摘要:

In muscle, energy supply is finely tuned to energy demand. Ca2+-activated ATP hydrolysis in the cytosol provides ADP to the mitochondrion to stimulate oxidative phosphorylation by acceptor control of mitochondrial respiration. Although mitochondria are responsive to increased concentrations of ADPin vitro, oxygen extraction in cardiac muscle may increase independently of any significant alterations in cellular ADP levels or of dramatic changes in cellular phosphate metabolites as determined by P-31 NMR. Alterations in ATP/ADP ratios in skeletal muscle with aerobic exercise may be dependent on fiber type, with maintained ATP levels seen in oxidative fibers during muscle work. These data are consistent with increased rates of NADH generation by mitochondrial dehydrogenases, so that ATP production keeps pace with ATP hydrolysis in the cytosol. The mechanism of increased ATP synthesis in muscle mitochondria is termed “stimulus-response-metabolism coupling.” Ca2+ion increases in the muscle cytosol enhance contractility and glycogen breakdown. The Ca2+signal is then transmitted to the mitochondria to provide matrix Ca2+concentrations, which activate Ca2+-sensitive dehydrogenase activities, leading to accelerated rates of NAD reduction and oxidative phosphorylation. Thus, Ca2+signaling to the mitochondria may explain the lack of dramatic fluctuations in the cytosolic phosphorylation potential over a large range of contractile activities in cardiac muscle.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Although the mechanisms underlying most aspects of excitation-contraction (EC) coupling in skeletal muscle are well understood, a very basic step, that of communication between the transverse tubule (TT) region of the plasmalemma and the terminal cisternae of the sarcoplasmic reticulum (SR), has not been elucidated. Several types of TT to SR communication have been proposed, including electrical, chemical, and mechanical coupling. Current evidence supports a combination of the latter two. Studies of single rabbit skeletal muscle fibers, skinned by peeling the sarcolemma, demonstrate that a chemical stimulus for SR Ca2+release, inositol trisphosphate (InsP3), could play a role in skeletal EC coupling. InsP3appears to open the same SR Ca2+channel that is activated by caffeine, Ca2+, and depolarization of TTs; all of these stimuli are inhibited by the SR Ca2+channel blocker ruthenium red.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Several studies have found that caffeine improved endurance exercise performance, but the factors which are responsible for this are not fully understood. Possibilities include an increased free fatty acid (FFA) oxidation and a resultant sparing of muscle glycogen as well as an enhancement of neuromuscular function during exercise. In order to further examine these factors, six varsity level runners (&OV0312;O2max= 63.3 ml·kg−1·min−1) were studied over 90 min of treadmill running (70% &OV0312;O2max) in a thermoneutral environment in order to determine the metabolic and neuromuscular effects of caffeine (6 mg·kg−1) administered in a randomized, crossover, double-blind manner. Subjects were habitual caffeine consumers (200 mg·d−1) and were given identical diets during each 3-d testing period. Caffeine administration, 60 min prior to exercise, significantly (P< 0.05) increased plasma FFA levels both prior to and during exercise. Caffeine administration did not alter any of the other variables examined: &OV0312;O2, HR, RER, rating of perceived exertion; plasma levels of glucose, lactate, epinephrine, and norepinephrine; or neuromuscular function (maximal voluntary strength, peak twitch torque, and motor unit activation). We conclude that caffeine administration (6 mg·kg−1) in athletic, habitual caffeine consumers increased plasma FFA levels but had neither metabolic nor neuromuscular effects that would be of potential ergogenic benefit in endurance running.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

There are conflicting data with regard to the effect of endurance training in children. On the basis of this information, the effects of 8 wk of run training on ventilatory threshold (VT) and &OV0312;O2maxof eight male children were investigated. Children ranged in age from 10 to 14 yr, with a mean age of 12.4 yr. All subjects were previously untrained. Training consisted of running 4 d·wk−1for a period of 8 wk. Continuous running was performed 2 d·wk−1for 10–30 min at 70–80% of &OV0312;O2max. Interval running was performed the remaining 2 d·wk−1. Repeated intervals of 100–800 m at 90–100% of &OV0312;O2maxwere used in this phase of the training. The total distance run for this type of training was 1.5–2.5 km. Incremental treadmill testing prior to and after the training period indicated a 19.4% increase in VT from 30.5 to 36.4 ml·kg−1·min−1(P < 0.05). When VT was expressed as a percentage of &OV0312;O2max, there was a significant (P< 0.05) increase from 66.6% to 73.8%. &OV0312;O2maxincreased 7.5% from 45.9 to 49.4 ml·kg−2·min−2(P< 0.05). None of these changes was noted in eight age- and size-matched children who served as control subjects. The results of this study indicate that 8 wk of endurance running training which is of sufficient frequency, intensity, and duration can significantly improve VT and aerobic capacity in made children.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

