We, members of the International Working Group on Isometric Exercise, read with great interest the article by Pagonas et al. on the comparative effects of aerobic and isometric handgrip exercise (IRT). However, we believe the finding, that aerobic exercise induces reductions in blood pressure (BP), whereas isometric exercise training (handgrip) does not, to be compromised for several reasons

Carlson, Debra J.

McGowan, Cheri

Smart, Neil A.

Swaine, Ian

Journal of Hypertension

We, members of the International Working Group on Isometric Exercise, read with great interest the article by Pagonas et al. on the comparative effects of aerobic and isometric handgrip exercise (IRT). However, we believe the finding, that aerobic exercise induces reductions in blood pressure (BP), whereas isometric exercise training (handgrip) does not, to be compromised for several reasons: First, the groups were not matched at baseline for resting SBP (office SBP- Table 2) differed by an egregious 8.8 mmHg between IRT and aerobic groups. Millar et al.[1] showed, some years ago, that account must be taken of baseline BP values, when analysing training-induced changes. The probability that a 9-mmHg difference in resting blood occurred by chance in a properly randomized study is very remote; moreover, the authors reported that this difference was not statistically significant (P = 0.36). Because of these sizeable differences in baseline BP measures, the aerobic training group clearly had greater potential to regress to the mean

Smart, Neil

Carlson, Debra J

Research UNE

Commentary on aerobic versus isometric handgrip exercise in hypertension: A randomized controlled trial

