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The effect of motivational interviewing-based intervention using self-determination theory on promotion of physical activity among women in reproductive age: A randomized clinical trial

Background Physical activity (PA) prevents chronic diseases. Self-determination theory (SDT) provides a useful framework to understand the nature of motivational interviewing (MI). Objective This study aimed to determine the effect of MI-based intervention using SDT on the promotion of PA among women in reproductive age. Methods Seventy women in reproductive age were selected by clustering sampling method for this randomized controlled trial. The questionnaire included the variables of physical fitness test, SDT, and global physical activity questionnaire (GPAQ). The validity of the questionnaires was approved using content validity ratio (CVR) and index (CVI). The reliability and internal consistency of the questionnaires and measures was approved using test-retest method and Cronbach’s alpha test, respectively. The intervention group (n=35) received four MI sessions through theory and one standard education session about PA. The control group (n=35) received a standard education session about PA. Results Four months after the intervention, an increase in the mean scores of total PA (p<0.001, ES=4.77), physical fitness tests including flexibility (p<0.001, ES=1.59), muscular endurance (p<0.001, ES=2.0), cardiorespiratory endurance (p<0.001, ES=0.51), and a decrease in mean scores of agility test (p<0.001, ES= − 0.51) and sedentary behavior (p<0.01, ES=− 0.74) was observed in the intervention group compared to the control group. The intervention group reported an increase in the scores of intrinsic motivation (p<0.001, ES=3.34), identified regulation (p<0.001, ES= 1.28), perceptions of competence (p<0.001, ES=0.81) and autonomy (p<0.001, ES=2.01), enjoyment (p<0.001, ES=0.98) and health motives (p<0.01, ES=0.19), health care climate (p<0.001, ES=4.6), and a decreased score of external regulation (p<0.01, ES=−0.55) and amotivation (p<0.01, ES= −0.56) over time, compared to the control group. Conclusion MI-based intervention using SDT was effective on the promotion of PA. Trial registration The Trial was registered at the Iranian Registry of Clinical Trial (http://www.irct.ir) with the Irct ID: IRCT2015101924592N1.


Cardiorespiratory endurance test
To assess cardiorespiratory endurance, maximal oxygen uptake was measured. For this purpose, Quinn step test was used, which is a physiologic index, to measure PA. In this test, the subject is required to step up and down on a 41cm step for 3 minutes. Rhythm per minute for women is 22 beats per minute. Immediately after completion of the activity, the subjects sit and their heart rate is counted for 15 seconds from 5 seconds to 20. Validity and reliability of the test has been proven in various studies (40)(41)(42). Maximal oxygen uptake was calculated using the following formula: [(4 × heart rate) × 0.1847]-65.81=Maximal oxygen uptake

Selection criteria
The Inclusion criteria were women aged between 15-49 years, married, willing to attend regular training sessions and the women having the least ability to read and write. Women with the mentioned characteristics and those with PA less than regular level (according to the categorization of GPAQ questionnaire) participated in the study. The Exclusion criteria were pregnant women, patients with major diseases and orthopedic problems and lack of adherence to the intervention program.

Interventions
In this study, the independent variable was MI, which was done in groups. Miller and Rollnik believe that since many effective intervention strategies are better offered in groups in health centers, the implementation of MI in groups has a better clinical justification (13). Therefore, in this study, the samples were divided into groups including 10-12 individuals. Before starting the MI sessions, a public training session was held about the generalities of regular PA (types and amounts), and the benefits of regular PA were mentioned for the intervention and control groups; at the end of the session, a training pamphlet including session summary was given to group members. An educational program was held in 4 sessions of MI with 90 minutes per session for the intervention group (43). Educational sessions were held at an urban health center. Before the sessions, the necessary arrangements were made with group members. At the beginning of each session, the researcher checked the present-absent participants and at the end of each session, the exact time of the next session was mentioned. Available studies and instructions in theses and articles were used in designing the training program sessions (Table1) (43, 44).

Outcomes
The primary outcome of our analysis was the rate of self-determination theory components. Also, the secondary outcome from the analysis was the effectiveness of self-determination theory components on PA and physical fitness.

Sample size
The sample size was estimated to be 70 women. It was calculated based on the results of previous studies (45) by considering α=5%, the statistical power of 80%. Considering drop up sample, we added 10 samples to the calculated sample size, so we considered 70 samples totally.

Statistical methods
The first assessment or pre-test was performed before starting the intervention, using subjective and objective instruments. The second assessment or post-test was performed immediately after finishing the intervention just using subjective instruments; the final assessment or follow-up was performed four months after finishing the intervention using subjective and objective instruments. SPSS version 16 (SPSS Inc., Chicago, Illinois, USA) was used to analyze the data. The two-tail value of p<0.05 was determined as statistically significant. We used descriptive statistics, chi-squared, independent t test, paired t test, repeated measure, Friedman, covariance, and U Mann-Whitney tests to analyze the primary and secondary outcome.

