Abstract
Objective
Study the effect of muscle strength training on muscle strength, maximal oxygen uptake (VO 2 max), hemodynamic and anthropometric parameters as well as quality of life after coronary artery bypass grafting (CABG).
Methods
After CABG surgery, 32 patients were randomized into two groups. The first group was to perform aerobic-type training with a cycle ergometer (AT = 16). The second group was to perform low-intensity muscle strength training of the quadriceps and hamstrings using an isokinetic dynamometer (i.e. 20 to 30% of peak torque) (ST = 16). Before and after the strength training program we conducted a stress test, evaluation of isokinetic force production, 6-minute walking test, body impedance analysis (BIA) and SF-36 quality of life test.
Results
Compared to the AT group, the ST group showed better results with improved quadriceps strength (48.2% vs. 8.2%), VO 2 max ( P < .001) and diastolic blood pressure at rest ( P = 0.01). Quality of life improved in both groups.
Conclusion
The dynamic-resistance muscle strength training protocol using isokinetic dynamometer can safely (i.e. without clinical symptoms or changes to the ECG and arterial blood pressure) improve muscle strength and VO 2 max without any major risks in patients post-CABG. These findings should encourage additional studies to validate the relevance of these strength training modalities in rehabilitation centers.
Résumé
Objectif
Étudier l’effet du renforcement musculaire (RM) sur la force musculaire, la consommation maximale d’oxygène (VO 2 max), les paramètres hémodynamiques et anthropométriques et la qualité de vie après un pontage aortocoronaire (PAC).
Méthode
Trente-deux patients après PAC étaient randomisés en deux groupes ; l’un pour effectuer un réentraînement à l’effort type aérobie avec un cycloergomètre (RA = 16), l’autre pour effectuer un protocole de renforcement musculaire du quadriceps et des ischiojambiers sur un dynamomètre isocinétique à faible intensité (soit : 20 à 30 % du pic de couple maximal) (RM = 16). Une épreuve d’effort, une évaluation de la force isocinétique, un test de marche de six minutes, une impédancemétrie et un test de qualité de vie « SF-36 » étaient faits avant et après le réentraînement.
Résultats
Pour le groupe RM et comparativement au groupe RA, nous avons noté une amélioration meilleure de la force du quadriceps (48,2 % versus 8,2 %), de la VO 2 max ( p < 0,001) et de la pression diastolique de repos ( p = 0,01). La qualité de vie s’améliore dans les deux groupes.
Conclusion
Le protocole de RM isocinétique type résistance dynamique peut sans danger (sans manifestations cliniques ni modification électrocardiographique ou des chiffres de tension artérielle) améliorer la force musculaire et la VO 2 max sans risque majeur chez les patients avec PAC. Cela devrait encourager les centres de rééducation à recourir à ces modalités de réentraînement au cours d’autres études complémentaires.
1
English version
1.1
Introduction
Commonly, aerobic-type physical activity with dynamic exercises constitutes the basis of training programs for cardiovascular rehabilitation . Muscle strength can be essential for performance and might be altered in patients with ischemic heart disease (IHD) . It is often recommended to use muscle strength training (ST) as a useful component of a cardiovascular rehabilitation program . Several randomized studies, controlled or not, have not only validated the positive impact of ST on muscle strength, without any adverse events, in low-risk patients , but also suggested that ST could improve their aerobic capacity. However, these study results present some limits related to the presence of an aerobic-type training (AT) component and/or with an indirect evaluation of the aerobic capacity .
A recent study concluded that women with coronary heart disease could benefit equally from an aerobic-type rehabilitation training protocol or from a protocol associating aerobic exercises and muscle ST.
Some questions remain however, regarding the eligibility and safety of muscle ST in cardiac patients because of the potential risks of arrhythmia or bouts of high blood pressure related to the isometric component of the protocol . Furthermore, previous studies in cardiac patients showed no deterioration of the left ventricular function or arrhythmias during isometric and isodynamic ST compared to isodynamic exercises alone , suggesting that muscle ST is safe in low-risk cardiac patients.
Maiorana et al. showed that a muscle ST program using a pulley therapy circuit without any aerobic component is safe and can improve in a safe manner the strength of major muscle groups in low-risk patients after coronary artery bypass grafting (CABG), but without significant improvement on VO 2 max.
