Influence of age and gender on cardiovascular response to isometric exercise in apparently healthy individuals

Introduction

Exercise, as defined by Awopetu (2014), is activity which requires physical effort and is conducted with the intention of sustaining or improving health and fitness. It is a form of self-induced stress to the body, capable of leading to changes in the cardiovascular and respiratory systems (Aldajah & Hariraja, 2015). It also impacts the metabolic system by leading to an increase in metabolic demand (Bhavsar et al., 2015). The magnitude of this change however depends on the type of exercise (for example, either static/isometric or dynamic/isotonic) being carried out. According to the literature, pure static contractions are observed only with in vitro models, however, isometric or static contraction has been described as a sustained muscle contraction (increase in tension) with no change in length of the involved muscle group (Mitchell & Wildenthal, 1974). Static or isometric exercise is an important therapeutic exercise modality employed by physiotherapists in patients’ management, particularly in advanced strength and endurance training exercise programmes (Aldajah & Hariraja, 2015). It is quite different from isotonic or dynamic exercises, where there is a change in the muscle length with tension remaining the same (Clark, 2010). Hand grip exercise (HGE) is one of the most widely studied isometric training protocols with varying number of contractions and degrees of maximal isometric voluntary contraction (MIVC) or an equivalent electromyographic value (Ray & Carrasco, 2000; Wiles et al., 2010; Badrov et al., 2013).

Previous studies have confirmed the effects of isometric exercise on the cardiovascular system, and that the larger the muscle groups involved in the isometric exercise, the greater the resultant effect on the cardiovascular parameters (Mbada et al., 2007; Srikanth et al., 2013; Thimmaraju & Anandarao, 2014). Furthermore, Maan et al. (2014) stated that the intensity of the isometric exercise and the number of the muscles recruited for the exercise also affect the influence of isometric exercise, and that it may lead to increased metabolic demands of the exercising muscle, with consequent changes in the circulatory and respiratory system. The sympathetic system has been found to be responsible for these changes leading to increased cardiac output which results in raised heart rate and systolic blood pressure as well as increased peripheral resistance, which results in raised diastolic blood pressure (Muthusamy et al., 2015). Following this disproportionate rise in HR, SBP and DBP, a significant pressure load is imposed on the heart which is presumed to increase perfusion to the contracting muscles (Maan et al., 2014).

There are reports of an association between aging and the cardiovascular system in the literature with subsequent alterations in cardiovascular physiology. The changes occurring with age differ from person to person with varying rates. The changes associated with aging in the cardiovascular system include a decrease in elasticity and an increase in stiffness of the arterial system (North & Sinclair 2012; Maan et al., 2014). This leads to increased afterload on the left ventricle, an increase in systolic BP (SBP), left ventricular hypertrophy, and other changes in the left ventricular wall that prolong relaxation of the left ventricle in diastole. Although resistance exercise is part of the overall fitness programme designed for healthy older adults, an understanding of the effects of age and gender on cardiovascular response is crucial, prior to prescription of static exercise in a patient’s rehabilitation. Age has been reported as the most important determinant of cardiovascular health (North & Sinclair, 2012). Advancing age has been shown to have a significant effect on the heart and arterial system, which may lead to increase in the susceptibility to cardiovascular disease including hypertension, atherosclerosis, myocardial infarction and stroke (Lakatta & Levy, 2003). Similarly, sex differences have also been identified in cardiovascular health. Researchers have opined that cardiovascular disease is widely considered as a man’s disease and mortality from coronary heart disease and stroke remains higher among men than women until old age (Mosca et al., 2011; Bots et al., 2017).

Although a number of studies have been conducted on isometric exercise (Mbada et al., 2007; Bhavsar et al., 2015; Rajasekhar et al., 2015; Akintomide et al., 2016), a study on the influence of age and sex on the cardiovascular response of apparently healthy adults has not been fully studied in Nigeria. A study of this kind may provide adequate information on the effects of age and gender on the cardiovascular response to isometric exercise, and consequently enhance the rehabilitation, particularly patients with cardiovascular diseases. This study was therefore designed to determine the effect of age and sex on cardiovascular response to isometric exercise, using hand held dynamometer (HHD) at 30% MIVC.

Methodology

Participants

This cross-sectional analytical study involved 60 apparently healthy participants (30 males and 30 females). The participants were students and staff of a Federal University and Teaching Hospital in Nigeria. The study included apparently healthy individuals who are between 21 and 50 years old. Individuals with history of cardiovascular (heart) disease, hypertension, diabetes mellitus, and deformity or weakness (paralysis) of the upper limb were excluded from this study. Participants were selected using consecutive sampling and screened for eligibility based on the inclusion criteria. The participants were grouped into 3 groups (21–30 years, 31–40 years and 41–50 years). Each group consisted of 20 participants with 10 males and 10 females.

