A Detailed Analysis of Cardiac Rehabilitation on 180-Day All-Cause Hospital Readmission and Mortality

PURPOSE

Cardiac rehabilitation (CR) is endorsed for coronary artery disease (CAD), but studies report inconsistent findings regarding efficacy. The objective of this study was to determine whether confounding factors, potentially contributing to these heterogeneous findings, impact the effect of CR on all-cause readmission and mortality.

METHODS

Patients (n = 2641) with CAD, CR eligible, and physically able were identified. Electronic medical records were inspected individually for each patient to extract demographic, clinical characteristic, readmission, and mortality information. Patients (n = 214) attended ≥1 CR session (CR group). Survival was considered free from: all-cause readmission; or composite outcome of all-cause readmission or death. Cox proportional hazards models, adjusting for demographics, comorbidities, and discharge criteria, were used to determine HR with 95% CI and to compare 180-d survival rates between the CR and no-CR groups.

RESULTS

During 180 d of follow-up, 12.1% and 18.7% of the CR and non-CR patients were readmitted to the hospital. There was one death (0.5%) in the CR group, while 98 deaths (4.0%) occurred in the non-CR group. After adjustment for age, sex, race, depression, anxiety, dyslipidemia, hypertension, obesity, smoking, type 2 diabetes, and discharge criteria, the final model revealed a significant 42.7% reduction in readmission or mortality risk for patients who attended CR (HR = 0.57: 95% CI, 0.33-0.98; P = .043).

CONCLUSIONS

Regardless of demographic characteristics, comorbidities, and cardiovascular discharge criteria, the risk of 180-d all-cause readmission or death was markedly decreased in patients who attended CR compared with those who did not.

Cardiopulmonary Exercise Testing in the Coronavirus Disease - 2019 Era: Safety and Protocol Considerations

ABSTRACT

Cardiopulmonary exercise testing (CPX) is a valuable tool in both clinical practice and research settings. Therefore, it is advantageous for human performance laboratories to continue operating during the coronavirus disease 2019 (COVID-19) pandemic. All institutions should adhere to general COVID-19 guidelines provided by the Centers for Disease Control. Because of the testing environment, CPX laboratories must consider additional precautionary safety measures. This article provides recommendations for modifying the CPX protocol to ensure safety for all stakeholders during the pandemic. These modifications are universal across all populations, types of institutions and testing modalities. Preliminary measures include careful review of federal, local, and institutional mandates. The description outlines how to evaluate a testing environment and alter workflow. Guidelines are provided on what specific personal protective equipment should be acquired; as well as necessary actions before, during, and after the CPX test. These precautions will limit the possibility of both clients and staff from contracting or spreading the disease while maintaining testing volume in the laboratory.

Aerobic Versus Resistance Training Effects on Ventricular-Arterial Coupling and Vascular Function in the STRRIDE-AT/RT Trial

Background: The goal was studying the differential effects of aerobic training (AT) vs. resistance training (RT) on cardiac and peripheral arterial capacity on cardiopulmonary (CP) and peripheral vascular (PV) function in sedentary and obese adults.

Methods: In a prospective randomized controlled trial, we studied the effects of 6 months of AT vs. RT in 21 subjects. Testing included cardiac and vascular ultrasoundography and serial CP for ventricular-arterial coupling (Ees/Ea), strain-based variables, brachial artery flow-mediated dilation (BAFMD), and peak VO₂ (pVO_2; mL/kg/min) and peak O₂-pulse (O₂p; mL/beat).

Results: Within the AT group (n = 11), there were significant increases in rVO₂ of 4.2 mL/kg/min (SD 0.93) (p = 0.001); O₂p of 1.9 mL/beat (SD 1.3) (p = 0.008) and the brachial artery post-hyperemia peak diameter 0.18 mm (SD 0.08) (p = 0.05). Within the RT group (n = 10) there was a significant increase in left ventricular end diastolic volume 7.0 mL (SD 9.8; p = 0.05) and percent flow-mediated dilation (1.8%) (SD 0.47) (p = 0.004). Comparing the AT and RT groups, post exercise, rVO₂ 2.97, (SD 1.22), (p = 0.03), O₂p 0.01 (SD 1.3), (p = 0.01), peak hyperemic blood flow volume (1.77 mL) (SD 140.69) (p = 0.009), were higher in AT, but LVEDP 115 mL (SD 7.0) (p = 0.05) and Ees/Ea 0.68 mmHg/ml (SD 0.60) p = 0.03 were higher in RT.

Discussion: The differential effects of AT and RT in this hypothesis generating study have important implications for exercise modality and clinical endpoints.

Skeletal muscle capillary density is related to anaerobic threshold and claudication in peripheral artery disease

Peripheral artery disease (PAD) is characterized by impaired blood flow to the lower extremities, causing claudication and exercise intolerance. Exercise intolerance may result from reduced skeletal muscle capillary density and impaired muscle oxygen delivery. This cross-sectional study tested the hypothesis that capillary density is related to claudication times and anaerobic threshold (AT) in patients with PAD. A total of 37 patients with PAD and 29 control subjects performed cardiopulmonary exercise testing on a treadmill for AT and gastrocnemius muscle biopsies. Skeletal muscle capillary density was measured using immunofluorescence staining. PAD had decreased capillary density (278 ± 87 vs 331 ± 86 endothelial cells/mm², p = 0.05), peak VO₂ (15.7 ± 3.9 vs 24.3 ± 5.2 mL/kg/min, p ⩽ 0.001), and VO₂ at AT (11.5 ± 2.6 vs 16.1 ± 2.8 mL/kg/min, p ⩽ 0.001) compared to control subjects. In patients with PAD, but not control subjects, capillary density was related to VO₂ at AT (r = 0.343; p = 0.038), time to AT (r = 0.381; p = 0.020), and time after AT to test termination (r = 0.610; p ⩽ 0.001). Capillary density was also related to time to claudication (r = 0.332; p = 0.038) and time after claudication to test termination (r = 0.584; p ⩽ 0.001). In conclusion, relationships between capillary density, AT, and claudication symptoms indicate that, in PAD, exercise limitations are likely partially dependent on limited skeletal muscle capillary density and oxidative metabolism.

Effects of a 12-Week mHealth Program on FunctionalCapacity and Physical Activity in Patients With PeripheralArtery Disease

Supervised exercise is beneficial for peripheral artery disease (PAD) patients limited by intermittent claudication (IC). However, supervised exercise for PAD remains widely underutilized. Mobile health (mHealth) provides an intermediate solution between supervised and independent home-based exercise. The purpose of this study was to determine the effects on functional capacity and physical activity patterns of a 12-week mHealth program in PAD patients with IC. Twenty patients were randomized into usual care or a 12-week mHealth intervention consisting of patient education, smartphones, and physical activity trackers. Patient education was disseminated through smartphone and a daily exercise prescription was given based on steps per day. Primary outcomes were 12-week changes in peak VO₂ and claudication onset time; and changes in physical activity measured by steps per/day and minutes of exercise per/week. mHealth patients significantly increased peak VO₂ from 15.2 ± 4.3 to 18.0 ± 4.8 ml/kg/min (20.3 ± 26.4%; p ≤0.05), while usual care did not change from 14.3 ± 5.4 to 14.5 ± 5.7 ml/kg/min (1.0 ± 6.9%; NS). Comparison of these changes resulted in a significant difference between groups (p ≤0.05) for peak VO₂. Claudication onset time significantly increased in mHealth (320 ± 226 to 525 ± 252 seconds; ≤ 0.05), while usual care demonstrated a worsening (252 ± 256 to 231 ± 196 seconds; NS). The comparison of these group changes resulted in a significant difference (p ≤0.05). Neither steps per day or minutes of activity reached significant differences between groups. In conclusion, a 12-week mHealth program in PAD patients with IC can improve peak VO₂ and claudication onset time; and mHealth interventions represent a promising alternative therapy for those patients who cannot participate in supervised exercise.

