不同训练负荷条件下SD大鼠运动模型的构建与评价

背景：目前对运动训练中机体能量代谢的研究多集中于骨骼肌线粒体生物发生及线粒体氧自由基等各指标的变化,不同训练负荷条件下身体能量代谢的系统的机制研究较少。 目的：建立SD大鼠有氧、无氧及有氧无氧代谢交叉训练运动模型,评价各组SD大鼠能量代谢水平指标的变化。 方法：实验建立有氧、无氧、有氧和无氧交替运动SD大鼠跑台运动训练模型,有氧运动时采用递增负荷训练,无氧运动时采用高速间歇训练,并设立正常对照组。测量运动后大鼠体质量减轻程度的变化,检测运动后大鼠血清中乳酸、乳酸脱氢酶、肌酐、尿素氮、肌酸激酶、丙酮酸激酶和琥珀酸脱氢酶的活性。 结果与结论：实验结果显示无氧组体质量减轻程度明显(P < 0.05),乳酸水平增高(P < 0.05),琥珀酸脱氢酶水平低于有氧组(P < 0.05);无氧组和交替运动组乳酸脱氢酶水平均增高(P < 0.05);运动后大鼠尿素氮水平增高非常显著(P < 0.001);交替组肌酸激酶、肌酐水平显著增高(P < 0.01),丙酮酸激酶水平增高(P < 0.05)。结果表明运动后大鼠代谢水平符合有氧、无氧、有氧和无氧交替运动的代谢评价,运动模型构建成功。     

Effects of N-acetylcysteine on glutathione oxidation and fatigue during handgrip exercise

Fatigue of hand and forearm muscle groups can limit task performance by astronauts wearing space suits. Countermeasures to delay fatigue would therefore be useful to the space program. N-acetylcysteine (NAC) has been shown to inhibit fatigue during other tasks so we tested its effects during handgrip exercise. Volunteers practiced isometric handgrip maneuvers until performance was reproducible over three successive sessions (baseline). Performance then was retested after ingesting NAC (150 mg.kg(-1)) or saline. Drug administration increased NAC and cysteine blood levels (P < 0.001). Performance of sustained maximal efforts was unaffected. During repetitive submaximal efforts, NAC delayed fatigue (130% baseline) and inhibited glutathione oxidation. Saline did not alter glutathione status or performance of sustained maneuvers; repetitive task performance was increased by 15% (P < 0.05), a placebo effect. These data indicate that NAC supports glutathione homeostasis in exercising humans and may delay muscle fatigue during repetitive handgrip exercise. Our findings support oxidative stress as a causal factor in human muscle fatigue and argue for larger translational studies to define NAC effects on human performance.     

Lipofuscin accumulation in the vastus lateralis muscle in patients with chronic obstructive pulmonary disease

Exercise-induced oxidative stress has been reported in patients with chronic obstructive pulmonary disease (COPD) and may play a role in muscle fatigue. It is speculated that oxidative stress during exercise originates from the contracting muscles but this has not been documented. The accumulation of lipofuscin, a marker of cellular oxidative damage, was evaluated in the vastus lateralis muscle in 17 patients with COPD and 10 healthy subjects of similar age. Each subject performed a stepwise exercise test up to maximal capacity during which oxygen uptake (VO(2)) was measured. Resting and peak exercise blood gases were also obtained. Two indices of lipofuscin accumulation were used: lipofuscin inclusions/fiber ratio (LI/F) and lipofuscin inclusions/fiber cross-sectional area ratio (LI/CSA). These ratios were also determined for each specific fiber-type. LI/F (P < 0.01) and LI/CSA (P < 0.01) were greater in COPD compared to healthy subjects. LI/F and LI/CSA for all fiber types were also greater in COPD (P < 0.001). In both groups, LI/F (P < 0.001) and LI/CSA (P < 0.01) were higher in type I than in type II fibers. LI/F and LI/CSA did not correlate significantly with resting PaO(2) and SaO(2), peak VO(2), and DeltaPaO(2) and DeltaSaO(2) during exercise (P > 0.05). Increased lipofuscin accumulation, a marker of oxidative damage, was found in the vastus lateralis muscle in patients with COPD compared to healthy subjects. Oxidative damage of muscle tissue may thus be involved in skeletal muscle dysfunction and wasting in COPD.     

