Reduced Muscle Endurance Research Articles

Adaptations in limb muscle function following pulmonary rehabilitation in patients with COPD – a review

Even though chronic obstructive pulmonary disease (COPD) is primarily a disease of the respiratory system, limb muscle dysfunction characterized by muscle weakness, reduced muscle endurance and higher muscle fatigability, is a common secondary consequence and a major systemic manifestation of the disease. Muscle dysfunction is especially relevant in COPD because it is related to important clinical outcomes such as mortality, quality of life and exercise intolerance, independently of lung function impairment. Thus, improving muscle function is considered an important therapeutic goal in COPD management. Pulmonary rehabilitation (PR) is a multidisciplinary, evidence-based and comprehensive approach used to promote better self-management of the disease, minimize symptom burden, optimize functional status, and increase participation in activities of daily life. Exercise training, including cardiovascular and muscle exercises, is the cornerstone of PR and is considered the best available strategy to improve exercise tolerance and muscle function among patients with COPD. This paper addresses the various components of exercise training within PR used to improve limb muscle function in COPD, providing clinicians and health-care professionals with an overview and description of these various exercise modalities and of their effects on limb muscle function. Guidance and recommendations to help design optimal limb muscle training regimens for these patients are also presented.

Relations between muscle endurance and subjectively reported fatigue, walking capacity, and participation in mildly affected adolescents with cerebral palsy

To investigate the relation between muscle endurance and subjectively reported fatigue, walking capacity, and participation in mildly affected adolescents with cerebral palsy (CP) and peers with typical development. In this case-control study, knee extensor muscle endurance was estimated from individual load-endurance curves as the load corresponding to a 15-repetition maximum in 17 adolescents with spastic CP (six males, 11 females; age 12-19y) and 18 adolescents with typical development (eight males, 10 females; age 13-19y). Questionnaires were used to assess subjectively reported fatigue (Pediatric Quality of Life Inventory Multidimensional Fatigue Scale) and participation (Life-Habits questionnaire). Walking capacity was assessed using the 6-minute walk test. Relations were determined using multiple regression analyses. Muscle endurance related significantly to subjectively reported fatigue and walking capacity in adolescents with CP, while no relations were found for adolescents with typical development (subjectively reported fatigue: regression coefficient β [95% confidence intervals] for CP=23.72 [6.26 to 41.18], for controls=2.72 [-10.26 to 15.69]; walking capacity β for CP=125m [-87 to 337], for controls=2m [-86 to 89]). The 15-repetition maximum did not relate to participation in adolescents with CP. Subjectively reported fatigue and reduced walking capacity in adolescents with CP are partly caused by lower muscle endurance of knee extensors. Training of muscle endurance might contribute to reducing the experience of fatigue and improving walking capacity. Reduced muscle endurance seems to have no effect on participation.

AB1459-HPR Despite low disease activity patients with poly- and dermatomyositis perceive activity limitation, reduced grip force and quality of life longitudinally

BackgroundPolymyositis (PM) and dermatomyositis (DM) are idiopathic inflammatory myopathies with muscle weakness and reduced muscle endurance. The impairments lead to activity limitation, participation restriction and reduced quality of life.ObjectivesTo investigate...

Nitric oxide prevents atorvastatin‐induced skeletal muscle dysfunction and alterations in mice

Myopathy is the most common side effect of statins. Because nitric oxide (NO) has a key role in regulating skeletal muscle function, we studied whether the NO-donating atorvastatin NCX 6560 could show a better profile on skeletal muscle function and structure compared with atorvastatin. C57BL/6 mice received atorvastatin 40 mg/kg/day or an equivalent dose of NCX 6560 for 2 months. Muscle function assessed by treadmill test, serum creatine kinase (CK) activity, citrate synthase (CS) activity, and muscle histology were evaluated. Atorvastatin significantly (P < 0.001) reduced muscle endurance, increased serum CK by 6-fold, and induced muscle fiber atrophy. Conversely, NCX 6560 preserved muscle function, prevented CK increase and did not modify muscle structure. Interestingly, atorvastatin reduced CS activity, a marker for mitochondrial function, in gastrocnemius, diaphragm, and heart, whereas NCX 6560 prevented such decrease. These findings suggest that NO may prevent statin-induced myopathy.

