Highlights
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Muscle Strength & Adverse Events: Lower quadriceps strength linked to more rehab complications.
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Functional Capacity & Adverse Events: Poor fitness raises adverse event risk during rehab.
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Fatigue, Muscle Strength, & Function: Fatigue, weak muscles, and poor fitness tied to rehab issues.
Abstract
Objective
To identify the associations between cardiorespiratory fitness and quadriceps muscle strength and the occurrence of minor adverse events in a cardiac rehabilitation (CR) program.
Design
Prospective cohort study.
Setting
Output of a CR programme for primary or secondary prevention of cardiovascular disease (CVD).
Patients
Seventy individuals who were diagnosed with CVD and/or risk factors and 7 who were excluded due to a low adherence rate in exercise sessions (<70%), 4 due to errors in oxygen consumption recorded during the cardiopulmonary exercise test (CPET) and 11 because they decided to withdraw from the study. The data of 38 participants were analyzed.
Interventions
Not applicable.
Main outcome measures
Quadriceps muscle strength was assessed by an isokinetic dynamometer and by a manual dynamometer. Functional capacity was assessed by the CPET and by a six-minute walk test (6MWT). Participants were monitored by a physiotherapist during 24 exercise sessions to identify and register adverse events.
Results
Significant associations were detected between adverse events and quadriceps muscle strength assessed by an isokinetic dynamometer (peak torque, B=-2.0(-2.0;0.0), p=0.047), between functional capacity assessed by the CPET (peak torque, B=-0.3(-2.4;0.0), p=0.019), between fatigue and functional capacity assessed by the CPET (VO2max, B=-1.3(-2.9;0.0), p=0.005) and between quadriceps muscle strength assessed by an isokinetic dynamometer (peak torque, B=-10.0(-2.7;0.0); p=0.010).
Conclusions
Lower functional capacity and quadriceps muscle strength seem to be associated with a greater incidence of adverse events during exercise sessions.
Graphical abstract
Introduction
Cardiovascular disease (CVD) is considered the leading cause of death worldwide. An estimated 17.7 million people die from CVD each year, and this number is estimated to increase by 25 million by 2030. Cardiac rehabilitation (CR) is a class 1A recommendation for the secondary prevention of individuals with CVD. Robust evidence suggests positive effects of CR participation, including increased cardiorespiratory fitness, improved quality of life and reduced cardiovascular events, morbidity and mortality. Exercise is one of the main components of CR programs. An increase in the metabolic demand needed to carry out exercise results in several body alterations, including increases in sympathetic activity, heart rate, and blood pressure. These alterations can facilitate the occurrence of adverse events in individuals with CVD. ,
Physical parameters such as low cardiorespiratory fitness and muscle strength have been associated with increased mortality risk and the occurrence of major adverse events in different populations. Minor adverse events such as arrhythmias, fatigue, muscle pain, angina, and abnormal increases in blood pressure (BP) are also observed during exercise in CR programs. , However, it is unknown whether physical parameters are associated with the occurrence of minor adverse events in individuals participating in CR programs. Understanding these aspects may allow health care professionals to identify patients at risk of developing minor adverse events early. It can improve safety in a CR setting, as minor adverse events can anticipate the occurrence of major adverse events such as sudden death and myocardial infarction. Thus, this study aimed to identify the associations between cardiorespiratory fitness and quadriceps muscle strength and the occurrence of minor adverse events in a CR program.
Methods
Compliance with ethical standards
This prospective cohort study was approved by the São Paulo State University School of Technology and Sciences Research Ethics Board (CAAE: 79213417.0.0000.5402). All participants were informed about the objectives of this study, and written informed consent was obtained. This study was performed in accordance with the Declaration of Helsinki.
Participants
Fifty-five individuals who participated in a CR program for primary or secondary prevention of CVD were included in the study. Individuals were excluded if they had <70% adherence in two months (24 sessions) of participation in a CR program, had errors capturing oxygen during the cardiopulmonary exercise test (CPET) or if they did not complete all the assessments proposed by this study.
