Small Muscle Mass Research Articles

Phosphocreatine Onset and Recovery Kinetics in Aging Skeletal Muscle

2438 Significant metabolic adaptations have been observed in human skeletal muscle within 5–7 days of endurance training. These studies, on young subjects, typically involved cycle ergometry at moderate exercise intensities and the use of muscfle biopsies. PURPOSE: To characterize the effects of age on metabolic adaptation to training we used 31P magnetic resonance spectroscopy (MRS) to examine metabolic changes in a small muscle mass during a period of short-term high intensity endurance training in an aged population. METHODS: We monitored the kinetics of phosphocreatine (PCr) breakdown at the onset of exercise, PCr recovery kinetics, and the levels of PCr depletion in the calf muscle during plantar flexion exercise over a 6-day training period. Each day, 6 healthy males, age 70 ± 2.7 yrs, performed 6 sets of 4 min plantar flexion exercise at 1 Hz. Initial training load was set at 80% of maximum work rate (WR max), with the load increased by 1 Watt each day if the subject could complete the previous days work without failure. Metabolic adaptations were monitored on days 0, 3, and 6 during exercise at 50% of initial WR max. RESULTS: WRmax increased by an average of 32.3 ± 4.4%. Time constants for PCr breakdown at the onset of exercise decreased from 58.1 ± 8.6s to 35.9 ± 5.7s (p < 0.05) pre- to post-training. PCr depletion was spared by 17.0 ± 4.3% (p < 0.05) after 6 days of training. PCr recovery time was unchanged. CONCLUSION: These metabolic adaptations suggest that aging skeletal muscle maintains the plasticity to adapt rapidly to endurance exercise training. The faster PCr onset kinetics indicate a more rapid metabolic adjustment to steady-state exercise which in part may account for the sparing of PCr for a given work rate post-training. The lack of decrease in PCr recovery rate suggests that these metabolic changes are independent of a change in skeletal muscle oxidative capacity. Supported by NIH HL-17731, AHA 9960064Y, TRDRP 10KT-0335, and NIH RR 14785

No Effect of Resistance Training on Autonomic Cardiovascular Control

2399 Resistance exercise with either a small or large muscle mass causes transient doubling or tripling of arterial pressures that may severely challenge autonomic cardiac and baroreflex regulation. Potential chronic adaptations may be linked to resistance training mode, but studies describing autonomic cardiovascular adaptations to different resistance training regimens do not exist. PURPOSE: To evaluate the influence of high- and moderate-intensity resistance training on autonomic cardiovascular regulatory mechanisms. METHODS: Thirty two subjects (age 22 ± 0.6 yr) were assigned to one of three groups: resistance training for strength (RS, n = 12), resistance training for strength and endurance (RE, n = 10), or no exercise control (CON, n = 10). Subjects trained each major muscle group using 7 isotonic weight training machines 3 d/wk for 8 wk with 3 sets of 10 repetitions and 2 min rest periods (RS) or 3 sets of 15 repetitions with 30 s rest periods (RE). Resistance was progressively increased when possible. Before and after training, ECG, finger photoplethysmographic arterial pressures, and muscle sympathetic nerve activity (MSNA) were recorded with subjects supine and breathing at a set rate (0.25 Hz). Data were analyzed in both time and frequency domains. Arterial baroreflex sensitivity was assessed from cross-spectral transfer function analysis between systolic pressures and R-R intervals. RESULTS: Whole body strength increased by 22% (RS;P = 0.01) and by 21% (RE;P = 0.01). Aerobic capacity increased from 3.3 ± 0.8 to 3.7 ± 0.79 l/min (RE;P = 0.01). Muscular strength and aerobic capacity did not change for CON (P > 0.05). Heart rate and arterial pressure variability, MSNA, and arterial baroreflex sensitivity were unaffected by RS and RE. CONCLUSION: Despite significant increases in muscular strength (RS and RE) and aerobic capacity (RE), resistance training does not affect autonomic cardiovascular regulation. Supported by American Heart Association Grant 0030203N