The effects of stabilizing exercises on pain and disability of patients with lumbar segmental instability

Lumbar segmental instability (LSI) is one of the subgroups of non-specific chronic low back pain. Pain, functional disability and reduced muscle endurance are common in such patients. The aim of this study was to determine the effects of stabilization exercise on pain, functional disability and muscle endurance in patients with LSI. A randomized clinical trial was carried out on 30 patients who had LSI aged between 18-45 years. They were divided into two groups; the control group underwent routine exercise only while the experimental group performed routine exercise plus stabilization training for 8 weeks. Both had 3 months follow-up. The variables included pain intensity, functional disability and flexion and extension range of motion and flexor, extensor and lateral flexor muscles endurance which were evaluated 3 times; before, post treatment and after three months. The data were analyzed using repeated measurement ANOVA. The results revealed that after treatment, the trunk muscle endurance and flexion range of motion increased significantly and the pain intensity and functional disability decreased significantly in both groups; however the rate of improvement was significantly higher in the experimental group. The process of decreasing pain intensity and functional disability in addition to increasing muscle endurance time %was were significantly faster in the experimental group during the three months follow up. Regarding the positive effects of stabilizing exercises with routine exercises in reduction of pain intensity, increasing functional ability and muscle endurance, it is recommended to use this method in treatment of patients with lumbar segmental instability.

Loss of quadriceps muscle oxidative phenotype and decreased endurance in patients with mild-to-moderate COPD

Being well-established in advanced chronic obstructive pulmonary disease (COPD), skeletal muscle dysfunction and its underlying pathology have been scarcely investigated in patients with mild-to-moderate airflow obstruction. We hypothesized that a loss of oxidative phenotype (oxphen) associated with decreased endurance is present in the skeletal muscle of patients with mild-to-moderate COPD. In quadriceps muscle biopsies from 29 patients with COPD (forced expiratory volume in 1 s [FEV1] 58 ± 16%pred, body mass index [BMI] 26 ± 4 kg/m(2)) and 15 controls (BMI 25 ± 3 kg/m(2)) we assessed fiber type distribution, fiber cross-sectional areas (CSA), oxidative and glycolytic gene expression, OXPHOS protein levels, metabolic enzyme activity, and levels of oxidative stress markers. Quadriceps function was assessed by isokinetic dynamometry, body composition by dual-energy X-ray absorptiometry, exercise capacity by an incremental load test, and physical activity level by accelerometry. Compared with controls, patients had comparable fat-free mass index, quadriceps strength, and fiber CSA, but quadriceps endurance was decreased by 29% (P = 0.002). Patients with COPD had a clear loss of muscle oxphen: a fiber type I-to-II shift, decreased levels of OXPHOS complexes IV and V subunits (47% and 31%, respectively; P < 0.05), a decreased ratio of 3-hydroxyacyl-CoA dehydrogenase/phosphofructokinase (PFK) enzyme activities (38%, P < 0.05), and decreased peroxisome proliferator-activated receptor-γ coactivator-1α (40%; P < 0.001) vs. increased PFK (67%; P < 0.001) gene expression levels. Within the patient group, markers of oxphen were significantly positively correlated with quadriceps endurance and inversely with the increase in plasma lactate relative to work rate during the incremental test. Levels of protein carbonylation, tyrosine nitration, and malondialdehyde protein adducts were comparable between patients and controls. However, among patients, oxidative stress levels were significantly inversely correlated with markers of oxphen and quadriceps endurance. Reduced muscle endurance associated with underlying loss of muscle oxphen is already present in patients with mild-to-moderate COPD without muscle wasting.

Can muscle regeneration fail in chronic inflammation: a weakness in inflammatory myopathies?

Idiopathic inflammatory myopathies (IIMs), collectively termed myositis, include three major subgroups: polymyositis, dermatomyositis and inclusion body myositis. IIMs are characterized clinically by muscle weakness and reduced muscle endurance preferentially affecting the proximal skeletal muscle. In typical cases, inflammatory cell infiltrates and proinflammatory cytokines, alarmins and eicosanoids are present in muscle tissue. Treatment with glucocorticoids and other immunosuppressants results in improved performance, but complete recovery is rarely seen. The mechanisms that cause muscle weakness and reduced muscle endurance are multi-factorial, and different mechanisms predominate in different phases of disease. It is likely that a combination of immune-mediated and nonimmune-mediated mechanisms contributes to clinical muscle symptoms. Immune-mediated mechanisms include immune cell-mediated muscle fibre necrosis as well as direct effects of various cytokines on muscle fibre contractility. Among the nonimmune-mediated mechanisms, an acquired metabolic myopathy and so-called endoplasmic reticulum stress may be important. There is also a possibility of defective repair mechanisms, with an influence of both disease-related factors and glucocorticoid treatment. Several proinflammatory molecules observed in muscle tissue of myositis patients, including interleukin (IL)-1, IL-15, tumour necrosis factor, high-mobility group box-1 and eicosanoids, have a role in muscle fibre regeneration, and blocking these molecule may impair muscle repair and recovery. The delicate balance between immunosuppressive treatment to downregulate proinflammatory molecules and an inhibitory effect on muscle fibre regeneration needs to be further understood. This would also be relevant for other chronic inflammatory diseases.

