Skeletal muscle contractility and fatigability in adults with cystic fibrosis

Peripheral Muscle Function and Body Composition in People With Cystic Fibrosis on Elexacaftor/Tezacaftor/Ivacaftor: A Cross-Sectional Single-Centre Study

BACKGROUND

People with cystic fibrosis (pwCF) often have multifactorial peripheral muscle abnormalities attributed to, for example, malnutrition, steroid use, altered redox balance and, potentially, CF-specific intrinsic alterations. Malnutrition in CF now includes an increasing prevalence of overweight and obesity, particularly in those receiving CF transmembrane conductance regulator (CFTR) modulator therapy (CFTRm). We aimed to characterise peripheral muscle function and body composition in pwCF on Elexacaftor/Tezacaftor/Ivacaftor (ETI) CFTRm, compared to healthy controls.

METHODS

Fifteen pwCF on ETI, and 15 healthy age- and sex-matched controls (CON), underwent whole-body dual-energy X-ray absorptiometry scans, and a comprehensive evaluation of peripheral muscle function. Tests included quadriceps maximal isometric force measurement, an intermittent isometric quadriceps fatiguing protocol, handgrip strength dynamometry, squat jump height assessment, and 1-min sit-to-stand testing.

RESULTS

No significant differences in quadriceps maximal isometric force (CON: 181.60 ± 92.90 Nm vs. CF: 146.15 ± 52.48 Nm, p = 0.21, d = 0.47), handgrip strength (CON: 34 ± 15 kg vs. CF: 31 ± 11 kg, p = 0.62, d = 0.18), peripheral muscle endurance, fatigue, or power were observed between the groups. Moreover, no significant differences in whole-body, trunk or limb lean mass, fat-free mass, fat mass, or whole-body bone mineral density were evident.

CONCLUSION

Comparable peripheral muscle mass and function has been demonstrated in pwCF on ETI, albeit a group with good lung function. Research is needed to confirm these findings longitudinally in pwCF, including those with more severe lung disease, who are less physically active, and have less optimal nutrition and exercise support.

Muscle endurance, neuromuscular fatigability, and cognitive control during prolonged dual-task in people with chronic obstructive pulmonary disease: a case-control study

PURPOSE

Recent studies suggest that, compared to healthy individuals, people with chronic obstructive pulmonary disease (pwCOPD) present a reduced capacity to perform cognitive-motor dual-task (CMDT). However, these studies were focused on short-duration CMDT offering limited insight to prolonged CMDT inducing fatigue, which can be encountered in daily life. The present study aimed to explore the effect of adding a cognitive task during repeated muscle contractions on muscle endurance, neuromuscular fatigability, and cognitive control in pwCOPD compared to healthy participants.

METHODS

Thirteen pwCOPD and thirteen age- and sex-matched healthy participants performed submaximal isometric contractions of the knee extensors until exhaustion in two experimental sessions: (1) without cognitive task and (2) with a concurrent working memory task (i.e., 1-back task). Neuromuscular fatigability (as well as central and peripheral components measured by peripheral magnetic stimulation), cognitive performance, and perceived muscle fatigue were assessed throughout the fatiguing tasks.

RESULTS

Independently to the experimental condition, pwCOPD exhibited lower muscle endurance compared to healthy participants (p = 0.039), mainly explained by earlier peripheral fatigue and faster attainment of higher perceived muscle fatigue (p < 0.05). However, neither effect of cognitive task (p = 0.223) nor interaction effect (group × condition; p = 0.136) was revealed for muscle endurance. Interestingly, cognitive control was significantly reduced only in pwCOPD at the end of CMDT (p < 0.015), suggesting greater difficulty for patients with dual tasking under fatigue.

CONCLUSION

These findings provide novel insights into how and why fatigue develops in COPD in dual-task context, offering a rationale for including such tasks in rehabilitation programs.

Implementation and outcomes of a quality improvement project to systematically assess the gross motor skills in school-aged children with cystic fibrosis

INTRODUCTION

Limited data exist on the gross motor abilities of children with cystic fibrosis (CF). The objective of this research project was to implement a systematic gross motor assessment in children with CF ages 4-12 years. Secondarily, we aimed to assess demographic characteristics associated with gross motor delays.

METHODS

Physical therapists aimed to evaluate at least 50% of eligible children (4-12 years) at our CF Center over 1 year using the Bruininks-Oseretsky Test of motor Proficiency, second edition (BOT-2). Delays are defined by scores less than 18th percentile. Demographic and clinical data included body mass index, hospitalizations, genotype, and comorbidities. Basic descriptive statistics summarized patient information. Parametric and nonparametric methods compared groups of interest. Linear regression assessed associations between BOT-2 measures and clinical characteristics.

RESULTS

The BOT-2 evaluation was successfully implemented with 69% of eligible patients being evaluated. Forty-five (62.5%) scored below average. Impaired strength (22.2%) was most common, followed by impaired balance (16.7%), running speed and agility (15.3%), and bilateral coordination (8.3%). 15.5% scored below average on their total motor composite score (TMC). Increased age, comorbidities and hospitalizations were associated with a lower TMC.

