Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments

Summary The surface electromyogram (EMG) from active muscle and oxygen uptake ( ) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W · min^–1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMG_bp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake ( ) and the iEMG_bp between 10 and 30, and 10 and 40 W · min –1 ramp exercises (P < 0.05). However, no significant differences were obtained in and corresponding to the iEMG_bp during the four ramp exercises. With respect to the relationship between and exercise intensity during the ramp increments, the -exercise intensity slope showed significant differences only for the upper half (i.e. above iEMG_bp). These results demonstrated that the and at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to and the iEMG_bp was varied by the change of ramp slopes. In addition, the significant differences in the exercise intensity slopes for the upper half of the tests would suggest that the recruitment patterns of MU and/or muscle metabolic state might be considerably altered depending upon the ramp slope increments.     

Responses to intensive training and methandrostenelone administration: II. Hormonal,organ weights,muscle weights and body composition

The hormonal levels of the gonadotropins, the weight of selected organs and of the triceps surae as well as body composition were determined in Sprague Dawley rats at 3 and 6 weeks after intensive training with or without a methandrostenelone (Dianabol) supplement (0.35 mg/kg/day). The controls were sedentary rats of similar age and weight at the start of the experiment. The dianabol treated rats in the sedentary and exercise groups had a depression of plasma LH levels. There were no differences in body weight, specific gravity, lean body weight, fat or % fat between the two trained groups. Dianabol had no apparent effect on the measured parameters other than a depression of LH.     

医用磷酸钙骨水泥的制备及性能的实验研究

探索了磷酸四钙（Ca4（PO4）2O，TTCP）的制备，并合成了磷酸钙骨水泥（CPC），对CPC固化时间、引起浸泡液pH值的变化、抗压强度、产物物相组成及微观结构进行了研究。结果表明：在真空条件下、1500℃下煅烧6h可制得TTCP，并含有少量CaO。CPC初凝时间为4min、终凝时间为15min，浸泡1d和7d后的抗压强度分别为20MPa和35MPa，浸泡液的pH值在6．4～8．9之间变化，这些性能均符合临床用CPC的性能要求。CPC水化产物为片状或针状羟基磷灰石（Ca5（PO4）3OH，HA），相互交错呈连续分布的网状结构，这种结构有利于材料强度的提高。实验研制的CPC材料可用于骨缺损的修复治疗。     

The anaerobic recovery of frog muscle

Summary The muscle may undergo a partial recovery of its high energy phosphate stores in the absence of oxygen by the way of glycolysis (anaerobic recovery). This process has been studied in 41 pairs of frog gastrocnemii at different degrees of exhaustion induced by variable trains of supramaximal stimuli. Anaerobic recovery appears to be inadequate to replenish the fraction of muscle high energy phosphate stores (GP=ATP+PC) split as a consequence of the stimulation. The maximal amount of recovery (on the average about 5 Moles of GP per gram of fresh tissue) occurs when the muscle resting stores have been reduced to about 50%. This limitation in the extent of recovery is not a consequence of a reduced availability of glycogen but it is possibly related to the production of some metabolic intermediate, limiting the rate of the glycolytic sequence, likely the accumulation of lactic acid in the fiber. The time course of the anaerobic recovery process is characterized by at1/2 of about 2 min. The efficiency of the process, i.e. the number of the high energy phosphate bonds resynthesized by one Mole of lactic acid, appears to vary between 1.5 and 1.8, being of the same order of magnitude as the GP/L.A. ratio obtained from muscle extracts.     

Facial Muscle Tonus During REM and NREM Sleep

Equipment and procedures were devised for quantifying relatively noise-free recordings of low amplitude chin and lip electromyograms (EMGs) during sleep. A total of 28 REM periods were recorded from 5 young adult female Ss. Tonic EMG levels tended to decline toward their lowest level of the night beginning 5 min in advance of REM periods. With very rare exceptions, the lowest EMG levels of the night were maintained throughout REM sleep. During the 20 min of NREM sleep which followed REM periods, mean EMG levels increased over the REM levels but were lower than those recorded during the 20 min of NREM sleep which preceded the REM periods. This pattern of tonic EMG variation obtained for each of the first 3 REM periods of the night.     