Long-Term Respiratory Muscle Endurance Training in Patients with Myasthenia Gravis: First Results after Four Months of Training

Myasthenia gravis (MG) is characterized by reduced muscle endurance and is often accompanied by respiratory complications. Improvement of respiratory function is therefore an important objective in MG therapy. A previous study demonstrated that respiratory muscle endurance training (RMET) over four weeks increased respiratory muscle endurance of MG patients to about 200% of baseline. The purpose of the present study was to establish an appropriate maintenance training and to test its effects over four months. Ten patients with mild to moderate MG participated in this study. During the first month, they performed five training sessions per week. For the following 3 months, training frequency was reduced to five sessions per two weeks. Myasthenia score, lung function, and respiratory endurance were determined prior to training, after the first month, and after 4 months. Myasthenia score improved from 0.71 ± 0.1 to 0.56 ± 0.1 (P = 0.007). Respiratory endurance time increased from 6.1 ± 0.8 to 20.3 ± 3.0 min (P < 0.001). In conclusion, this RMET maintenance program is feasible and is significantly beneficial for MG patients.

Surgery-Induced Inflammation in Relation to Age, Muscle Endurance, and Self-Perceived Fatigue

Elective abdominal surgery can be considered as a model for an important acute inflammatory trigger in human participants. The aim of the study was to explore the effect of surgery-induced inflammation on muscle strength, endurance, and self-perceived fatigue and its relation with age. Sixty-six elective abdominal surgery patients aged 24-91 years were assessed before and at the second and fourth day after surgical intervention. Outcome parameters were grip strength, muscle endurance, fatigue subscale of the Profile of Mood State and visual analog scale for pain, and the circulating inflammatory mediators C-reactive protein, interleukin (IL)-6, and tumor necrosis factor-alpha (TNF-alpha). All parameters worsened postoperatively (p < .01) and remained significantly (p < .05) worse until the fourth day postsurgery, except for TNF-alpha (no significant change). Older age was related to higher surgery-induced IL-6 levels at the second (p < .05) and fourth postoperative (p < .01) day and to worse self-perceived fatigue and muscle endurance (both p < .05) at the fourth postoperative day. Higher pain levels at the second day following surgery was related to more self-perceived fatigue (p < .05). Worsening muscle endurance following surgery was significantly related to higher IL-6 release following surgery (p < .01) and self-perceived fatigue (p < .05) at the fourth day following the intervention. Age and surgery-induced increase in circulating IL-6 at Day 4 postsurgery was highest in patients showing both worsened muscle endurance and self-perceived fatigue (p < .05). Surgery-induced inflammation is related to reduced muscle endurance and the sensation of fatigue. Elderly patients suffer from a higher impact of surgery on muscle endurance.

EFFECTS OF CHRONIC HYPOXIA ON UPPER AIRWAY AND DIAPHRAGM MUSCLE ENDURANCE IN THE DEVELOPING RAT

Chronic hypoxia (CH) is common in respiratory disease and is known to alter skeletal muscle structure and oxidative capacity. We hypothesized that CH in early development would alter respiratory muscle function. Wistar rats were reared in normobaric normoxia or hypobaric hypoxia (PB=450mmHg) for 7 days beginning at P1, P11, P21 or P31. Isolated muscle function studies were conducted at P19, P29 or P39. Fatigue was assessed in response to repeated tetanic contractions (40Hz, 300msec) every 2 sec for 5 minutes. Chronic hypoxia during early development (beginning P1 and P11) increased sternohyoid specific force but significantly reduced muscle endurance (fatigue index ie ratio of force at 5 min of fatigue to initial force, measured at P19 was 83+/−7% vs. 59+/−7%* and 63+/−4%*; control vs. P1 and P11 hypoxic groups, *P&lt;0.05 ANOVA). CH in older animals did not affect sternohyoid endurance. CH increased diaphragm specific force but had no effect on muscle endurance (eg fatigue index at P19 was 81+/−6% vs. 76+/−4% and 88+/−4%; control vs. P1 and P11 hypoxic groups, P&gt;0.05 ANOVA). We conclude that CH elicits plasticity in respiratory muscles with differential effects in diaphragm and upper airway muscles. Increased fatigue of the sternohyoid muscle may have important consequences for the control of upper airway patency in vivo.

