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APPLIED PSYCHOLOGY: HEALTH AND WELL-BEING, 2014, 6 (3), 300–317 doi:10.1111/aphw.12029

Effects of a New Sports Companion on Received Social Support and Physical Exercise: An Intervention Study Pamela Rackow,* Urte Scholz, and Rainer Hornung University of Zurich, Switzerland

Background: The role of social support in physical exercise is well documented. However, the majority of studies that investigate the associations between social support and physical exercise target perceived instead of received social support. Moreover, most studies investigate the effects of received social support using a descriptive correlational design. Thus, our study aimed at investigating the effects of received social support by conducting an intervention study. Methods: Participants were randomly assigned to an intervention (n = 118) or control group (n = 102). The intervention comprised regularly exercising with a new sports companion for eight weeks. To investigate the time course of physical exercise and received social support, growth curve modelling was employed. Results: Generally, both groups were able to improve their physical exercise. However, the control group tended to decrease again during the final point of measurement. Received social support, however, decreased slightly in the control group, but remained stable in the intervention group. Conclusions: The intervention was suitable to sustain received social support for physical exercise across a two-month interval. Overall, these findings highlight the importance of further investigating social support for physical exercise applying an experimental approach. Keywords: growth curve model, intervention, physical exercise, received social support

INTRODUCTION In most Western industrialised countries, adults lead a sedentary lifestyle (Hardman & Stensel, 2009). This is in spite of the fact that regular exercise is important to achieve and maintain physical and psychological health (Cavill, Kahlmeier, & Racioppi, 2006). Thus, it is important to identify effective strategies to enhance physical exercise among sedentary adults. One can * Address for correspondence: Pamela Rackow, University of Zurich, Department of Psychology, Applied Social Psychology, Binzmuehlestrasse 14/ Box 14, CH-8050 Zurich, Switzerland. Email: [email protected] © 2014 The International Association of Applied Psychology

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distinguish between strategies that mainly focus on the person themselves, such as self-regulation abilities (e.g. Gollwitzer & Sheeran, 2006), and strategies that focus on the person’s environmental and social context, such as social support. The latter, however, has been mostly examined in studies applying correlational designs (e.g. van Stralen, De Vries, Mudde, Bolman, & Lechner, 2009), which excludes causal inferences on this particular association. The present study sets out to contribute to the question of causality between received social support and physical exercise by using an experimental approach.

Social Support and Physical Activity Social support can be differentiated into perceived social support and received social support (cf. Uchino, 2009). Perceived social support refers to the anticipation of potential help from the social network. Received social support refers to the reported receipt of supporting acts typically during a specific time frame (Uchino, 2009). Although not a measure of actual support transactions, it is still more common to investigate perceived than received social support (Boehmer, Luszczynska, & Schwarzer, 2007; Knoll, Rieckmann, & Kienle, 2007). Several types or functions of social support can be distinguished, such as emotional, instrumental, and informational social support (Schwarzer & Knoll, 2007). Emotional social support refers to the emotional well-being of the recipient and covers aspects such as encouragement and comfort. Instrumental social support refers to supporting the recipient by means of assisting with the problem or donating goods (Schwarzer & Knoll, 2010). Finally, informational social support covers functions like providing relevant information and giving advice (Schulz & Schwarzer, 2003; Schwarzer & Knoll, 2007). The social support of important others (e.g. family and friends) can play a crucial role in the adoption and maintenance of physical activity and exercise (Courneya, Plotnikoff, Hotz, & Birkett, 2000; Lippke, 2004; Trost, Owen, Bauman, Sallis, & Brown, 2002; Spanier & Allison, 2001). In a metaanalysis, Carron, Hausenblas, and Mack (1996) identified family support and support of significant others as important factors for exercise adherence behaviour. In their literature review on determinants for initiation and maintenance of physical activity among older adults, van Stralen et al. (2009) identified social support from significant others and having a sports partner as positively associated with the initiation of physical activity. In terms of maintaining physical activity, positive associations for being supported by group members and sport partners were found as well. In terms of instrumental and emotional social support, several studies showed © 2014 The International Association of Applied Psychology

