Relationship between muscle oxygenation and electromyography activity during sustained isometric contraction

The purpose of this study was to clarify the relationship between electromyography (EMG) spectrum changes and muscle oxygenation measured by near-infrared time-resolved spectroscopy (TRS). Each subject performed sustained isometric knee extension at 50% of the maximal voluntary contraction load for 1 min. Surface EMG and TRS were simultaneously recorded from the right vastus lateralis muscle. Mean power frequency (MPF) of the power spectrum was calculated every 5 s during isometric contraction using fast Fourier transform, and decrease in the slope of MPF for 1 min was calculated using the least squares method. The maximal changes in oxygenated haemoglobin and myoglobin (Oxy Hb/Mb) and in deoxygenated haemoglobin and myoglobin (Deoxy Hb/Mb) from pre-contraction values of 1 min were calculated. There were significant relationships between the decrease in the slope of MPF and the maximal changes in Oxy Hb/Mb and Deoxy Hb/Mb (P < 0.05). These findings suggested that changes in Oxy Hb/Mb and Deoxy Hb/Mb indicate muscle fatigue assessed by EMG.     

Gender differences in muscle blood volume reduction in the tibialis anterior muscle during passive plantarflexion

Physical flexibility, such as joint range of motion and muscle extension, may influence muscle blood volume. Women have been shown to have a greater degree of flexibility than men. We examined whether there is a gender difference in the relationship between fascicle length and muscle blood volume or oxygenation in untrained men and women. In 16 untrained men and thirteen untrained women, we measured the total‐[haemoglobin (Hb) + myoglobin (Mb)] (total‐[Hb + Mb]) and relative oxy‐[Hb + Mb] after calibrating baseline and arterial occlusion deoxygenation levels with near‐infrared spectroscopy. Also, fascicle length was measured with B‐mode ultrasonography at the tibialis anterior muscle during passive plantarflexion. Increases in fascicle length from baseline (ankle joint angle 120°, composed from the caput fibulae, the malleolus (pivot), and the distal epiphysis of the fifth metatarsal bone) were greater in women than in men during plantarflexion of 140° and 160° and the maximal angle without pain. However, the decreases in total‐[Hb + Mb] and relative oxy‐[Hb + Mb] from baseline were not different between women and men at any degree of plantarflexion. Moreover, fascicle length and total‐[Hb + Mb]/muscle thickness (men > women) showed a similar relationship, with muscle thickness increasing capillary compression. These findings indicate the possibility of a mechanical function underlying muscle blood volume during muscle stretching, which is greater in women than in men.     

Interindividual variability of surface EMG changes during cycling exercise in healthy humans

We studied surface electromyogram (SEMG) changes during 1‐h endurance cycling in 12 healthy subjects of whom five were involved in mountain bike training programme. The work load was set at 50% of the predicted maximal heart rate. The surface EMG and the compound evoked muscle action potential (M‐wave) from the vastus lateralis muscle were recorded at rest, during the 1‐h cycling period, and the 20‐min recovery period. The root mean square (RMS) and the median frequency (MF) of SEMG power spectrum were computed. In all subjects, there was no shift in the median frequency throughout the cycling period and the increase in RMS remained stable. In subjects untrained to endurance cyclism, the M‐wave duration increased at the end of the cycling period and these changes persisted for a consecutive 15‐min period during recovery of exercise. By contrast, in trained mountain bikers the M‐wave duration decreased after 2 min of exercise – the effect persisting for 2 min during recovery. These data suggest that the interpretation of M‐wave changes during cycling must take into consideration the sport practices of the subjects and also that SEMG power spectrum and M‐wave explore different electrophysiological events.     

