Triple Hop Distance Test: Return-to-Sport Assessment Protocol

Nine months after ACL reconstruction, quad strength reads 94% of the uninvolved side, the running program is complete, and the athlete feels ready. Then the surgeon asks for one more number before signing off on cutting and pivoting sports, and that number usually comes from three consecutive hops on one leg. It feels almost too simple for a decision this consequential — but a static strength test measures force under controlled, braced conditions, and a torn ACL rarely fails an athlete in a controlled, braced moment. It fails during deceleration, at the third step of a cut, when the limb has to absorb load it did not expect. The triple hop distance test recreates exactly that demand, which is why Noyes and colleagues built it into the original hop test battery back in 1991 and why it has outlasted three decades of competing return-to-sport metrics.

Why This Test Catches What Others Miss

Noyes, Barber, and Mangine published the paper that started it all in the American Journal of Sports Medicine in 1991, testing 49 patients with ACL deficiency or reconstruction against a healthy control group. Their finding was blunt: isokinetic quadriceps strength testing missed functional deficits that showed up the moment patients performed a task requiring rapid force absorption and reproduction. Roughly a third of patients with normal-looking strength scores still failed the hop battery. That gap between what a dynamometer reports and what a limb can actually do under sport-like load is why hop testing exists at all.

The triple hop adds something a single hop cannot. One hop measures a single concentric push; three consecutive hops force the leg to absorb landing force and immediately re-express it twice more before the distance is even measured. That repeated stretch-shortening demand fatigues compensation strategies faster — an athlete can mask a deficit for one hop through momentum, but rarely across three.

Reid, Birmingham, Stratford, Alcock, and Giffin followed up in 2007 with a reliability and validity study on 49 patients pre- and post-ACL reconstruction, published in Physical Therapy. They reported intraclass correlation coefficients between 0.82 and 0.93 across the four standard hop tests, and found hop performance correlated more strongly with patient-reported knee function (IKDC scores) than isokinetic strength did — the hop test tracks how the knee actually feels to the athlete better than a leg-extension machine does.

Equipment and Space Setup

Nothing about this test requires a lab. You need a hard, non-slip, flat surface at least 4–5 meters long, a tape measure or marked measuring line taped to the floor, and a clear starting line. Carpet or grass introduces variability in push-off and landing that will contaminate your numbers session to session, so pick one surface and stay on it for the entire rehab timeline.

Athletes should wear the same footwear — or bare feet, if that is your standard — at every testing session. A change from cushioned trainers to flat court shoes between the six-week and twelve-week test can shift distance by several centimeters on its own, with nothing to do with the knee.

Step-by-Step Protocol

This follows the Noyes protocol with the practical adjustments most clinics actually use:

1. Warm up generally — five minutes of light cycling or jogging, then two to three submaximal practice hops on each leg so the athlete understands the task before it counts.
2. Test the uninvolved limb first. This gives you the reference distance and lets the athlete build confidence before attempting the surgical or previously injured leg.
3. Starting position: athlete stands on the test leg, toes just behind the starting line, hands free to swing.
4. Execute three consecutive maximal-effort hops forward on the same leg. The non-test leg must not touch the ground at any point between hops — if it does, the trial is void and repeated.
5. Stick the landing on the third hop and hold it for a minimum of two seconds without additional hopping, stepping, or touching down with the opposite foot for balance.
6. Measure the distance from the starting line to the back of the heel at the point of final landing — not the toe, not wherever the athlete overbalances to afterward.
7. Allow 15–30 seconds of rest between attempts, and perform two to three scored trials per leg. Use the best trial, not the average, per the original protocol.
8. Repeat the entire sequence on the involved limb using identical instructions and rest periods.

A trial is discarded and repeated if the athlete loses balance on landing, touches down with the free leg during the hop sequence, or visibly favors the limb with a hitch or hop-adjustment mid-sequence. Discarding bad trials matters more than most clinicians assume — a single compensated trial can shift LSI by 4–6 percentage points, enough to flip a pass into a fail.

Calculating the Limb Symmetry Index

The Limb Symmetry Index (LSI) compares the involved limb's best distance against the uninvolved limb's best distance, expressed as a percentage. The formula is simple, but the numbers deserve a worked example because clinics regularly transpose the fraction by mistake.

