Methods
This is a prospective cohort study designed according to the Strengthening the Reporting of Observational Studies in Epidemiology guidelines (STROBE) with extension for Sports Injury and Illness Surveillance (STROBE-SIIS),23 a consensus statement on how to report such data recommended by the International Olympic Committee.23
Participants
Adolescent men and women aged 15–19 years, participating in sports and attending either national sports high schools (NIU or RIG) or regular high schools, are eligible to participate. Inclusion criteria will be: (1) attending high school, (2) competing in their sport and aiming to reach a national or international level of sports. All types of sports will be included.
Exclusion criteria will be athletes practising sports at a recreational level. Participants who drop out of school or finish their sports career will be excluded from further data collection from their next semester. However, they will be included in the total analyses. Athletes who meet the inclusion criteria will be invited to participate in the project by oral and written information. Schools and athletes deciding to participate will receive more detailed information.
An internal pilot study has been performed to test the implementation of the questionnaires related to the project. The pilot showed satisfying results regarding feasibility and validity (unpublished data).
Data collection
All athletes will be followed prospectively from the time point of inclusion until they graduate from high school (1–4 years). Traditionally, high school in Sweden is 3 years; however, for some national sports high schools (eg, Alpine schools), the duration is 4 years. The reason for 4 years is a prolonged high school to achieve the academic requirements. The athletes will answer a baseline questionnaire at the time of recruitment and, after that, a weekly questionnaire. They will fill out a shorter version of the baseline questionnaire at the beginning of each new school year.
All data collection will be completed by a web application (app) through the athlete’s smartphone, whereby all athletes will receive a personal text message weekly with the questionnaire link. If there is no response, a reminder text message will be sent out the next day. The app will be distributed by the researcher responsible for the project, together with the company developing the app. The athletes can track their results through the app, that is, after completing the weekly questionnaire. They receive a chart of, for example, their sleeping, stress and perceived exertion pattern.
Questionnaires
The different questionnaires have been developed meticulously to confirm both validity and reliability. Initially, a reference group constructed the questionnaires after reviewing the literature based on the aim of the study and to suit the target population. All questionnaires have been developed by the researchers responsible for the project based on studies evaluating similar subjects such as injuries and physical and psychosocial load. The questions were then reformulated better to suit the target population and purpose of the project. To increase the content and construct validity, the first draft of the questionnaires was sent to the research group, which consisted of medical doctors and physiotherapists experienced in sports medicine, mental health and working with adolescents. After revisions, updated questionnaires were developed. A pilot study was conducted to validate the method and questionnaires. The questionnaires were pretested by young athletes (the target population) to ensure the feasibility and validity of the method and questionnaires. Based on the results from this pilot study, the questionnaires were once again revised before the final draft was confirmed.
Baseline questionnaire
The baseline questionnaire addresses potential risk factors contributing to sports injuries, demographics and general health status. The athletes are assessed in different areas, including sport, training and competing: sport discipline, training and match/competing exposure, playing position, junior/senior class, other sports participation, age of sport specialisation, changes in training/competing habits and current level of sport; health: injuries, illness, medication, sleep habits and diet habits; psychosocial: changes in living conditions (ie, moving away from home), club-transfer, change of coaches and mental health. A short version of the Warwick Edinburgh Mental Well-being Scale (SWEMWBS)24 is included to assess mental health and well-being. The SWEMWBS consists of seven statements, each answered on a Likert scale, summarised and converted into metric scores. The SWEMWBS has been translated and validated into Swedish.24 It is an established score previously used to measure mental health in the National Public Health Survey—Health on Equal Terms by the Public Health Agency of Sweden.
