Approximately 7.3 million deaths per year occur worldwide as a result of cardiovascular disease (CVD), a number that is expected to exceed 23.6 million by 2030. ¹ In Brazil, 300,000 people die each year from CVD, including stroke, heart failure, and heart attack or sudden cardiac death, representing 820 deaths per day, 30 deaths per hour, or one death every 2 minutes. ^{2 , 3}

Heart diseases result in physical deconditioning and skeletal muscle changes, such as atrophy and decreased strength, that interfere with functional capacity and quality of life. ^{4 , 5} Therefore, it is of paramount importance that individuals with heart disease be included in a cardiac rehabilitation program (CRP). ⁵

A CRP consists of four phases, with the first beginning in hospital, and is an ongoing process which aims to maintain well-being and facilitate resumption of social and professional activities. ^{6 , 7} Phase 2 of cardiac rehabilitation begins after hospital discharge or a few days after a cardiovascular event. At this stage, resistance training can be initiated to increase fatigue resistance and muscle strength, with a view to return to work or recreational activities. ^{8 , 9}

In clinical practice, resistance training to improve muscle strength is conventionally performed by means of free weights or weight machines, however, these require extensive physical space and are usually located at outside facilities, such as gyms and rehabilitation centers, which poses an additional challenge to patients with restricted mobility. ⁴ On the other hand, elastic tubes are practical, low-cost, portable, safe devices which can be used for resistance training, with the added advantage of increasing tension linearly from the start of the contraction until the end of the movement, which tends to be less damaging to the joints compared to free-weight or weight machine training. ^{10 , 11}

Training with elastic tubing has been associated with increased muscle strength in older adults with heart and lung diseases, ^{4 , 12} and has been shown to promote cardiorespiratory improvement in patients with chronic obstructive pulmonary disease. ¹³ However, whether this exercise modality can have a positive impact on cardiorespiratory capacity and quality of life in patients with heart disease remains unclear. ¹² We hypothesized that this alternative method of strength training would yield short-term gains in muscle strength, functional ability, aerobic capacity, and quality of life of these patients.

Thus, the objective of this study was to analyze the effects of a strength training program based on elastic tubing on functional capacity, maximum aerobic capacity, muscle strength, and quality of life in individuals with CVD in phase 2 of cardiovascular rehabilitation.

Due to the difficulty of adherence and the musculoskeletal limitations of some patients presented, only 13 subjects with heart disease were evaluated. One patient left the study due to hospitalization. Maximum aerobic capacity data ( Table 3 ) is only available for eight patients, due to failure to capture data during one CPET at the final time point of evaluation. Data on functional capacity were excluded from one patient who experienced ankle pain.

Table 3

Variables	Moments (n=8)		p-value
	Baseline	6 weeks
VO 2peak (mL·kg/min)	12.19±2.92	14.70±5.12	0.1200
VO 2peak (L)	0.94±0.32	1.17±0.59	0.1186
vVO 2peak (km/h)	3.12±0.58	3.54±0.66	0.0533

VO _2peak: peak oxygen consumption, vVO _2peak: exercise velocity corresponding to peak oxygen consumption; mL·kg/min: milliliters/kilograms/minute; L: liters; km/h: kilometers/hour. Results presented as mean ± standard deviation. Shapiro-Wilk test followed by Student’s t-test.

The sample consisted of 12 patients with heart disease, 8 men and 4 women, with a mean age of 63.33±10.80 years. The mean weight, height, and BMI were 77.35±13.95 kg, 1.60±0.07 m, and 29.92±4.28 kg/m ² respectively. The most commonly used drugs were antihypertensives (n=6), antiplatelet agents (n=6), and antilipemics (n=8). The most prevalent comorbidities were hypertension, diabetes, coronary heart disease, and a history of myocardial revascularization .

Figure 1 shows the differences in peripheral muscular strength between the baseline and week 6 time points. Significant differences were found after resistance training with elastic tubing. In the lower limbs, significant increases in strength were observed during both knee extension and flexion, while in the upper limbs, a significant difference was noted only in shoulder abduction.

Figure 1

Significant differences in 6MWT were also found between the baseline and 6-week time points. These analyses are described in Table 2 .

Table 2

Variables	Moments (n= 11)		p value
	Baseline	6 weeks
Distance traveled (m)	485.50±123.30	578.70±110.50	0.0399
Distance Predicted (m)	531.10±126.30	531.10±126.30	1.0000

M – meters. The results are presented as mean ± standard deviation. Shapiro-Wilk test followed by Student t test.

Table 3 shows the maximum aerobic capacity values of the evaluated patients. Analysis of VO _2peak (in mL·kg/min and L) and vVO _2peak did not demonstrate a significant increase after 6 weeks of training with elastic tubing.

The distribution of SF-36 quality of life scores is shown in Table 4 . There was no significant difference in any of the eight dimensions of the questionnaire after 6 weeks of training with elastic tubing as compared to baseline.

Table 4

Dimensions	Moments (n=10)		p-value
	Baseline	6 weeks
Functional capacity	76.00±14.10	74.50± 4.80	0.3898
Physical functioning	41.67±50.00	52.50±47.8	1.0000
Pain	63.33±22.88	56.60±22.69	0.4407
General health	58.28±22.57	56.80±13.31	0.9702
Vitality	63.89±14.31	59.50±19.5	0.7759
Role functioning, social	78.33±25.59	88.00±17.35	0.2228
Role functioning, emotional	55.51±47.16	46.20±45.00	0.6250
Mental health	72.89±13.38	68.70±20.18	0.9174

Results expressed as mean ± standard deviation. Shapiro–Wilk test followed by Student’s t-test.