Exercise-induced quadriceps oxidative stress and peripheral muscle dysfunction in patients with chronic obstructive pulmonary disease.

Exercise-induced muscle oxidative stress may be involved in the myopathy associated with chronic obstructive pulmonary disease (COPD). This study was designed to look at whether local exercise induces muscle oxidative stress and whether this oxidative stress may be associated with the reduced muscle endurance in patients with COPD. Quadriceps endurance was measured in 12 patients with COPD (FEV1 = 0.96 +/- 0.14 SEM) and 10 healthy sedentary subjects by repeated knee extensions of the dominant leg. Biopsies of the vastus lateralis muscle were obtained before and 48 hours after exercise. Muscle oxidative stress was measured by lipid peroxidation and oxidized proteins. Muscle antioxidant was evaluated by peroxidase glutathion activity. Quadriceps endurance was significantly reduced in patients with COPD when compared with the healthy control subjects (p < 0.01). Forty-eight hours postexercise, only patients with COPD had a significant increase in muscle lipid peroxidation (p < 0.05) and oxidized proteins (p < 0.05), whereas increased peroxidase glutathion activity was only observed in control subjects (p < 0.05). Both increases in muscle lipid peroxidation and oxidized proteins were significantly and inversely correlated with quadriceps endurance capacity in COPD (p < 0.05). In summary, local exercise induced muscle oxidative stress in patients with COPD, whereas it failed to raise antioxidant activity. In these individuals, muscle oxidative stress was associated with a reduced quadriceps endurance.

A Study to Investigate Whether Golfers with a History of Low Back Pain Show a Reduced Endurance of Transversus Abdominis

Recently published evidence has shown an increasing number of golfers reporting the presence of low back pain (LBP). Research has shown the occurrence and recurrence of LBP to be associated with the dysfunction of the deep abdominal muscle, transversus abdominis (TrA). To investigate the reduction in its stabilising role, the pressure biofeedback unit (PBU) was developed as an objective assessment and monitoring tool. This instrument is also used in the rehabilitation of TrA.Twenty male golfers, age 20-44, were recruited by newsletter article and direct approach to see whether golfers with a history of LBP showed a reduced muscle endurance time of TrA compared with golfers with no such history.Subjects were taught TrA contraction in prone kneeling and in prone lying using the PBU. Using a cycle of 10 seconds contraction followed by 20 seconds rest, the total time each subject could maintain a TrA contraction was measured.The results showed that golfers with a history of LBP had a statistically significant reduction (p<0.025) in the endurance of the static contraction time of TrA compared to golfers without a history of LBP.The results are discussed in relation to previous research, and the implications for clinicians for the rehabilitation of golfers with LBP are identified.

Use of exercise for treatment of chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) is a condition that results in moderate to severe disability, the primary feature of which is fatigue of unknown origin. There is a lot of interest in classifying, characterising and treating patients with CFS. Currently, the two major theories of a medical cause of CFS are viral infection and immune dysregulation. Patients report critical reductions in levels of physical activity, and many experience 'relapses' of severe symptoms following even moderate levels of exertion. Despite this, most studies report CFS patients to have normal muscle strength and either normal or slightly reduced muscle endurance. Histological and metabolic studies report mixed results: CFS patients have either no impairment or mild impairment of mitochondria and oxidative metabolism compared with sedentary controls. Current treatments for CFS are symptom-based, with psychological, pharmacological and rehabilitation treatments providing some relief but no cure. Immunological and nutritional treatments have been tried but have not provided reproducible benefits. Exercise training programmes are thought to be beneficial (if 'relapses' can be avoided), although few controlled studies have been performed. CFS is a long-lasting disorder that can slowly improve with time, but often does not. Further studies are needed to better understand the multiple factors that can cause chronic fatigue illness, as well as the effect that exercise training has on the symptoms of CFS.