Muscles and exercise

Exercise and muscle trauma can increase serum CK. Sustained exercise, such as in weU-trained long-distance runners, increases the CK-MB content of skeletal muscle, which may produce abnormal serum CK-MB concentrations. 

Bessman, S. and F. Savabi, The role of phosphocreatine energy shuttle in exercise and muscle hypertrophy, in Creatine and Creatine Phosphate Scientific and Clinical Perspectives, M.A. Conway and J.F. Clark, Eds. Academic Press, San Diego, CA,... 

Failure to maintain hydration status has serious consequences for the active individual. A body water deficit of as little as 1-2% of total body mass can result in a significant reduction in exercise capacity. Endurance exercise is affected to a greater extent than high-intensity exercise, and muscle strength is not adversely affected until water losses reach 5% or more of body mass. Hypohydration greatly increases the risk of heat illness, and also abolishes the protection conferred by prior heat acclimation. 

Hargreaves, M., 1997. Interactions between muscle glycogen and blood glucose during exercise. Exercise and Sport Sciences Reviews 25 21-39. 

Shulman, R. G., and Rothman, D. L., 1996. Nuclear magnetic resonance studies of muscle and applications to exercise and diabetes. Diabetes 45 S93-S98. 

Figure 6. Glycogen content in the vastus lateralis muscle as a function of cycling time at 75-80% of maximal oxygen uptake (VO2 max). Data points are mean values from 10 subjects. For each subject, exercise was performed repeatedly in periods of 15 min separated by 15 min rest periods. At the point of exhaustion and muscle fatigue, muscle glycogen stores were depleted. From Bergstrom and Hultman (1967) with permission from the publisher.

Figure 9. One-legged exercise studies showing the muscle glycogen content of the exercised (—) and rested legs (—) in two subjects. A. Muscle biopsy samples were obtained immediately after exercise (a) and during three days when fed a carbohydrate-rich diet (a). B and C. The diet was total starvation (z) for two days following exercise (B) or carbohydrate-poor (o) for three days following exercise (C). This was followed by a second one-leg exercise bout (T) and a carbohydrate-rich diet ). Redrawn from Bergstrom and Hultman (1966) in panel A, and from Hultman and Bergstrom (1967) in panels B and C.

Hultman, E. Nilsson, L.H. (1971). Liver glycogen in man. Effect of different diet and muscular exercise. In Muscle Metabolism During Exercise (Pemow, B. Saltm, B., eds.), pp. 143-151, Plenum Press, New York. 

Free Radicals and Exercise-induced Muscle Damage 178 7. References 180... 

In recent years free-radical species have been implicated in the pathogenesis of a wide variety of disorders (see Hal-liwell and Gutteridge, 1989), and attention has been drawn to the possibility that these agents might mediate some of the effects of excessive or unaccustomed exercise on muscle function and structure. In addition, free radicals may play a role in a number of muscle diseases. The aim of this short review is to examine these areas, drawing particular attention to those situations where the role of free radicals is controversial or where further studies are required. 

Fatigue of muscles is found post-exercise and in some patients with disorders of limb or respiratory muscles. Peripheral muscle fatigue is generally characterized by the changes in force frequency relationships that occur. The process is traditionally divided into a failure of force production at either low or high frequencies of electrical stimulation. 

Repeated periods of exercise reduce the likelihood of damage to skeletal muscle during subsequent bouts of the same form of exercise and this appears to be associated with an increase in the activity of muscle SOD (Higuchi et al. 1985), a reduced level of lipid peroxidation products during exercise in trained rats (Alessio and Goldfarb, 1988), and a modification of the concentration of antioxidants and activity of antioxidant enzymes in trained humans (Robertson etal., 1991). Packer and colleagues (Quintanilha etui., 1983 Packer, 1984) have also examined the exercise endurance of animals of modified antioxidant capacity and found that vitamin E-deficient rats have a reduced endurance capacity, while Amelink (1990) has reported that vitamin E-deficient rats have an increased amount of injury following treadmill exercise. 

Warren, J.A., Jenkins, R.R, Packer, L., Witt, E.H. and Armstrong, P.B. (1992). Elevated muscle vitamin E does not attenuate eccentric exercise-induced muscle injury. J. Appl. Physiol. 72, 2168-2175. 

Assess nonpharmacologic interventions for preventing osteoporotic fractures, including nutrition, weightbearing and muscle-strengthening exercise regimens, and fall risk. 

Occupational and physical therapy may help patients to preserve joint function, extend joint range of motion, and strengthen joints and muscles through strengthening exercises. Patients with joint deformities may benefit from the use of mobility or assistive devices that help to minimize disability and allow continued activities of daily living. In situations where the disease has progressed to a severe form with extensive... 

Perhaps the most intriguing perspective is that caffeine s major effects have little to do with muscles and fat metabolism but result from its psychostimulant effects, enhancing mood, improving attitude towards exercise, and thus motivating athletes to work harder and longer. This would account for its purported inability to alter strength, which may be a less psychologically malleable variable, while endurance performance is sometimes believed to be more amenable to force of will. 

How does physical exercise alleviate depression One possibility is that it increases the release of endorphins that produce a sense of well-being, sometimes referred to as the runner s high . Another possibility is that it is a placebo effect. But even if it is a placebo effect, consider the differences between exercise and antidepressants in side effects. Side effects of antidepressants include sexual dysfunction, nausea, vomiting, insomnia, drowsiness, seizures, diarrhoea and headaches. Side effects of physical exercise include enhanced libido, better sleep, decreased body fat, improved muscle tone, greater life expectancy, increased strength and endurance and improved cholesterol levels. So if both antidepressants and exercise work by means of the placebo effect, which placebo would you prefer ... 

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