Correlations between event-related potential components and nitric oxide in maximal anaerobic exercise among sportsmen trained at various levels

Physical exercise has influence on all organs except its effects on the central nervous system have not been fully elucidated. This study attempts to determine whether the degree of training could affect the response to physical stress by comparing the three groups of males in different levels of the physical fitness. Serum samples from high (n = 11), moderate (n = 10), and low physical activity sportsmen (n = 10) were collected to determine nitrite/nitrate levels before and after carrying out an anaerobic maximal exercise test. An "oddball paradigm" of auditory stimuli was used to evoke the N200 and P300 before and after the exercise. The amplitude of the N200 decreased significantly after anaerobic maximal exercise compared to the values of the recorded pre-exercise at Fz area in high physical activity group. There was a negative correlation between event-related potentials component and both nitrite/nitrate serum level changes and the heart rate changes in low physical activity subjects. However, in high and moderate physical activity groups, these relationships were positive.     

Inhibitory effect of electroacupuncture (EA) on the pressor response induced by exercise stress

Abstract. We examined the effect of EA on the exercise stress-induced pressor response in healthy adult subjects of both sexes. Each subject was subjected to a bicycle exercise test using a ramp protocol once/week for three or four weeks. Subjects were asked to perform the following tests in random order: 1) a baseline exercise test without EA and 2) exercise after acupuncture at P 5–6, LI 4-L 7 and/or G 37–39 acupoints. Brachial systolic (SBP), diastolic (DBP), and mean blood pressures (MBP), heart rate (HR) and the rate-pressure product (RPP, systolic BP x HR/100) were measured every three min, while a 12 lead ECG was monitored continuously. We observed increases in MBP, SBP, HR and RPP in all 17 subjects during exercise. In 12 of the 17 subjects (71 %), EA for 30 min before exercise, either at Jianshi-Neiguan acupoints (P 5–6) or Hegu-Lique acupoints (LI 4-L 7), led to an increase in maximal workload, and reduced peak SBP, MBP and RPP responses to exercise; EA did not alter DBP or HR responses in these subjects. EA at control acupoints (Guangming-Xuanzhong acupoints, G 37–39) in five subjects did not alter the hemodynamic responses. Seven additional subjects were enrolled to study the effect of EA during a bicycle exercise test using a constant workload. The results were similar, in five of the seven subjects SBP, MBP and RPP after exercise were attenuated significantly by EA at P 5–6. We conclude that EA at specific acupoints improves exercise capacity and reduces the hemodynamic responses in approximately 70% of normal subjects.This project is supported by the DANA Foundation, the Susan-Sameuli Center for Integrative Medicine at UCI, the Larry K. Dodge Chair in Integrative Biology (JCL), and the General Clinical Research Center of UCI (5M61RR000827).     

Lowered cardiac sympathetic nerve performance in response to exercise in Parkinson's disease

We examined whether cardiac sympathetic denervation influences the cardiovascular response to exercise in Parkinson's disease (PD). Sixteen patients with PD were divided into two groups, according to their cardiac uptake of ¹²³I‐metaiodobenzylguanidine (denervated group, 10 patients with heart to mediastinum (H/M) ratio < 1.7; innervated group, six patients with H/M ratio > 1.7) and compared changes in blood pressure (BP), heart rate (HR), and cardiac contractility with 13 control subjects during ergometric exercise stress. Velocity index (VI), an indicator of cardiac contractility, was measured using impedance cardiography and recorded every minute. Exercise began at a power output of 20 W for the first 2 min and increased 10 W every 2 min to a maximal intensity of 60 W. All control subjects accomplished the procedure while six patients with PD could not continue after the first minute of 50 W loading. There were no significant differences in BP or HR change between the three groups. However, a significant reduction in VI was observed from the first minute of the 30 W workload in the denervated group compared to the control group. This lowered response continued till 50 W loading and was significantly different to the innervated group at 50 W loading. No significant VI changes were observed between the control and innervated groups throughout the exercise test. Patients with PD with reduced MIBG uptake had a lowered cardiac contractility than innervated subjects during exercise, suggesting that this response represents theimpaired exercise capacity of patients with PD with cardiac sympathetic denervation. © 2010 Movement Disorder Society     

