Purpose: An open, randomized, controlled study was designed to study the effects of exclusive strength training (ST) in patients with severe chronic heart failure (CHF) in comparison with conventional endurance (ET) and combined ET-ST training (CT). The hypothesis was that ST would at least be equal to ET or CT, because peripheral muscle atrophy and weakness play a key role in exercise limitation in CHF patients.
Methods: Three groups of 15 patients underwent ST, ET, or CT during 40 sessions, three times a week, for 45 min. Fifteen patients served as control group. Before and after intervention, left ventricular ejection fraction (LVEF), peak oxygen consumption (V˙O2peak), peak workload, thigh muscle volume, knee extensor strength, endurance, and quality of life (QoL) were assessed.
Results: All measured parameters improved significantly in the three training groups, except for knee extensor strength in ET. Training outcome was superior in all three training groups compared with the control group, but statistical significance was only reached for V˙O2peak and peak workload, thigh muscle volume, and knee extensor endurance. In contrast, knee extensor strength, LVEF, and QoL did not reach statistical significance. None of the training modalities proved to be superior to any other, although small differences between the three groups were observed.
Conclusion: Independently of the training modality, intensive exercise training is efficient in increasing cardiac function, exercise capacity, peripheral muscle function, and QoL in CHF patients.
1Department of Cardiology, Centre Hospitalier de Luxembourg, LUXEMBOURG; 2Clinical Epidemiology and Public Health, Centre for Health Studies, CRP-Santé, LUXEMBOURG; and 3Department of Radiology, Centre Hospitalier de Luxembourg, LUXEMBOURG
Address for correspondence: Patrick Feiereisen, Department of Cardiology, Centre Hospitalier de Luxembourg, 4, rue Barblé, L-1210 Luxembourg; E-mail: firstname.lastname@example.org.
Submitted for publication January 2007.
Accepted for publication July 2007.
Whereas 15 yr ago, exercise training was contraindicated in chronic heart failure (CHF), numerous studies, mainly using endurance training (ET), have shown that training interventions are highly efficient in improving patients' symptoms (6), exercise capacity (3,6,11,28,31,37), quality of life (3,31,37), and prognosis (3,12). The improvements in physical ability and symptoms have been mostly attributed to enhanced skeletal muscle function and structure (14). In healthy adults, but also in people with several chronic diseases such as COPD, sarcopenia, osteoporosis, as well as in frail elderly people, strength training (ST) has been accepted as the best method for developing or maintaining muscle mass, strength, power, and endurance. Current guidelines are very cautious about the use of ST in CHF (31,37), although, in this disease, peripheral muscle dysfunction is responsible for the key symptoms, dyspnea, fatigue, and exercise intolerance (7). Therefore, it is possible that ST might be more adequate in the rehabilitation of these patients than ET. So far, the safety of resistance training in CHF patients has been a concern, although some recent studies have shown that the hemodynamic burden during ST does not exceed that of cardiopulmonary exercise testing (20,26,36). In a pilot study (8), we have shown that ST, in combination with ET, improved patients' fitness without any negative consequences on left ventricular ejection fraction. These data were confirmed by other studies (22,32). Comparing ET with combined ST-ET training (CT) (9), we found that there were functional, cardiac, and peripheral dividends when endurance exercise is replaced partly by adapted ST. The goal of the present study was to compare, in an open, randomized, controlled design, the effectiveness of ST against traditional ET and CT training programs in patients with CHF.
Forty-five patients with CHF attributable to ischemic or dilated cardiomyopathy (CMP) were prospectively enrolled into an ambulatory training program at the cardiology department of the Centre Hospitalier de Luxembourg. They were randomly assigned to one of the three training protocols consisting of cardiovascular ET, resistive ST, or CT. Fifteen patients who were unable to regularly attend the ambulatory training sessions because of geographic constraints were included in a control group (CONT).
Inclusion criteria were age (range: 40-70 yr), NYHA classification II to III, LVEF < 35%, optimal medical treatment, and a stable clinical condition for 6 wk before inclusion. Exclusion criteria were NYHA class IV, malignant ventricular arrhythmias, renal dysfunction, stroke, COPD, and orthopedic limitations.