Research ethics
This study was approved by the Ethics Committee of Shahid Sadoughi University of Medical Sciences. Participation in the study was completely voluntary. Participants read and signed the informed consent forms prior to the study. Also, each of the participants could be excluded from the study at any time during the program. Furthermore, confidentiality of all participants' information was ensured. Participants determine the importance and the value of positive and negative aspects Fourth session: Temptation and self-confidence, goal setting and preparing for change -with an emphasis on the principle of empowering the clients Participants become familiar with the basis of creation of temptation Participants identify the situations where much temptation is created to quit the regular program of PA. Participants identify situations with confidence Participants learn how to set appropriate goals Subjects express goals and write a change layout for its realization

Results
Seventy women in reproductive age were randomly assigned to the randomized controlled trial. With Chi-squared test, no significant difference was observed between intervention and control groups regarding the demographic characteristics (age, educational level, job, spouse's job) and body composition (p>0.05).

SDT components
The results of the psychological variables of SDT are shown in Table 2. With repeated measures test, the intervention group showed a higher level of autonomy, identified regulation, perception of competence, challenge and enjoyment motives through time than before the intervention. Friedman's non-parametric test also showed an increased intrinsic motivation, introjected regulation, perception of self-determination and fitness/health motive and a reduction in amotivation in the intervention group compared to before intervention over time (Table 2). Comparing the intervention and control groups within 4 months, variables such as intrinsic motivation, identified regulation, perception of autonomy, perception of competence and perception of relatedness, enjoyment motive, and health care climate, indicated moderate to high effect sizes. Conversely, introjected regulation, external regulation, amotivation and fitness/health, challenge, social and appearance motives, showed low or negative effect sizes (Table 3).

Physical activity and sedentary behavior
With repeated measures tests, the participants in the intervention group showed a higher level of PA over time and a lower level of sedentary behavior in the non-parametric Friedman test compared to pre-intervention time ( Table 2). Within 4 months after intervention, the subjects in the intervention group showed higher level of PA with high effect size and lower level of sedentary behavior with negative effect size compared with the control group.

Body composition and physical fitness tests
In the intervention group, the repeated measures tests showed a significant reduction in body mass index, and paired t-test showed a significant increase in body flexibility, muscle endurance, and cardiorespiratory endurance and a significant reduction in agility score over time ( Table 2). The subjects in the intervention group indicated lower scores of body mass index and agility, with a negative effect size and higher levels of cardiorespiratory endurance, muscular endurance and flexibility of the body with medium to high effect sizes, in 4 months after intervention compared with the control group (Table 4).