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associations between both types of social support and physical activity engagement (Fischer Aggarwal, Liao, & Mosca, 2008), and physical activity maintenance (Kouvonen et al., 2011). One facet of instrumental social support is concrete assistance. With regard to exercising, a number of studies reported positive associations between having someone to exercise with (e.g. having an exercise companion) and physical exercise levels (cf. Brehm & Eberhardt, 1995; Dunton, Berrigan, Ballard-Barash, Graubard, & Atienza, 2009; Gellert, Ziegelmann, Warner, & Schwarzer, 2011; Giles-Corti & Donovan, 2002) as well as exercise adherence (e.g. Brehm & Eberhardt, 1995; Oliveira et al., 2011). However, some important issues have not yet been covered by the reported studies. Most of the studies have addressed perceived social support, but only a few have focused on received social support (Boehmer et al., 2007; Knoll et al., 2007). Even fewer studies have dealt with the support received from a sports companion. Moreover, those studies that have taken this source of social support into account have focused exclusively on sports companions whom participants had already exercised with for a long period of time. In doing so, the potential consequences and effects of exercising together cannot be investigated appropriately, because both partners are already a wellestablished team.

Aim of the Present Study If social support is to be used as an intervention strategy, it is indispensable to find out whether social support works as such a strategy. Thus, our study aimed at exploring the effects on exercising of having a new sports companion, and on received instrumental and emotional social support, by conducting a randomised intervention study.

METHODS

Intervention Procedure and Recruitment Modes The intention to begin or to increase one’s own physical exercise was the inclusion criterion for participating in our study.1 In our study, we conducted a social support intervention, which comprises finding a new sports companion and exercising together for eight weeks. Received instrumental 1 Exercise-specific behavioural intentions were assessed with four items (item example: “I intend to exercise on a regular basis”; from Scholz, Schüz, Ziegelmann, Lippke, & Schwarzer, 2008). At T1, intervention (M = 5.05, SD = 0.92), and control groups (M = 5.09, SD = 0.84) did not differ in their exercise-specific behavioural intentions, t(161) = 0.33, p = .74, d = 0.05.

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and emotional social support should be addressed this way and utilised to enhance physical exercise on the part of the respondent. In line with the work of Abraham and Michie (2008), social support can be classified as an important behaviour change technique. At baseline, intervention and control groups received a baseline questionnaire (T0, either online questionnaire or paper and pencil), where each participant could choose between three possible dates to begin the study. Afterwards, the participants received three online questionnaires at four-week intervals (T1, T2, and T3). Participants who answered all the questionnaires received an incentive (a voucher worth 30 CHF, c. 33 USD, for an online book and media store) after completing the study. The recruitment mode was twofold. First, we recruited participants in two locations of a Swiss federal research institute. Paper and pencil questionnaires with two different instructions were randomly distributed among 35 people who wanted to enhance their physical exercise (n = 13 control group; n = 22 with intervention group instruction). Of these 35 questionnaires, 26 were returned (n = 6 control group, n = 20 intervention group). The second recruitment mode was distributing the link for an online questionnaire (with exactly the same content as the paper and pencil questionnaire) via health-related websites, an advertisement in a university journal, and flyers for display within group practices of a health insurance company. In so doing, we were able to reach 301 people who clicked on the link of the baseline questionnaire (T0; see Figure 1). By clicking on the link the participants were randomised to the intervention (n = 150) or control group (n = 151). Both groups were informed that the aim of the present study was to study the processes that help people with their attempt to exercise more or more regularly and that the duration of the study was eight weeks. After randomisation, participants in the intervention group were instructed to search for a new sports companion and to exercise with this person for the next eight weeks. Participants were explicitly instructed to choose a new sports companion, that is, not one with whom the participating person was already exercising. Moreover, participants were instructed to keep the same individual during the whole eight weeks as their new sports companion. The control group did not receive such an instruction. All participants were treated in accordance with the ethical guidelines of the Helsinki Declaration 2000 (World Medical Association, 2014), and informed consent was obtained. Altogether, 104 participants (n = 55 control, n = 49 intervention group) did not provide their email address, which means that we could not send a second questionnaire (T1) to these participants, and they thus dropped out after T0. Moreover, the participants in the intervention group were asked at T1, T2, and T3 if they still exercised with their new sports companion. Every participant confirmed this. The participants’ flow for both recruitment modes is displayed in Figure 1. © 2014 The International Association of Applied Psychology

