Landing Error Scoring System (LESS): The Full Assessment Guide

A physical therapist watches a college volleyball player land from a block jump in clinic and the knee drifts inward before anyone has said a word about pain. That read is not a hunch. It has a name, a validated scoring sheet, and a decade of research behind it: the Landing Error Scoring System, built by Darin Padua's group to turn what a trained eye already sees into a repeatable number, without needing a 3D motion capture lab. Most teams that own a force plate or a jump mat can already tell you how high an athlete jumps. Almost none of them can tell you, in a way that's been checked against lab data, whether the way that athlete lands is quietly building toward a noncontact ACL tear. That's the gap LESS was built to close, and this guide walks through the protocol, the scoring, and where the tool's real limits sit.

LESS is a video-based clinical screening tool that scores landing biomechanics during a standardized jump-landing task. An athlete jumps forward off a box, lands on both feet, and immediately performs a maximal vertical jump. Two cameras — one facing the athlete, one from the side — capture the landing, and a trained rater scores 17 discrete items covering trunk position, hip and knee flexion, knee valgus, foot position, and the overall softness or stiffness of the landing. Each item flags the presence of a movement pattern linked in prior lab research to higher loading on the ACL. The items are summed into a single total score, and unlike a vertical jump number, lower is better here — a higher LESS score means more error patterns were present, not more athleticism.

The point of building it this way was practical. Full 3D motion analysis with reflective markers and force plates gives the gold-standard read on landing mechanics, but it needs equipment and expertise that almost no team, clinic, or school athletic program has on hand. LESS was designed as a field-usable substitute — two cameras and a trained rater instead of a lab — aimed specifically at the kind of screening a sports medicine staff might run on 40 or 80 athletes in a single afternoon before a season starts.

Padua, Marshall, Boling, Thigpen, Garrett, and Beutler (2009, American Journal of Sports Medicine) introduced LESS as part of the JUMP-ACL project. Fifty-one collegiate-age athletes performed the jump-landing task while both a 3D motion capture system and human raters scored the same trials, letting the researchers check whether a video-based rater could catch what the lab equipment caught. Reliability held up well for a tool that depends on human judgment: intra-rater ICCs of 0.91 for real-time scoring and 0.83 for video-delayed scoring, with inter-rater ICCs of 0.84 (real-time) and 0.91 (video). Total LESS score also correlated moderately-to-well with a composite 3D kinematic and kinetic score built from the same trials — athletes who scored worse on LESS showed measurably greater peak vertical ground reaction force, knee valgus moment, and reduced hip and knee flexion excursion on the lab equipment.

The correlation was real but not perfect, and that matters for how the tool should be used. LESS agrees with lab-based movement analysis closely enough to be useful as a screening instrument, but it is not a drop-in replacement for 3D analysis when a specific case is ambiguous or when research-grade precision is required. A separate, smaller prospective study in elite youth female soccer players (Smith et al., 2012, American Journal of Sports Medicine) followed athletes across multiple seasons and found that those who went on to suffer a noncontact ACL injury had scored worse on LESS at baseline than teammates who stayed healthy. Because so few ACL injuries occurred during that follow-up window — a persistent problem in any prospective ACL screening study, since the injury itself is thankfully rare — the study is better read as supporting evidence for LESS than as proof of a hard predictive cutoff. Treat a single LESS score as a flag worth acting on, not a diagnosis.

• Box: A 30cm (12in) box, stable enough to stand on without wobble.
• Landing target line: Marked on the floor at a distance equal to 50% of the athlete's standing height from the box. A 1.70m athlete jumps forward to land at roughly the 0.85m mark — measure per athlete rather than using one fixed distance for the whole squad.
• Two cameras: One positioned directly in front of the landing area (frontal plane view) and one at the side (sagittal plane view), both at the athlete's approximate hip height, far enough back to capture the full body from just before takeoff through the second jump.
• Firm, non-slip flooring: A gym floor or turf surface the athlete already trains on. Testing on an unfamiliar surface changes landing strategy independent of an athlete's actual mechanics.
• Standard athletic footwear: The shoes the athlete trains in, not barefoot and not a formal dress shoe substitute — footwear changes ground contact and ankle stiffness enough to shift scores.
• A trained rater, ideally two: LESS is a judgment-based tool. Reliability in the original study depended on raters who had practiced against a reference standard before scoring live athletes; an untrained rater scoring cold will produce noisier numbers than the published reliability figures suggest.

Warm-up (8–10 minutes): Light jogging, dynamic hip and ankle mobility, and 2–3 practice jumps at submaximal effort so the athlete understands the task before it's scored. Practice reps should stop well short of the point where the athlete starts consciously grooving a soft landing — over-rehearsing the task before scoring can mask exactly the pattern the test is trying to catch.

