Dynamic exercise has been advocated by national and international committees as part of a comprehensive regimen for the treatment of hypertension.1, 2 There has been a paucity of data, however, regarding recommendations for isometric or resistance exercise. The fear has been that this type of exercise increases blood pressure (BP) and is not a conditioning exercise, like the dynamic exercise, which is a conditioning exercise, and lowers resting BP and heart rate.3 Recently there has been a craze in which body fitness and isometric exercises are performed daily by many people in fitness centers or at home regardless of BP levels. Also, daily activities, such as lifting, holding, and carrying a suitcase involve isometric exercises. Although the hemodynamic effects of dynamic exercise have been well studied,3there is limited knowledge regarding the hemodynamic, circulatory, and BP effects of isometric exercise in hypertensive patients. An updated Medline search was conducted from 2000 to 2009, since the subject was reviewed by Kelley and coworkers in 2000.4 Using the terms isometric and resistance exercise, we identified 82 articles. Of these, 6 were selected that included normotensive and hypertensive patients. Thus, in this concise review, the hemodynamic and circulatory effects of isometric or resistance exercise in hypertensive patients and its merits as complimentary to antihypertensive treatment will be discussed.

Underlying Hemodynamic and Circulatory Mechanisms of Isometric Exercise in Normotensive and Hypertensive Patients

Normotensive Patients

The immediate response to a sustained handgrip (SHG) is a rise in heart rate and BP.4-7Studies in normotensive young adults have shown that the initial increase in heart rate and BP to an SHG for 3 minutes at 30% maximal voluntary contraction (MVC) was due to vagal withdrawal, since this response was blocked with pretreatment with atropine. The late response was due to sympathetic nervous system stimulation, because this action was not blocked by previous atropinization of the patients, but only by the combined administration of atropine and propranolol.5 In our studies of normotensive patients,7 an SHG for 2 minutes at 30% MVC was associated with a rapid rise of heart rate, BP, and cardiac output and no change in peripheral vascular resistance (PVR), as depicted in Figures 1–3. The hemodynamic studies were performed in the morning after an overnight fast without premedication. Briefly, small segments of polyethylene tubing were percutaneously introduced into the antecubital vein and brachial artery up to the shoulder level. This enabled continuous direct recording at 25 mm/s and 100 mm/s paper speeds of arterial and venous pressures simultaneously with the electrocardiogram (LII). After a 15‐minute supine rest on a tilt table, the control hemodynamic measurements were taken. The cardiac output, in triplicate, was obtained with 5 mL of indocyanine green (cardiogreen) injected intravenously, followed by 5 mL of normal saline flush. After inscription of each indicator dilution curve, the withdrawn blood was returned to the patient. These curves were plotted semilogarithmically to calculate the cardiac output per minute. The cardiac output was repeated after an SHG at 30% and MVC for 1 minute before and during the hemodynamic measurements. The 30% MVC was previously determined by having the patient grip a hand ergometer (Stoelting Co, Chicago, IL) to his MVC. From this value, the 30% MVC of SHG was calculated for the individual patient. After 15 minutes of supine rest, the Valsalva maneuver was performed by having the patient blow against a resistance of 40 mm Hg for 30 seconds, and the hemodynamic measurements were repeated. After another 15 minutes of supine rest, the patient was tilted at 50 degrees upright for 5 minutes, and the hemodynamic measurements were repeated. From these measurements, the following hemodynamic parameters were calculated: (1) cardiac index by dividing the cardiac output by the body surface area in m²; (2) mean arterial pressure by adding to the diastolic arterial pressure one third of pulse pressure; (3) peripheral vascular resistance (PVR) index by dividing the PVR by the body surface area in m² and expressed in arbitrary units; and (4) the percent of diastolic arterial pressure overshoot of the Valsalva maneuver by dividing the difference of diastolic arterial pressure pre‐ and post‐Valsalva maneuver by the pre‐Valsalva maneuver diastolic arterial pressure and multiplying it by 100. The same hemodynamic measurements were performed in both normotensive and hypertensive patients. The patients had either never received medications or had discontinued their medication for 2 weeks. Their baseline clinical characteristics are listed in the Table. Similar findings to ours have been demonstrated by other investigators.5, 8-10 Our knowledge regarding the circulatory responses to isometric exercise comes from earlier studies,11 which show that the blood supply to a contracting muscle is a compromise of two opposing events. One event concerns the dilatation of the blood vessels in an effort to increase flow and the second event represents the throttling effect on these vessels from the mechanical compression of the contracting muscles. It was found that the blood flow to the calf muscles was cut off during sustained contractions at a tension of 20% of MVC.11 Other investigators studied this phenomenon by having their patients grip a hand dynamometer at 30% MVC.5, 12, 13 They found that the arterial pressure reached 200/135 mm Hg and quickly returned to control levels after the exercise. In these studies, like in ours, the BP rise during the handgrip was caused by an increase in cardiac output, because the heart rate and stroke volume both increased and the PVR either did not change or showed a slight decrease. Also, activities involving lifting, holding, and carrying weights, brought about the same sort of responses, whether the forearm muscles are used to grip the handle of the weight or whether the weight is allowed to hang from the crook of the fingers. The holding of a 20‐kg weight (equivalent to a moderately heavy suitcase), produced a mean increase in BP in 4 patients of 45/30 mm Hg, systolic/diastolic, and a heart rate increase of 24 beats per minute after only 2 minutes.14 Heavier weight lifting can lead to extremely high levels of BP. A study in professional weight lifters showed that bench pressing at 80%, 90%, 95%, and 100% MVC resulted in a mean BP increase at peak exercise of 320/250 mm Hg and, in one patient, 480/350 mm Hg.15 The BP returned to control levels shortly after completion of exercise, however.