The effect of varied fractional inspired oxygen on arm exercise performance in spinal cord injury and able-bodied persons

Hopman MT, Houtman S, Groothuis JT, Folgering HT. The effect of varied fractional inspired oxygen on arm exercise performance in spinal cord injury and able-bodied persons. Arch Phys Med Rehabil 2004;85:319–23. Objective To examine the effect of different levels of fractional inspired oxygen (F io 2) (15%, 21%, 50%) on peak oxygen consumption (V o 2peak) during arm exercise in persons with spinal cord injury and in able-bodied controls. Design Case-control study. Setting University medical center in the Netherlands. Participants Ten able-bodied controls, 6 persons with paraplegia, and 6 persons with tetraplegia. Interventions Inspiration of 15%, 21%, and 50% oxygen during a 15-minute period before and during arm exercise. Main outcome measures Oxygen uptake (V o 2peak, V o 2peak/kg), power output, ventilation, and base excess. Results In the able-bodied controls, significant F io 2 dependency was seen in power output, V o 2peak, and V o 2peak/kg. Persons with paraplegia showed significant F io 2 dependency in V o 2 and V o 2/kg. In persons with tetraplegia, no F io 2 dependency was observed; however, V o 2 and V o 2/kg were significantly higher at 50% than at 15% F io 2. Ventilation and base excess did not change in able-bodied controls or in persons with paraplegia with different levels of F io 2. In persons with tetraplegia, ventilation was significantly higher at 15% than at 50% F io 2, and base excess did not change. No significant interactions between groups and F io 2 were observed. Conclusions Oxygen consumption during peak arm-cranking exercise is enhanced with an increased inspiratory oxygen fraction in able-bodied controls as well as in persons with paraplegia and to a lesser extent in persons with tetraplegia, indicating that peak oxygen consumption during arm exercise is limited by oxygen supply rather than by the small muscle mass and related biochemical limitations.

Chronic Transcutaneous Electrical Stimulation of Calf Muscles Improves Functional Capacity without Inducing Systemic Inflammation in Claudicants

Objectives. To assess whether electrical stimulation of ischaemic calf muscles in claudicants causes a systemic inflammatory response and to evaluate effects of its chronic application on muscle function and walking ability.Design. Prospective randomised controlled trial of calf muscle stimulation.Materials and methods. Stable claudicants were randomised to receive either active chronic low frequency (6 Hz) motor stimulation (n=15) or, as a control treatment, submotor transcutaneous electrical nerve (TENS) stimulation (n=15) of calf muscles in one leg, 3×20 min per day for four weeks. Leucocyte activation was quantified by changes in cell morphology, vascular permeability by urinary albumin:creatinine ratio (ACR), calf muscle function by isometric twitch contractions and walking ability by treadmill performance pre- and post-intervention.Results. Acute active muscle stimulation activated leucocytes less (28% increase) than a standard treadmill test (81% increase) and did not increase ACR. Chronic calf muscle stimulation significantly increased pain-free walking distance by 35 m (95% CI 17, 52, P<0.001) and maximum walking distance by 39 m (95% CI 7, 70, P<0.05) while control treatment had no effect. Active stimulation prevented fatigue of calf muscles during isometric electrically evoked contractions by abolishing the slowing of relaxation that was responsible for loss of force.Conclusions. Chronic electrical muscle stimulation is an effective treatment for alleviating intermittent claudication which, by targeted activation of a small muscle mass, does not engender a significant systemic inflammatory response.

Reduced mechanical efficiency in chronic obstructive pulmonary disease but normal peak VO2 with small muscle mass exercise.