Central fatigue of the first dorsal interosseous muscle during low-force and high-force sustained submaximal contractions

The aim of this study was to compare the extent of central fatigue in the first dorsal interosseous (FDI) muscle of healthy adults in low, moderate and high-force submaximal contractions. Nine healthy adults completed four experimental sessions where index finger abduction force was recorded during voluntary contractions and in response to brief trains (five pulses at 100 Hz) of electrical stimulation. The ability to maximally activate FDI under volition, or voluntary activation, and its change with sustained activity (central fatigue) was assessed using the twitch interpolation technique. The fatigue tasks consisted of continuous isometric index finger abduction contractions held until exhaustion at four target force levels: 30%, 45%, 60% and 75% of the maximal voluntary contraction. The main finding was the presence of central fatigue for the 30% task, but not for the three other fatigue tasks. The extent of central fatigue was also associated with changes in a measure reflecting the status of peripheral structures/mechanisms. It appears that central fatigue contributed to task failure for the lowest force fatigue task (30%), but not for the other (higher) contraction intensities.     

Automated measurements of isolated heart muscle contractions: Effects of halothane, calcium, and magnesium on guinea pig left atrial muscle

An in vitro method for automatically measuring muscle contraction force has been demonstrated in a study of the effects of the inhalation anesthetic halothane followed by calcium chloride or magnesium sulfate on isolated guinea pig left atrial muscle. An automated computer-controlled system was used to collect muscle contraction force waveforms and to analyze contraction waveforms for comparison of variables before and after drug administration. Two concentrations of halothane (0.5 and 1.5%) were administered to the atrial preparation for 30 minutes and followed by calcium chloride or magnesium sulfate. Six variables (latency, time to peak tension, peak tension, maximum rate of change of pressure, force time integral, and relaxation time) were automatically determined from averaged stimulus-response curves. Results were normalized and compared with controls administered only calcium and magnesium and with controls administered no drugs. The automated system greatly simplified data collection and accumulation and statistical analysis of multiple responses. The system made possible averaging and analysis of more data with less variability than is normally obtained with manual systems. The results confirm several known actions of these agents. Halothane prolongs latency (9 and 21% for 0.5 and 1.5% halothane, respectively) and shortens time to peak tension (6 and 17% for 0.5 and 1.5% halothane, respectively) and relaxation time (17 and 39% for 0.5 and 1.5% halothane, respectively). At high halothane concentrations (1.5%), calcium chloride shortens latency (10%) and prolongs time to peak tension (11%); magnesium sulfate prolongs latency (14%) and shortens time to peak tension (10%).     

Automated measurements of isolated heart muscle contractions: Effects of halothane,calcium, and magnesium on guinea pig left atrial muscle

An in vitro method for automatically measuring muscle contraction force has been demonstrated in a study of the effects of the inhalation anesthetic halothane followed by calcium chloride or magnesium sulfate on isolated guinea pig left atrial muscle. An automated computer-controlled system was used to collect muscle contraction force waveforms and to analyze contraction waveforms for comparison of variables before and after drug administration. Two concentrations of halothane (0.5 and 1.5%) were administered to the atrial preparation for 30 minutes and followed by calcium chloride or magnesium sulfate. Six variables (latency, time to peak tension, peak tension, maximum rate of change of pressure, force time integral, and relaxation time) were automatically determined from averaged stimulus-response curves. Results were normalized and compared with controls administered only calcium and magnesium and with controls administered no drugs. The automated system greatly simplified data collection and accumulation and statistical analysis of multiple responses. The system made possible averaging and analysis of more data with less variability than is normally obtained with manual systems. The results confirm several known actions of these agents. Halothane prolongs latency (9 and 21% for 0.5 and 1.5% halothane, respectively) and shortens time to peak tension (6 and 17% for 0.5 and 1.5% halothane, respectively) and relaxation time (17 and 39% for 0.5 and 1.5% halothane, respectively). At high halothane concentrations (1.5%), calcium chloride shortens latency (10%) and prolongs time to peak tension (11%); magnesium sulfate prolongs latency (14%) and shortens time to peak tension (10%).     