Neil A. Smart

Debra J. Carlson

Ian Swaine

Cheri McGowan

Crossref

Commentary on aerobic versus isometric handgrip exercise in hypertension

Greenwich Academic Literature Archive

CorrespondenceCommentary on aerobic versusisometric handgrip exercise inhypertension: a randomizedcontrolled trialNeil A. Smarta, Debra J. Carlsona, Ian Swaineb,and Cheri McGowancWe, members of the International Working Groupon Isometric Exercise, read with great interest thearticle by Pagonas et al. on the comparativeeffects of aerobic and isometric handgrip exercise (IRT).However, we believe the finding, that aerobic exerciseinduces reductions in blood pressure (BP), whereas iso-metric exercise training (handgrip) does not, to be com-promised for several reasons:First, the groups were not matched at baseline for restingSBP (office SBP – Table 2) differed by an egregious8.8mmHg between IRT and aerobic groups. Millar et al.[1] showed, some years ago, that account must be taken ofbaseline BP values, when analysing training-inducedchanges. The probability that a 9-mmHg differences inresting blood occurred by chance in a properly randomizedstudy is very remote; moreover, the authors reported thatthis difference was not statistically significant (P¼ 0.36).Because of these sizeable differences in baseline BP mea-sures, the aerobic training group clearly had greater poten-tial to regress to the mean.The randomized allocation of patients into the threegroups appears to have introduced selection bias. In theaerobic training group, 11 patients performed more thanthree exercise sessions weekly at baseline, compared withonly six patients, doing a similar amount of aerobic exer-cise, in the handgrip training group. Moreover, the authors’stated there was no statistical significance of this, but thesecond paragraph of the results states that the significancelevel was less than 0.05. Surely, if the difference was NS,would it be more than 0.05? This also illustrates concernsabout the ‘parity’ of the training stimulus provided to thepatient groups. It is likely that about 40% of the aerobictraining group were performing the precise training dose(of 2.5 h/week). When one considers that this aerobicexercise was neither structured nor supervised (unlikethe isometric exercise – which is carefully controlled at aprecise dose). We cannot ascertain the IRT as the maximumvoluntary contraction (MVC) values are not reported byPagonas et al. In order for the reader to determine whetherthe isometric training stimulus was adequate, MVC valuesbefore and after training should be shown. Inmost previousstudies, an increase in MVC after training confirms theadequacy of the isometric training stimulus.A suggestionof attritionbias could alsobe levelledPagonaset al.’s study because of the 25% drop-out rate in the aerobicgroup. Although this is at the upper end of expectations, it isnot atypical in aerobic studies. Nevertheless, an intention totreat analysis showed significant antihypertensive effects dis-appear when the nonadherent patients are included in theaerobic groupanalysis. This indicates theprimary analysiswasflawed, as statistical significance would have emphasized themost dedicated 75%of the original aerobic group; the authors’conclusions about the relative superiority of aerobic exerciseare incorrect. We do, however, acknowledge that aerobicexercise offers additional physiological adaptations that areunlikelywithhandgrip training, suchas changes in lipoproteinsubfractions and cardiorespiratory fitness improvements.We are also concerned because Pagonas et al.’s study isclearly underpowered. The size of the baseline BP SDs,especially office BP – upon which the study seems to havebeen powered, were estimated at 10mmHg when in factmost SD values for change in BPs are above 14mmHg.This underestimation would have compromised the samplesize calculation. In fact, one group mean office SBP SD was22.7mmHg, which would require a sample size of over 200participants to show the desired 7mmHg reduction in SBP!Although numerous studies in hypertensive populationsuse bilateral handgrip training interventions, we do haveadditional concerns about its use in the current study basedon recent meta-analysis findings. In brief, Inder et al. [2]showed that bilateral interventions appear to be suboptimalfor isometric training-induced BP reduction. We suspectthat IRT lowers BP through a local and not systemic effect,so, the study design, which alternates the hand grip exercisewould have diluted the local muscle effects of IRT in thatgroup. Furthermore, it is unclear if participants in all groupswere asked to refrain from aerobic physical activity at least24 h prior to their testing sessions. It is possible that par-ticipants from the aerobic training group had the benefit ofpostexercise hypotension at their posttesting session, andwe are unsure this was not controlled. At the very least,these should be acknowledged as potential limitations ofthe study.Finally, there are several incorrect statements or omis-sions that should be corrected via an erratum. First, in theIntroduction, the authors state ‘there is no data on theeffects of isometric exercise on 24-h ambulatory BP. . .inpatients with hypertension’. This is incorrect, as Stiller-Moldovan et al. [3] (no. 24 in the current reference list)observed clinically relevant reductions in mean 24-h ambu-latory BP in a population of well controlled medicatedhypertensive patients. This should also be reflected onPg. 6 in the discussion of no. 24 findings. A second pointfor correction relates to the statement that the study ofPagonas et al. is NOT the first to utilize a sham low-intensitycontrol group working at 5% MVC. Previous research hasutilized low-intensity isometric training, the most recentwas published in December 2016, Carlson et al. [4]. Third,the statement ‘There are no homogenous results on hyper-tensive patients’ on Pg. 6 is misleading. Pagonas et al. failedto cite the recent randomized controlled trial of isometrichandgrip training in medicated hypertensive patients con-ducted by Badrov et al. [5] which supported handgrip-induced BP-lowering effects, and the supportive trial ofTaylor et al. [6] (Pagonas et al. reference no. 26) was also of omitted. Fourth, the statement ‘Hence, handgrip exercisewas not included in the current guidelines on treatment ofhypertension’ on Pg. 6 is also misleading. Handgrip exer-cise is recommended as an adjunct to traditional aerobicexercise in both the 2013 American Heart AssociationPosition Statement [7] entitled ‘Beyond Medications andDiet: Alternative Approaches to Lowering Blood PressureA Scientific Statement From the American Heart Associa-tion’, the 2016 Canadian Hypertension Guidelines [8] aswell as Australian guidelines [9].We strongly urge more-carefully considered studydesigns and reporting in comparative studies like theone of Pagonas et al. Compromised randomization ofpatients, use of small sample sizes and use of bilateral limbprescriptions should all be avoided. Isometric training is avaluable adjunct therapy to manage hypertension, andcompromised study designs and subsequent analyses suchas this one erroneously prevent the transition of this valu-able tool into clinical practice.ACKNOWLEDGEMENTSConflicts of interestThere are no conflicts of interest.REFERENCES1. Millar PJ, Bray SR, McGowan CL, MacDonald MJ, McCartney N.Effects of isometric handgrip training among people medicated forhypertension: a multilevel analysis. Blood Press Monit 2007;12:307–314.2. Inder JD, Carlson DJ, Dieberg G, McFarlane JR, Hess NC, Smart NA.Isometric exercise training for blood pressuremanagement: a systematicreview and meta-analysis to optimize benefit. Hypertens Res 2016;39:88–94.3. Stiller-Moldovan C, Kenno K, McGowan CL. Effects of isometric hand-grip training on blood pressure (resting and 24h ambulatory) and heartrate variability in medicated hypertensive patients. Blood Press Monit2012; 17:55–61.4. Carlson DJ, Inder J, Palanisamy SK, McFarlane JR, Dieberg G, Smart NA.The efficacy of isometric resistance training utilizing handgrip exercisefor blood pressure management: a randomized trial. Medicine (Balti-more) 2016; 95:e5791.5. Badrov MB, Horton S, Millar PJ, McGowan CL. Cardiovascular stressreactivity tasks successfully predict the hypotensive response of isometrichandgrip training in hypertensives. Psychophysiology 2013; 50:407–414.6. Taylor AC, McCartney N, Kamath MV, Wiley RL. Isometric traininglowers resting blood pressure and modulates autonomic control. MedSci Sports Exerc 2003; 35:251–256.7. Brook RD, Appel LJ, Rubenfire M, Ogedegbe G, Bisognano JD, ElliottWJ, et al. Beyond medications and diet: alternative approaches to  lowering blood pressure: a scientific statement from the American Heart Association. Hypertension 2013; 61:1360–1383.8. Leung AA, Nerenberg K, Daskalopoulou SS, McBrien K, Zarnke KB,Dasgupta K, et al. Hypertension Canada’s 2016 Canadian HypertensionEducation Program Guidelines for blood pressure measurement, diag-nosis, assessment of risk, prevention, and treatment of hypertension.Can J Cardiol 2016; 32:569–588.9. National Heart Foundation Australia. Guideline for the diagnosis and  management of hypertension in adults – 2016. 2016.aSchool of Science and Technology, University of New England, Armidale, New SouthWales, Australia, bCentre for Science andMedicine in Sport and Exercise, University ofGreenwich, ChathamMaritime, Kent, UK and cDepartment of Kinesiology, Universityof Windsor, Windsor, Ontario, CanadaCorrespondence to Neil A. Smart, PhD, School of Science and Technology, University New England, Armidale, New South Wales, Australia. Tel: +61 416176288;fax: +61 267735011; e-mail: nsmart2@une.edu.au

Commentary on Aerobic versus isometric handgrip exercise in hypertension: a randomized controlled trial

Commentary on Aerobic versus isometric handgrip exercise in hypertension: a randomized controlled trial

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