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FIGURE 1. Flow chart: Upper level represents the two different recruitment modes at the research institute and via the online questionnaire. Lower level is the flow diagram after Consort standard. Analysed1 refers to the participants imputed and analysed for the growth curve model for physical exercise. Three individuals in the intervention group reported that they did not find a sports companion and were therefore excluded from all imputation procedures and the analyses. Analysed2 refers to the participants imputed and analysed for the growth curve model for emotional and instrumental social support. © 2014 The International Association of Applied Psychology

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TABLE 1 Percentages, Means, and Standard Deviations (in Parentheses) of the Baseline Questionnaire (T0) Displayed Separately for Intervention and Control Groups Variable Female Age (years) Physical exercise (minutes of exercise in the past 7 days)

Control Group (n = 102)

Intervention Group (n = 1181)

62.75 % 34.45 (11.00)

65.53 % 34.66 (11.11)

146.28 (139.12)

160.95 (129.05)

Work Student Unemployed Full-time work (more than 32 hours per week)

32.35 % 0.98 % 51.96 %

33.88 % 5.79 % 52.07 %

Family status Married/living with partner Single/divorced

36.27 % 47.08 %

41.32 % 41.32 %

Education High school degree

48.03 %

57.02 %

Health-related variables Height (cm) Weight (kg) Portions fruit/veg. per day Smoking “yes”2 Weekly alcohol consumption “yes”3

169.34 (7.47) 69.42 (15.01)

170.07 (7.27) 65.04 (10.79)

2.79 (1.29) 10.30 % 34.31 %

2.72 (1.25) 13.30 % 33.88 %

Note: 1 This sample size refers to those participants in the intervention that reported having found a new sports companion. Three participants were excluded because they reported not having found one; 2 This information refers to the question “Do you smoke—even if rarely?”; 3 This means alcohol consumption in general at least once a week.

Participants A full and detailed description of the baseline characteristics of the 220 participants who underwent randomisation, answered at least the T0 questionnaire, and reported having found a sports companion (this only applies to participants in the intervention group) is shown in Table 1. Participants’ mean age was around 35 years and most participants were female. At T0, participants reported having exercised for between 146 and 160 minutes in the past seven days. More than half of the participants reported working full time, and a good third reported being college/university students. No significant differences between control and intervention groups emerged in any of these measures. Thus, the randomisation was successful.

Measures The socio-demographic and health-related variables were assessed at T0. Physical exercise was measured at T0, T1, T2, and T3. Received instrumental © 2014 The International Association of Applied Psychology

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TABLE 2 Means (Standard Deviations) of Physical Exercise and the Psychological Variable under Study in Intervention and Control Groups for all Measurement Time Points Variable

Group

T0

T1

T2

T3

Physical Exercise*

Control (n = 102) Intervention (n = 118)

146.28 (139.12) 160.95 (129.05)

166.90 (168.76) 184.48 (141.17)

218.91 (147.35) 204.71 (152.13)

172.60 (177.28) 266.50 (246.73)

Emotional Support

Control (n = 72) Intervention (n = 83)

—

5.26 (1.36) 5.22 (1.26)

4.79 (1.34) 5.06 (1.10)

4.59 (1.45) 4.98 (1.40)

Control (n = 72) Intervention (n = 83)

—

4.26 (1.52) 4.79 (1.37)

3.87 (1.56) 4.63 (1.33)

3.76 (1.76) 4.63 (1.62)

Instrumental Support

—

—

Note: * Minutes of exercise in the past seven days.

and emotional social support were assessed at T1, T2, and T3. The sample means of the respective constructs are reported below. The group means for all variables are reported in Table 2. Physical Exercise. Vigorous physical exercise at all measurement points was assessed following the International Physical Activity Questionnaire (IPAQ; Booth, 2000). Participants were asked to indicate how often during the past seven days they had engaged in vigorous physical activities such as, for example, jogging, swimming, or weight lifting. In addition, they indicated how much time they usually spent performing those activities per exercise occasion. Frequency and average duration per exercise occasion were then multiplied in order to obtain a measure of weighted duration for the past seven days. The IPAQ has admissible validity values when comparing accelerometer data (Craig et al., 2003). Data cleaning and handling followed the guidelines for use of the IPAQ (IPAQ Group, 2005). At T0, all participants exercised on average 155.60 minutes per week (SD = 159.77 minutes). At T1, they exercised on average 183.81 minutes per week (SD = 160.66), at T2, 211.44 minutes per week (SD = 189.84), and at T3, the participants exercised on average 224.15 minutes per week (SD = 219.16). Received Emotional Social Support. To determine the degree to which participants felt emotionally supported by their sports companion at T1, the subscale emotional social support of the Berlin Social Support Scale (Schulz © 2014 The International Association of Applied Psychology