The relationship between hamstring length and gluteal muscle strength in individuals with sacroiliac joint dysfunction

It has been suggested that tight hamstring muscle, due to its anatomical connections, could be a compensatory mechanism for providing sacroiliac (SI) joint stability in patients with gluteal muscle weakness and SIJ dysfunction. The purpose of this study was to determine the relationship between hamstring muscle length and gluteal muscle strength in subjects with sacroiliac joint dysfunction. A total of 159 subjects with and without low back pain (LBP) between the ages of 20 and 65 years participate in the study. Subjects were categorized into three groups: LBP without SIJ involvement (n = 53); back pain with SIJ dysfunction (n = 53); and no low back pain (n = 53). Hamstring muscle length and gluteal muscle strength were measured in all subjects. The number of individuals with gluteal weakness was significantly (P = 0.02) higher in subjects with SI joint dysfunction (66%) compared to those with LBP without SI joint dysfunctions (34%). In pooled data, there was no significant difference (P = 0.31) in hamstring muscle length between subjects with SI joint dysfunction and those with back pain without SI involvement. In subjects with SI joint dysfunction, however, those with gluteal muscle weakness had significantly (P = 0.02) shorter hamstring muscle length (mean = 158±11°) compared to individuals without gluteal weakness (mean = 165±10°). There was no statistically significant difference (P>0.05) in hamstring muscle length between individuals with and without gluteal muscle weakness in other groups. In conclusion, hamstring tightness in subjects with SI joint dysfunction could be related to gluteal muscle weakness. The slight difference in hamstring muscle length found in this study, although statistically significant, was not sufficient for making any definite conclusions. Further studies are needed to establish the role of hamstring muscle in SI joint stability.     

Segmental and plurisegmental modulation of pressure pain thresholds during static muscle contractions in healthy individuals.

The purpose of this study was to assess possible segmental (uni- and/or bilateral) and plurisegmental changes in pressure pain thresholds (PPTs) during static muscle contractions. Twenty-four healthy subjects (12 female, 12 male) performed a standardised isometric contraction with the dominant m. quadriceps femoris (MQF) and m. infraspinatus (MI), respectively. PPTs were assessed using pressure algometry at the contracting muscle, at the contralateral (resting) muscle and at a distant resting muscle (MI during contraction of MQF and vice versa). The PPT assessments were performed before, during and 30min. following each contraction. The contractions were held until exhaustion or for a maximum of 10 PPT assessments/muscle. During contraction of MQF PPTs increased compared to baseline at the middle ( p<0.001) and the end (p<0.001) of the contraction period at all assessed sites alike. During contraction of MI PPTs increased compared to baseline at the middle (p<0.001) and the end (p<0.007) of the contraction period at all sites. The increase was more pronounced at the contracting muscle compared to the contralateral (p<0.002; p<0.01) and the distant (p<0.002; p<0.002) site. No statistically significant difference was seen in PPTs between the latter two. Following the contractions PPTs returned to baseline. Submaximal isometric contraction of MQF and MI gave rise to a statistically significant increase in PPTs at the contracting muscle, the resting homologous contralateral muscle and at the distant resting muscle indicating that generalised pain inhibitory mechanisms were activated. Contraction of MI, but not of MQF, gave rise to an additional activation of unilateral segmental antinociceptive effects.     

Influence of repeated isometric contractions on muscle deoxygenation and pulmonary oxygen uptake kinetics in humans

The purpose of the present study was to compare simultaneously vastus lateralis (VL) deoxygenation and pulmonary O(2) uptake (O(2)) kinetics during fatiguing knee extension exercise with minimal cardiac load. Eight healthy subjects realized an intermittent bilateral knee-extension exercise (3-s contraction/3-s relaxation) at 40% of maximum voluntary contraction for 10 min. VL deoxygenation was recorded by near infrared spectroscopy at 2 Hz (NIRO-300, Hamamatsu Photonics, Japan) and O(2) was determined breath-by-breath (K4b(2), Cosmed, Italy). After a time delay of 16 +/- 5 s, deoxygenation kinetics at the onset of exercise followed an exponential time course at a significant faster rate than O(2) (time constant of 5.4 +/- 4.0 s vs. 31.6 +/- 10.4 s, P<0.01) reflecting a mismatch between local O(2) consumption and perfusion. Thereafter, a rise in O(2) of 223 +/- 123 ml min(-1) (consistent with the mathematical model, 259 +/- 126 ml min(-1)) was observed between minutes 2 and 10. During the same exercise time, changes in tissue oxygenation index decreased significantly and were individually correlated with the corresponding increased O(2) (P<0.05), suggesting that the majority of the slow rise of O(2) arose from the exercising limbs. Averaged heart rate increased from 67 +/- 11 to 116 +/- 20 beats min(-1) during exercise. Knee extension exercise may be relevant to estimate the cardiopulmonary and deoxygenation of working skeletal muscle responses for assessment of exercise limiting factors in clinical settings or in the exercise physiology.     

