Maximal isometric force and neural activity during bilateral and unilateral elbow flexion in humans

We investigated maximal isometric force and electromyographic (EMG) activity of the biceps brachii muscle during rapid bilateral (BL) and unilateral (UL) elbow flexion in 11 right-handed subjects. The BL exhibited a deficit in force for both arms and more so for the right than the left arm during the rising phase of force generation. The EMG of the left biceps brachii muscle was similar during UL and BL, but for the right arm EMG was lower during BL than during UL for the rising phase of force generation. The BL to UL ratio of mean power frequency of the EMG was lower for the right than for the left arm. The data would suggest that the relatively small BL strength was associated with a equally small EMG and a shift to a lower mean power frequency especially for the fast motor units of the dominant muscle.

Identification and characterization of genes encoding polycyclic aromatic hydrocarbon dioxygenase and polycyclic aromatic hydrocarbon dihydrodiol dehydrogenase in Pseudomonas putida OUS82

Naphthalene and phenanthrene are transformed by enzymes encoded by the pah gene cluster of Pseudomonas putida OUS82. The pahA and pahB genes, which encode the first and second enzymes, dioxygenase and cis-dihydrodiol dehydrogenase, respectively, were identified and sequenced. The DNA sequences showed that pahA and pahB were clustered and that pahA consisted of four cistrons, pahAa, pahAb, pahAc, and pahAd, which encode ferredoxin reductase, ferredoxin, and two subunits of the iron-sulfur protein, respectively.

Neuromuscular fatigue during prolonged pedalling exercise at different pedalling rates

The purpose of this study was to estimate the differences in neuromuscular fatigue among prolonged pedalling exercises performed at different pedalling rates at a given exercise intensity. The integrated electromyogram (iEMG) slope defined by the changes in iEMG as a function of time during exercise was adopted as the measurement for estimating neuromuscular fatigue. The results of this experiment showed that the relationship between pedalling rate and the means of the iEMG slopes for eight subjects was a quadratic curve and the mean value at 70 rpm [1.56 (SD 0.65) microV.min-1] was significantly smaller (P < 0.01) than that at 50 and 60 rpm [2.25 (SD 0.54), and 2.22 (SD 0.68), respectively]. On the other hand, the mean value of oxygen consumption obtained simultaneously showed a tendency to increase linearly with the increase in pedalling rate, and the values at 70 and 80 rpm were significantly higher than those at 40 and 50 rpm. In conclusion, it was demonstrated that the degree of neuromuscular fatigue estimated by the iEMG changes for five periods of prolonged pedalling exercise at a given exercise intensity was different among the different pedalling rates, and that the pedalling rate at which minimal neuromuscular fatigue was obtained was not coincident with the rate at which the minimal oxygen consumption was obtained, but was coincident with the rate which most subjects preferred. These findings would suggest that the reason why most people prefer a relative higher pedalling rate, even though higher oxygen consumption is required, is closely related to the development of neuromuscular fatigue in the working muscles.

Determination of maximal power output at neuromuscular fatigue threshold

The purpose of this study was to determine the maximal power output at the neuromuscular fatigue threshold (EMGFT), as estimated from electromyographic (EMG) data from representative leg muscles during cycling. The rate of rise in integrated EMG activity as a function of time (iEMG slope) was calculated at each of four constant-power-output ergometer bouts for 20 subjects. The iEMG slopes were plotted against work rates that were well described as linear functions (0.84 < R2 < 0.99). This iEMG slope vs. work rate relationship was extrapolated to zero slope to give an intercept on the power axis that was interpreted as the highest work rate sustainable without EMG evidence of neuromuscular fatigue (EMGFT). Each individual EMGFT was then expressed in terms of an O2 output (VO2) equivalent on the basis of the individual delta efficiency calculated during a linearly increasing maximal exercise test on the same bicycle ergometer. Results indicated a highly significant correlation (r = 0.92, P < 0.01) between EMGFT VO2 and anaerobic threshold VO2, as determined by conventional gas exchange criteria. The mean EMGFT VO2 (1.84 +/- 0.55 l/min) was, however, significantly greater (P < 0.01) than the anaerobic threshold VO2 (1.72 +/- 0.54 l/min). It was suggested that the EMGFT may provide an attractive alternative to the measurement of the highest work rate that can be sustained without evidence of neuromuscular fatigue.

