Isometric exercise is generally used to overcome a "sticking point" in the range of motion during an exercise. Today's professional athletes seldom practice it, according to Brooks, Fahey and Baldwin in the journal Exercise Physiology. That may be because of the toll a heavy isometric load puts on the heart. Isometric exercises generally come close to a maximum effort and therefore put a strain on the heart by increasing blood pressure.
Background
Blood pressure is measured as systolic pressure over diastolic pressure. The systolic measurement is the pressure the heart faces while it is contracting. The diastolic measurement is the pressure the heart faces while it is resting and filling. High numbers would indicate a large amount of pressure, and low numbers indicate low pressure. There must be some pressure to aid in blood flow throughout the body, but too much pressure can be detrimental to the heart over time. According to the American Heart Association, hypertension occurs when the blood pressure reaches over 140 mm Hg (hemoglobin) over 90 mm Hg.
History
Isometric exercises began gaining popularity between 1950 to 1960, report Brooks, Fahey and Baldwin. This type of exercise gained acclaim when a study was released that stated six seconds of isometric exercise at 75 percent of effort could increase strength. Nowadays, isometric exercise is seldom practiced. Isometric exercises are particular to a specific joint angle and don't improve strength over a full range of motion. Athletes generally use isometric exercises to improve a deficit at a certain point in the range of motion. Brooks, Fahey and Baldwin state that if it is used, most benefits are gained early in training and maximum effort is necessary for full effect.
Effects
Exercise involving high muscle tension causes excess strain on the heart, according to Exercise Physiology. Weight lifting, especially isometric, raises the heart rate for a prolonged period of time. This is due to an increase in afterload. Afterload is a resistance to ventricular emptying. The heart is able to compensate by increasing contractility so that enough blood can be release by the heart. The stroke volume or amount of pumped blood is decreased, which then leads to a higher amount of blood in the heart during diastole, or the filling phase. Blood pressure becomes raised as an increased pressure is put on the heart to pump the excess blood.
Chronic Afterload
Chronic afterload causes hypertrophy of the cardiac muscle. Chronic isometric exercises increase wall thickness of the heart. Exercise Physiology states that increased size results in increased load of the heart and increased metabolic requirements. In other words, the heart is under more stress, can suffer from hypertension and requires more oxygen to perform a given amount of work versus a heart that has not been under chronic afterload.
Considerations
Although useful for certain aspects of weight training, heavy isometric exercise is hard on the heart and can increase blood pressure during exercise as well as chronically. Since hypertension is often associated with coronary artery disease, Exercise Physiology suggests that the combination of hypertrophy and impaired coronary blood flow places the heart under great stress. It seems more beneficial to perform dynamic strength training exercises to ease the workload for the heart.
References
- The American Heart Association: Understanding Blood Pressure Readings
- "Exercise Physiology"; Brooks, George A., Fahey, Thomas D., Baldwin, Kenneth M.; 2005