The study was approved by the local ethics committee, and written informed consent was obtained from all subjects.
Patients attended the ambulatory training program for 40 sessions with a frequency of three sessions per week. As previously mentioned, patients were randomly assigned to one of three training programs: ET, CT, or ST. Every training session consisted of 45 min of exercise, with 5 min of warm-up and 40 min of training, where the conditioning effect was applied. Warm-up was performed on a bicycle with a heart rate corresponding to 30% of V˙O2peak, because conditioning effects have already been described at 40% of V˙O2peak in CHF patients (2). Cardiovascular ET and peripheral muscle ST are completely different modalities that are difficult to compare. For this reason, attention was paid so that the total duration of muscle contraction would be 40 min in each training modality.
After warm-up, patients exercised for 20 min on a bicycle at a target heart rate corresponding to 60% V˙O2peak during the first 10 sessions, and then they exercised at a heart rate corresponding to 75% V˙O2peak for the final 30 sessions. Training load was progressively adapted to attain target heart rate if necessary. The bicycle training was followed by 20 min of treadmill, where walking speed and incline were adjusted to reach target heart rate.
After warm-up, patients used 10 different weight machines to exercise the muscle groups of the upper body (pull down, reverse butterfly, rowing, arm abduction), the lower body (knee extension, knee flexion, leg press, and calf raises), and the trunk (trunk flexion and trunk extension). The targeted muscle groups were those that are responsible for posture, because these groups have been shown to atrophy preferably with age and disuse (18). On each station, four series of 10 repetitions were performed. Rest time between the series was 2 min. Contraction duration was 3 s for the concentric and 3 s for the eccentric phase of the lift. To respect contraction duration, patients had to acoustically follow the rhythm imposed by a metronome. As a result, one series lasted exactly 1 min, and the total contraction time during ST was 40 min. Contraction intensity was 60% of the one-repetition maximum (1RM) (measured without Valsalva maneuver) for the 20 first sessions, and it was then increased to 70% 1RM for the 20 last sessions. 1RM was reevaluated every 10 sessions, and training load was adapted if necessary.
After warm-up, patients exercised for 20 min on the bicycle with the same training protocol as used during bicycle training in the ET group. The endurance part was followed by an ST part where five different exercises were selected (pull down, reverse butterfly, rowing, knee extension, and knee flexion) and executed at the same modality described previously, ensuring an ST time of 20 min, for a total of 40 min of training.
Cardiac function was assessed by radionuclide ventriculography (General Electric Optima camera, Milwaukee, WI). Left ventricular ejection fraction (LVEF), left ventricular end systolic volume (LVESV), and left ventricular end diastolic volume (LVEDV) were determined semiautomatically, without observer intervention.
Cardiopulmonary Exercise Testing
Symptom-limited cardiopulmonary exercise (CPX) testing was performed on an upright bicycle, using a ramp protocol where incremental load was set at 10 W·min−1. The test was performed under medication, late in the morning, under no fasting conditions. Exercise tests were performed by the same team, and patients were encouraged to perform until exhaustion. Heart rate was measured continuously on a 12-lead ECG, and blood pressure was measured by arm cuff every 3 min. Ventilation (V˙E), oxygen uptake (V˙O2), and carbon dioxide production (V˙CO2) were measured breath-by-breath. Data were collected for 30 s and averaged every 10 s (Sensormedics, Vmax 29C).
Isokinetic Strength Testing
Isokinetic strength testing is a precise, objective, and reproducible evaluation tool for assessing strength of human muscle. It has been widely used to document strength parameters and outcomes of rehabilitation in cardiac patients (8,9,30). This testing method was chosen not only because of its precise measurements but also because contraction mode is different from that produced on weight machines or during bicycle training. This ensures that the obtained results were not attributable to neuronal adaptations to a certain training method but were more likely to represent changes in muscle strength. The evaluation consisted of four maximal repetitions at an angular velocity of 60°·s−1 and 20 repetitions of 180°·s−1 for knee extension (quadriceps) and knee flexion (hamstrings) (Biodex Pro 3, Shirley, NY). Parameters analyzed were peak torque (PT) at 60°·s−1 (maximal strength) and 180°·s−1 (strength at functional angular velocity) as well as total work (TW) through 20 repetitions at 180°·s−1 to document endurance and fatigability of the muscle. Both sides were evaluated, and the strongest side was considered for analysis. Isokinetic evaluation concentrated on the lower body because, during ET, no upper body workout was performed.
