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Patients palliated with Total Cavopulmonary Connection have a lower muscle mass and a lower exercise capacity. We assessed calf muscle oxidative metabolism during and after heel raise exercise to exhaustion in young patients with TCPC compared to healthy peers. Near-infrared spectroscopy was used for measuring oxygen metabolism in the medial portion of the gastrocnemius muscle. Forty-three patients with TCPC, aged 6–18 years, were compared with 43 age and sex-matched healthy control subjects. Subgroups were formed to include children (6–12 years) and adolescents (13–18 years) to determine if these age groups influenced the results. During exercise, for the patients compared to controls there was a lower increase in deoxygenated hemoglobin (oxygen extraction) (5.13 ± 2.99au vs. 7.75 ± 4.15au, p = 0.001) and a slower rate of change in total hemoglobin (blood volume) (0.004 ± 0.015au vs 0.016 ± 0.01au, p = 0.001). Following exercise, patients exhibited a slower initial increase in tissue oxygenation saturation index (0.144 ± 0.11au vs 0.249 ± 0.226au, p = 0.007) and a longer half-time to maximum hyperemia (23.7 ± 11.4 s vs 16.8 ± 7.5 s, p = 0.001). On the subgroup level, the adolescents differed compared to healthy peers, whereas the children did not. Young patients with TCPC had impaired oxidative metabolism during exercise and required a longer time to recover. In that the differences were seen in the adolescent group and not in the children group may indicate a declining function with age.

Background:Patients with CHD exhibit reduced isometric muscle strength and muscle mass; however, little is known how these parameters relate. Therefore, the aim was to investigate the relation between isometric limb muscle strength and muscle mass for patients in comparison to age- and sex-matched control subjects.Methods:Seventy-four patients (35.6 ± 14.3 years, women n = 22) and 74 matched controls were included. Isometric muscle strength in elbow flexion, knee extension, and hand grip was assessed using dynamometers. Lean mass, reflecting skeletal muscle mass, in the arms and legs was assessed with dual-energy x-ray absorptiometry.Results:Compared to controls, patients had lower muscle strength in elbow flexion, knee extension, and hand grip, and lower muscle mass in the arms (6.6 ± 1.8 kg versus 5.8 ± 1.7 kg, p < 0.001) and legs (18.4 ± 3.5 kg versus 15.9 ± 3.2 kg, p < 0.001). There was no difference in achieved muscle force per unit muscle mass in patients compared to controls (elbow flexion 0.03 ± 0.004 versus 0.03 ± 0.005 N/g, p = 0.5; grip strength 0.008 ± 0.001 versus 0.008 ± 0.001 N/g, p = 0.7; knee extension 0.027 ± 0.06 versus 0.028 ± 0.06 N/g, p = 0.5). For both groups, muscle mass in the arms correlated strongly with muscle strength in elbow flexion (patients r = 0.86, controls, r = 0.89), hand grip (patients, r = 0.84, controls, r = 0.81), and muscle mass in the leg to knee extension (patients r = 0.64, controls r = 0.68).Conclusion:The relationship between isometric muscle strength and limb muscle mass in adults with CHD indicates that the skeletal muscles have the same efficiency as in healthy controls.

Adults with complex congenital heart disease (CHD) show reduced aerobic exercise capacity and impaired skeletal muscle function compared with healthy peers. Peripheral muscle factors are presumed to be important contributors to the aerobic capacity, but the mechanisms are poorly understood. The aim of the present study was to investigate differences between adults with CHD and controls in muscle oxygenation kinetics at rest, and during and after exercise.Seventy-four patients with complex CHD (mean age 35.6 ± 14.3 years, female n = 22) were recruited. Seventy-four age- and sex-matched subjects were recruited as controls. Muscle oxygenation was successfully determined on the anterior portion of the deltoid muscle using near-infrared spectroscopy in 65 patients and 71 controls. Measurements were made at rest, during isotonic shoulder flexions (0-90°) to exhaustion, and during recovery.The patients with CHD performed fewer shoulder flexions (40 ± 17 vs 69 ± 40; P0.001), had lower muscle oxygen saturation (StOIn comparison with age- and sex-matched controls, adults with complex CHD had slower oxygenation kinetics. This altered skeletal muscle metabolism might contribute to the impaired skeletal muscle endurance capacity shown and thereby also to the reduced aerobic capacity in this population.

OBJECTIVE: This study systematically summarizes biochemical biomarker research in non-traumatic musculoskeletal disorders (MSD). Two research questions guided the review: (i) Are there biochemical markers associated with neck and upper-extremity MSD? and (ii) Are there biochemical markers associated with the severity of neck and upper-extremity MSD? METHODS: A literature search was conducted in PubMed and SCOPUS, and 87 studies met primary inclusion criteria. Following a quality screen, data were extracted from 44 articles of sufficient quality. RESULTS: Most of the 87 studies were cross-sectional and utilized convenience samples of patients as both cases and controls. A response rate was explicitly stated in only 11 (13%) studies. Less than half of the studies controlled for potential confounding through restriction or in the analysis. Most sufficient-quality studies were conducted in older populations (mean age in one or more analysis group >50 years). In sufficient-quality articles, 82% demonstrated at least one statistically significant association between the MSD and biomarker(s) studied. Evidence suggested that: (i) the collagen-repair marker TIMP-1 is decreased in fibro proliferative disorders, (ii) 5-HT (serotonin) is increased in trapezius myalgia, and (iii) triglycerides are increased in a variety of MSD. Only 5 studies showed an association between a biochemical marker and MSD severity. CONCLUSION: While some MSD biomarkers were identified, limitations in the articles examined included possible selection bias, confounding, spectrum effect (potentially heterogeneous biomarker associations in populations according to symptom severity or duration), and insufficient attention to comorbid conditions. A list of recommendations for future studies is provided.

Background: Unlike the usual skeletal muscles, ciliary muscles responsible for focusing the crystalline eye lens and extraocular muscles responsible for convergence eye movements appear resistant t ...

