Single-Leg Hop Test: ACL Return-to-Sport Testing Protocol

TL;DR

• The single-leg hop test battery combines the single hop, triple hop, crossover hop, and 6-meter timed hop.
• Clinicians commonly use a 90% Limb Symmetry Index on each test as a minimum benchmark.
• Passing hop tests alone does not eliminate subsequent ACL injury risk, and distance symmetry may conceal movement differences.
• Clinicians should interpret hop performance alongside quadriceps strength, psychological readiness, sport demands, and other return-to-sport criteria.

What the single-leg hop test measures and why it's used for ACL clearance

The single-leg hop test provides a functional measure of an athlete’s ability to generate force, accept load, and control landing on one limb after ACL reconstruction. Hop distance captures overall task performance, while the landing also lets you observe balance, trunk position, knee control, and movement strategy.

Hop testing has clinical relevance because approximately 70% of ACL injuries occur without contact, often during landing, cutting, or deceleration. A forward hop cannot reproduce every demand of sport, but it exposes the reconstructed limb to rapid propulsion and single-limb load acceptance. Crossover hops add a change-of-direction component that more closely challenges multiplanar control.

Distance alone cannot show whether both limbs use comparable joint mechanics. An athlete may reach similar distances by shifting work toward the hip or ankle and reducing knee loading. Clinicians therefore use the single hop within a battery that also includes triple, crossover, and timed hopping tasks. The combined results provide a broader view of dynamic limb function, but they remain one part of ACL return-to-sport testing rather than an independent clearance decision.

Equipment and setup

Prepare a level, nonslip lane with a 10-meter tape measure, floor tape, and a dowel or yardstick for marking landings. Tape a start line across the lane, and position the athlete’s toes behind it. Mark a 6-meter course and use automated timing gates for the timed hop because stopwatch error can obscure limb differences.

For the crossover hop, secure two parallel lines 6 inches apart. Use the same surface and footwear throughout testing. The published protocol allows one practice trial followed by three scored trials on each limb. Apply the same instructions, arm-use rules, limb order, and rest intervals to both sides.

Step-by-step procedure for each hop test

Single hop for distance

Ask the athlete to stand on the test leg with the toes behind the start line. The athlete flexes the hip, knee, and ankle, then hops forward as far as possible using unrestricted arm movement. Measure from the start line to the back of the landing heel to the nearest 0.5 cm, and require the athlete to hold the landing for two seconds.

Void the trial if the athlete takes a running start, touches down with another body part, or fails to maintain the landing. Record each valid distance for later Limb Symmetry Index calculation according to the selected standardized hop-testing protocol.

Triple hop for distance

Ask the athlete to complete three continuous forward hops on the same leg. The athlete should preserve forward momentum between hops rather than pausing or resetting. Measure from the start line to the back of the heel after the third landing, and require a controlled two-second hold on that final landing.

Void the trial if the opposite foot or another body part touches the floor, the athlete pauses between hops, or the final landing cannot be held. Record the total distance across all three hops.

Crossover hop for distance

Ask the athlete to perform three continuous forward hops while crossing laterally over the two parallel lines. The first hop should move toward the side of the test leg. For example, an athlete testing the right leg moves right, left, then right before holding the final landing.

Void the trial if the athlete begins in the wrong direction, lands on either tape line, fails to clear the gap, or touches down with the opposite foot or a hand. Loss of balance on the final landing also invalidates the trial. Measure the total forward distance to the back of the heel.

6-meter timed hop

Ask the athlete to cover six meters as quickly as possible using repeated hops on the test leg. Start timing when the athlete begins and stop when the athlete crosses the finish line. Record elapsed time, with a lower value indicating faster performance.

Void the trial if the opposite foot touches down, the athlete leaves the marked course, or the athlete fails to cross the finish line under control. Use automated timing gates when comparing limbs. Stopwatch error can equal or exceed the small timing difference between legs, which limits the value of hand-timed symmetry calculations.

Scoring with the Limb Symmetry Index and the 90% threshold

Calculate the Limb Symmetry Index separately for each hop. For distance tests, divide the involved-limb distance by the uninvolved-limb distance and multiply by 100. For the timed hop, divide the uninvolved-limb time by the involved-limb time and multiply by 100 because a shorter time indicates better performance. An LSI of 90% means the involved limb achieved 90% of the uninvolved limb’s result.

The 90% cutoff reflects healthy-subject reference data rather than a biological clearance point. Munro and Herrington reported a mean LSI near 100% across four hop tests, and every healthy participant reached at least 90%, according to a summary of the normative study. Clinicians commonly treat 90% or greater on every test as the minimum passing criterion.

Some clinicians favor thresholds above 95% because a 90% score still permits a meaningful side-to-side difference. Higher cutoffs remain proposed targets rather than universally accepted return-to-play criteria. LSI can also overestimate recovery when the uninvolved limb has lost capacity during rehabilitation.

