Reduction In Aerobic Capacity Research Articles

Cardiopulmonary Stress Testing in Children With Sickle Cell Disease Who are on Long-term Erythrocytapheresis

The purpose of the study was to assess the feasibility and safety of symptom-limited cardiopulmonary stress testing (CPST) in children with sickle cell disease (SCD), who are on long-term erythrocytapheresis. Maximal symptom-limited CPST was performed in 16 children with SCD who were maintained on long-term erythrocytapheresis and the exercise response in this patient cohort was compared with those of a healthy control population. All patients completed the CPST without any complications. Twelve patients with SCD had significant reduction in aerobic capacity [peak oxygen consumption (VO2) <80% predicted]. No patient demonstrated evidence of myocardial ischemia. In summary, symptom-limited CPST can be performed safely in a subgroup of children with SCD and can yield valuable clinical information.

Reduction in Aerobic Capacity and Cardiac Output in Diabetic Adolescents

Aerobic capacity is reduced in diabetic adults. Type 1 diabetic (T1D) adolescents also have reduced aerobic capacity; however it is not known whether recently diagnosed type 2 diabetic (T2D) adolescents have similarly impaired aerobic capacity. PURPOSE: To determine whether T2D and T1D adolescents have reduced aerobic capacity and whether stroke volume (SV) and heart rate (HR) response to exercise are impaired in diabetic adolescents. METHODS: Eight T2D, 10 non-diabetic obese (NDO), 11 T1D and 7 lean (L) female adolescents were recruited for this study. Baseline data included peak aerobic capacity (cycle ergometer) and a DEXA scan. On a separate day, cardiac output (CO) was determined at rest and during workloads eliciting 100(±5)and 120 (±5) beats per minute (bpm). RESUITS: Maximal O2 consumption (ml/kgFFM/min) and HR (bpm) were lower in the T2D vs. NDO, T1D and L groups (p< 0.05). Resting CO and SV indexed for fat free mass (COFFM and SVFFM) were lower in both diabetic and NDO groups compared to L group (p< 0.05). Exercise COFFM and SVFFM were lower during both workloads in the T1D and T2D vs. NDO and L groups (p< 0.05). Arterio-venous O2 difference was not different in any condition (p> 0.05). CONCLUSION: T2D adolescents have lower aerobic capacity than T1D and NDO adolescents even when indexed to fat free mass. However both T1D and newly diagnosed T2D adolescents have blunted stroke volume response to exercise.TableData are means ± standard deviation. B= p< 0.05 significantly ≠ between T2D and O, C= p< 0.05 significantly ≠ between T2D and L, D= p< 0.05 significantly ≠ between O and T1D, E= p< 0.05 significantly ≠ between O and L, F= p< 0.05 significantly ≠ between T1D and L.

Muscle blood flow and mitochondrial function: influence of aging.

Skeletal muscle mitochondrial capacity (mito), tissue blood flow (BF) capacity, and oxygen exchange capacity (e.g., DO2) appear to be well matched. The different skeletal muscle fiber types and muscle remodeled, due to inactivity (e.g., related to aging or disease) or exercise training, exhibit widely differing aerobic capacities (VO2max). Yet, there are remarkably coordinated alterations in these 3 parameters in each of these conditions. With such a balance, there is likely shared control among these parameters in limiting VO2max of muscle, although this is a matter of considerable debate. The reduction in aerobic capacity in elderly can be improved by submaximal aerobic exercise training; this is related to increases in muscle mitochondria concentration and capillarity, but probably not BF capacity, as this is limited by central cardiovascular function. Thus, exercise-induced biochemical adaptations and angiogenesis occur in the elderly. The increase in muscle capillarity likely contributes to the increased oxygen exchange capacity, typical of endurance type training. The increase in [mito] appears essential to realize the increased in muscle VO2max with training and amplifies the rate-limiting influence of the muscles oxygen exchange capacity. Further, vascular remodeling induced by exercise in the elderly could be effective at improving flow capacity, if limited by peripheral obstruction. Thus, the limits to aerobic function specific to aged muscle appear most influenced by inactivity, whereas central cardiovascular changes impact whole body performance. Some may consider the aged myocyte as a small, inactive, normal myocyte in need of activity!