The present study showed that 6 weeks of resistance training with elastic tubing had a positive influence on muscle strength of the lower limbs and shoulder abductors, as well as on functional capacity, in patients with heart disease. However, there was no significant difference in maximum aerobic capacity or quality of life.

A gain in muscle strength is an expected result of resistance training, ²⁴ and is of great clinical relevance, as it is related to improved ability to perform activities of daily living and work in patients with heart disease. Moreover, in the specific population of patients with CVD, improved muscle strength is associated with less overload on the cardiovascular system . ¹⁴ One previous study of resistance training with elastic tubing demonstrated this effect of increasing muscle strength and increasing functional capacity in patients with heart disease. ⁴ The authors compared the use of a resistance training program based on elastic tubing and conventional weight training. The intensity of resistance with elastic tubing was varied by changing the elastic tube length in relation to the body segment of the patient under evaluation, which differs from the present study, where resistance was increased by using different diameters of elastic tubing; the studies also followed different training schedules. ²⁵

In relation to the initial resistance of the elastic tubing, Turban et al., ⁴ assessed the one-repetition maximum (1RM), unlike in our study, where increasing resistance was measured according to perceived exertion on the Borg scale. Turban et al., ⁴ reported improvement in functional capacity and increased muscle strength and noted that this training modality may be a tool with which to begin cardiac rehabilitation, not excluding the use of conventional equipment, but as an adjunct.

Ramos et al., ¹⁴ compared resistance training performed with elastic tubing versus training carried out with a conventional weight machine in patients with COPD. The elastic resistance protocol used individualized repetitions according to the fatigue resistance test; series started with two repetitions and progressed to seven at the end of the intervention, while the conventional training protocol consisted of three sets of 10 repetitions. Both training programs provided benefits in muscle strength and quality of life, however, greater gains in functional capacity were found in the elastic tubing group. ¹⁴

Some important differences in protocol between the aforementioned study of COPD patients and the present study must be mentioned; for example, those authors used 8 weeks of training, while the present study used 6 weeks. Another difference concerns the way in which resistance and the number of repetitions were increased. In the present study, a gradual increase in resistance and series and a decrease in number of repetitions were implemented, so that the training was designed to increase muscular strength and not just fatigue resistance, as in the study of COPD patients. ¹⁴

Regarding functional capacity, our participants exhibited a significant improvement after 6 weeks of resistance training. A recent meta-analysis reported similar behavior: conventional resistance with weight machines was associated with a significant gain in functional capacity as soon as 4 weeks after the start of training. ²⁶ Ramos et al., ¹⁴ observed greater effects on functional capacity in training with elastic tubing when compared to conventional training, which demonstrates an advantage of this resource.

This gain in functional capacity observed in these studies may be explained by an increase in type I muscle fiber area and in oxidative enzyme activity in the skeletal musculature, both of which are known to be promoted by resistance training. ²⁷

The aerobic capacity of these patients did not demonstrate any significant change. This finding may be related to the lack of aerobic activity during the study training protocol. It is known that both the practice of aerobic exercise in isolation and aerobic exercises combined with resistance training promote improvement in VO _2peak ¹⁴ however, there are no studies to provide evidence of the influence of resistance training with elastic tubing alone on aerobic capacity in patients with heart disease. Other studies have shown similar values when evaluating initial aerobic capacity of similar patient populations; however, in their protocols, aerobic training or combined aerobic and resistance training were performed over a prolonged period (11 months on average), before and after intervention. This indicates that aerobic capacity tends to increase significantly with long-term training. ²⁸

Analysis of quality of life in our patients did not show significant change in any of the eight SF-36 dimensions. However, it should be noted that, at the start of training, the patients already had a good perception of quality of life (i.e., values above 50 points) in seven of the eight dimensions. The exception was the physical limitation domain, which scored below 50 points on average at baseline and improved after the intervention, although the difference was not significant. The quality of life dimension is more related to functional capacity than muscle strength, as observed in a study by Nogueira et al., which showed a direct correlation between functional capacity and quality of life. ²⁹

The intervention proposed herein – resistance training with the use of elastic tubing – facilitates adaptation of the neuromuscular system to changes in intensity throughout the range of motion of the exercise, since the elastic tube generates resistance not only in the plane of movement, thus favoring constant modulation of the muscle strength used over the range of motion, but also promoting joint safety as compared to conventional exercise. This characteristic was shown to be beneficial and effective as an alternative to a conventional resistance training program within the context of a CRP. ³⁰

Limitations of this study include the small sample size and the use of a subjective variable (Borg rating of perceived exertion) as the determinant of training progression. We suggest that future studies consider other measures, such as the 1RM. In addition, future studies to measure the force exerted by elastic tubes of different diameters, which could be readily accomplished using Hooke’s law, may also contribute to the literature.

Short-term resistance training with elastic tubing was able to promote improvement in peripheral muscle strength and functional capacity in patients with heart disease. However, no changes were observed in maximal aerobic capacity or quality of life.