Table 2 Detailed information about the ANHEQ scale for NHE intervention studies and criterion-based reference values for studies I1 [23], I2 [24], I3 [20] and I4 [25]

(1) Rigid fixation

2 points: fixed/rigid resistance at the heels

0 points: partner assistance or not reported

2

0

0

2

(2) Knee position

2 points: feasible patellar glide (tuberositas tibiae placed on an edge, knees do not touch the floor)

1 point: limited or partially feasible patellar glide (appropriately cushioned surface)

0 points: patellar glide not feasible or not identifiable

1

0

0

0

(3) Kneeling height

1 point: shanks are placed at least 15 cm above the floor to enable full knee extension

0 points: no/insufficient elevation or not identifiable

0

0

0

0

(4) Separate familiarization

1 point: a separate familiarization session was conducted to teach proper NHE technique

0 points: instructions/‘familiarization’ at testing day or not reported

1

0

0

0

(5) Progression and individualization of program variables

2 points: exercise intensity and/or volume progress and interindividual differences are assessed

1 point: progression of exercise intensity and/or volume

0 points: no progression or not reported

2

1

1

0

(6) Feedback of execution quality

2 points: visually (real-time feedback on a monitor) and audibly (e.g., by a coach or physiotherapist)

1 point: visually (real-time feedback on a monitor) or audibly (e.g., by a coach or physiotherapist)

0 points: no feedback or not reported

0

1

0

0

(7) Inter-set rest

1 point: adequate rest of ≥ 3 min (inter-repetition rest of ~ 6 s between eccentric NHEs)

0 points: inadequate rest or not reported

0

0

0

0

(8) Compliance

2 points: participants performed ≥ 85% of NHEs repetitions

1 point: participants performed 66–85% of NHEs repetitions

0 points: participants performed < 66% of NHEs repetitions or not reported

2

2

2

0

Total ANHEQ Score

8

4

3

2