Physiological basis of temperature-dependent biogeography: trade-offs in muscle design and performance in polar ectotherms

Polar, especially Antarctic, oceans host ectothermic fish and invertebrates characterized by low-to-moderate levels of motor activity; maximum performance is reduced compared with that in warmer habitats. The present review attempts to identify the trade-offs involved in adaptation to cold in the light of progress in the physiology of thermal tolerance. Recent evidence suggests that oxygen limitations and a decrease in aerobic scope are the first indications of tolerance limits at both low and high temperature extremes. The cold-induced reduction in aerobic capacity is compensated for at the cellular level by elevated mitochondrial densities, accompanied by molecular and membrane adjustments for the maintenance of muscle function. Particularly in the muscle of pelagic Antarctic fish, among notothenioids, the mitochondrial volume densities are among the highest known for vertebrates and are associated with cold compensation of aerobic metabolic pathways, a reduction in anaerobic scope, rapid recovery from exhaustive exercise and enhanced lipid stores as well as a preference for lipid catabolism characterized by high energy efficiency at high levels of ambient oxygen supply. Significant anaerobic capacity is still found at the very low end of the activity spectrum, e.g. among benthic eelpout (Zoarcideae). In contrast to the cold-adapted eurytherms of the Arctic, polar (especially Antarctic) stenotherms minimize standard metabolic rate and, as a precondition, the aerobic capacity per milligram of mitochondrial protein, thereby minimizing oxygen demand. Cost reductions are supported by the downregulation of the cost and flexibility of acid-base regulation. At maintained factorial scopes, the reduction in standard metabolic rate will cause net aerobic scope to be lower than in temperate species. Loss of contractile myofilaments and, thereby, force results from space constraints due to excessive mitochondrial proliferation. On a continuum between low and moderately high levels of muscular activity, polar fish have developed characteristics of aerobic metabolism equivalent to those of high-performance swimmers in warmer waters. However, they only reach low performance levels despite taking aerobic design to an extreme.

Age-related changes in growth hormone secretion: should the somatopause be treated?

Growth hormone (GH) secretion declines progressively with aging, and many age-related changes resemble those of the adult GH deficiency (GHD) syndrome, including a decrease in lean body mass; an increase in body fat, especially in the visceral/abdominal compartment; adverse changes in lipoproteins; and a reduction in aerobic capacity. The increase in central obesity can further inhibit GH secretion. GH replacement is effective in reversing many of these changes in adult GHD, and GH is now FDA approved for treatment of adults with documented GHD or hypopituitarism, although there is still only limited experience with its long-term benefits, side effects, and risks. This early experience with GHD has led to speculation that replacing GH or stimulating its secretion may also be beneficial in normal aging, and to widespread off-label use of GH in this context; however, there are still very few well controlled studies of the effects and side effects of GH or GH secretagogues in aging. All published studies are of 6 months or shorter treatment periods. From this limited experience there is a consensus that GH has effects on body composition, but reports disagree on effects on psychological or physical functional performance. Older adults are much more susceptible to the dose-related side effects of GH, including peripheral edema, carpal tunnel syndrome, and a variable decrease in insulin sensitivity; and it is not known whether chronic GH treatment affects the risk of malignancy or has other long-term risks. Thus while short-term results are somewhat encouraging, the evidence on risks and clinically pertinent benefits is still lacking to support the use of GH in normal aging outside of clinical studies. In evaluating patients with clinical features suggesting GHD, which can be quite nonspecific, it is important to assess the presence or absence of true GH deficiency by the context (pituitary disease or its treatment, childhood GHD) and by appropriate GH stimulation tests before considering GH replacement.

Response to Symptom-Limited Exercise in Patients With the Hepatopulmonary Syndrome