In our work, we chose to study the effects of a low-intensity dynamic-resistance training using an isokinetic dynamometer in patients after CABG. These patients represented a low-risk group according to the recommendations of the American Heart Association , and they could especially benefit from ST during the bed-ridden recovery period after the surgery. The isokinetic dynamometer was mainly used as an evaluation tool to quantify the decrease in muscle strength during the cardiac pathology and its progression after muscle ST, especially for patients with congestive heart failure (CHF) . For CHF patients, isokinetic ST improves muscle strength and endurance as well as heart rate variability . Nevertheless, according to our knowledge, no data comparing isokinetic resistance training versus aerobic ST are available to justify the systematic use of the former in cardiovascular rehabilitation programs. The objective of this study was to compare, in patients after CABG, the effects of an 8-week low-intensity isokinetic muscle ST program not preceded by aerobic ST with an aerobic-type onlytraining program.
Primary results focus on muscle strength and aerobic capacity (VO 2 max). Secondary results concern the cardiovascular pathology, anthropometric parameters and quality of life.
1.2
Method
1.2.1
Participants
Patients were recruited between June and December 2006 within the cardiac rehabilitation unit of the Physical Medicine and Rehabilitation Department of the Habib Bourguiba University Hospital in Sfax.
1.2.2
Inclusion criteria
Patients were included 8–12 weeks after CABG (double bypass, triple bypass in patients with myocardial infarction), they needed to be at a low risk of recurrence (normal left ventricular function, coronary angiography showing the lack of residual ischemia). The group was deemed representative of a clinically stable population with a history of coronary heart disease. None of the patients were involved in another rehabilitation program at the time of inclusion.
1.2.3
Exclusion criteria
We excluded patients with the presence of moderate to severe left ventricular (LV) dysfunction, defined by a dysfunction of the left ventricular ejection fraction (LVEF) (< 40% during the preoperative angiography), patients with high blood pressure at rest (systolic blood pressure [SBP] > 160 mmHg or diastolic blood pressure [DBP] > 100 mmHg) and exercise-induced high blood pressure defined by: SBP 220 mmHg or PAD > 120 mmHg, chest pain or significant ST-segment depression (> 0.1 mV) during the stress test and finally patients with musculoskeletal or orthopedic impairments.
1.2.4
Study protocol
The patients’ medical treatment remained unchanged during the study. All patients were taking β-blockers and aspirin. Almost half of our patients suffered from type 2 diabetes ( Table 1 ). Patients were informed about the procedures and eventual risks and signed a consent form. This was a prospective, randomized two-arm controlled study. After initial tests including body composition (BC), muscle strength (MS), and aerobic capacity (AC), patients were randomized into two groups: isokinetic muscle ST and AT. Failures to complete the program were related to the following: re-hospitalization due to poorly managed diabetes suspected clinically and validated by biological analyses (one case in the ST group), exclusion from the rehabilitation program related to knee osteoarthritis pain (three patients in the AT group; six patients in the ST group). Four patients (three AT, one ST) were excluded for lack of protocol observance.
| Group | AT ( n = 16) | ST ( n = 16) |
|---|---|---|
| Age (years) | 59 ± 5.85 | 59.25 ± 1.7 |
| Weight (kg) | 82.2 ± 10.07 | 77.2 ± 5.46 |
| BMI (kg/m 2 ) | 27.9 ± 2.98 | 27.2 ± 1.18 |
| LVEF (%) | 58.28 ± 6.31 | 58.87 ± 4.78 |
| Smoking | 8 | 11 |
| Diabetes (type 2) | 8 | 6 |
| Hypertension | 10 | 13 |
| Dyslipidemia | 10 | 12 |
| Aspirin | 16 | 16 |
| Beta blockers | 16 | 16 |
| ACE inhibitor | 13 | 11 |
| Cordarone | 11 | 9 |
| Statins | 9 | 11 |
| Time from CABG (days) | 60 ± 26 | 71.37 ± 14 |
1.2.5
Evaluations
All evaluations took place at the beginning and at the end of the ST program. Stress tests were conducted on an electromagnetic cycle ergometer (Ergometrics 800; Sensor Medircs) with a triangular protocol supervised by a physician. The initial power was set at 20% of the theoretical maximum oxygen uptake (VO 2 max) with 10 to 15% incremental increase per minute. Theoretical VO 2 max values were obtained using Wasserman’s equation: maximum oxygen uptake to VO 2 max = weight × (50.72 – 0.372 × age) for men; from this equation we can deduct the theoretical VO 2 max = (VO 2 max – VO 2 at rest)/10.3 . Oxygen uptake was determined using an open-circuit technique. During the entire evaluation, gas exchanges were analyzed with a rubber mouthpiece mounted on a unidirectional valve with low resistance and reduced dead volume (Vmax; Legacy 229). The flow was calibrated using a scaled 3-liter pump with various speeds. DBP and SBP were controlled while the heart rate was continuously monitored by ECG (Corina; CardioSoft; Version 0.3). The maximal and minimal values were recorded for the heart rate and both types of arterial blood pressures (ABP).