Effects of a 12-week mHealth program on peak VO2 and physical activity patterns after completing cardiac rehabilitation: A randomized controlled trial

BACKGROUND

Site-based cardiac rehabilitation (CR) provides supervised exercise, education and motivation for patients. Graduates of CR have improved exercise tolerance. However, when participation in CR ceases, adherence to regular physical activity often declines, consequently leading to worsening risk factors and clinical events. Therefore, the purpose of this pilot study was to evaluate if a mHealth program could sustain the fitness and physical activity levels gained during CR.

METHODS AND RESULTS

A 12-week mHealth program was implemented using physical activity trackers and health coaching. Twenty-five patients were randomized into mHealth or usual care after completing CR. The combination of a 4.7±13.8% increase in the mHealth and a 8.5±11.5% decrease in the usual care group resulted in a difference between groups (P≤.05) for absolute peak VO₂. Usual care decreased the amount of moderate-low physical activity minutes per week (117±78 vs 50±53; P<.05) as well as moderate-high (111±87 vs 65±64; P<.05). mHealth increased moderate-high physical activity (138±113 vs 159±156; NS). The divergent changes between mHealth and usual care in moderate-high physical activity minutes/week resulted in a difference between groups (21±103 vs - 46±36; P<.05).

CONCLUSIONS

A 12-week mHealth program of physical activity trackers and health coaching following CR graduation can sustain the gains in peak VO₂ and physical activity achieved by site-based CR.

Diabetes status differentiates endothelial function and plasma nitrite response to exercise stress in peripheral arterial disease following supervised training

AIMS

To determine if type 2 diabetes mellitus (T2D) differentiates endothelial function and plasma nitrite response (a marker of nitric oxide bioavailability) during exercise in peripheral arterial disease (PAD) subjects prior to and following 3 months supervised exercise training (SET).

METHODS

In subjects with T2D+PAD (n = 13) and PAD-only (n = 14), endothelial function was measured using brachial artery flow-mediated dilation. On a separate day, venous blood draws were performed at rest and 10 min following a symptom-limited graded treadmill test (SL-GXT). Plasma samples were snap-frozen for analysis of nitrite by reductive chemiluminescence. All testing was repeated following 3 months of SET.

RESULTS

Prior to training both groups demonstrated endothelial dysfunction, which was correlated with a net decrease in plasma nitrite following a SL-GXT (p ≤ 0.05). Following SET, the PAD-only group demonstrated an improvement in endothelial function (p ≤ 0.05) and COT (p ≤ 0.05), which was related to a net increase in plasma nitrite following the SL-GXT (both p ≤ 0.05). The T2D+PAD group had none of these increases.

CONCLUSIONS

T2D in the presence of PAD attenuated improvements in endothelial function, net plasma nitrite, and COT following SET. This suggests that T2D maybe associated with an inability to endogenously increase vascular NO bioavailability to SET.

Alteration in angiogenic and anti-angiogenic forms of vascular endothelial growth factor-A in skeletal muscle of patients with intermittent claudication following exercise training

The aims of this study were twofold: (1) to identify whether peripheral artery disease (PAD) patients had increased muscle concentration of angiogenic VEGF-A, anti-angiogenic VEGF₁₆₅b or VEGF receptor 1 (VEGF-R1) when compared with control subjects, and (2) to evaluate whether exercise training in PAD patients was associated with changes in muscle concentration of VEGF-A, VEGF₁₆₅b or VEGF-R1. At baseline, 22 PAD and 30 control subjects underwent gastrocnemius muscle biopsy. Twelve PAD patients were treated with supervised exercise training (SET) and underwent muscle biopsy after 3 weeks and 12 weeks of training and had sufficient tissue to measure VEGF-A, VEGF₁₆₅b and VEGF-R1 concentrations in skeletal muscle lysates by ELISA. Muscle concentrations of VEGF-A and VEGF₁₆₅b were similar in PAD patients versus controls at baseline. At both time points after the start of SET, VEGF-A levels decreased and there was a trend towards increased VEGF₁₆₅b concentrations. At baseline, VEGF-R1 concentrations were lower in PAD patients when compared with controls but did not change after SET. Skeletal muscle concentrations of VEGF-A are not different in PAD patients when compared with controls at baseline. SET is associated with a significant reduction in VEGF-A levels and a trend towards increased VEGF₁₆₅b levels. These somewhat unexpected findings suggest that further investigation into the mechanism of vascular responses to exercise training in PAD patients is warranted.

Exercise dose response in muscle

Exercise increases peak VO2 partially through muscle adaptations. However, understanding muscle adaptations related to exercise dose is incomplete. This study investigated exercise training dose on capillaries per fiber and capillaries per area; and citrate synthase from vastus lateralis and related both to changes in peak VO2. This randomized trial compared 3 exercise doses: low amount-moderate intensity (n=40), low amount-high intensity (n=47), high amount-high intensity (n=41), and a control group (n=35). Both measures of capillary supply increased in all exercise groups (p<0.05). Low amount-high intensity and high amount-high intensity improved citrate synthase (p<0.05) and the low amount-moderate intensity citrate synthase approached significance (p=0.059). Muscle improvements were only related to improvements in peak VO2 in high amount-high intensity (citrate synthase, r=0.304; capillaries:fiber, r= - 0.318; p<0.05 and capillaries/mm2 r= - 0.310, p<0.05). These data suggest muscle adaptations occur following both low and high exercise doses, but are only related to improved peak VO2 following high amount-high intensity training.

Angiogenesis in skeletal muscle precede improvements in peak oxygen uptake in peripheral artery disease patients

OBJECTIVE

Peripheral artery disease (PAD) is characterized by impaired blood flow to the lower extremities, causing claudication and exercise intolerance. The mechanism(s) by which exercise training improves functional capacity is not understood. This study tested the hypothesis that in PAD patients who undergo supervised exercise training, increases in capillary density (CD) in calf muscle take place before improvements in peak oxygen uptake (VO(2)).

METHODS AND RESULTS

Thirty-five PAD patients were randomly assigned to 12 weeks of directly supervised or home-based exercise training. Peak VO(2) testing and gastrocnemius muscle biopsies were performed at baseline and after training. CD (endothelial cells/mm(2)) was measured using immunofluorescence staining. After 3 weeks of directly supervised training, patients had an increase in CD (216±66 versus 284±77, P<0.01) but no increase in peak VO(2). However, after 12 weeks, peak VO(2) increased (15.3±2.8 versus 16.8±3.8, P<0.01), whereas in muscle, CD remained increased over baseline, but there were no changes in markers of oxidative capacity. Within subjects, CD was related to peak VO(2) before and after directly supervised training.

CONCLUSION

Changes in CD in ischemic muscle with training may modulate the response to training, and those changes precede the increase in VO(2).

Chronic heart failure and exercise intolerance: the hemodynamic paradox

Heart failure represents a major source of morbidity and mortality in industrialized nations. As the leading hospital discharge diagnosis in the United States in patients over the age of 65, it is also associated with substantial economic costs. While the acute symptoms of volume overload frequently precipitate inpatient admission, it is the symptoms of chronic heart failure, including fatigue, exercise intolerance and exertional dyspnea, that impact quality of life. Over the last two decades, research into the enzymatic, histologic and neurohumoral alterations seen with heart failure have revealed that hemodynamic derangements do not necessarily correlate with symptoms. This “hemodynamic paradox” is explained by alterations in the skeletal musculature that occur in response to hemodynamic derangements. Importantly, gender specific effects appear to modify both disease pathophysiology and response to therapy. The following review will discuss our current understanding of the systemic effects of heart failure before examining how exercise training and cardiac resynchronization therapy may impact disease course.