To study the response to symptom-limited exercise in patients with the hepatopulmonary syndrome (HPS). The response to maximal cardiopulmonary exercise (CPX) was studied in 5 patients with HPS and compared with 10 case control (normoxemic, NC) cirrhotics (matched for age, gender, etiology and severity of liver disease, tobacco use, and beta-blocker therapy) and 9 hypoxemic control cirrhotics (HC) without clinical evidence of HPS. Cardiopulmonary exercise physiology laboratory in a tertiary care referral center. Cirrhotics referred for CPX as part of their preliver transplantation evaluation. Standard pulmonary function tests and echocardiography were performed to assess resting pulmonary and cardiac function. Peak oxygen consumption (VO2), minute ventilation, arterial blood gases, and dead space (VD/VT) were determined during symptom-limited maximal CPX. Resting spirometry and lung volumes were similar between HPS and NC subjects, while HC subjects had restrictive physiology. Differences existed in diffusing capacity corrected for hemoglobin and alveolar volume percent predicted (HPS, 45+/-2 vs NC, 68+/-3, p<0.05; vs HC, 70+/-4, p<0.05), PaO2 (HPS, 70+/-5 mm Hg; HC, 79+/-3 mm Hg, vs NC, 102+/-3 mm Hg, p<0.05) and alveolar-arterial (A-a) O2 gradient (HPS, 42+/-8 mm Hg vs HC, 27+/-2 mm Hg, p<0.05; vs NC, 6+/-2 mm Hg, p<0.05). During CPX, HPS patients achieved a lower peak VO2 percent predicted (HPS, 55+/-6 vs NC, 73+/-3, p<0.05; vs HC, 71+/-5, p<0.05) and VO2 at the ventilatory threshold as percent predicted peak VO2 (HPS, 36+/-2 vs NC, 55+/-4, p<0.05; vs HC 55+/-5, p<0.05). While no differences existed in heart rate and breathing reserve, HPS patients had significantly lower PaO2 (HPS, 50+/-5 mm Hg vs NC, 97+/-4 mm Hg, p<0.05; vs HC, 87+/-6 mm Hg, p<0.05), wider A-a O2 gradient (HPS, 73+/-5 mm Hg vs NC, 13+/-3 mm Hg, p<0.05; vs HC, 31+/-5 mm Hg, p<0.05) and higher VD/VT (HPS, 0.36+/-.03 vs NC, 0.18+/-.02, p<0.05; vs HC, 0.28+/-.02, p<0.05) at peak exercise. For HPS patients, VO2 was negatively correlated with VD/VT (r2=0.9) and positively correlated with PaO2 (r2=0.41) at peak exercise. Patients with HPS demonstrate a severe reduction in aerobic capacity, beyond that found in cirrhotics without syndrome. The significant hypoxemia and elevated VD/VT at peak exercise suggest that an abnormal pulmonary circulation contributes to further exercise limitation in patients with HPS.

SEVERE MYOCARDIAL INFARCTION DIMINISHES AEROBIC CAPACITY OF RAT SKELETAL MUSCLE 364

Studies of heart failure in humans and rats have demonstrated that alterations in skeletal muscle metabolism and aerobic capacity occur. The purpose of this study was to determine whether myocardial infarction-induced alterations in skeletal muscle enzyme activities are generalized in muscles or are specific to muscles composed primarily of a given fiber type. The activity of several enzymes involved in glycolysis (phosphofructokinase [PFK] and lactate dehydrogenase [LDH]), terminal oxidation (citrate synthase [CS] and malate dehydrogenase [MDH]) and β-oxidation of fatty acids (3-hydroxyacyl CoA dehydrogenase [HADH]) were measured in soleus (S; type I fibers), plantaris (P; mixed fiber type), and the deep red (GR; type I and IIA fibers), middle (GM; mixed fiber type) and superficial white(GW; type IIB fibers) portions of gastrocnemius muscles from female Wistar rats. The animals were divided into three groups: shamoperated controls(n=13) and rats with moderate (45 ± 2%; n=10) and large (59 ± 4%; n=7) myocardial infarcts (MI). MI were surgically induced by ligating the left main coronary artery and after 2 months resulted in increases (P<0.05) in left ventricular end diastolic pressure (sham 5 ± 1 mmHg; moderate MI 11 ± 1; large MI 25 ± 1). Neither PFK nor LDH was different in either MI group compared to controls. Additionally, moderately sized MI induced little change in any of the enzyme activities. However, in rats with large MI, CS was lower in S (sham 24 ± 1μmol·min-1·g wet wt-1; large MI 18 ± 1), GR (sham 37 ± 2; large MI 31 ± 1) and GW (sham 8± 2; large MI 6 ± 1); MDH was lower in GR (sham 779± 2 μmol·min-1·g wet wt-1; large MI 656± 37) and GW (sham 210 ± 2; large MI 171 ± 4); and HADH was lower in P (sham 12 ± 1 μmol·min-1·g wet wt-1; large MI 9 ± 1) and GR (sham 17 ± 1; large MI 12 ± 1). These data indicate that reductions in aerobic capacity associated with heart failure occur in skeletal muscle regardless of fiber composition, and changes in enzyme activities appear to occur when severe heart failure is present.