1.2.6
Analysis of the isokinetic muscle strength
The strength of peripheral muscles was measured for knee flexors and extensors (quadriceps and hamstrings) using an isokinetic dynamometer (Cybex Norm II; Medimex). Isokinetic tests were conducted at two different angular velocities, 150°/s and 180°/s in concentric mode. The subjects had some time to adapt to the machine and movements in order to reduce the learning curve effect. The isokinetic evaluation protocol consisted in two series comprising five repetitions for each different velocity and each knee. A 1-minute recovery period was set between the two series. Subjects were encouraged to give their maximum. The maximal isokinetic force was defined as the mean value of peak torque reached during each repetition (in Newton × meter [Nm]). Tests were conducted by the same examiner and within the same test conditions (in the morning before any exercise, without drinking caffeine or smoking in the hours preceding the test). This evaluation was associated to an ECG and HR monitoring (Sicard 460; Siemens; Germany). Blood pressure was measured by a sphygmomanometer every minute.
1.2.7
Six-minute walking test (6MWT)
A 6-minute walking test (6MWT) took place in a 30-m long hallway. Subjects were asked to walk as fast as possible, without running, for 6 minutes and they were allowed to slow down or rest if needed. Before the first test, patients were familiarized with the environment by walking normally back and forth down the hallway. Then patients would sit down, next to the starting point, for 10 minutes before the beginning of the test. During this time, HR and BP were checked. In order to ensure standardization and reproducibility of the procedure, the time was told to the patient for each passed minute but without any particular motivating words. The total walking distance during the 6 minutes was recorded in meters. The heart rate and oxygen uptake were registered every minute . The test was repeated 30 minutes later and the better of the two tests was set as a reference value for each patient.
1.2.8
Body composition measurement
Lean body mass (LBM) and body fat (BF) were evaluated by body impedance analysis (BIA), early in the morning, before having eaten, according to the conventional standardized technique . Tetrapolar bioelectrical impedance analysis (electric current 50 kHz, 0.8 mA) was conducted by the Tanita ® (TBF-300 model). Electrodes were placed on the ankle with the patient standing up. LBM was calculated according to the specific equation devised by Gray et al. .
1.2.9
SF-36 questionnaire
The SF-36 is a multipurpose, short-form health survey with only 36 questions. It yields an 8-scale profile of functional health and well-being scores as well as psychometrically-based physical and mental health summary measures and a preference-based health utility index . Each criterion gets a grade from 0 to 100; 0 means the worst health-related quality and 100 the best one.
1.2.10
Strength training protocol
The level of physical activity in both protocols was developed and adapted by a qualified physician to each individual patient according to the results of the stress test and the patient’s maximum heart rate (HRmax). Both groups were trained at the same relative intensity corresponding to the target HR calculated according to the Karvonen equation (target HR = HRrest + 0.7 × HR reserve [HRmax − HRrest]). The training protocol was adapted to each individual and monitored by a physiotherapist, nurse and PM&R physician. Our study requirements stated that subjects in both arms had three training sessions a week, at the same intensity level, the difference between both groups was only on the type of exercise.
