Forearm metabolic asymmetry detected by 31P-NMR during submaximal exercise

MR compatible ergometers for dynamic 31P MRS

Magnetic Resonance (MR) compatible ergometers are specialized ergometers used inside the MR scanners for the characterization of tissue metabolism changes during physical stress. They are most commonly used for dynamic phosphorous magnetic resonance spectroscopy (31P MRS), but can also be used for lactate production measurements, perfusion studies using arterial spin labelling or muscle oxygenation measurements by blood oxygen dependent contrast sequences. We will primarily discuss the importance of ergometers in the context of dynamic 31P MRS. Dynamic 31P MRS can monitor muscle fatigue and energy reserve during muscle contractions as well as the dynamics of recuperation of skeletal muscle tissue during the following recovery through signal changes of phosphocreatine (PCr), inorganic phosphate and adenosine triphosphate (ATP). Based on the measured data it is possible to calculate intracellular pH, metabolic flux of ATP through creatine-kinase reaction, anaerobic glycolysis and oxidative phosphorylation and other metabolic parameters as mitochondrial capacity. This review primarily focuses on describing various technical designs of MR compatible ergometers for dynamic 31P MRS that must be constructed with respect to the presence of magnetic field. It is also expected that the construction of ergometers will be easy for the handling and well accepted by examined subjects.

Efeitos da dominância unilateral dos membros inferiores na flexibilidade e no desempenho isocinético em mulheres saudáveis

INTRODUÇÃO: A dominância unilateral dos membros inferiores pode causar desequilíbrios entre os grupos musculares contralaterais, predispondo ambas as pernas a lesões. Assim, o conhecimento de deficits comparativos unilaterais é importante nas medidas de prevenção e avaliação do paciente. OBJETIVO: Verificar a influência das atividades diárias na diferença dos membros dominante (MD) e não dominante (MND) quanto a flexibilidade, Pico de Torque (PT), Trabalho Máximo (TM), Potência Máxima (PM) dos flexores e extensores do joelho. MÉTODOS: A amostra foi constituída por 23 mulheres saudáveis e não praticantes de atividade física. A flexibilidade foi avaliada pelo Teste do Ângulo Poplíteo (TAP) para isquiostibiais e Teste de Thomas (TT) para quadríceps-femoral; a avaliação isocinética foi realizada no modo concêntrico para extensão e flexão do joelho. Para o PT e o TM, foram realizadas cinco repetições na velocidade angular de 60º/seg e, para PM, 15 repetições em 240º/seg. Todas as avaliações foram realizadas pelo mesmo pesquisador. RESULTADOS: Não houve diferença estatisticamente significante quanto à flexibilidade obtida pelo TAP e pelo TT (p > 0,05). Porém, em todas as variáveis isocinéticas avaliadas houve uma diferença significativamente relevante entre o MD e o MND (p < 0,01), com média do índice de simetria dos membros superior a 10%. CONCLUSÃO: De acordo com os dados obtidos, as atividades do cotidiano em mulheres saudáveis causam diferenças entre o MD e o MND, sendo constatadas pela avaliação isocinética quanto a PT, TM e PM; porém, tais diferenças não foram visualizadas quanto à flexibilidade.

Deoxygenated hemoglobin/myoglobin kinetics of forearm muscles from rest to exercise in patients with chronic obstructive pulmonary disease

Exercise capacity is frequently decreased in patients with chronic obstructive pulmonary disease (COPD), and muscle dysfunction is one factor in this reduction. Studies using (31)-phosphorus magnetic resonance spectroscopy ((31)P-MRS) have shown that phosphocreatine (PCr) and muscle pH (pHi) are significantly decreased in patients with COPD during mild exercise, suggesting the early activation of anaerobic glycolysis in their muscles. Thus, muscle oxygenation states during exercise might differ between patients with COPD and healthy individuals. We simultaneously measured oxygenation state and pHi in the muscles of patients with COPD during the transition from rest to exercise (on-transition) using near infrared spectroscopy (NIRS) and (31)P-MRS. Sixteen patients with COPD (aged 68.6 +/- 7.5 years) and 7 healthy males (controls; aged 63.3 +/- 7.5 years) performed dynamic handgrip exercise (lifting a weight by gripping at a rate of 20 grips per min for 3 min). Patients were classified based on pHi data at the completion of exercise as having a normal (>or= 6.9; n = 8) or a low (< 6.9; n = 8) pHi. The deoxygenated hemoglobin/myoglobin (deoxy-Hb/Mb) in NIRS recordings remained constant or slightly decreased initially (time delay), then increased to reach a plateau. We calculated the time delay and the time constant of deoxy-Hb/Mb kinetics during the on-transition. The time delay was shorter in the group with a low pHi than in the controls. These findings might reflect a slower increase in O(2) delivery in patients with a low pHi, which might partly account for altered muscle energy metabolism.