Thigh Muscle Volume Measurement
Muscle volume of the thighs, representing peripheral muscle mass, was measured by CT scan (Light Speed 16, GE, Milwaukee, WI). The examination field ranged from the inferior limit of the ischiatic bones to the upper limit of the rotula. The acquired data were then used to calculate the muscular volume within these limits. The muscles were highlighted by choosing the appropriate Hounsfield units, and the muscle volume was obtained by an automatic three-dimensional volume-calculating program.
Quality of Life
The Minnesota Living with Heart Failure questionnaire was used for the assessment of quality of life (QoL). This self-administered test, specially designed for heart failure patients, is composed of 21 questions that reflect the physical, emotional, and social dimensions of the disease.
Descriptive statistics were produced as means and standard deviations. Correlations were studied between continuous variables. One-way ANOVA was used to assess group comparability at baseline and after 3 months of training. The change between baseline and posttraining intervention was studied through an ANOVA, with the groups as the independent factor. In case of a significant Kolmogorov-Smirnov test for normal distribution of the data, a logarithmic transformation was used; otherwise, a nonparametric Kruskall-Wallis test was performed. Homogeneity of variance was assessed with the Bartlett test, and a Welch-adjusted ANOVA was carried out if variances were unequal.
Pairwise comparison of the mean values between group modalities were further investigated with the Ryan-Einot-Gabriel-Welsch (REGWQ test) multiple range test when the homogeneity of variance was verified, otherwise using the Tukey post hoc test. A paired t-test was used to compare baseline and posttraining mean values. In the case of a nonsignificant Shapiro-Wilk test for normal data or nonhomogeneity of the variances, a nonparametric Wilcoxon sign rank test for matched pairs were used.
A P value of < 0.05 was considered statistically significant. All tests were two tailed. Statistical analyses were carried out with the statistical package SAS version 9.3.1 (SAS Institute, Cary, NC).
At baseline, there were no differences in terms of age, sex, NYHA classification, or origin of CHF between the four groups (ST, ET, CT, CONT), as shown in Table 1. The different groups were under standard drug treatment, as illustrated in Table 2. Drug treatment remained unchanged during the whole training period. There was no dropout, because all patients who were initially included in the study finished their 40 training sessions. No serious incident occurred during the whole training period. In the ET group, one patient presented paroxystic atrial fibrillation after treadmill (session 21 of 40). He could resume training at the next programmed session without further problems. In the ST group, one patient had to rest for 1 wk because of low-back pain that could not be directly related to the training program.
Baseline parameters for cardiac function (LVEF), exercise capacity (V˙O2peak and peak workload during CPX), knee extensor strength and endurance (PT ext 60°·s−1, PT ext 180°·s−1, and TW ext 180°·s−1), thigh muscle volume, and QoL presented in Table 3. There were no statistically significant differences measured between the four groups, ET, CT, ST and CONT for any of these parameters. Concerning QoL, one patient from the ST group who faced serious social problems at the end of the study was withdrawn from analysis because he was a clear outlier (Table 3).
Measurements after 40 Training Sessions
After 40 sessions of exercise training, LVEF increased in the ET (P = 0.0001), CT (P = 0.0056), and ST (P = 0.0062) group, whereas there was no significant change in the CONT (P = 0.22) group. There was no difference in the changes between the four groups (P = 0.21, ANOVA), even though the training effect on LVEF was more pronounced in the ET group (+30.2%) and in the CT group (+29.3%) compared with the ST group (+17.8%) and the CONT group (+9.7%). LVESV and LVEDV also improved in each modality after training, whereas no difference was found in the CONT group. However, the changes in LVESV and LVEDV between the four groups did not reach statistical significance (Table 3).
Cardiopulmonary exercise testing.