1.2.11
Muscle strength training protocol
Recruited subjects had no aerobic training before the isokinetic ST protocol. For this low-resistance ST training protocol of the lower limbs, we used an isokinetic dynamometer (Cybex Norm II; Medimex) at 180°/s in concentric mode. During this protocol, we decreased the resistance intensity (low intensity: 20 to 30% of peak torque max) while increasing the number of repetitions . The subjects were asked to reach the target intensity by using the biofeedback technique. The amount of exercise was increased via the number of repetitions (20 to 40 repetitions), and we asked patients to increase or decrease this number to reach their target HR set at 70% of their HR reserve. When their target HR was reached, subjects were asked to maintain that number of repetitions. When patients were unable to reach their target HR by increasing the number of repetitions, we slightly increased the resistance by 5 or 10%. Our ST program consisted in 10 repetition series each lasting 1 minute, separated by a rest period (10 1-minute rest periods), for each leg at the speed of 180°/s. The total training duration (excluding rest periods) was 20 minutes (same time for the AT) at the target HR (same intensity for the AT). The training session lasted for 40 minutes in all and was preceded by 5 minutes of aerobic-type exercise to ensure proper warm up. A low-intensity pre-training session was conducted prior to the first session over a limited number of repetitions (20 to 30 per minute) at 20% of their peak torque. Patients had to complete the repetitions during 1 minute without holding their breath (Valsalva maneuver). During the entire session, patients were invited to exhale during knee extension and inhale during flexion. When the patient completed the exercises without any abdominal pain or any other symptoms while reaching the target HR (±10 bpm), the particular setting was noted as the proper protocol to follow. Patients were monitored by ECG (Sicard 460; Siemens; Germany). Heart rate and blood pressure were measured and noted 1 minute before the end of each series.
1.2.12
Aerobic training protocol
For each session, patients were under ECG monitoring for their HR and their blood pressure was also checked (ErgolineZan 600). The program lasted 8 weeks and consisted in three weekly sessions at 70% of their HR reserve . After a 10-minute warm up period, patients biked at 60 rpm on an electromagnetic cycle ergometer (ErgolineZan 600), during two series of 10 minutes each with the same intensity, separated by a 5-minute rest period and followed by a 10-minute recovery period. During each session, the training prescription was adjusted for each patient in order to ensure an incremental increase of the performance level.
1.2.13
Results analysis
Results are expressed in mean values ± standard deviation (SD). We set the significance at P ≤ 0.05. All analyses were done according to the SPSS statistics module, version 13. To measure the differences between groups at baseline, we used the Student t -test for independent sample and the Chi 2 test. The difference (in %) between the pre and post-training values for each variable was calculated by the equation: ΔS = post − pre/post × 100, afterwards these differences in percentage were compared between both groups. The values collected before and after the ST were analyzed by a paired t -test.
1.3
Results
1.3.1
Baseline characteristics for both groups
Table 1 lists the initial clinical parameters for both groups of patients who completed the 8-week training program. The initial values for muscle strength, body composition (BC), and cardiopulmonary tolerance to exercises are presented respectively in Tables 2–4 . There was no significant difference between both groups for the initial values of BC, muscle strength and VO 2 max.
| AT ( n = 16) | ST ( n = 16) | |||
|---|---|---|---|---|
| Strength parameters (N/m) | BL | 8-W | BL | 8-W |