This study tested the hypothesis that endurance training initiated 28 d following grafting of the soleus muscle would increase fiber cross-sectional area concomitant with an increase in mass. Nerve-implant orthotopic grafting operations were performed on 6-wk-old rats anesthetized with pentobarbital sodium. A cohort of animals began running 28 d later. Control muscles were from age-matched, untrained rats. Mass and fiber cross-sectional area of grafts were 37 and 66% less than the respective control values at both 56 and 112 d post-grafting. Training increased graft mass by 49% over the non-run graft value of 82 ± 8 mg at 56 d post-grafting. Continued training did not increase mass further. The grafts of trained rats were 33% greater than untrained at day 112 due to growth of grafts in untrained rats. Running had no effect on fiber cross-sectional area of grafts through 56 d, but by 112 d the cross-sectional area of Type I fibers was 30% greater than the non-run graft value of 1,271 ± 81 μm2. By 112 d fiber type profiles were not different between control muscle and grafts from trained and untrained rats. We conclude that there is a dissociation between mass and fiber cross-sectional area in grafts compared to control muscle, and training affects these variables by similar magnitudes but at different times.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Skeletal muscle biopsies from highly trained endurance athletes have been shown to contain an increased percentage of the creatine kinase MB (CK-MB) isoenzyme, which has been attributed to continuous regeneration of the skeletal muscle fibers in response to exercise-induced injury. The purpose of this study was to determine whether myocardium undergoes a similar degenerative-regenerative process as a result of exercise training. Fifteen mongrel dogs underwent a 12-wk period of training (N= 8) or cage confinement (N= 7). The animals were then sacrificed, and samples of left and right ventricular myocardium were analyzed for total CK activity and CK-MB isoenzyme content. Percentages of CK-MB were slightly but insignificantly higher from both ventricles of exercise-trained as compared with cage-confined dogs: left ventricle, 4.6 ± 0.6% vs 3.3 ± 0.6%, respectively (P= 0.15); right ventricle, 4.0 ± 0.4% vs 3.0 ± 0.8%, respectively (P= 0.29). We conclude that chronic exercise training does not induce physiologically important degenerative changes in myocardium.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

Vitamin B1, B2, B6, C, A, and E status was assessed by combining determination of dietary intake with biochemical indices in 55 young male athletes. When compared with 20 matched sedentary controls, a similar number of individuals with biochemical deficiency was found in both groups for vitamins B1, B6, and E despite a higher mean dietary intake of these three vitamins in young athletes. Markedly reduced levels of pyridoxal 5'-phosphate, the biologically active form of the vitamin B6compounds, were found in both populations. Supplementation administered for one month improved the vitamin status of the control subjects but not entirely those of the young athletes.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The performance of ten elite powerlifters were analyzed in a simulated competition environment using three-dimensional cinematography and surface electro-myography while bench pressing approximately 80% of maximum, a maximal load, and an unsuccessful supramaximal attempt. The resultant moment arm (from the sagittal and transverse planes) of the weight about the shoulder axis decreased throughout the upward movement of the bar. The resultant moment arm of the weight about the elbow axis decreased throughout the initial portion of the ascent of the bar, recording a minimum value during the sticking region, and subsequently increased throughout the remainder of the ascent of the bar. The electromyograms produced by the prime mover muscles (sternal portion of pectoralis major, anterior deltoid, long head of triceps brachii) achieved maximal activation at the commencement of the ascent phase of the lift and maintained this level essentially unchanged throughout the upward movement of the bar. The sticking region, therefore, did not appear to be caused by an increase in the moment arm of the weight about the shoulder or elbow joints or by a minimization of muscular activity during this region. A possible mechanism which envisages the sticking region as a force-reduced transition phase between a strain energy-assisted acceleration phase and a mechanically advantageous maximum strength region is postulated.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The purpose of this study was to determine the three-dimensional kinematics of the knee joint during running on level surfaces and surfaces of different degrees of camber. Fifteen college-age students (eight males, seven females) having no previous history of knee injury were subjects. A triaxial elgon was used to measure the movement of each subject's right and left knees when running on a horizontal or laterally inclined treadmill at 2.4 m·s−1during each experimental condition (on the horizontal surface and on cambers of +0.087, +0.174, −0.087, and −0.174 radians). There was a significant difference (P< 0.05) between +0.174 and −0.174 rad camber mean values for all six dependent variables (i.e., support and swing, flexion-extension, internal and external rotation, and valgus-varus range of motion). There was also a significant difference (P< 0.05) when +0.174 and −0.174 rad camber were compared to 0 rad camber during both the support and swing phases of flexion-extension. Surface camber mean values for +0.087 and −0.087 rad were significantly different (P< 0.05) during the swing phase for internal and external rotation. This study showed that the kinematics of the knee joint are significantly altered when running on a laterally inclined surface.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID

摘要:

The preferred stride frequency (SF) and stride length (SL) of male recreational distance runners were measured on a level treadmill under a variety of conditions over the typical distance running speed range of 3.15–4.12 m·s−1. At a given speed, the correlation coefficients between the subjects' anthropometric variables (APV) (such as stature, leg length, and limb segment mass) and their preferred stride variables were consistently low (·0.36) and not significantly different from zero. As speed increased through the experimental range, SF remained nearly constant (only a 4% increase) while SL increased by 28%. The use of dimensionless velocity was shown to be no more effective than conventional methods in the prediction of a SL vs velocity relationship, but the dimensionless form of the relationship was remarkably similar to those observed for other animal species and other forms of gait. The addition of masses up to 1.1 kg at each ankle produced no significant change in SF or SL. The results indicate that factors other than APV are the primary determinants of preferred SF and SL. Since it has been shown previously that the preferred SL is usually the most economical, APV cannot be used to accurately predict or prescribe SF or SL on an individual basis.

ISSN:0195-9131    

出版商:OVID    

年代:1989

数据来源: OVID