Utilization of carbohydrates and free fatty acids by the gastrocnemius of the dog during long lasting rhythmical exercise

Summary Utilization of carbohydrates and free fatty acids (FFA) has been investigated in gastrocnemii of dogs during long lasting isotonic rhythmical exercise induced by supramaximal stimulation of the sciatic nerve. Uptake or output of gases and substrates was determined according to the Fick principle. The first measurements were done at about 2 min after the beginning of work when blood flow has reached a steady state, and the latest at about 100 min after the beginning of exercise.During the first 7 min when the work performed exceeded 5 kg/100g×min and O₂ consumption exceeded 11 ml/100g×min, uptake of arterial glucose and FFA was low, accounting for less than 40% of the total O₂ consumption. Since the RQ values at the same time were about 1.0, glycogen must have been oxidized as the major aerobic energy source.About 13 min after the beginning of exercise, the work the muscles could perform declined to about half of the initial value and remained so for the following 90 min. During this time the oxygen extraction ratio of FFA was about 50% and of arterial glucose was 40–50%, while the RQ value was about 0.8.During initial strong exercise an output of lactic acid (LA) of about 10 mg/100 g×min was measured. With the decrease of work as a consequence of fatigue, LA output became negligible, and in many experiments small amounts of LA were taken up by the working gastrocnemii.It is concluded that glycogen is the major aerobic energy source for strong muscular exercise which cannot be substituted for by the oxidation of arterial glucose or FFA.Supported by the Deutsche Forschungsgemeinschaft.     

The effects of creatine supplementation on muscular performance and body composition responses to short-term resistance training overreaching

To determine the effects of creatine supplementation during short-term resistance training overreaching on performance, body composition, and resting hormone concentrations, 17 men were randomly assigned to supplement with 0.3 g/kg per day of creatine monohydrate (CrM: n=9) or placebo (P: n=8) while performing resistance exercise (5 days/week for 4 weeks) followed by a 2-week taper phase. Maximal squat and bench press and explosive power in the bench press were reduced during the initial weeks of training in P but not CrM. Explosive power in the bench press, body mass, and lean body mass (LBM) in the legs were augmented to a greater extent in CrM (P0.05) by the end of the 6-week period. A tendency for greater 1-RM squat improvement (P=0.09) was also observed in CrM. Total testosterone (TT) and the free androgen index (TT/SHBG) decreased in CrM and P, reaching a nadir at week 3, whereas sex hormone binding globulin (SHBG) responded in an opposite direction. Cortisol significantly increased after week 1 in CrM (+29%), and returned to baseline at week 2. Insulin was significantly depressed at week 1 (–24%) and drifted back toward baseline during weeks 2–4. Growth hormone and IGF-I levels were not affected. Therefore, some measures of muscular performance and body composition are enhanced to a greater extent following the rebound phase of short-term resistance training overreaching with creatine supplementation and these changes are not related to changes in circulating hormone concentrations obtained in the resting, postabsorptive state. In addition, creatine supplementation appears to be effective for maintaining muscular performance during the initial phase of high-volume resistance training overreaching that otherwise results in small performance decrements.     