Discussion
The main objective of this study was to assess the impact of MI-based intervention on PA among women in reproductive age. The next objective was to examine some psychological variables of SDT that play an important role in these effects. For this purpose, 70 women in reproductive age were randomly assigned to the randomized controlled trial. In this study, the mean score of the overall PA (moderate + intense) was increased four months after the intervention in intervention group compared with the control group, with the change from 90.33 minutes mean in a week before the intervention, to 213.5 minutes per week in the four following months. In a similar study (45)(46)(47), the mean score of PA was also increased over time in the intervention group. While this change was not observed in the control group. Behavior is a complex issue and several factors are involved. Effective education can change unhealthy behavior in order to achieve healthy behavior, but this process needs time. The mean score of sedentary behavior between the intervention and control groups showed a significant difference within four months after the intervention, and a negative effect size was observed which was lower in the intervention group than the control group. The mean score was decreased overtime in the intervention group and changed from 5.61 hours a day preintervention to 4.26 hours a day, four months after the intervention, while no change was observed in the control group. According to the evidence (48), if the amount of daily sedentary behavior reaches to four hours or more, people are considered as sedentary. So, in this regard, a decreased sedentary behavior in the intervention group members was created over time, but a little more is needed to achieve the desired level. So, in future educational programs, this important issue must be considered in order to increase PA. The mean score of intrinsic motivation components between intervention and control groups within the 4 months after intervention had a significant difference, and high effect size was identified. The mean score of intrinsic motivation indicated a significant increase over time in the intervention group, while the control group indicated a brief increase. Similar results were found in other studies (45,49). According to the principles of MI and SDT, having intrinsic motivation in performing PA is an important factor in the onset and continuity of this behavior. Increased intrinsic motivation confirms an increase in internalization process of autonomy regulation of PA by intervention over time. The mean score of amotivation within four months after intervention, was less than the control group. Similar findings were observed in the study conducted by Gourlan et al. (46). While in the study of Sweet et al. (49) there was no significant difference between groups. The mean score of amotivation was also decreased in the intervention group over time. The amotivation had a negative relationship with performing behavior. If the lack of motivation decreases, the probability of intervention success in creating motivation for performing activity will increase. The mean score of relative autonomy index between intervention and control groups had a significant difference within four months after the intervention and indicated high effect size. The mean score was increased in the intervention group over time, while there was no significant difference in the control group. In other studies (47), selfdetermination index had no significant difference over time in the intervention group. While a significant difference was observed in the mean autonomy index within three different periods of time in the control group with a decreasing process. According to these findings, the more autonomy index increases overtime, the more success will be obtained in the intervention program, and onset and continuity of PA will have more progress. Several studies clearly showed that autonomy in behavior is a crucial predictor of long term and sustainable behavior change (50). This is also true in case of exercise, where research has shown that more autonomous motivations will result in longer-term commitment to PA (51). In this study, the mean score of perception of autonomy and competence had a significant difference between intervention and control groups within 4 months, which was identified with high effect size. In the intervention group, the satisfaction with needs was increased over time, but there was no significant difference in the control group. Similar findings were also observed in other studies (45,52), through the follow up period; while another study (47) indicated no significant difference in the mean score of perception of autonomy in the intervention group, and it was decreased in the control group. Increasing the perception of autonomy is one of the important aims of MI. Perception of the autonomy means the independency in choosing a behavior (18). In this case, the individual chooses a behavior by their own decision and interest, and performs the behavior in their own way (53). This issue is an important factor in the onset and continuity of a behavior. Perception of competence indicates the individual's capabilities (54). In this case, individuals believe that doing exercise will bring the desired results, and feel like they are capable and competent, and have constant participation in behavior (25). The mean score of perception of relatedness between intervention and control group had no significant difference within 4 months after intervention. Also, no change was observed over time in intervention and control groups; this finding is consistent with the study of Levy & Cardinal (55) that after the intervention, no increase was reported in relatedness. While in another study (47), perception of relatedness in exercise behavior had significant difference in intervention and control groups in different periods of time. Similar results were also reported in the study of Edmond et al. (53).
In the intervention group, the mean score of enjoyment motive was increased after 4 months, while it was decreased in the control group, and the effect size of intervention was identified as high for this variable. Also, enjoyment motive was increased in the intervention group over time, whereas it was decreased in the control group. Internal motivations, such as doing exercise for fun, can be understood as increased perception of self-determination (21). In agreement with the principles of MI, the present intervention had a great emphasis on the promotion of perception of autonomy, which will consequently lead to an increase in enjoyment motive. The mean score of appearance motive in the intervention group was less than the control group within 4 months, while it was not significant. The mean score had no significant difference in intervention and control groups over time. But in the study of Silva et al. (45), the appearance motive had a significant difference in intervention and control groups after one year of follow-up, so that it was higher in the intervention group. But the effect size of intervention was reported as 0.35. External motives, such as exercise for weight control, can be perceived as a controlled motive by which self-determination becomes less and causes lack of enjoyment of exercise (21). In this study, the mean score of health care climate 4 months after intervention, was higher in the intervention group than the control group, which was identified with high effect size. This finding was consistent with the results of similar studies (45 and 46). In this study, the mean BMI in the intervention group was reduced over time. In a study conducted by Gourlan, the intervention group reported a decrease in the BMI three months after the intervention, while no difference was observed 6 months after the intervention (46). Although a significant decrease was found in the mean BMI, people are still in the overweight range. Commitment to regular PA is one way of gaining desirable weight. Other factors are also involved, such as appropriate nutrition. A significant difference was observed in the mean score of body flexibility, muscular endurance and cardiorespiratory endurance between the intervention and control groups within four months after the intervention, and showed a high and moderate effect size. The mean score was increased in the intervention group four months after the intervention, compared to pre-intervention. No difference was observed in the control group.
In the study of Fathi (56), on the effect of six weeks of aerobic exercise on cardiovascular endurance, body composition, flexibility etc. among female students, there was no significant increase in flexibility score after the intervention, and the difference in results is due to the short training course or also insufficient intensity and type of exercise. In the study by Anbari et al. (57), the mean score of abdominal muscle endurance in sit-ups was increased in the intervention group after the intervention. Also in the study by Gourlan et al. (46), the energy consumption also had a significant difference between groups in different times; energy consumption was weaker in the intervention group before to the intervention. Compared with the control group, energy consumption was increased in the intervention group over time. There was a significant difference in the mean score of agility test (4×9 sprint) between the two groups within four months after the intervention, so that the score was lower in the intervention group and the effect size was negative. In the intervention group, the mean score was significantly decreased compared to the pre-intervention, and the duration of exercise reduced to 13.21 seconds from 15.58 seconds within four months after the intervention. No difference was observed in the control group, and similar results were reported in the other studies (57,58). The study had some limitations. First, the nature of the control group limited the direct comparison of intervention with other PA promotion programs. Decision making about choosing the standard control group was related to other objectives of this trial, that enable us to perceive the mechanisms strengthening self-determined motivation for PA. While demographic variables and some SDT variables had no difference in two groups at the baseline, the possibility of differences between the groups at baseline cannot be absolutely prohibited. One of the prominent points in this study was the objective measurement to evaluate PA using physical fitness tests and measuring body's composition through measuring height and weight tests to measure BMI, which reduces the errors induced by self-report measurement. Finally, the results of the present study, showed that the intervention has been performed well and that it caused significant changes in PA, body composition, and physical fitness of women in reproductive age.

Conclusions
The results showed that designing an MI-based intervention using SDT can promote the PA. Therefore, informing health educators about this educational method would be useful in offering interventions aimed at promoting PA among women in reproductive age.