Table 2 Exercise description

1. Load magnitude

Corresponding to 12 repetitions maximum (RM)

2. Number of repetitions

12

3. Number of sets

3

4. Rest between sets

Minimum 30 s, or until sufficiently recovered from previous set

5. Number of exercise interventions

Group 2 (2 sessions per week)

Group 4 (4 sessions per week)

Group 6 (6 sessions per week)

6. Duration of the experimental period

12 weeks

7. Fractional and temporal distribution of the contraction modes per repetition and duration (s) of 1 repetition

Concentric phase (3 s)

Isometric phase (1 s)

Eccentric phase (4 s)

Total duration of 1 repetition (8 s)

8. Rest between repetitions

None, that is, right after finishing one repetition the next is commenced

9. Time-under-tension (TUT)

Repetition TUT (8 s)

Set TUT with 12 repetitions (1 min, 36 s)

Session TUT (3 sets × 12 repetitions) (4 min, 42 s)

10. Volitional muscular failure

No, but contractions should be continued until volitional muscular failure is very close. That is, until the knee-extensor muscles are maximally fatigued and the patient is not able to perform further repetitions. If volitional muscular failure occurs before the 12 RM, the resistance of the elastic band is adjusted so that the pre-determined number of repetitions can be completed

11. Range of motion

Starting position: 80–90° of knee flexion (0 = full extension)

End-range of motion position: 0–10 (as close to full extension as possible)

12. Recovery time between exercise sessions

Group 2: 3 days

Group 4: 1 day

Group 6: 0 days

13. Anatomical definition of the exercise (exercise form)

The knee-extensor strength exercise is performed sitting in a stable chair. Sitting position in the chair is determined by the distance from the edge of the seat to the back of the knee; this distance should be 2–3 cm. If possible, the back rest can be used as well as the armrest. If the chair is without an armrest one can hold at the (side) edge of the seat. To ensure that the foot is free of the floor at 80–90° of flexion an object (e.g., a pillow) is placed under the thigh (Fig. 3). The elastic exercise band is fixated to an immoveable object (e.g., an elastic exercise band anchor behind a closed door) and wrapped around the ankle of the exercised leg (Fig. 9).

Starting position: The exercise leg is relaxed with 80–90° of flexion (0 = full extension)

Concentric phase: The exercise leg is extended as much as possible towards full extension using 3 s

Isometric phase: The extended position is held for 1 s

Eccentric phase: Slow controlled flexion of the knee joint (4 s) until the knee joint is flexed 80–90°

These slow movements are chosen to ensure long time-under-tension (TUT) in the muscle