Background This study systematically summarizes quantitative imaging biomarker research in non-traumatic neck and shoulder musculoskeletal disorders (MSDs). There were two research questions: 1) Are there quantitative imaging biomarkers associated with the presence of neck and shoulder MSDs?, 2) Are there quantitative imaging biomarkers associated with the severity of neck and shoulder MSDs? Methods PubMed and SCOPUS were used for the literature search. One hundred and twenty-five studies met primary inclusion criteria. Data were extracted from 49 sufficient quality studies. Results Most of the 125 studies were cross-sectional and utilized convenience samples of patients as both cases and controls. Only half controlled for potential confounders via exclusion or in the analysis. Approximately one-third reported response rates. In sufficient quality articles, 82% demonstrated at least one statistically significant association between the MSD(s) and biomarker(s) studied. The literature synthesis suggested that neck muscle size may be decreased in neck pain, and trapezius myalgia and neck/shoulder pain may be associated with reduced vascularity in the trapezius and reduced trapezius oxygen saturation at rest and in response to upper extremity tasks. Reduced vascularity in the supraspinatus tendon may also be a feature in rotator cuff tears. Five of eight studies showed an association between a quantitative imaging marker and MSD severity. Conclusions Although research on quantitative imaging biomarkers is still in a nascent stage, some MSD biomarkers were identified. There are limitations in the articles examined, including possible selection bias and inattention to potentially confounding factors. Recommendations for future studies are provided. Electronic supplementary material The online version of this article (doi:10.1186/s12891-017-1694-y) contains supplementary material, which is available to authorized users.

The goal was to investigate the effect of acute moderate hypobaric exposure on the physiological responses to sustained contractions (local) and light to moderate dynamic exercise (systemic) for cabin attendants (CAB) and a matched control group (CON).There were 14 CAB and 13 CON who participated. The experimental protocol was designed as a 2 x 2 randomized crossover study for which subjects performed a forearm isometric test and a cycling test in normobaric (NORM) and hypobaric [HYPO; 574 mmHg approximately 8000 ft (2440 m) above sea level (ASL)] conditions. Oxygen saturation (StO2%) was measured in the extensor carpi radialis muscle at rest and during an isometric wrist extension (20% MVC). Heart rate (HR), ventilation (V(E)), and oxygen uptake (VO2) were measured at rest, during cycling exercise at intensities of 50 W and 100 W, and during recovery. Blood samples were collected and analyzed for hemoglobin concentrations.Local response: There was a significant effect of HYPO for both CAB and CON with a decrease in StO2% of 6.5% both at rest and during contraction. Systemic response: there was no general effect of HYPO on HR, VE, or VO2. No differences were found between groups in either the local or systemic response or in the blood parameters.This study shows an effect of moderate hypobaric exposure on local muscle oxygenation during rest and sustained contraction. Whether this has an impact on fatigue development during work among cabin attendants is discussed.

Background: Type 1 diabetic patients and non-diabetic patients were referred for evaluation for chronic exertional compartment syndrome (CECS) based on clinical examination and complaints of activity-related leg pain in the region of the tibialis anterior muscle. Previous studies using near-infrared spectroscopy (NIRS) showed greater deoxygenation during exercise for CECS patients versus healthy controls; however, this comparison has not been done for diabetic CECS patients. Methods: We used NIRS to test for differences in oxygenation kinetics for Type 1 diabetic patients diagnosed with (CECS-diabetics, n = 9) versus diabetic patients without (CON-diabetics, n = 10) leg anterior chronic exertional compartment syndrome. Comparisons were also made between non-diabetic CECS patients (n = 11) and healthy controls (CON, n = 10). The experimental protocol consisted of thigh arterial cuff occlusion (AO, 1-minute duration), and treadmill running to reproduce symptoms. NIRS variables generated were resting StO(2)%, and oxygen recovery following AO. Also, during and following treadmill running the magnitude of deoxygenation and oxygen recovery, respectively, were determined. Results: There was no difference in resting StO2% between CECS-diabetics (78.2 +/- 12.6%) vs. CON-diabetics (69.1 +/- 20.8%), or between CECS (69.3 +/- 16.2) vs. CON (75.9 +/- 11.2%). However, oxygen recovery following AO was significantly slower for CECS (1.8 +/- 0.8%/sec) vs. CON (3.8 +/- 1.7%/sec) (P = 0.002); these data were not different between the diabetic groups. StO2% during exercise was lower (greater deoxygenation) for CECS-diabetics (6.3 +/- 8.6%) vs. CON-diabetics (40.4 +/- 22.0%), and for CECS (11.3 +/- 16.8%) vs. CON (34.1 +/- 21.2%) (P

Much is still unknown concerning the mechanisms underlying the development of chronic muscle pain. The presence and magnitude of inflammatory substances and neurotransmitters in chronic painful conditions is not clear. The aims of the present study were to determine, with the use of microdialysis, the interstitial concentrations and the equilibration times for PGE2 and glutamate in the trapezius muscles of nine female subjects with chronic muscle pain, and nine pain-free age-matched controls. A microdialysis probe was implanted in the upper part of the trapezius muscle and perfused with Ringer-acetate solution at a flow rate of 0.3 microL/min. Samples were obtained every 30 min, during a 4-h rest period. At equilibration, the mean concentrations (+/-SE) of PGE2 were 0.71 (+/-0.11) ng/mL for the pain-group and 0.97 (+/-0.35) ng/mL for the controls. For glutamate the mean concentrations for the pain-group were 66.3 (+/-13.3) micromol/L and 60.6 (+/-22.9) micromol/L for the controls. For the pain group and the control group, respectively, equilibration for PGE2 was reached at 180 and 150 min, and for glutamate at 150 and 120 min. The present study showed no differences between groups in the concentrations of PGE2 and glutamate in the trapezius muscle. Further, it revealed that when using the slow-flow method, a period of at least 2.0-2.5 h is needed, after probe insertion, to reach steady state for glutamate and PGE2.

We tested hypotheses of (a) reduced oxygen usage, oxygen recovery, blood flow and oxygen consumption; and (b) increased muscle activity for patients diagnosed with work-related muscle pain (WRMP) in comparison to healthy controls. Oxygenation was measured with near infrared spectroscopy (NIRS), and muscle activity with EMG for the extensor carpi radialis (ECR) and trapezius descendens (TD) muscles. Eighteen patients with diffuse neck-shoulder-arm pain and 17 controls (matched in age and sex) were equipped with NIRS and EMG probes. After determining an individual's maximum voluntary contraction (MVC) force, short-term (20 s) isometric contractions for the ECR and TD of 10, 30, 50 and 70 % MVC generated ∆StO₂ and StO₂% recovery (Rslope) from NIRS, and RMS%max from EMG signals. In addition, upper arm venous (VO) and arterial (AO) occlusions generated slopes of total hemoglobin (HbTslope) and deoxyhemoglobin (HHbslope) for the resting ECR as surrogates of blood flow and oxygen consumption, respectively. Mixed model analyses, t tests, and Mann-Whitney test were used to assess differences between groups. There was no significant difference in MVC between groups for either muscle. Also, ∆StO₂%, Rslope for either muscle, and ECR-HbTslope were not different between groups, thus our hypotheses of reduced oxygen use, recovery, and blood flow for patients were not confirmed. However, patients had a significantly lower ECR-HHbslope confirming our hypothesis of reduced consumption. Further, there was no difference in RMS%max during contractions meaning that the hypothesis of increased activity for patients was not confirmed. When taking into account the number of NIRS variables studied, differences we found between our patient group and healthy controls (i.e., in forearm oxygen consumption and shoulder oxygen saturation level) may be considered modest. Overall our findings may have been impacted by the fact that our patients and controls were similar in muscle strength, which is in contrast to previous studies.