Ventilatory and circulatory responses at the onset of dominant and non-dominant limb exercise

We compared the ventilatory and circulatory responses during 20 s of light dynamic leg and arm exercises performed separately using dominant and non-dominant limbs. Seventeen subjects performed a 20-s single-leg knee extension-flexion exercise with a load of 5% of maximal muscle strength attached to the ankle. Fifteen of the seventeen subjects also did a single-arm elbow flexion-extension exercise in which a load was attached to the wrist in the same way as in the leg exercise. Similar movements were passively performed on the subjects by experimenters to avoid the effects of central command. The magnitude of change from rest (gain) in minute ventilation during passive movement (PAS) was significantly smaller in the dominant limbs than in the non-dominant limbs, though a significant difference was not detected during voluntary exercise (VOL). In contrast, heart rate and blood pressure responses did not show any differences between the dominant and non-dominant limbs during either VOL or PAS. In conclusion, the initial ventilatory response to PAS in the dominant limbs was lower than that of the non-dominant limbs, though the ventilatory response to VOL was not. Circulatory responses were not different between the dominant and non-dominant limbs. These results suggest that peripheral neural reflex during exercise could be different between dominant and non-dominant limbs and that ventilatory response at the onset of exercise might be controlled by the dual neural modulation of central command and peripheral neural reflex, resulting in the same ventilatory response to both dominant and non-dominant limb exercise.

Noninvasive monitoring of deterioration in skeletal muscle function with forearm cast immobilization and the prevention of deterioration

Background

In this research inactivity was simulated by immobilizing the forearm region in a plaster cast. Changes in skeletal muscle oxidative function were measured using near-infrared spectroscopy (NIRS), and the preventative effect of the training protocol on deterioration of skeletal muscle and the clinical utility of NIRS were examined.

Methods

Fourteen healthy adult men underwent immobilization of the forearm of the non-dominant arm by plaster cast for 21 days. Eight healthy adult subjects were designated as the immobilization group (IMM) and six were designated as the immobilization + training group (IMM+TRN). Grip strength, forearm circumference and dynamic handgrip exercise endurance were measured before and after the 21-day immobilization period. Using NIRS, changes in oxidative function of skeletal muscles were also evaluated. Muscle oxygen consumption recovery was recorded after the completion of 60 seconds of 40% maximum voluntary contraction (MVC) dynamic handgrip exercise 1 repetition per 4 seconds and the recovery time constant (TcVO₂mus) was calculated.

Results

TcVO₂mus for the IMM was 59.7 ± 5.5 seconds (average ± standard error) before immobilization and lengthened significantly to 70.4 ± 5.4 seconds after immobilization (p < 0.05). For the IMM+TRN, TcVO₂mus was 78.3 ± 6.2 seconds before immobilization and training and shortened significantly to 63.1 ± 5.6 seconds after immobilization and training (p < 0.05).

Conclusions

The training program used in this experiment was effective in preventing declines in muscle oxidative function and endurance due to immobilization. The experimental results suggest that non-invasive monitoring of skeletal muscle function by NIRS would be possible in a clinical setting.

Exercise-induced sympathetic activation is correlated with cerebral hemisphere laterality, but not handedness

To investigate whether sympathetic responses are correlated with central laterality or handedness, muscle sympathetic nerve activity (MSNA), heart rate (HR) and blood pressure (BP) were compared between right (RA) and left arm (LA) grip exercise with volitional maximum effort (MVHG) for 2 min and post-exercise arterial occlusion (PEAO) in right- and left-handed volunteers. MVHG and PEAO led to a greater increase in MSNA in RA than in LA exercise (180 vs. 150%, P=0.004; 140 vs. 85%, P=0.005). MVHG elevated HR to a significantly lesser extent in RA than in LA (35 vs. 46%, P=0.030), and the difference was maintained during PEAO. The BP rise during MVHG and PEAO was the same in RA and in LA. Muscle sympathetic nerve activity, HR and BP responses during MVHG and PEAO showed no difference between the dominant and non-dominant arm. These results suggested that the effects of central motor command and metaboreflex on sympathetic outflow to the vasculature and the heart may be selectively modulated partly by hemispherical laterality.