Slower conduction velocity and motor unit discharge frequency are associated with muscle fatigue during isometric exercise in type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is associated with a peripheral neuropathy that reduces nerve conduction velocity. This may impair high motor-unit discharge frequencies (MUDF), decrease muscle activation, and curtail the ability to sustain repetitive contractile tasks. We examined (1) whether MUDF, the contractile properties of the knee extensors, and the conduction velocity of persons with T1DM differed from controls; (2) whether persons with T1DM can maintain adequate MUDF during a fatigue protocol; and (3) the relationship between these parameters and impaired glycemic control. We studied male and female subjects with T1DM and controls matched for age, height, weight, and gender. Single motor unit recordings were made from vastus lateralis during maximal and submaximal contractions and during a fatigue protocol. Glycemic control was assessed from blood glucose concentration and glycosylated hemoglobin (HbA1c). Control femoral conduction velocities were comparable to literature values and those of the T1DM subjects were slower. These values correlated with plasma glucose and HbA1c. T1DM subjects fatigued 45% sooner than controls, and time to fatigue and conduction velocity were correlated (r = 0.54, P < 0.05). Discharge frequencies tended to be slower during 50% maximal voluntary contractile force in the T1DM subjects at task failure. Persons with T1DM had slower conduction velocities and lower MUDF than their controls, which apparently leads to impaired activation of muscle and decreased endurance during isometric fatigue.     

The effect of fibrinogen genotype on fibrinogen levels after strenuous physical exercise

We have examined the effect of two beta-fibrinogen gene promoter polymorphisms (-455G>A and -854G>A) on the fibrinogen response to severe exercise in a group of male army recruits undergoing basic training. Fibrinogen was measured pre-training and again serially after severe 48 h final military exercise (FME). Out of 884 subjects, 762 completed training of whom 250 were selected for post-FME study. Fibrinogen levels (g/l) were significantly elevated over baseline levels 2, 48 and 96 h after FME, representing increases of 15.7%, 3.4% and 7.6% (p <0.005; p = 0.05 and p <0.005 respectively), with higher levels in -455A allele carriers than genotype -455GG: 3.17+/-0.05 vs. 2.94+/-0.05 (p <0.001), 2.86+/-0.05 vs. 2.60+/-0.05 (p <0.0005) and 2.98+/-0.06 vs. 2.69+/-0.06 (p <0.0005) at 2, 48 and 96 h respectively. There was no effect of the -854G>A polymorphism on fibrinogen, even after taking into account beta-fibrinogen -455 genotype. Thus the fibrinogen -455G>A polymorphism influences fibrinogen levels following exercise. The effect of genotype might be clinically relevant at times of hyperfibrinogenaemia such as following an acute inflammatory response.     

Serum potassium exercise test in the diagnosis of familial periodic paralysis

ABSTRACT We studied the serum potassium rise during a 30-min 100 W exercise test in 5 controls, 3 familial periodic paralysis (FPP) patients and their 2 symptom-less brothers. The controls showed a steep and high exercise response (the 10-min rise was 0.59 ± 0.13 mmol/l and the maximal rise was 0.71 ± 0.11 mmol/l). The FPP patients showed a slow and flat exercise response (the 10-mm rise was 0.08 ± 0.11 mmol/l and the maximal rise was 0.17 ± 0.12 mmol/l, P < 0.001 for both values). The 2 symptom-less brothers showed a similar divergence. The values of 0.05 mmol/l (10-min) and 0.25 mmol/l (maximal) of one brother suggest the diagnosis of FPP, whereas the values of 0.55 (10-min) and 0.65 mmol/l (maximal) of the other brother suggest the exclusion of the disease. We regard the serum potassium exercise test to be worthy of further study as a diagnostic test of FPP.     

The effects of arm cranking exercise and training on platelet aggregation in male spinal cord individuals

Platelet aggregation at rest and in responses to exercise and training were compared between spinal cord injured (SCI) individuals (N=5) and able-bodied subjects (N=7). All participants performed arm cranking exercise at 60-65% VO(2peak) for 30 min. Venous blood samples were obtained before and after sub-maximal exercise and measured for platelet aggregation using ADP and collagen. To assess the effects of arm cranking training, platelet aggregation was re-measured in all subjects at rest and in response to the sub-maximal arm cranking exercise after 12 weeks of individually supervised training programme. Before training, the resting mean values of platelet aggregation induced by ADP and collagen were not different (P>0.05) between SCI and able-bodied. However the SCI individuals, but not the able-bodied subjects, exhibited a significantly (P<0.05) higher maximal platelet aggregation induced by ADP and collagen following sub-maximal arm cranking exercise. Although VO(2peak) after training was significantly increased (P<0.05) in both groups, the resting mean values of platelet aggregation induced with ADP and collagen were not significantly different (P>0.05) from those observed before training and were not different (P>0.05) between SCI and able-bodied. Post-training, the SCI individuals, but not able-bodied individuals, exhibited a significant decrease (P<0.05) in platelet aggregation following sub-maximal arm cranking exercise and this occurred with both ADP and collagen. These results suggest that SCI individuals, but not normal subjects increase their platelet aggregation following sub-maximal arm cranking exercise. Furthermore, arm cranking training in SCI individuals, appears to diminish the percentage of platelet aggregation ex vivo.     