Rapid increase in the number of androgen receptors following electrical stimulation of the rat muscle

The changes in the number of androgen receptors in rat gastrocnemius muscle following muscle contraction caused by electrical stimulation were investigated. The gastrocnemius muscle of one leg, which was selected at random for each rat, was stimulated with needle type electrodes, e.g. for 2 s at 10 V and 100 Hz, with 5-s intervals. The contralateral leg was left unstimulated as a control. One set consisted of ten such stimuli, followed by 5-min rest. Three sets every 2 days caused a statistically significant increase in muscle mass, the increase being about 2.5% after the 3rd day of stimulation, 4.4% after the 5th day, 5.9% after the 13th day and 8.3% after the 27th day compared with each control muscle (P < 0.001 in each case). The protein content also increased but the water content did not change. Stimulation over 4 weeks induced an increase in the area of the cross-section of the muscle fibres to about 30% more than that of the control muscles, though the total muscle fibre numbers were slightly, but significantly, reduced. Electromechanical properties supported the development of the muscle by stimulation, because the maximal isometric tetanic force and peak twitch force markedly increased in the stimulated muscle. The androgen receptors in the muscle cytosol fraction were determined by means of a binding assay involving [3H]methyltrienolone, which is an analogue of testosterone, the number having rapidly increased in the stimulated leg, when compared with that in the control leg, by about 25% after the 3rd day. The increase then slowed down, reaching a plateau after the 5th-day of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Does critical swimming velocity represent exercise intensity at maximal lactate steady state?

The purpose of this investigation was to determine whether the critical swimming velocity (vcrit), which is employed in competitive swimming, corresponds to the exercise intensity at maximal lactate steady state. vcrit is defined as the swimming velocity which could theoretically be maintained forever without exhaustion and expression as the slope of a regression line between swimming distances covered and the corresponding times. A total of eight swimmers were instructed to swim two different distances (200 m and 400 m) at maximal effort and the time taken to swim each distance was measured. In the present study, vcrit is calculated as the slope of the line connecting the two times required to swim 200 m and 400 m. vcrit determined by this new simple method was correlated significantly with swimming velocity at 4 mmol.l-1 of blood lactate concentration (r = 0.914, P < 0.01) and mean velocity in the 400 m freestyle (r = 0.977, P < 0.01). In the maximal lactate steady-state test, the subjects were instructed to swim 1600 m (4 x 400 m) freestyle at three constant velocities (98%, 100% and 102% of vcrit). At 100% vcrit blood lactate concentration showed a steady-state level of approximately 3.2 mmol.l-1 from the first to the third stage and at 98% of vcrit lactate concentration had a tendency to decrease significantly at the fourth stage. On the other hand, at 102% of vcrit, blood lactate concentration increased progressively and those of the third and fourth stages were significantly higher than those at 100% of vcrit (P < 0.05). These data suggest that vcrit, which can be calculated by performing two timed, maximal effort swimming tests, may correspond to the exercise intensity at maximal lactate steady state.

Neuromuscular adaptations during the acquisition of muscle strength, power and motor tasks

Neuromuscular performance is determined not only by the size of the involved muscles, but also by the ability of the nervous system to appropriately activate the muscles. Adaptive changes in the nervous system in response to training are referred to as neural adaptation. This article briefly reviews current evidence regarding the neural adaptations during the acquisition of muscle strength power and motor tasks and will be organized under four main topics, namely: (i) muscle strength gain: neural factors versus hypertrophy, (ii) neural adaptations during power training, (iii) neuromuscular adaptations during the acquisition of a motor task, and (iv) neuromuscular adaptations during a ballistic movement.

[CT features of chronic maxillary osteomyelitis in adults]

CT findings were reviewed in four adult patients with chronic maxillary osteomyelitis (CMO) that was histologically proved. The CT features of CMO included bone destruction and soft tissue mass, predominantly in the inferior portion of the maxillary antrum (all 4 cases), thickening of the antral wall (3 cases) and abnormal soft tissue around the antrum associated with or without bony wall destruction (3 cases). CMO could not be distinguished from cancer of the maxillary antrum on CT because of the similar findings. However, abnormal soft tissue around the antrum together with an undestructed bony antral wall may be useful for differentiating the two diseases.

Effects of chronic hypoxia on the whole-body insulin action in rats

The effect of chronic hypoxia on the whole-body insulin action in rats was investigated. Rats were kept in a hypobaric hypoxia chamber maintained at a simulated altitude of 4000 m for 10 weeks. At the end of the experimental period, the mean body weight of the hypoxic rats was significantly lower than that of the control rats. The muscle weight to body ratio of the quadriceps muscle in hypoxic rats was larger than that in control rats, but those of the gastrocnemius, soleus, and extensor digitorum longus muscles did not differ between the control and hypoxic rats. On the other hand, the epididymal fat pads of hypoxic rats were markedly smaller than those of the control rats. The results of a euglycemic clamp experiment with infusions of 14 and 3.6 mU insulin.kg-1.min-1 indicated that the steady-state glucose infusion rate was not statistically different between hypoxic and control rats. It is suggested that chronic hypoxia did not influence the whole-body insulin action on glucose transport activity.

