Vertical and horizontal hop performance: contributions of the hip, knee, and ankle

In short

Do single-leg vertical and horizontal hop tests measure the same thing, and which one actually reflects knee function?

Vertical and horizontal hops do not measure the same aspects of leg function. The knee drives about a third of vertical hop height but only about an eighth of horizontal hop distance, so a horizontal hop is a poor way to judge knee recovery.

DescriptiveRead paper

Primary study20 ParticipantsLimited evidence

Key points

During vertical hop propulsion, the hip, knee, and ankle contribute roughly equally (about 31%, 34%, 35%).
Horizontal hop distance is mostly produced by the hip and ankle, with the knee contributing only about 13%.
On horizontal hop landing the knee absorbs most of the load (about 65%), while on vertical landing the three joints share the work more evenly.
Both hops use a proximal-to-distal sequence during push-off, but landing patterns differ markedly between the two.
Because the knee plays a small role in horizontal hop distance, a horizontal hop does not capture knee function well during knee rehabilitation.

How it was conducted

Design: Cross-sectional cohort study, Level 3 evidence
Participants: 20 healthy, physically active adult males (sports at least 3 times/week)
Tasks: Instrumented single-leg vertical (countermovement) hop and horizontal hop for distance
Measurement: 42-marker 14-camera Vicon motion capture (250 Hz) with 5 Kistler force plates (1000 Hz); inverse dynamics for hip, knee, ankle
Outcomes: Joint peak power, work generated or absorbed, and percentage contribution of each joint during propulsion and landing
Analysis: Paired t tests, Cohen d, spm1d; P < 0.05

What they found

Horizontal hop propulsion work was dominated by the hip (44.3 +/- 6.6%) and ankle (42.8 +/- 4.5%), with the knee contributing only 12.9 +/- 4.5%.
Vertical hop propulsion work was shared more evenly: hip 31.2 +/- 5.7%, knee 34.1 +/- 6.4%, ankle 34.7 +/- 4.9% (knee contribution differed between tasks, P < 0.001, d = 3.89).
On horizontal hop landing the knee absorbed most of the work (64.7 +/- 5.8%) versus 34.3 +/- 9.3% on vertical landing (P < 0.001, d = 4.04).
Knee joint work on landing was greater for horizontal (-2.78 +/- 0.66 J/kg) than vertical (-1.22 +/- 0.46 J/kg) hops (P < 0.001, d = 2.76).
Ankle peak power during propulsion was higher for horizontal (24.85 +/- 4.24 W/kg) than vertical (16.17 +/- 3.41 W/kg) hops (P < 0.001, d = 2.27); knee peak power was lower for horizontal (6.91 +/- 2.43 vs 12.11 +/- 2.48 W/kg, P < 0.001, d = 2.12).
Total work was greater for horizontal than vertical hops in both propulsion (4.77 +/- 0.78 vs 4.35 +/- 0.78, P = 0.007, d = 0.53) and landing (-4.27 +/- 0.85 vs -3.49 +/- 0.74, P < 0.001, d = 0.97).

Limitations

Only 20 healthy recreational adult males were studied, so results may not apply to women, older people, or injured patients.
No injured or post-surgical cohort was included, despite the clinical rehabilitation framing.
Testing was done in a controlled laboratory setting that may not reflect real sport or clinic conditions.
Joint contributions were derived from inverse dynamics, which has inherent measurement limitations.

Why it matters

For patients: If you are recovering from a knee injury, a single-leg jump for distance may make your leg look more recovered than it is, because the hip and ankle do most of the work.
For clinicians: Do not use a horizontal single-leg hop to judge knee function in rehabilitation; a vertical hop better reflects the knee's contribution, for example after ACL reconstruction.
For readers: Two hop tests that look similar measure different things, so the choice of test changes what conclusion you can draw about a specific joint.

Source

doi:10.1177/1941738120976363

Read the original paper

Clinically assessing this area? See the knee special tests.