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& Schwarzer, 2003) was adapted to the domain of physical exercise. It comprises five items, for example, “This person encouraged me with regard to my physical exercise”. Response range was from 1 = “not at all true” to 7 = “exactly true”. The item wording was equal for the intervention and control groups. However, the item introduction was slightly different for both groups. In the intervention group, the participants were asked to think of their new sports companion when answering the items. In the control group, participants should have someone in mind with whom they have been exercising on a regular or irregular basis. T1 received emotional social support had a sample mean of 5.26 (SD = 1.29) and Cronbach’s α = .86. T2 received emotional social support had a sample mean of 4.93 (SD = 1.23; Cronbach’s α = .85), and T3 received emotional social support had a sample mean of 4.79 (SD = 1.43; Cronbach’s α = .87). Received Instrumental Social Support. This was also assessed by a domain-specific adapted version of the corresponding subscale of the Berlin Social Support Scale (Schulz & Schwarzer, 2003). It comprises seven items, for example, “This person offered me his/her help to maintain my physical exercise”. The item wording and introduction were given in the same way as reported for received emotional social support. Having the same response range as received emotional social support, T1 received instrumental social support had a sample mean of 4.58 (SD = 1.48) and Cronbach’s α = .90. At T2, received instrumental social support had a sample mean of 4.25 (SD = 1.44; Cronbach’s α = .93), and T3 received instrumental social support had a sample mean of 4.19 (SD = 1.69; Cronbach’s α = .94). Furthermore, all participants had the opportunity to write comments at the end of each questionnaire.

Data Analysis Descriptive statistics, scale values, and Cronbach’s alphas were computed with SPSS 18. Missing data were treated using the multiple imputation (MI) function of SPSS 18 (SPSS, 2009). In so doing and in the sense of an intention-to-treat-analysis, all participants who filled in at least T0 and fulfilled the inclusion criterion, which was the intention to begin or to increase their physical exercise, remained in the analyses. Three individuals in the intervention group reported that they did not find a sports companion and they were therefore excluded from all imputation procedures and the analyses. When comparing MI with other types of missing data handling (e.g. mean substitution, averaging available items; see Schafer & Graham, 2002, for a survey of methods), the advantage of the MI procedure is the generation of error variance in the sense of random noise. MI accounts for missing data uncertainty by creating multiple values for the missing data point, by creating © 2014 The International Association of Applied Psychology

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several data-sets, and by adding between-imputation variance. In contrast, regression-based single imputation procedures lead to imputed values that lie right on the regression line and, thus, this does not represent real data (Graham, 2009). For the present study MI was conducted separately for physical exercise and for received social support and because of this the number of individuals analysed for physical exercise and for received social support differ (Figure 1). We chose this approach because we wanted to ensure that the sample analysed for received social support comprises individuals who answered these items at least once (i.e. at T1; in contrast to physical exercise, social support was not assessed at T0). Finally, five data sets for each sample were generated and analysed. To calculate the progress of physical exercise and received social support over the time of study, growth curve modelling was employed. The shape of the growth curve for all models was defined a priori as linear and according to this the loadings were fixed with 0, 1, 2, 3 for physical exercise (four measurement points in time), and with 0, 1, 2 for received instrumental and emotional social support (three measurement points in time; e.g. Geiser, 2010). The growth curve models for received instrumental and emotional social support are composed of three measurement points, and no restrictions that reduce the number of parameters for the mean-structure were applied. Thus, these models are saturated and for this no model fit indices will be reported for received instrumental and emotional social support (Geiser, 2010). On the other hand, the growth curve model for physical exercise is composed of four measurement points in time. Therefore the following goodness-of-fit indices are reported for the growth curve model of physical exercise. The χ2 goodness-of-fit statistics describe the magnitude of discrepancy between the sample and the fitted covariance matrix (Hu & Bentler, 1999). In addition, the Tucker Lewis Index (TLI) and the Comparative Fit Index (CFI) are utilised. They are incremental fit indices, which compare the fit of the target model with the baseline model (Geiser, 2010). Acceptable fit is indicated by values greater than .90 (Hu & Bentler, 1999). The Root-MeanSquare-Error-of-Approximation (RMSEA) measures the approximate data fit of the model and is important to evaluate the residuals. It should be lower than .05 (Geiser, 2010). All models were calculated with Mplus 6.1 (Muthén & Muthén, 2010). To compare the control and intervention groups multigroup modelling was applied (Hoyle, 2011). By forcing the slopes in both groups to be equal, nested models were created, which can be compared via χ2 difference test (Crayen, 2010; Geiser, 2010).