We studied six patients with chronic obstructive pulmonary disease (COPD) (FEV1 = 1.1 +/- 0.2 L, 32% of predicted) and six age- and activity level-matched control subjects while performing both maximal bicycle exercise and single leg knee-extensor exercise. Arterial and femoral venous blood sampling, thermodilution blood flow measurements, and needle biopsies allowed the assessment of muscle oxygen supply, utilization, and structure. Maximal work rates and single leg VO2max (control subjects = 0.63 +/- 0.1; patients with COPD = 0.37 +/- 0.1 L/minute) were significantly greater in the control group during bicycle exercise. During knee-extensor exercise this difference in VO2max disappeared, whereas maximal work capacity was reduced (flywheel resistance: control subjects = 923 +/- 198; patients with COPD = 612 +/- 81 g) revealing a significantly reduced mechanical efficiency (work per unit oxygen consumed) with COPD. The patients had an elevated number of less efficient type II muscle fibers, whereas muscle fiber cross-sectional areas, capillarity, and mitochondrial volume density were not different between the groups. Therefore, although metabolic capacity per se is unchanged, fiber type differences associated with COPD may account for the reduced muscular mechanical efficiency that becomes clearly apparent during knee-extensor exercise, when muscle function is no longer overshadowed by the decrement in lung function.

Effects of hypothyroidism on the skeletal muscle blood flow response to contractions.

Hypothyroidism is associated with impaired blood flow to skeletal muscle under whole body exercise conditions. It is unclear whether poor cardiac and/or vascular function account for blunted muscle blood flow. Our experiment isolated a small group of hindlimb muscles and simulated exercise via tetanic contractions. We hypothesized that muscle blood flow would be attenuated in hypothyroid rats (HYPO) compared with euthyroid rats (EUT). Rats were made hypothyroid by mixing propylthiouracil in their drinking water (2.35 x 10-3 mol/l). Treatment efficacy was evidenced by lower serum T3 concentrations and resting heart rates in HYPO (both P<0.05). In the experimental preparation, isometric contractions of the lower right hindlimb muscles at a rate of 30 tetani/min were induced via sciatic nerve stimulation. Regional blood flows were determined by the radiolabelled microsphere method at three time points: rest, 2 min of contractions and 10 min of contractions. Muscle blood flow generally increased from rest ( approximately 5-10 ml/min per 100 g) through contractions for both groups. Further, blood flow during contractions did not differ between groups for any muscle (eg. red section of gastrocnemius muscle; EUT, 59.9 +/- 14.1; HYPO, 61.1 +/- 15.0; NS between groups). These findings indicate that hypothyroidism does not significantly impair skeletal muscle blood flow when only a small muscle mass is contracting. Our findings suggest that impaired blood flow under whole body exercise is accounted for by inadequate cardiac function rather than abnormal vascular function.

The re-establishment of the normal blood lactate response to exercise in humans after prolonged acclimatization to altitude.

1. One to five weeks of chronic exposure to hypoxia has been shown to reduce peak blood lactate concentration compared to acute exposure to hypoxia during exercise, the high altitude 'lactate paradox'. However, we hypothesize that a sufficiently long exposure to hypoxia would result in a blood lactate and net lactate release from the active leg to an extent similar to that observed in acute hypoxia, independent of work intensity. 2. Six Danish lowlanders (25-26 years) were studied during graded incremental bicycle exercise under four conditions: at sea level breathing either ambient air (0 m normoxia) or a low-oxygen gas mixture (10 % O(2) in N(2), 0 m acute hypoxia) and after 9 weeks of acclimatization to 5260 m breathing either ambient air (5260 m chronic hypoxia) or a normoxic gas mixture (47 % O(2) in N(2), 5260 m acute normoxia). In addition, one-leg knee-extensor exercise was performed during 5260 m chronic hypoxia and 5260 m acute normoxia. 3. During incremental bicycle exercise, the arterial lactate concentrations were similar at sub-maximal work at 0 m acute hypoxia and 5260 m chronic hypoxia but higher compared to both 0 m normoxia and 5260 m acute normoxia. However, peak lactate concentration was similar under all conditions (10.0 +/- 1.3, 10.7 +/- 2.0, 10.9 +/- 2.3 and 11.0 +/- 1.0 mmol l(-1)) at 0 m normoxia, 0 m acute hypoxia, 5260 m chronic hypoxia and 5260 m acute normoxia, respectively. Despite a similar lactate concentration at sub-maximal and maximal workload, the net lactate release from the leg was lower during 0 m acute hypoxia (peak 8.4 +/- 1.6 mmol min(-1)) than at 5260 m chronic hypoxia (peak 12.8 +/- 2.2 mmol min(-1)). The same was observed for 0 m normoxia (peak 8.9 +/- 2.0 mmol min(-1)) compared to 5260 m acute normoxia (peak 12.6 +/- 3.6 mmol min(-1)). Exercise after acclimatization with a small muscle mass (one-leg knee-extensor) elicited similar lactate concentrations (peak 4.4 +/- 0.2 vs. 3.9 +/- 0.3 mmol l(-1)) and net lactate release (peak 16.4 +/- 1.8 vs. 14.3 mmol l(-1)) from the active leg at 5260 m chronic hypoxia and 5260 m acute normoxia. 4. In conclusion, in lowlanders acclimatized for 9 weeks to an altitude of 5260 m, the arterial lactate concentration was similar at 0 m acute hypoxia and 5260 m chronic hypoxia. The net lactate release from the active leg was higher at 5260 m chronic hypoxia compared to 0 m acute hypoxia, implying an enhanced lactate utilization with prolonged acclimatization to altitude. The present study clearly shows the absence of a lactate paradox in lowlanders sufficiently acclimatized to altitude.