Prolonged computer use, especially if fatigue ensues, is associated with visual and musculoskeletal symptoms. The aim was to determine the time-course of perceived fatigue in the wrist, forearm, sh ...

The aim was to investigate the relationship between oxygen saturation (StO(2)%) measured with near-infrared spectroscopy (NIRS) and myoelectric activity (root mean square, RMS) for the extensor carpi radialis (ECR) and trapezius muscles. In addition, gender differences were examined for submaximal (10-70% MVC) and sustained (10% MVC for 5 min) isometric contractions. Thirteen males and 15 females participated. Changes in StO(2)% (∆StO(2)%) and RMS, expressed as percentages of maximum, were calculated for each submaximal contraction. A good correlation between ∆StO(2)% and RMS was seen for the ECR (r = -0.53) and a moderate correlation seen for the trapezius muscle (r = -0.44). The ANOVA showed a significant decrease in ECR-∆StO(2)% over force with females demonstrating a tendency for larger changes than males. ECR-RMS increased over force with no impact of gender. For the trapezius, ∆StO(2)% decreased over force but was not gender dependent. Trapezius-RMS increased over force with females demonstrating a tendency for greater change than males. For the sustained contraction, ECR-StO(2)% changed over time but was not gender dependent. ECR-RMS increased over time with females showing a greater response than males. Trapezius-StO(2)% changed over time and differed between genders, i.e., males increased while females decreased. RMS increased over time similarly for both genders. In conclusion, our data show that the ECR and trapezius aerobic demands during isometric contractions are negatively correlated to electromyography (EMG) RMS. The present study also suggests some gender specificity for forearm and shoulder myoelectric activity and oxygenation for submaximal and sustained contractions.

The main aim was to examine the effects of measurement depth on tissue oxygenation, and haemoglobin kinetics in the oxidative supraspinatus/trapezius muscle and in the deltoid muscle. Seven female subjects performed dynamic arm abductions (0.5 Hz, 2 min) with an external load of 1.2 kg at level of the elbows. Tissue oxygenation (StO 2 ) expressed as %StO 2 saturation, total haemoglobin (Hb T ), oxyhaemoglobin (HbO 2 ) and deoxyhaemoglobin (Hb) were measured in two different measurement depth using near infrared spectroscopy (NIRS). Hb T reflects blood volume. Measurements were performed simultaneously in the supraspinatus/trapezius and in the anterior part of the deltoid muscles. The average StO 2 level at rest was in general lower in the supraspinatus/trapezius muscles (67.7(5.3) %StO 2 ) than in the deltoid muscle (85.4(4.4) %StO 2 ). Submaximal dynamic arm abductions resulted in decreased StO 2 in both muscles. However, the initial decrease was steeper and larger for the deltoid muscle than for the supraspinatus/trapezius region. Correspondingly, the initial reoxygenation in the recovery phase was faster for the deltoid muscle than for the supraspinatus/trapezius muscle. At rest no differences in StO 2 were found with increasing measurement depth in any of the two muscles. However, during exercise StO 2 decreased with increasing measurement depth in the deltoid muscle whereas StO 2 was more homogeneous in the supraspinatus/trapezius muscle. Furthermore, Hb T and HbO 2 were largely maintained in the supraspinatus/trapezius muscle whereas Hb T and HbO 2 decreased during exercise and with increasing measurement depth (Hb T ) in the deltoid muscle. Hb increased during exercise in both muscles. The hemodynamic differential responses to exercise for the two regions may reflect a combined effect of differences in muscle fibre composition and a dependency of depth related changes in the intramuscular pressure during exercise. Thus, the supraspinatus/trapezius muscles seem to be more efficiently adapted to the oxygen demand during submaximal dynamic exercise than the deltoid muscle although the intramuscular pressure during the contractions is expected to be higher in the supraspinatus muscle than in the deltoid muscle. In conclusion, muscle hemodynamic responses to dynamic exercise are highly muscle specific and may be spatially homogeneous or inhomogeneous depending on the muscle. Relevance to industry Understanding tissue oxygenation and haemoglobin kinetics of the shoulder muscles in response to submaximal exercise may be beneficial for future design of safe workplaces.

We examined the effect of a low-level sustained contraction on the muscle contractile properties, hemodynamics and oxygenation of the flexor digitorum superficialis muscle (FDS) of the finger. We tested the hypothesis that hemodynamics and oxygenation, reflecting the muscle metabolic characteristics, would recovery more quickly than the muscle contractile properties. Eleven subjects (26 ± 4 yrs) were equipped with electrodes for electrical stimulation and a near-infrared spectroscopy (NIRS) probe on the forearm over the FDS. The experimental protocol consisted of three baselines measurements (-60 min, -30 min, pre-exercise), immediately after a sustained 15-min contraction of the FDS at 10% maximal voluntary contraction (post-exercise), and after 30 min, 60 min and 120 min of recovery. For each time point, participants were subjected to a battery of test that included upper arm venous occlusion (at rest), a computer-mouse point and click task (standardized voluntary task), and electrical stimulation. For venous occlusion (50 mmHg, 1 min), slopes were calculated for NIRS-derived total hemoglobin (HbTslope) and deoxyhemoglobin (HHbslope) as estimates of blood flow and oxygen consumption, respectively. The computer-mouse task entailed using the mouse to point and click on targets presented on the screen during which NIRS signals were monitored for determination of change in total hemoglobin (ΔHbT) and oxygen saturation (ΔStO2%). Electrical stimulation (2 Hz, 5 trains of 15 twitches) provided twitch force (Tw-force), contraction time (CT) and one-half relaxation time (½RT) data. Statistical analysis revealed significant changes over time for all contractile parameters as well as for HHbslope (P < 0.05 for each). Post-hoc testing demonstrated significant decreases for Tw-force post-exercise and at 60 min; for CT at post-exercise, 30 min and 60 min; and for ½RT at post-exercise and at 30 min. HHbslope was significantly higher post-exercise as compared to pre-exercise. During the computer-mouse point and click task, no significant differences were detected forΔHbT, however,ΔStO2% showed a tendency to decrease, albeit not significant (P = 0.11). Further testing showedΔStO2% was significantly lower post-exercise and at 30 min as compared to pre-exercise. The present study shows that NIRS provides insight into muscle hemodynamics and oxygenation for low-level sustained activity to fatigue. The overall quick recovery of hemodynamic and oxygenation responses, and a more prolonged recovery of contractile responses confirms our hypothesis, and this may fit well with the classical definition of low frequency fatigue.