Insights into muscle diseases gained by phosphorus magnetic resonance spectroscopy

Phosphorus magnetic resonance spectroscopy (P-MRS) has now been used in the investigation of muscle energy metabolism in health and disease for over 15 years. The present review describes the basics of the metabolic observations made by P-MRS including the assumptions and problems associated with the use of this technique. Extramuscular factors, which may affect the P-MRS results, are detailed. The important P-MRS observations in patients with mitochondrial myopathies, including the monitoring of experimental therapies, are emphasized. The findings in other metabolic myopathies (those associated with glycolytic defects or endocrine disturbances) and in the destructive myopathies (the dystrophies and the inflammatory myopathies) are also described. Observations made in normal and abnormal fatigue, fibromyalgia, and malignant hyperthermia are considered. Finally, a summary of the possible diagnostic use of P-MRS in exercise intolerance is provided.

Spatial distribution of blood flow in electrically stimulated human muscle: a positron emission tomography study

Neuromuscular electrical stimulation (NMES) was studied with positron emission tomography (PET) and H(2)(15)O in the quadriceps muscle of 11 men. The subjects were submitted to simultaneous bilateral isometric contraction (5 s)-rest (5 s) cycles for 12 min, with a workload corresponding to 5% of quadriceps maximal isometric voluntary torque (QMIVT) for one thigh (5%T) and 10% of QMIVT for the other (10%T). Scans were centered at the electrodes and tissue blood flow (TBF) was evaluated in square regions of interest (ROIs) (3.5 cm(2)) in the transverse section (TS) of both thighs. The mean TBF reached 8.9 mL min(-1) 100 g(-1) in the TS of the 5%T and 11.5 mL min(-1) 100 g(-1) in the TS of the 10%T (P > 0.05). A negative linear relationship was found for both thighs between the ROI-electrode distance and the TBF (P </= 0.009). The mean percentage of activated ROIs (TBF > 5 mL min(-1) 100 g(-1)) was lower in the 5%T than in the 10%T (50.6% vs. 62.2%; P = 0.017). With NMES, the pattern of spatial recruitment appears linked to electrode proximity and is spatially extended. These results confirm the utility of combining NMES with voluntary exercise in the treatment of atrophied muscle.

Muscle phosphorus magnetic resonance spectroscopy oxidative indices correlate with physical activity

The purpose of this study was to assess the effect of physical deconditioning on skeletal muscle's oxidative metabolism as evaluated by phosphorus-31 magnetic resonance spectroscopy ((31)P MRS). Twenty-seven subjects without muscle disease, representing a wide range of fitness levels, were evaluated with (31)P MRS. Spectra were obtained at rest and during recovery from in-magnet exercise. The data show a significant correlation between maximum resting metabolic equivalent (MET) score and the following (31)P MRS recovery indices: adenosine diphosphate and phosphocreatine recovery half-time; initial phosphocreatine resynthesis rate; calculated estimation of mitochondrial capacity; pH at end of exercise; and phosphocreatine depletion. In addition, significant differences between the deconditioned and conditioned group were found for all of the aforementioned recovery indices. At rest, only the inorganic phosphate concentration was significantly different between the two groups. These data indicate that physical activity level should be taken into account when assessing patients' oxidative metabolism with (31)P MRS.

Forearm metabolism during infusion of adrenaline: comparison of the dominant and non-dominant arm