Relationship between leg muscle capillary density and peak hyperemic blood flow with endurance capacity in peripheral artery disease

The aim of this study was to determine if skeletal muscle capillary density is lower in patients with peripheral artery disease (PAD) and if capillary density relates to functional limitations. PAD patients with intermittent claudication (IC) have a decreased exercise tolerance due to exercise-induced muscle ischemia. Despite the apparent role diminished arterial flow has in this population, the degree of walking pain and functional limitation is not entirely explained by altered hemodynamics of the affected limbs. We hypothesized that skeletal muscle capillary density is lower in PAD and is related to the functional impairment observed in this population. Sixty-four patients with PAD and 56 controls underwent cardiopulmonary exercise testing and a gastrocnemius muscle biopsy. A subset of these patients (48 PAD and 47 controls) underwent peak hyperemic flow testing via plethysmography. Capillary density in PAD patients was lower compared with controls (P < 0.001). After adjustment for several baseline demographic imbalances the model relating capillary density to peak oxygen consumption (Vo(2)) remained significant (P < 0.001). In PAD subjects, capillary density correlated with peak Vo(2), peak walking time (PWT), and claudication onset time (COT). Peak hyperemic blood flow related to peak Vo(2) in both PAD and control subjects. PAD is associated with lower capillary density, and capillary density is related to the functional impairment as defined by a reduced peak Vo(2), PWT, and COT. These findings suggest that alterations in microcirculation may contribute to functional impairment capacity in PAD.

Plasma nitrite flux predicts exercise performance in peripheral arterial disease after 3months of exercise training

Plasma nitrite is a major oxidation product of nitric oxide. It has also recently been suggested to perform an endocrine-like function as a nitric oxide donor in hypoxic tissues, allowing vasodilation. Exercise performance is limited in peripheral arterial disease because of an inadequate blood supply to working tissues. We hypothesized that exercise training in peripheral arterial disease subjects will improve "plasma nitrite flux" and endothelial function, to accompany increased exercise performance. Peripheral arterial disease subjects were tested at baseline and after 3 months supervised or home exercise training. Venous blood (arm) was drawn at rest and 10 min after a maximal graded treadmill test. Samples were added to heparin and centrifuged and plasma was snap-frozen for analysis by reductive chemiluminescence. Brachial artery endothelial function was measured in response to a hyperemic stimulus (flow-mediated dilation). At 3 months the peripheral arterial disease-supervised exercise group showed increases in claudication onset pain time (+138 s, p< or =0.05), peak walking time (+260 s, p< or =0.01), VO(2peak) (1.3 ml/kg/min, p< or =0.05), brachial artery flow-mediated dilation (+2%, p< or =0.05), and plasma nitrite flux (+33% p< or =0.05). There were no changes in the peripheral arterial disease-home exercise group. The change in plasma nitrite flux predicted the change in claudication onset pain (r(2)=0.59, p< or =0.01). These findings suggest that changes in plasma nitrite are related to endothelial function and predict exercise performance in peripheral arterial disease.

Plasma nitrite response and arterial reactivity differentiate vascular health and performance

NO is crucial for endothelial function and vascular health. Plasma nitrite (NO(2)(-)) is the main oxidation product of NO and has been shown to reflect changes in eNOS activity. We hypothesized that plasma NO(2)(-) response to physical exercise stress along with physiological endothelial function would be reduced with increasing severity of vascular disease. Subject groups were: (a) risk factors but no vascular disease (RF); (b) Type 2 diabetes with no vascular disease (DM); (c) diagnosed peripheral arterial disease (PAD); and (d) DM+PAD. Venous blood was drawn at rest and 10min following maximal exercise. Plasma samples were analyzed by reductive chemiluminescence. Brachial diameters were imaged prior to, during and following 5min of forearm occlusion (BAFMD). There were no differences in resting plasma NO(2)(-) or BA diameters between groups. The PAD groups had lower age adjusted BAFMD responses (p0.05). Within group analysis revealed an increase in NO(2)(-) in the RF group (+39.3%), no change in the DM (-15.51%), and a decrease in the PAD (-44.20%) and PAD+DM (-39.95%). This was maintained after adjusting for age and VO(2peak) (p0.05). DeltaNO(2)(-) and BAFMD were the strongest independent predictors of VO(2peak) in multivariate linear regression. These findings suggest DeltaNO(2)(-) discriminates severity of cardiovascular disease risk, is related to endothelial function and predicts exercise capacity.

Effect of exercise intensity and volume on persistence of insulin sensitivity during training cessation

The purpose of this study was to determine whether exercise prescriptions differing in volume or intensity also differ in their ability to retain insulin sensitivity during an ensuing period of training cessation. Sedentary, overweight/obese subjects were assigned to one of three 8-mo exercise programs: 1) low volume/moderate intensity [equivalent of approximately 12 miles/wk, 1,200 kcal/wk at 40-55% peak O(2) consumption (Vo(2peak)), 200 min exercise/wk], 2) low volume/vigorous intensity ( approximately 12 miles/wk, 1,200 kcal/wk at 65-80% Vo(2peak), 125 min/wk), and 3) high volume/vigorous intensity ( approximately 20 miles/wk, 2,000 kcal/wk at 65-80% Vo(2peak), 200 min/wk). Insulin sensitivity (intravenous glucose tolerance test, S(I)) was measured when subjects were sedentary and at 16-24 h and 15 days after the final training bout. S(I) increased with training compared with the sedentary condition (P < or = 0.05) at 16-24 h with all of the exercise prescriptions. S(I) decreased to sedentary, pretraining values after 15 days of training cessation in the low-volume/vigorous-intensity group. In contrast, at 15 days S(I) was significantly elevated compared with sedentary (P < or = 0.05) in the prescriptions utilizing 200 min/wk (low volume/moderate intensity, high volume/vigorous intensity). In the high-volume/vigorous-intensity group, indexes of muscle mitochondrial density followed a pattern paralleling insulin action by being elevated at 15 days compared with pretraining; this trend was not evident in the low-volume/moderate-intensity group. These findings suggest that in overweight/obese subjects a relatively chronic persistence of enhanced insulin action may be obtained with endurance-oriented exercise training; this persistence, however, is dependent on the characteristics of the exercise training performed.

A sex-specific relationship between capillary density and anaerobic threshold

Although both capillary density and peak oxygen consumption (Vo(2)) improve with exercise training, it is difficult to find a relationship between these two measures. It has been suggested that peak Vo(2) may be more related to central hemodynamics than to the oxidative potential of skeletal muscle, which may account for this observation. We hypothesized that change in a measure of submaximal performance, anaerobic threshold, might be related to change in skeletal muscle capillary density, a marker of oxidative potential in muscle, with training. Due to baseline differences among these variables, we also hypothesized that relationships might be sex specific. A group of 21 subjects completed an inactive control period, whereas 28 subjects (17 men and 11 women) participated in a 6-mo high-intensity exercise program. All subjects were sedentary, overweight, and dyslipidemic. Potential relationships were assessed between change in capillary density with both change in Vo(2) at peak and at anaerobic threshold with exercise training. All variables and relationships were assessed for sex-specific effects. Change in peak Vo(2) was not related to change in capillary density after exercise training in either sex. Men had a positive correlation between change in Vo(2) at anaerobic threshold and change in capillary density with exercise training (r = 0.635; P < 0.01), whereas women had an inverse relationship (r = -0.636; P < 0.05) between the change in these variables. These findings suggest that, although enhanced capillary density is associated with training-induced improvements in submaximal performance in men, this relationship is different in women.