Both physical as well as mental demands result in an increased activity in the sympathetic nervous system (SNS) with changes in blood-pressure and heart-rate. Through local release of catecholamines, e.g. noradrenaline (NAd) SNS exerts various actions at the muscle level. The aims of this study were to investigate the effects of low-load repetitive work alone and in combination with mental demands on local muscle interstitial noradrenaline concentration [NAd](i), muscle activity and oxygenation, assessed with microdialysis, surface electromyography, and near-infrared spectroscopy, respectively. Healthy females (n = 15) were exposed to (1) 30 min repetitive work (RW) and (2) 30 min repetitive work with superimposed mental load (RWML) on two different occasions. Muscle [NAd](i) and muscle activity increased significantly in response to RW, but did not increase further during RWML. For RW, [NAd](i) was found to be inversely correlated to muscle activity. Oxygenation decreased significantly during work, independently of occasion. Our findings indicate that low-load work causes significantly increased trapezius muscle [NAd](i) in healthy females, and short periods of superimposed mental load do not add to this increase and further, that both muscle activity and oxygenation were unaffected by the superimposed mental load.

In the present study, we assessed the wrist kinetics (range of motion, mean position, velocity and mean power frequency in radial/ulnar deviation, flexion/extension, and pronation/supination) associated with performing a mouse-operated computerized task involving painting rectangles on a computer screen. Furthermore, we evaluated the effects of the painting task on subjective perception of fatigue and wrist position sense. The results showed that the painting task required constrained wrist movements, and repetitive movements of about the same magnitude as those performed in mouse-operated design tasks. In addition, the painting task induced a perception of muscle fatigue in the upper extremity (Borg CR-scale: 3.5, p

The present study investigated the effects of time pressure and precision demands during computer mouse work on muscle oxygenation and position sense in the upper extremity. Twenty-four healthy subjects (12 males and 12 females) performed a 45-min standardized mouse-operated computer task on two occasions. The task consisted of painting rectangles that were presented on the screen. On one occasion, time pressure and precision demands were imposed (more demanding task, MDT), whereas, on the other occasion, no such restraints were added (less demanding task, LDT). The order of the two task versions was randomized. Tissue oxygen saturation in the trapezius and extensor carpi radialis muscles was recorded throughout, and the position-matching ability of the wrist was measured before and after the tasks. In addition, measurements of autonomic nervous system reactivity and subjective ratings of tenseness and physical fatigue were obtained. Performance was measured in terms of the number of rectangles that were painted during the task. During MDT, oxygen saturation in extensor carpi radialis decreased (P < 0.05) compared to LDT. These data were paralleled by increased electrodermal activity (P < 0.05), skin blood flow (P < 0.05), ratings of tenseness and fatigue (P < 0.01), and increased performance (P < 0.01) during MDT. Females exhibited lower oxygen saturation than males, during rest as well as during the computer tasks (P < 0.01). Wrist repositioning error increased following LDT as compared to MDT (P < 0.05). In conclusion, computer mouse work under time pressure and precision demands caused a decrease in forearm muscle oxygenation, but did not affect wrist position sense accuracy. We attribute our changes in oxygenation more to increased oxygen consumption as a result of enhanced performance, than to vasoconstriction.

Objective: To study the effects of a muscle stretching regimen for the rectus femoris muscle on subjective stretch sensation and range of motion (ROM). Design: A2 2 crossover design comprising 2 treatments and 2 intervention periods. Setting: A military base in Sweden. Participants: A volunteer sample of 29 male military conscripts divided into 2 groups, with each group subjected to both experimental and control treatments at different time periods. Intervention: Two weeks of supervised stretching (4 times/ wk) of the rectus femoris muscle (experimental treatment) and the calf muscles (control treatment). Main Outcome Measures: Subjective rating of the stretch sensation for the anterior aspect of the thigh determined on a category ratio scale. Passive knee flexion ROM determined on each test with the same applied torque, specific for each subject. Results: An additive analysis of variance revealed that the stretch sensation after the experimental treatment was decreased, compared with the control treatment (p .01). The knee flexion, however, remained the same regardless of the treatment. Conclusion: Sensory adaptation seems to be an important mechanistic factor in the effect stretching has on ROM changes. The lack of change in knee flexion suggests that the stretching, as performed in this study, did not influence stiffness of the rectus femoris muscle. Sensory adaptation may also be an underlying mechanism in the alleviating effect of stretching when applied to tired, tender, and painful muscles.

Intramuscular pressure and electromyographic responses of the vastus lateralis muscle during repeated maximal isokinetic knee extensions.

Repetitive work to fatigue is soundly associated with work-related musculoskeletal disorders (WMSD), although the underlying mechanisms are poorly understood. In the present study, we tested the hypothesis that fatiguing work leads to proprioceptive deficits, which can be an initiating factor for the occurrence of WMSD. Thus, the position sense of the shoulder was determined for 13 males and 13 females before and after performing repetitive low-intensity arm work to fatigue in a simulated occupational setting. From a starting position of 45 degrees to the sagittal plane, position sense tests consisted of subjects attempting to actively reproduce target positions of horizontal movements to 15 degrees and 30 degrees (shoulder adduction) and to 60 degrees and 75 degrees (shoulder abduction). An analysis of variance revealed that the absolute error was significantly increased following fatigue for the subjects as a group (P0.001). Furthermore, females had an overall higher error than males (P0.01). No difference in error was detected for the shorter movements versus the longer movements. However, the overall absolute error for adduction was significantly higher than for abduction (P0.001). The results of the present study support the hypothesis of diminished proprioceptive acuity following low-intensity work to fatigue. A reduction in position sense acuity could lead to impairment in motor control, which would further impact on position sense. Thus, a vicious cycle may be activated that might result in WMSD. The poorer position sense acuity observed for females may contribute to the explanation of why females demonstrate a higher incidence of WMSD than males.