Note the order: involved limb distance divided by uninvolved limb distance, not the reverse. Reversing the fraction produces a number greater than 100% and clinicians who are tired at the end of a long clinic day make this error more often than anyone likes to admit — always sanity-check that your LSI is below 100 unless the operated limb has genuinely outperformed the healthy one, which does happen but should prompt a second look at your measurements.

Interpreting the Numbers: What Counts as Passing

Noyes et al. (1991) originally proposed 85% LSI as the cutoff below which a limb was classified as functionally abnormal. That threshold held for years, but subsequent research pushed most return-to-sport protocols toward a stricter line.

Grindem, Snyder-Mackler, Moksnes, Engebretsen, and Risberg published the Delaware-Oslo ACL cohort study in the British Journal of Sports Medicine in 2016, following 106 athletes after ACL reconstruction. Athletes who met a set of return-to-sport criteria — quadriceps strength LSI of at least 90%, hop test LSI of at least 90% across all four hop tests, and a self-reported knee function score above a set threshold — had an 84% lower rate of reinjury within the following two years compared to athletes who returned without meeting those criteria. That single study is largely why 90% has replaced 85% as the working standard in most modern clinics.

One caution worth taking seriously: Kotsifaki, Korakakis, King, and colleagues, writing the Aspetar clinical practice guideline on ACL reconstruction rehabilitation in the British Journal of Sports Medicine in 2023, pointed out a structural weakness in LSI itself. Because LSI compares the involved limb only to the uninvolved limb, an athlete whose healthy leg has also detrained during a long rehab — which happens more often than clinics like to admit, especially past nine months post-op — can post a 90%+ LSI while both limbs sit well below their pre-injury capacity. A passing LSI is necessary, but treat it as one data point rather than the whole clearance decision.

Mistakes That Quietly Inflate the Score

A handful of technique errors show up constantly in clinical hop testing, and all of them push the number in a falsely reassuring direction:

• Measuring to the toe instead of the heel. Athletes often land with the trailing foot rotated or the heel lifted; measuring to whichever point is furthest forward can add 3–8 cm per hop, compounding across three hops into a meaningfully inflated distance.
• Allowing a hop-and-stick recovery step. If the athlete takes a small correcting hop after the third landing before holding still, and the tester doesn't catch it, the trial should have been voided but often isn't.
• Skipping practice trials. An athlete's first attempt at triple hopping in months is almost always shorter than their second or third simply from unfamiliarity with the task — testing cold underestimates true capacity and can produce a false-fail.
• Switching testing surfaces between sessions. Comparing a baseline test done on a sprung gym floor to a six-month retest on a concrete clinic floor introduces a confound that has nothing to do with knee function.
• Treating LSI as the entire clearance decision. A single leg that hops 90% of its partner's distance says nothing about whether either leg has returned to the athlete's own pre-injury baseline, or whether the athlete trusts the limb enough to cut at game speed without hesitating.

Beyond LSI: Building the Full Return-to-Sport Battery

The triple hop distance test is one leg of a four-test hop battery that also includes the single hop for distance, the crossover hop for distance, and the 6-meter timed hop. Noyes' original protocol recommended running all four, since each stresses the limb slightly differently — the crossover hop, for instance, adds a frontal-plane demand that the triple hop does not, and catches deficits the triple hop alone can miss.

The Delaware-Oslo criteria that drove the 84% reinjury reduction combined hop testing with two other pillars: quadriceps and hamstring strength LSI at or above 90% measured isokinetically or with a reliable handheld dynamometer, and a psychological readiness score, typically the ACL-Return to Sport after Injury (ACL-RSI) questionnaire, above an established cutoff. An athlete can pass every hop test and still not be ready if their ACL-RSI score reveals persistent fear of reinjury — that fear itself is a documented, independent risk factor, not just a feeling to talk through on the way out the door.

Practically, this means scheduling the full battery — strength testing, all four hop tests, and the psychological questionnaire — in a single session roughly every four weeks from month five or six post-op onward, rather than testing hop distance in isolation and treating a single passing number as clearance.