Blood Pressure Considerations
Blood pressure is defined as the pressure exerted on arterial walls as the heart forces blood through the body. Blood pressure is measured using two numbers--the first number (systolic pressure) indicates the level of pressure after the heart contracts; the second (diastolic pressure) is measured while the heart is at rest. Ideal blood pressure for a person at rest is 120/80 millimeters of mercury (mm Hg) or below. When blood pressure is higher than 140/90 medical professionals diagnose the condition as "hypertension."
Isometric exercise is a form of resistance training. However, instead of moving weight in a continuous fashion, you hold the joints and working muscles in a fixed position, exerting force against a static object for a specific length of time. The muscles in use are constantly contracted, without movement. Individuals diagnosed with high blood pressure or hypertension are advised to avoid isometric types of exercise due to the fact that they can cause a sudden and dangerous spike in blood pressure.
BP Increases Gradually During Dynamic Exercise
Blood pressure responds very differently to active movement or dynamic exercises (walking, bicycling, jogging, roller skating) than it does to resistance training or isometric exercise. In a healthy individual, the systolic blood pressure rises slowly and steadily in accord with the intensity or duration of the dynamic exercise, while the diastolic blood pressure changes only slightly. It is not uncommon for blood pressure to increase to anywhere between 160-210/90 during an intense workout, though this is entirely dependent upon your resting blood pressure, the intensity of your workout, medication, tiredness and other factors. If either systolic or diastolic blood pressure drops below the starting rate or systolic rises above 240, exercise should be stopped immediately.
Blood Pressure and Isometric Exercise
The effect on the body when performing extremely heavy resistance training or isometrics is very similar; both can cause sharp increases in blood pressure. During heavy lifting or isometric contractions, the pressure within the muscle increases, which compresses small blood vessels and prevents fresh, oxygen-rich blood from reaching active muscle tissue.
Tissue hypoxia (tissues deprived of a sufficient supply of oxygen), causes a rapid rise in both systolic and diastolic blood pressure readings. The speed and degree of the rise in systolic and diastolic blood pressure is directly related to the intensity and duration of the muscular contraction. Most importantly, when blood pressure increases rapidly, the workload on the heart increases as well, which could be extremely dangerous for patients with coronary artery disease.
Avoid the Valsalva Maneuver
Exercisers should be careful to avoid holding their breath during the contraction of an isometric exercise. Holding your breath while performing a continual muscular contraction reduces blood flow to the heart, which is called a "valsalva maneuver." A reduced flow of blood to the heart leads to a decrease in the quantity and quality of blood flowing to the brain. Take care to use proper breathing form when exercising. Exhale on the lifting (working) portion of the exercise, and inhale when the weight lowers or the muscles relax.
The very high blood pressure associated with vigorous or sustained isometric contractions could cause a stroke or split a weak aortic wall, a serious risk for heart patients or hypertensives. Resistance training recommendations for individuals with hypertension generally focus on high repetition/low weight protocols or circuit training. Always consult with your physician before beginning an exercise program for specific guidelines and recommendations.