Introduction
Changes in hemodynamic factors, such as blood pressure, rate of pressure product (RPP) and flow mediated dilation (FMD), are the most important cardiovascular changes in old age. Aerobic exercise in the elderly with hypertension reduces systolic and diastolic blood pressures by 11 and 8 mm Hg, respectively [4]. On the other hand, older adults are unable to do long-term aerobic exercises due to low physical strength or chronic diseases. It is possible that resistance training can improve the strength and mass of skeletal muscle, physical performance, and balance and prevent diseases related to aging and be an effective non-pharmacological method in the treatment of hypertension in the elderly [8]. Resistance training can be a supplement to aerobic exercise for the treatment, control or prevention of hypertension [9]. This study aims to investigate the effect of resistance training on some hemodynamic and functional factors in older men.

Methods
This is a quasi-experimental study. The study population included all older men over 65 years of age residing in Kahrizak Nursing Home in Alborz Province, Iran (n=100). Of these, 24 men were selected using convenience and purposive sampling methods and randomly divided into two groups of training (n=12) and control (n=12). They were asked to avoid any sports activity and consuming fatty and salty foods 24 hours before the start of the study. After anthropometric evaluations [17] before and after eight weeks of resistance training, FMD of the brachial artery, timed up & go test (TUG), hand grip strength test using a hand dynamometer, and maximum strength test were performed. Also, on the day of the test, systolic blood pressure, diastolic blood pressure, mean blood pressure (MBP), heart rate and RPP were measured. The resistance training protocol included seven movements for the front arm, back of the arm, front thigh, back of the leg, chest, head, and abdomen [14]. In the first two weeks, participants performed each movement in 4 set of 10 repetitions with an intensity of 45-50 % of one repetition maximum (1RM) for 40 minutes. At the end of each two weeks, 5% of 1RM was added to the training intensity. Independent t-test and paired t-test were used to examine the differences in the baseline and assess within-group changes in the pre-test and post-test stages.

Results
The results of the independent t-test showed no significant difference in the anthropometric characteristics between the two control and training groups at baseline. Within-group comparison by t-test indicated an increase in hand grip strength (P=0.028), a significant decrease in TUG time (P=0.018), a significant decrease in MBP (P=0.033), a significant increase in FMD changes (P=0.019) and a significant decrease in RPP (P=0.032) in the training group after eight weeks of resistance training. Also, the between-group comparison by t-test showed an increase in the hand grip strength (P=0.019), a significant decrease in the TUG time (P=0.032), a significant decrease in MBP (P=0.027), a significant increase in FMD changes (P=0.022) and a significant decrease in RPP (P=0.023) in the training group compared to the control group after eight weeks of resistance training (Table 1).



Conclusion
The results of the present study showed that eight weeks of resistance training led to a decrease in MBP, RPP, TUG time and an increase in FMD and hand grip strength in older men. These results confirm the important role of resistance training in improving the hemodynamic and functional conditions of the elderly. The decrease in vasomotor tonus and increase in parasympathetic activity following resistance training can be possible causes of lower MBP and RPP after resistance training. Also, the increase of mediators such as nitric oxide can have a positive effect on increasing the vagal tone of the training group, which might cause changes in blood pressure. The increase in FMD is probably because of endothelial growth factors, prostaglandins, nitric oxide, adenosine and potassium, which cause a decrease in peripheral vascular resistance [34].

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of the Sport Sciences Research Institute of Iran, Tehran, Iran (Code: IR.SSRI.REC.1397.219).

Funding
This article was extracted from PhD dissertation of Sajad Karami, approved by the Department of Physical Education and Sport Science, School of Physical Education and Sports Sciences, Shahid Rajaee Teacher Training University, Tehran, Iran.

Authors' contributions
All authors equally contributed to preparing this article.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgments
The authors would like to thank the Kahrizak Charity Foundation in Karaj City and all seniors participated in this study for their cooperation.


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