Position sense testing has increased as a tool for augmenting evaluation of joint injury. In the present study, we investigated the inter-day reliability for four different types of position sense tests using a fully automated system. The tests included (1) passive presentation/active replication, (2) passive presentation/passive replication, (3) semi-passive presentation/semi-passive replication (where semi-passive denotes passive movement during antagonist muscle contraction), and (4) active presentation/active replication. The absolute difference between presented target and replicated position was used as a measure of position sense accuracy. Ten healthy subjects who were blindfolded and seated with the arm in a moveable rig performed the tests on two occasions, separated by 3-4 days. For each type of position sense test, horizontal abduction from a starting position of 0 degrees (relative to the sagittal plane) to target positions of 32 degrees and 64 degrees, and horizontal adduction from a starting position of 80 degrees to 48 degrees and 16 degrees were conducted. A two-way ANOVA revealed no differences in absolute error between days or between testing procedures. However, intra-class correlations (ICC), which are most often used to express test-retest reliability, were moderate at best, ranging from 0.40 to 0.61 for the four types of position sense tests. Hence, the present study indicates that the ability of repositioning tests to detect alterations in proprioceptive function is limited, suggesting that their use in clinical evaluation be approached with prudence.

During dynamic (isokinetic) maximal contractions the mechanical output will decrease steeply during the initial 20-60 contractions (the fatigue phase) followed by a stable level (the endurance level). From visual inspections it is obvious that the breakpoint between these two phases differs between individuals. Based upon regression techniques we have investigated two variables of interest with respect to the breakpoint: the number of contractions (Bp-no) before the breakpoint and the angle (°) between the two phases (Bp-deg). We also investigated the interrelationship between output, sex, muscle morphology, and the two variables of the breakpoint during maximal dynamic knee extensions. Twenty clinically healthy subjects (11 males and 9 females) participated. Muscle biopsies of vastus lateralis were obtained from 19 out of 20 subjects. Bp-no was fqund at 42 ± 14 contractions (no sex difference). A significant difference (p = 0.001) between the two sexes was found for the Bp-deg (males: 100 ± 14 vs. females: 121 ± 16). No significant correlation existed between Bb-no and Bp-deg. Bp-deg and initial peak torque mainly correlated with the fibre areas. Bp-deg could be predicted in a model with sex and fibre areas as significant variables. The slope and endurance level (absolute and relative) of peak torque and Bp-no correlated negatively with % type 2b. Analyses of the relationship between output and morphology showed that different morphological variables (area or proportions) were of significant importance in different stages of the endurance test. In conclusion a method for determination of the breakpoint has been presented. The two variables presented correlated with important physiological aspects.

The effect of pre-anaesthetic ketamine on ensemble coding of different stimuli consisting of muscle stretches of various amplitudes was studied for ensembles of simultaneously recorded primary muscle spindle afferents (MSAs). The experiments were conducted on 8 α -chloralose anaesthetised cats. Three of the cats received a pre-anaesthetic dose of ketamine (25 mg/kg) injected subcutaneously (ketamine group), while the remaining five animals did not (non-ketamine group). Data for ensemble coding were collected both before and after cutting the ventral root. A method based on principal component analysis and algorithms was used to quantify stimulus discrimination and an ANOVA tested differences between groups as well as differences due to ventral root cutting. When the fusimotor supply was intact, a general trend of an increase in the ability to discriminate stimuli with increasing ensemble size was observed for both groups, however, this trend was significantly greater for the non-ketamine group as compared to the ketamine group. When the ventral root was cut, the discrimination pattern for the non-ketamine group decreased significantly (as compared to before ventral root cutting), however, no change occurred for the ketamine group. Consequently, no difference in discrimination pattern was detected between groups after ventral root cutting. The reduction in information transmitted by ensembles of primary MSAs when ketamine is used as a pre-anaesthetic may suggest that ketamine elicits an adverse affect on the fusimotor system.

Patients suffering from work-related muscle pain (WRMP) fatigue earlier during exercise than healthy controls. Inadequate oxygen consumption and/ or inadequate blood supply can influence the ability of the muscles to withstand fatigue. However, it remains unknown if oxygenation and hemodynamics are associated with early fatigue in muscles of WRMP patients. In the present study we applied near-infrared spectroscopy (NIRS) on the extensor carpi radialis (ECR) and trapezius (TD) muscles of patients with WRMP (n = 18) and healthy controls (n = 17). Our objective was to determine if there were group differences in endurance times for a low-level contraction of 15% maximal voluntary contraction (MVC) -sustained for 12-13 min, and to see if these differences were associated with differences in muscle oxygenation and hemodynamics. At baseline, oxygen saturation (StO(2)%) was similar between groups for the ECR, but StO2% was significantly lower for TD for the WRMP patients (76%) compared to controls (85%) (P < 0.01). Also, baseline ECR blood flow was similar in the two groups. For both muscles there were a larger number of patients, compared to controls, that did not maintain the 15% MVC for the allotted time. Consequently, the endurance times were significantly shorter for the WRMP patients than controls (medians, ECR: 347 s vs. 582 s; TD: 430 s vs. 723 s respectively). Responses in StO(2)% during the contractions were not significantly different between groups for either muscle, i.e. no apparent difference in oxygen consumption. Overall, we interpret our findings to indicate that the early fatigue for our WRMP patients was not associated with muscle oxygenation and hemodynamics., Funded by internal funds from the University of Gävle.

A gender comparison of electromyography (EMG) during repetitive arm work with and without mental stress

The mechanisms behind trapezius myalgia are unclear. Many hypotheses have been presented suggesting an altered metabolism in the muscle. Here, muscle microdialysate from healthy and myalgic muscle is analysed using metabolomics. Metabolomics analyse a vast number of metabolites, enabling a comprehensive explorative screening of the cellular processes in the muscle. Microdialysate samples were obtained from the shoulder muscle of healthy and myalgic subjects that performed a work and stress test. Samples from the baseline period and from the recovery period were analysed using gas chromatography-mass spectrometry (GC-MS) together with multivariate analysis to detect differences in extracellular content of metabolites between groups. Systematic differences in metabolites between groups were identified using multivariate analysis and orthogonal partial least square discriminate analysis (OPLS-DA). A complementary Mann-Whitney U test of group difference in individual metabolites was also performed. A large number of metabolites were detected and identified in this screening study. At baseline, no systematic differences between groups were observed according to the OPLS-DA. However, two metabolites, l-leucine and pyroglutamic acid, were significantly more abundant in the myalgic muscle compared to the healthy muscle. In the recovery period, systematic difference in metabolites between the groups was observed according to the OPLS-DA. The groups differed in amino acids, fatty acids and carbohydrates. Myristic acid and putrescine were significantly more abundant and beta-d-glucopyranose was significantly less abundant in the myalgic muscle. This study provides important information regarding the metabolite content, thereby presenting new clues regarding the pathophysiology of the myalgic muscle. Originally published in thesis in manuscript form.