Experimental approach
The study comprised five visits. The first visit aimed to assess information for sample characterization, including age, time of participation in a CR program, referring diagnosis, medication use, weight, height, and abdominal, waist and hip circumferences. Each visit was performed within an interval of 48 hours. Quadriceps muscle strength was assessed by an isokinetic dynamometer at visit two and by a digital dynamometer at visit three. Functional capacity was assessed by the CPET at visit four and by the six-minute walk test (6MWT) at visit five. After that, a trained physiotherapist closely monitored participants for 24 supervised exercise sessions performed in a CR program to identify and register the occurrence of adverse events. A better description of the CR program performed by participants in this study was described by Vanzella et al
Adverse events
Trained physiotherapists used a checklist to identify and register the occurrence of adverse events in exercise sessions performed in a CR program. Adverse events included in the checklist were the most prevalent signs and symptoms reported in the literature in this population. Symptoms were observed by physiotherapists and included pulse alterations, abnormal increases in BP (> 220/110 mmHg), tachypnea, and pallor. Symptoms were reported by participants and included fatigue, muscle pain, angina, nausea, cramp, and dizziness.
Quadriceps muscle strength
Quadriceps muscle strength was assessed by both isokinetic and manual dynamometers. In the isokinetic dynamometer, participants seated on the equipment’s chair with bands fixing their chest, hip, and ankle of the dominant lower limb. They performed a warm-up consisting of 10 repetitions of knee flexion and extension (quadriceps concentric contraction) at 180°/s of amplitude and a maximal isometric voluntary contraction (MIVC) for five seconds with the dominant lower limb positioned at 60° of knee flexion. MIVC was performed three times within two minutes. A greater peak of torque (Nm) normalized to body weight was considered for analysis.
In the manual dynamometer (Meditec®, Brazil), participants also seated on a chair with bands fixing their chest, hip, and ankle of the dominant lower limb. They performed MIVC at 60% of knee flexion for five seconds. MIVC was performed three times within 2 minutes. Higher muscle strength (N) normalized by body weight was considered for analysis.
Functional capacity
Functional capacity was assessed by the CPET and 6MWT. CPET was performed on a treadmill (Super ATL, Inbrasport, Brazil) following the Bruce protocol. It consisted of a progressive increase in speed and slope every three minutes. Participants were monitored using an electrocardiogram during the whole test. The test was terminated if one or more of the following criteria were met: volitional fatigue (participant’s choice to stop), maximum aged predicted heart rate (HR) achieved (predict HRmax = 220 – age), plateau in oxygen consumption, excessive blood pressure rise (i.e., SBP > 240 mmHg and DBP > 120 mmHg), ECG abnormalities (i.e., ST depression > 2 mm suggestive of new ischemia, significant supraventricular or ventricular arrhythmia), or symptoms (i.e., chest pain, shortness of breath, dizziness). The oxygen consumption (VO 2 max) was assessed by a commercial Quark PFT system (Cosmed, Rome, Italy) calibrated with known volume and gas concentrations. Tests were carried out by a physician.
The 6MWT was performed on a flat, hard surface 30-meter hall. Participants walked as fast as possible without running for 6 minutes. The test was performed twice within 30 minutes following the American Thoracic Society recommendations. A greater walking distance (metres) was considered for analysis.
Data analysis
Descriptive statistics are presented as the mean, standard deviation, percentage, and absolute number. The normality of the data was verified by the Shapiro‒Wilk test. A linear regression model adjusted for CVD incidence, time of participation in CR programs, age and sex was used to evaluate the associations between the most prevalent adverse events, quadriceps muscle strength and functional capacity. Significance was fixed at 5%. Statistical analysis was performed using SPSS version 15.0 (SPSS, Chicago, USA).
Results
Fig. 1 shows the study flow diagram. Seventy-five individuals who participated in a CR program were screened for eligibility. Of those, 5 were not eligible, and 10 were not interested in participating in the study. Of those included in the study, 7 were excluded due to a low rate of adherence to exercise sessions (<70%), and 4 were excluded due to errors in oxygen consumption recorded during the CPET. Eleven participants decided to withdraw from the study. Finally, the data of 38 participants were analyzed.
