Study setting and design
This cross-sectional study was part of the ongoing longitudinal Finnish Health Promoting Sports Club study . The baseline data used in this study were collected in 2013–2014. The study was conducted in accordance with the Declaration of Helsinki. Ethical approval was received from the Ethics Committee of Health Care District of Central Finland (record number 23 U/2012).
For the questionnaire data, written informed consent was received from the participating youth and their guardians were informed about their child’s participation in the study. According to the approval of the Ethics Committee of Health Care District of Central Finland, written or verbal consent was not required from the guardians for the questionnaire data. For the accelerometer-measured physical activity data, written informed consent was obtained from a guardian and the adolescent him/herself.
The study protocol has been described in detail earlier . In short, sports club participants were recruited via sports clubs in two stages. First, the clubs were stratified depending on 1) winter and summer sports (according to the main competition season) and team and individual sports, and 2) club’s magnitude, geographical location, area type, and certification by the Young Finland Association. Ten most popular sports disciplines in Finland were included in the study: basketball, cross-country skiing, floorball, gymnastics, ice hockey, orienteering, skating, soccer, swimming, and track and field. Twenty-four sports clubs from each of the sports disciplines were targeted and 156 clubs took part.
In the second stage, sports club participants aged 14–16 years were invited to the study. Individual sports participants were randomly selected from name lists provided by clubs. Of the team sports clubs, one team was randomly chosen, and the researchers randomly selected the individuals from team participant name lists. In total, 1889 sports club participants were invited and 759 (40%) of them completed the study questionnaire.
Similarly, the age-matched sample of non-participants was collected via schools in two stages. First, ten secondary schools from each of six different areas in Finland were targeted, and the schools were stratified depending on school’s magnitude and area type. Second, one randomly selected class of ninth graders from each school was asked to respond to the questionnaire. Overall, 2074 pupils were invited from one hundred schools and 1650 (80%) of them responded to the study questionnaire.
Adolescents with missing information about age, who were not 14–16 years old, who had inadequate information about weight or height, or who had contradicting answers regarding sports club participation, duplicate answers, improper answers, or who forbade the use of data for research were removed from the data (166 sports club participants and 285 pupils). The school-based sample included both sports club participants and non-participants. The questionnaire of the school-based sample did not include the competitive goal question. Hence, pupils participating in sports clubs (n = 547) were not included.
In total, 593 adolescents via sports clubs and 818 adolescents via schools participated in the study. Sports club participants who did not have competitive goals in sports (n = 118) were included in the reference group in the analyses. Therefore, the competitive goals in sports (CGS) group comprised 475 participants and the reference group consisted of 936 participants.
The data were collected using two Internet-based questionnaires. Sports club participants replied to the questionnaire on their spare time and pupils in class during a school day. Whether participants had competitive goals in sports were assessed by the question: “What is your competitive goal as an athlete?” Adolescents who aimed to succeed in junior competitions (at the regional, national, or international level) or adult competitions (at the international or national level) were considered as the CGS group. Those who replied that “I have no competitive goals, I exercise to develop in sports” or “I have no competitive goals, I exercise in a recreational sense” formed the reference group.
Body size perception was assessed with the question described in the Health Behaviour in School-aged Children study : “Do you think your body is [much too thin / a bit too thin / about the right size / a bit too fat / much too fat]?” The test-retest stability of the question has been good among Finnish adolescents . The initial variable with five categories was re-coded into a three-class variable, where the “a bit too thin” and “too thin” categories and the “a bit too fat” and “too fat” categories were combined. “Too thin” and “too fat” were considered as the examined responses and “about the right size” was a reference category.
The motives to exercise were investigated by a modified version of the Nigg’s questionnaire : “Are the following issues important for your exercising [not important / somewhat important / very important]?” The answers were re-coded into binomial variables with answer options “very or somewhat important” and “not important”. The motives to exercise were categorized into four categories [24, 25]:
appearance/weight (to look good, to control weight, to lose weight)
health/fitness (to improve health, to improve physical fitness, to gain muscle)
social (to win, to be good in sports, to make new friends, to meet my friends, to please my parents, to be “cool”)
enjoyment (to have fun, to appreciate the sensations during exercise, exercise is exhilarating)
For further analysis, initial responses were scored as: not important = 0, somewhat important = 1, and very important = 2. The values were summed (range 0–12 for social motives and 0–6 for other motives) and a higher score indicated a higher motive.
Self-rated health and perceived physical fitness were separately assessed by the question: “Would you say your health/physical fitness is… [excellent / good / fair / poor]?” The responses were dichotomized as “good” (excellent/good) and “poor” (fair/poor). BMI was calculated from self-reported height and weight data. Age- and sex-specific cut-off points for adolescents’ BMI were based on the international growth reference data [26, 27]. Cut-off points for underweight individuals were set for BMI < 17 kg/m2, for normal weight at BMI = 17–25 kg/m2, and for overweight at BMI > 25 kg/m2.
Accelerometer-measured physical activity
Moderate to vigorous physical activity (MVPA) was measured from a randomly selected sample of sports club participants (n = 334) and non-participants (n = 131) (Fig. 1). Adolescents were instructed to use a hip-worn, light tri-axial accelerometer (AM20 Activity Meter, Hookie Technologies Ltd., Helsinki, Finland) for seven consecutive days during waking hours with the exception of during shower or water activities. Swimmers (n = 31) were excluded as they were unable to use the accelerometer during water activities. The device has been shown to be a valid measurement tool for continuous monitoring of physical activity among both youths  and adults [29, 30].
The tri-axial data were collected with a sampling frequency of 100 Hz. The mean amplitude deviation (MAD) of the resultant was analysed in 6 s epoch length and converted to metabolic equivalents (MET). Cut-points were set as 3.0–6.0 MET for moderate activity and over 6.0 MET for vigorous activity. The mean daily moderate and vigorous activities were summed to obtain the amount of MVPA.
All the statistical analyses were stratified by gender. The descriptive analyses were performed using cross-tabulation and χ2 test for categorical variables. For continuous normally distributed variables, the independent samples t test and one-way ANOVA were used. For non-normally distributed variables, Mann Whitney U test and Kruskal-Wallis test were employed. The multinomial logistic regression models were built to assess the associations between competitive goals in sports and BSP: “too fat” and “too thin” were used as the examined responses and “about the right size” was a reference category. The models were controlled for competitive goals in sports, BMI, perceived physical fitness, self-rated health, appearance/weight motives, enjoyment motives, health/fitness motives, social motives, and MVPA. Statistical analyses were performed using SPSS version 25 (Armonk, New York, IBM Corp.). The significance level was set at p < 0.05.