The isometric athlete.
A number of normal daily and athletic activities require isometric or static exercise. Such sports as weight lifting and other high-resistance activities are used by athletes to gain strength and skeletal muscle bulk. However, static exercise also causes significant increases in blood pressure, heart rate, myocardial contractility, and cardiac output. These changes occur in response to central neural irradiation, called central command, as well as a reflex originating from statically contracting muscle. Studies have demonstrated that blood pressure appears to be the regulated variable, presumably because the increased pressure provides blood flow into muscles that have compressed their arterial inflow as a result of increases in intramuscular pressure created by contraction. Thus, static exercise is characterized by a pressure load to the heart and can be differentiated from dynamic (isotonic) exercise, which involves a volume load to the heart. Physical training with static exercise leads to concentric cardiac, particularly left ventricular, hypertrophy, whereas training with dynamic exercise leads to eccentric hypertrophy. Furthermore, the magnitude of cardiac hypertrophy is much less in athletes training with static than dynamic exercise. Neither systolic nor diastolic function is altered by the hypertrophic process associated with static exercise training. Many of the energy requirements for static exercise, particularly during more severe levels of exercise, are met by anaerobic glycolysis because the contracting muscle becomes deprived of blood flow. Training with repetitive static exercise therefore causes little increase in oxygen transport capacity, so that maximal oxygen consumption is either not or only minimally increased. Peripheral cardiovascular adaptations also can occur in response to static exercise training. Although controversial, these adaptations include modest decreases in resting blood pressure, smaller increases in blood pressure during a given workload, increases in muscle capillary-to-fiber ratio, improved lipid and lipoprotein profiles, and increases in glucose and insulin responsiveness. Some of these adaptations also have been found in cardiac patients and hypertensive patients and without any concomitant cardiovascular complications. However, in both healthy individuals and those with cardiovascular disease, the manner in which resistance training is performed may dictate the extent to which these adjustments take place. Specifically, training that involves frequent repetitions of moderate weight (and hence contains dynamic components) seems to produce the most beneficial results.
Longhurst
J C
JC
Department of Internal Medicine, University of California, Davis.
Stebbins
C L
CL
D002318:Cardiovascular Diseases / Q000503:physiopathology; D002320:Cardiovascular Physiological Phenomena; D002319:Cardiovascular System / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D010101:Oxygen Consumption; D016277:Ventricular Function, Left / Q000502:physiology