Table 1

Operational definitions

Training sessionTeam training that involved physical activity under the supervision of the coaching staff
MatchCompetitive or friendly match against another team
InjuryAny physical complaint sustained by a player that resulted from a football match or football training and led to the player being unable to take full part in future football training or match play
Hamstring injuryAn acute onset distraction injury or gradual onset injury to the hamstring muscle group
Recurrent injuryInjury of the same type and at the same site as an index injury occurring previously during the same season
Early recurrenceRecurrent injury that occurs within 2 months after return to full participation from the index injury
Injury incidenceNo of injuries per 1000 player hours ((Σ injuries/Σ exposure hours)×1000)
Injury burdenNo of lay-off days per 1000 player hours ((Σ lay-off days/Σ exposure hours)×1000)