Identification of Explanatory Factors for the Lack of Muscle Strength Gain Following a Pulmonary Rehabilitation Program in COPD Patients

Overview

Chronic Obstructive Pulmonary Disease (COPD) is a chronic respiratory disease associated with various comorbidities, including muscle weakness (MW), which is very worrying due to its negative impact on patients' quality of life and survival. To address this issue, muscle strengthening is incorporated into pulmonary rehabilitation programs. However, its effectiveness is unclear, as although there is an average improvement in muscle strength, one in two patients does not show a clinically relevant improvement. To understand this non-response, it is crucial to examine the effect of muscle strengthening programs on the two main determinants of force production: the muscle and the central command. Muscle adaptations following a muscle strengthening program are well-documented, showing improvements in muscle function (cross-sectional area, lean mass, etc.). Conversely, only one study has investigated central adaptations after a muscle strengthening program, clearly demonstrating a lack of effect. The investigators hypothesize that patients showing no improvement in muscle strength after pulmonary rehabilitation (non-responders) have a significantly lower level of voluntary activation before starting the program compared to responding patients (responders).

Chronic Obstructive Pulmonary Disease (COPD) is a chronic respiratory disease. Beyond respiratory symptoms, COPD is linked to comorbidities like muscle weakness (MW), significantly worrying due to its impact on patients' quality of life and survival. MW affects 32% to 57% of patients, predominantly in the lower limbs, contributing to exercise intolerance, reduced quality of life, and increased healthcare costs. To address MW, muscle strengthening is incorporated into pulmonary rehabilitation (PR) programs. Despite significant average improvements in quadriceps muscle strength reported in the literature, a recent study highlight that 50% of patients did not clinically enhance their strength and were called non-responders (NR). To understand this non-response, it's crucial to investigate the impact of muscle strengthening programs on the determinants of strength loss. While muscle atrophy was initially considered a major factor, studies have shown that muscle mass does not entirely explain the loss of strength. Impairment of motor control has emerged as a significant secondary determinant of muscle strength loss. Peripheral muscle adaptations, including increased muscle surface and lean thigh mass, are well-documented. However, regarding motor control adaptations, a single study using a reference method on the quadriceps indicates a lack of effect of PR programs on central control. This observation suggests that non-responders in terms of strength may exhibit impaired motor control from the onset of the PR program.