| QPT (150°/s) | 89.5 ± 14 | 96.3 ± 13.5 | 90 ± 16 | 132 ± 17 |
| P = 0.006 | P < 0.001 | |||
| QPT (180°/s) | 82.5 ± 9 | 88.9 ± 11 | 82 ± 14 | 115 ± 22 |
| P < 0.001 | P < 0.001 | |||
| HPT (150°/s) | 50.9 ± 7 | 53.5 ± 8.2 | 54 ± 6 | 58 ± 12 |
| P = 0.03 | P < 0.001 | |||
| HPT (180°/s) | 46.8 ± 6.3 | 46.7 ± 9.7 | 50 ± 5 | 54 ± 10 |
| NS | NS | |||
| Body composition | AT ( n = 16) | ST ( n = 16) | ||
|---|---|---|---|---|
| BL | 8W | BL | 8W | |
| Weight (kg) | 82.2 ± 10 | 81.2 ± 9 NS | 77.2 ± | 77.5 ± 4 NS |
| BMI (kg/m 2 ) | 27.9 ± 3 | 27.8 ± 3 NS | 27.2 ± 1 | 27.5 ± 1 NS |
| LBM (kg) | 51.3 ± 3 | 52 ± 4 P = .001 | 50.4 | 51.9 P < .001 |
| BF (kg) | 29.7 ± 2 | 28.5 ± 3 P = .003 | 29.7 | 27.4 P = .001 |
| AT ( n = 16) | ST ( n = 16) | |||
|---|---|---|---|---|
| BL | 8-W | BL | 8-W | |
| MET | ||||
| VO 2 peak (mL/kg/min) | 20.4 ± 4 | 22.1 ± 4 P < .001 | 18.5 ± 5 | 22.5 ± 6 P = .01 |
| Resting data | ||||
| HR (beats/min) | 67 ± 10 | 57 ± 10 P = .001 | 73.1 ± 5 | 61.2 ± 6 P < .001 |
| SBP (mmHg) | 128 ± 17 | 114 ± 11 P = .005 | 136 ± 16 | 114.8 ± 14 P < .001 |
| DBP (mmHg) | 76.2 ± 11 | 70 ± 7 P = .004 | 81 ± 5 | 70 ± 5 P < .001 |
| MET (submaximal values) | ||||
| HR (beats/min) | 116 ± 14 | 109 ± 13 P = .001 | 127 ± 18 | 116 ± 18 P = .006 |
| SBP (mmHg) | 182 ± 17 | 169 ± 13 P = .005 | 184 ± 20 | 169 ± 23 P < .001 |
| DBP (mmHg) | 95 ± 11 | 88.5 ± 8.5 P = .002 | 100 ± 9 | 90 ± 9 P = .002 |
| MP (watts) | 114 ± 24 | 124 ± 24 P = .002 | 106 ± 24 | 126 ± 30 P < .001 |
| 6MWD | ||||
| Distance (m) | 496 ± 75 | 572 ± 57 P < .001 | 459 ± 41 | 559 ± 39 P < .001 |
| HRmax (beats/min) | 103 ± 9 | 98 ± 9 P = .02 | 109.6 ± 5 | 95 ± 9 P = .01 |
1.3.2
Exercise intensity
There was no difference between both groups regarding mean intensity during each 8-week training program. The mean heart rate during training (HR mean) was109 beats/minute (bpm) ± 11 for the ST group and 101 ± 9 bpm. There was no significant difference between HRmean values calculated for both groups.
1.3.3
Adverse events during the training programs
Some patients complained of knee pain (three in the ST group and five in the AT group), leading to changing temporarily the intensity of the training program. No undesirable cardiovascular symptoms were reported (arrhythmia or ST-segment abnormality) in the ST group. Two patients in the AT group presented significant exercise-induced ST-segment depression without chest pain at weeks 4 and 6 of the program. These patients had to be hospitalized for 3 days for additional examinations but received no additional treatment. After a week, they were able to get back to the program and complete at the same intensity.
1.3.4
Muscle strength
Changes in muscle strength for both groups are detailed in Tables 2 and 5 . Both groups showed significant improvement in their quadriceps and hamstrings muscle strength. In the ST group, quadriceps strength improved by 48.2%, from 90 ± 16 N*m to 132 ± 17 N*m ( P < .001) and a 7% increase in hamstrings strength from 54 ± 6 N*m to 58 ± 12 N*m ( P < .001) at the angular velocity of 150°/s in concentric mode.
| AT ( n = 16) (%) | ST ( n = 16) (%) | P | |
|---|---|---|---|
| QPT 150°/s | 8.2 | 48.2 | < .001 |
| QPT 180°/s | 7.6 | 41.4 | < .001 |
| HPT 150°/s | 5.7 | 7 | NS |
| HPT 180°/s | 2.4 | 9.5 | NS |
| Weight | −0.9 | −1.4 | NS |
| BMI | −0.3 | −1.3 | NS |
| Lean body mass | 1 | 2.3 | .05 |
| Body fat | −1.8 | −3.1 | NS |
| VO 2 peak | 13.3 | 22.4 | .004 |
| HR rest | −13.5 | −15.16 | NS |
| SBP rest | −10 | −16 | NS |
| DBP rest | −8.1 | −15 | .018 |
| Submaximal HR (MET) | −6 | −8 | NS |
| Submaximal SBP | −6.6 | −7.8 | NS |
| Submaximal DBP | −2.3 | −6.7 | NS |
| MP | 9.5 | 18.5 | .014 |
| Distance (6MWD) | 16.6 | 24 | .04 |
| HRmax (6MWD) | 5 | 20 | .004 |
In the AT group, the improvement was limited to 8.2% for quadriceps strength, from 89.5 ± 14 N*m to 96.3 ± 13.5 N*m ( P = .006) at 150°/s and to 5.7% for hamstrings strength from 50.9 ± 7 N*m to 53.5 ± 8.2 N*m at 150°/s ( P = .03).