Influence of simulated microgravity on cardiac output and blood flow distribution during exercise.

Rats exposed to simulated conditions of microgravity by head-down suspension (HDS) exhibit reductions in aerobic capacity. This may be due to an impaired ability to augment cardiac output and to redistribute blood flow during exercise. The purpose of this investigation was to measure cardiac output and blood flow distribution in rats that were exposed to 14 days of HDS or cage control conditions. Measurements were obtained at rest and during light-intensity (15 m/min) and heavy-intensity (25 m/min; 10% grade) treadmill exercise. Cardiac output was similar in HDS and cage control rats at rest and light exercise but was significantly lower in HDS rats (-33%) during heavy exercise. Soleus muscle blood flow (ml/min) was lower at rest and during exercise in HDS rats; however, when expressed relative to muscle mass (ml.min-1.100 g-1), soleus blood flow was lower only during light exercise. Plantaris muscle blood flow was lower in HDS rats during heavy exercise. Blood flow to the ankle flexor, knee extensor, and knee flexor muscles was not altered by HDS. Blood flow to the spleen and kidney was significantly higher in HDS rats. It was concluded that the reduction in aerobic capacity associated with HDS is due in part to an impaired ability to augment cardiac output during exercise.

Left Ventricular Diastolic Filling Performance in Older Male Athletes

To determine whether older men who have undergone intensive endurance training over many years demonstrate less age-associated impairment of early diastolic left ventricular (LV) filling performance than their sedentary peers. Cross-sectional prospective study. Community-dwelling research volunteers. Sixteen older competitive male endurance athletes aged 52 through 76 years and 17 young (< 40 years) and 23 older (52 through 76 years) sedentary control subjects from the Baltimore Longitudinal Study of Aging. All subjects underwent resting Doppler echocardiography and determination of maximal aerobic capacity (VO2max) during graded treadmill exercise. Doppler echocardiographic studies were interpreted without knowledge of the subject's age or exercise habits. Doppler-derived measures of LV diastolic filling performance: peak early (E) filling velocity, peak late (A) filling velocity, ratio of peak E to peak A velocities (E/A), and atrial filling fraction. Older athletes demonstrated higher VO2max (47 +/- 6 mL/kg per minute [mean +/- SD]) than either the young controls (41 +/- 7 mL/kg per minute) or older controls (30 +/- 7 mL/kg per minute) (P < .05) as evidence of their superior conditioning status. However, peak E diastolic LV filling velocity was higher in young controls (79 +/- 17 cm/s) than in older athletes (56 +/- 15 cm/s) or older controls (68 +/- 18 cm/s) (P < .001). This age difference persisted after normalizing peak E velocity for mitral stroke volume. Peak E/A ratio and atrial filling fraction were also similar in older athletes (1.2 +/- 0.5 and 0.41 +/- 0.1, respectively) and older controls (1.1 +/- 0.4 and 0.41 +/- 0.1, respectively), and differed significantly from corresponding values of 1.7 +/- 0.4 and 0.33 +/- 0.1 in young controls (P < .001 and P < .05, respectively). By multiple regression analysis, age but not treadmill VO2max was a significant predictor of peak E velocity, peak A velocity, peak E/A ratio, and atrial filling fraction. Older men with a long history of intensive endurance training demonstrate impaired early diastolic LV filling similar to that of their sedentary peers. Thus, impairment of early diastolic filling appears to be intrinsic to normative aging and not secondary to the reduction in aerobic capacity that accompanies the aging process.