RESULTS The time course of physical exercise is depicted in Figure 2, and the time course for received instrumental and emotional social support is depicted in Figure 3. © 2014 The International Association of Applied Psychology

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FIGURE 2. Time course of physical exercise for intervention (n = 118) and control groups (n = 102) (based on multiple imputation data).

The interindividual change in physical exercise over time is displayed by the slope factor of the respective model. For the intervention group (Mlinear = 24.38, z = 2.92, p = .01) as well as for the control group (Mlinear = 25.62, z = 2.83, p = .01) the slope factor was significant, which means that physical exercise changed over time in that physical exercise in both groups significantly increased. A second function of latent growth curve models is to estimate interindividual differences in intraindividual changes. Significant variance in the slope factor represents interindividual variability in the change of physical exercise over time (Legge, Davidov, & Schmidt, 2008). In our case, there was no interindividual variability in the intraindividual change in physical exercise over time, either for the intervention group (Varlinear = 555.91, z = 0.51, p = .61) or for the control group (Varlinear = 2225.44, z = 1.46, p = .15). This means that physical exercise increased to the same extent for all participants, contingent upon their respective group, over the course of time and that there were no significant differences between respondents (see Figure 2). The model fit can be considered to be satisfactory (χ2 = 10.34, df = 10, p = .41; TLI = .99; CFI = .99; RMSEA = .02, 90% CI from .00 to .11). To evaluate whether the slope of the intervention group and the slope of the control group significantly differed from each other, they were forced to be equal. Comparison of fit of the unconstrained model and this nested model resulted in an insignificant result, χ2 (Δ df = 1) = −0.24; p = .12, indicating that there was no difference between the two groups. Due to the apparent difference between groups at T3, which was not captured by this model comparison, we ran a t-test for physical © 2014 The International Association of Applied Psychology

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FIGURE 3. Time course of emotional and instrumental social support for intervention (n = 83) and control group (n = 72) (based on multiple imputation data). Note: Emot. = received emotional social support, Instru. = received instrumental social support.

exercise at T3 as a further post-hoc test. Results demonstrated that both groups significantly differed from each other, t(288) = −3.40, p = .001; d = 0.43. In order to test whether the intervention and control groups started at the same level of received instrumental and emotional social support at T1, we conducted t-tests. At T1, there were significant differences in received instrumental social support between the control and intervention groups (t(153) = 2.24, p = .03, d = 0.36). The participants in the intervention group reported receiving more instrumental social support. In contrast, concerning emotional social support, there were no significant differences between the groups at T1 (t(153) = −0.19, p = .85; d = 0.03). In order to test whether the time courses of received emotional and instrumental social support were significant and if they significantly differed between the intervention and control groups, two growth curve models were calculated. With regard to change in received emotional social support, there was significant change over time in the control group (Mlinear = −0.29, z = −3.56, p < .001), but not in the intervention group (Mlinear = −0.12, z = −1.56, p = .12) (see Figure 3). The received emotional social support in the control group significantly decreased over time. Again, there was no interindividual variability in the intraindividual change in received emotional social support over time in either group (intervention group: Varlinear = .05, z = 0.37, p = .71; control group: Varlinear = 0.22, z = 1.01, p = .31). Again, both © 2014 The International Association of Applied Psychology

