Effects of a single session of isometric handgrip exercise on blood pressure in hypertensive women: a randomized crossover trial

doi:10.21203/rs.3.rs-4069563/v1

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Effects of a single session of isometric handgrip exercise on blood pressure in hypertensive women: a randomized crossover trial

https://doi.org/10.21203/rs.3.rs-4069563/v1

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Background: While there are consistent chronic reductions in blood pressure following an extended period of isometric training, the acute effects exhibit notable variation. These results suggest potential variability in individual responses to exercise, emphasizing the need to investigate whether various factors, such as age, medications, among others, can account for these diverse responses.

Aim: The aims of this study were to analyze acute blood pressure responses after isometric handgrip exercise and to identify factors associated with responsiveness in hypertensive women.

Methods: 18 medicated hypertensive women were randomly allocated to perform two experimental sessions: Handgrip (4[two on each arm] x 2-min set at 30% of their maximal voluntary contraction) or Sham (the same protocol as the handgrip session, but with an anti-stress ball, without any isometric component). Pre-and post-interventions (Post 15’, Post30’, Post45’ and Post60’) resting blood pressure was evaluated. Average and interindividual responses for handgrip session were analyzed, while the linear regression was used to identify factors associated with responsiveness.

Results: No significant changes were observed in systolic and diastolic blood pressure after both the Handgrip and Sham sessions (p>0.05). Interindividual variation was 3.6 mmHg for systolic blood pressure and 1.6 mmHg for diastolic blood pressure. Half of hypertensive women experienced a reduction in systolic blood pressure above 4 mmHg. Age, body mass index, pre-intervention blood pressure, and medications were not found to be predictors of these responses (p>0.05). Conclusion: Isometric handgrip exercise did not reduce blood pressure reduction in hypertensive women, although 50% reduced systolic blood pressure.

Resistance training

Blood pressure

Hypertension

Exercise

Women

Isometric handgrip training has been recommended for prevention and treatment of hypertension by American Heart Association, Exercise and Sports Science Australia [1], Hypertension Canada [2] and the World Hypertension League and European Society of Hypertension [3], as it has been shown to reduce systolic blood pressure by 8 mmHg and diastolic blood pressure by 4 mmHg [4–6].

The chronic effects of training may be the result of cumulative exposure to acute stimuli provided in each training session [7]. Although there are consistent chronic reductions in blood pressure following an extended period of isometric training, the acute effects show notable variation. Some studies indicate reductions [8, 9], while others report the maintenance [10–13] or even increases [14] of blood pressure after a single exercise session. These results suggest potential variability in individual responses to exercise [15, 16], emphasizing the need to investigate whether various factors, such as age, medications, among others, can account for these diverse responses.

In addition, we were unable to find any studies investigating the effects of a typical isometric handgrip exercise session on blood pressure in exclusively in hypertensive women. Consequently, there is a need for further research to fill this knowledge gaps. Thus, the aims of this study were to analyze acute blood pressure responses after isometric handgrip exercise and to identify factors associated with responsiveness in hypertensive women.

Trial design and ethical

This study is a randomized crossover trial that follows the CONSORT (Consolidated Standards of Reporting Trials) checklist [17]. We included hypertensive women who were assigned to two experimental sessions (handgrip and sham) in a 1:1 allocation ratio. There was a washout period of at least 48 hours between the sessions. All participants gave written informed consent to participate in the study, which was approved by the institutional review board, in compliance with the Brazilian National Research Ethics System Guidelines.

Participants, settings, and location

Participants were recruited through local community announcements and media releases. Inclusion criteria were as follows: i) diagnosis of hypertension controlled by up to three antihypertensive drugs, ii) women age over 18 y.o., ii) no medical history of high cardiovascular risk (i.e., signs or symptoms and/or cardiovascular, metabolic, renal, or pulmonary disease) [18], iii) do not participate in an exercise program for at least six months, and iv) non-smokers.

Randomization and Allocation

Simple randomization was used in this study. A researcher not directly involved in recruitment or data collection using an open, web-based system (https://www.randomizer.org) generated the codes. In addition, the allocation information was concealed from the researchers performing the measurements.

Pre-experimental procedures

Participants provided demographic data, medical history, and details of their medication use. Height and weight were measured using standardized protocols, and the body mass index was calculated. Resting blood pressure was measured using an automated blood pressure monitor (HEM- 742, Omro Healthcare, Japan) after participants were seated for at least 10 minutes. Consecutive measurements were taken one minute apart on the right arm, until a difference of less than 4 mmHg was reached between two measurements. The value used was the mean of the last two measurements, as recommended by the Brazilian Guidelines of Hypertension [19].

Experimental Design

The experimental sessions were divided into three periods: pre-intervention, intervention, and post-intervention. All participants were instructed to maintain their sleep pattern, not to perform physical exercise or consume beverages containing caffeine and/or alcohol at least 24 hours before each session. In the pre-intervention period, following 10 minutes of rest, resting blood pressure was measured using the same protocol as pre-experimental procedures, however in supine position. During the intervention period, participants performed one of the experimental sessions (handgrip and sham) in random order. In the post-intervention period, participants rested in a supine position for 60 minutes, and resting blood pressure was measured every 15 minutes using following the same procedures as already described.

