%; AAP-AAC, 92%). These results provide quantitative evidence to support the notion of specificity between the aerobic and the anaerobic work performances and support the distinction between capacity and power of the three energy systems.

Thigh muscle mass and function in patients treated with glucocorticoids.

Treatment with glucocorticoids causes wasting of proximal skeletal muscles. There is evidence that physical training improves muscle mass and strength in glucocorticoid-treated rats. Whether this is also true in humans is unknown. The present investigation was designed to establish in what respect moderate physical training may alter muscle mass and function as assessed quantitatively by computed tomography (CT) and with an isokinetic dynamometer (Cybex II). Compared with matched controls, both female (n = 17) and male (n = 22) patients treated with prednisone (15.4 +/- 6.6 mg die-1) had a lower mid-thigh muscle area of 20 and 45% and an increased mid-thigh fat/muscle ratio of 25 and 100%, respectively. The mean peak torque and the total work output of the thigh muscle were lower by 20-30% (n = 14). Fifty days of isokinetic training in six patients increased the thigh muscle area, decreased the thigh fat area and normalized the mean peak torque and total work output. Thus, glucocorticoid-induced muscle wasting can be reversed by increasing physical activity.

Muscle metabolism during exercise in the heat in unacclimatized and acclimatized humans.

The effect of heat acclimatization on aerobic exercise tolerance in the heat and on subsequent sprint exercise performance was investigated. Before (UN) and after (ACC) 8 days of heat acclimatization, 10 male subjects performed a heat-exercise test (HET) consisting of 6 h of intermittent submaximal [50% of the maximal O2 uptake] exercise in the heat (39.7 degrees C dB, 31.0% relative humidity). A 45-s maximal cycle ride was performed before (sprint 1) and after (sprint 2) each HET. Mean muscle glycogen use during the HET was lower following acclimatization [ACC = 28.6 +/- 6.4 (SE) and UN = 57.4 +/- 5.1 mmol/kg; P less than 0.05]. No differences were noted between the UN and ACC trials with respect to blood glucose, lactate (LA), or respiratory exchange ratio. During the UN trial only, total work output during sprint 2 was reduced compared with sprint 1 (24.01 +/- 0.80 vs. 21.56 +/- 1.18 kJ; P less than 0.05). This reduction in sprint performance was associated with an attenuated fall in muscle pH following sprint 2 (6.86 vs. 6.67, P less than 0.05) and a reduced accumulation of LA in the blood. These data indicate that heat acclimatization produced a shift in fuel selection during submaximal exercise in the heat. The observed sparing of muscle glycogen may be associated with the enhanced ability to perform highly intense exercise following prolonged exertion in the heat.

Evidence that prednisone-induced myopathy is reversed by physical training.

Treatment with glucocorticoids causes wasting of proximal skeletal muscles. There is evidence that physical training improves muscle mass and strength in glucocorticoid-treated rats. Whether this is also true in humans is not known. The present investigation was designed to establish in what respect moderate physical training may alter muscle mass and function as assessed quantitatively by computed tomography (CT) and an isokinetic dynamometer (Cybex II). Compared with matched normal subjects (n = 12), patients (n = 12) treated with prednisone [12.6 +/- 3.3 (+/- SD) mg/day] had a 20% lower midthigh muscle area and a 36% increase in midthigh fat to muscle ratio. The mean peak torque and the total work output of the thigh muscle were lower by more than 20%. Baseline measurements of total work output or peak torque at all tested velocities increased with midthigh muscle area (r = 0.73; n = 24; P less than 0.001). Fifty days of isokinetic training in 12 patients increased the thigh muscle area, decreased the thigh fat area, and normalized the mean peak torque and total work output. The increase in peak torque was inversely correlated with the daily dose of prednisone (r = 0.60; n = 12; P less than 0.05). Thus, glucocorticoid-induced muscle wasting can be reversed by increasing physical activity in patients taking a low to moderate dose of prednisone.