CONCLUSIONS

The BOT-2 was successfully implemented as part of routine CF care to screen for gross motor delays in children. Results suggest that a high percentage of children with CF, especially older children with comorbid conditions or a history of hospitalization, have impaired gross motor function. These findings support the need for routine gross motor evaluations and physical therapy interventions within pediatric CF clinics.

Extrapulmonary manifestations of pulmonary arterial hypertension

INTRODUCTION

Extrapulmonary manifestations of pulmonary arterial hypertension (PAH) may play a critical pathobiological role and a deeper understanding will advance insight into mechanisms and novel therapeutic targets. This manuscript reviews our understanding of extrapulmonary manifestations of PAH.

AREAS COVERED

A group of experts was assembled and a complimentary PubMed search performed (October 2023 - March 2024). Inflammation is observed throughout the central nervous system and attempts at manipulation are an encouraging step toward novel therapeutics. Retinal vascular imaging holds promise as a noninvasive method of detecting early disease and monitoring treatment responses. PAH patients have gut flora alterations and dysbiosis likely plays a role in systemic inflammation. Despite inconsistent observations, the roles of obesity, insulin resistance and dysregulated metabolism may be illuminated by deep phenotyping of body composition. Skeletal muscle dysfunction is perpetuated by metabolic dysfunction, inflammation, and hypoperfusion, but exercise training shows benefit. Renal, hepatic, and bone marrow abnormalities are observed in PAH and may represent both end-organ damage and disease modifiers.

EXPERT OPINION

Insights into systemic manifestations of PAH will illuminate disease mechanisms and novel therapeutic targets. Additional study is needed to understand whether extrapulmonary manifestations are a cause or effect of PAH and how manipulation may affect outcomes.

Mathematical modeling of exercise fatigability in the severe domain: A unifying integrative framework in isokinetic condition

Muscle fatigue is the decay in the ability of muscles to generate force, and results from neural and metabolic perturbations. This article presents an integrative mathematical model that describes the decrease in maximal force capacity (i.e. fatigue) over exercises performed at intensities above the critical force Fc (i.e. severe domain). The model unifies the previous Critical Power Model and All-Out Model and can be applied to any exercise described by a changing force F over time. The assumptions of the model are (i) isokinetic conditions, an intensity domain of Fc Collapse

Key Words

• All-out
• Anaerobic capacities
• Critical power
• Endurance
• Exercise fatigability
• Fatigue
• Maximal force capacity
• Muscular capacities
• Power-time relationship
• Time to exhaustion

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MESH Headings

• Exercise/physiology
• Muscle Fatigue
• Muscles/physiology
• Models, Theoretical
• Muscle, Skeletal/physiology

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Grants Collapse

Affiliation(s)

M Bowen Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France.
P Samozino Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France
M Vonderscher Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France
D Dutykh Mathematics Department, Khalifa University of Science and Technology, PO Box 127788, Abu Dhabi, United Arab Emirates; Causal Dynamics Pty Ltd, WA 6009, Perth, Australia
B Morel Laboratoire Interuniversitaire de Biologie de la Motricité LIBM, EA 7424, Savoie Mont Blanc University, F-7300, Chambéry, France

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Guidance and standard operating procedures for functional exercise testing in cystic fibrosis

Regular exercise testing is recommended for all people with cystic fibrosis (PwCF). A range of validated tests, which integrate both strength and aerobic function, are available and increasingly being used. Together, these tests offer the ability for comprehensive exercise evaluation. Extensive research and expert consensus over recent years has enabled the adaptation and standardisation of a range of exercise tests to aid the understanding of the pathophysiology related to exercise limitation in PwCF and has led to the development of novel exercise tests which may be applied to PwCF. This article provides expert, opinion-based clinical practice guidance, along with test instructions, for a selection of commonly used valid tests which have documented clinimetric properties for PwCF. Importantly, this document also highlights previously used tests that are no longer suggested for PwCF and areas where research is mandated. This collaboration, on behalf of the European Cystic Fibrosis Society Exercise Working Group, represents expert consensus by a multidisciplinary panel of physiotherapists, exercise scientists and clinicians and aims to improve global standardisation of functional exercise testing of PwCF. In short, the standardised use of a small selection of tests performed to a high standard is advocated.

Computed tomography reveals hypertrophic remodelling of the diaphragm in cystic fibrosis but not in COPD

Background

Computed tomography (CT) is increasingly used for assessing skeletal muscle characteristics. In cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD), reduced limb muscle mass predicts poor clinical outcomes. However, the degree to which quantity or quality of respiratory and nonrespiratory muscles is affected by these diseases remains controversial.

Methods

Thoracic CT images of 29 CF, 21 COPD and 20 normal spirometry control subjects were analysed to measure indices of muscle quantity (volume or cross-sectional area) and quality (radiodensity) in respiratory (diaphragm, abdominal) and nonrespiratory (pectoralis, lumbar paraspinal) muscles. Multivariable linear regression assessed relationships of CT measurements with body mass index (BMI), forced expiratory volume in 1 s (FEV1) % pred, inflammation and infection biomarkers, nutritional status and CF genotype.