Each hop may provide different information. In a study of 21 collegiate athletes after ACL reconstruction, single-hop LSI had the strongest individual correlation with psychological readiness. However, crossover-hop LSI was the only significant predictor retained in regression and explained 66% of ACL-RSI variance. Timed-hop LSI showed no significant correlation. The small cross-sectional sample does not justify formal weighting, but it supports interpreting each result separately rather than treating all four scores as interchangeable.

Where hop testing fits in the full return-to-sport decision

Clinicians should use the hop battery alongside quadriceps strength testing, movement-quality assessment, and psychological readiness screening. Hop distance and time quantify functional symmetry, while strength testing can identify deficits that an athlete may compensate for during hopping. Landing control also warrants direct observation because similar distances can result from different joint-loading strategies.

Psychological readiness can influence performance and the return-to-sport decision. In a study of 21 NCAA Division I athletes after ACL reconstruction, single-hop LSI correlated strongly with ACL-RSI scores, while crossover-hop LSI accounted for 66% of the variance in ACL-RSI scores within that small cohort. The timed 6-meter hop showed no significant correlation with readiness. These ACL-RSI findings support assessing physical performance and psychological readiness together, although the cross-sectional study cannot establish causation.

Before testing, a clinician-directed home exercise program can deliver and track the strength and neuromuscular-control work that prepares an athlete for hopping tasks. Physitrack supports this follow-on exercise delivery but does not determine when an athlete should undergo testing or return to sport.

The final decision should also account for sport demands, competition level, rehabilitation progress, symptoms, and time since surgery. A 90% hop-test LSI may satisfy one criterion, but the clinician should interpret it within the complete return-to-sport assessment.

Why passing hop tests doesn't eliminate reinjury risk

A passing LSI can conceal different movement strategies between limbs. An athlete may reach the same distance with both legs while unloading the reconstructed knee through greater hip or ankle contribution, reduced knee flexion, or altered landing control. Research published in the British Journal of Sports Medicine found that athletes after ACL reconstruction reached a 97% limb symmetry index in hop distance, but symmetry in the knee's work during propulsion was only 69%, confirming that hop distance alone can mask a real mechanical deficit.

Return-to-sport test results also do not map cleanly to reinjury risk. Research summarized in the International Journal of Sports Physical Therapy reports that only 23% of athletes fully passed a return-to-sport testing battery before resuming sport. Passing may reduce the risk of ipsilateral graft rupture while coinciding with greater contralateral ACL injury risk, so the overall risk of another ACL injury may remain.

Clinicians should interpret hop performance within a broader testing battery. Quadriceps strength, landing quality, sport-specific movement, psychological readiness, and contextual factors can reveal limitations that distance or time scores miss. Sport demands, competition level, and timing within the season also affect whether an athlete can safely resume participation.

Documenting hop test results

Record the best valid result for each limb, the calculated LSI, the threshold applied, and any voided trials.

• Single hop. Involved 156 cm, uninvolved 170 cm, LSI 92%, pass.
• Triple hop. Involved 455 cm, uninvolved 500 cm, LSI 91%, pass.
• Crossover hop. Involved 410 cm, uninvolved 460 cm, LSI 89%, fail.
• Six-meter timed hop. Involved 2.55 seconds, uninvolved 2.30 seconds, LSI 90%, pass.

Document the composite finding rather than describing the single-leg hop test as passed. For example, “Athlete met the 90% LSI criterion on three of four tests. Crossover hop remained below threshold at 89%, so the full hop battery criterion was not met. Results require interpretation alongside strength testing, movement quality, psychological readiness, and clinical findings.”

Conclusão

Hop testing provides necessary evidence of functional recovery after ACL reconstruction, but the battery cannot clear an athlete by itself. Similar hop performance between limbs may coexist with strength deficits, altered movement strategies, or limited confidence.

Clinicians should interpret hop results alongside quadriceps strength and movement quality. Psychological readiness, sport demands, and the athlete’s broader clinical course should also inform the return-to-sport decision. Clinical judgment integrates these findings into an individualized clearance decision.

Perguntas frequentes

What minimum LSI counts as passing?
Clinicians commonly use an LSI of at least 90% for each hop test. Distance tests divide involved-limb performance by uninvolved-limb performance and multiply by 100. Healthy-subject findings helped establish the 90% convention, but individual protocols may set higher criteria.

When should hop testing begin after ACL reconstruction?
Testing timing depends on the surgical and rehabilitation protocol rather than a universal postoperative date. Clinicians typically wait until the athlete meets prerequisite criteria for symptoms, range of motion, strength, and single-leg control. Calendar time should inform testing without replacing criterion-based progression.

Can hop testing alone clear an athlete for return to sport?
Hop testing cannot independently establish return-to-sport readiness. A multifactor assessment should also examine strength, movement quality, psychological readiness, sport demands, and clinical findings. Passing distance-based tests may still conceal altered landing mechanics or loading strategies.

How does hop testing differ from quadriceps strength testing?
Hop tests assess functional performance during explosive single-leg tasks. The quadriceps index compares force output between limbs, usually through dynamometry or isokinetic testing. An athlete may reach 90% hop symmetry through compensatory movement despite a remaining quadriceps deficit, so clinicians should interpret both measures together.