1.3.5
Cardiopulmonary tolerance and effectiveness of rehabilitation training protocols
The results of the stress test and 6-minute walking test are presented in Table 4 . After the training program, the resting HR significantly decreased by 15.1% ( P < .001) in the ST group and 13.5% ( P = .001) in the AT group. The submaximal heart rate (detected during the stress test) also significantly decreased by 8% ( P = .006) in the ST group and by 6% ( P = .001) in the AT group.
A significant decrease of submaximal SBP was noted in both groups: 7.8% ( P < .001) in the ST group and 6.6% ( P = .005) in the AT group. There was a significant increase of the maximal power in both groups: 18.5% ( P < .001) in the ST group and 9.5% in the AT group ( P = .002).
The ST group showed a greater increase in VO 2 max with 22.4%, from 18.5 ± 5 mL/kg per minute to 22.5 ± 6 mL/kg per minute ( P < .001) compared to the AT group with 13.3%, from 20.4 to 22.1 mL/kg per minute ( P = .01). The distance during the 6-minute walking test increased in both groups. This increase was significantly higher in the ST group (24% vs. 16.6%; P = .04).
1.3.6
Body composition
Data collected on body composition are presented in Tables 3 and 5 . There were no changes in body weight or body mass index after training program in both groups. However, there was a slight but significant increase of the LBM in both groups: 1% ( P = .001) in the AT group and 2.3% ( P < .001) in the ST group and a significant decrease in the body fat by 1.8% ( P = .003) in the AT group and by 3.1% ( P = .001) in the ST group.
1.3.7
Quality of life
Results of the SF-36 questionnaire are presented in Table 6 . Patients in both groups showed a better health status, as measured by the scores of the SF-36 scale. This improvement was visible in six of the eight health-related domains for the ST group and in four to eight health-related domains for the AT group. The results were higher and sensibly better in the domains: “physical function” ( P < .001) and “social function” ( P < .01) for patients in the ST group versus the AT group.
| SF-36 scores | AT ( n = 16) | ST ( n = 16) | ||
|---|---|---|---|---|
| BL | 8-W | BL | 8-W | |
| PA | 66 ± 23 | 65 ± 30 NS | 62 ± 14 | 75 ± 18 P < 001 |
| PR | 22 ± 12 | 59 ± 14 P = .003 | 12.5 ± 12 | 43 ± 11 P = .002 |
| BP | 52 ± 18 | 55 ± 23 NS | 70 ± 14 | 73 ± 19 NS |
| GH | 46 ± 27 | 46 ± 26 NS | 35 ± 22 | 37 ± 18 NS |
| VT | 50 ± 17 | 52 ± 25 NS | 33 ± 10 | 45 ± 15 P = .001 |
| SF | 62 ± 25 | 57 ± 28 P = .05 | 41 ± 28 | 56 ± 31 P < .001 |
| ER | 33 ± 12 | 55 ± 12 P = .04 | 37 ± 13 | 41 ± 15 P = .001 |
| MH | 56 ± 16 | 63 ± 21 P = .03 | 59 ± 12 | 73 ± 12 P = .001 |
1.4
Discussion
Our results showed improved aerobic capacity and muscle strength for both groups. The two types of exercise also yielded significant cardiovascular improvements for body composition and quality of life parameters. However, the low-intensity dynamic ST program with an isokinetic dynamometer showed a more significant increase of the aerobic capacity and muscle strength. Even though aerobic training has been part of the international recommendations for prevention and rehabilitation of cardiovascular diseases for the past 30 years, yet teams have been more reluctant to prescribe ST for these patients . This hesitation is mainly based on the notion that elevation of systolic and DBP during ST increases the risk of cardiovascular complications, mainly in elderly patients or those with prior disorders . ST in patients with coronary heart disease (CHD) with good aerobic performance capacities and LV function was not contraindicated . In patients with chronic heart failure (CHF), the relevance of ST added to an AT program has been studied, authors reported that ST was well tolerated and improved the patients’ quality of life, muscle strength and endurance .