The standard energetics of mammalian carnivores: Felidae and Hyaenidae

Data concerning the energy expenditure of nine species in the family Felidae and one species in the family Hyaenidae are presented, all of which were obtained under standard conditions. An examination of basal rates of metabolism in these felids and in two species reported in the literature indicates that basal rate is primarily correlated with body mass; of these species, nine have a high basal metabolic rate by general mammalian standards, the two exceptions being the margay and jaguarundi. The low basal metabolic rate of the margay may be related to its arboreal habit in association with small muscle mass, but the reason for the low rate in the jaguarundi is unknown. The omnivorous striped hyaena and termitivorous aardwolf have typical mammalian basal rates. Felids that weigh less than 7 kg have slightly low minimal thermal conductances relative to mammals generally; larger species have high conductances. Felids have slightly high body temperatures.

The relationship between heart rate and oxygen uptake during non-steady state exercise

In this study the validity of using heart rate (HR) responses to estimate oxygen uptake ([Vdot]O2) during varying non-steady state activities was investigated. Dynamic and static exercise engaging large and small muscle masses were studied in four different experiments. In the first experiment, 16 subjects performed an interval test on a cycle ergometer, and 12 subjects performed a field test consisting of various dynamic leg exercises. Simultaneous HR and [Vdot]O2 measurements were made. Linear regression analyses revealed high correlations between HR and [Vdot]O2 during both the interval test (r= 0.90±0.07) and the field test (r= 0.94±0.04). In the second experiment, 14 non-wheelchair-bound subjects performed both an interval wheelchair test on a motor driven treadmill, and a wheelchair field test consisting of dynamic and static arm exercise. Significant relationships were found for all subjects during both the interval test (r = 0.91±0.06) and the field test (r= 0.86±0.09). During non-steady state exercise using both arms and legs in a third experiment, contradictory results were found. For 11 of the 15 subjects who performed a field test consisting of various nursing tasks no significant relationship between HR and [Vdot]O2 was found (r= 0.42±0.16). All tasks required almost the same physiological strain, which induced a small range in data points. In a fourth experiment, the influence of a small data range on the HR-[Vdot]O2 relationship was investigated: five subjects performed a field test that involved both low and high physiological strain, non-steady state arm and leg exercise. Significant relationships were found for all subjects (r = 0.86±0.04). Although the r-values found in this study were less than under steady state conditions, it can be concluded that [Vdot]O2 may be estimated from individual HR-[Vdot]O2 regression lines during non-steady state exercise.

Oxygen tension and content in the regulation of limb blood flow.