 

	Normotensive Patients	Hypertensive Patients
No. of patients	26	18
Age, y	47±2	51±2
SAP, mm Hg	124±2	164±2
DAP, mm Hg	82±1	98±1
MAP, mm Hg	96±1	120±3
HR, beats per min	71±2	74±2

• Abbreviations: DAP, diastolic arterial pressure; HR, heart rate; MAP, mean arterial pressure; SAP, systolic arterial pressure. Values are expressed as mean ± standard error of the mean.

Discussion

The data presented in this concise review suggest that isometric or resistance exercise results in either no change or small reductions in resting systolic and diastolic BP and, more important, does not appear to raise it, as it was feared in the past. For this reason, it was not recommended to hypertensive patients by national and international committee guidelines.1, 2 The rise in BP during the performance of isometric exercise is due mostly to the increase in cardiac output and not to PVR7 and returns quickly to baseline levels after the completion of exercise. Similar findings have been reported by recent meta‐analyses on the subject.4, 27, 28 This suggests that the repeated performance of isometric exercise leads to resetting of the baroreceptors, leading to lower BP in the long‐term, and may enhance the action of antihypertensive drugs.29 Additional benefits of the isometric or resistance exercise are the increase in muscle bulk, upper and lower body strength, decrease in body fat, increase in bone density, decrease in bone fractures, and increase in quality of life, especially in older persons.4, 27, 28, 30 These are very important benefits despite the modest decreases in BP. According to recent meta‐analyses and the review of published studies, the modest decreases in systolic and diastolic BP were due to the inclusion in these studies of mostly normotensive patients and very few hypertensive patients. In addition, these studies were small and of short duration to see long‐term benefits. Therefore, large, long‐term, randomized, prospective studies, restricted to hypertensive patients, are needed to provide more definitive information on the effects of isometric exercise in resting BP, alone and in combination with antihypertensive drugs. It is now time to recommend individualized training with isometric exercise in patients with hypertension. Therefore, based on the available evidence, we believe that mild to moderate isometric exercise, either alone or in combination with dynamic exercise, should be recommended to patients with hypertension and be part of a comprehensive treatment regimen.3, 4, 27, 28 A new hand‐held dynamometer (Zona Plus; Zona Health, Boise, ID) has been approved by the US Food and Drug Administration, which can be used at home by patients who are able to ambulate or not and has been shown to reduce BP.24, 25, 31 The Zona Plus dynamometer looks like an electric razor (Figure 4), and can be held by the right or left hand. Exercises can be performed at home while the person is sitting down watching TV. It is fully automated and, according to their instructions, the person must squeeze as hard as possible for 5 seconds. The device measures the maximal strength of the person’s squeeze and calculates the 30% MVC. The device then prompts the individual through four 2‐minute bouts of squeezing, with a minute rest between squeezes. It also informs the patient whether the grip is kept at 30% MVC and will count down the time for the user. The entire session lasts about 12 minutes and should be performed at least 3 times per week. Results become evident after 1 to 2 weeks of training. The BP effects, like drugs, are not permanent. They last as long as the exercises are performed. The cost of the device is $300 and is not reimbursable as yet by Medicare or other health insurances, but is a good investment long‐term.