Experimental sessions

Handgrip session. All participants were previously familiarized with the handgrip (Zona Health, Boise, USA). The volunteers performed the sessions while seated, maintaining their elbows flexed at a 90° angle, with their arms neither resting on their bodies nor on the chair. They were also instructed beforehand to maintain normal breathing, avoid performing the Valsalva maneuver, during the procedure, and to follow the exercise guidance provided during the sessions. Four sets (two on each arm) of two minutes isometric contractions were performed at 30% of the maximum voluntary contraction with a one-minute rest interval between sets. The 30% contraction intensity was automatically determined by the handgrip equipment, based on each participants’ individualized strength level at the beginning of the session.

Sham session.The sham session followed the same protocol as the handgrip session (4 sets, two in each hand, of 2 minutes exercise), However, in this case, no isometric contraction was involved. Participants were guided to maintain continuous, gentle squeezing and releasing of a foam anti-stress ball, which was used to simulate the exercise.

Statistical analyses

Normality and homogeneity of variance of data were conﬁrmed by Shapiro-Wilk and Levene tests, respectively. Paired t-test was used to compare blood pressure at the pre-intervention period. Two-way analysis of variance for repeated measures was employed, with factors including session (Handgrip and Sham) and Time (Pre, Post 15’, Post 30’, Post 45’ and Post 60’) to compare the effects of the experimental sessions for both resting systolic and diastolic blood pressure. Sphericity was tested using Mauchly’s test.

The individual variation of blood pressure responses were calculated by the standard deviation (SD) of the individual responses (SD_ir) as previously reported [20]. SD_ir represents the true magnitude of the interindividual variation of blood pressure responses adjusted for the random variations derived from biological and measurement sources, being calculated by the formula: SD_ir = √(SD²_handgrip – SD²_sham), where SD_handgrip and SD_sham are the SDs of blood pressure responses (i.e., the difference between blood pressure measured pre-intervention and lower post-intervention value) observed in the handgrip and the sham sessions. Patients who reduced their blood pressure by ≥ 4 mmHg were considered responder.

Linear regression was used to identify factors associated with greater net-effect in the post-intervention period [(lower post-intervention blood pressure value in the handgrip session – pre-intervention blood pressure in the handgrip session) – (lower post-intervention blood pressure in the sham session – pre-intervention blood pressure in the sham session)]. To this, the age, medications, body mass index and pre-intervention blood pressure of hypertensive women were tested. The Statistical Package for the Social Sciences was used for the analysis. A p value of <0.05 was used to establish statistical signiﬁcance. Data are presented as mean ± SD and frequency.

As data collections started between May 2019 and March 2020, due to the COVID-19 pandemic, the collections were suspended and resumed in January 2021, concluding in May 2022. The study ﬂowchart is shown in Figure 1. In total, 18 hypertensive women completed the experimental sessions. There were no adverse effects, and all participants completed both experimental sessions. The women's age was 55 ± 9 yrs, body mass index was 29.8±5.4 kg/m² and systolic blood pressure was 129 ± 18 mmHg and diastolic was 77 ± 8. The most used medication was angiotensin receptor blockers (77.8%).

Pre-intervention resting blood pressure values were similar between the handgrip and sham sessions (Systolic: handgrip – 123 ± 15 mmHg vs. sham – 120 ± 11 mmHg, p=0.159; Diastolic: handgrip – 75 ± 7 mmHg vs. sham – 74 ± 7, p=0.337). The resting blood pressure responses to the experimental sessions are presented in Figure 2. There were no significant Session vs. Time interaction effects for systolic blood pressure (Handgrip: Pre: 123±15 mmHg; Post 15’: 123±14 mmHg; Post 30’: 126±15 mmHg; Post 45’: 126±17 mmHg; Post 60’: 127±19 mmHg vs. Sham: Pre: 120±11 mmHg; Post 15’: 121±14 mmHg; Post 30’: 123±14 mmHg; Post 45’: 124±17 mmHg; Post 60’: 125±18 mmHg, η²=0.014) and diastolic blood pressure (Handgrip: Pre: 75±7 mmHg; Post15’: 76±7 mmHg; Post 30’: 77±8 mmHg; Post 45’: 77±9 mmHg; Post 60’: 77±9 mmHg. vs. Sham: Pre: 74±6 mmHg; Post 15’: 74±7 mmHg; Post 30’: 74±8 mmHg; Post 45’: 75±8 mmHg; Post 60’: 75±8 mmHg, η²=0.011).

The interindividual variation of systolic blood pressure was 3.7 mmHg, whereas for diastolic blood pressure was 1.6 mmHg. Among hypertensive women, 50% were responders for systolic blood pressure, considering the greater net-effect in the post-intervention period (Figure 3). No factor was associated with individual net-effect in the post-intervention (p>0.05 for all).