Results

Diaphragm volume in CF was significantly higher than in COPD (by 154%) or controls (by 140%). Abdominal muscle area in CF was also greater than in COPD (by 130%). Nonrespiratory muscles in COPD had more low radiodensity muscle (marker of lipid content) compared to CF and controls. In CF but not COPD, higher BMI and FEV1 % pred were independently associated with higher diaphragm and/or abdominal muscle quantity indices. Serum creatinine also predicted respiratory and nonrespiratory muscle quantity in CF, whereas other biomarkers including genotype correlated poorly with muscle CT parameters.

Conclusions

Our data suggest that the CF diaphragm undergoes hypertrophic remodelling, whereas in COPD the nonrespiratory muscles show altered muscle quality consistent with greater lipid content. Thoracic CT can thus identify distinctive respiratory and nonrespiratory muscle remodelling signatures associated with different chronic lung diseases.

Characterization of skeletal muscle wasting pathways in diaphragm and limb muscles of cystic fibrosis mice

BACKGROUND

Cystic fibrosis (CF) patients often suffer from skeletal muscle atrophy, most often attributed to physical inactivity and nutritional factors. CF is also characterized by abnormally elevated systemic inflammation. However, it is unknown whether the lack of a functional CF transmembrane conductance regulator (CFTR) gene predisposes to exaggerated inflammation-induced muscle proteolysis.

METHODS

CF mice (CFTR-/-) and their wild-type (WT=CFTR+/+) littermate controls were systemically injected with Pseudomonas-derived lipopolysaccharide (LPS). After 24 hours, the diaphragm and limb muscles (fast-twitch tibialis anterior, slow-twitch soleus) were assessed for induction of inflammatory cytokines (TNFa, IL1b, IL6), oxidative stress, canonical muscle proteolysis pathways (Calpain, Ubiquitin-Proteasome, Autophagy), muscle fiber histology, and diaphragm contractile function.

RESULTS

At baseline, CF and WT muscles did not differ with respect to indices of inflammation, proteolysis, or contractile function. After LPS exposure, there was significantly greater induction of all proteolysis pathways (Calpain activity; Ubiquitin-Proteasome: MuRF1 and Atrogin1; Autophagy: LC3B, Gabarapl-1, BNIP3) in CF mice for the diaphragm and tibialis anterior, but not the soleus. Proteolysis pathway upregulation and correlations with inflammatory cytokine induction were most prominent in the tibialis anterior. Diaphragm force normalized to muscle cross-sectional area was reduced by LPS to an equivalent degree in CF and WT mice.

CONCLUSIONS

CF skeletal muscles containing a high proportion of fast-twitch fibers (diaphragm, tibialis anterior) exhibit abnormally exaggerated upregulation of multiple muscle wasting pathways after exposure to an acute inflammatory stimulus, but not under basal conditions.

Body functions and structure, activity, and participation limitations of adult cystic fibrosis patients under the international classification of functioning, disability, and health framework

Objective: There is no study in the literature evaluating impairments and functional limitations in adults with cystic fibrosis (CF) under the framework of the International Classification of Functioning, Disability, and Health (ICF). To evaluate the adults with CF using ICF model. Methods: Twenty-three adults with CF and 23 age-sex matched healthy individuals included in this cross-sectional study. The participants evaluated according to the selected items for domain b, domain s, and domain d from the Obstructive Pulmonary Diseases (OPD) Comprehensive Core Set. The body composition, pulmonary functions, respiratory and peripheral muscle strength/endurance tests and anxiety/depression level were evaluated for domain b and s. For domain d, the Incremental Shuttle Walk Test (ISWT) and Short Form-36 (SF-36) Health Survey were used. Results: The fat-free mass (p = .044), pulmonary functions (p < .05), respiratory muscle endurance (p = .010), absolute and %quadriceps muscle strength (p = .001, p = .025, respectively), number of sit-ups (p = .020), walking speed (p = .035), ISWT and ISWT% distance (p < .001) and peak oxygen consumption (p < .001) were significantly lower in adults with CF compared to healthy individuals (p < .05). There were only significant differences in SF-36 physical functioning and role physical subdimension scores between groups (p = .009, p = .045 respectively). Conclusions: The ICF framework is applicable to comprehensively evaluate limitations of adults with CF among rehabilitation professionals. Especially age, respiratory function, respiratory muscle strength and endurance, dyspnea perception, peripheral muscle endurance were related to activity and participation limitation.

The Exercising Brain: An Overlooked Factor Limiting the Tolerance to Physical Exertion in Major Cardiorespiratory Diseases?

“Exercise starts and ends in the brain”: this was the title of a review article authored by Dr. Bengt Kayser back in 2003. In this piece of work, the author highlights that pioneer studies have primarily focused on the cardiorespiratory-muscle axis to set the human limits to whole-body exercise tolerance. In some circumstances, however, exercise cessation may not be solely attributable to these players: the central nervous system is thought to hold a relevant role as the ultimate site of exercise termination. In fact, there has been a growing interest relative to the “brain” response to exercise in chronic cardiorespiratory diseases, and its potential implication in limiting the tolerance to physical exertion in patients. To reach these overarching goals, non-invasive techniques, such as near-infrared spectroscopy and transcranial magnetic stimulation, have been successfully applied to get insights into the underlying mechanisms of exercise limitation in clinical populations. This review provides an up-to-date outline of the rationale for the “brain” as the organ limiting the tolerance to physical exertion in patients with cardiorespiratory diseases. We first outline some key methodological aspects of neuromuscular function and cerebral hemodynamics assessment in response to different exercise paradigms. We then review the most prominent studies, which explored the influence of major cardiorespiratory diseases on these outcomes. After a balanced summary of existing evidence, we finalize by detailing the rationale for investigating the “brain” contribution to exercise limitation in hitherto unexplored cardiorespiratory diseases, an endeavor that might lead to innovative lines of applied physiological research.

