Strength Unit

Choose unit; LSI & ratios are unaffected. Alternate-unit equivalent shown below each strength input.

Thigh Circumference (Involved)

Measured 20cm above patella. Proxy for muscle mass; aim for ≤5% side-to-side difference.

Thigh Circumference (Uninvolved)

Reference limb for symmetry calculation.

Y-Balance Reach (Involved)

Composite = (ANT + PM + PL) / (3 × limb length) × 100. Target symmetry ≥90%.

Y-Balance Reach (Uninvolved)

Normalize with limb length below.

Limb Length (cm)

Used to normalize Y-Balance reaches.

Quadriceps LSI

--%

Target ≥90%

Hamstrings LSI

--%

Target ≥90%

H:Q Ratio

--

Ref ~1.2–1.8

Thigh Symmetry

--%

Target ≥95%

Y-Balance LSI

--%

Target ≥90%

Composite (Inv)

--%

Normalized

Composite (Un)

--%

Normalized

Quadriceps LSI

Compares involved to uninvolved limb quadriceps strength (usually via isometric/isokinetic or jump/force measures) as a percentage: LSI = (involved / uninvolved) × 100. A common clinical threshold for return-to-sport candidacy is **≥90%**, with higher symmetry linked to reduced reinjury risk, though many athletes struggle to reach it early in rehab. :contentReference[oaicite:0]{index=0}

Measurement tips: Standardize testing position, warm-up, and use the same device/method on both limbs.
Caveat: If the contralateral limb is deconditioned or weakness is masked, LSI can overestimate true recovery; comparing to estimated pre-injury capacity (EPIC) adds robustness. :contentReference[oaicite:1]{index=1}

Hamstrings LSI

Same calculation as quadriceps but for hamstring strength. Symmetry here is crucial for dynamic knee stability and controlling anterior tibial translation; target is also **≥90%** to minimize asymmetrical loading. :contentReference[oaicite:2]{index=2}

Why it matters: Disproportionate deficits (e.g., strong quads but weak hamstrings) may predispose to aberrant knee mechanics, though the hamstring-to-quadriceps ratio's predictive power for re-injury is complex and context-dependent. Some recent data show the isolated HQ-ratio may not independently predict second ACL injury but still offers insight into muscular balance. :contentReference[oaicite:3]{index=3}

Measurement: Use consistent dynamometry protocols or validated field surrogates; fatigue and testing order can influence values.

Quad:Ham Ratio (Same Limb)

Ratio of quadriceps to hamstring strength on the same limb. Provides a snapshot of agonist/antagonist balance: typical working ranges are roughly **1.2–1.8** depending on population and testing modality. :contentReference[oaicite:4]{index=4}

A skewed ratio (very high quad dominance or unusually low) could signal control deficits or imbalance; it’s one piece in the broader strength profile. The ratio alone does not strongly predict re-injury but contextualizes symmetry data. :contentReference[oaicite:5]{index=5}

Y-Balance Composite & LSI

Dynamic balance test using anterior, posteromedial, and posterolateral reach distances normalized to limb length: Composite = (ANT + PM + PL) / (3 × limb length) × 100. Then compare involved vs uninvolved to get LSI. Target symmetry is **≥90%** and less than ~4 cm absolute difference in anterior reach for some protocols. :contentReference[oaicite:6]{index=6}

Utility: Reflects neuromuscular control, single-leg stability, and integrated strength. Early deficits (e.g., >4 cm anterior discrepancy) correlate with poorer functional outcomes later in RTS progression. :contentReference[oaicite:7]{index=7}

Reliability: High inter- and intra-rater reliability when performed correctly. :contentReference[oaicite:8]{index=8}

Thigh Circumference Symmetry

Proxy for muscle mass / atrophy measured at a consistent point (e.g., 20 cm above the patella). Symmetry is calculated as (involved / uninvolved) × 100; within **~95–100%** (~≤5% difference) suggests minimal residual atrophy. :contentReference[oaicite:9]{index=9}

Why track it: Persistent size discrepancy can reflect ongoing neuromuscular inhibition or insufficient hypertrophic response, which may underlie strength asymmetries.

Limitations: Circumference is crude—doesn't distinguish between fat and muscle, so pair with strength testing for deeper insight.