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slopes were constrained to be equal and a χ2 difference test was computed that again showed an insignificant result, χ2 (Δ df = 1) = 2.31; p = .13, indicating no significant differences between the slopes of the two groups. With regard to received instrumental social support the pattern was very similar. There was significant change over time of received instrumental social support in the control group (Mlinear = −0.25, z = −1.98, p = .04), but not in the intervention group (Mlinear = −0.09, z = −0.87, p = .38). Like received emotional support, the received instrumental social support in the control group decreased over time (see Figure 3). Moreover, there was no interindividual variability in the intraindividual change in received instrumental social support over time in either group (intervention group: Varlinear = 0.22, z = 1.20, p = .23; control group: Varlinear = 0.14, z = 0.39, p = .69). In other words, there were no interindividual differences in the development of received instrumental social support within the two groups over time. When comparing the slopes between the intervention and control groups by forcing them to be equal, the χ2 difference test resulted in an insignificant result, χ2 (Δ df = 1) = 1.08; p = .30. This indicates that the groups did not differ from each other. Again, due to the apparent differences between the groups at T2 and T3 (see Figure 3), which were not captured by this model comparison, we ran t-tests for instrumental social support at T2 and T3 as further post-hoc tests. Results demonstrated that the groups significantly differed from each other at T2, t(153) = −3.27, p = .001, d = 0.52; and at T3, t(153) = −3.20, p = .001; d = 0.51.

DISCUSSION The present study investigated the effect of having a new sports companion for enhancing physical exercise. Moreover, we tested whether this sports companion also enhanced received emotional and instrumental social support. This study was designed as an intervention study with randomised allocation of the participants to intervention and control groups. Physical exercise changed over time in that the overall trend was positive for both groups. In the control group, however, a decrease occurred between T2 and T3. This was further validated with a post-hoc t-test that indicated a significant difference in physical exercise at T3 between the intervention and control groups. Received emotional social support remained stable in the intervention group, but significantly decreased in the control group. Comparing both groups, however, did not result in a significant difference with regard to the slope of received emotional support. The results for instrumental social support showed the same pattern. Received instrumental social support significantly decreased over time and the different slopes between groups were not significant. We did not expect this kind of time course for instrumental or for emotional social support. Instead, we expected that in the intervention group © 2014 The International Association of Applied Psychology

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received instrumental social support might increase at the beginning of the study, and would remain stable until the end of the study, because every exercising dyad had found its modus operandi. In contrast, for the control group, we expected the received instrumental social support to remain stable on a low level for the time of the study, because the control group was not instructed to search for a new sports companion. However, it seems that having a new sports companion ensures the maintenance of receiving instrumental and emotional social support. One possible reason for this result could be that the boosting effect of receiving social support took place in the phase when the participant and his/her sports companion began to make plans about their new exercising behaviour. It is highly likely that this happened in the time period between the questionnaires T0 and T1 when the randomised allocation to the two groups took place and participants in the intervention group had the task of finding a new sports companion. However, we did not collect data in this time period. The next measurement was at T1. At that time, the sports companions already exercised together, meaning that participants in the intervention group already received instrumental and emotional social support. Thus, future research should try to capture the received social support in the phase when the sports companions participate, e.g. by applying a daily diary design during this critical period. Moreover, the assumption of a booster effect for received social support between T0 and T1 for the intervention group is also supported by the significant difference between the intervention and control groups in T1 instrumental social support. This is another pointer to the likely scenario that during the period between finding the sports companion and completing the T1 questionnaire, functional and tangible exchanges took place between the participants in the intervention group and their new sports companions. To revisit the above-mentioned issue of the best time point for assessing received social support for the first time, one could argue that an assessment at T0 would be useful. The reason why we did not include this assessment in the present study was that received social support in the intervention group was related to the new sports companion that was, due to the study’s design, not yet available. Some limitations of the present study need to be addressed. Our sample was already very active at the beginning of the study. Thus, there was relatively little room for improvement. Future studies should therefore focus on participants with lower exercise levels at the beginning in order to have even greater potential for change. These high levels of exercising might have also occurred due to the measurement of physical exercise with the IPAQ (see Mäder, Martin, Schutz, & Marti, 2006). Another limitation is the dropout rate during the first study phase (T0 and T1). We used two modes of recruitment in this study and the dropout in the intervention and control groups seems to be different depending on the recruitment mode. For the first © 2014 The International Association of Applied Psychology