During submaximal exercise, muscle blood flow increases when arterial oxygen content (CaO2) is reduced. The increase in blood flow is brought about by elevating cardiac output (CO) and enhancing leg vascular conductance. Conversely, increased CaO2 elicits lower limb blood flow (LBF) and CO. During maximal exercise, the influence of CaO2 on muscle blood flow is modulated depending on the amount of muscle mass recruited. When a small muscle mass is activated and the pumping capacity of the heart is not limited, changes in CaO2 barely influence the level of blood flow attained at peak exercise. However, when a large muscle mass is engaged in the exercise, as occurs for example during cycling and running, muscle blood flow is decreased if maximal CO is reduced, as happens during exercise in severe hypoxia. In contrast, maximal muscle blood flow and CO are maintained at peak exercise when CaO2 is increased. As such, exercise intensity, muscle mass and CaO2 appear to be the critical factors determining muscle blood flow during exercise.

Limiting factors for maximum oxygen uptake and determinants of endurance performance.

In the exercising human, maximal oxygen uptake (VO2max) is limited by the ability of the cardiorespiratory system to deliver oxygen to the exercising muscles. This is shown by three major lines of evidence: 1) when oxygen delivery is altered (by blood doping, hypoxia, or beta-blockade), VO2max changes accordingly; 2) the increase in VO2max with training results primarily from an increase in maximal cardiac output (not an increase in the a-v O2 difference); and 3) when a small muscle mass is overperfused during exercise, it has an extremely high capacity for consuming oxygen. Thus, O2 delivery, not skeletal muscle O2 extraction, is viewed as the primary limiting factor for VO2max in exercising humans. Metabolic adaptations in skeletal muscle are, however, critical for improving submaximal endurance performance. Endurance training causes an increase in mitochondrial enzyme activities, which improves performance by enhancing fat oxidation and decreasing lactic acid accumulation at a given VO2. VO2max is an important variable that sets the upper limit for endurance performance (an athlete cannot operate above 100% VO2max, for extended periods). Running economy and fractional utilization of VO2max also affect endurance performance. The speed at lactate threshold (LT) integrates all three of these variables and is the best physiological predictor of distance running performance.

Muscle growth, cell number, type and morphometry in single and twin fetal lambs during mid to late gestation

Muscle growth, myofibre number, type and morphometry were studied in large hindlimb muscles of single and twin fetal lambs during mid to late gestation. Placental insufficiency, evident by lower total placentome weight and number per fetus, resulted in reduced fetal weights from 100 to 140 days gestation in twins compared with singletons (at 140 days: 5016 +/- 108 g v. 5750 +/- 246 g, respectively; P<0.05). However, competition between littermates did not consistently reduce muscle mass (15-22%) until 140 days gestation. Apparent myofibre number increased with age, indicating that the full complement of myofibres in some large hindlimb muscles may be achieved during early postnatal life. Litter size did not impact on apparent myofibre number in the semitendinosus, plantaris or gastrocnemius muscles. However, a transient effect on myofibre number in the adductor femoris muscle was observed from 80-120 days gestation. The phenotypic maturation of myofibres was unaffected by increasing litter size. Smaller muscle mass in twins was associated with smaller myofibre cross-sectional area in the semitendinosus, adductor femoris and gastrocnemius muscles at 140 days gestation. A similar trend was observed for the plantaris muscle. These results indicate that while competition between littermates for nutrients in late gestation can impact on both fetal and muscle mass, the fetus has the capacity to buffer against the effects of restricted nutrient supply on myofibre hyperplasia and phenotypic maturation, but myofibre hypertrophy is compromised.

Effects of diet forage:concentrate ratio and metabolizable energy intake on visceral organ growth and in vitro oxidative capacity of gut tissues in sheep.