Physical fitness modulates incidental but not intentional statistical learning of simultaneous auditory sequences during concurrent physical exercise

In real-world auditory environments, humans are exposed to overlapping auditory information such as those made by human voices and musical instruments even during routine physical activities such as walking and cycling. The present study investigated how concurrent physical exercise affects performance of incidental and intentional learning of overlapping auditory streams, and whether physical fitness modulates the performances of learning. Participants were grouped with 11 participants with lower and higher fitness each, based on their Vo₂max value. They were presented simultaneous auditory sequences with a distinct statistical regularity each other (i.e. statistical learning), while they were pedaling on the bike and seating on a bike at rest. In experiment 1, they were instructed to attend to one of the two sequences and ignore to the other sequence. In experiment 2, they were instructed to attend to both of the two sequences. After exposure to the sequences, learning effects were evaluated by familiarity test. In the experiment 1, performance of statistical learning of ignored sequences during concurrent pedaling could be higher in the participants with high than low physical fitness, whereas in attended sequence, there was no significant difference in performance of statistical learning between high than low physical fitness. Furthermore, there was no significant effect of physical fitness on learning while resting. In the experiment 2, the both participants with high and low physical fitness could perform intentional statistical learning of two simultaneous sequences in the both exercise and rest sessions. The improvement in physical fitness might facilitate incidental but not intentional statistical learning of simultaneous auditory sequences during concurrent physical exercise.     

Changes in fibrinolysis following exercise above and below lactate threshold

This study sought to compare fibrinolytic responses to exercise above lactate threshold (LT) to longer-duration, equicaloric exercise below LT. Fifteen males performed cycle ergometer tests above (77% VO(2)peak) and below LT (41% VO(2)peak) to comparatively evaluate tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) responses. tPA activity significantly (P < 0.05) increased during the >LT test (pre-exercise = 1.57 +/- 0.44 IU ml(-1), post-exercise = 3.85 +/- 4.72 IU ml(-1)), but not the LT (pre-exercise = 8.32 +/- 4.48 ng ml(-1), post-exercise = 14.23 +/- 5.40 ng ml(-1)) and LT test. PAI-1 activity significantly (P < 0.05) decreased during both the >LT (pre-exercise = 15.00 +/- 2.73 AU ml(-1), post-exercise = 10.12 +/- 2.90 AU ml(-1)) and LT test. Our results suggest that exercise 相似文献   

A comparison of respiratory and peripheral muscle strength,functional exercise capacity,activities of daily living and physical fitness in patients with cystic fibrosis and healthy subjects

There are limited reports that compare muscle strength, functional exercise capacity, activities of daily living (ADL) and parameters of physical fitness of cystic fibrosis (CF) patients with healthy peers in the literature. The purpose of this study was to assess and compare respiratory and peripheral muscle strength, functional exercise capacity, ADL and physical fitness in patients with CF and healthy subjects. Nineteen patients with CF (mean forced expiratory volume in one second-FEV₁: 86.56 ± 18.36%) and 20 healthy subjects were included in this study. Respiratory (maximal inspiratory pressure-MIP and maximal expiratory pressure-MEP) and peripheral muscle strength (quadriceps, shoulder abductors and hand grip strength) were evaluated. Functional exercise capacity was determined with 6 min walk test (6MWT). ADL was assessed with Glittre ADL test and physical fitness was assessed with Munich fitness test (MFT). There were not any statistically significant difference in MIP, %MIP, MEP and %MEP values between two groups (p > 0.05). %Peripheral muscle strength (% quadriceps and shoulder abductors strength), 6MWT distance and %6MWT distance were significantly lower in patients with CF than those of healthy subjects (p < 0.05). Glittre ADL-test time was significantly longer in patients with CF than healthy subjects (p < 0.05). According to Munich fitness test, the number of bouncing a ball, hanging score, distance of standing vertical jumping and standing vertical jumping score were significantly lower in patients with CF than those of healthy subjects (p < 0.05). Peripheral muscle strength, functional exercise capacity, ADL performance and speed, coordination, endurance and power components of physical fitness are adversely affected in mild-severe patients with CF compared to healthy peers. Evaluations must be done in comprehensive manner in patients with CF with all stages.     

