Effect of diazepam treatment on metabolic indices in trained and untrained rats.

Exercise training, like diazepam, is commonly employed as a means of reducing anxiety. Both diazepam and exercise training have been shown to modify carbohydrate and lipid metabolism as well as influence calcium metabolism in skeletal muscle. As receptor binding and thereby efficacy of diazepam has been demonstrated to be modulated by the lipid environment of the receptor, and changes in calcium levels can affect a number of intracellular signalling pathways, we sought to determine if the interaction of both chronic diazepam and exercise training would modify selected metabolic indices in an animal model. For this purpose, muscle and liver glycogen, blood glucose and plasma free fatty acids (FFA) were measured in sedentary, exercise trained and exercise trained, acutely exhausted animals. Alterations in lipid and carbohydrate metabolism were observed in all experimental groups. Diazepam treatment alone exerts metabolic consequences, such as elevated muscle glycogen and plasma FFA and depressed blood glucose levels, which are similar to those observed with exercise training. When animals are acutely exercised to exhaustion, however, differences appear, including a reduced rise in plasma FFA, which suggests that long-term diazepam treatment does influence exercise metabolism, possibly as a result of effects on the sympatho-adrenal system.

Sleep deprivation: effects on work capacity, self-paced walking, contractile properties and perceived exertion.

The primary purpose of this study was to examine the effect of a 48-hour period of sleep deprivation on the performance of selected physical work tasks [30-45% of maximum oxygen consumption (VO2max)]. In addition, this study assessed the effect of continual performance of physical work during sleep deprivation on standardized physiological and psychological test scores. Nineteen male subjects performed six different physical tasks, designed to involve all major muscle groups, during a 48-hour period of sleep deprivation. Fourteen subjects served as sleep-deprivation controls. Performance on all physical work tasks decreased significantly. Neither sleep deprivation (SD) or sleep deprivation in conjunction with continuous physical work (SDW) had any effect on muscle contractile properties, anaerobic power measures or resting blood glucose and lactate concentrations. Only SD subjects demonstrated a decline in cardiorespiratory function. Self-selected walking pace decreased and perceived exertion increased significantly in the SDW group. Positive and negative mood scores were adversely affected in both groups, the total change being greatest in SD subjects. The results indicate that performance of physical work tasks requiring 30-45% VO2max declines significantly over a 48-hour period of sleep deprivation. However, maximal physiological function is not unduly compromised by either the work tasks in conjunction with sleep deprivation or by sleep deprivation alone.

Shifts in rat plantaris motor unit characteristics with aging and compensatory overload.

Contractile characteristics of single motor units from plantaris muscles of young (6 mo), middle-aged (14 mo), and older (20 mo) rats were examined. Some of the muscles were subjected to a short-term (30 days) compensatory overload. After overload, the absolute increase in muscle weight was less for the 20-mo-old rats (38%) than the other groups (62%). However, when muscle weight per unit body weight was examined, the ratio was increased to a similar extent for all age groups. Aging was associated with an increase in slow (6 mo, 12.5%; 14 mo, 17.7%; 20 mo, 30.2%) and transitional (6 mo, 2.5%; 14 mo, 15.2%; 20 mo, 12.7%) motor unit proportions. This increase initially occurred at the expense of fast-fatigable motor units (6 mo, 36.3%; 14 mo, 13.9%; 20 mo, 20.7%) and then fast-intermediate units (6 mo, 40%; 14 mo, 39.2%; 20 mo, 26.7%). In addition, the maximal tension of individual motor units tended to increase with age. In younger rats compensatory overload produced changes in the motor unit profile similar to those that occurred with aging. In contrast, overload of the plantaris from 20-mo-old rats resulted in an increase in the force contribution from fast motor units. These results demonstrate that aging is accompanied by a gradual reorganization of the skeletal muscle motor unit pool, such that there is a loss of fast motor units and an increase in the proportion of slow motor units. While compensatory overload initially appears to mimic the aging effect, in older animals it may delay or reverse some of the age-related changes.

Appearance of "transitional" motor units in overloaded rat skeletal muscle.

The contractile characteristics of single motor units, isolated from rat plantaris muscles subjected to short-term (30 days) compensatory overload, were assessed to determine whether motor units in transition could be detected. In the control plantaris 88% of the motor units were classified as fast. After overload, a large decline (26.5%) in the proportion of typical fast motor units was noted. The estimated contribution of fast fatigable units to whole muscle tetanic tension (Po 200) also declined (from 55 to 25%), whereas that of fast intermediate motor units increased (from 33 to 55%). In the overloaded plantaris, motor units that exhibited unusual "sag" and contraction time characteristics were detected. These motor units, which could be further subdivided into two distinct types by a variety of indexes, exhibited characteristics intermediate to fast and slow units and therefore were termed "transitional." Transitional units accounted for 12% of the estimated whole muscle Po200 after overload. These experiments characterize novel classifications of motor units undergoing transformation and further detail the motor unit shift that accompanies compensatory overload.

Effect of dietary manipulation on a high intensity performance test.

The effects of dietary manipulation (low- or high-carbohydrate) on performance of a short-duration exercise were studied with endurance- and intermittent-trained athletes. Eight subjects performed a depletion drill of 10 one minute workbouts at 7 W/kg and 85 rpm on a cycle ergometer. The subjects followed a dietary regimen of three days on a low-carbohydrate diet followed by three days on a high-carbohydrate diet. Muscle biopsy samples were taken immediately prior to and immediately after the testing sessions. Dietary manipulation did not affect resting muscle glycogen levels. However, subjects accustomed to continuous training regimens used less glycogen, produced less muscle lactate and exercised longer than subjects accustomed to intermittent training programs. These biochemical changes appeared to be related to the fibre type distribution and the training background of the athletes.

Changes in rat plantaris motor unit profiles with advanced age.

The physiological characteristics of single motor units in rat plantaris muscles were determined in situ, for young adult (3 months) and very old (30-34 months) Fischer 344 rats. Old muscles generated 43% less tetanic force (P0) per gram. Motor units classified as "slow", using criteria of fatigue resistance and "sag" during unfused tetani, had a mean P0 which was 255% of that in young muscles, while fast motor units were similar in P0 in the two groups. Estimates were made of motor unit numbers using whole muscle and mean motor unit P0 values. The typical young plantaris contained 48 units, of which 5-6 were slow, while old plantaris contained 29 units, of which 11 were slow. In spite of this large increase in slow motor unit presence (increased mean motor unit P0, plus increased number) in old muscles, a comparatively modest (72%) increase occurred in the muscle cross-section occupied by histochemically demonstrated slow fibres. During senescence, there occurs a loss in muscle tetanic force capability which is accompanied by a loss of motor units and a reorganization of the remaining motor unit profile. An increase in slow motor unit number and size with advancing age can evidently occur without concomitant histochemical changes. Motor units do not "dedifferentiate", but maintain their physiological distinctiveness into very old age.