Hop Test Battery for ACL Return-to-Sport: Protocol, Scoring, and Cutoffs

An athlete finishes rehab, clears the quad strength bench, and has been jogging pain-free for six weeks. The surgeon signs off. Someone runs one hop test - a single hop for distance - and the number comes back at 92% of the uninjured leg. Cleared, right? Not so fast. A single hop for distance loads the quad and hip extensors in a straight sagittal-plane line and rewards momentum carried into the takeoff; it tells you almost nothing about how that same knee tolerates a lateral cut, a repeated landing, or a short controlled stop over 6 meters. Athletes pass it and still go down again in the first month of preseason.

That's the reason serious return-to-sport testing after ACL reconstruction never leans on one hop score alone. It runs a battery of four hop tests, each loading the knee a different way, and only calls the limb ready when symmetry holds up across all four - not just the one that happens to look best on the day. What follows is the exact setup, order, scoring math, and cutoffs for that battery, plus what actually happens to reinjury numbers when the criteria get waved through anyway.

Why One Hop Test Isn't Enough

Picture an athlete about nine months post-ACL reconstruction. On the single hop for distance, the involved leg lands 155cm against 168cm on the uninjured side - a limb symmetry index (LSI) of 92.3%, comfortably above the usual 90% bar. Triple hop tells the same story: 430cm versus 460cm, 93.5% LSI. Two green lights. Then the crossover hop, which forces a diagonal hop across a line three times in a row rather than straight ahead, comes back at 390cm against 460cm - 84.8% LSI, a clear fail. The knee that looked fine going straight forward loses control the moment a rotational demand gets added.

That gap is why the four-test battery exists instead of a single score. Each test stresses the limb differently: straight-line power, repeated power under fatigue, frontal-plane control, and speed under time pressure. A limb can compensate for a weakness in one plane and still fail badly in another - and an athlete tested once, on whichever hop looks best, walks back onto the field with a real deficit nobody measured.

Equipment and Space Setup

None of the four tests need a force plate or a lab. A clear stretch of firm, non-slip flooring at least 8 meters long is the main requirement, since the crossover and timed hops both need continuous space to run without a turn.

Test the uninjured leg first on every measure, so the reference value isn't influenced by fatigue carried over from testing the surgical side first. Give at least 30 seconds between trials on the same leg and roughly 2 minutes between tests in the battery.

The Four Tests, Step by Step

Run the tests in this order - single, triple, crossover, then timed - so fatigue accumulates from the least demanding to the most demanding pattern rather than compromising an early test.

1. Single hop for distance. Stand on the test leg with the toe at the start line. Hop forward as far as possible, land on the same leg, and hold the landing motionless for a minimum of 2 seconds. A step, hop, or touchdown of the other foot voids the trial. Measure from the start line to the back of the heel at landing. Give 1 practice trial, then score 2 maximal trials per leg and keep the better distance.

2. Triple hop for distance. Same starting position, but the athlete performs three consecutive forward hops on the same leg with no pause between landings, holding only the final landing for 2 seconds. Measure total distance from the start line to the final landing point. Score the sum of the best trial, not an average across attempts.

3. Crossover hop for distance. Mark a straight line at least 6m long. The athlete hops three consecutive times along the line, crossing over it with each hop in a zigzag pattern - right foot lands to the left of the line, next hop crosses back to the right, and so on - holding the final landing for 2 seconds. Measure total distance covered. This is the test most likely to expose a frontal-plane or rotational control deficit that the straight-line hops miss entirely.

4. Six-meter timed hop. Mark a 6m distance on the floor. The athlete hops on the test leg as fast as possible from start to finish line; the clock starts on the first hop and stops the instant the lead foot crosses the 6m mark. Unlike the three distance tests, a lower time is the better score. Run 2 trials and keep the faster one, discarding any trial with an obvious stumble or extra stabilizing step.

Total testing time for both legs across all four tests, including rest, typically runs 20-25 minutes.