In our study, only three out of 16 patients in the ST group and five out of 16 in the AT group complained of knee pain. We were able to temporarily decrease the number of repetitions per minute, or reduce the cycling power so these patients did not have to interrupt their rehabilitation training. In the AT group, two patients were hospitalized for a few days following significant ST-segment depression, but they were able to return to training and complete the program at the same intensity level after having stopped for a week. Several studies indicated that ST could be safe for patients as an added component to cardiac rehabilitation training programs . All studies reported the absence of chest pain, ischemia with ST-segment depression, hemodynamic disorders, ventricular arrhythmia and cardiovascular complications. Thus, suggesting that ST could be safely used in clinically stable subjects suffering from CHF when actively participating in a cardiac rehabilitation training program. The reasons for arrhythmias reported during isometric exercises are not clearly determined, but could be related to the degradation of ventricular functions in some patients .
The response to aerobic dynamic exercise is an increased HR alongside the increase in exercise intensity. There is a progressive elevation of the SBP with a preservation or slight decrease of the DBP. During isometric exercise, the increase in HR, SBP and DBP is proportional to the intensity of the maximal voluntary force .
In our study, we used a ST protocol with isokinetic dynamometer comprised of dynamic-resistance exercise, and the cardiovascular responses were similar to the ones observed during aerobic/dynamic and isometric exercises. The level of the developed pressure load depends on the magnitude of the resistance (percent MVC) required and the duration of the muscle contraction in relation to the rest periods . The magnitude of the volume load on the cardiovascular system during a dynamic-resistance exercise is often greater when resistance is relatively low (because of the higher number of repetitions the subject is able to complete: 20 to 30). In our study, the increase in HR during sessions was the same in both groups. Mean values for SBP and DBP measured during the sessions increased similarly in both protocols. Equal increases in BP and HR were observed during the AT protocol and low-intensity resistance-dynamic type ST (20–30% MVC), with 20–40 repetitions, on the isokinetic dynamometer. Whereas the DBP should have decreased or remained stable with AT, substantial elevations of DBP were observed with ST. However, we should underline that these potential responses regarding HR and BP are not very likely to happen in ST since patients are strictly monitored and submitted to moderate-intensity exercises . Measures of intra-ABP in cardiac patients showed that during low-intensity resistance training (40–60% of MVC) with 15–20 repetitions, only slight BP elevations were revealed, similar to the ones observed during moderate-endurance rehabilitation training programs .
ABP response to heavy resistance training depends on the magnitude of the isometric component, load intensity (in percentage of MVC) , and importance of the trained muscle mass . It also depends on the number of repetitions and load duration. The highest ABP values were reached when several repetition series at 70–95% of MVC were performed up to exhaustion. In that case, ABP values were higher than the ones recorded at a lower intensity, or for one unique set of repetitions at maximal intensity .
The positive cardiovascular effects in the present study were mainly observed on the resting HR and results of the stress test for patients who benefited from AT and ST. Compared to the AT group, DBP at rest decreased significantly in the ST group (15% vs. 8.1%).
This isokinetic dynamic-resistance protocol seems more effective on ABP at rest and during stress tests and especially on DBP at rest. Several studies have reported the improvement in BP and HR values after rehabilitation training as well as decreased HR rest values , DPB and SBP . However, Ghilarducci et al. did not notice any significant changes in HR and ABP values at rest measured in persons after aerobic-type rehabilitation training. Worsornu et al. did find a significant decrease in HR rest values in ST as well as during submaximal exercise.
The present study contributes to document further the improvement in muscle strength after ST rehabilitation program for patients after CABG. A significant improvement in muscle strength was observed in the quadriceps for patients in the ST group, with a mean strength increase of 48.2% at the angular velocity of 150°/s. This improvement was significantly greater than the one observed in the AT group (8.2% at 150°). The mean increase in hamstrings strength was 7% at the angular velocity of 150°/s after ST. This modest improvement in hamstrings strength can be due to the high level of repetitions preventing patients to maintain a really active participation during knee flexion for all repetitions.
According to the results by Maiorona et al. , moderate-intensity training performed on a weight training circuit is safe and can effectively stimulate the development of muscle strength in the major muscle groups for men belonging to a low-risk category after CABG. Muscle strength improved in five of the seven tested exercises with a mean overall 18% increase. These results are in accordance with the conclusions from previous studies regarding same duration and low-intensity muscle ST in healthy patients and cardiac patients .
The authors reported significant improvement in muscle strength from 17% to 33%. The aerobic capacity in our study significantly increased in both groups. VO 2 max increase was higher in the ST group (22.4 vs. 13.3%). This difference between both groups could be related to a greater improvement of muscle strength in the ST group.