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recruitment mode, the recruitment at the research institute, the proportion of returned questionnaires was unequal in the intervention and control groups. More questionnaires in the intervention condition were returned. At this point, we can only speculate about reasons for this. One possible explanation might be that participants, who also happened to be working or studying at the research institute where this study was conducted, communicated with each other about the study and became aware that some people were given the task of finding a sports companion whereas others did not. Therefore, it may be that the control group condition was an unattractive choice for participants. Considering the dropout pattern in the second recruitment mode, there is weak evidence for this assumption, because for the second recruitment mode this problem did not appear. In contrast, for the second recruitment mode via the distribution of links for the online questionnaire, we observed high dropout rates between the first (T0) and second (T1) points of measurement. However, here the number of participants who declined participation is relatively equal in the control and in the intervention groups. That indicates that, for the second recruitment mode, the dropout was not related to the condition of searching for a new sports companion, but to other reasons. When taking a closer look at the dropout rates from T1 to T3, we again lost nearly half of our participants in both groups. On the one hand, this is a well-documented problem in longitudinal studies (e.g. Bolger & Laurenceau, 2013; Scholz, Knoll, Roigas, & Gralla, 2008) and this is the reason why we decided to offer incentives for regular participation. On the other hand, we compensated for these high dropout rates by using an appropriate method of missing data imputation (Graham, 2009). Our participants were free to choose their sports companion as long as this companion remained the same person during the eight weeks of the intervention. Thus, the source of social support was stable within but different between intervention group participants. Future studies should thus examine potential differences in support quality or advantages/disadvantages related to different sources of support, and under which circumstances and whose support is best for physical exercise. There are, for example, several advantages and disadvantages if the spouse were to be the sports companion. On the one hand, the chance is higher that this person is more available for physical activities compared to friend or a work colleague, just because of the greater frequency of contact with each other. Indeed, our participants reported geographical conditions (e.g. having the same place of residence) and conditions concerning time (e.g. having the same schedule) as important reasons for choosing someone as their new sports companion. From other comments from our participants, we know that one main reason for not exercising together as intended was lack of time. On the other hand, if someone usually does a lot of leisure time activities with his/her spouse © 2014 The International Association of Applied Psychology

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anyway, this might result in too many shared activities. In particular, when taking into account that one person has the desire to enhance physical exercise, then this person might experience the shared physical activity as being too controlling (e.g. Okun, Huff, August, & Rook, 2007) or they might get the impression of losing their autonomy. Thus, this would speak in favour of finding someone other than the spouse as exercise companion. However, finding someone else would be associated with other challenges such as finding a person who is willing to exercise with the target person at all, then, for example, finding a time and date that suits both, and finding a sport both companions would like to perform together. Hence, there are numerous questions that need to be addressed in future research. Besides the impact of the source of social support, further investigation into the kind of sport would be of interest. It might be that some kinds of sport are better suited to this type of intervention. Similarly, the social support provider’s gender ought to be considered in future research. Findings on the stress-buffering effects of received social support indicate that both genders benefit more from social support from a female provider (e.g. Glynn, Christenfeld, & Gerin, 1999; Neff & Karney, 2005). In addition, there are comparable findings in the domain of health (e.g. Scholz et al., 2012) and health behaviour (Hankonen, Absetz, Ghisletta, Renner, & Uutela, 2010). Another important issue, which has not been addressed in our study, is the dyadic perspective. We focused on the recipient of the social support but not on the supporting person. Collecting data from both parts of the exercising dyad would provide insights into the supporting process per se. That means that possible mechanisms could be investigated more precisely. The mechanisms of social support also play an important role in answering the question of how social support can be used as an intervention strategy. Future studies might thus want to test the mediating mechanisms of received social support on physical exercise.

Conclusions This study is, to our knowledge, among the first that has applied an experimental approach to investigate the effects of received social support on physical exercise. Both the intervention and control groups were able to increase their exercise levels during the time of study. The intervention enabled participants to maintain high levels of received instrumental and emotional social support for exercise across a two-month interval. Future studies should also take potential longer-term effects into account.

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