Effects of 12 weeks of power-oriented resistance training plus high-intensity interval training on metabolic syndrome factors in older people with COPD

Introduction

Chronic obstructive pulmonary disease (COPD) is a disease characterized by a range of persistent respiratory symptoms and airflow limitation that can be caused by abnormalities in the airways and alveoli [1]. One of the most common causes of COPD is prolonged exposure to harmful particles or gases. In developed countries, it is estimated that around 95 % of COPD cases are caused by smoking [1]. According to the World Health Organization, COPD affects one-tenth of the world’s population and may become the third leading cause of death by 2030 [2]. Furthermore, COPD is directly related to a deterioration in the quality of life of patients [3]. Although the most common symptom of the disease is dyspnoea, there are other systemic manifestations associated with it [4]. Limitations in gas exchange may cause alterations in peripheral tissues, and the release of inflammatory mediators into the circulation can initiate or worsen numerous comorbid diseases such as cachexia, osteoporosis or metabolic syndrome (MetS) [5].

Metabolic syndrome has been defined as a set of metabolic disorders including dyslipidaemia, hypertension and insulin resistance, which are also commonly associated with central obesity. MetS is diagnosed in those patients presenting at least two or more of these cardiovascular risk factors [6]: abdominal obesity, high blood pressure, impaired fasting glucose, high triglyceride levels and low HDL cholesterol levels. A relevant proportion of COPD patients present with obesity and MetS, which in turn have a negative influence on dyspnoea and exercise tolerance [7]. These comorbidities aggravate COPD progression and increase mortality risk [8]. Therefore, the reduction of MetS factors in COPD patients may be a key therapeutic target for the improvement of COPD symptomatology and quality of life [7]. In this regard, physical exercise is an effective tool in the individual treatment of both COPD and MetS [9]. The combination of resistance and endurance exercise in the same training session (i.e., concurrent training) has been shown to be the most effective methodology for achieving improvements in strength, exercise tolerance and quality of life in COPD patients [10, 11]. On one hand, power-oriented resistance training (RT) can provide additional functional benefits over traditional RT in older people [12], and preserve muscle oxygenation levels during exercise [13]. On the other hand, both continuous endurance training and high-intensity interval training (HIIT) are equally effective in improving exercise capacity in COPD patients [14], however the intermittent nature of HIIT was found to be better tolerated by COPD patients [15]. In a previous study, we found that combining power-oriented RT and HIIT led to significant improvements in muscle function, exercise capacity, functional capacity, quality of life and systemic oxidative stress in COPD patients [16]. However, although the benefits of concurrent exercise programs on COPD patients and MetS patients are well known [16, 17], no previous studies have assessed the effects of a concurrent exercise program on MetS markers in COPD patients. Of note, an improvement in MetS markers in COPD patients may lead to an improvement in dyspnoea and exercise tolerance [7], and reductions in COPD progression and mortality risk [8].

Therefore, the main goal of this study was to investigate the effects of a 12-week concurrent exercise program combining power-oriented RT and HIIT on markers of MetS in older people with COPD. A graphical representation of the study is shown in Figure 1.

Figure 1:

Graphical representation of the study. Key points: (1) the combination of power-oriented resistance training and high-intensity interval training might be an excellent time-efficient option to treat older people with different comorbidities. (2) This type of intervention improved mean arterial pressure, avoided an increase in waist circumference and lowered an index of metabolic syndrome in older people with chronic obstructive pulmonary disease. (3) An individualized exercise training program consisting of two 30-min sessions per week was well tolerated by older people with chronic obstructive pulmonary disease and proved to be feasible in the clinical setting.

Materials and methods

Results

A total of 9 COPD outpatients completed the concurrent training program and 14 COPD outpatients completed the control period (Figure 2). Compliance for the ET participants was 93 ± 8 %. The baseline characteristics of the participants who completed the study are shown in Table 2. Five out of the 9 ET participants and 7 out of the 14 CON participants presented MetS.

Figure 2:

Flowchart of the study.

