This paper has been prepared for the purpose of:

1. defining the problem of high blood pressure
2. reviewing indirect evidence of isometrics lowering of blood pressure
3. showing the direct evidence that controlled isometric exercise can reduce and maintain blood pressures in humans
4. providing evidence from recent studies of physiological mechanisms modified by the isometric training which contribute to the blood pressure reduction and control.
5. summarizing mechanisms theory, supported by published medical research, which explains the relationship of isometric training to blood pressure reduction and control

Hypertension is defined as a diastolic blood pressure of 90 mmHg or higher and/or a systolic pressure of 140 mmHg or higher. It is present in an estimated 50 -60 million Americans and is more common in blacks and older adults¹. Hypertension is a leading risk factor for coronary heart disease, congestive heart failure, stroke, ruptured aortic aneurysm, renal disease, and retinopathy. These complications of hypertension are among the most common and serious diseases in the U.S., and successful efforts to lower blood pressure could thus have substantial impact on population morbidity and mortality. Heart disease is the leading cause of death in the U.S., accounting for nearly 740,000 deaths each year (287 deaths per 100,000 population), and cerebrovascular disease, the third leading cause of death, accounts for about 150,000 deaths each year (58/100,000). Milder forms of hypertension predict progression to more severe elevations and development of cardiovascular disease. Coronary heart disease mortality begins to increase at systolic blood pressures above 110 mmHg and at diastolic pressures above 70 mmHg.

Results from the Framingham Heart Study show that the benefit of reducing blood pressure, by even a few mmHg, leads to significant reductions in the risk of coronary heart disease and stroke incidents. ² A reduction of diastolic blood pressure of only 2 mmHg leads to a 9% reduction of coronary heart disease, and a 15% reduction in stroke incidents. A 7.5 mmHg reduction leads to a 29% reduction of coronary heart disease, and a 48% reduction in stroke incidents. This new isometric exercise therapy is a very important finding, considering the large blood pressure reductions that are obtained, and the correspondingly large reduction of cardiovascular risk factors it provides.

The 1985 report by Buck and Donner³ studied the relationship between occupational isometric activity and incidence of hypertension. Their study found that males with moderate to high isometric content in their job function had a 7.4% incidence of five-year hypertension, compared to 10.4% of those in jobs with low isometric activity. This is a 29% reduction in the incidence rate attributed to the daily isometric content of the job function. This study included over 4,000 men, from low, middle, and upper social classes. Their result is the largest study to date of the relationship between isometric exercise and hypertension.

Isometric contractions, if held for extended periods, lead to increases in both systolic and diastolic blood pressure. This fact was being used to investigate the ability of U.S. Airforce pilots to withstand high "g" load maneuvers in the cockpits of airplanes. It was found that isometrics could extend the "g" range of a pilot, thus enhancing their ability to out maneuver their enemies. This research involved controlled isometric handgrip contractions. The protocol was to measure a resting blood pressure, measure blood pressure while performing the contractions, and measure blood pressure after the contractions until a return to pre-exercise level was attained. It was noticed, as this project continued over several weeks, that the test subject's initial resting blood pressures were decreasing. This was the first observation of controlled isometric handgrip efforts having an effect of lowering resting blood pressure.

Controlled studies were needed to determine the exact combination of isometric force, duration of exertions, rest periods in an interrupted exercise, and number of repetitions for an effective protocol. The CardioGrip® protocol was developed as a means to consistently instruct users in performing the isometric exercise protocol so they could optimize the blood pressure reduction benefits of isometric therapy while minimizing physical stress and duration of effort. The protocol consists of brief, interrupted, sub-maximal, isometric hand contractions. Each hand contraction lasts two minutes or less (depending upon protocol selected), is separated from the next effort by a one minute rest period, and is repeated with alternate hands for a total of four efforts. The entire exercise takes less than 12 minutes to perform. This protocol is then performed regularly, from 3 to 7 times per week.

Clinical trials^{4 - 8} have shown that the CardioGrip® protocol has led to blood pressure reductions in those subjects tested. This effect is achieved in 4 to 8 weeks, and can be maintained for a period greater than one year. Table 1 summarizes these results.

These trials covered a broad range of individuals, from normal blood pressure, well into the hypertensive range. Plotting the entry and exit blood pressures, it is readily seen that all groups had a significant lowering of blood pressure during the weeks of performing the CardioGrip® protocol. All groups follow the same trend, lowering of both systolic and diastolic blood pressure. Each of these trials included at least 4 weeks of exercise training using the CardioGrip® protocol. Most individuals performed the exercise for no more than 12 weeks. The exact format of each study has been summarized to allow comparisons across studies included in this summary.

