Table 2 Description of the functional tasks

Single limb mini squat

Performed according to Ageberg et al. [7] but without allowing fingertip support for maintaining balance. The patient is standing on one leg with the second toe placed on a marked longitudinal line. He/she is instructed to flex the injured knee until he/she cannot see the toes (approximately 50°) and then to return to extension. Repeated 5 times.

Stair descending

Performed according to Pfeifer et al. [33] and modified to use a step board 27 cm off the ground. The patient stands on the step board. He/she is instructed to step down to the floor with the non-injured leg and then return to the starting position. The injured leg, which is in contact with the step board throughout the entire movement, is evaluated. Repeated 5 times.

Forward lunge

Performed according to Alkjaer et al. [34]. The patient is standing with his/her feet hip-width apart on the floor. He/she is instructed to take a long stride forward, about 1 m, with the injured leg and to flex the knee to approximately 90° and then push back to the starting position by extending the front leg. Repeated 3 times.

Drop jump

Performed according to Hewett et al. [9] but modified to use the second landing instead of the first landing, because the second landing may better represent the situation when an ACL injury occur [35]. The patient stands on a step board 27 cm off the ground with the feet hip-width apart. He/she is instructed to drop from the step board and directly perform a maximal vertical jump. Arm swing is allowed during the jump. Repeated 3 times.