Human skeletal muscle metabolism is often investigated by measurements of substrate fluxes across the forearm. To evaluate whether the two forearms give the same metabolic information, nine healthy subjects were studied in the fasted state and during infusion of adrenaline. Both arms were catheterized in a cubital vein in the retrograde direction. A femoral artery was catheterized for blood sampling, and a femoral vein for infusion of adrenaline. Forearm blood flow was measured by venous occlusion strain-gauge plethysmography. Forearm subcutaneous adipose tissue blood flow was measured by the local 133Xe washout method. Metabolic fluxes were calculated as the product of forearm blood flow and a-v differences of metabolite concentrations. After baseline measurements, adrenaline was infused at a rate of 0.3 nmol kg-1 min-1. No difference in the metabolic information obtained in the fasting state could be demonstrated. During infusion of adrenaline, blood flow and lactate output increased significantly more in the non-dominant arm (8.12 +/- 1.24 versus 6.45 +/- 1.19 ml 100 g-1 min-1) and (2.99 +/- 0.60 versus 1.83 +/- 0.43 micromol 100 g-1 min-1). Adrenaline induced a significant increase in oxygen uptake in the non-dominant forearm (baseline period: 4.98 +/- 0.72 micromol 100 g-1 min-1; adrenaline period: 6.63 +/- 0.62 micromol 100 g-1 min-1) while there was no increase in the dominant forearm (baseline period: 5.69 +/- 1.03 micromol 100 g-1 min-1; adrenaline period: 4. 94 +/- 0.84 micromol 100 g-1 min-1). It is concluded that the two forearms do not respond equally to adrenaline stimulation. Thus, when comparing results from different studies, it is necessary to know which arm was examined.

Dynamic phosphorus-31 magnetic resonance spectroscopy of the quadriceps muscle: effects of age and sex on spectroscopic results

RATIONALE AND OBJECTIVES

Phosphorus-31 (31p) magnetic resonance spectroscopy (MRS) is used to assess the influence of sex and age on quadriceps muscle metabolism before and after exercise.

METHODS

Fifty-four healthy volunteers and 56 patients with an arterial occlusive disease were examined by dynamic 31p MRS. In the magnet, the quadriceps muscle was stressed by an isometric and an isotonic form of exercise until exhaustion.

RESULTS

Older subjects showed a significantly larger ratio of inorganic phosphate (P(i)) to phosphocreatine (PCr) than younger subjects (r = 0.52, P = 8 x 10(-9)). With subjects' increasing age, the ratio of adenosine triphosphate (beta-ATP) to total phosphate decreased (r = -0.36, P = 5 x 10(-5)). The ratio of phosphomonoester to beta-ATP and phosphodiester (PDE) to beta-ATP showed a strong age dependence (r = 0.71 and 0.69, P = 3 x 10(-17) and 4 x 10(-15), respectively). The pH was the only one of the evaluated spectroscopic parameters that showed a sex dependence. Female subjects had a significantly lower pH (7.03+/-0.02) than male subjects (7.05+/-0.03) (P = 6 x 10(-4)). With increasing age, the maxima of P(i) to PCr were less extreme during both of the exercises (r = -0.51, P = 3 x 10(-16)). Likewise, the exercise-induced acidosis was less severe with increasing age (r = -0.51, P = 7 x 10(-16)). After the exercises ended, the times of half recovery of P(i) to PCr and the pH neither correlated with the subjects' age nor with sex or the cross-sectional area of the quadriceps muscle.

CONCLUSIONS

The sex and age of volunteers or patients may affect spectroscopic results in a significant way. This influence has to be considered in the interpretation of spectroscopic studies. According to the recovery rates of P(i) to PCr and the pH, an age-related deterioration of muscular metabolism seems to be avoidable by appropriate physical activity.

Impairment of the exercise-induced increase in muscle perfusion in McArdle's disease

In McArdle's disease (myophosphorylase deficiency) exercise intolerance is generally attributed to a lack of glycogenolysis, which decreases energy production during exercise. Magnetic resonance imaging data have recently suggested an impairment of the increase in muscle perfusion during exercise in these patients. We have tested this hypothesis by direct measurement of local muscle perfusion increase. Increase in muscle perfusion was assessed by positron emission tomography with oxygen-15 labelled water in five patients with McArdle's disease and five age- and sex-matched healthy volunteers. Radioactivity was measured in both forearms before and after exercise of the right forearm. The exercise intensity was biochemically assessed by in vivo phosphorus-31 magnetic resonance spectroscopy. The estimated increase in muscle perfusion with exercise was 5.7+/-5.5-fold in the patients (range 1.5-12.8) and 22.3+/-12.0-fold in the healthy subjects (range 10.1-37) (P=0.022). The results show a significant impairment of increase in muscle perfusion with exercise in McArdle's disease. Thus patients may suffer not only from a direct lack of glycogenolysis but also from indirectly impaired vasodilation.

