Methods
Subjects and setting
Participants for this prospective cohort study were recruited
among players entering the Toppvolley Norge (TVN) program.
TVN is located in Sand, Norway and combines an elite volleyball
training program with a 3-year senior high school boarding school
program. The students started at the age of 15–16 years, and they
were expected to complete 3 years for a college-entry baccalaureate
degree. Some students entered the program in the second or
third year directly. TVN aimed to recruit the most talented junior
volleyball players in Norway, and the athletes represented the
school in the Norwegian national leagues at various levels.
However, players could also play tournaments and league matches
for their home clubs. Many of the players also qualified for different
junior national team programs.
The recruitment process began when school started every
autumn with an information meeting. Potential participants were
also informed in writing before their written consent was obtained,
and also that of their parents if the athlete was younger than 18
years old. To be included, they had to be free of jumper’s knee at
the time of inclusion. The athletes were a part of the study as long
as they attended TVN until they first developed jumper’s knee on
at least one side. The study was approved by the Regional Committee
for Research Ethics and the Data Inspectorate.