摘要:

In this review, the term muscle fibre regionalization signifies the presence of regional intramuscular differences in fibre type composition. As is well known, highly regionalized muscles commonly have greater concentrations of slow fibres deep than superficially. However, the degree of regionalization varies markedly between muscles and is not confined to deep vs. superficial locations. Fibres of the same myosin type may show regionalized differences in their metabolic enzyme activity, even within single motor units (Larsson, 1992). Regionalization of fibre type composition occurs also within single neuromuscular partitions. The intraspinal position of motoneurones is often coarsely related to the intramuscular sites of their muscle units. Muscles with a marked fibre type regionalization tend to show a corresponding regionalization of activity; in several muscles, however, the activity regionalization may vary depending on the motor task. During early development, fibre type regionalization emerges even under aneural conditions. The mechanisms are still unknown; relevant aspects of early development are briefly reviewed.Key words:skeletal muscle, fiber type, topography, activity, development

ISSN:1066-7814    

DOI:10.1139/h98-001

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Reactive oxygen species, including free radicals, are produced through a number of biochemical reactions, often as a consequence of aerobic metabolism. A system of antioxidant enzymes and scavenger substrates provides protection of membrane lipids, proteins, and DNA. An imbalance between production of reactive oxygen species and antioxidant protection results in "oxidative stress." Oxidative stress is believed to contribute to numerous pathological conditions including atherosclerosis, obstructive lung disease, aging, and fatigue of skeletal muscles including the diaphragm. Strenuous exercise, inflammation, infection, obstructive lung diseases, etc. increase exposure of the diaphragm to reactive oxygen species. Emerging data indicate that reactive oxygen species alter diaphragm contractions primarily in response to low-frequency stimulation. The response of the diaphragm is profoundly influenced by the degree of oxidative stress, fatigue state, glutathione status, and age. Exercise training results in an upregulation of antioxidant enzyme activities in the diaphragm and thus could provide additional protection against oxidative stress.Key words:aging, excitation-contraction coupling, exercise, fatigue, free radicals, glutathione peroxidase, oxidation/reduction, reactive oxygen species, respiratory muscles, skeletal muscle, superoxide dismutase

ISSN:1066-7814    

DOI:10.1139/h98-002

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A paucity of data exists related to the usefulness of Ratings of Perceived Exertion(RPE) to set exercise intensity in non-laboratory settings. The purpose of this study was to determine if RPE could be used on an outdoor track to generate blood lactate and heart rate (HR) responses similar to those obtained on a treadmill (tm) run. Nine experienced runners (6 males, 3 females;) completed a horizontal, incremental tm test. HR, RPE, and lactate were measured for each stage. Subsequently, subjects ran for 30 min on an outdoor track at the RPE corresponding with 2.5 mM lactate during the tm run. Repeated measures ANOVA compared lactate and HR values at 2.5 mM lactate on the tm run and values obtained during the track run. Lactate during the track run was significantly higher (p < .05) than 2.5 mM throughout the 30 min (6.9 ± 2.9, 63 ± 2.9, and 5.8 ± 3.0 mM at 10, 20, and 30 min, respectively). HR at 2.5 mM lactate during the tm run (173 ± 6.1 bpm) was significantly lower (p < .05) than at min 10 and 20 of the track run (182.6 ± 9.3 and 182.9 ± 8.0 bpm, respectively) but not different from min 30 (181.3 ± 10.6 bpm). In summary, it is difficult to generate specific physiological responses using RPE.Key words:RPE, Borg Scale, exercise, lactate, training

ISSN:1066-7814    

DOI:10.1139/h98-003

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The purpose of this study was to investigate the effects of beverage ingestion on fluid balance during 1.5 hr of low intensity cross country skiing. In Part I, 6 skiers drank water ad libitum during ski training. In Part II, 10 skiers were matched by body weight (BW) and assigned to ingest 2.5 ml kg−1BW of water or a carbohydrate/electrolyte (CE) beverage every 2.5 km. Skiing speed averaged 11.5 km hr−1for 90 min around a 5 km groomed track. Following 20 min of seated rest, blood samples were collected immediately before and approximately 30 min after skiing. Part I data indicated that subjects ingested 576 ± 189 ml of fluid and produced 266 ± 205 ml of urine: BW, plasma and urine osmolality, and plasma protein decreased significantly. In Part II, the CE group produced less urine (135 u75 vs 450 ± 262 ml) and had smaller decreases in plasma osmolality (−1.0 ± 1.0 vs. −7.0 ± 2.4 mOsm kg H2O) and protein (−0.11 ± 08 vs. −0.42 ± 0.24 g L−1) than the water group. No differences were observed for BW loss, % change in PV, FWC, or change in urine osmolality. It was concluded that ad lib water ingestion was inadequate to minimize fluid balance disruption, Plain water ingestion also led to significant dilution of the plasma and increased urine output. However, the ingestion of CE led to attenuation of fluid balance disruption, presumably due to the maintenance of osmotic balance in the plasma.Key words:fluid balance, cross country skiing

ISSN:1066-7814    

DOI:10.1139/h98-004

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

We evaluated the effect of endurance training (cycling 3 times per week for 12 weeks) on succinate dehydrogenase (SDH) activity in the subsarcolemmal(SS)and intermyofibrillar (IMF) regions of vastus lateralis muscle fibres in 7 individuals (4 females and 3 males). SDH activity of the SS region increased 9.4% and 12.8% in type I and II fibres, respectively (p < .05). SDH activity of the IMF region increased 4.7% and 6.7% in type I and II fibres, respectively (p < .05). This was less than the increase in the SS region (p < .O5). No significant changes were observed in a control group (4 females and 3 males). These data suggest that mitochondria in the SS and IMF regions of human vastus lateralis muscle fibres are sensitive to endurance training. The greater response in the SS region suggests that the metabolic requirements of SS mitochondria were stressed to a greater extent than IMF mitochondria with endurance training.Key words:subsarcolemmal mitochondria, intermyofibrillar mitochondria

ISSN:1066-7814    

DOI:10.1139/h98-005

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Motor unit firing rates in human muscle can be determined from recordings made with small-diameter microelectrodes inserted directly into the muscle during voluntary contraction. Frequently, these counts are pooled to give an average motor unit firing rate under a given set of conditions. Since the fibers of one motor unit are dispersed among the cells of several others, it is conceivable that discharge rates can be measured in more than one cell from the same unit. If this occurred frequently, the distribution of firing rates could be influenced by those from units counted more than once. Based on literature values, we made the following assumptions: vastus lateralis contains approximately 300 motor units, with an average innervation ratio of 1500. Muscle cell diameter is about 50 to 100 μm and cells are randomly distributed over a motor unit territory of 10 μm diameter. The recording range of a microelectrode is about 600 μm. Given the distribution of cells normally found in whole human muscle, the probability of recording from two or more cells of the same motor unit at 50% MVC follows a Poisson distribution with a mean of 0.44. This model suggests that although there is a low probability of some duplication in this technique, the extent to which it influences the distribution of average motor unit firing rates is minimal over the entire range of forces produced by vastus lateralis.Key words:probability, motor unit, single unit recording, human muscle, rate coding

ISSN:1066-7814    

DOI:10.1139/h98-006

出版商:NRC Research Press    

年代:1998

数据来源: NRC