Ethical consideration

Prior to the commencement of this study, ethical approval was sought for and obtained from the Health Research and Ethics Committee of the Lagos University Teaching Hospital, Lagos state. Informed written consent was obtained from participants prior to the commencement of the study.

Instrumentation

A hand-held dynamometer (HHD) was used to carry out the static exercise, Sphygmomanometer (Honbrand Med, Germany) and a stethoscope (Wenzhous Kangju, China) were used to measure the blood pressure, a stop watch was used while counting the pulse rate of the participant. A portable weighing scale (Hana, China) graduated in kilograms with a maximum capacity of 120 kilograms was used to measure the participants’ weight. A vertical scale made of steel and calibrated in inches and meters with a moveable wooden pointer attached which indicates the height of an individual was used to measure the height of the participants.

Research procedure

The procedure for the data collection was explained to the participants. Participants’ weight and height were measured using the weighing scale and height-meter respectively. Thereafter, participants’ cardiovascular parameters (SBP, DBP and HR) were measured and recorded in a sitting position. The blood pressure measurement, (for example, SBP and DBP) were obtained at the brachial artery from the arm not being used for contraction (for example, non-dominant arm). While heart rate measurement was obtained at radial artery of the arm not being used for contraction. Blood pressure and heart rate measurement were obtained during each of the sustained exercise protocols (for example, 1-minute, 2-minutes and 3-minutes).

Prior to the isometric exercise protocol, maximal isometric voluntary contraction (MIVC) was determined from the participant’s best single voluntary contractions of three trials. 30% of the MIVC was employed in this study (that is, sub maximal exercise) for isometric contraction, using the protocol described by Ray and Carrasco (2000). To obtain the 30% of MIVC, the maximal contraction of the participants was multiplied by 30% (0.3) (for example, dynamometer peak value for each participant × 30/100).

Data analysis

The data obtained were analysed using SPSS, version 20. Data was normally distributed following Shapiro Wilk Test for normality of data. Data was summarised using descriptive statistics of mean, standard deviation, frequency, percentages and charts. Independent t-test was used to compare the data of males and female participants while analysis of variance was used to compare the data across the 3 groups and 4 stages of assessment (rest, 1 min, 2 mins, and 3 mins). Level of significance was set at p <0.05.

Table 1: Demographic characteristics of the participants.

*Significance: p <0.05.

Table 2: Participants cardiovascular response to isometric exercise at rest and 3 exercise durations.

*Significance at p <0.05.

HR = heart rate; SBP = Systolic blood pressure; DBP = Diastolic blood pressure.

See Figure 1: Systolic blood pressure (SBP) and diastolic blood pressure (DBP) of the participants across the 3 groups.

SBP = Systolic blood pressure (mmHg); DBP = Diastolic blood pressure (mmHg).

See Figure 2: Heat rate (HR) response of the male and female of the participants across the groups.

See Figure 3: Change in cardiovascular response from rest to the end of 1 min, 2 mins and 3 mins of contraction.

Results

This study involved 60 participants. Each of the three age groups consisted of 10 males and 10 females. As expected, a statistically significant difference (p <0.05) was observed in the mean age across the three the groups but no statistically significant difference (p >0.05) was noted in the body mass index (BMI) (Table 1).

There was a statistically significant increase (p <0.05) in the mean SBP, DBP and HR with increase in duration of static handgrip contraction from 1 minute to 3 minutes in the three groups, except HR for group one, that is, 21–30 years (Table 2).

Following independent t-test, there was no gender difference (p >0.05) in SBP and DBP of the participants within the three groups, although males, particularly in group 2 had higher SBP (Figure 1). Also, for participants in group 2, there was a statistically significant increase in the HR of female participants compared to males (Figure 2). Figure 3 showed that isometric contraction for 3 minutes produced the greatest change (increase) in cardiovascular parameter across all the groups but this is more marked among participants in group 2, that is, 31–40 years.

Discussion

This study was carried out to evaluate the changes in cardiovascular response to static exercise across different age groups and gender. It sought to evaluate the systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) responses in male and female. Static exercise is considered to be an isometric contraction based on the fact it causes increase in intramuscular tension without a change in muscle length (Gabriel, 2000; Gabriel et al., 2006).

