Introduction
One of the critical stages of human life is the old age [1]. People face declined physiological and psycho-social functions as they get older [6]. Physical inactivity is a big threat to the health of older people, because it makes them susceptible to diseases [5]. Exercise is an important method for dealing with this threat, which can improve the quality of life of older adults at the same time. It is necessary to pay attention to physical activity of older adults. This study aims to investigate factors affecting physical activity of the older adults in Iran.

Methods
This is a meta-analysis and systematic review study. The descriptive studies (survey or correlational) conducted in Iran (in Persian or English) assessing the factors affecting the exercise and physical activity of older adults in Iran were reviewed. A search was conducted in SID, MagIran, Noormagazs, website of National Library of Iran, and Google Scholar databases using the determined keywords for related studies published from 2011 to 2021. A total of 17 articles were finally selected. To extract information from each study, a checklist was used. Also, to assess the risk of bias, the observational study quality evaluation checklist was used. In this checklist, titles and abstracts, introduction and texts, methods, participants, objectives, sample size, allocation of participants, implementation method, statistical methods, sampling method, primary data, consequences and Estimates, quantitative analyses, explanations, interpretations, and generalizability were evaluated. To analyze the studies, the effect size for each study, the mixed effect size with two fixed- and random-effects models, funnel plot, sensitivity analysis, homogeneity test, I2 statistic and the failsafe statistic (FS-N) were used.

Results
The most of effect sizes, except for the effect size of group No.9, were significant. the biggest significant effect size was 0.930 ([26], communication factor) while the smallest significant effect size was 0.062 ([27], motivation factor). After entering 73 initial effect sizes in the meta-analysis process, the mixed effect size of the factors affecting exercise and physical activity of the elderly was r=0.528 in the fixed-effects model and r=0.532 in the random-effects model, and the values of both models were statistically significant (P<0.05). After checking the funnel plot, Egger’s and Begg’s tests were used to check its accuracy. Also, the value FS-N after sensitivity analysis was obtained 5446 using Rosenthal's method and 274 using Orwin's method, which are very favorable values. After ensuring the absence of publication bias, to determine the final meta-analysis model, a set of heterogeneity analyses was conducted. Based on the results, the Q index value was 3254.342, which was statistically significant. This indicates that there is a real difference between the effect sizes of the studies. Also, the value of I2 was 97.788, indicating that 97% of the distribution in the results of the primary research was real. 
The difference in summary effect sizes between variables of motivation, interpersonal factors, economic factors, individual factors, sociocultural factors, and environmental factors caused heterogeneity to some extent. The total heterogeneity value was 294.2014 where the environmental factors caused the highest heterogeneity. As a result, it can be said that there was a difference between the sizes of the reported effects. The biggest effect size was related to sociocultural factors (r=0.622) followed by individual factors, motivation, environmental factors, economic factors, and interpersonal factors.

Conclusion
In general, the meta-analysis of the studies reported the factors affecting the exercise and physical activity of the elderly in Iran showed that the most of them reported sociocultural, individual, motivational, environmental, economic, and interpersonal factors that can predict sports and physical activity of the elderly. The effect sizes of these factors are different; the biggest effect size was related to sociocultural factors (0.622), and the smallest effect size was related to interpersonal factors (0.431). Hence, it is not possible to increase the exercise and physical activity of the elderly by emphasizing only one of these factors. Policymakers and the planners should use the networking strategy for these factors to increase the exercise and physical activity of the elderly in Iran.

Ethical Considerations

Compliance with ethical guidelines
This study was approved by the Ethics Committee of Sport Sciences Research of Iran Ministry of Sciences, Research & Technology (Code: IR.SSRI. REC1401.1776).

Funding
This study was extracted from PhD dissertation of Leila Esmi, approved by Department of Physical Education and Sport Science, Faculty of Sport Management, Islamic Azad University, South Tehran Branch, and was funded by Islamic Azad University, South Tehran Branch.

Authors' contributions
The authors equally contributed to preparing this paper.

Conflicts of interest
The authors declared no conflict of interest.