We used 28 crossbred wether lambs to determine the effects of dietary forage:concentrate ratio and metabolizable energy intake on visceral organ growth and oxidative capacity of gut tissues in lambs. Lambs were assigned randomly to a factorial arrangement of dietary treatments consisting of pelleted diets containing either 75% orchardgrass or 75% concentrate fed once daily at either .099 or .181 Mcal ME x (kg BW(.75))(-1) x d(-1). After a 52-d feeding period, lambs were slaughtered to obtain measurements of visceral organ mass and composition and oxidative capacity of isolated epithelial cells. Lamb performance, as measured by DMI, ADG, and efficiency of gain, was greater (P = .0001) for both diets at high ME intake. Likewise, lambs fed 75% concentrate gained faster and more (P < or = .01) efficiently than lambs fed 75% forage. Total digestive tract (TDT; includes rumen, reticulum, omasum, abomasum, and intestines) weight increased (P = .0001) with ME intake and was greater (P = .03) in lambs fed 75% forage than in those fed 75% concentrate. As a percentage of empty body weight (EBW), TDT weight increased with ME intake in lambs fed 75% forage, but it was unaffected by ME intake in lambs fed 75% concentrate (diet x intake, P = .03). Liver weight increased (P = .0001) with ME intake and was greater (P = .005) in lambs fed 75% concentrate vs 75% forage; however, liver weight as a percentage of EBW was increased (P = .0002) with ME intake but was unaffected by diet. Greater ME intake increased (P < or = .02) small intestinal (SI) epithelial and muscle mass of 15-cm sections, whereas jejunal epithelial mass was greater (P = .01) for lambs fed 75% forage vs 75% concentrate. Rumen epithelial concentrations of DNA and RNA increased (P < or = .02) with greater ME intake, whereas SI concentrations of DNA and RNA were largely unaffected by diet or ME intake. The activity of Na(+)-K(+)-ATPase increased in ileal epithelium (P < or = .02) with ME intake and concentrate in the diet, but activity in ruminal epithelium increased (P = .05) with concentrate. Total oxygen consumption by isolated ruminal and intestinal epithelial cells was unaffected by treatment. These data suggest that ME intake and level of dietary forage affect ruminal and intestinal growth via changes in cellular hyperplasia. Additionally, this study supports the concept that ME intake and diet composition alter gut energy expenditure, at least in part, through changes in mass rather than mass specific metabolism.

Ischemic muscle chemoreflex response elevates blood flow in nonischemic exercising human forearm muscle.

We tested the hypothesis that forearm blood flow (FBF) might be reduced during forearm exercise when a vasoconstrictor response was evoked by calf exercise during calf ischemia (CE + I). In nine healthy subjects, brachial artery FBF and finger-cuff mean arterial pressure (MAP) were measured beat by beat during rest and forearm exercise. CE + I initiated before 5 min of forearm exercise (condition A) increased MAP by 24% and reduced resting forearm vascular conductance (FVC) by 24% such that FBF remained at the same level as without CE + I (control, condition C). With the onset of forearm exercise, the difference in FVC between condition A and condition C was abolished; consequently, the FBF adaptation to exercise was greater after 3 min of exercise in condition A (247.0 +/- 14.8 ml/min) than in condition C (197.1 +/- 9.4 ml/min, P < 0. 05) because of the elevated MAP. Gradual stimulation of the chemoreflex by the addition of CE + I at 3 min of a 9-min bout of forearm exercise (condition B) did not affect FVC such that progressive elevations in MAP resulted in proportional increases in FBF. We concluded that chemoreflex-mediated increases in systemic sympathetic nervous activity appear to affect resting FVC. Evidence from this study suggests that local factors responsible for initiating and maintaining vasodilation during moderate, small-muscle mass exercise can quickly override this vasoconstrictor influence such that FBF is elevated during exercise in direct proportion to the elevation in MAP.

Evidence of skeletal muscle metabolic reserve during whole body exercise in patients with chronic obstructive pulmonary disease.