The cardiovascular parameters increased in all the three group among both males and females following 3 minutes of sustained static exercise. The finding that there was a significant increase in the cardiovascular parameters after the isometric exercise is corroborated by the finding of earlier studies by Krzeminski et al. (2012), Akintomide et al. (2016) and Muthusamy et al. (2015). Increased systolic blood pressure often arises from the increased cardiac output which accompanies increasing rates of work in order to improve blood flow to the contracting muscles (Bhavsar et al., 2015). The increased cardiac output may stem from the activation of sympathetic adrenergic system, which was indicated by an increase in the plasma catecholamine level (Krzeminski et al., 2012). This rise in cardiovascular parameters, particularly for SBP were more marked in the males than females, for participants in group 2. This finding is consistent with the trend in the literature, and it agrees with the finding of Thimmaraju and Anandarao (2014), who in a study exploring the gender differences in cardiovascular response in apparently healthy individuals to upper limb isometric exercises, reported a highly significant increase in post exercise HR, SBP, DBP and RPP in males compared to females. Muthusamy et al. (2015) reported that the plasma levels of all three catecholamines are higher in males compared to the females. Although among the older population, females showed slightly higher SBP. However, it was observed that HR was higher among females compared to males particularly in group 2. This finding is also consistent with the literature as it has been established that women generally have higher heart rates than men (Prabhavathi et al., 2014); the reported gender difference in heart rate may be accounted for by the size of the heart, which is typically reported in females than males. Because of this small size of the heart, less blood is pumped in each minute, therefore the heart needs to beat at a faster rate to meets its demands.

The finding of this study also showed that cardiovascular parameters were highest in group 3 (which comprised the older population) at rest and throughout the exercise. Literature has established that cardiovascular parameters increase with increasing age (Pollock et al., 2000; Mann et al., 2014). The significant difference noted in blood pressure at the 1 and 3 minute/s durations, when the age groups were compared, agreed with the report of Mann et al. (2014) and has been suggested to be due to the increased stiffness and decreased elasticity of arterial tree that have reported at older age (Pollock et al., 2000). Furthermore, static contraction sustained for 3 minutes produced the highest increase in cardiovascular parameters. The fact that isometric exercises narrow the blood vessels, raising the total peripheral resistance may lead to increase pressure load on the heart, resulting in increased cardiovascular response. This knowledge may be useful in the management of the elderly and patients with cardiovascular disease. These categories of individuals may benefit more when they are gradually exposed to sub maximum isometric training in supervised cardiac rehabilitation programmes.

Conclusion and recommendation

The result of this study revealed that submaximal (30% MIVC) isometric upper limb exercise elicited increase in blood pressure and heart rate in both males and females and this was greatest when the exercise was sustained for 3 minutes. Hence, it is recommended that health care professionals, fitness instructors as well as coaches should measure the blood pressure before isometric exercise in order to prescribe safe level of exercise as prolonged isometric exercise further increases cardiovascular parameters.

Limitation of the study

The study sample size was 60 apparently healthy individuals, in the age group of 21–50 years. This may be a potential limitation. So, further study may be required using a larger sample, for more generalisable results.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Conflict of interest

There is no potential conflict of interest associated with this study.

Acknowledgement

The authors acknowledged those consented to participant in this study.

Akintomide, A. O., Asafa, M. A., Omole, J. G., Ogunlade, O., Ayoka, A. O. (2016). Sex differences in cardiovascular response to handgrip exercise among apparently healthy young adult nigerians. Journal of Cardiology & Current Research, 7(2), 00244. https://doi.org/10.15406/jccr.2016.07.00244.

Aldajah, S., & Hariraja, M. (2015). Effects of back and respiratory muscle exercise on posture and respiratory function in elderly patients with osteoporosis. International Journal of Therapy and Rehabilitation, 22(5), 233–237.

Awopetu, A. R. (2014). A review of the physiological effects of exercise duration and intensity during walking and jogging. Journal of Emerging Trends in Educational Research and Policy Studies, 5(6), 660–667.

Badrov, M. B., Bartol, C. L., DiBartolomeo, M. A., Millar, P. J., McNevin, N. H., & McGowan, C. L. (2013). Effects of isometric handgrip training dose on resting blood pressure and resistance vessel endothelial function in normotensive women. European Journal of Applied Physiology, 113(8), 2091–2100. https://doi.org/10.1007/s00421-013-2644-5.

Bhavsar, S. D., Afroz, S., Abhange, R. S. (2015). Evaluation of gender variation in response to isometric exercise in normal adolescents. International Journal of Dental and Medical Sciences, 14(5), 69–73.

Bots, S. H., Peters, S. A. E., & Woodward, M. (2017). Sex differences in coronary heart disease and stroke mortality: A global assessment of the effect of ageing between 1980 and 2010. BMJ Global Health, 2. https://doi.org/10.1136/bmjgh-2017-000298.