The effects of the concurrent training program and control period over the 12-week period are shown in Table 3. There was a main effect of time on waist circumference (+1.5 [0.1, 2.8] cm; p=0.027), although it only increased significantly in the CON group (p=0.023; ES=0.14) but not in the ET group (p=0.386; ES=0.07). No significant time-by-group interaction was found for waist circumference (p=0.507), and no main effects of time were detected for triglycerides (−4.9 [−18.8, 8.9] mg dL-1; p=0.456; ES=0.08–0.28), HDL cholesterol (+1.9 [-1.6, 5.5] mg dL⁻¹; p=0.255; ES=0.08–0.23) or glucose (−2.5 [−7.5, 2.4] mg dL⁻¹; p=0.290; ES=0.04–0.15) levels. In addition, no significant within-group changes were observed in any of the groups nor significant time-by-group interactions were found for triglycerides, HDL cholesterol or glucose levels (all p>0.05). A main effect of time was noted for SBP (−8.1 [−14.4, −1.7] mmHg; p=0.009) and MAP (−4.3 [−7.8, −0.8]; p=0.012) but not for DBP (−2.5 [−5.2, 0.3] mmHg; p=0.067). However, a significant drop in MAP (p=0.003; ES=0.65), DBP (p=0.014; ES=0.47) and SBP (p=0.009; ES=0.65) was found in the ET group, but not in the CON group (p=0.424, ES=0.09; p=0.889, ES=0.03; and p=0.377, ES=0.18; respectively). No significant time-by-group interactions were reported for SBP (p=0.153), DBP (p=0.056) or MAP (p=0.069). Regarding MetS z scores, no main effect of time was noted (−0.41 [-0.95, 0.14]; p=0.126). Nevertheless, a significant reduction in MetS z-score was observed in the ET group (−0.88 [−1.74, −0.03]; p=0.033; ES=0.31) but not in the CON group (−0.07 [-0.62, 0.76]; p=0.846; ES=0.02). No significant time-by-group interaction was reported in MetS z-score (p=0.087).

Discussion

The main results of this study were that after 12 weeks, the combination of power-oriented RT and HIIT, twice a week, achieved a significant reduction in blood pressure and prevented an increase in waist circumference in older people with COPD, while no significant effects were observed in the rest of the MetS markers. In addition, MetS z-score was diminished in the exercising participants but remained unchanged in the control group.

The prevalence of MetS is almost twice as high in COPD patients compared with non-COPD controls, and approximately 50 % of COPD patients have at least one MetS factor [23]. Moreover, when both pathologies coexist, the complications of each are amplified and COPD patients require more medication due to increased dyspnoea and reduced pulmonary capacity [23]. One of the reasons that may account for the increased prevalence of MetS in COPD patients is the elevated concentration of pro-inflammatory cytokines in the peripheral blood due to COPD-related lung inflammation. This elevation in inflammatory cytokines promotes systemic inflammation, one of the mediators of MetS [23, 24]. On the other hand, physical inactivity, as a consequence of COPD symptoms, can increase the risk of obesity and adipose tissue inflammation, augmenting the risk of MetS in COPD patients [23]. However, more studies are required to improve the understanding of the mechanisms that lead COPD patients to have an increased risk of MetS.