The effects of human ankle muscle vibration on posture and balance during adaptive locomotion

This study investigated the contribution of ankle muscle proprioception to the control of dynamic stability and lower limb kinematics during adaptive locomotion, by using mechanical vibration to alter the muscle spindle output of individuals' stance limbs. It was hypothesised that muscle length information from the ankle of the stance limb provides information describing location as well as acceleration of the centre of mass (COM) with respect to the support foot during the swing phase of locomotion. Our prediction, based on this hypothesis was that ankle muscle vibration would cause changes to the position and acceleration of the COM and/or compensatory postural responses. Vibrators were attached to both the stance limb ankle plantarflexors (at the Achilles tendon) and the opposing dorsiflexor muscle group (over tibialis anterior). Participants were required to walk along a 9-m travel path and step over any obstacles placed in their way. There were three task conditions: (1) an obstacle (15 cm in height) was positioned at the midpoint of the walkway prior to the start of the trial, (2) the same obstacle was triggered to appear unexpectedly one step in front of the participant at the walkway midpoint and (3) the subjects' walking path remained clear. The participants' starting position was manipulated so that the first step over the obstacle (when present) was always performed with their right leg. For each obstacle condition participants experienced the following vibration conditions: no vibration, vibration of the left leg calf muscles or vibration of the anterior compartment muscles of the lower left leg. Vibration began one step before the obstacle at left leg heel contact and continued for 1 s. Vibrating the ankle muscles of the stance limb during the step over an obstacle resulted in significant changes to COM behaviour [measured as displacement, acceleration and position with respect to the centre of pressure (COP)] in both the medial/lateral (M/L) and anterior/posterior planes. There were also significant task-specific changes in stepping behaviour associated with COM control (measured as peak M/L acceleration, M/L foot displacement and COP position under the stance foot during the step over the obstacle). The results provide strong evidence that the primary endings of ankle muscle spindles play a significant role in the control of posture and balance during the swing phase of locomotion by providing information describing the movement of the body's COM with respect to the support foot. Our results also provide supporting evidence for the proposal that there are context-dependent changes in muscle spindle sensitivity during human locomotion.     

Clonorchis sinensis: molecular cloning and localization of myosin regulatory light chain

One cDNA clone was purified from an adult Clonorchis sinensis cDNA library, and its deduced polypeptide sequence was found to be homologous with myosin regulatory light chain (MRLC) of invertebrates and vertebrates. Two amino-acid residues, Thr and Ser, were conserved at the phosphorylation sites that regulate the function of MRLCs. Recombinant C. sinensis MRLC (rCsMRLC) protein was produced and purified from Escherichia coli, and mouse anti-CsMRLC immune sera recognized a protein of molecular weight 24 kDa from a soluble protein preparation of C. sinensis. The CsMRLC protein was immunohistochemically localized to the muscle fibers of the subtegumental muscle layer and to the muscles of oral and ventral suckers. However, the rCsMRLC protein proved to be less useful antigen for the serodiagnosis of human clonorchiasis.The nucleotide sequence reported herein was submitted to GenBank and assigned accession number AY519356.     

Increase of elastic fibres in muscle spindles of rats following single or repeated denervation with or without reinnervation

Summary Muscle spindles in the lower lumbrical muscles of rats were studied by transmission electron microscopy following denervation with or without reinnervation. The number and total area of elastic fibres per muscle spindle increased at 3–12 months following various experimental procedures: (1) denervation and reinnervation after a single crush lesion to the sciatic nerve; (2) reinnervation after four-fold repeated crush injuries; and (3) transection and suture of the nerve. The increased number of oxytalan and elaunin fibres, the precursors of mature elastic fibres, within these muscle spindles provided further evidence for their numerical and dimensional increase. An attachment site of elastic fibres at the spindle pole was identified at the inner cells of the outer spindle capsule. The processes of these cells embraced terminating elastic fibres tightly. Attachment of elastic fibres to intrafusal muscle fibres was less conspicuous since they were not similarly embraced but were rather indistinctly, though closely, associated with the basal lamina along longitudinal surface indentations of intrafusal muscle fibres. It is concluded from this series of experiments that muscle spindles, as dynamic mechanoreceptors, maintain their elastic properties even under pathological conditions. The increase of elastic fibres following denervation and reinnervation represents an obviously meaningful reaction that may compensate for loss of tonic properties of muscle spindles without causing stiffness.