Sex-specific alterations in mRNA level of key lipid metabolism enzymes in skeletal muscle of overweight and obese subjects following endurance exercise

Endurance exercise (EE) leads to beneficial alterations in skeletal muscle lipid metabolism in overweight and obese individuals; however, the mechanisms of these improvements are poorly understood. The primary goal of the current investigation was to test the hypothesis that long-term EE training (6 mo) leads to alterations in the mRNA abundance of key lipid metabolism enzymes in skeletal muscle of overweight and obese middle-aged women and men. A secondary aim of this study was to investigate the hypothesis that exercise-mediated adaptations in mRNA levels differ between women and men. The mRNA abundance of representative lipogenic and lipolytic genes from major lipid metabolism pathways, as well as representative lipogenic and lipolytic transcription factors, were determined by real-time PCR from skeletal muscle biopsies collected before and approximately 24 h after the final bout of 6 mo of EE. Six months of EE led to increases in muscle lipoprotein lipase, peroxisome proliferator-activated receptor-gamma coactivator-1alpha, carnitine palmitoyltransferase-1 beta, diacylglycerol acyltransferase-1, and acid ceramidase mRNA in women, but not men. In contrast, in men, EE led to reductions in the mRNA content of the lipogenic factors sterol regulatory element binding protein-1c and serine palmitoyl transferase. These data suggest that EE-mediated alterations in the abundance of the lipid metabolism genes studied here are fundamentally different between overweight and obese middle-aged women and men. Future studies should determine whether these adaptations in mRNA levels translate into changes in protein function.

Plasma levels of soluble Tie2 and vascular endothelial growth factor distinguish critical limb ischemia from intermittent claudication in patients with peripheral arterial disease

OBJECTIVES

Our purpose was to determine whether factors that regulate angiogenesis are altered in peripheral arterial disease (PAD) and whether these factors are associated with the severity of PAD.

BACKGROUND

Alterations in angiogenic growth factors occur in cardiovascular disease (CVD), but whether these factors are altered in PAD or correlate with disease severity is unknown.

METHODS

Plasma was collected from patients with PAD (n = 46) and healthy control subjects (n = 23). Peripheral arterial disease patients included those with intermittent claudication (IC) (n = 23) and critical limb ischemia (CLI) (n = 23). Plasma angiopoietin-2 (Ang2), soluble Tie2 (sTie2), vascular endothelial growth factor (VEGF), soluble VEGF receptor 1 (sVEGFR-1), and placenta growth factor (PlGF) were measured by enzyme-linked immunoadsorbent assay. In vitro, endothelial cells (ECs) were treated with recombinant VEGF to investigate effects on sTie2 production.

RESULTS

Plasma concentrations of sTie2 (p < 0.01), Ang2 (p < 0.001), and VEGF (p < 0.01), but not PlGF or sVEGFR-1, were significantly greater in PAD patients compared with control subjects. Plasma Ang2 was significantly increased in both IC and CLI compared with control subjects (p < 0.0001), but there was no difference between IC and CLI. Plasma VEGF and sTie2 were similar in control subjects and IC but were significantly increased in CLI (p < 0.001 vs. control or IC). Increased sTie2 and VEGF were independent of CVD risk factors or the ankle-brachial index, and VEGF treatment of ECs in vitro significantly increased sTie2 shedding.

CONCLUSIONS

Levels of VEGF and sTie2 are significantly increased in CLI, and sTie2 production is induced by VEGF. These proteins may provide novel biomarkers for CLI, and sTie2 may be both a marker and a cause of CLI.

Impact of hormone replacement therapy on exercise training-induced improvements in insulin action in sedentary overweight adults

Exercise training (ET) and hormone replacement therapy (HRT) are both recognized influences on insulin action, but the influence of HRT on responses to ET has not been examined. To determine if HRT use provided additive benefits for the response of insulin action to ET, we evaluated the impact of HRT use on changes in insulin during the course of a randomized, controlled, aerobic ET intervention. Subjects at baseline were sedentary, dyslipidemic, and overweight. These individuals were randomized to 6 months of one of 3 aerobic ET interventions or continued physical inactivity. In 206 subjects, an insulin sensitivity index (S(I)) was obtained with a frequently sampled intravenous glucose tolerance test pre- and post-ET. Baseline and postintervention fitness, regional adiposity, general adiposity, skeletal muscle biochemistry and histology, and serum lipoproteins were measured as other putative mediators influencing insulin action. Two-way analyses of variance were used to determine if sex or HRT use influenced responses to exercise training. Linear modeling was used to determine if predictors for response in S(I) differed by sex or HRT use(.) Women who used HRT (HRT+) demonstrated significantly greater improvements in S(I) with ET than women not using HRT (HRT-). In those HRT+ women, plasma triglyceride change best correlated with change in S(I). For HRT- women, capillary density change and, for men, subcutaneous adiposity change best correlated with change in S(I). In summary, in an ET intervention, HRT use appears to be associated with more robust responses in insulin action. Furthermore, relationships between ET-induced changes in insulin action and potential mediators of change in insulin action are different for men, and for women on or off HRT. These findings have implications for the relative utility of ET for improving insulin action in middle-aged men and women, particularly in the setting of differences in HRT use.

Increased levels of apoptosis in gastrocnemius skeletal muscle in patients with peripheral arterial disease

Intermittent claudication (IC) is the major clinical manifestation of peripheral arterial disease (PAD). Apoptosis has been linked to skeletal muscle pathophysiology in other chronic diseases such as congestive heart failure. This study tested the hypothesis that there would be increased levels of apoptosis in the skeletal muscle of patients with PAD compared with control individuals. In total, 26 individuals with PAD and 28 age-appropriate controls underwent studies of peak oxygen consumption (peak VO2) and a gastrocnemius muscle biopsy in the most symptomatic leg. Muscle biopsies were analyzed for apoptosis and caspase-3 activity. Patients with PAD had a reduced peak VO2 compared with controls. Apoptosis was increased in those with PAD compared with age-appropriate controls (3.83% +/- 2.6 vs 1.53% +/- 0.96; p < 0.001). In conclusion, PAD is associated with increased levels of apoptosis in the peripheral skeletal muscle. Further study is required to ascertain whether apoptosis plays a role in decreased functional capacity.

Exercise training amount and intensity effects on metabolic syndrome (from Studies of a Targeted Risk Reduction Intervention through Defined Exercise)

Although exercise improves individual risk factors for metabolic syndrome (MS), there is little research on the effect of exercise on MS as a whole. The objective of this study was to determine how much exercise is recommended to decrease the prevalence of MS. Of 334 subjects randomly assigned, 227 finished and 171 (80 women, 91 men) had complete data for all 5 Adult Treatment Panel III-defined MS risk factors and were included in this analysis. Subjects were randomly assigned to a 6-month control or 1 of 3 eight-month exercise training groups of (1) low amount/moderate intensity (equivalent to walking approximately 19 km/week), (2) low amount/vigorous intensity (equivalent to jogging approximately 19 km/week), or (3) high amount/vigorous intensity (equivalent to jogging approximately 32 km/week). The low-amount/moderate-intensity exercise prescription improved MS relative to inactive controls (p <0.05). However, the same amount of exercise at vigorous intensity was not significantly better than inactive controls, suggesting that lower-intensity exercise may be more effective in improving MS. The high-amount/vigorous-intensity group improved MS relative to controls (p <0.0001), the low-amount/vigorous-intensity group (p = 0.001), and the moderate-intensity group (p = 0.07), suggesting an exercise-dose effect. In conclusion, a modest amount of moderate-intensity exercise in the absence of dietary changes significantly improved MS and thus supported the recommendation that adults get 30 minutes of moderate-intensity exercise every day. A higher amount of vigorous exercise had greater and more widespread benefits. Finally, there was an indication that moderate-intensity may be better than vigorous-intensity exercise for improving MS.