Calculating the Limb Symmetry Index

For the three distance-based tests, the formula is: LSI = (involved limb distance ÷ uninvolved limb distance) × 100. Using the single hop example above - 155cm involved, 168cm uninvolved - the LSI is (155 ÷ 168) × 100 = 92.3%.

The timed hop inverts the ratio, since a faster time is the better result: LSI = (uninvolved limb time ÷ involved limb time) × 100. If the uninvolved leg completes the 6m hop in 1.92 seconds and the involved leg takes 2.15 seconds, LSI = (1.92 ÷ 2.15) × 100 = 89.3% - just under the standard 90% line, even though the raw time difference is under a quarter of a second. Small time gaps on this test compound into meaningful LSI drops, which is worth remembering before dismissing a 0.2-0.3 second difference as noise.

Score each of the four tests separately rather than averaging them into one composite number. Averaging is exactly how the crossover hop failure in the earlier example - 84.8% against three passing scores - gets buried inside an acceptable-looking mean.

What the Research Actually Shows

Reid, Birmingham, Stratford, Alcock, and Giffin (2007), in Physical Therapy, established the reliability and validity of this exact four-test battery in ACL-reconstructed patients, reporting intraclass correlation coefficients between 0.82 and 0.93 - solid enough to trust a change in score as real rather than noise. Their data also showed a real limitation: hop LSI correlated only moderately with patient-reported outcomes like the IKDC (roughly r = 0.55-0.66), and a meaningful share of patients hit high hop symmetry while still reporting functional limitations - a ceiling effect meaning passing all four hops confirms an athlete isn't grossly deficient, not that the knee feels fully normal.

Kyritsis, Bahr, Landreau, Miladi, and Witvrouw (2016), in the British Journal of Sports Medicine, followed ACL-reconstructed athletes back into competitive sport and compared those who met a full discharge criteria set - including the 90% LSI threshold on this hop battery plus quadriceps strength symmetry - against those who returned without meeting it. Athletes who returned without meeting the criteria had roughly four times the risk of a subsequent ACL graft rupture compared with those who met every criterion first, the strongest case for treating the 90% line as a real gate rather than a target to round up to.

Wellsandt, Failla, and Snyder-Mackler (2017), in the Journal of Orthopaedic & Sports Physical Therapy, raised the limitation that matters most in practice: limb symmetry indexes, hop tests included, can overestimate true knee function when the uninvolved leg has also lost capacity relative to pre-injury levels, common after months of reduced training load. Their cohort showed athletes clearing 90% hop LSI who still carried substantial quadriceps strength asymmetry undetected by the hop scores alone - a hop battery pass should never stand in for a separate quadriceps strength test, since the two measure different things.

Cutoffs and How to Read Them

The 90% LSI threshold below is the figure used across the return-to-sport criteria research cited above, applied identically to all four tests rather than varying by test.

All four tests need to individually clear 90% before the battery counts as passed. A single failing test - the crossover hop in the earlier example - overrides three passing scores; it does not average out. And because the Kyritsis et al. (2016) findings tie the hop battery specifically to reinjury risk when combined with quad strength testing, treat the hop battery as one component of a larger return-to-sport panel, not a standalone clearance.

Mistakes That Skew the Battery

Where Hop Results Fit in the Return-to-Sport Decision

A clean pass on all four hops is a green light for one part of the picture: single-leg power and control across four loading patterns. It is not, on its own, a green light for full competitive sport. Pair it with a quadriceps and hamstring strength symmetry test - a hop battery pass alongside a quad strength deficit is exactly the combination Wellsandt et al. (2017) flagged as under-detected by hop scores alone - and add a patient-reported outcome measure like the IKDC or ACL-RSI to capture the psychological readiness the Reid et al. (2007) data showed hop scores don't fully track.

When an athlete fails one test in the battery - the crossover hop is the most common single failure, since it is the least-trained movement pattern in typical rehab programming - resist retesting just that one test the next day hoping for a better number. Build 2-4 weeks of targeted work on that pattern (lateral bounds, controlled crossover landings at submaximal distance, single-leg deceleration drills) before retesting the full battery, since a score improved through practice effect on one isolated test tells you less than a battery re-run from a clean baseline.