Biochemical changes and catecholamine responses in Down's syndrome adolescents in relation to incremental maximal exercise

ABSTRACT. The aim of this study was to determine biological responses in Down's syndrome subjects for an incremental exercise lasting 10 min. After a training programme specially adapted for children and adolescents with mental handicaps, 11 healthy Down's syndrome subjects, seven boys and four girls aged from 15 to 20 years, performed a progressive exercise until exhaustion on an ergometric bicycle. The results were compared with those taken from the literature for similar aged normal subjects. The results in our series of Down's syndrome subjects showed: (a) no differences in haematologic parameters, except for a high concentration of uric acid at rest which did not increase after the test; (b) a lower blood lactate level than in maximal exercise for this age range; (c) a late mobilization of FFA; and (d) a slightly lower maximal value of catecholamines. These results may suggest a reduced sympathetic response to maximal exercise.     

Blood coagulation and fibrinolysis before and after exhaustive exercise in patients with IDDM

Diabetes mellitus involves changes in haemostasis which leads to the opinion that diabetes mellitus is a hypercoagulable state. However, little is known about the relationship of exercise and haemostasis in diabetics. Therefore, first of all the aim was to investigate if differences in blood coagulation and fibrinolysis can be demonstrated in subjects with insulin-dependent diabetes mellitus (IDDM) compared to controls and secondly, if differences concerning exercise induced changes can be seen in diabetics. 16 moderately fit subjects with IDDM and 16 matched controls underwent a maximal step test. Blood samples were taken after a 30 min rest, immediately and 1h after exercise and in addition after 30 min rest 7 days later at the same time of day. The rest values (mean of the two rest samples) in extrinsic total thrombin potential (TTPex, P=0.049), tPA-activity (P=0.007) were significantly higher and in PAI-1-antigen (P=0.002) -activity (P=0.049) lower in the diabetic group. APTT, PT, TAT (only control), TTPin, tPA-activity and -antigen and PAP were increased immediately and D-dimer (only control) 1 h after exercise, whereas PAI-1-activity and -antigen (only control) decreased immediately or 1 h after exercise (all minimal P<0.05). The increase of tPA-antigen and decrease in PAI-1-antigen after exercise were both lower in the diabetics (P<0.05). IDDM led to higher extrinsic total thrombin and fibrinolytic potential at rest, and reducing the exercise provoked distribution of tPA-antigen and decrease of PAI-1-antigen. Nevertheless a higher thrombotic risk after maximal exercise has not been investigated in young IDDM patients without complications and in good metabolic control.     

THE EFFECT OF PHYSICAL CONDITIONING SUGGESTS ADAPTATION IN PROCOAGULANT AND FIBRINOLYTIC POTENTIAL

Acute exercise evokes a transient increase in procoagulant activity. We evaluated the effect of physical conditioning on the activation of the coagulation and fibrinolytic systems. Two groups of subjects of different aerobic endurance levels (athletes and controls with maximal oxygen uptake (VO_{2 max}) 68,4 and 52,6 ml·kg⁻¹·min⁻¹, respectively), were tested at rest and after standardized exercise at 80 % of their individual VO_{2 max}. There was a significant increase in prothrombinfragment 1+2 (F1+2) level among controls in response to standardized exercise (p<0.05), whereas no significant difference in the level of F1+2 between athletes and controls at rest or in response to exercise was demonstrated. Tissue plasminogen activator (tPA) antigen level at rest was significantly lower in athletes compared to controls (p<0.03). A significant increase was found in the tPA level after standardized exercise in both groups (p<0.02), which was lower in athletes compared to controls (p<0.05). There were no significant differences between athletes and controls in plasminogen activator inhibitor-1 (PAI-1) and thrombin antithrombin complex (TAT) levels at rest. Athletes had a significantly lower PAI-1 level than controls after exercise (p<0.05). In conclusion, the present study suggests an increased activation of the coagulation system in response to exercise in controls only. It also suggests adaptive changes in fibrinolytic potential induced by physical conditioning, as demonstrated by the lower level of tPA at rest and the lower levels of tPA and PAI-1 after exercise in athletes compared to controls. © 1997 Elsevier Science Ltd     

Electrophysiologic changes during exercise testing in patients with chronic obstructive pulmonary disease