Inactivity, exercise training and detraining, and plasma lipoproteins. STRRIDE: a randomized, controlled study of exercise intensity and amount

Exercise has beneficial effects on lipoproteins. Little is known about how long the effects persist with detraining or whether the duration of benefit is effected by training intensity or amount. Sedentary, overweight subjects ( n = 240) were randomized to 6-mo control or one of three exercise groups: 1) high-amount/vigorous-intensity exercise; 2) low-amount/vigorous-intensity exercise; or 3) low-amount/moderate-intensity exercise. Training consisted of a gradual increase in amount of exercise followed by 6 mo of exercise at the prescribed level. Exercise included treadmill, elliptical trainer, and stationary bicycle. The number of minutes necessary to expend the prescribed kilocalories per week (14 kcal·kg body wt−1·wk−1for both low-amount groups; 23 kcal·kg body wt−1·wk−1for high-amount group) was calculated for each subject. Average adherence was 83–92% for the three groups; minutes per week were 207, 125, and 203 and sessions per week were 3.6, 2.9, and 3.5 for high-amount/vigorous-intensity, low-amount/vigorous intensity, and low-amount/moderate-intensity groups, respectively. Plasma was obtained at baseline, 24 h, 5 days, and 15 days after exercise cessation. Continued inactivity resulted in significant increases in low-density lipoprotein (LDL) particle number, small dense LDL, and LDL-cholesterol. A modest amount of exercise training prevented this deterioration. Moderate-intensity but not vigorous-intensity exercise resulted in a sustained reduction in very-low-density lipoprotein (VLDL)-triglycerides over 15 days of detraining ( P < 0.05). The high-amount group had significant improvements in high-density lipoprotein (HDL)-cholesterol, HDL particle size, and large HDL levels that were sustained for 15 days after exercise stopped. In conclusion, physical inactivity has profound negative effects on lipoprotein metabolism. Modest exercise prevented this. Moderate-intensity but not vigorous-intensity exercise resulted in sustained VLDL-triglyceride lowering. Thirty minutes per day of vigorous exercise, like jogging, has sustained beneficial effects on HDL metabolism.

Minimal versus umbilical waist circumference measures as indicators of cardiovascular disease risk

OBJECTIVE

Measures of central obesity are strongly correlated with cardiovascular disease (CVD) risk. Although waist circumference (WC) is a commonly used measure of central obesity, there is no standard measurement location. We examined two WC locations to determine which was more highly correlated with CVD risk factors and metabolic syndrome (MS).

RESEARCH METHODS AND PROCEDURES

WC measures were taken on 266 sedentary, overweight men and women 45 to 60 years old. Intravenous glucose tolerance tests, fasting plasma lipid analysis, and computed tomography scans were conducted. Correlational analyses followed by the Test for Equal Correlations determined whether one WC measure better correlated with the cardiovascular risk factors.

RESULTS

In women, minimal waist had higher correlation coefficients than umbilical waist for all eight variables presented. High-density lipoprotein-cholesterol, low-density lipoprotein particle size, and MS score were significantly correlated with minimal waist, but not umbilical waist. For high-density lipoprotein size and insulin sensitivity, minimal waist was a better correlate, although the difference between waist measures only approached statistical significance (p < 0.06). In men, minimal waist had a higher correlation coefficient than umbilical waist for insulin sensitivity, fasting insulin, and visceral adipose tissue. Additionally, minimal waist was significantly correlated with MS in men and umbilical waist was not. For both genders, minimal waist was more highly correlated with visceral adipose tissue than umbilical waist.

DISCUSSION

For every metabolic variable presented, minimal WC was more highly correlated with CVD risk than was umbilical WC in women. The data for women indicate that WC location is important when determining CVD risk. In men, minimal waist was better, although the data were less compelling.

Response of high-sensitivity C-reactive protein to exercise training in an at-risk population

BACKGROUND

High-sensitivity C-reactive protein (hsCRP) is promoted as an independent predictor of atherosclerotic risk. In addition, cardiorespiratory fitness is inversely related to hsCRP in single-sex cross-sectional analyses. Our objective was to determine if modulating fitness with exercise training imposes changes in high-sensitivity C-reactive protein in a mixed-sex population at risk for cardiovascular disease.

METHODS

We studied baseline and postintervention plasma hsCRP in 193 sedentary, overweight to mildly obese, dyslipidemic men and women who were randomized to 6 months of inactivity or 1 of 3 aerobic exercise groups: low amount-moderate intensity (energy equivalent of approximately 19.3 km/wk at 40%-55% peak VO2), low amount-high intensity (energy equivalent of approximately 19.3 km/wk at 65%-80% peak VO2), or high amount-high intensity (energy equivalent of approximately 32.2 km/wk at 65%-80% peak VO2).

RESULTS

At baseline, the study population was at intermediate to high cardiovascular risk as defined by hsCRP. Cardiorespiratory fitness was inversely related to hsCRP (P < .001) even after adjusting for significant and expected sex differences. Fitness, hormone replacement therapy use, and high-density lipoprotein cholesterol accounted for the sex difference in baseline hsCRP. Fitness, high-density lipoprotein cholesterol, fasting insulin, hormone replacement therapy, and visceral adiposity were all independent predictors for baseline hsCRP (r2 = 0.34 for the entire model, P < .0001). However, despite significant improvements in fitness, visceral adiposity, subcutaneous adiposity, and insulin sensitivity, hsCRP did not change in response to exercise training (P > .20).

CONCLUSIONS

Cardiorespiratory fitness is inversely related to hsCRP independent of sex and accounts for most of the large sex disparity in hsCRP. Nonetheless, in the absence of a significant change in diet, 6 months of aerobic exercise training does not produce a significant change in hsCRP in an at-risk population.

Effects of Exercise Training Amount and Intensity on Peak Oxygen Consumption in Middle-Age Men and Women at Risk for Cardiovascular Disease

STUDY OBJECTIVES

Although increasing aerobic fitness by exercise training is advocated as part of a healthy lifestyle, studies examining the different effects of intensity and amount on peak consumption (V(O2)) remain sparse.

DESIGN

This randomized controlled trial compared the effects of three different exercise regimens differing in amount and intensity on fitness improvements.

PARTICIPANTS

Overweight men and women with mild-to-moderate dyslipidemia were recruited.

INTERVENTIONS

The exercise groups were as follows: (1) low amount/ moderate intensity (LAMI, n = 25), the caloric equivalent of walking 19 kilometers (km)/wk at 40 to 55% of peak V(O2); (2) low amount/high intensity (LAHI, n = 36), the equivalent of jogging 19 km/wk at 65 to 80% of peak V(O2); (3) high amount/high intensity (HAHI, n = 35), the equivalent of jogging 32 km/wk at 65 to 80% of peak V(O2); and (4) a control group (n = 37).

MEASUREMENTS AND RESULTS

Peak V(O2) and time to exhaustion (TTE) were tested before and after 7 to 9 months of training. All exercise groups increased peak V(O2) and TTE compared to baseline (p < or = 0.001). Improvements in peak V(O2) were greater in the LAHI and HAHI groups compared to the control group (p < 0.02); HAHI group improvements were greater than the LAMI group (p < 0.02) and the LAHI group (p < 0.02). Increased TTE for all exercise groups was higher compared to the control group (p < 0.001)

CONCLUSIONS

Exercising at a level of 19 km/wk at 40 to 55% of peak V(O2) is sufficient to increase aerobic fitness levels, and increasing either exercise intensity or the amount beyond these parameters will yield additional separate and combined effects on markers of aerobic fitness. Therefore, it is appropriate to recommend mild exercise to improve fitness and reduce cardiovascular risk yet encourage higher intensities and amounts for additional benefit.