A simple method for determining critical speed as swimming fatigue threshold in competitive swimming

The purpose of this investigation was to determine whether the concept of the critical power could be applied to competitive swimming by using critical swimming speed (CS) as determined both in the swimming flume (CS-flume) and in the normal swimming pool (CS-pool) and whether CS could be utilized as a practical index for assessing a swimmer's endurance performance. CS defined as the swimming speed which could be theoretically maintained continuously without exhaustion was expressed as the slope of a regression line between swimming distance (D) and its duration (T) obtained at various swimming speeds. Eight highly trained swimmers were instructed to swim until onset of fatigue at four predetermined swimming speed levels in the swimming flume and at maximal effort over four different swimming distances in the swimming pool. In the results of CS-flume and CS-pool, the regression relations between D and T were expressed in the general form, D = a+b x T, with r2 being higher than 0.998 (p less than 0.01), respectively. These results both from the flume and the pool indicated extremely good linearity. Furthermore, maximal oxygen uptake (VO2max) during the incremental exercise test, swimming speed corresponding 4 mM of blood lactate concentration (V-OBLA) and mean velocity in the 400 m freestyle (V-400) were measured on each subject.(ABSTRACT TRUNCATED AT 250 WORDS)

H-reflex testing to determine the neural basis of movement disorders of neurologically impaired individuals

The H-reflex is an indirect measure of the excitability levels of alpha motoneurons. The authors have developed an adaptation of H-reflex testing which allows the continuous monitoring of human alpha motoneuron activity during movement. The technique differs from previously used H-reflex testing techniques in that it utilizes a 5 Hz stimulation to elicit the H-reflex. This allows for continuous and concomitant H- and M-wave recordings during a movement. This is an improvement over past single stimulus techniques in that the time and discomfort associated with this type of experimentation is greatly decreased. The repetitive stimulation technique enables H-reflex testing to be used clinically with neurologically impaired patient populations. Thus far, the authors have used the repetitive H-reflex testing procedures to assess alpha motoneuron activation and reciprocal inhibition of antagonist musculature during voluntary movement and anticipatory postural control responses of non-disabled individuals and of individuals with cerebral palsy. This paper describes the methodology involved in this technique and reports the results obtained.

Increase in neuromuscular activity and oxygen uptake during heavy exercise

In order to examine the contribution of neuromuscular activity to the slow increase in VO2 during heavy exercise, integrated electromyogram (iEMG) of dominant working muscle and VO2 was compared in seven subjects during constant-load cycling exercise at the intensity of 10% below and 30% above ventilatory threshold (VT) for seven minutes. VO2 and iEMG after 4th min in above VT test was significantly correlated (r = 0.53, p less than 0.01) and VO2/iEMG was constant after 4th min, indicating coupling of iEMG with VO2. The results suggested that the slow increase in VO2 during heavy exercise may result from the changes in the recruitment pattern of motor units.

Validity of critical velocity as swimming fatigue threshold in the competitive swimmer

The purpose of this investigation was to determine whether the critical velocity (CV) as the swimming speed which can be theoretically maintained for a very long time without exhaustion could be applied to estimate the swimmer's endurance performance. CV was based on the concept of critical power originality established by Monod and Scherrer (1965) and extended by Moritani et al. (1981), and expressed as the slope of a regression line between swimming distance (D) at each velocity and its sustained time (T). Seventeen highly trained swimmers were instructed to swim the four different swimming distances (50 m, 100 m, 200 m and 400 m) at maximal effort using the swimming pool. In the results of CV, the regression relations between D and T were expressed in the general form, D = a + bxT, with r2 showing higher than 0.997 (p less than 0.001). These results indicate extremely good lineality. Furthermore, VO2max during incremental exercise test, swimming speed corresponding 4 mM of blood lactate concentration (V-OBLA) and mean velocity in the 200 m and 400 m freestyle (V-200 and V-400) were measured on nine subjects. Significant correlations were found between CV and V-OBLA (r = 0.862, p less than 0.01), CV and V-200 (r = 0.781, p less than 0.01), CV and V-400 (r = 0.999, p less than 0.001), V-OBLA and V-400 (r = 0.869, p less than 0.01) and V-200 and V-400 (r = 0.776, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)