The objectives of this study were to determine whether the occurrence of delayed onset muscle soreness (DOMS) for the vastus lateralis muscle was associated with elevated intramuscular pressure (IMP); and to assess, whether high eccentric forces occurred at an increased muscle length (as determined by joint angle). Therefore, peak knee extension torque, peak IMP of the vastus lateralis muscle, and the joint angle at which peak torque (JAPT) occurred were determined in eight male subjects during repetitive eccentric and concentric activities until fatigue occurred. Peak torque was significantly higher for eccentric compared to concentric activity (P < 0.01) and declined significantly for both activities (P < 0.01) throughout the protocols. When comparing the start (prior to fatigue) to the end (fatigue state), mean torque for eccentric activity declined from 191 to 147 (N · m) and for concentric activity declined from 166 to 104 (N · m). In contrast, peak IMP was not significantly different between the types of activity and did not change significantly with time. At the start and the end, the mean IMP remained constant for eccentric activity at 54 mmHg (7.2 kPa) but for concentric activity was 78 mmHg (10.4 kPa) and 96 mmHg (12.8 kPa), respectively. All the subjects, however, experienced DOMS of the vastus lateralis muscle exclusively for the eccentric activity leg. The JAPT was not different between activity types and did not change significantly with time; however, a significant interaction between activity type and time was observed (P = 0.01). For eccentric activity JAPT (0° = fully extended leg) was 81° (1.38 rad) and 79° (1.34 rad) and for concentric activity was 76° (1.29 rad) and 83° (1.41 rad) at the start and the end, respectively. From our studies we concluded that during eccentric activity the magnitude of IMP for the vastus lateralis muscle did not reflect the high muscles forces; therefore it would appear that IMP was not an etiologic indicator of DOMS, and that JAPT measurements did not offer an explanation for the high forces which were associated with eccentric activity.

This study investigated changes in intramuscular fluid pressure (IMP), torque and swelling related to delayed onset muscle soreness (DOMS) of the vastus lateralis muscle. IMP was measured via catheterization in the unstretched (0 degree, full extension) and stretched (90 degrees of knee flexion) muscle at rest; then IMP and knee extension torque were determined during maximal contractions pre and 2 d after (post) repetitive eccentric activity in one leg for eight male subjects. DOMS of the vastus lateralis muscle was associated with a significant elevation in IMP at rest as indicated by pre (0 degree: 5.4 mmHg, 90 degrees: 80 mmHg) and post (0 degree: 8.4 mmHg, 90 degrees: 13.2 mmHg) comparisons (P = 0.02). Soreness symptoms were aggravated when the muscle was stretched and this was accompanied by a significantly higher post IMP at 90 degrees vs. 0 degree (P = 0.01). During maximal contractions, peak torque declined by 15% relative to pre and peak IMP declined by 26%; DOMS symptoms, however, were most severe during this manoeuvre. Biopsies from the sore vastus lateralis muscle revealed significantly larger fibre areas for all fibre types as compared with contralateral controls (P < 0.01); however, no differences were detected for extracellular volume percent comparisons. This study shows that DOMS of the vastus lateralis muscle is associated with extensive intracellular swelling and with elevated IMP. In line with previous studies, fibre swelling may be a common subsequence to repetitive eccentric activity; the ability of IMP measurements to detect this swelling at rest and during various manoeuvres for other muscles may depend on compartmental compliance.

This study determined the day-to-day reliability of NIRS-derived oxygenation responses (∆StO(2)%) for isometric contractions and for cuff occlusion. Twenty-four subjects (12 males and 12 females) were tested for 2 days (4-6 days interval). Variables generated were: (1) ∆StO(2)% for isometric contractions (10, 30, 50 and 70% MVC) for descending trapezius (TD) and extensor carpi radialis (ECR) muscles; (2) slope changes in total haemoglobin (HbTslope) and deoxyhaemoglobin (HHbslope) for the ECR using upper arm venous (VO, 50 mmHg) and arterial occlusion (AO, 250 mmHg); (3) recovery slopes (Rslope) for oxygen saturation (StO(2)) following isometric contractions and AO. For each variable, an intraclass correlation (ICC) was calculated to assess the ability to differentiate between subjects, and limits of agreement (LOA) were computed to assess day-to-day consistency of the measurement. ICCs for ΔStO(2)% were lowest at 10% MVC for both ECR (0.58) and TD (0.55), and highest at 30% MVC for ECR (0.95) and at 70% MVC for TD (0.79). For both muscles, LOA for ΔStO(2)% was lowest at 10% and highest at 50 and 70% MVC. ICC for HbTslope was 0.17. For HHbslope ICC was higher for AO (0.83) than for VO (0.73), and LOA was lower for AO. For the ECR Rslope ICCs ranged from 0.88 to 0.90 for contraction, but was lower for AO (0.33); LOA was lowest at 70% MVC. For trapezius Rslope ICCs ranged from 0.63 to 0.73 and LOA was lowest at 30% MVC. For this study, establishing reliability data for the ECR and TD and including variables commonly reported are expected to have meaning for future NIRS studies of work-related upper-extremity pain as well as for other NIRS research and clinical applications.

Muscle oxygenation responses are reportedly greater in the distal muscle region than in the proximal muscle region. We combined near infrared spectroscopy and electromyography (EMG) to determine whether regional differences in oxygenation are associated with differences in (1) muscle activation and/or (2) fatigue development. Nine males performed 2-min sustained isometric knee extensions at 15% and 30% maximum voluntary contraction during which oxygenation and EMG were recorded simultaneously from proximal and distal locations of the vastus lateralis muscle. Near infrared spectroscopy variables for oxygen saturation (StO(2)%) were initial slope at contraction onset, peak drop, and recovery slope at contraction end. Electromyography produced the root mean square to indicate muscle activation and mean power frequency changes over time (decreasing slope) to indicate fatigue development. For StO(2)%, significantly greater peak drop and steeper recovery slope were found for the distal muscle region than for the proximal muscle region. Root mean square, however, was not different between locations. Mean power frequency decreased throughout the contractions but changes were not different between locations. Our results indicate that for modest submaximal contractions, regional differences in oxygenation are not associated with differences in muscle activation or with fatigue development (as interpreted by changes in mean power frequency over time).

