Table 1.

Abbreviated description of the treatment protocol stages, progression and differences between treatment groups

Early lengthening exercises	Delayed lengthening exercises
Physiotherapy stage 1: low load exercises and the lengthening exercises were introduced in this stage. Examples include: manual resisted isometric knee flexion with and without shank rotation in varying ranges of knee flexion, active unresisted through range knee flexion/extension in prone, exercise bike, two and one legged squats. Criteria to progress to stage 2: pain-free single leg squat and 5 min of stationary cycling at a power output of 150% bodyweight in Watt.	Physiotherapy stage 1: low load exercises were introduced in this stage. Examples include: manual resisted isometric knee flexion with and without shank rotation in varying ranges of knee flexion, active unresisted through range knee flexion/extension in prone, exercise bike, two and one legged squats. Criteria to progress to stage 2: pain-free single leg squat and 5 min of stationary cycling at a power output of 150% bodyweight in Watt.
Physiotherapy stage 2: the running protocol was introduced and the exercises of stage 1 were progressed. Criteria to progress to stage 3: able to run pain-free at more than 70% of self-rated maximal speed	Physiotherapy stage 2: the running protocol was introduced and the exercises of stage 1 were progressed. Criteria to progress to stage 3: able to run pain free at more than 70% of self-rated maximal speed.
Physiotherapy stage 3: running protocol was progressed and modified T-drill was introduced and progressed. The Nordic hamstring exercise was introduced and exercises from previous stages were progressed. Criteria to progress to sports-specific stages: able to run pain-free at 100% self-rated speed in both the linear running and the modified T-drill.	Physiotherapy stage 3: the lengthening exercises were introduced in this stage. Running protocol was progressed and modified T-drill was introduced and progressed. The Nordic hamstring exercise was introduced and exercises from previous stages were progressed. Criteria to progress to sports-specific stages: able to run pain free at 100% self-rated speed in both the linear running and the modified T-drill.
Sports-specific stage 4, 5 and 6: progressive sports-specific on field training that mimicked training and game situations. Emphasis on running, sprinting, change of direction and sports-specific skills. Criteria to progress to return to sport assessment: complete a stage 6 training without pain.	Sports-specific stage 4, 5 and 6: progressive sports-specific on field training that mimicked training and game situations. Emphasis on running, sprinting, change of direction and sports-specific skills. Criteria to progress to return to sport assessment: complete a stage 6 training without pain.