Inactivity, exercise, and visceral fat. STRRIDE: a randomized, controlled study of exercise intensity and amount

Despite the importance of randomized, dose-response studies for proper evaluation of effective clinical interventions, there have been no dose-response studies on the effects of exercise amount on abdominal obesity, a major risk factor for metabolic syndrome, diabetes, and cardiovascular disease. One hundred seventy-five sedentary, overweight men and women with mild to moderate dyslipidemia were randomly assigned to participate for 6 mo in a control group or for approximately 8 mo in one of three exercise groups: 1) low amount, moderate intensity, equivalent to walking 12 miles/wk (19.2 km) at 40-55% of peak oxygen consumption; 2) low amount, vigorous intensity, equivalent to jogging 12 miles/wk at 65-80% of peak oxygen consumption; or 3) high amount, vigorous intensity, equivalent to jogging 20 miles/wk (32.0 km). Computed tomography scans were analyzed for abdominal fat. Controls gained visceral fat (8.6 +/- 17.2%; P = 0.001). The equivalent of 11 miles of exercise per week, at either intensity, prevented significant accumulation of visceral fat. The highest amount of exercise resulted in decreased visceral (-6.9 +/- 20.8%; P = 0.038) and subcutaneous (-7.0 +/- 10.8%; P < 0.001) abdominal fat. Significant gains in visceral fat over only 6 mo emphasize the high cost of continued inactivity. A modest exercise program, consistent with recommendations from the Centers for Disease Control/American College of Sports Medicine (CDC/ACSM), prevented significant increases in visceral fat. Importantly, a modest increase over the CDC/ACSM exercise recommendations resulted in significant decreases in visceral, subcutaneous, and total abdominal fat without changes in caloric intake.

Gender and racial differences in lipoprotein subclass distributions: the STRRIDE study

Recent research has focused on the potential atherogenicity of various lipoprotein subclasses and their link to coronary heart disease (CHD) risk. This investigation seeks to identify differences in lipoprotein subclass distributions among a biracial, middle-aged population, while controlling for a number of confounding risk factors. Fasting plasma samples were analyzed in 285 sedentary, mildly dyslipidemic, overweight individuals between 40 and 65 years with no known history of CHD or diabetes. Women had lower levels of small and medium LDL, medium VLDL, large VLDL, and small HDL with a much higher concentration of large HDL than men. Whites had significantly more IDL, small LDL, medium VLDL, and large VLDL with lower levels of large LDL than blacks. HDL and LDL size were larger among blacks and women; VLDL size was greater among whites and men. There was also a trend for men to have more LDL particles than women and whites to have a higher LDL particle concentration than blacks. Within this homogenous population, there were distinct differences between gender and racial groups. Blacks and women had less atherogenic profiles than whites and men, which was not evident from the standard lipid panel.

Effects of the amount of exercise on body weight, body composition, and measures of central obesity: STRRIDE--a randomized controlled study

BACKGROUND

Obesity is a major health problem due, in part, to physical inactivity. The amount of activity needed to prevent weight gain is unknown.

OBJECTIVE

To determine the effects of different amounts and intensities of exercise training.

DESIGN

Randomized controlled trial (February 1999-July 2002).

SETTING AND PARTICIPANTS

Sedentary, overweight men and women (aged 40-65 years) with mild to moderate dyslipidemia were recruited from Durham, NC, and surrounding communities.

INTERVENTIONS

Eight-month exercise program with 3 groups: (1) high amount/vigorous intensity (calorically equivalent to approximately 20 miles [32.0 km] of jogging per week at 65%-80% peak oxygen consumption); (2) low amount/vigorous intensity (equivalent to approximately 12 miles [19.2 km] of jogging per week at 65%-80%), and (3) low amount/moderate intensity (equivalent to approximately 12 miles [19.2 km] of walking per week at 40%-55%). Subjects were counseled not to change their diet and were encouraged to maintain body weight.

MAIN OUTCOME MEASURES

Body weight, body composition (via skinfolds), and waist circumference.

RESULTS

Of 302 subjects screened, 182 met criteria and were randomized and 120 completed the study. There was a significant (P<.05) dose-response relationship between amount of exercise and amount of weight loss and fat mass loss. The high-amount/vigorous-intensity group lost significantly more body mass (in mean [SD] kilograms) and fat mass (in mean [SD] kilograms) (-2.9 [2.8] and -4.8 [3.0], respectively) than the low-amount/moderate-intensity group (-0.9 [1.8] and -2.0 [2.6], respectively), the low-amount/vigorous-intensity group (-0.6 [2.0] and -2.5 [3.4], respectively), and the controls (+1.0 [2.1] and +0.4 [3.0], respectively). Both low-amount groups had significantly greater improvements than controls but were not different from each other. Compared with controls, all exercise groups significantly decreased abdominal, minimal waist, and hip circumference measurements. There were no significant changes in dietary intake for any group.

CONCLUSIONS

In nondieting, overweight subjects, the controls gained weight, both low-amount exercise groups lost weight and fat, and the high-amount group lost more of each in a dose-response manner. These findings strongly suggest that, absent changes in diet, a higher amount of activity is necessary for weight maintenance and that the positive caloric imbalance observed in the overweight controls is small and can be reversed by a modest amount of exercise. Most individuals can accomplish this by walking 30 minutes every day.

Effect of the volume and intensity of exercise training on insulin sensitivity

Physical activity enhances insulin action in obese/overweight individuals. However, the exercise prescription required for the optimal enhancement is not known. The purpose of this study was to test the hypothesis that exercise training consisting of vigorous-intensity activity would enhance insulin sensitivity more substantially than moderate-intensity activity. Sedentary, overweight/obese subjects (n = 154) were randomly assigned to either control or an exercise group for 6 mo: 1) low-volume/moderate-intensity group [ approximately 12 miles walking/wk at 40-55% peak O2 consumption (Vo2 peak)], 2) low-volume/high-intensity group ( approximately 12 miles jogging/wk at 65-80% Vo2 peak), and 3) high-volume/high-intensity group ( approximately 20 miles jogging/wk at 65-80% Vo2 peak). Training volume (miles/wk) was achieved by exercising approximately 115 min/wk (low-volume/high-intensity group) or approximately 170 min/wk (low-volume/moderate-intensity and high-volume/high-intensity groups). Insulin action was measured with an insulin sensitivity index (SI) from an intravenous glucose tolerance test. In the control group, there was a decrement (P < 0.05) in SI. In contrast, all the exercise groups significantly (P < 0.05) increased SI; the relative increment in the low-volume/moderate-intensity and high-volume/high-intensity groups ( approximately 85%) were greater than in the low-volume/high-intensity group ( approximately 40%). In conclusion, physical activity encompassing a wide range of intensity and volume minimizes the insulin resistance that develops with a sedentary lifestyle. However, an exercise prescription that incorporated approximately 170 min of exercise/wk improved insulin sensitivity more substantially than a program utilizing approximately 115 min of exercise/wk, regardless of exercise intensity and volume. Total exercise duration should thus be considered when designing training programs with the intent of improving insulin action.

Differential effects of exercise training in men and women with chronic heart failure

BACKGROUND

Abnormalities of myosin heavy chain (MHC) isoforms, enzyme activity, and capillarity contribute to the exercise intolerance that is characteristic of patients with heart failure. To what extent these changes can be reversed with exercise training and whether differences exist in the responses of men and women remains uncertain. We described and compared the effects of exercise training on exercise capacity and skeletal muscle histochemistry in men and women with chronic heart failure.

METHODS

Fifteen patients (10 male) undergoing standard medical therapy completed a 14- to 24-week exercise training program. Peak oxygen consumption, MHC isoforms, capillary density, and selected metabolic enzymes were assessed before and after training.

RESULTS

Peak oxygen consumption was improved 14% (P <.05); however, this increase was mostly because of the improvement observed in men versus women (+20% versus +2%, respectively, P <.01). At baseline, MHC I content was lower in men than in women (33% +/- 3% vs 49.6% +/- 5.5%, P <.05). MHC I improved with training in men, to 45.6% +/- 4.5% (+38%, P <.05), versus women (-3%, P =.82), and the increase in men tended (P =.12) to be significant when compared with that in women. There were no significant changes in capillary density or muscle enzyme activity with training in the group as a whole or in men and women separately.

CONCLUSION

Among patients with chronic heart failure, improvements in peak exercise capacity may be more pronounced in men than in women. This difference in response of functional capacity to training paralleled differences observed between men and women for changes in MHC I isoforms.