Epidemiological research provides strong evidence for a link between repetitive work (RW) and the development of chronic trapezius myalgia (TM). The aims were to further elucidate if an accumulation of sensitising substances or impaired oxygenation is evident in painful muscles during RW. Females with TM (n=14) were studied during rest, 30 minutes RW and 60 minutes recovery. Microdialysate samples were obtained to determine changes in intramuscular microdialysate (IMMD) [glutamate], [PGE2], [lactate], and [pyruvate] (i.e., [concentration]) relative to work. Muscle oxygenation (%StO2) was assessed using near-infrared spectroscopy. During work, all investigated substances, except PGE2, increased significantly: [glutamate] (54%,P<.0001), [lactate] (26%,P<.005), [pyruvate] (19%,P<.0001), while the %StO2decreased (P<.05). During recovery [PGE2] decreased (P<.005), [lactate] remained increased (P<.001), [pyruvate] increased progressively (P<.0001), and %StO2had returned to baseline. Changes in substance concentrations and oxygenation in response to work indicate normal increase in metabolism but no ongoing inflammation in subjects with TM.

The efficacy of a modified fibre optic transducer-tipped catheter system for measuring intramuscular pressures during exercise was determined. A microcapillary infusion technique using a catheter was employed as the standard of comparison due to its established dynamic properties. Pressures were measured in the tibialis anterior muscle of six healthy adults at rest before exercise, during isometric and concentric exercise, and at rest after exercise. The fibre optic system measured contraction pressures equal to the microcapillary infusion technique during all phases of the exercise protocols but recorded a lower relaxation pressure during isometric exercise and a lower rest pressure following 20 min of concentric exercise. Negative relaxation pressures were recorded by the fibre optic system for two subjects during continuous concentric exercise. It is hypothesized that a piston effect, due to the sliding of muscle fibres at the catheter tip following a contraction, rendered falsely low pressures during relaxation and that this artefact was reflected in the subsequent rest pressure following exercise. The larger volume (157 mm3) and area (3.49 mm2) of the fibre optic catheter in the muscle made it more prone to this effect than the conventional catheter (39 mm3 and 0.87 mm2, respectively). The fibre optic system may be preferred when recording the muscle contraction pressures during complex limb movements but should not be used when assessing the relaxation pressures or the pressure at rest following exercise.

The present study aimed to elucidate possible physiological mechanisms behind impaired endurance during chewing as previously reported in WAD. We tested the hypothesis of a stronger autonomic reaction in WAD than in healthy subjects in response to dynamic loading of the jaw-neck motor system.Cardiovascular reactivity, muscle fatigue indicies of EMG, and perceptions of fatigue, exhaustion and pain were assessed during standardised chewing. Twenty-one WAD subjects and a gender/age matched control group participated. Baseline recordings were followed by two sessions of alternating unilateral chewing of a bolus of gum with each session followed by a rest period.More than half of the WAD subjects terminated the test prematurely due to exhaustion and pain. In line with our hypothesis the chewing evoked an increased autonomic response in WAD exhibited as a higher increase in heart rate as compared to controls. Furthermore, we saw consistently higher values of arterial blood pressure for WAD than for controls across all stages of the experiment. Masseter EMG did not indicate muscle fatigue nor were there group differences in amplitude and mean power frequency. Pain in the WAD group increased during the first session and remained increased, whereas no pain was reported for the controls.More intense response to chewing in WAD might indicate pronounced vulnerability to dynamic loading of the jaw-neck motor system with increased autonomic reactivity to the test. Premature termination and autonomic involvement without EMG signs of muscle fatigue may indicate central mechanisms behind insufficient endurance during chewing.

Laboratory and clinical tests were used to determine the efficacy of a new fiber optic "transducer-tipped" catheter for measuring intramuscular pressures. When pressures ranging from 0 to 250 mm Hg were applied by a mercury manometer, the fiber optic system accurately recorded the pressures. In addition, the fiber optic system showed long-term stability by accurately recording the manometer pressure over a 3 day period. The Slit system showed a higher magnitude of hydrostatic pressure artifacts with catheter tip movement as compared to the fiber optic system. The two catheters showed no difference when measuring pressures in pig muscle at rest or when being compressed throughout a range of 0 to 250 mm Hg. In human volunteers, both catheters measured essentially equal pressures at rest, during venous stasis, and during a combination of venous stasis and compression. For long-term assessment, the Slit system required as many as three saline flushes, whereas the fiber optic system measured pressures continuously without manipulation. We conclude that the fiber optic system is as accurate as the Slit catheter for measuring tissue fluid pressures at rest. In addition, the fiber optic system offers distinct advantages over conventional fluid-filled systems for measuring intramuscular pressures due to a lack of hydrostatic pressure artifacts caused by limb position and to the lack of flushing for long-term measurements.

Stretching is common among athletes as a potential method for injury prevention. Stretching-induced changes in the muscle spindle properties are a suggested mechanism, which may imply reduced proprioception after stretching; however, little is known of this association.To evaluate whether acute stretching of the shoulder muscles affects position sense.A crossover design with subjects randomized to 3 groups.A university human research laboratory.Nine male (age = 24 +/- 3 years) and 9 female (age = 21 +/- 2 years) healthy volunteers.Stretching of shoulder (1) agonists or (2) antagonists or (3) nonstretching control.We determined position sense acuity of the right shoulder before and after the interventions by having subjects attempt to reproduce arm positions of 15 degrees and 30 degrees (shoulder adduction) while starting at 45 degrees to the sagittal plane. The outcome variables were response variability (variable error) and overall accuracy (absolute error).The relative change in variable error (ie, variable error after/variable error before) was not significantly different between the interventions ( P = .38). Similarly, no change in absolute error was found ( P = .76). Furthermore, no differences were noted regarding test sequence or the interaction of intervention x sequence for either variable error ( P = .73 and .53, respectively) or absolute error ( P = .71 and .67, respectively).We found no effect on shoulder position sense after an acute bout of stretching of either agonist or antagonist shoulder muscles.

The aim of this study was to investigate the effects of duration of low-load repetitive work on intramuscular lactate, pyruvate, glutamate and prostaglandin E(2) (PGE(2)), and oxygen saturation in the trapezius muscle. Twenty healthy females were studied during baseline rest, during low-load repetitive work for either 30 (REP 30) or 60 min (REP 60) and 60 min recovery. Intramuscular microdialysate (IMMD) samples were obtained, and local muscle tissue oxygenation (%StO(2)) assessed with near-infrared spectroscopy (NIRS). Subjects rated their perceived exertion (Borg CR-10 scale) and capillary blood was sampled for lactate analysis. The results showed a significant increase in IMMD lactate in response to both REP 30 and REP 60 (P < 0.05 and P < 0.01, respectively) and glutamate (P < 0.0001), but no progressive increase with increasing work duration. Both IMMD pyruvate and lactate tended to be significantly increased during the recovery period. No corresponding increase in blood lactate was found. Local muscle %StO(2) did not change significantly in response to work and was not correlated to the IMMD lactate concentration. The ratings of perceived exertion increased in response to work, and remained increased after recovery for REP 60. In conclusion, the results of this study show significantly increased IMMD lactate and, glutamate concentrations in the trapezius muscle of healthy females in response to low-load work, but no progressive increase with increased work duration. Further, they do not indicate that the increased IMMD lactate concentration was caused by a locally decreased or insufficient muscle tissue oxygenation.