The effects of length on fatigue and twitch potentiation in human skeletal muscle

Fatigue is the decrease in active force that happens after repeated muscle stimulation, and post tetanic twitch potentiation (PTP) is the increase in twitch force observed after repeated muscle stimulation. This study investigated the effects of length on the interaction between fatigue and PTP, as these two forms of force regulation are length‐dependent and may coexist. A total number of 14 subjects were tested in 3 days, in which fatigue and PTP were induced in the knee extensor muscles in three different knee angles (30°, 60° and 90°; full extension=0°). PTP was evaluated in rested and fatigued muscles with twitch contractions elicited before and after 10 s maximal voluntary contraction (MVC), and fatigue was evaluated with nine 50 Hz electrically elicited contractions (5 s duration, 5 s interval between contractions). Fatigue was length‐dependent, with force values that were (mean ± SEM) 59 ± 5, 56 ± 3 and 38 ± 1% of maximal force at 90°, 60° and 30°, respectively. PTP was also length‐dependent. Rested muscles showed PTP of 39 ± 4, 47 ± 2 and 68 ± 5% at 90°, 60° and 30°, respectively. Fatigued muscles showed PTP of 44 ± 3, 55 ± 6 and 68 ± 5%, at 90°, 60° and 30°, respectively. This study shows that fatigue and PTP may represent independent mechanisms, as they regulate force in opposite directions and are both enhanced in short muscle lengths.     

Temporal summation of pressure pain during muscle hyperalgesia evoked by nerve growth factor and eccentric contractions

Nerve growth factor (NGF) has a key role in the generation and potentiation of pain. Its centrally sensitizing effects may facilitate pain responses to noxious stimulus. This study assessed (1) the influence of NGF on delayed onset muscle soreness (DOMS) in shoulder muscles; and (2) the temporal summation of pressure pain during hyperalgesia induced by NGF and DOMS. In a blinded design, 10 healthy subjects were injected with NGF in the trapezius muscle on one side and with isotonic saline on the contralateral side as control. The subjects undertook shoulder eccentric exercise to induce DOMS in the shoulder muscles 3 h after the injections. The soreness intensity to muscle contraction, pressure pain thresholds (PPT), and pain intensity to sequential stimuli (i.e. temporal summation at 1 and 30 s inter-stimulus interval (ISI)) were assessed before injections – 3, 24 h, and 4, 7, and 21 days after injections. The soreness intensity to muscle contraction significantly increased at 3 and 24 h in both shoulders (P < 0.05) and went back to baseline levels at day 7. The same development was seen in PPT as reduced thresholds (P < 0.05). The NGF injected side had higher pain ratings during temporal summation at 1 s ISI compared with the contralateral side 24 h after injections. Intramuscular administration of NGF intensified the DOMS responses, evoking facilitated temporal summation. Central as well as peripheral sensitization mechanisms may play a role in the facilitation.     

Perceived disability,fatigue, pain and measured isometric muscle strength in patients with post‐polio symptoms