Clark J. E. (2010). Examining matched acute physiological responses to various modes of exercise in individuals who are overweight. Journal of Strength and Conditioning Research, 24(8), 2239–2248. https://doi.org/10.1519/JSC.0b013e3181ce245c.

Gabriel D. A. (2000). Reliability of SEMG spike parameters during concentric contractions. Electromyography and Clinical Neurophysiology, 40(7), 423–430.

Gabriel, D. A., Kamen, G., & Frost, G. (2006). Neural adaptations to resistive exercise: Mechanisms and recommendations for training practices. Sports Medicine (Auckland, N.Z.), 36(2), 133–149. https://doi.org/10.2165/00007256-200636020-00004.

Krzeminski, K., Cybulski, G., Ziemba, A., & Nazar, K. (2012). Cardiovascular and hormonal responses to static handgrip in young and older healthy men. European Journal of Applied Physiology, 112(4), 1315–1325. https://doi.org/10.1007/s00421-011-2069-y.

Lakatta, E. G., & Levy, D. (2003). Arterial and cardiac aging: major shareholders in cardiovascular disease enterprises: Part I: aging arteries: A ‘set up’ for vascular disease. Circulation, 107(1), 139–146. https://doi.org/10.1161/01.cir.0000048892.83521.58.

Maan, R., Gupta, V., & Badyal, H. (2014). Effect of age on acute cardiovascular responses to isometric handgrip exerciser. International Journal of Medical Science and Public Health, 3(8), 935–939.

Mbada, C. E., Akinwande, O. A., Babalola, J. F., Seyi-Adeyemo, O. R., Odejide, A. S. (2007). Gender differences in cardiovascular response to upper extremities exercises in normotensive subjects. Nigerian Journal of Medical Rehabilitation, 12(20), 30–34.

Mitchell, J. H., & Wildenthal, K. (1974). Static (isometric) exercise and the heart: Physiological and clinical considerations. Annual Review of Medicine, 25, 369–381. https://doi.org/10.1146/annurev.me.25.020174.002101.

Mosca, L., Barrett-Connor, E., & Wenger, N. K. (2011). Sex/gender differences in cardiovascular disease prevention: What a difference a decade makes. Circulation, 124(19), 2145–2154. https://doi.org/10.1161/CIRCULATIONAHA.110.968792.

Muthusamy, H., Aldajah, S., Ramar, S., Omoush, A. (2015). Comparison of cardiovascular response between men and women to isometric exercise of lower limb. International Journal of Health and Rehabilitation Sciences, 4(3), 193–200.

North, B.J., & Sinclair, D.A. (2012). The intersection between aging and cardiovascular disease. Circulation Research, 110(8), 1097–1108.

Pollock, M. L., Franklin, B. A., Balady, G. J., Chaitman, B. L., Fleg, J. L., Fletcher, B., Limacher, M., Piña, I. L., Stein, R. A., Williams, M., & Bazzarre, T. (2000). AHA Science Advisory. Resistance exercise in individuals with and without cardiovascular disease: Benefits, rationale, safety, and prescription: An advisory from the Committee on Exercise, Rehabilitation, and Prevention, Council on Clinical Cardiology, American Heart Association; Position paper endorsed by the American College of Sports Medicine. Circulation, 101(7), 828–833. https://doi.org/10.1161/01.cir.101.7.828.

Prabhavathi, K., Selvi, K. T., Poornima, K. N., & Sarvanan, A. (2014). Role of biological sex in normal cardiac function and in its disease outcome – a review. Journal of Clinical and Diagnostic Research, 8(8), BE01–BE4. https://doi.org/10.7860/JCDR/2014/9635.4771.

Rajasekhar, P., Veena, C. N., & Hemasankar, C. (2015). Gender differences in the cardiovascular autonomic response during isometric handgrip exercise. Journal of Evidence Based Medicine and Healthcare, 2(37), 5854–5858.

Ray, C. A., & Carrasco, D. I. (2000). Isometric handgrip training reduces arterial pressure at rest without changes in sympathetic nerve activity. American Journal of Physiology, Heart and Circulatory Physiology, 279(1), H245–H249. https://doi.org/10.1152/ajpheart.2000.279.1.H245.

Srikanth, S., NagaTeja, D., & Pragathi, B. H. (2013). Gender differences in cardiovascular responses to isometric exercise. Indian Journal of Research and Reports in Medical Sciences, 3(4), 24–27.

Wiles, J. D., Coleman, D. A., & Swaine, I. L. (2010). The effects of performing isometric training at two exercise intensities in healthy young males. European Journal of Applied Physiology, 108(3), 419–428. https://doi.org/10.1007/s00421-009-1025-6.