Study W1⁴: This study was a randomized controlled study involving 15 healthy volunteers (8 in the exercise group and 7 in the control group) with resting blood pressure levels in the upper end of the normal range. Subjects were sought in this range as a cautious approach in the first-ever controlled study before moving on to subjects with higher pressures. The exercise group conducted a systematic isometric exercise using the CardioGrip® protocol 3 days a week over an 8 week period. Both groups were instructed to maintain their normal lifestyle. None of the subjects were receiving any other treatment for their blood pressure. The results showed a mean reduction of systolic blood pressure (SBP) of 12.7 mmHg (134.1± 0.95 mmHg to 121.4 ± 1.34mmHg) and a mean reduction in diastolic blood pressure (DBP) of 14.9 mmHg (86.5± 2.01mmHg to 71.6 ± 3.50mmHg) in the exercise group and no change in resting blood pressure in the control group (initial: SBP; 134.0± 3.30 mmHg, DBP; 83.4 ± 1.67 mmHg, final: SBP; 136.6 ± 2.78 mmHg , DBP; 85.0 ± 2.43 mmHg) A reduction in blood pressure levels was seen in all subjects in the exercise group.

Study W2⁴: This study was a within patient comparison of the effects of the isometric exercise using the CardioGrip® protocol and no exercise. The exercise sessions were conducted 5 days/ week for 5 weeks until 24 sessions were completed (to compare with the 24 treatments in Study W1). During weeks 6 - 10, no isometric exercise was performed. Ten patients were enrolled in this study. The results showed a decline in both systolic blood pressure (SBP) and diastolic blood pressure (DBP) over the 5 week training period (initial: SBP; 127.0 ± 2.28, DBP; 86.2 ± 1.85, 5 weeks: SBP; 117.5 ± 2.23, DBP; 77.4 ± 1.49). Both the SBP and DBP returned to initial levels during the 6 - 10 week no exercise period, indicating that cessation of the isometric exercise protocol will result in a slow return in resting blood pressure.

        

Study W4⁸: This unpublished study was a cross-over comparison to evaluate the effect of conducting the CardioGrip® isometric exercise program one session per day versus two sessions per day. One of two schedules were performed (once a day or twice a day), 3 days/week over a 5 week period . Subjects then performed no sessions over a 3 months period and then performed the second schedule, 3 days/week for another 5 week period. Nine healthy volunteers were enrolled in the study with blood pressure levels in the upper end of the normal range. The result was that the group average blood pressures entering the study were 140/90 and declined to 129/85 mmHg. When repeated months later, similar starting pressures and similar declines were observed. This indicates that 2 per day exercises were not more beneficial than 1 per day.

Study W5⁸: This was an uncontrolled study to evaluate the effect of the CardioGrip® isometric exercise program in patients with borderline hypertension. Seven healthy volunteers with borderline hypertension were enrolled in the study. The result was that the group mean decline in blood pressure was from 134.9/89.5 to 128/78.8, for a decline of 6.9/10.7 mmHg. The decline fit a linear model, suggesting that continuation of the exercise for more than 8 weeks might have led to a further decrease in blood pressure.

Study W6 (a&b) ⁸: This study was a parallel group comparison of two isometric exercise programs, one program involved the performance of 1 isometric contraction per session per day, and the second program involved performing 6 isometric contractions per session. Seven subjects participated in the first program and 6 subjects participated in the second program. All subjects had blood pressure levels in the upper end of the normal range or in the hypertensive range. The result for the first group was that the average systolic blood pressure decreased from 144.6 to 132.6 mmHg, and diastolic from 92.6 to 82.9 mmHg; decreases of 12.0/9.7 mmHg. The result for the second group was that the average systolic blood pressure declined from 149.0 to 137.8, and the diastolic declined from 95.5 to 89.5 mmHg., decreases of 11.2/6.0 mmHg.

Study W7⁸: This study was conducted to evaluate the effect of the CardioGrip® isometric exercise program to simultaneously reduce both blood pressure and blood cholesterol and total lipids. The protocol prescribed conducting the isometric exercise 4 days/week for 6 weeks. The result was that resting blood pressure averages for the group changed from 129.1/83.8 to 124.2/78.2, for a decline of 4.9/5.6 mmHg. While the group mean data for cholesterol and total lipids did not show a significant change, it appeared that some individuals showed a trend for a desirable shift in lipids. The lipid results are likely due to recruiting subjects whose lipid levels were not dramatically different from normal at the start.

