Exercise as it relates to Disease/Drowning out the pressure: Can swimming help to reduce the effects of hypertension?

Image Credit: Svilen Enev

Topic ArticleEdit

Tanaka, H., Bassett D., Howley, E., Thompson, D., Ashraf, M. & Rawson, F. (1997) Swimming training lowers the resting blood pressure in individuals with hypertension. Journal of Hypertension, 15(6), 651-657. Doi: 10.1097/00004872-199715060-00012

Research findings in this article describe the benefits of a ten-week exercise program in patients with hypertension. This has been created by student number (u)3065916 from the University of Canberra, Australia.[1]

What is the background to this research?Edit

Hypertension describes a state of abnormally high blood pressure. Chronic hypertension can have many long term health consequences and it currently (2014–15) affects approximately 2.6million people in Australia.[2] If not noticed, or left untreated, Hypertension can lead to serious health complications including; cardiac events, kidney failure, stroke and stenosis (narrowing) of arteries, all of which can be fatal.[1][3] Treatments for hypertension include drug-based therapies, lifestyle changes such as cessation of smoking or reduction in alcohol consumption, and also regular exercise.[3] Physical impairments such as obesity, deformity and injury can make exercise very difficult due to increased demand on joints and muscles. Swimming is a popular exercise option as it allows individuals to work for a long time in a relatively low-impact environment.[1]

Where is the research from?Edit

Research was facilitated by The University of Tennessee- Knoxville, and the University of Tennessee Medical Centre.[1] The study was conducted by a combination of health scientists and exercise scientists. The original article was presented to the Journal of Hypertension and was published in March 1997, it claims to be the first study to analyse the effects of swimming on hypertension.[1]

What kind of research was this?Edit

Tanaka’s study was, technically, a pseudo-randomised controlled trial involving an exercise intervention.[1][4] Participants in the intervention group participated in three swimming sessions per week and control group were instructed to behave as they normally would.[1] The pseudo-randomised control trial is considered to have a high level of accuracy, though may have exaggerated estimates of effect caused by bias.[4] Tanaka’s study could be improved through more strict allocation of groups – this would give the study more credibility – allowing some participants to change group based on preference is considered poor practice.[4] Findings from this study are consistent with the results of other studies looking at repetitive-motion long-duration exercise bouts on hypertension.[5] The added benefit of reduced load is important when considering risk of injury in participants.[1]

What did the research involve?Edit

This research by Tanaka et al. involved 18 sedentary men and women with chronic high blood pressure.[1] The subjects were divided into two groups, these were; an intervention group comprised of 12 individuals, and a control group of just 6. The intervention group participated in a 10-week long swimming program and were required to exercise in a pool for one hour three times per week working up to 45-minute continuous swimming bouts.[1] Participants were required to maintain a workload of 60% of their individual maximal heart rate reserve (related to oxygen consumption[1]) which was calculated in pre-testing, and on average participants attended 94% of intervention sessions.[1] The control group remained sedentary, and both groups were instructed not to alter their behaviours other than the specific changes required as a part of the intervention.[1] The primary measured outcomes in Tanaka’s study were resting heart rate (RHR) systolic blood pressure (SBP) and diastolic blood pressure (DBP) measured with the participants seated, and then again with participants lying down (supine).[1] A two-way analysis of variance test was used to ensure that before and after results in both the control and intervention groups were not simply due to chance.[1]

What were the basic results?Edit

The results of the study by Tanaka et al. indicated that the swimming intervention had a significant effect on all outcome measurements. Results were compared before and after and contrasted between the intervention group and the control group as follows:[1]

  • Individuals in the training group experienced a significant change in RHR from 80.8 beats per minute (bpm) to 70.7bpm over the couse of the intervention;
  • Individuals in the intervention group experienced a drops in seated SBP and DBP of 6mmHg and 2mmHg respectively;
  • Supine SBP and DBP also dropped by 6mmHg and 5mmHg, bringing them to near normal levels.[2]

What conclusions can we take from this research?Edit

The Tanaka et al. study concluded that there is a significant association between swimming and hypertension in humans.[1] There were a number of flaws in the study and the research was presented without comparison to other forms of physical activity which have also been shown to influence hypertension[5][6],. Even though the authors stress that any methodological errors in the selection of test subjects did not change the overall results whether excluded or not, it is important that the findings of the Tanaka study be reinvestigated to ensure there is no exaggerated estimate of effect.[4] Fifteen years after the publication of the Tanaka et al. study, another research project conducted in São Paulo, Brazil also looked at the effectiveness of swimming as an intervention for treatment of hypertension.[7] The results of this study also confirmed that swimming is highly effective at reducing blood pressure in hypertensive individuals.[7]

Practical adviceEdit

Tanaka’s study demonstrated that swimming is a valuable exercise intervention in reducing blood pressure in individuals with chronic hypertension.[1] The results of his study have now been confirmed by more recent research and future research should focus on manipulations in frequency, volume and intensity in order to determine the best possible results.[7] Individuals looking to improve their own health and reduce hypertension should gradually increase their workload over a number of weeks, similar to the intervention group in the study.[1] These individuals should also take careful note of the high compliance rate of participants in the study (94% of sessions attended) and seek to swim regularly to gain the best possible outcome.[1]

Further Information/ResourcesEdit


More information on hypertension is available from The Heart Foundation website accessible at: https://heartfoundation.org.au/

Prof. Hirofumi TanakaEdit

If you would like to know more about the primary author of the original study, please visit his profile page available from the University of Texas webpage, accessible at: https://education.utexas.edu/faculty/hirofumi_tanaka


  1. a b c d e f g h i j k l m n o p q r s t Tanaka H, Bassett D, Howley E, Thompson D, Ashraf M, Rawson F. Swimming training lowers the resting blood pressure in individuals with hypertension. Journal of Hypertension. 1997;15(6):651-657.
  2. a b 4364.0.55.001 - National Health Survey: First Results, 2014-15 [Internet]. Abs.gov.au. 2016 [cited 27 September 2016]. Available from: http://www.abs.gov.au/ausstats/abs@.nsf/mf/4364.0.55.001
  3. a b High blood pressure (hypertension) Treatments and drugs - Mayo Clinic [Internet]. Mayoclinic.org. 2016 [cited 27 September 2016]. Available from: http://www.mayoclinic.org/diseases-conditions/high-blood-pressure/basics/treatment/con-20019580
  4. a b c d NHMRC additional levels of evidence and grades for recommendations for developers of guidelines [Internet]. 1st ed. The National Health and Medical Research Council (NHMRC); 2016 [cited 27 September 2016]. Available from: https://www.nhmrc.gov.au/
  5. a b Martin J, Dubbert P, Cushman W. Controlled trial of aerobic exercise in hypertension. Circulation. 1990;81(5):1560-1567.
  6. Kelley G, Kelley K, Tran Z. Walking and resting blood pressure in adults: A Meta-analysis. Preventive Medicine. 2001;33(2):120-127.
  7. a b c Guimarães G, Cruz L, Tavares A, Dorea E, Fernandes-Silva M, Bocchi E. Effects of short-term heated water-based exercise training on systemic blood pressure in patients with resistant hypertension. Blood Pressure Monitoring. 2013;18(6):342-345.