Canadian journal of applied physiology = Revue canadienne de physiologie appliquee最新文献

Oxidative stress and subsequent damage to cellular proteins, lipids, and nucleic acids, as well as changes to the glutathione system, are well documented in response to aerobic exercise. However, far less information is available on anaerobic exercise-induced oxidative modifications. Recent evidence indicates that high intensity anaerobic work does result in oxidative modification to the above-mentioned macromolecules in both skeletal muscle and blood. Also, it appears that chronic anaerobic exercise training can induce adaptations that act to attenuate the exercise-induced oxidative stress. These may be specific to increased antioxidant defenses and/or may act to reduce the generation of pro-oxidants during and after exercise. However, a wide variety of exercise protocols and assay procedures have been used to study oxidative stress pertaining to anaerobic work. Therefore, precise conclusions about the exact extent and location of oxidative macromolecule damage, in addition to the adaptations resulting from chronic anaerobic exercise training, are difficult to indicate. This manuscript provides a review of anaerobic exercise and oxidative stress, presenting both the acute effects of a single exercise bout and the potential for adaptations resulting from chronic anaerobic training.

Skeletal muscles induced to contract repeatedly respond with a progressive loss in their ability to generate a target force or power. This condition is known simply as fatigue. Commonly, fatigue may persist for prolonged periods of time, particularly at low activation frequencies, which is called low-frequency fatigue. Failure to activate the contractile apparatus with the appropriate intracellular free calcium ([Ca2+]f) signal contributes to fatigue but the precise mechanisms involved are unknown. The sarcoplasmic reticulum (SR) is the major organelle in muscle that is responsible for the regulation of [Ca2+]f, and numerous studies have shown that SR function, both Ca2+ release and Ca2+ uptake, is impaired following fatiguing contractile activity. The major aim of this review is to provide insight into the various cellular mechanisms underlying the alterations in SR Ca2+ cycling and cytosolic [Ca2+]f that are associated both with the development of fatigue during repeated muscle contraction and with low-frequency or long-lasting fatigue. The primary focus will be on the role of the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) in normal muscle function, fatigue, and disease.

A failure in membrane excitability, defined as an inability of the sarcolemma and T-tubule to translate the neural discharge command into repetitive action potentials, represents an inviting cause of mechanical disfunction in both health and disease. A failure at this level would precipitate a disturbance in signal transmission between the T-tubule and the calcium release channels of the sarcoplasmic reticulum, resulting in reduced release of Ca2+, lower cytosolic free Ca2+ levels, and depressed myofibrillar activation and force generation. The ability of the sarcolemma and T-tubules to conduct repetitive action potentials is intimately dependent on active transport of Na+ and K+ following an action potential. The active transport of these cations is mediated by the Na+-K+-ATPase, an integral membrane protein that uses the energy from the hydrolysis of 1 ATP to transport 3 Na+ out of the cell and 2 K+ into the cell. A failure to recruit sufficient Na+-K+-ATPase activity during contractile activity could result in a rundown of the transmembrane gradients for Na+ and K+, leading to a loss of membrane excitability. The Na+-K+-ATPase activity depends on the amount and isoform composition of the protein, substrate availability, and acute regulatory factors. Each of these factors is examined as a potential cause of altered activation of the Na+-K+-ATPase activity and loss of membrane excitability in fatigue. Regular exercise represents a potent stimulus for upregulating Na+-K+-ATPase levels and for increasing the ability for cation transport across the sarcolemma and T-tubule membrane. As such, training may be a valuable tool in the management of fatigue in health and disease.

The aim of this study was to evaluate the effect of a 15% increase in preferred pedal rate (PPR) on both time to exhaustion and pulmonary O(2) uptake (VO(2)) response during heavy exercise. Seven competitive cyclists underwent two constant-power tests (CPT) at a power output that theoretically requires 50% of the difference in VO(2) between the second ventilatory threshold and VO(2)max (Pdelta50). Each cyclist cycled a CPT at PPR (CPTPPR) and a CPT at +15% of PPR (CPT+15%) in a randomized order. The average PPR value was 94 +/- 4 rpm, and time to exhaustion was significantly longer in CPTPPR compared with CPT+15% (465 +/- 139 vs. 303+/- 42 s, respectively; p = 0.01). A significant decrease in VO(2) values in the first minutes of exercise and a significant increase in VO(2) slow component was reported in CPT+15% compared with CPT(PPR). These data indicate that the increase of 15% PPR was associated with a decrease in exercise tolerance and a specific VO(2) response, presumably due to an increase of negative muscular work, internal work, and an altering of motor unit recruitment patterns.

It has been suggested that gender differences in running should disappear as distances increase, particularly past the marathon. This suggestion is primarily based on differences in fuel utilization, muscle damage following exercise, relative improvements in performance over the past decades, and on the analysis of marathon vs. ultramarathon performances of men and women. We reasoned that the best comparison of the potential of a human is by the use of world best times, which should be reasonable indicators of the effect of distance on relative performance of women and men. We compared current world best running performances at distances from 100 m to 200 km. Records as of December 2002 were obtained. T-tests analyzed speed differences between genders, and regression analysis tested the percent differences between men and women across distance. Speeds were different, with the average difference being 12.4% faster for men. There was a significant slope to the speed difference across distances in that longer distances were associated with greater differences. These results may be confounded by the reduced number of women in longer distance events. Furthermore, the proposed metabolic advantage for women because of increased fat metabolism may be masked by regular feeding during endurance races.