Metabolic adaptations to endurance training in older individuals

The purpose of this study was to describe the effects of moderate intensity exercise training on the muscle energy utilization, blood flow, and exercise performance of four sedentary older individuals (58 +/- 4 yrs). Subjects trained the dominant forearm each day for 12 weeks. The nondominant arm was not trained and served as a within-subject control. 31P nuclear magnetic resonance spectroscopy (31P NMRS) was used to identify the power output in watts (W) at the onset, or threshold, of intracellular acidosis (IT) in the exercising muscle during progressive exercise tests to fatigue. After 6 weeks of training, power output at the IT increased by 14% (p < 0.05) in the dominant arm; however, an additional 6 weeks of the same exercise program failed to produce a further increase in IT power. IT power of the nondominant forearm was not changed. In the dominant forearm, endurance time for a submaximal wrist flexion test was increased 34% and 58% at 6 and 12 weeks, respectively. Maximal voluntary strength was not affected by training, nor was resting or exercising blood flow. The training program delayed the onset of intracellular acidosis during progressive exercise and increased the capacity for submaximal work. These effects did not appear to depend on an increase in muscle blood flow.

Comparison of muscle sympathetic nerve activity during exercise in dominant and nondominant forearm

To determine whether or not muscle endurance training alters exercise-induced sympathetic nerve response, we recorded muscle sympathetic nerve activity (MSNA) microneurographically during forearm exercise and compared MSNA between dominant (D) and non-dominant (ND) forearms of players of racket sports. Three kinds of forearm exercise were conducted on each side; static (SHG) and dynamic (DHG, at a rate of 1 Hz) handgrip exercise at a loading of 25% of maximal voluntary contraction until exhaustion, and 10-min submaximal dynamic handgrip (at a rate of 1 Hz) at an intensity of 0.9 W. Heart rate, ventilation and blood pressure were also monitored at rest and during SHG and DHG exercises. During the last minute of SHG exercise, MSNA burst rate had increased on average by 290 (SEM 46)% in D and 330 (SEM 46)% in ND, while during DHG it increased by 288 (SEM 38)% in D and 344 (SEM 36)% in ND, respectively. There were no significant differences in the MSNA responses between D and ND forearms in either exercise modes. Significant increases in heart rate, ventilation and blood pressure during the last minute of fatiguing SHG and DHG were observed, but there were no significant differences between the two forearms. During submaximal DHG, while MSNA increased significantly above control values in both D and ND, the MSNA response was less in D than that in ND forearm. The results would suggest that exercise-induced MSNA responsiveness is influenced little by muscle endurance training but the intensity of response may be due to the magnitude of metaboreceptor stimulation in the exercising muscle.

Hydrogen ion concentration is not the sole determinant of muscle metaboreceptor responses in humans

We examined the effects of exercise conditioning on muscle sympathetic nerve activity (MSNA) during handgrip and posthandgrip circulatory arrest (PHG-CA). Two conditioning stimuli were studied: forearm dominance and bodybuilding. Static handgrip at 30% maximal voluntary contraction followed by PHG-CA led to a rise in MSNA smaller in dominant than in nondominant forearms (99% vs. 222%; P less than 0.02) and in body builders than in normal volunteers (28% vs. 244%; P less than 0.01). Separate 31P NMR experiments showed no effect of dominance on forearm pH but a pH in bodybuilders higher (6.88) than in normal volunteers (6.79; P less than 0.02) during PHG-CA. Our second goal was to determine if factors besides attenuated [H+] contribute to this conditioning effect. If differences in MSNA during exercise were noted at the same pH, then other mechanisms must contribute to the training effect. We measured MSNA during ischemic fatiguing handgrip. No dominance or bodybuilding effect on pH was noted. However, we noted increases in MSNA smaller in dominant than nondominant forearms (212% vs. 322%; P less than 0.02) and in bodybuilders than in normal volunteers (161% vs. 334%; P less than 0.01). In summary, MSNA responses were less during exercise of conditioned limbs. Factors aside from a lessening of muscle acidosis contribute to this effect.