Weekly questionnaire
The weekly questionnaire includes an injury and pain report, the session rate of perceived exertion (session-RPE) for total physical load and a ‘Wellness score’ for physiological load. The injury and pain report include pain grading using the Numeric Rating Scale, a modified version of the Oslo Sports Trauma Research Center Questionnaire on health problems (OSTRC-H),25 pain drawing and injury mechanism (acute with/without contact, gradual during practice or outside practice). The OSTRC-H has been translated and validated into Swedish for adolescents and used in several previous studies.4 10
It has been shown that a total physical load index (combining external load (training and competing hours) and internal load (self-reported intensity)) is associated with injury risk in athletes.2 10 Therefore, the total physical load will be analysed using the session RPE. Session-RPE records training and competing hours in relation to perceived exertion, estimated on the Borg Scale, and is the most commonly used measure for this purpose.10
The psychological load will be analysed using a ‘Wellness-score’. A recent systematic review concluded that subjective measures were more sensitive than objective measures when examining acute and chronic changes in the athlete’s psychological load.26 A ‘Wellness score’ is the most frequently used measure to investigate this in a sports population. Hence, the athletes will answer questions regarding fatigue, sleep, mental stress and recovery on a five-graded Likert scale.26
Yearly questionnaire
A shortened and modified version of the baseline questionnaire will be filled out at the beginning of every new school year (years 2, 3 and 4). The modification involves deleting some demographic questions. In contrast, questions regarding finishing high school and/or their sports career are added as well as reasons for finishing school and/or their sports careers. Questions regarding sports, training and competing, health (injuries, illness, sleep, diet) and psychosocial areas (living and club transfer, mental health and SWEMWBS) are also included.
Five-year follow-up questionnaire
A follow-up questionnaire will be distributed to the included athletes approximately 5 years after graduation. This questionnaire contains the Tegner activity scale, SWEMWBS,24 and questions partly derived from the Swedish Sports Confederation report The Roads to the National Team21 regarding sport, career and injuries. Examples of questions are current age, the age when starting an elite sports career, whether the athlete is still pursuing an elite sports career, what goals the athlete has for their elite sports career, whether the athlete is at the desired level of sport, and if not, the reason for this, the number of injuries with complete or partial absence from sports for at least 3 months, and the nature of these injuries and if applicable, reasons for not pursuing an elite sports career.
Sample size
The sample size is calculated using the formula recommended by Riley et al27 (calculator accessible via https://riskcalc.org/samplesize/clinical prediction models with a time-to-event outcome). This formula gives a sample size of 370 participants, with 15 candidate predictor parameters, an approximate 95% CI for the overall outcome proportion, a margin of error (δ) ≤0.05 and an overall event rate in the population of interest of 33% (0.33) based on the pilot study results (injury incidence of 33%, unpublished material).
Statistical methods
Each year, a compilation of data will be executed. The HIFAA study will include a large number of research questions. Hence, different statistical analyses will be executed. The study will partly be a descriptive study, where injury frequency, type and grade of injuries, physical and psychological load and well-being, including the SWEMWBS, will be analysed and described with numbers, percentages, means and SD for the entire group as well as stratified by sex, age and type of sport. A generalised linear model will be used to investigate differences in the prevalence of injuries between sex, age and type of sport and will be presented as a prevalence ratio with a corresponding 95% CI and incidence as number of injuries/1000 exposure hours. Using linear and logistic mixed model regression analyses, the risk of reporting injuries will be explored based on, for example, the wellness score or physical load from the previous week. Predicting current mental health and wellness will also be explored using linear mixed model regression analyses, including injury as an independent variable. ORs will be presented with a 95% CI. The plan is to use mixed models to investigate changes over time (repeated measures). Furthermore, the Cox regression analyses will also be performed to investigate potential risk factors for the first reported injury, with consideration taken into potential confounders. Based on the Cox regression models, the hazard rate ratio (HRR) will be presented with a corresponding 95% CI. Kaplan-Meier curves will be constructed to plot injury risk for covariates of gender and those with a significant HRR. As mentioned above, the HIFAA study includes many research questions, and the exact statistical method that will be used will, therefore, depend on the specific research question. A p value of<0.05 will be considered as statistically significant.
Time plan
Athletes will be recruited from the beginning of 2023 and then continuously until we reach over 370 athletes. The athletes will be invited to participate once they start high school, followed once weekly throughout high school and then again 5 years after graduation.
Ethics approval and consent to participate
This study was approved by the Regional Ethical Review Authority in Sweden, with diary number 2021-05496-01. All included athletes will receive oral and written information regarding the study. They will also give their written informed consent at the time of recruitment. The individual answers and results in the app are strictly confidential and will not be shared with, for example, coaches or teachers. Hence, it will not influence the athletes’ chances of making teams or competitions.
The study will be executed according to the Helsinki Declaration and reported in accordance with the STROBE-SIIS.
Availability of data and materials
The datasets analysed during this project will not be publicly available. However, it will be available from the authors on reasonable request.