When freed from central cardiorespiratory limitations, healthy human skeletal muscle has exhibited a significant metabolic reserve. We studied the existence of this reserve in 10 severely compromised (FEV1 = 0.97 +/- SE 0.01) patients with chronic obstructive pulmonary disease (COPD). To manipulate O2 supply and O2 demand in locomotor and respiratory muscles, subjects performed both maximal conventional two-legged cycle ergometry (large muscle mass) and single-leg knee extensor exercise (KE, small muscle mass) while breathing room air (RA), 100% O2, and 79% helium + 21% O2 (HeO2). With each gas mixture, peak ventilation, peak heart rate, and perceived breathlessness were lower in KE than cycle exercise (p < 0. 05). Arterial O2 saturation and maximal work capacity increased in both exercise modalities while subjects breathed 100% O2 (work: +10% bike, +25% KE, p < 0.05). HeO2 increased maximal work capacity on the cycle (+14%, p < 0.05) but had no effect on KE. HeO2 resulted in the greatest maximum minute ventilation in both bike and KE (p < 0. 05) but had no effect on arterial O2 saturation. Thus, a skeletal muscle metabolic reserve in these patients with COPD is evidenced by: (1) greater muscle mass specific work in KE; (2) greater work rates with higher fraction of inspired oxygen (FIO2); (3) an even greater effect of FIO2 during KE (i.e., when the lungs are less challenged); and (4) the positive effect of HeO2 on bicycle work rate. This skeletal muscle metabolic reserve suggests that reduced whole body exercise capacity in COPD is the result of central restraints rather than peripheral skeletal muscle dysfunction, while the beneficial effect of 100% O2 (with no change in maximum ventilation) suggests that the respiratory system is not the sole constraint to oxygen consumption.

Gender Differences in the Oxygen Transport System During Maximal Exercise in Hypertensive Subjects

To analyze gender differences in the oxygen transport system at peak exercise with particular emphasis on the difference in systemic arteriovenous oxygen extraction and in mixed venous oxygen saturation. Cardiopulmonary graded exercise testing and hemodynamic assessment were performed on a cycle ergometer in 64 hypertensive patients (32 female and 32 male) varying in age from 23 to 64 years. Female and male patients were matched for age and BP. Peak oxygen uptake was significantly lower in women than in men, and when expressed in absolute units (L/min: -39%) and when normalized for body mass (mL/min/kg: -33%) or statistically adjusted for height and weight (-29%). This resulted essentially from a significantly lower cardiac output in women, both when expressed in absolute units and when adjusted for body size. At the peripheral level, female patients had a lower arteriovenous oxygen content difference at peak exercise, which resulted from a lower hemoglobin concentration and the inability to decrease mixed venous oxygen saturation to the same level as in men. The lower peak oxygen uptake of women results from both central and peripheral factors. The significantly higher value for mixed venous oxygen saturation, which contributes to the lower arteriovenous oxygen difference of women, could result from their smaller muscle mass, lower capillary density, and lower oxidative potential.

An unusual flexor hallucis longus muscle.

During the dissection of the posterior compartment of the left leg, an unusual flexor hallucis longus muscle of a fifty two years-old male cadaver was observed. On the medial side of the flexor hallucis longus, on its lower distal half, a prominent aponeurotic structure was observed. A small unusual muscle mass was attached to this aponeurotic structure. The muscular fibres of the unusual mass were arranged in form of bipennate muscle. It originated via a broad tendon from the muscular fibres of the tibialis posterior and the deep transverse fascia covering the same muscle. It inserted on the aponeurosis of the lower medial half of the flexor hallucis longus muscle. Having in mind the very different pathology in the region of the ankle and the foot, the significance of such a muscle mass could be of practical importance.

Skeletal muscle metabolism limits exercise capacity in patients with chronic heart failure.