V˙O2peak increased after 40 sessions in the ET (+11%, P = 0.0415), CT (+14%, P = 0.0006), and ST (+17%, P = 0.0024), whereas it slightly decreased in the CONT group. There was no difference between the different training modalities. Peak RER remained at the same level after training for the four groups, indicating that exhaustion during CPX was identical between the groups before and after training. Maximal workload increased significantly with training in the ET, CT, and ST groups, but not in the CONT group. The increases in workload were more important in the ET group (+13%) and the CT group (+19%) than in the CONT group (−1.5%). No difference was observed between ST, CT, and ET.
Isokinetic strength testing.
After 40 sessions, PT ext 60°·s−1 and PT ext 180°·s−1 increased in the CT and ST group, but they did not increase in the ET or the CONT group. TW ext 180°·s−1 increased in all three training groups, whereas it did not increase in the CONT group. Comparisons of changes between the four groups were not significant for PT ext 60°·s−1 and PT ext 180°·s−1 (Table 3). For TW ext 180°·s−1, the change was significantly more important in the training groups compared with the CONT group (P = 0.02); no differences were found in between the three training modalities.
Thigh muscle volume.
After 40 training sessions, there was a significant increase in muscle volume in the training groups, whereas in the CONT group, muscle volume slightly decreased (−2%) in a nonsignificant manner. The change in muscle volume was significantly more important in the training intervention groups compared with the CONT group (P < 0.05), but there was no difference between ET, CT, and ST.
After training, QoL improved in the ET, CT, and ST groups. In the CONT group, no change in QoL was noted. None of the four groups improved in a significant way to any other group.
Correlations between Changes in V˙O2peak and Changes in Cardiac and Peripheral Muscle Parameters
Correlations between the changes in V˙O2peak and the changes in LVEF, PT ext 60°·s−1, PT ext 180°·s−1, TW ext 180°·s−1, and thigh muscle volume were analyzed, as well for the whole population of 45 patients undergoing exercise training, as for each of the three subgroups ST, ET, and CT. However, no positive correlation between any of these parameters, in any of those populations, could be found.
The main result of our study is that the three compared training modalities are almost equivalent in improving peak V˙O2, workload, cardiac function (LVEF), peripheral muscle mass and function, and QoL in CHF patients. V˙O2peak increased in the three training groups, whereas in the CONT group a slight decrease was observed. The changes are comparable with those obtained in the literature, which attain 15-20% after ET or CT (29) or 10-18% during ST (28). The results with ST are more inconsistent, because some studies failed to reach significant improvements (5,32). The 16% increase in V˙O2peak after ST is remarkable, because in healthy, sedentary individuals, ST increases V˙O2peak by less than 3% (34). Although there was no difference in change of V˙O2peak between the three training modalities, there was a small trend for better results if strength components were included into training.
Even if we could not find a correlation between changes in V˙O2peak and in peripheral muscle mass and strength, changes in V˙O2peak seem to parallel changes in muscle mass and strength (Fig. 1). This is in accordance with the studies of Jondeau et al. (19), who have demonstrated the role of reduced muscle mass in the limitation of exercise capacity in patients with severe CHF. The increase in V˙O2peak in our study might be a direct consequence of the recruitment of supplementary muscle mass obtained by ST, CT, and, to a lesser extent, ET. Furthermore, the fact that in CHF skeletal muscle mass is an independent predictor of V˙O2peak supports these arguments (4).
To analyze the effects of training on peripheral muscle function in detail, we considered three aspects in our study: muscular strength, endurance, and mass. Peripheral muscle strength was improved with CT and ST, confirming previous studies (8,9,17,21,24,32,33), but not with ET. Identical results have been observed after one-legged, high-intensity knee extensor exercise in CHF patients (23). This indicates that ET is probably not sufficient to enhance muscle strength in CHF patients, although this is considered to be a primary target of training intervention, because potentially irreversible damage to the heart in CHF limits the potential gain in cardiac function (35). However, ET remains by far the most used training modality. A significant increase in peripheral muscle endurance was obtained with the three training modalities, with a small trend of greater increase with ET. Muscle mass was increased with the three training methods. In the CONT group, a small but significant decrease of muscle mass and V˙O2peak was observed. It probably reflects the accelerated decrease in muscle mass in CHF patients, which may eventually lead to cardiac cachexia (1). Remarkably, each training modality seems to stop this deleterious process. All these data confirm the key role of peripheral muscle in the ability to perform exercise in CHF, and that improvement of muscle strength and mass are fundamental goals of rehabilitation in CHF patients.