Effects of explosive type strength training on physical performance characteristics in cross-country skiers

To investigate the effects of a combination of simultaneous strength and endurance training on selected neuromuscular and aerobic performance characteristics seven male cross-country skiers underwent training for a period of 6 weeks. The experimental group trained 6-9 times per week with a programme consisting of 34% explosive type strength training and 66% endurance training during the first 3 weeks of the experiment and 42% and 58% respectively during the last 3 weeks of the experiment. The total volume of training of the control group (eight skiers) was of the same magnitude but consisted of 85% pure endurance training and 15% endurance type strength training. The experimental training regime resulted in specific changes in neuromuscular performance. This was demonstrated by improvements (P less than 0.01) in the maximal heights of rise of the centre of gravity in the squat and countermovement jumps. A significant decrease (P less than 0.05) took place also in the time of rapid isometric force production during experimental training, while no changes occurred in the maximal force of the trained muscles. Aerobic performance characteristics of the experimental group did not change during the experimental training period. No significant changes occurred in neuromuscular or aerobic performance characteristics in the control group. These findings indicated that training-induced improvements in explosive force production may not be fully inhibited by this kind of aerobic training. They also suggested that endurance athletes could undertake explosive type strength training programmes without a concomitant reduction in aerobic capacity, if the overall loading of training were within predefined limits.

Metabolic evaluation of obese and nonobese siblings

To test the hypotheses that obese adolescents have a lower resting metabolic rate and less aerobic endurance than their nonobese siblings. Case-referent study of obese and nonobese siblings from the same kindred. Tertiary referral center. Telephone screening of community volunteers resulted in a consecutive sample of 16 kindreds. Obese and nonobese siblings were similar in age, height, and pubertal status. Significantly more female subjects were in the obese group (p less than 0.01). Body composition studies revealed that the obese siblings had higher body fat (p less than 0.001) but that fat-free mass was similar to that of the lean siblings. Resting metabolic rates determined by indirect calorimetry for the obese and nonobese pairs did not differ. Although the obese siblings appeared less fit when maximal oxygen consumption was measured in relation to total weight, maximal oxygen consumption did not differ when values were standardized for fat-free mass. The obese adolescents did not have a reduced resting metabolic rate. As in adults, the relationship between resting metabolic rate and fat-free mass was similar for obese and nonobese children and adolescents. Any decreased sport participation by the obese siblings was not due to inherent reductions in aerobic capacity.

Exercise responses in females with anorexia nervosa

Exercise responses were evaluated in 42 primary anorexic females (Pri-AN; mean age 18.8 years) and 33 bulimic females (Bul-AN; mean age 19.7 years) and compared with 14 healthy unconditioned lean females (Lean Control; mean age 19.6 years). All subjects performed isometric handgrip at 50% of maximum voluntary contraction (MVC) for 90 seconds and treadmill exercise to subjective exhaustion (Balke Protocol). Resting heart rate (HR) and blood pressure (BP) were not different in the three groups. Maximal grip strength and 90 second isometric handgrip systolic blood pressure (SBP) was significantly lower (p <.05) in Pri-AN compared with Bul-AN and Lean Controls. With treadmill exercise, maximal HR and BP were similar for all groups. However, estimated treadmill work capacity (METs) for Pri-AN (10.7 ± 3) and Bul-AN (10 ± 8.3) was significantly lower (p <.05) than lean Control subjects (12.3 ± 3). There was a positive correlation between maximal SBP and body weight (wt), percent body fat (% fat) and lean body mass (LBM). These findings indicate that Pri-AN and Bul-AN are associated with a substantial reduction in aerobic capacity. The attenuated BP response to exercise seen in both anorexia groups appears to be a general function of tissue mass and may be an appropriate adaptation to weight loss.

Distribution of hemoglobin and functional consequences of anemia in adult males at high altitude

In order to assess better the normal hemoglobin (Hb) range among adult males at high altitude, a hematological survey was completed in La Paz, Bolivia (3700 m). Two statistical methodologies were utilized to identify the anemic and polycythemic contributions to the Hb distribution of normal healthy men (n = 526). The Hb of normal men has a Gaussian distribution with mean and SD of 18.8 +/- 1.4 g/dl. Cutoff levels of 15.8 and 22.0 g/dl Hb were selected to identify the anemic and polycythemic subpopulations. Iron status in this high altitude population is similar to that of low altitude populations, and iron deficiency is the cause of most anemia found. An exercise test on a subsample of 56 men was utilized to validate the anemia cutoff level. Anemics as identified by the 15.8 g/dl Hb level showed a significant reduction in aerobic capacity as measured by PWC150 and estimated VO2max.