Several studies have indicated that skeletal muscle is important in determining the exercise capacity of patients with chronic heart failure (CHF). However, this theory has been investigated only in experiments based on local exercise involving a small muscle mass. We investigated skeletal muscle metabolism during maximal systemic exercise to determine whether muscle metabolism limits exercise capacity in patients with CHF. We also studied the relationship between muscle metabolic abnormalities during local and systemic exercise. Skeletal muscle metabolism was measured during maximal systemic exercise on a bicycle ergometer by a combination of the metabolic freeze method and 31P magnetic resonance spectroscopy in 12 patients with CHF and 7 age- and size-matched normal subjects. We also evaluated skeletal muscle metabolism during local exercise while subjects performed unilateral plantar flexion. Muscle phosphocreatine (PCr) was nearly depleted during maximal systemic exercise in patients with CHF and normal subjects (12.5+/-0.04% and 12.3+/-0.07%, respectively, of initial level). PCr depletion occurred at a significantly lower peak oxygen uptake (peak VO2) in patients with CHF than in normal subjects (CHF, 20.2+/-3.0 versus normal, 31.8+/-3.7 mL . min-1 . kg-1, P<0. 0001). Muscle metabolic capacity, evaluated as the slope of PCr decrease in relation to increasing workload, was correlated with peak VO2 during maximal systemic exercise in patients with CHF (r=0.83, P<0.001). Muscle metabolic capacity during local exercise was impaired in patients with CHF and was correlated with capacity during systemic exercise (r=0.76, P<0.01) and with peak VO2 (r=0. 83, P<0.001). These results suggest that impaired muscle metabolism associated with early metabolic limitation determines exercise capacity during maximal systemic exercise in patients with CHF. There was a significant correlation between muscle metabolic capacity during systemic and local exercise in patients with CHF.

KINETICS OF OXYGEN UPTAKE AND MUSCLE PHOSPHATES DURING NORMOXIC AND HYPOXIC EXERCISE.

1065 The purpose of this study was to compare the kinetics of pulmonary oxygen uptake (VO2) and muscle phosphocreatine (PCr) metabolism during the transition to and recovery from, normoxic (NORM) and hypoxic (HYP) exercise. Six healthy, active men (27±2 yr) performed a series of constant load, plantar flexion exercise tests while breathing 21% and 12% O2. Throughout exercise, VO2 was measured breath-by-breath and PCr metabolism was monitored in the lateral gastroonemius using 31P magnetic resonance spectroscopy. At the on- and off-transient, the phase 2 time constant (τ) for VO2 was greater (p<0.05) in HYP (on, 23s; off, 30s) than NORM (on, 13s; off, 23s). HYP also resulted in a longer(p<0.05) τPCr (on, 43s; off, 33s) compared to NORM (on & off, 28s). The on-transient τVO2 was faster than τPCr, howeverτVO2 and τPCr were similar during in the off-transient. These data suggest that hypoxia slows the kinetics of both PCr and VO2 during the on- and off-transient. However the slower τPCr, compared toτVO2 during the on-transient suggests either that τPCr, andτVO2 are dissociated or more likely, that it was not possible to distinguish between phase 1 and phase 2 VO2 kinetics during light exercise with a small muscle mass.

Physiologic comparison of forward and reverse wheelchair propulsion

Objectives: Conventional wheelchair propulsion is physiologically demanding because of the small muscle mass that is used and the low mechanical efficiency of the movement. Previous research has suggested that a reverse wheeling technique might be more economical than conventional forward wheeling. The present study sought to compare the physiologic demands of forward and reverse wheeling techniques. Design: A repeated measures design was used to compare the dependent variables between forward and reverse wheeling techniques in the same subjects. Setting: Human exercise research laboratory. Participants: Ten able-bodied men. Intervention: Subjects completed graded, discontinuous exercise tests on a wheelchair ergometer, using both forward and reverse wheeling techniques. Main Outcome Measures: Oxygen uptake (V̇o 2), ventilation (V̇ E), and heart rate were measured during the last 30 seconds of each 3-minute exercise stage. Blood lactate concentration ([la]) and rating of perceived exertion (RPE) were determined immediately after each stage. Results: Repeated measures analysis of variance demonstrated that V̇o 2, V̇ E, heart rate, [la], and RPE were all significantly greater ( p < .05) with reverse wheeling compared with forward wheeling. Vo 2 values with reverse wheeling averaged 9% higher than forward wheeling at identical power outputs. Conclusions: Reverse wheelchair propulsion is physiologically more demanding than conventional forward wheelchair propulsion and does not appear to offer potential for improving the economy of wheelchair propulsion.