Abstract
Eccentric ergometer training (EET) is increasingly being proposed as a therapeutic strategy to improve skeletal muscle strength in various cardiorespiratory diseases, due to the principle that lengthening muscle actions lead to high force-generating capacity at low cardiopulmonary load. One clinical population that may particularly benefit from this strategy is chronic obstructive pulmonary disease (COPD), as ventilatory constraints and locomotor muscle dysfunction often limit efficacy of conventional exercise rehabilitation in patients with severe disease. While the feasibility of EET for COPD has been established, the nature and extent of adaptation within COPD muscle is unknown. The aim of this study was therefore to characterize the locomotor muscle adaptations to EET in patients with severe COPD, and compare them with adaptations gained through conventional concentric ergometer training (CET). Male patients were randomized to either EET (n = 8) or CET (n = 7) for 10 weeks and matched for heart rate intensity. EET patients trained on average at a workload that was three times that of CET, at a lower perception of leg fatigue and dyspnea. EET led to increases in isometric peak strength and relative thigh mass (p < 0.01) whereas CET had no such effect. However, EET did not result in fiber hypertrophy, as morphometric analysis of muscle biopsies showed no increase in mean fiber cross-sectional area (p = 0.82), with variability in the direction and magnitude of fiber-type responses (20% increase in Type 1, p = 0.18; 4% decrease in Type 2a, p = 0.37) compared to CET (26% increase in Type 1, p = 0.04; 15% increase in Type 2a, p = 0.09). EET had no impact on mitochondrial adaptation, as revealed by lack of change in markers of mitochondrial biogenesis, content and respiration, which contrasted to improvements (p < 0.05) within CET muscle. While future study is needed to more definitively determine the effects of EET on fiber hypertrophy and associated underlying molecular signaling pathways in COPD locomotor muscle, our findings promote the implementation of this strategy to improve muscle strength. Furthermore, contrasting mitochondrial adaptations suggest evaluation of a sequential paradigm of eccentric followed by concentric cycling as a means of augmenting the training response and attenuating skeletal muscle dysfunction in patients with advanced COPD.
Highlights
Locomotor muscle dysfunction is a highly prevalent and disabling condition associated with chronic obstructive pulmonary disease (COPD), and is characterized by significant weakness and increased fatigability
Are many patients with advanced disease unable to participate in exercise rehabilitation, there is great variability in training responsiveness within the COPD patient population, emphasizing the need to redesign and personalize the exercise rehabilitation approach to optimize therapeutic efficacy (Spruit et al, 2015)
Our current study demonstrates the safety and efficacy of ergometer training (EET) in patients with moderate to severe COPD, and provides evidence for its inclusion into current pulmonary rehabilitation programs
Summary
Locomotor muscle dysfunction is a highly prevalent and disabling condition associated with chronic obstructive pulmonary disease (COPD), and is characterized by significant weakness and increased fatigability. It has been shown that at the same metabolic demand, eccentric exercise allows for a four- to fivefold higher muscle mechanical load than conventional concentric exercise (Lindstedt et al, 2001; Meyer et al, 2003; IsnerHorobeti et al, 2013). Because the intensity of muscle contraction is a principal determinant of muscle growth and strength development, moderate load eccentric-based cycling protocols are being applied at relatively low cardiovascular demands in both healthy aging and cardiac disease populations, and shown to yield significant improvements in skeletal muscle strength (Meyer et al, 2003; Steiner et al, 2004; Zoll et al, 2006; Gremeaux et al, 2010)
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