Background and Purpose. Several years after the acute polio illness, patients may develop new post‐polio symptoms. The purpose of the present study was to evaluate patients with post‐polio symptoms with regard to perceived fatigue, functional ability, muscle strength, pain and with regard to measured physical fitness and isometric muscle strength. In addition, the relationship between the results of these subjective and objective measurements was investigated. Method. This was a prospective cross‐sectional study in which 32 patients with post‐polio symptoms were included. Main outcome measures were the Fatigue Severity Scale (FSS), the Disability Rating Index (DRI), pain intensity, pain distribution, self‐reported and measured muscle strength and oxygen uptake. Results. A marked reduction in isometric muscle strength compared to normal data, high scores in fatigue, widespread pain, low oxygen uptake and difficulties in performing some daily activities were found. Self‐reported general muscle strength, pain intensity and pain distribution correlated significantly with patients' perceived fatigue and function at the activity level. There was no significant correlation between self‐reported and measured results except for that found between isometric muscle strength in the legs and patients' perceived general muscle strength and oxygen uptake. Conclusions. Evaluation of pain intensity, pain distribution, perceived muscle strength, fatigue and ability to perform daily tasks reveals important aspects of health status in patients with post‐polio symptoms. Reduction in isometric muscle strength was not reflected in those tests or in reported symptoms, and should be monitored independently using a sensitive assessment tool. Accurate screening of isometric muscle strength in isolated muscle groups contributes to therapeutic management in making a functional diagnosis at the level of body function and structure when designing specific training programmes and in motivating patients. An evaluation combining self‐reports with sensitive muscle strength measures provide supplementary information and is appropriate for evaluating these patients in physiotherapy practice. Copyright © 2007 John Wiley & Sons, Ltd.     

温热银质针疗法三种体外留针长度银质针温度及对大鼠骨骼肌作用的比较研究

目的:研究温热银质针疗法时体外留针长度与温热银质针温度及大鼠骨骼肌形态学变化的关系,以明确最适的留针长度。方法:将54只大鼠随机分为3组采用温热银质针治疗,银针刺入鼠左后腿皮肤深度均为3cm,各组体外留针长度分别为9cm、7cm、5cm,艾条在针柄顶端点燃。使用数字测温仪测量针尖、皮肤进针点及二者中点的温度。光镜下观察针尖处肌肉组织形态学变化及波形蛋白和结蛋白表达情况。结果:温热银质针治疗过程中,各组针尖、中点、皮肤进针点温度波动明显(体外留针9cm组针尖温度除外),第10min时最高。体外留针5cm组针尖(43.6±0.6℃)和皮肤进针点温度(46.8±1.1℃)最高,体外留针9cm组皮肤进针点温度(36.6±0.6℃)最低,体外留针9cm组针尖温度(35.2±0.7℃)与体外留针7cm组(35.6±0.7℃)无显著差异。各组大鼠骨骼肌细胞呈现损伤-修复过程,体外留针5cm组组织损伤范围大,程度严重,以瘢痕修复为主,波形蛋白和结蛋白表达少,另两组以肌细胞再生修复为主。结论:根据温热银质针体内针身温度和大鼠骨骼肌损伤-修复情况,体外留针9cm和7cm时更合适。     

In vitro effects of the cyclooxygenase inhibitor indomethacin and of the phospholipase‐C inhibitor U‐73122 on carbachol‐induced contractions of porcine detrusor muscle

Prostaglandin synthetase inhibitors belong to one substance class additionally used in the treatment of bladder dysfunctions associated with involuntary bladder contractions. However, the mechanism of action of non‐steroidal anti‐inflammatory drugs (NSAIDs) on the detrusor muscle is not clear. In this study, it was examined in vitro whether the NSAID indomethacin exhibited an inhibitory effect on carbachol‐induced contractions of the porcine detrusor muscle. Additionally, the inhibitory effect of the phospholipase‐C inhibitor U‐73122 on carbachol‐induced contractions of the porcine detrusor muscle was investigated. Experiments were performed on the muscle strips of the porcine detrusor muscle suspended in a tissue bath. Effects of indomethacin at 10^?6 and 10^?5 m on the maximum carbachol‐induced contraction and on the carbachol–response curve were investigated. Additionally, the inhibitory influence of U‐73122 at a concentration of 10^?5.5 m on the carbachol–response curve was investigated. Pretreatment with indomethacin at both concentrations did not result in a significant reduction in the maximum contraction compared with the control. In the experiments in which carbachol concentration‐response curves were generated, indomethacin exhibited at both concentrations a very small but significant change at carbachol concentrations of 10^?8 and 10^?7.5 m . In the experiments with U‐73122, a significant change was found in the concentration–response curve of carbachol at all concentrations of carbachol from 10^?6.5 to 10^?4 m . The mean maximum carbachol‐induced contraction was 141.8 ± 6.8% after incubation with U‐73122 and 166.0 ± 6.4% in the control group (P < 0.05). Indomethacin did not inhibit the carbachol‐induced contractions of the porcine detrusor muscle. The cyclooxygenase does not play a significant role in the carbachol‐induced bladder contraction of the porcine detrusor muscle. The inhibitory action of the phospholipase‐C inhibitor U‐73122 on the carbachol‐induced contraction was significant, but small. The results point to an inferior role of this pathway.     