Effects of the amount and intensity of exercise on plasma lipoproteins

BACKGROUND

Increased physical activity is related to reduced risk of cardiovascular disease, possibly because it leads to improvement in the lipoprotein profile. However, the amount of exercise training required for optimal benefit is unknown. In a prospective, randomized study, we investigated the effects of the amount and intensity of exercise on lipoproteins.

METHODS

A total of 111 sedentary, overweight men and women with mild-to-moderate dyslipidemia were randomly assigned to participate for six months in a control group or for approximately eight months in one of three exercise groups: high-amount-high-intensity exercise, the caloric equivalent of jogging 20 mi (32.0 km) per week at 65 to 80 percent of peak oxygen consumption; low-amount-high-intensity exercise, the equivalent of jogging 12 mi (19.2 km) per week at 65 to 80 percent of peak oxygen consumption; or low-amount-moderate-intensity exercise, the equivalent of walking 12 mi per week at 40 to 55 percent of peak oxygen consumption. Subjects were encouraged to maintain their base-line body weight. The 84 subjects who complied with these guidelines served as the basis for the main analysis. Detailed lipoprotein profiling was performed by nuclear magnetic resonance spectroscopy with verification by measurement of cholesterol in lipoprotein subfractions.

RESULTS

There was a beneficial effect of exercise on a variety of lipid and lipoprotein variables, seen most clearly with the high amount of high-intensity exercise. The high amount of exercise resulted in greater improvements than did the lower amounts of exercise (in 10 of 11 lipoprotein variables) and was always superior to the control condition (11 of 11 variables). Both lower-amount exercise groups always had better responses than the control group (22 of 22 comparisons).

CONCLUSIONS

The highest amount of weekly exercise, with minimal weight change, had widespread beneficial effects on the lipoprotein profile. The improvements were related to the amount of activity and not to the intensity of exercise or improvement in fitness.

Deconditioning fails to explain peripheral skeletal muscle alterations in men with chronic heart failure

It remains controversial whether the skeletal muscle alterations in chronic heart failure (CHF) are due to disease pathophysiology or result from chronic deconditioning. The purpose of this study was to compare the skeletal muscle of CHF patients to peak oxygen consumption (peak VO(2)) matched sedentary controls. It has been established that skeletal muscle abnormalities are related to the exercise intolerance observed in patients with CHF. We studied the skeletal muscle of sedentary controls and patients with CHF matched for age, gender and peak VO(2). Hypothesis testing for the effects of group (CHF vs. normal), gender, and the interaction group x gender were performed. For capillary density only gender (p = 0.002) and the interaction of group x gender (p = 0.007) were significantly different. For 3-hydroxyl coenzyme A (CoA) dehydrogenase only group effect (p = 0.004) was significantly different. Mean values for capillary density were 1.46 +/- 0.28 for CHF men versus 1.87 +/- 0.32 for sedentary control men, 1.40 +/- 0.32 for CHF women versus 1.15 +/- 0.35 for sedentary control women. The activities for 3-hydroxyl CoA dehydrogenase were 3.09 +/- 0.88 for CHF men versus 4.05 +/- 0.42 for sedentary control men, 2.93 +/- 0.72 for CHF women versus 3.51 +/- 0.78 for sedentary control women. This study suggests that women and men adapt to CHF differently: men develop peripheral skeletal muscle abnormalities that are not attributable to deconditioning; women do not develop the same pathologic responses in skeletal muscle when compared with normal women matched for aerobic capacity.

Studies of a targeted risk reduction intervention through defined exercise (STRRIDE)

PURPOSE

The Studies of a Targeted Risk Reduction Intervention through Defined Exercise (STRRIDE) trial is a randomized controlled clinical trial designed to study the effects of exercise training regimens differing in dose (kcal.wk-1) and/or intensity (relative to peak VO2) on established cardiovascular risk factors and to investigate the peripheral biologic mechanisms through which chronic physical activity alters carbohydrate and lipid metabolism to result in improvements in these parameters of cardiovascular risk in humans.

METHODS

We will recruit 384 subjects and randomly assign them to one of three exercise training regimens or to a sedentary control group. The recruiting goal is to attain a subject population that is 50% female and 30% ethnic minority. The overall strategy is to use graded exercise training regimens in moderately overweight subjects with impairments in insulin action and mild to moderate lipid abnormalities to investigate whether there are dose or intensity effects and whether adaptations in skeletal muscle (fiber type, metabolic capacity, and/or capillary surface area) account for improvements in insulin action and parameters of lipoprotein metabolism. We will study these variables before and after exercise training, and over the course of a 2-wk detraining period. The study sample size is chosen to power the study to examine differences in responses between subjects of different gender and ethnicity to exercise training with respect to the least sensitive parameter-skeletal muscle capillary density.

RESULTS

The driving hypothesis is that improvements in cardiovascular risk parameters derived from habitual exercise are primarily mediated through adaptations occurring in skeletal muscle.

CONCLUSION

Identification that amount and intensity of exercise matter for achieving general and specific health benefits and a better understanding of the peripheral mechanisms mediating the responses in carbohydrate and lipid metabolism to chronic physical activity will lead to better informed recommendations for those undertaking an exercise program to improve cardiovascular risk.

Differences in skeletal muscle between men and women with chronic heart failure

Men with chronic heart failure (CHF) have alterations in their skeletal muscle that are partially responsible for a decreased exercise tolerance. The purpose of this study was to investigate whether skeletal muscle alterations in women with CHF are similar to those observed in men and if these alterations are related to exercise intolerance. Twenty-five men and thirteen women with CHF performed a maximal exercise test for evaluation of peak oxygen consumption (VO(2)) and resting left ventricular ejection fraction, after which a biopsy of the vastus lateralis was performed. Twenty-one normal subjects (11 women, 10 men) were also studied. The relationship between muscle markers and peak VO(2) was consistent for CHF men and women. When controlling for gender, analysis showed that oxidative enzymes and capillary density are the best predictors of peak VO(2.) These results indicate that aerobically matched CHF men and women have no differences in skeletal muscle biochemistry and histology. However, when CHF groups were separated by peak exercise capacity of 4.5 metabolic equivalents (METs), CHF men with peak VO(2) >4.5 METs had increased citrate synthase and 3-hydroxyacyl-CoA dehydrogenase compared with CHF men with peak VO(2) <4.5 METs. CHF men with a lower peak VO(2) had increased capillary density compared with men with higher peak VO(2). These observations were not reproduced in CHF women. This suggests that differences may exist in how skeletal muscle adapts to decreasing peak VO(2) in patients with CHF.

Normal skeletal muscle Na(+)-K(+) pump concentration in patients with chronic heart failure

Intrinsic changes in skeletal muscle are being increasingly suspected as part of the underlying cause of exercise intolerance in patients with chronic heart failure (CHF). The objective of the present study was to determine whether differences existed between CHF patients and age-matched healthy controls in the concentration of skeletal muscle Na(+)-K(+)-ATPase (adenosine triphosphatase), a cation pump that functions to restore Na(+)-K(+) gradients and protect membrane excitability. Moreover, given the potency for physical activity in altering long-term regulation of the pump, an additional objective was to examine the role of activity level in pump expression in CHF patients. Na(+)-K(+)-ATPase concentration (pmol/g wet wt) determined in the vastus lateralis muscle of 27 CHF males (ejection fraction, 23 +/- 1.6%), using the vanadate facilitated [(3)H] ouabain binding technique, was not different (264 +/- 10) from 10 sedentary controls (268 +/- 19,P > 0.05). Similarly, no differences (P > 0.05) could be found between female patients (228 +/- 16, n = 7) and controls (243 +/- 13, n = 9). Differences between untrained control (294 +/- 20, n = 7), chronically active (251 +/- 20, n = 9), and trained (252 +/- 16, n = 6) CHF groups in Na(+)-K(+) pump expression were also insignificant. This study indicates that long-term regulation of Na(+)-K(+)-ATPase concentration is not altered in moderate CHF patients, regardless of the history of regular activity. However, the positive correlations (P < 0.05) that were observed between peak aerobic power (VO(2) peak) and Na(+)-K(+)-ATPase (r = 0.422) and VO(2) peak and maximal citrate synthase activity (r = 0.404) suggests a role for the skeletal muscle in explaining exercise intolerance in CHF patients.