Phosphorus magnetic resonance spectroscopy (31P MRS) in neuromuscular disorders

Phosphorus magnetic resonance spectroscopy monitors muscle energy metabolism by recording the ratio of phosphocreatine to inorganic phosphate at rest, during exercise, and during recovery from exercise. In mitochondrial diseases, abnormalities may appear during some or all these phases. Low phosphocreatine-inorganic phosphate ratios at rest are not disease-specific, but can be increased by drug therapy in several myopathies. Phosphorus magnetic resonance spectroscopy can also record intracellular pH and thus identify disorders of glycogen metabolism in which the production of lactic acid is blocked during ischemic exercise. The measurements of accumulated sugar phosphate intermediates further delineate glycolytic muscle defects. Myophosphorylase deficiency responds to intravenous glucose administration with improved exercise bioenergetics, but no such response is seen in phosphofructokinase deficiency. The muscular dystrophies show no specific bioenergetic abnormality; however, elevation of phospholipids metabolites and phosphodiesters was detected in some cases. While phosphorus magnetic resonance spectroscopy remains primarily a research tool in metabolic myopathies, it will be clinically useful in identifying new therapies and monitoring their effects in a variety of neuromuscular disorders.

Evidence of fibre hyperplasia in human skeletal muscles from healthy young men? A left-right comparison of the fibre number in whole anterior tibialis muscles

Cross-sections (thickness 10 microns) of whole autopsied left and right anterior tibialis muscles of seven young previously healthy right-handed men (mean age 23 years, range 18-32 years) were prepared for light-microscope enzyme histochemistry. Muscle cross-sectional area and total number of fibres, mean fibre size (indirectly determined) and proportion of the different fibre types (type 1 and type 2 on basis of myofibrillar adenosine triphosphatase characteristics), in each muscle cross-section were determined. The analysis showed that the cross-sectional area of the left muscle was significantly larger (P less than 0.05), and the total number of fibres was significantly higher (P less than 0.05), than for the corresponding right muscle. There was no significant difference for the mean fibre size or the proportion of the two fibre types. The results imply that long-term asymmetrical low-level daily demands on muscles of the left and the right lower leg in right-handed individuals provide enough stimuli to induce an enlargement of the muscles on the left side, and that this enlargement is due to an increase in the number of muscle fibres (fibre hyperplasia). Calculations based on the data also explain why the underlying process of hyperplasia is difficult, or even impossible, to detect in standard muscle biopsies.

Heterogeneity of metabolic response to muscular exercise in humans. New criteria of invariance defined by in vivo phosphorus-31 NMR spectroscopy

31P NMR spectroscopy at 4.7 T has been used in vivo to follow metabolic changes associated with exercise and subsequent recovery in the forearm flexor digitorum superficialis muscle of 14 healthy volunteers. The muscle content in phosphomonoesters at rest provides an index of glycogenolytic activity. Quantitative linear correlations have been shown to link end-of-exercise acidosis to recovery kinetics of phosphocreatine and phosphocreatine/organic phosphate ratio. These linear relationships constitute new metabolic invariants to be used in the study of myopathies and muscle adaptation to exercise.

Skeletal muscle response to exercise training in congestive heart failure

To examine the ability of the skeletal muscle of congestive heart failure (CHF) patients to adapt to chronic exercise, five patients performed localized nondominant wrist flexor training for 28 d. Inorganic phosphate (Pi) and phosphocreatine (PCr) were monitored by magnetic resonance spectroscopy in both forearms at rest and during submaximal wrist flexion exercise at 6, 12, 24, and 36 J.min-1 before and after exercise training. Simultaneous measurements of limb blood flow were made by plethysmography at 12, 24, and 36 J.min-1. Forearm muscle mass and endurance were measured by magnetic resonance imaging and wrist flexion exercise before and after training. The Pi/PCr ratio and pH were calculated from the measured Pi and PCr. Exercise cardiac output, heart rate, plasma norepinephrine, and lactate measured during training were not elevated above resting values, confirming that training was localized to the forearm flexor muscles. After training, muscle bioenergetics, as assessed by the slope of the regression line relating Pi/PCr to submaximal workloads, were improved in the trained forearm of each patient, although muscle mass, limb blood flow, and pH were unchanged. Forearm endurance increased by greater than 260% after training. In the dominant untrained forearm, none of the measured indices were affected. We conclude that localized forearm exercise training in CHF patients improves muscle energetics at submaximal workloads in the trained muscle, an effect which is independent of muscle mass, limb blood flow, or a central cardiovascular response during training. These findings indicate that peripheral muscle metabolic and functional abnormalities in CHF can be improved without altering cardiac performance.