The current study yielded three main findings: i) isometric handgrip exercise did not reduce blood pressure in hypertensive women; ii) there is an important interindividual variation in the magnitude of acute blood pressure responses to exercise; and iii) no clinical factors were associated with responsiveness to isometric handgrip exercise.

The lack of the acute reductions of blood pressure observed in the present study agrees with some studies in the literature [10–13], but contrasts with two studies that have observed a reduction in blood pressure in medicated hypertensive patients and in hypertensive/pre-hypertensives patients. The low baseline values of blood pressure observed in our sample (≅ 129/77 mmHg) may account for the lack of observed effects, as previous studies on acute reductions in blood pressure following isometric exercise included samples with baseline blood pressure values of 134/84 mmHg [8] and 135/77 mmHg [9]. In fact, acute changes in blood pressure have been suggested to be associated with baseline blood pressure levels following aerobic exercise and dynamic resistance exercises in hypertensives [21].

As hypothesized, we observed an important variability in the individual responses to an acute session of isometric exercise, with 50% hypertensive women presenting clinically relevant reductions in systolic blood pressure. In practical terms, this data indicates that one in every two hypertensive women with controlled blood pressure obtain beneficial acute effects of isometric exercise. These values are higher than those reported by Silva et al. [10] (25% for systolic and 33% for diastolic blood pressure) and by Carpes et al. [22] that found rates of 22% for systolic and 44% for diastolic ambulatory blood pressure responsiveness after a single session of isometric handgrip exercise.

In contrast to the studies by Silva and Carpes, we analyzed interindividual responses to isometric handgrip exercise while taking into consideration the interindividual responses to the sham session, as recommended [20]. This approach may help explain the differences observed between the present study and others. It has been proposed that a true interindividual variation in physiological responses to exercise can only be accepted if the variations in the changes under exercise conditions are larger than those obtained in a control condition [20, 23]. We observed a low SD_ir for diastolic blood pressure (1.6 mmHg), suggesting that the true variation in diastolic blood pressure induced by isometric handgrip exercise may have little clinical significance. However, for systolic blood pressure, the true variation was 3.6 mmHg, which has been demonstrated to be a protective factor against ischemic heart disease and stroke [24].

Age, pre-intervention blood pressure, body mass index, and medication were not associated with responsiveness to a session of isometric handgrip exercise in hypertensive women. Silva et al. [10] observed that obese hypertensive individuals were more responsive to isometric handgrip exercise, however, they did not analyzed the true interindividual variation before assessment of the factors associated with responsiveness [20, 23], which may explain the differences between studies. Future studies could investigate other clinical factors that could be predictors of responsiveness to isometric handgrip exercise.

Limitations of this study involves the homogeneous small sample size. Autonomic and vascular measurements were not collected, which limits our ability to fully understand the mechanisms associated with blood pressure responses following an isometric handgrip exercise session. Finally, generalizability of results to other populations (men, advanced hypertension, or clinical other populations) should be performed with caution.

Isometric handgrip exercise did not reduce blood pressure among hypertensive women. However, it is worth noting that half of the women did experience a reduction in systolic their blood pressure above 4 mmHg. Age, pre-intervention blood pressure, body mass index, and medication were not found to be predictors of acute responses to isometric handgrip exercise in hypertensive women.

Acknowledgments: Supported by grants from “Conselho Nacional de Desenvolvimento Cientíﬁco e Tecnológico – CNPQ” (#409077/2018-6) and “Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – CAPES.”

Data Availability: The data associated with this manuscript is available from the corresponding author upon reasonable request.

Conflict of interest: The authors have no competing interests to declare that are relevant to the content of this article.

Human and Animal Rights: This study was approved by the ethics committee of our university and conformed to the tenets of the 1964 Declaration of Helsinki and its later amendments.

Informed consent: The experimental procedures, study design, and possible risks were explained, and the participants signed an informed consent form.

Author Contribution

Conception and design of the research: Farah, BQ, Barros, RLM. Acquisition of data: Barros, RLM, Santana, MO, Silva, JMF. Analysis and interpretation of the data: Barros, RLM, Farah, BQ, Ritti-Dias, RM, Kanegusuku, H. Correia, MAC. Obtaining financing: Farah, BQ. Writing of the manuscript: Barros, RLM. Critical revision of the manuscript for intellectual content: All authors

Sources of support: This study was also supported by ‘Coordenação de Aperfeiçoamento de Pessoal de Nível Superior’ and ‘Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPQ) (#409077/2018-6). MSO and JMFS received a research fellowship granted ‘Fundação de Amparo à Ciência e Tecnologia do Estado de Pernambuco’. RMRD received a research fellowship granted CNPQ.

Conflict of interest: The authors have no conflicts of interest relevant to this article to disclose.

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Effects of a single session of isometric handgrip exercise on blood pressure in hypertensive women: a randomized crossover trial

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