1. Athlete stands on the 30cm box with feet shoulder-width apart, toes at the front edge.
2. On a verbal cue, the athlete jumps forward off both feet, aiming to land with the middle of both feet at the marked line (50% of standing height from the box).
3. Immediately upon landing, without pausing to reset, the athlete performs a maximal vertical jump straight up.
4. Both cameras record the entire sequence from just before takeoff through the peak of the second jump.
5. Repeat for 3 trials, with roughly 30–45 seconds of rest between reps — enough to reset, not enough for the athlete to start problem-solving the landing technique.
6. Score each trial from the recorded video, either in real time on a second monitor or frame-by-frame in slow motion for the frontal and sagittal criteria that are hard to catch at full speed.

The forward jump distance is not incidental. Landing from a jump that's too short turns the task into a drop with almost no horizontal momentum to manage, which tends to flatter an athlete's mechanics; too long a distance manufactures errors that have more to do with an arbitrary target than real movement quality. The 50%-of-height standard keeps the demand consistent across athletes of different sizes.

LESS scores 17 discrete items split across the frontal-plane view, the sagittal-plane view, and an overall impression of the landing. Most items are scored as present (1 point, an error) or absent (0 points), so a lower total is the goal.

• Frontal plane (viewed from the front): Knee valgus at initial contact and again at maximum knee flexion, stance width relative to shoulder width, foot rotation at contact, and side-to-side symmetry of the two feet touching down together.
• Sagittal plane (viewed from the side): Trunk flexion angle at initial contact, hip and knee flexion angle at initial contact, and the total displacement of trunk, hip, and knee flexion from contact to the deepest point of the landing — a landing that stays stiff through the hips and knees scores worse than one that absorbs load through a deeper bend.
• Overall impression: A single holistic rating of the landing as excellent, good, average, or poor, scored separately as a sanity check against the summed score.

Because several items hinge on a joint angle at one instant — initial ground contact — raters who only watch in real time tend to miss what a frame-by-frame review catches.

Total LESS score is the sum of errors across all 3 trials, or the average of the 3 individually scored trials, depending on which protocol variant a program follows — pick one method and stay consistent across an athlete's retests, since averaging versus summing changes the raw number even when the underlying movement quality hasn't changed. The categorization below, developed in follow-up work refining LESS for real-time clinical use, is the version most commonly cited in practice.

A score of 5 or higher has been used in some screening programs as an at-risk cutoff, drawing on the Smith et al. (2012) soccer cohort described earlier. Given how few injuries that study recorded during follow-up, a single cutoff score should inform priority for coaching attention, not function as a pass/fail gate that clears or benches an athlete on its own. The categories are most useful compared against an athlete's own prior score, tracking whether a training block is actually changing the pattern it targeted.

• Too many practice reps before scoring. Give athletes 8–10 unscored trials and most will land noticeably softer than their real first attempt would show, masking the pattern the test exists to catch. Two or three familiarization reps is enough.
• Scoring only in real time at full speed. Several items hinge on a joint angle at the instant of initial contact. Skipping the slow-motion review measurably increases scoring error compared to the original protocol.
• Fixed jump distance regardless of athlete height. Using one box-to-line distance for a full roster ignores the 50%-of-height standard, turning taller and shorter athletes into different, non-comparable tests.
• Only using one camera angle. Frontal errors like knee valgus and sagittal errors like limited hip flexion displacement can't both be caught from one viewpoint — skipping either camera drops roughly half the scoring criteria.
• Treating one score as final. A single session captures one day's mechanics, which shifts with fatigue or footwear. Retesting at intervals is where LESS earns its value as a training tool rather than a label.

A raw total score tells a coaching staff how much error is present; the individual items tell them where to spend training time. An athlete flagged mainly on knee valgus benefits from hip abduction and external rotation strengthening plus cued single-leg landing drills, since valgus collapse at contact usually traces back to weak hip control rather than a knee problem itself. An athlete flagged on limited hip and knee flexion displacement — a stiff landing that doesn't absorb load through a deeper bend — needs eccentric strength work and explicit soft-landing cues before jump volume increases further, since that stiffness pattern was linked to higher ground reaction force in the original validation data.

A practical progression: start with double-leg drop landings from a low box (15–20cm), no subsequent jump, cueing the athlete to sit back into the hips rather than stay upright. Progress to the full LESS task as a training drill once double-leg landings look clean, then add single-leg variations once mechanics hold up across fatigue — single-leg control is where most asymmetry that a double-leg test misses tends to surface. Retest every 6–8 weeks using the identical box height, jump distance, and camera setup.