The three objectives of the present review of the literature were to: characterize the evolution of habitual physical activity (HPA) during growth; evaluate the tracking of HPA from childhood to adulthood; and analyse the level of HPA in children and adolescents according to public health recommendations. Data indicates that HPA decreases from childhood to adulthood about 7% per year, with a great reduction during puberty and adolescence concurrent to changes in the type of physical activity. It appears that HPA is not quite steady (0.09 < r < 0.66) during growth, which means that behavioural changes occur. Being very active during childhood or adolescence does not necessarily translate into a high level of HPA in adulthood. The mean values of HPA of children and adolescents vary from 15 to 90 min.day(-1) between studies, and for most of them HPA has been higher or close to public health recommendations. However, these results mask a great number of children and adolescents who are inactive or becoming inactive (40 to 45% of the population).

Perfused mammalian skeletal muscle preparations either in vitro or in situ are one of the options to be considered when planning a physiological research program or project. Such preparations have been and continue to be used to investigate research questions as diverse as skeletal muscle function and metabolism, peripheral vascular function, and an approximation of exercise. When selecting a perfused muscle preparation, both anatomical and physiological organization must be evaluated in the context of the planned experiment. In any experiment, a number of physiologically significant variables can be manipulated, such as the level of flow and the arterial or inflow concentration of a gas or substance to control substrate supply and metabolite removal as well as the stimulation parameters to alter metabolic rate. The choice of blood or an artificial perfusate is of paramount importance because, when compared to blood-perfused preparations, those receiving artificial perfusates show depressed vascular autoregulation among other changes, indicating a decrease in physiological quality. Overall, perfused skeletal muscle preparations can be used to examine many and varied research questions with close to in-vivo quality and a high degree of accuracy and control if blood-perfused.

In the present study, 30 male rats (age 3 mos, Wt 128.6 +/- 3.7 g) were randomly divided into Control group (CG), Experimental group (EG), and Supplemented group (SG), 10 per group. An exercise protocol (3 hrs swimming per day, 5 days a week for 4 weeks) was followed in EG and SG, with no exercise in CG. In SG, alpha-tocopherol succinate was injected sub-cutaneously at a dose of 50 mg x kg(- 1) per body weight per day. After 4 weeks of exercise, significant diminutions (p < 0.05) were noted in somatic indices of testes and accessory sex organs; seminiferous tubuler diameter (STD); testicular (delta (5), 3 beta-hydroxysteroid dehydrogenase delta(5), 3 beta-HSD), 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activities; plasma levels of testosterone (T), luteinizing hormone (LH); preleptotine spermatocytes (pLSc), mid-pachytene spermatocytes (mPSc), and Stage 7 spermatids (7 Sd); testicular alpha-tocopherol and glutathione (GSH) content; superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione-s-transferase (GST) activities in EG when compared to CG. Moreover, a significant elevation (p < 0.05) in malondialdehyde (MDA) was found in testes of EG compared to CG. No significant alteration was noted in body weight among the groups. Co-administration of alpha-tocopherol succinate restored the above parameters. Intensive swimming exercise-induced oxidative stress causes dysfunction in the male reproductive system, which can be protected by alpha-tocopherol succinate.

The purpose of this study was to estimate the genetic and environmental contribution to variation in skeletal muscle mass and strength. In addition, important determinants were analyzed by stepwise multiple regression. In a large (N = 748) sibling pair sample of young brothers, ages 24.3 +/- 4.5 years, upper-limit heritabilities (t2) were estimated as a proportion of genetic and shared environmental variability over total phenotypic variability by the variance components method in QTDT. Maximal isometric strength measures of knee, trunk, and elbow had higher t2 (82 to 96%) than concentric strength (63 to 87%) on Cybex isokinetic dynamometers. Indicators of muscle mass revealed very high transmissions (>90%) whereas t2 was lower for adiposity (<70%). Stepwise regression showed that fat-free mass was the primary determinant in knee and trunk strength (partial explained variance, R2 = 33-45%), but a local muscularity estimate (forearm circumference) was the main covariable for elbow strength (partial R2 = 18-39%). In this sample neither age nor physical activity, measured by the sport index of Baecke, appeared to be an important determinant of muscle mass or strength. These results show that maximal muscle strength and mass are highly transmissible and that muscle mass is the primary determinant of muscle strength.

The aim of this study was to examine the effects of a prolonged high-intensity exercise, jumping, on procollagen alpha(1)(I) mRNA level and collagen concentration in different muscles of trained (T) and control (C) rabbits. Procollagen alpha(1)(I) mRNA expression was much higher (2.8 to 23.5 times) in semimembranosus proprius (SMP), a slow-twitch oxidative muscle, than in extensor digitorum longus (EDL), rectus femoris (RF), and psoas major (Psoas) muscles, both fast-twitch mixed and glycolytic, whatever group was considered (p < 0.001). Procollagen alpha(1)(I) mRNA level also decreased significantly between 50 and 140 days in all muscles (0.001< p < 0.01). However, mRNA levels were 16 to 97% greater at 140 days in all muscles of T animals compared to C ones (0.01< p <0.05). Collagen concentrations of EDL and RF muscles were also higher (14 to 19%) in T than in C rabbits at 90 and 140 days (0.001 < p < 0.05). In the whole sample, collagen concentration was negatively associated with the procollagen alpha(1)(I) mRNA level in EDL and RF muscles (- 0.49 < r < (- 0.44, p < 0.05), while being positively related to mRNA expression in SMP and Psoas muscles (0.65 < r < 0.85, p < 0.01). It is concluded that jump training clearly restricts the decrease of procollagen (I) mRNA level and probably affects collagen synthesis level. In trained rabbit muscles, the maintenance of a better synthesis level could partly explain the higher collagen concentrations found in EDL and RF at 140 days. Nevertheless, the collagen degradation process seems to play the main role in the increase of total collagen concentration with age in EDL and RF muscles.