Rethinking physical exercise training in the modern era of cystic fibrosis: A step towards optimising short-term efficacy and long-term engagement

Exercise is considered as an important component of the package of care delivered to people with cystic fibrosis (pwCF). However, despite the well-known short-term physiological and psychological benefits, training effects are heterogenous and the transfer of structured exercise programmes to the daily life of pwCF is challenging. Training concepts and strategies developed over the last decades must be adapted to consider the aging population of pwCF with associated comorbidities, and also a new generation of young pwCF that are healthier than ever. In the present review we propose a new framework for optimising the choice among available exercise training procedures and we provide a theoretical and scientifically justified rationale for considering and testing new exercise training modalities. We propose a multidisciplinary approach, considering various physiological, psychological and logistical factors, with the aim to increase effects of exercise training and build positive long-term exercise behaviour.

Peripheral muscle strength is associated with aerobic fitness and use of antibiotics in patients with cystic fibrosis

AIMS

Individuals with cystic fibrosis (CF) may develop muscle abnormalities, although little is known on its clinical and functional impact. This study aimed to evaluate the association of peripheral muscle strength with aerobic fitness, habitual physical activity, lung function and the use of antibiotics (ATB) in patients with CF.

METHODS

A cross-sectional study where individuals aged ≥6 years underwent peripheral muscle strength evaluation (biceps, quadriceps and hamstrings) and performed a cardiopulmonary exercise test. Demographic, anthropometric, genetic, lung function and total days of ATB use within 1 year of tests were also collected.

RESULTS

Correlation was found for biceps (r = .45; P = .002) strength with the peak oxygen consumption (VO₂ peak). Muscle strength (biceps and quadriceps) also correlated with the ventilatory equivalent for oxygen consumption (V_E /VO₂ ) at anaerobic threshold (AT) and with the ventilatory equivalent for carbon dioxide production (V_E /VCO₂ ) both at AT and peak exercise. Negative correlations were found for quadriceps (r = -.39) and hamstrings (r = -.42) with the total days of ATB use in the following year. Patients needing to use ATB presented lower biceps strength (P = .05) and individuals with VO₂ peak lower than 37 mL·kg^-1 ·min^-1 presented lower muscle strength for both biceps (P = .01) and quadriceps (P = .02).

CONCLUSIONS

The results have shown that peripheral muscle strength is associated with aerobic fitness and the use of antibiotics in patients with CF.

Limb muscle size and contractile function in adults with cystic fibrosis: A systematic review and meta-analysis

BACKGROUND

There is conflicting evidence regarding the presence of limb muscle impairments in adults with cystic fibrosis (CF), and the factors associated with these muscle impairments. The objectives of this study were to compare limb muscle size and function between adults with CF and healthy controls; and to examine their associations with demographic and clinical variables in adults with CF.

METHODS

The systematic review was performed using PRISMA guidelines. Studies were included if they measured any aspect of limb muscle size or function in adults with CF. Meta-analyses were performed to compare muscle variables between CF and healthy controls; and to examine their associations with demographic and clinical variables.

RESULTS

Twenty-eight studies were included, with 747 adults with CF. The meta-analyses showed that adults with CF have smaller thigh muscles [standardized mean difference (SMD) = 0.57, p<.0011, I²=0%], and lower handgrip strength (SMD = 0.89, p=.0034, I²=74.03%), which was weakly correlated with forced expiratory volume in one second (FEV₁) (r=0.24, p=.035, I²=0%) and lower in females with CF (SMD = 2.05, p<.0001, I²=0%). There is no significant difference between adults with CF and controls in knee extensor strength (SMD = 0.25, p=.095, I²=42.79%).

CONCLUSIONS

Leg muscle atrophy and lower handgrip strength were noted. There may be a subgroup of adults with CF with knee extensor (quadriceps) weakness. Future studies are needed to better understand muscle impairments in people with CF; to explore the factors that can predict these muscle impairments; and to investigate their clinical significance in people with CF.

Interval versus constant-load exercise training in adults with Cystic Fibrosis

BACKGROUND

The efficacy of interval exercise (IE) compared to constant-load exercise (CLE) training remains unsettled in adults with Cystic Fibrosis (CF).

METHODS

Twenty-four adults with CF were randomised to 30-min IE (100 % peak work capacity (WRpeak) for 30-s alternated with 40 % WRpeak for 30-s; n = 12) or 30-min CLE (70 % WRpeak; n = 12) training, 3 times weekly, for 12 weeks. Isometric quadriceps muscle strength was assessed using a strain gauge Myometer.