Study G1⁶: This study was a case study to evaluate the effects of the CardioGrip® isometric exercise over a 1 year period in patients with high normal to high blood pressure. The protocol design was for the patients to perform the isometric exercise 3 times/week, with the criterion that they must average at least 2 exercise sessions per week and not miss more than 6 consecutive sessions. Each patient experienced large decreases in resting blood pressure within a few weeks of the study, with some showing declines over several more weeks. A description of each patient's experience is given below:

There were four individuals who completed the study:

Study G2⁶: This study was a case study to evaluate the effects of the CardioGrip® isometric exercise over a 1 year period in patients with high normal to high blood pressure. The protocol design was the same as for G1, above. These patients are the ones who did not meet the criteria of average sessions per week, or who did not stay in the study for the full year. Each patient experienced large decreases in resting blood pressure within a few weeks of the study, with some showing declines over several more weeks. A description of each patient's experience is given below.

There were eight individuals who participated in the study:

1. A 47 year old male entered with blood pressure of 154/98 on 2 anti-hypertensive drugs, which were withdrawn at the end of week 5 with a blood pressure at that time of 122/81, continued through week 58. Although he averaged only 0.9 visits per week, his blood pressure at week 58 was 128/88, for a decline of 26/10 mmHg.
   
2. A 64 year old female started with a blood pressure of 155/98 mmHg and declined to 134/80 in 13 weeks, for a decline of 21/18, before dropping out of the study.
   
3. A 64 year old female entered with a blood pressure of 168/85 mmHg and declined by 28/10 to 140/75 mmHg in 81 weeks.
   
4. A 64 year old male entered with a blood pressure of 153/89 and declined by 10/9 to 143/80 in 76 weeks.
   
5. A 61 year old female entered at 157/64 and declined by 29/6 to 128/58 mmHg by week 69.
   
6. An 82 year old female entered at 152/73 and declined by 15/2 to 137/71 in week 43.
   
7. An 87 year old female entered at 177/81 and declined by 28/7 to 149/74 in week 28.
   
8. Individual entered at 178/86 and declined by 30/18 to 148/68 in week 30.

Study R1⁷: This study was a randomized control group study to evaluate any change in control of the blood vessels by the sympathetic nervous system after isometric exercise using the CardioGrip® protocol. Seventeen healthy volunteers were enrolled in the study (9 in the exercise group and 8 in the control group). The exercise group conducted the systematic isometric exercise using the CardioGrip® protocol 3 days a week over an 8 week period. Both groups were instructed to maintain their normal lifestyle. None of the subjects were receiving any other treatment for their blood pressure. The result was that diastolic blood pressures were significantly decreased (67 to 62 mmHg on average) even though the initial blood pressure average for the group was quite normal. Systolic blood pressure showed a trend to be lower, but was not significant statistically (116 to 113 mmHg). The nerve recordings did not show a change comparing them before and after training.

Reviewing the clinical trials, it becomes evident that the effect of isometric exercise on lowering blood pressure is not limited to any particular range of pre-exercise blood pressure. A wide range of entry blood pressures are included in these studies, many have been stable on anti-hypertensive medication, many have been on anti-hypertensive medication and either reduced or withdrawn from those medications. These results show that this isometric training is an effective tool in the treatment of high blood pressure

Since the discovery of the vasodilating effects of nitric oxide, numerous studies of its origin, effects and genetic control have been completed. These studies enable a theoretical proposal of mechanisms impacted by isometric therapy (see illustration). Study M1, described above, demonstrated a decrease in sympathetic activity and an increase in parasympathetic activity following imposition of shear stress of isometric exercise. This result confirms an important element in the mechanisms theory ascribed to isometric training and its lowering of blood pressure. However, it is noted that no studies are known to have been completed yet which directly measure responses of the release of nitric oxide resulting in vasodilation and lowering of blood pressure as a result of isometric exercise training. Yet the evidence is compelling and encourages studies of this nature to be done.

This evidence clearly shows that the CardioGrip® protocol is useful in the treatment of high blood pressure as a preventative treatment, as a primary treatment, as a supplement in pharmacological treatment, as a substitute in pharmacological treatment and as a replacement to pharmacological treatment.

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