Intramuscular water movement during and after isometric muscle contraction: evaluation at different exercise intensities

We aimed at evaluating the effect of isometric muscle contraction on intramuscular water movement at different exercise intensities. Seven men performed 1‐min isometric ankle dorsiflexion (20% and 50% maximal voluntary contractions [MVCs]) with a non‐magnetic custom‐made dynamometer, inside a magnetic resonance (MR) device. Axial diffusion‐weighted images were obtained before, during and at 1–20 min (1‐min interval) after the exercise to calculate the apparent diffusion coefficient (ADC) of the tibialis anterior. Under the same exercise condition, the concentration change of total haemoglobin (Hb) and myoglobin (Mb) (total Hb/Mb) within the tibialis anterior was assessed by performing near‐infrared spectroscopy before, during and after the exercise outside the MR device. The 20% MVC exercise significantly increased the ADC only at 1 min postexercise (P<0·01), whereas the ADC significantly increased during and at 2–20 min after the 50% MVC exercise (P<0·01). The 20% MVC exercise decreased the total Hb/Mb during exercise (P<0·01), but the value significantly increased at 1 min postexercise (P<0·01). The total Hb/Mb significantly decreased during the 50% MVC exercise, but significantly increased at 1–5 min postexercise (P<0·01). One‐minute moderate‐intensity isometric exercise activates intramuscular water movement during and after the exercise. This activation was found even after a low‐intensity exercise, but the effect was small and did not last long. The effect of intramuscular hyperaemia on the postexercise ADC elevation may be limited to the very early period after low‐ to moderate‐intensity exercises.     

Evaluation of oxygen uptake kinetics and oxygen kinetics of peripheral skeletal muscle during recovery from exercise in patients with chronic obstructive pulmonary disease

The biochemical features of skeletal muscle and its contribution to exercise intolerance in patients with chronic obstructive pulmonary disease (COPD) is under active investigation. Near-infrared spectroscopy (NIRS) can non-invasively provide information on the oxidative capacity of muscle. To clarify whether oxygenation of peripheral muscle is one determinant of exercise tolerance, we simultaneously examined the oxygen uptake (V O 2off) kinetics and oxygen kinetics of peripheral skeletal muscle evaluated by NIRS during recovery from exercise in COPD patients. Fifteen patients with COPD and five normal control subjects performed a symptom-limited incremental exercise test. On the following day, all patients performed a constant work rate exercise test while being monitored using NIRS continuously for changes in concentration of oxygenated haemoglobin (HbO2) and during expired gas analysis. We found that the time constant of during recovery from constant work rate exercise (V O 2off) and the time constant of V O 2off during recovery (tau V O 2off) were significantly longer in COPD patients than in normal control subjects. was inversely correlated with absolute values of forced expiratory volume in 1 s (FEV1.0) and FEV1.0 (% predicted). However, no significant correlation was found between and FVC (forced vital capacity), FEV1.0/FVC, or diffusing capacity of the lung for CO (DLCO). Moreover, was inversely correlated with maximal V O 2off and maximal work rate. In contrast, exhibited a significant positive correlation with tau V O 2off. These results indicate that V O 2off kinetics during recovery is related to re-oxygenation of peripheral skeletal muscle evaluated by NIRS in patients with COPD. Therefore, NIRS may be a useful tool to estimate the impairment of cardiopulmonary responses and re-oxygenation of peripheral skeletal muscle during the immediate recovery phase after exercise in COPD patients.