RESULTS

The magnitude of improvement in quadriceps muscle strength was greater (p = 0.037) in the IE (by 32 ± 13 Nm) compared to the CLE (by 23 ± 12 Nm) groups. Maximum inspiratory and expiratory mouth pressures were significantly improved only in the IE group (by 30 ± 10 cmH₂O; p = 0.009 and 13 ± 4 cmH₂O; p = 0.007, respectively). Arterial oxygen saturation during training was higher (p = 0.002) for IE (94 ± 1%) compared to CLE (91 ± 1%), whereas dyspnoea scores were lower (p = 0.001) for IE (3.8 ± 0.7) compared to CLE (5.9 ± 0.8) CONCLUSIONS: IE is superior to CLE in improving peripheral and respiratory muscle strength and preferable to CLE because it is associated with lower exercise-induced arterial oxygen desaturation and breathlessness.

Measurement properties of the one-minute sit-to-stand test in children and adolescents with cystic fibrosis: A multicenter randomized cross-over trial

Background

Functional exercise capacity assessment is recommended in children with cystic fibrosis (CF). The six-minute walk test (6MWT) is a valid evaluation of exercise capacity but can be technically complex. Inversely, the sit-to-stand test (STST) is a simple method to evaluate exercise capacity, and is validated in healthy children and adults with CF. This study aimed to evaluate STST measurement properties in children and adolescents with CF.

Methods

In this multicenter study, children with CF (6 to 18 years) performed two iterations of both the STST and the 6MWT in a randomized order. Criterion validity was determined by assessing correlations between STST repetitions and 6MWT distance (6MWD). Intra-rater reliability, test-retest repeatability, mean bias and limits of agreement were also assessed. Relationships with other outcomes (i.e. respiratory and quadriceps muscle strength) and cardio-respiratory responses were analysed for both tests.

Results

Thirty-six children with CF were included (mean age 12.0 ±3.5 years and FEV1 95.8 ±25.0%). On average, 39.6 ±10.5 repetitions were performed during the STST and mean 6MWD was 596.0 ±102.6 meters. STST number of repetitions was significantly correlated with 6MWD (r = 0.48; p<0.01). Both tests had very good intra-rater reliability (ICC_STST = 0.91 (95%CI 0.76–0.96) and ICC_6MWT = 0.94 (95%CI 0.85–0.97)), and a significant test-retest learning effect. The number of STST repetitions was not correlated with quadriceps or respiratory muscle strength test, and the STST induced fewer cardio-respiratory responses than the 6MWT.

Conclusions

The STST is an easy-to-use functional test with moderate criterion validity when compared to the 6MWT in children with CF, probably because both tests measure different components of functional exercise capacity. The STST is useful when the 6MWT is unfeasible, however further investigations are required to explore the clinical implications of STST results in children with CF.

Clinical trial registration

NCT03069625.

Neurophysiological relationship of neuromuscular fatigue and stress disorder in PTSD patients

INTRODUCTION

Apart from mental disorders, other complications that have been reported in some patients with Post-Traumatic Stress Disorder (PTSD), include physical pain and being quick to fatigue, which can severely affect the patients' daily life. Therefore, this study aims to evaluate the relationship between PTSD and physical fatigue in people with PTSD.

METHOD

18 military men with (n = 9) and without PTSD (n = 9), with an age range of 45-60 years, volunteered to participate. They were randomly assigned into two groups: PTSD and non-PTSD groups. Recording of the surface electromyography (EMG) in a specific muscle was conducted twice in both groups, once at baseline and then again after a single session of fatiguing exercise. Data were analyzed by ANOVA with repeated measure (2✕2) at the significance level of 0.05.

RESULTS

Results showed that there was a significant main effect of intervention on electrical activity and neural conduction variables in the PTSD group (p = 0.04, p = 0.02). There was also an effect of time for the both variables (P < 0.001).

CONCLUSION

Stress disorders may affect the time to fatigue in PTSD patients and subsequently cause some difficulties in their daily life.

The role of peripheral muscle fatigability on exercise intolerance in COPD

INTRODUCTION

Exercise limitation in chronic obstructive pulmonary disease (COPD) is multi-factorial; however, growing evidence indicates that muscle dysfunction may contribute in some patients.

AREAS COVERED

This work outlines current evidence for and against increased peripheral muscle fatigability in COPD through a comprehensive review of relevant literature available on PubMed/MEDLINE until May 2020. The authors first discuss key methodological issues relative to muscle fatigue assessment by non-volitional techniques, particularly magnetic stimulation. The authors then provide a detailed discussion of critical studies to have objectively measured skeletal muscle fatigue in individuals with COPD.

EXPERT OPINION

Current evidence indicates that localized (knee extension) and cycling exercise are associated with increased quadriceps fatigability in most COPD patients. Increased fatigability, however, has not been consistently found in response to walking, likely reflecting the tendency of 'central' respiratory constraints to overshadow potential functional impairments in the appendicular muscles in this form of exercise. Thus, addressing skeletal muscle abnormalities may be critical to translate improvements in lung mechanics (e.g., due to bronchodilator therapy) into better exercise tolerance. The positive effects of pulmonary rehabilitation on muscle fatigability are particularly encouraging and suggest a role for these measurements to test the efficacy of emerging adjunct training strategies focused on the peripheral muscles.