To determine whether skeletal muscle is involved in the exercise limitation of chronic obstructive pulmonary disease (COPD), we investigated electrical adaptations in muscle during incremental cycling exercise testing. Changes in quadriceps activity were compared using surface electromyography (SEMG) and motor point stimulation in ten COPD patients and ten healthy subjects. Patients showed significantly lower exercise capacity, and M-wave duration was increased from exercise onset (P < 0.05) with a parallel decrease in amplitude (P < 0.05). The SEMG power spectrum median frequency was always higher (P < 0.04) in patients and its decline was earlier (P < 0.01). The ratio of the root mean square of the SEMG to oxygen uptake was decreased (P < 0.001) during exercise in patients, although it remained constant in controls. Electromyographic parameters were significantly more involved in the exercise limitation than ventilatory factors. Thus, modified electrical activity in muscle appeared in COPD patients from exercise onset, indicating that skeletal muscle function is clearly implicated in the exercise intolerance of these patients.     

Effects of high-intensity endurance exercise training in the G93A mouse model of amyotrophic lateral sclerosis

The G93A transgenic mouse has a mutation in copper/zinc superoxide dismutase (CuZnSOD) that results in oxidative stress and motor neuron loss. Endurance exercise training is known to increase antioxidant capacity in skeletal muscle. Therefore, we hypothesized that endurance training may extend onset of disease or survival in the G93A mouse. We examined the effects of high-intensity endurance exercise training (45 min/day, 5 times/week, progressive increase from 9 to 22 m/min) on disease onset and survival in G93A mice. Endurance training did not affect clinical onset, although it hastened death in male mice (P < 0.05). Endurance-trained males had a statistically significant decrease in rotarod performance at 112 days (P < 0.05), whereas sedentary males decreased at 119 days (P < 0.05). Endurance-trained and sedentary females decreased at 126 days and 129 days, respectively (P < 0.05). Female mice lived longer than males (P < 0.05), and there was a trend for hastened clinical onset in males (P = 0.062). We conclude that high-intensity endurance exercise training does not affect onset of clinical symptoms in G93A mice but hastens a decrease in motor performance and death following onset of clinical symptoms in male mice only. In light of a recent report describing increased survival following low-intensity endurance training, it appears that training intensity is an important determinant of survival in the G93A mouse.     

Impaired abdominal muscle contractility after high-intensity exhaustive exercise assessed by magnetic stimulation

High-intensity exercise can induce diaphragm fatigue which can, in turn, limit exercise performance. We investigated whether expiratory muscles fatigue similarly during exhaustive exercise. Eleven healthy male volunteers cycled to exhaustion at 85% maximal power. Before, immediately after exercise, and after 30 and 60 min of recovery, the nerve roots supplying the abdominal muscles were stimulated magnetically at the T10 level in the prone position after full potentiation. Twitch gastric pressure (Pga,tw) was simultaneously recorded. After cycling, Pga,tw was significantly reduced compared to before exercise (40.2 +/- 6.6 vs. 45.3 +/- 7.5 cmH2O; P < 0.001), whereas after 30 and 60 min of recovery differences were no longer significant. The reduction in Pga,tw directly after exercise correlated neither with the fitness level nor with abdominal muscle work, respiratory sensations, or blood lactate concentration during exercise. These results indicate that the ventilatory requirements during intensive exercise can impair abdominal muscle contractility similar to diaphragmatic contractility. Thus, abdominal muscle fatigue may also contribute to exercise limitation, especially when expiratory resistance is increased as in patients with chronic obstructive pulmonary disease.     

Knee extensor fatigability after bedrest for 8 weeks with and without countermeasure

We analyzed the effects of gravitational unloading on muscular fatigability and the effectiveness of resistive vibration exercise to counteract these changes. Changes in knee extensor fatigability as a consequence of 8 weeks of horizontal bedrest with or without daily resistive vibration exercise were evaluated in 17 healthy male volunteers. Bedrest increased fatigability (% decrease in maximal voluntary isometric torque per minute exercise) from -7.2 +/- 0.5 to -10.2 +/- 1.0%/min (P < 0.05), which was accompanied by a decline (of 52.0 +/- 3.7%, P < 0.05) in muscle blood flow. Daily resistive vibration exercise training during bedrest prevented increases in fatigability (from -10.8 +/- 1.8 to -8.4 +/- 1.6%/min, P < 0.05), and mitigated the reduction in blood flow (decline of 26.1 +/- 5.1%, P < 0.05). Daily resistive exercise may thus be suggested as an effective countermeasure during spaceflight and illness-related prolonged bedrest to combat the detrimental changes in muscle endurance that result from gravitational unloading.