We investigated the effects of active versus passive pauses implemented during computer mouse work on muscle oxygenation and EMG of the forearm extensor carpi radialis muscle, and on wrist position sense. Fifteen healthy female subjects (age: 19-24 years) performed a 60-min mouse-operated computer task, divided into three 20 min periods, on two occasions separated by 3-6 days. On one occasion a passive pause (subjects resting) was implemented at the end of each 20-min period, and on another occasion an active pause (subjects performed a number of high intensity extensions of the forearm) was implemented. Also at the end of each 20-min period, test contractions were conducted and subjective ratings of fatigue and stress were obtained. Another parameter of interest was total haemoglobin calculated as the summation of oxy-and deoxy-haemoglobin, since it reflects blood volume changes. The most interesting findings were an overall increasing trend in total haemoglobin throughout the mouse work (P

Reproducibility And Gender Comparisons Of Oxygenation, Blood Flow And Oxygen Consumption For The Forearm

Lonn J, Crenshaw AG, Djupsjobacka M, Pedersen J, Johansson H. Position sense testing: influence of starting position and type of displacement. Arch Phys Med Rehabil 2000;81:592-7. Objective: To assess the effect of starting position, target position, and various types of limb displacement on repositioning tests commonly used for clinical evaluation of rehabilitation. Setting: Controlled laboratory environment. Participants: Sixteen healthy volunteer subjects. Main Outcome Measure: Absolute error, ie, the absolute difference between target and replicate positions. Design: Each subject performed four testing procedures consisting of different types of limb displacement (active, passive, and passive during antagonist muscle contraction). For each procedure, horizontal movements were performed ipsilaterally about the right glenohumeral joint from one intermediate starting position (40°) and two extreme starting positions (0° and 80°). Four fixed target positions (16°, 32°, 48°, 64°) were presented for each starting position. The subjects were required to replicate target position after returning to the respective starting position. Results: Lower repositioning errors occurred with active displacement procedures compared with passive, and with the intermediate starting position compared with the extreme. Target position, however, had no effect on repositioning errors. Conclusions: Starting position and type of displacement should be considered in interpretations and comparisons of data from clinical studies. © 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Contractile properties and hemodynamics for a sustained submaximal contraction studied with electrical stimulation and NIRS

This study is an investigation of the relationship between muscle morphology and surface electromyographic (EMG) parameters [mean frequency of the power spectrum (MNF), signal amplitude (root mean square, RMS) and the signal amplitude ratio (SAR; i.e. the ratio between the RMS level during the passive part of the contraction cycle and the RMS level during the active part of the contraction cycle)] during 100 maximal dynamic knee extensions at 90 degrees. s(-1). Each contraction cycle comprised of 1 s of active knee extension and 1 s of passive knee flexion. The surface EMG was recorded from the vastus lateralis muscle. Twenty clinically healthy subjects participated in the study, and muscle biopsy samples of the vastus lateralis were obtained from 19 of those subjects. The relationships between muscle morphology and EMG were investigated at three stages of the test: initially, during the fatigue phase (initial 40 contractions), and at the endurance level (the final 50 contractions). Major findings on correlations are that SAR and MNF tended to correlate positively with the proportion of type 1 fibres, and RMS correlated positively with the proportion of type 2 muscle fibres. The muscle fibre areas showed little correlation with the EMG variables under investigation. The results of the present study showed that the three EMG variables of a dynamic endurance test that were investigated (RMS, MNF and SAR) were clearly correlated with the proportions of the different fibre types, but only to a small extent with fibre areas. These findings contradict some of the theoretical models of the EMG, especially for parameters in the frequency domain.

This study investigated the relationship between muscle morphology and surface electromyographic parameters (mean frequency, f(mean); and signal amplitude, RMS) during sustained static knee extension to exhaustion at 25% maximal voluntary contraction (MVC) and at 70% MVC. Twenty clinically healthy subjects participated. EMGs were registered from the quadriceps. Muscle forces during knee extension at a 90 degree joint angle were maintained at the respective levels throughout the measurement periods. A biopsy was obtained of the vastus lateralis muscle. The total time to exhaustion was normalized for each subject. By means of regression analysis, the intercept (i) (i.e. the unfatigued state) and the regression coefficient (k) were determined for each EMG parameter. The endurance time increased with decreasing force level. A significantly higher perception of fatigue was found at 25% MVC than at 70% MVC. From principal component analyses it was concluded that RMS-k at 25% MVC mainly correlated with the type 2 muscle fibre proportions (%), and at 70% MVC mainly with the areas of type 2 muscle fibre. At 25% MVC, f(mean)-k correlated with the areas of type 2A, 2B and 2C fibres, and at 70% MVC negatively with the proportion of type 2B and to some extent with areas of type 2A, 2B and 2C fibres. f(mean)-i at 25% MVC correlated with fibre type proportions (%); f(mean)-i at 70% MVC correlated with the areas of type 2A, 2B and 2C. The present study indicates relationships between surface EMG and muscle morphology, which is contrary to presented models of the EMG.

Monitoring oxidative metabolic states may provide information on the mechanism behind computer use related musculoskeletal disorders. PURPOSE: To compare tissue oxygen saturation (Sat-O2) profiles ...

Intramuscular pressures, electromyography (EMG) and torque generation during isometric, concentric and eccentric maximal isokinetic muscle activity were recorded in 10 healthy volunteers. Pressure and EMG activity were continuously and simultaneously measured side by side in the tibialis anterior and soleus muscles. Ankle joint torque and position were monitored continuously by an isokinetic dynamometer during plantar flexion and dorsiflexion of the foot. The increased force generation during eccentric muscular activity, compared with other muscular activity, was not accompanied by higher intramuscular pressure. Thus, this study demonstrated that eccentric muscular activity generated higher torque values for each increment of intramuscular pressure. Intramuscular pressures during antagonistic co-activation were significantly higher in the tibilis anterior muscle (42-46% of maximal agonistic activity) compared with the soleus muscle (12-29% of maximal agonistic activity) and was largely due to active recruitment of muscle fibers. In summary, eccentric muscular activity creates higher torque values with no additional increase of the intramuscular pressure compared with concentric and isometric muscular activity.

Letter to the editor: Position sense acuity is diminished following repetitive low-intensity work to fatigue in a simulated occupational setting : a critical comment