Physical exercise as a tool to minimize the consequences of the Covid-19 quarantine: An overview for cystic fibrosis

Coronavirus (SARS-CoV-2) outbreak leading to the coronavirus disease (Covid-19) has become a global pandemic. Patients with Cystic fibrosis are considered of major risk, as respiratory tract infections are more severe than in the general population, with a higher risk of complications and a negative impact on lung function. The performance of physical exercise is considered as key for its well-known general benefits and also as a complementary method to help airway clearance. Therefore, physical exercise is also considered as key in the therapeutic strategy during the quarantine period. However, the impossibility to perform exercise with appropriate prescription and monitoring is of considerable worry to health care professionals. Thus, alternative strategies, such as online measures to monitor this therapy and, consequently, to achieve a safe and effective dose are highly needed. Exercise regimens should include strength and endurance, as well as balance and flexibility exercises. Patients are highly encouraged to participate in exercise programs to maintain fitness and exercise should be continued during the quarantine period. This commentary provides a summary of the main effects and benefits of physical exercise, as well as the main recommendations for its adequate execution, including exercise modality, frequency, intensity, and volume.

Clinimetric evaluation of muscle function tests for individuals with cystic fibrosis: A systematic review

Accurate testing of muscle function is essential in individuals with cystic fibrosis (CF). A literature search was conducted in MEDLINE, CENTRAL, CINAHL, PEDro, ScienceDirect and Web of Science according to PRISMA and COSMIN guidelines from inception to September 2019 to investigate the clinimetric properties of muscle tests in individuals with CF. The search identified 37 studies (1310 individuals) and 34 different muscle tests. Maximal inspiratory pressure, inspiratory work capacity and quadriceps strength measured by computerised dynamometry were identified as reliable tests of muscle function. The one-minute sit-to-stand test was found to have high reliability but its validity to measure quadriceps strength is unknown. The clinimetric properties of other routinely used tests have not been reported in people with CF. Very different measurement procedures were identified. Inspiratory muscle and quadriceps testing can be considered as reliable but high-quality studies evaluating tests of other muscles function (e.g. muscle endurance) are lacking.

Size-adjusted muscle power and muscle metabolism in patients with cystic fibrosis are equal to healthy controls - a case control study

Background

Skeletal muscle function dysfunction has been reported in patients with cystic fibrosis (CF). Studies so far showed inconclusive data whether reduced exercise capacity is related to intrinsic muscle dysfunction in CF.

Methods

Twenty patients with CF and 23 age-matched controls completed an incremental cardiopulmonary cycling test. Further, a Wingate anaerobic test to assess muscle power was performed. In addition, all participants completed an incremental knee-extension test with ³¹P magnetic resonance spectroscopy to assess muscle metabolism (inorganic phosphate (Pi) and phosphocreatinine (PCr) as well as intracellular pH). In the MRI, muscle cross-sectional area of the M. quadriceps (qCSA) was also measured. A subgroup of 15 participants (5 CF, 10 control) additionally completed a continuous high-intensity, high-frequency knee-extension exercise task during ³¹P magnetic resonance spectroscopy to assess muscle metabolism.

Results

Patients with CF showed a reduced exercise capacity in the incremental cardiopulmonary cycling test (VO₂peak: CF 77.8 ± 16.2%predicted (36.5 ± 7.4 ml/qCSA/min), control 100.6 ± 18.8%predicted (49.1 ± 11.4 ml/qCSA/min); p < 0.001), and deficits in anaerobic capacity reflected by the Wingate test (peak power: CF 537 ± 180 W, control 727 ± 186 W; mean power: CF 378 ± 127 W, control 486 ± 126 W; power drop CF 12 ± 5 W, control 8 ± 4 W. all: p < 0.001). In the knee-extension task, patients with CF achieved a significantly lower workload (p < 0.05). However, in a linear model analysing maximal work load of the incremental knee-extension task and results of the Wingate test, respectively, only muscle size and height, but not disease status (CF or not) contributed to explaining variance. In line with this finding, no differences were found in muscle metabolism reflected by intracellular pH and the ratio of Pi/PCr at submaximal stages and peak exercise measured through MRI spectroscopy.

Conclusions

The lower absolute muscle power in patients with CF compared to controls is exclusively explained by the reduced muscle size in this study. No evidence was found for an intrinsic skeletal muscle dysfunction due to primary alterations of muscle metabolism.

