# Abstract

 

## 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. # 3. 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). 

## 3.1. 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](#)). 

## 3.2. 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. 

## 3.3. 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](#)). ::::table-wrap

::: caption
Intervention program in MI sessions
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Sessions Description of the intervention

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First session: Introducing the motivational approach, facilitators' philosophy, and group principles-with an emphasis on the principle of avoiding the intention to reform the client Knowing motivational approach
Knowing the facilitator philosophy (supporting the autonomy)\
Determining rules and norms of the group\
Second session: Studying a single day of subject's life in terms of the amount of PA and the effects of physical inactivity Increasing participants' awareness about the quantity and quality of their PA behavior
Increasing participants' awareness about the effects of physical inactivity\
Third session: Values and negative and positive aspects-with an emphasis on the perception of client's motivation. Participants identify their values
Participants recognize how their values are in conflict with their sedentary behavior.\
Participants recognize the positive and negative aspects of sedentary behavior.\
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:::: ::::table-wrap
::: caption
Comparison of SDT Components, Physical fitness tests, total PA and
sedentary behaviors during the assessment process.
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Variables Mean±SD of Pre-test; Intervention (control) Mean±SD of Post-test; Intervention (control) Mean±SD of Follow up after 4 months; Intervention (control) p-value; Intervention[1](#) (control[1](#))

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Intrinsic Motivation 3.03±1.47 (4.32±1.95) 10.80±2.0 (4.90±1.88) 13.50±1.79 (5.51±2.39) \<0.001 (\<0.001)
Identified Regulation 6.43±2.19 (8.19±2.61) 10.66±1.72 (8.48±2.36) 12.03±1.60 (8.58±2.68) \<0.001 (>0.05)
Introjected Regulation 1.40±1.52 (2.29±1.83) 3.20±2.65 (2.93±2.23) 3.33±2.78 (3.29±1.81) \<0.001 (>0.05)
External Regulation 0.13±0.43 (0.32±0.17) 0.30±0.79 (0.38±0.98) 0.43±1.04 (1.19±1.37) >0.05 (\<0.001)
Amotivation 0.93±2.46 (0.61±1.28) 0.33±1.06 (0.70±1.24) 0.06±0.36 (0.58±0.92) \<0.05 (>0.05)
Relative Autonomy Index 4.04±0.24 (6±0.26) 11.59±0.23 (6.27±2.17) 14.25±2.35 (6.04±0.26) \<0.001 (>0.05)
Perception of Autonomy 15.60±4 (20.14±5.17) 26.60±4.43 (19.89±4.56) 30.40±2.83 (19.85±5.24) \<0.001 (>0.05)
Perception of Competence 12.20±3.66 (15.71±5.53) 13.6±3.05 (14.71±3.87) 17.20±3.46 (14.10±3.82) \<0.01 (>0.05)
Perception of Relatedness 13.36±1.01 (13±8.34) 13.10±7.38 (12.89±6.85) 15.63±7.61 (12.14±6.21) >0.05 (>0.05)
Enjoyment motive 20±9.36 (28.28±4.75) 27.30±6.77 (26±4.68) 30±3.83 (24.89±5.20) \<0.001 (\<0.05)
Appearance motive 19.80±9.44 (24.82±6.38) 20.26±8.88 (23.39±6.68) 20.96±8.40 (23.03±6.94) >0.05 (>0.05)
Fitness/health motive 20.06±8.04 (23.92±3.36) 23.23±6.19 (23.21±3.33) 25.73±3.02 (25.32±1.10) \<0.001 (>0.05)
Challenge motive 15±7.25 (18.25±6.12) 16.80±6.34 (16.75±5.66) 17.90±5.17 (16.46±5.38) \<0.001 (>0.05)
Social motive 13.83±6.88 (13.03±4.15) 13.43±5.94 (12.60±5.49) 12.90±5.73 (12.35±5.34) >0.05 (>0.05)
Health care climate 77.56±1.32 (72.25±1.54) 80.50±9.97 ()69.89±1.59 83.10±1.37 (69.57±1.61) >0.05 (>0.05)
BMI 26.04±3.37 (26.44±3.59) 25.78±3.30 (26.53±3.53) 25.32±3.05 (26.59±3.53) \<0.001 (>0.05)
Flexibility 31.46±6.88 (27.35±5.95) - 35.53±5.87 (26.83±5.47) \<0.001 (>0.05)
Muscular endurance 13.30±3.03 (12.51±3.16) - 17.83±2.70 (12.48±2.90) \<0.001 (>0.05)
Agility 15.58±1.89 (13.78±1.17) - 13.21±1.44 (13.80±1.14) \<0.001 (>0.05)
Cardiorespiratory endurance 36.39±3.20 (37.99±2.24) - 39.10±2.76 (37.99±2.14) \<0.001 (>0.05)
Total Physical activity (Met-min/Week) 361.33±98.11 (477.85±108.91) 487.33±111.47 (453.57±60.87) 854±271.60 (470±80.46) \<0.001 (>0.05)
Sedentary behavior (hour/day) 5.61±2.65 (5.45±2.04) 5.28±2.34 (5.75±2.34) 4.26±1.76 (5.91±2.21) \<0.001 (\<0.05)