Capillary density of skeletal muscle: a contributing mechanism for exercise intolerance in class II-III chronic heart failure independent of other peripheral alterations

OBJECTIVES

The study was conducted to determine if the capillary density of skeletal muscle is a potential contributor to exercise intolerance in class II-III chronic heart failure (CHF).

BACKGROUND

Previous studies suggest that abnormalities in skeletal muscle histology, contractile protein content and enzymology contribute to exercise intolerance in CHF.

METHODS

The present study examined skeletal muscle biopsies from 22 male patients with CHF compared with 10 age-matched normal male control patients. Aerobic capacities, myosin heavy chain (MHC) isoforms, enzymes, and capillary density were measured.

RESULTS

The patients with CHF demonstrated a reduced peak oxygen consumption when compared to controls (15.0+/-2.5 vs. 19.8+/-5.0 ml x kg(-1) x min(-1), p <0.05). Using cell-specific antibodies to directly assess vascular density, there was a reduction in capillary density in CHF measured as the number of endothelial cells/fiber (1.42+/-0.28 vs. 1.74+/-0.35, p = 0.02). In CHF, capillary density was inversely related to maximal oxygen consumption (r = 0.479, p = 0.02). The MHC IIx isoform was found to be higher in patients with CHF versus normal subjects (28.5+/-13.6 vs. 19.5+/-9.4, p <0.05).

CONCLUSIONS

There was a significant reduction in microvascular density in patients with CHF compared with the control group, without major differences in other usual histologic and biochemical aerobic markers. The inverse relationship with peak oxygen consumption seen in the CHF group suggests that a reduction in microvascular density of skeletal muscle may precede other skeletal muscle alterations and play a critical role in the exercise intolerance characteristic of patients with CHF.

Altered expression of myosin heavy chain in the vastus lateralis muscle in patients with COPD

This study was designed to further characterize peripheral skeletal muscle alterations in patients with chronic obstructive pulmonary disease (COPD) and to evaluate the possible relationship between myosin heavy chain (MyoHC) isoform expression and exercise tolerance in these individuals. MyoHC composition from biopsy of the vastus lateralis muscle was examined in 12 COPD patients (forced expiratory volume in one second (FEV1)=31+/-9% predicted, peak oxygen consumption (V'O2)=15+/-4 mL x kg(-1) x min(-1)) and 10 age-matched normal male subjects (peak V'O2=20+/-5 mL x kg(-1) x min(-1)). The proportion of MyoHC type I was smaller in COPD than in normals (27+/-17% versus 41+/-9%, p<0.05) with an increase in MyoHC type IIa (51+/-15% versus 39+/-9%, p<0.05) and the proportion of MyoHC type IIx being comparable between both groups. A significant relationship was found between peak V'Oo2 mL x kg(-1) x min(-1) and FEV1 % pred (r=0.91, p<0.0001) and the percentage of MyoHC type I (r=0.61, p=0.016). In stepwise multiple regression, only FEV1 % pred was found to be a significant determinant of peak V'O2 (p<0.0001). This variable explained 83% of the total variance of peak V'O2. In summary, this study showed considerable modifications in the phenotypic expression of the myosin heavy chain in the vastus lateralis muscle in patients with chronic obstructive pulmonary disease. An independent effect of myosin heavy chain expression on exercise capacity was not found. These results suggest that chronic inactivity and muscle deconditioning may not be the sole factors explaining peripheral muscle dysfunction in patients with chronic obstructive pulmonary disease.

Altered expression of myosin heavy chain in human skeletal muscle in chronic heart failure

To explore further alterations in skeletal muscle in chronic heart failure (CHF), we examined myosin heavy chain (MHC) isoforms from biopsies of the vastus lateralis in nine male patients with class II-III (CHF) (left ventricular ejection fraction (LVEF) 26 +/- 11%, peak oxygen consumption (peak VO2) 12.6 +/- 2 mL.kg-1.min-1) and nine age-matched sedentary normal males (NL). The relative content of MHC isoforms I, IIa, and IIx was determined by gel electrophoresis as follows: The normal sedentary group (NL) had a higher percent of MHC type I when compared with the patients (NL 48.4 +/- 7% vs CHF patients 24 +/- 21.6%, P < 0.05, no difference between MCH IIa (NL 45.1 +/- 10.5% vs CHF 56.0 +/- 12.5%), and CHF patients had a higher relative content of MHC type IIx than did the normal group (NL 6.5 +/- 9.6% vs CHF 20.0 +/- 12.9%, P < 0.05. Three of nine patients had no detectable MHC type I. In patients relative expression of MHC type I (%) was related to peak VO2 (r = 0.70, P < 0.05). Our results indicate that major alterations in MHC isoform expression are present in skeletal muscle in CHF. These alterations parallel previously reported changes in fiber typing that may affect contractile function i skeletal muscle and possibly exercise performance. The absence of MHC type I in some CHF patients suggests that skeletal muscle changes in this disorder are not solely a result of deconditioning, buy may reflect a specific skeletal muscle myopathy in this disorder.

A carbohydrate loading regimen improves high intensity, short duration exercise performance

This investigation examined the effect of a carbohydrate loading regimen on high intensity, short duration run performance. Using a random crossover design, 8 trained runners completed a 15-min submaximal run and a performance run to exhaustion after two dietary treatments. The mixed diet (MD) contained 4.0 +/- 0.5 g.kg-1.d-1 of carbohydrate (CHO) for 6 days. The experimental diet (HCD) contained 4.5 +/- 0.5 g CHO.kg-1.d-1 for 3 days followed by 8.2 +/- 0.4 g CHO kg-1.d-1 for 3 days. Training consisted of daily runs of 90, 40, 40, 20, and 20 min at approximately 75% of VO2max. Day 6 was a rest day, and testing was completed on Day 7. Preexercise lactate, body weight, submaximal VO2, and heart rate did not differ significantly between treatments. Carbohydrate oxidation during submaximal running was higher (p < 0.05) after HCD than after MD. Time to exhaustion in the performance run was longer after HCD compared to MD. Results indicate that a carbohydrate loading regimen increases CHO oxidation during submaximal exercise and improves high intensity, short duration run performance.

Skeletal muscle pH assessed by biochemical and 31P-MRS methods during exercise and recovery in men

The present study was designed to compare evaluation of skeletal muscle metabolism (vastus lateralis) evaluated by 31P-magnetic resonance spectroscopy (MRS) and biochemical analysis. During identical isometric knee extensor exercise protocols to fatigue in eight men, biopsy samples were taken at rest, peak exercise, and 32 s postexercise and 31P-MRS data were collected continuously for phosphocreatine (PCr), pH, ATP, and P(i) at 8- or 32-s intervals. There was no difference in ATP or pH measurements between the two techniques at rest, during peak exercise, or in recovery. Corresponding measurements of pH by the two techniques were closely related (r = 0.88, P < 0.01), and pH measured by 31P-MRS was closely related to muscle lactate accumulation (r = -0.84, P < 0.001). The level of PCr at peak exercise, expressed as a percentage of the baseline value, was not different between the two techniques (42 +/- 15 vs. 46 +/- 15%). The results indicate that, in skeletal muscle in normal subjects, 1) measurements of pH and PCr at rest and during exercise do not differ between the 31P-MRS and biopsy techniques and 2) muscle pH measured by 31P-MRS is closely related to lactate accumulation in men. Our data suggest that direct comparison of results of studies of exercise metabolism using these two techniques is warranted.