Exercise Physiology Across the Lifespan in Cystic Fibrosis

Cystic fibrosis (CF), a severe life-limiting disease, is associated with multi-organ pathologies that contribute to a reduced exercise capacity. At present, the impact of, and interaction between, disease progression and other age-related physiological changes in CF on exercise capacity from child- to adult-hood is poorly understood. Indeed, the influences of disease progression and aging are inherently linked, leading to increasingly complex interactions. Thus, when interpreting age-related differences in exercise tolerance and devising exercise-based therapies for those with CF, it is critical to consider age-specific factors. Specifically, changes in lung function, chronic airway colonization by increasingly pathogenic and drug-resistant bacteria, the frequency and severity of pulmonary exacerbations, endocrine comorbidities, nutrition-related factors, and CFTR (cystic fibrosis transmembrane conductance regulator protein) modulator therapy, duration, and age of onset are important to consider. Accounting for how these factors ultimately influence the ability to exercise is central to understanding exercise impairments in individuals with CF, especially as the expected lifespan with CF continues to increase with advancements in therapies. Further studies are required that account for these factors and the changing landscape of CF in order to better understand how the evolution of CF disease impacts exercise (in)tolerance across the lifespan and thereby identify appropriate intervention targets and strategies.

Alterations of skeletal muscle bioenergetics in a mouse with F508del mutation leading to a cystic fibrosis-like condition

High energy expenditure is reported in cystic fibrosis (CF) animal models and patients. Alterations in skeletal muscle oxidative capacity, fuel utilization, and the creatine kinase-phosphocreatine system suggest mitochondrial dysfunction. Studies were performed on congenic C57BL/6J and F508del (Cftr^tm1kth) mice. Indirect calorimetry was used to measure gas exchange to evaluate aerobic capacity during treadmill exercise. The bioenergetic function of skeletal muscle subsarcolemmal (SSM) and interfibrillar mitochondria (IFM) was evaluated using an integrated approach combining measurement of the rate of oxidative phosphorylation by polarography and of electron transport chain activities by spectrophotometry. CF mice have reduced maximal aerobic capacity. In SSM of these mice, oxidative phosphorylation was impaired in the presence of complex I, II, III, and IV substrates except when glutamate was used as substrate. This impairment appeared to be caused by a defect in complex V activity, whereas the oxidative system of the electron transport chain was unchanged. In IFM, oxidative phosphorylation and electron transport chain activities were preserved, whereas complex V activity was reduced, in CF. Furthermore, creatine kinase activity was reduced in both SSM and IFM of CF skeletal muscle. The decreased complex V activity in SSM resulted in reduced oxidative phosphorylation, which could explain the reduced skeletal muscle response to exercise in CF mice. The decrease in mitochondrial creatine kinase activity also contributed to this poor exercise response.

Neuromuscular and Muscle Metabolic Functions in MELAS Before and After Resistance Training: A Case Study

Mitochondrial encephalomyopathy, lactic acidosis, and recurrent stroke-like episodes syndrome (MELAS) is a rare degenerative disease. Recent studies have shown that resistant training (RT) can ameliorate muscular force in mitochondrial diseases. However, the effects of RT in MELAS are unknown. The aim of this case report was to investigate the effects of RT on skeletal muscle and mitochondrial function in a 21-years old patient with MELAS. RT included 12 weeks of RT at 85% of 1 repetition maximum. Body composition (DXA), in vivo mitochondrial respiration capacity (mVO2) utilizing Near-infrared spectroscopy on the right plantar-flexor muscles, maximal voluntary torque (MVC), electrically evoked resting twitch (EET) and maximal voluntary activation (VMA) of the right leg extensors (LE) muscles were measured with the interpolated twitch technique. The participant with MELAS exhibited a marked increase in body mass (1.4 kg) and thigh muscle mass (0.3 kg). After the training period MVC (+5.5 Nm), EET (+2.1 N⋅m) and VMA (+13.1%) were ameliorated. Data of mVO2 revealed negligible changes in the end-exercise mVO2 (0.02 mM min-1), Δ mVO2 (0.09 mM min-1), while there was a marked amelioration in the kinetics of mVO2 (τ mVO2; Δ70.2 s). This is the first report of RT-induced ameliorations on skeletal muscle and mitochondrial function in MELAS. This case study suggests a preserved plasticity in the skeletal muscle of a patient with MELAS. RT appears to be an effective method to increase skeletal muscle function, and this effect is mediated by both neuromuscular and mitochondrial adaptations.

Exercise as a therapeutic intervention for people with cystic fibrosis

INTRODUCTION

The complex multisystem nature of cystic fibrosis (CF) commonly results in reduced exercise tolerance, which is independently associated with poor clinical outcomes. Exercise is routinely recommended as part of the therapeutic regimen in CF to improve both respiratory and non-respiratory impairments. Areas covered: This article summarises the most recent evidence regarding the use of exercise as a therapeutic intervention in CF and discusses some of the practical considerations for exercise prescription in this setting. Clinical trials in progress and future research priorities are outlined. Expert opinion: On the balance of available evidence, exercise is likely to assist in improving physical fitness and health-related quality of life (HRQOL) and may be associated with a slower rate of decline in respiratory function in CF. Limitations to current studies include small sample sizes, study durations insufficient to achieve a training effect and difficulty distinguishing the effects of exercise training from that of other interventions implemented as part of a package of care. Larger, multi-centred trials are required to clarify the role of exercise in CF in improving physical fitness, respiratory function, HRQOL, as a substitute for traditional airway clearance techniques and in the management of common CF-related comorbidities.

Energy Balance and Mechanisms of Weight Gain with Ivacaftor Treatment of Cystic Fibrosis Gating Mutations

OBJECTIVE

To determine if ivacaftor treatment results in weight gain and improved pulmonary function in people with cystic fibrosis transmembrane conductance regulator gating mutations.