While the effects of physical exercise in people with COPD and MetS have been largely studied in both diseases separately, the interaction between these pathologies with a concurrent exercise training program has been poorly investigated. A previous study [25] observed an improvement in the inflammatory profile of COPD patients with MetS after a combination of pharmacological treatment (simvastatin) and RT consisting of upper- and lower-limb exercises (volume and intensity were not specified). In addition, a 4-month high-intensity exercise program combining ergometer-based cycling and walking (volume and intensity were not reported) achieved a reduction in triglycerides in COPD patients, but no other changes were reported in other cardiometabolic markers [26]. In our case, exercise training had substantial benefits in physical performance, muscle function, aerobic capacity, oxidative damage and quality of life [16]; in addition, we observed moderate positive effects in some MetS markers, while others remained unchanged. Specifically, we observed a significant decline in DBP and SBP. Reductions in both SBP and DBP were also observed by Morales-Palomo et al. [27] in MetS patients after conducting 16 weeks of HIIT (3 sessions per week; 4 sets of 4 min at 90 % of maximal heart rate plus 3 min at 70 % of maximal heart rate per session). The physiological mechanisms behind the positive effects of exercise on blood pressure have been suggested to be an improvement of endothelial function induced by nitric oxide production, the induction of pro-angiogenic pathways, and an increase in insulin sensitivity [28]. In addition, we observed a significant increase in waist circumference in the control group, while this deleterious effect was prevented in the exercising participants. Similarly, Da Silva et al. [17] observed a positive effect of RT plus HIIT on waist circumference in patients with MetS. Other studies have observed larger cardiometabolic benefits derived from the combination of RT and HIIT on MetS markers in patients with MetS alone [17, 29]. The different findings reported by these investigations may be the result of differences in the exercise dose. For example, in the current study, the main part of the exercise sessions consisted of ∼10 min of power-oriented RT plus ∼10 min of HIIT at the beginning of the exercise program, which progressed to ∼12–15 min of power-oriented RT plus ∼20 min of HIIT at the end of the exercise program. In contrast, other studies finding broader benefits derived from exercise on MetS factors included higher weekly frequency and longer exercise sessions [29]. Thus, it is possible that more frequent and longer exercise sessions are necessary to achieve greater metabolic benefits. For example, a reduction in obesity has been reported to be necessary to impact positively on MetS factors [7], which may be compatible with the necessity of more frequent and longer exercise sessions to achieve a higher energy expenditure. Nevertheless, it must be considered that the participants of the current study were older people with COPD, while the studies showing broader effects of physical exercise on MetS did not include older people with COPD. In this regard, a multidisciplinary pulmonary rehabilitation (including exercise, nutrition and education) has been suggested to be the most appropriate intervention for COPD [30]. This type of intervention has also been suggested to be appropriate to improve cardiovascular risk factors such as high blood pressure and high cholesterol levels [31, 32]. Thus, the inclusion of strategies targeting changes in nutrition and lifestyle is recommended for better management of MetS factors in older people with COPD. Of note, the current study was conducted in a hospital setting, and the exercise training program was conceived to be affordable and well-tolerated by older people with COPD; perhaps longer exercise sessions or a higher weekly frequency would have produced a higher number of dropouts. In this regard, it is important that the exercise dose provided can be repeated over time, and perhaps a more prolonged exercise intervention would have improved all MetS markers without the need to increase exercise volume or weekly frequency. These aspects merit investigation in future studies.

Finally, it is important to note that the exercising participants of the current study, apart from the effects reported in the current manuscript, experienced relevant benefits in physical performance, muscle function, exercise tolerance and quality of life [16] that were maintained after 10 months of detraining [20]. Therefore, despite the lack of benefits observed in some MetS factors (glucose, triglycerides and HDL cholesterol), the applied exercise program achieved clinical improvements in other important outcomes for healthy aging in COPD [33]. This is particularly important as having mobility limitations or frailty is a risk factor for MetS in older people [34]. Thus, improving physical performance and muscle function may potentially reduce the risk of MetS in the long term, which deserves to be investigated.

Among the limitations of the current study, the sample size was relatively small. Of note, older people with COPD are frequently reluctant to participate in exercise programs. The main barriers that COPD participants usually report are difficulties with transportation, mobility, distance and location of programs, which are more likely to affect the participants involved in the exercise program [35]. In addition, patients with COPD can experience disease exacerbations that impede them from attending exercise sessions. Therefore, future studies should test the feasibility and efficacy of this kind of exercise training performed at home, while ensuring the safety of the participants. Finally, only approximately half of the participants presented with MetS; thus, it is possible that the observed effects of exercise on MetS factors would have been greater if all the participants had presented with MetS. In any case, according to MetS z-score values, the participants of the current study were not metabolically healthy.

Conclusions

A 12-week exercise program combining power-oriented RT and HIIT decreased MetS z-score and blood pressure in older people with COPD and prevented the increase in waist circumference observed in the older adults with COPD who received usual care. No effects were noted in serum glucose, triglycerides, and HDL cholesterol levels. Different exercise parameters (e.g., higher weekly frequency and longer exercise sessions) or a longer intervention period may be required to achieve greater metabolic benefits.