The improvement in LVEF was significant for all three training methods. LVEF also increased, but not in a significant way, in the CONT group. All patients were on a stable drug regimen before the beginning of training. Nevertheless, the increases in LVEF can be partly explained by ongoing drug effects. The improvements in LVEF tend to be more impressive when endurance parts are used (ET and CT). Our results seem to be in accordance with the literature in that 6 months of ET raised LVEF between 16 and 22% (10,13,16) in severe CHF patients, and 8 wk of ST improved LVEF by 13% (22). Concomitant to the increase of LVEF, both LVEDV and LVESV decreased after exercise in the training groups, whereas there was no change in the CONT group, thus indicating that exercise training has an antiremodeling effect in CHF patients. This is in accordance with several studies that have demonstrated either a reduction of end diastolic and systolic volumes (13,16) or of end diastolic and systolic diameters of the left ventricle (10,16). As opposed to our study, where LVEDV and LVESV, measured by radionuclide ventriculography, decreased after ST, there were no significant changes in end diastolic or systolic diameters as measured by echocardiography in the study of Levinger et al (22), although LVEF increased by 13%. Exercise training can potentially add to the effect of medication by inducing endothelium-dependent vasodilation, reducing peripheral vascular resistance and afterload and resulting in a further increase of LVEF. Endothelium-dependent vasodilation has been reported with ET (15,16) and CT (25). After ST, Selig et al. (33) found increased forearm blood flow. Reduction in peripheral vascular resistance was found after both ET (10,16) and ST (27). Even if LVEF increased almost twice as much with ET and CT than with ST, this did not translate into a superior improvement in V˙O2peak, confirming the lack of correlation between LVEF measured at rest and exercise capacity. This supports the notion that the primary target for improving exercise capacity in CHF is the peripheral, rather than the central, component.
QoL equally improved with the three training methods. This further demonstrates the general benefit of a prolonged, thrice-weekly training program.
There are two major limitations to this study. First, the study was not fully randomized, because the CONT group was chosen on the basis of where the patients lived. However, considering that training therapy has clearly demonstrated additional benefits to the conventional medical treatment, we included all patients who were able to easily attend the sessions in the training groups, and we selected patients who, for logistic reasons, were unable to regularly attend the sessions in the CONT group. Another small limitation about the CONT group was that a higher percentage of patients received spironolactone compared with the training groups. Second, as previously mentioned, the number of subjects included in this single-center study is relatively small. A more important number of subjects may have permitted detection of more robust differences between the different training modalities.
Further studies, including more patients, should be performed to determine whether ST and ET, as some trends in our study might suggest, have additional effects. This would permit the optimization of training programs for CHF patients.
Exercise training is efficient in increasing cardiac function, exercise capacity, peripheral muscle function, and QoL in CHF patients, regardless of the training modality applied. Our hypothesis that ST could be superior to CT or ET has not been verified, and the training effects are of the same magnitude than with the other modalities. CT seems to be the most beneficial modality because it combines important improvements in cardiac function and in peripheral muscle strength, endurance, and mass. Nevertheless, the main concern of CHF patients is to achieve activities of daily life at the lowest possible cost. Exercise capacity, for instance, V˙O2peak, which integrates central and peripheral components, seems to be equally improved by the three training modalities. The same is true for QoL. Because many daily tasks require short, intensive physical demands, ST involving the upper and the lower body should be a part of rehabilitation programs in CHF, and it should partly replace the more conventional ET. The amount of endurance and strength components of the rehabilitation program probably should be individually tailored depending on each patient's limitations and needs.
This work was funded by the "Société Luxembourgeoise de Recherche sur les maladies cardio-vasculaires."
The authors thank Prof. J Duchâteau, Prof Ph. Van de Borne, Dr D. Wagner, and Michel Lamotte for their helpful comments.
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Keywords:©2007The American College of Sports Medicine
RANDOMIZED CONTROLLED STUDY; V˙O2peak; MUSCLE STRENGTH; MUSCLE VOLUME; LEFT VENTRICULAR EJECTION FRACTION; QUALITY OF LIFE