STUDY DESIGN

Children and adults with cystic fibrosis and at least 1 cystic fibrosis transmembrane conductance regulator gating mutation were evaluated in this observational study before and after 3 months of ivacaftor treatment. Body size and composition, total energy expenditure, resting energy expenditure (REE%) as percent predicted, coefficient of fat absorption (CFA%), fecal calprotectin, fecal elastase, and quality of life were assessed. Some outcomes were explored by pancreatic status.

RESULTS

There were 23 patients (5-61 years of age) who completed the study; 70% had pancreatic insufficiency (PI). Patients gained 2.5 ± 2.2 kg (P < .001) with increased (P < .05) fat-free mass (0.9 ± 1.9 kg) and fat mass (1.6 ± 1.5 kg). REE% decreased by 5.5 ± 12.0% (P < .05), fecal calprotectin decreased by 30 ± 40 µg/g stool (P < .01), and total energy expenditure was unchanged. Improvements were greater for PI than patients who were pancreatic-sufficient. CFA% increased significantly only with PI. The change (Δ) in weight was positively correlated with the percent change in forced expiratory volume at 1 second (r = 0.46; P = .028) and ΔCFA% (r = 0.47; P = .032) and negatively with ΔREE% (r = -0.50; P = .017). Together, ΔREE%, ΔCFA%, and the percent change in forced expiratory volume at 1 second explained 58% of the variance in weight gain (adjusted R² = 0.579; P = .0007). Growth status and muscle strength improved, as did quality of life in several domains. Fecal elastase increased in most patients with pancreatic sufficiency, with no change in those with PI.

CONCLUSIONS

Mechanisms identified for ivacaftor-associated weight gain were decreased REE, gut inflammation, and fat malabsorption (CFA).

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02141464.

Fatigue in Chronic Respiratory Diseases: Theoretical Framework and Implications For Real-Life Performance and Rehabilitation

Fatigue is a primary disabling symptom in chronic respiratory diseases (CRD) with major clinical implications. However, fatigue is not yet sufficiently explored and is still poorly understood in CRD, making this symptom underdiagnosed and undertreated in these populations. Fatigue is a dynamic phenomenon, particularly in such evolving diseases punctuated by acute events which can, alone or in combination, modulate the degree of fatigue experienced by the patients. This review supports a comprehensive inter-disciplinary approach of CRD-related fatigue and emphasizes the need to consider both its performance and perceived components. Most studies in CRD evaluated perceived fatigue as a trait characteristic using multidimensional scales, providing precious information about its prevalence and clinical impact. However, these scales are not adapted to understand the complex dynamics of fatigue in real-life settings and should be augmented with ecological assessment of fatigue. The state level of fatigue must also be considered during physical tasks as severe fatigue can emerge rapidly during exercise. CRD patients exhibit alterations in both peripheral and central nervous systems and these abnormalities can be exacerbated during exercise. Laboratory tests are necessary to provide mechanistic insights into how and why fatigue develops during exercise in CRD. A better knowledge of the neurophysiological mechanisms underlying perceived and performance fatigability and their influence on real-life performance will enable the development of new individualized countermeasures. This review aims first to shed light on the terminology of fatigue and then critically considers the contemporary models of fatigue and their relevance in the particular context of CRD. This article then briefly reports the prevalence and clinical consequences of fatigue in CRD and discusses the strengths and weaknesses of various fatigue scales. This review also provides several arguments to select the ideal test of performance fatigability in CRD and to translate the mechanistic laboratory findings into the clinical practice and real-world performance. Finally, this article discusses the dose-response relationship to training and the feasibility and validity of using the fatigue produced during exercise training sessions in CRD to optimize exercise training efficiency. Methodological concerns, examples of applications in selected diseases and avenues for future research are also provided.

The 1-min sit-to-stand test in cystic fibrosis - Insights into cardiorespiratory responses

BACKGROUND

We aimed to characterize the cardiopulmonary response during a 1-min sit-to-stand (STS) test and compare peak exercise cardiorespiratory variables to a maximal cardiopulmonary exercise test (CPET) in cystic fibrosis (CF). We further aimed to assess the validity of the STS power index (Power_STS) as a measure of exercise capacity.

METHODS

Fifteen adult CF patients performed spirometry, CPET and the 1-min STS test with respiratory gas analysis.

RESULTS

Peak-exercise cardiorespiratory variables during the 1-min STS test correlated strongly (r=0.69-0.98) with those measured during the CPET. Oxygen uptake, carbon dioxide production, heart rate, ventilation, and tidal volume at peak exercise were 24%, 26%, 9%, 10% and 21% lower in the 1-min STS test, while respiratory frequencies were 14% higher. Power_STS showed strong to very strong correlations with CPET-derived absolute peak oxygen uptake and maximal workload.

CONCLUSIONS

The 1-min STS test elicits a substantial but lower cardiorespiratory response compared to a maximal cycle ergometry CPET. While Power_STS and STS repetitions are both valid outcome measures of functional capacity, STS repetitions are clinically more practical.