Table 1 shows the sample characterization. Individuals included in this research study participated in a CR program for 6.8±6.2 years. Most of them were elderly (61.6±11.6 years old) and were classified as overweight according to their BMI (28.9±4.2 kg/m 2 ). The most prevalent referral diagnosis was coronary heart disease (57.9%; n=22), and the most common medications used were beta-blockers (68.4%; n=26), statins (68.4%; n=26) and anticoagulants (63.2%; n=24).
| Variables | Mean±SD N (%) |
|---|---|
| Age | 61.6 ± 11.6 |
| Sex (male) | 19 (50%) |
| Weight (kg) | 77.8 ± 15.1 |
| Height (m) | 1.6 ± 0.0 |
| BMI (kg/m 2 ) | 28.9 ± 4.2 |
| Waist circumference (m) | 100.5 ± 12.1 |
| Waist/hip ratio | 0.9 ± 0.8 |
| Time of participation in CR (y) | 6.8 ± 6.25 |
| Referring diagnosis | |
| Coronary heart disease | 22 (57.9%) |
| Primary prevention | 8 (21.2) |
| Arrythmia | 2 (5.3%) |
| Valvopathy | 1 (2.6%) |
| Heart failure | 1 (2.6%) |
| Congenital cardiovascular disease | 1 (2.6%) |
| Medication | |
| Beta-blockers | 26 (68.4%) |
| Statins | 26 (68.4%) |
| Anticoagulant | 24 (63.2%) |
| Hypoglycemic agents | 21 (55.3%) |
| Diuretics | 11 (28.9%) |
| ACE inhibitors | 8 (21.1%) |
| Angiotensin II receptor blocker | 1 (2.6%) |
| Vasodilators | 8 (21.1%) |
| Calcium channel blockers | 8 (21.1%) |
| Fibrates | 3 (7.9%) |
| Digitalis | 1 (2.6%) |
| Potassium channel blockers | 1 (2.6%) |
| Other medications | 22 (57.9%) |
An average of 6.02±6.68 adverse events were registered. Signs – Pulse alterations: 3.15±5.80; Abnormal BP: 0.18±0.39; Pallor: 0.00±0.00; Tachypnea: 0.02±0.16; Symptoms – Fatigue: 1.15±1.73; Muscle pain: 1.05±1.45; Dizziness: 0.21±0.81; Angina: 0.07±0.27; Cramp: 0.10±0.38; Nausea: 0.02±0.16.
Table 2 shows associations between total number of adverse events, fatigue, muscle pain, pulse alterations, functional capacity and quadriceps muscle strength. The functional capacity and quadriceps muscle strength assessed by the CPET and by an isokinetic dynamometer were significantly associated with the total number of adverse events and fatigue (p<0.05). No significant associations were detected between adverse events, functional capacity or muscle strength assessed by the 6MWT or manual dynamometer (p>0.05).
| Total of Signs/Symptoms | Arrhythmias | Muscle pain | Fatigue | |||||
|---|---|---|---|---|---|---|---|---|
| B (95%IC) | p | B (95%IC) | p | B (95%IC) | p | B (95%IC) | p | |
| ISOKINETIC DYNAMOMETER | ||||||||
| Muscle strength | ||||||||
| Peak Torque (N-M) * | -2.0 (-2.0;0.0) | 0.047 | -2.0 (-1.7;0.0) | 0.085 | -1.8 (-0.3;0.7) | 0.705 | -10.0 (-2.7;0.0) | 0.010 |
| MANUAL DYNAMOMETER | ||||||||
| Muscle strength | ||||||||
| Peak of Strength (N) * | -4.6 (-1.7;0.0) | 0.092 | -5.3 (-1.7;0.0) | 0.095 | -5.3 (-0.4;0.6) | 0.678 | -7.1 (-0.6;0.5) | 0.511 |
| CPET | ||||||||
| Functional capacity | ||||||||
| Peak VO2 | -0.3 (-2.4;0.0) | 0.019 | -0.2 (-1.9;0.0) | 0.053 | -0.4 (-0.8;0.4) | 0.421 | -1.3 (-2.9;0.0) | 0.005 |
| 6MWT | ||||||||
| Functional capacity | ||||||||
| Total Distance | -1.3 (-8.1;0.4) | 0.421 | -0.3 (-0.1;0.8) | 0.082 | -9.5 (-1.2;0.2) | 0.227 | -11.1 (-1.7;0.0) | 0.087 |
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