p-value is reported for comparison within intervention group during
times;

p-value is reported for comparison within control group during times:::: ::::table-wrap
::: caption
Characteristics of SDT components, PA and sedentary behaviors within 4
months after the intervention by groups
:::

Variables Follow up after 4 months; Mean ± SD p-value ES[1](#)

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Intervention Control\
Intrinsic Motivation 13.50 ± 1.79 5.51 ± 2.39 \<0.001[2](#) 3.34
Identified Regulation 12.03 ± 1.60 8.58 ± 2.68 \<0.001[3](#) 1.2805
Introjected Regulation 3.33 ± 2.78 3.29 ± 1.81 0.5[2](#) 0.02
External Regulation 0.43 ± 1.04 1.19 ± 1.37 0.002[2](#) \<−0.55
Amotivation 0.06 ± 0.36 0.58 ± 0.92 0.004[2](#) −0.56
Relative Autonomy Index 14.25 ± 2.35 6.04 ± 0.26 \<0.001[3](#) 3.52
Perception of Autonomy 30.40 ± 2.83 19.85 ± 5.24 \<0.001[2](#) 2.01
Perception of Competence 17.20 ± 3.46 14.10 ± 3.82 0.001[3](#) 0.81
Perception of Relatedness 15.63 ± 7.61 12.14 ± 6.21 0.082[2](#) 0.1
Enjoyment motive 30 ± 3.83 24.89 ± 5.20 \<0.001[3](#) 0.98
Appearance motive 20.96 ± 8.40 23.03 ± 6.94 0.252[3](#) >−0.2
Fitness/health motive 25.73 ± 3.02 25.32 ± 1.10 0.003[2](#) . 0.19
Challenge motive 17.90 ± 5.17 16.46 ± 5.38 0.36[3](#) >0.26
Social motive 12.90 ± 5.73 12.35 ± 5.34 0.78[3](#) 0.1
Health care climate 83.10 ± 1.37 69.57 ± 1.61 0.001[3](#) >4.6
Total Physical activity (Met-min/Week) 854 ± 271.60 470 ± 80.46 \<0.001[3](#) >0. 4.77
Sedentary behavior (hour/day) 4.26 ± 1.76 5.91 ± 2.21 0.002[2](#) −0.74

Effect Size,

U Mann--Whitney test,

t-test:::: ::::table-wrap
::: caption
Characteristics of BMI and physical fitness sizes within 4 months after
intervention by groups
:::

Variables Follow up after 4 months; Mean ± SD p-value ES

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Intervention Control\
BMI 25.32 ± 3.05 26.59 ± 3.53 0.13[1](#) −0.35
Flexibility 35.53 ± 5.87 26.83 ± 5.47 \<0.001[2](#) 1.59
Muscular endurance 17.83 ± 2.70 12.48 ± 2.90 \<0.001[1](#) 2.0
Agility 13.21 ± 1.44 13.80 ± 1.14 \<0.001[2](#) −0.51
Cardiorespiratory endurance 39.10 ± 2.76 37.99 ± 2.14 \<0.001[2](#) 0.51

t-test,

Covariance test::::


Extracted trial result:
Outcome: Scores of external regulation (continuous)
Intervention: Motivational interviewing through self-determination theory sessions
Comparator: Standard education session
Intervention group size: 35
Intervention mean: 0.3
Intervention standard deviation: 0.79
Comparator group size: 35
Comparator mean: 0.38
Comparator standard deviation: 0.98