By using dynamic-resistance-type low-intensity exercise with an isokinetic dynamometer (20–30% of the MVF), with several repetitions by series (20–40) and resting periods in between series, the activity can end up being more aerobic in nature and thus maximize the aerobic effect. This increase in aerobic capacity could make this type of exercise attractive for physicians and patients alike. We should underline that the intensity used in our ST protocol was low for the muscle ST aspect, but quite “high” for the cardiovascular system. Slight improvements of the aerobic capacity have been reported in previous studies on ST for cardiac patients . However, in these studies, either ST was combined to AT or oxygen uptake was not directly measured. The improved aerobic capacity in these studies could be due to the increased muscle strength in the legs (allowing to perform greater exercises) while not necessarily being systematically associated to an increase in VO 2 max.
Patients who followed a rehabilitation ST program in the study by Kelemen et al. increased by 12% the duration of the stress test according to the “Bruce Treadmill Test” protocol, whereas no changes were reported in patients in the AT rehabilitation program on a cycle ergometer. VO 2 max was not measured during the treadmill test, so it is difficult to know if the endurance increase results from the improvement of the “oxygen” cycle or an effect due to the increase in leg muscle strength.
Haennel et al. have studied the effect of ST on maximum oxygen uptake. These authors compared the effects of hydraulic-resistance rehabilitation training to those obtained with a cycle ergometer alone in 24 men who underwent an 8-week rehabilitation program 9 to 10 weeks after their CABG. A VO 2 max increase was noted in both groups (11% in the “ST” group vs. 20% in the group trained on a cycle ergometer), but only patients in the ST group showed real gains in dynamic strength and endurance. In our study, patients in the ST group did present a slight but significant increase of the LBM (2.3% vs. 1% on the AT group). This increase in LBM could be explained by the individual strength gain obtained by cardiac patients in the ST program. This result suggests that ST could be an effective approach to increase and retain LBM in cardiac patients. We also noted a significant decrease of body fat (BF) after rehabilitation training in both groups.
Other studies have shown that ST can be effective to increase LBM in women .
Several studies showed that patients performing twice more resistance-type training than aerobic exercise lost more body fat and tended to gain more LBM than a group of patients in an AT-only program.
Ghilarducci et al. observed no significant changes for these variables in all cardiac patients, mostly because their subjects attended an individual AT program for at least 3 months, time during which the significant changes in body composition could have occurred. Persons with a fragile health have a hard time performing daily life physical activities, for this population, these endurance and ST exercises could significantly contribute to improving their of life .
Patients who are bed-ridden for the treatment of various chronic diseases tend to quickly lose muscle strength and endurance and might be confronted to a decreased ability in performing daily life activities, with a loss of autonomy and quality of life. Adding this ST component to their rehabilitation program could reduce these immobility-related negative effects . By adding ST to an aerobic program we can positively impact their psychosocial well-being and quality of life .
The improve muscle strength in the ST group is the most logical explanation in regards to the physical and social functions in this group.
Due to the randomized and controlled nature of this study, the clinical and anthropometric characteristics of both groups were similar. Maximum oxygen uptake was measured directly. The protocol (ST) used in our study is not commonly used in rehabilitation center and was not preceded nor followed by an aerobic-type rehabilitation training. The first limit to this study is related to the low number of subjects included; the second limit is that these patients were clinically stable at a very low risk of recurrent cardiac events, thus the results could not be extrapolated to a random population with coronary disorders. Another limit is the lack of women as recruited subjects. Finally, the difference between the two types of exercises (cycle ergometer and isokinetic dynamometer) makes it hard to compare both protocols.
1.5
Conclusion
This low-intensity dynamic-resistance strength straining protocol, using an isokinetic dynamometer (20–30% of MVC) comprising several repetitions (20–40) and a resting period in between series, can safely improve quadriceps and hamstrings strength along with a significant VO 2 max increase for low-risk patients after CABG. This aerobic capacity and increase in muscle strength should make this type of exercise attractive for physicians and patients alike. Furthermore, this ST protocol seems to improve cardiovascular parameters, BMI and quality of life parameters. These results could be extrapolated to other populations of cardiac patients. The feasibility and promising preliminary results of this ST protocol should encourage rehabilitation centers to use this training modality in other studies even if it is more time consuming and costly.
Disclosure of interest
The authors declare that they have no conflicts of interest concerning this article.
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