Knee Flexion Rehab Simulator

Therapy Session

Target flexion angle 60°

Exercise mode

Repetitions 10

Post-op knee: stiff and guarded. Choose a target angle within reach and start a session.

Patient Status

Current angle

0.0°

Max comfortable ROM

28.0°

Inflammation / pain15%

Quad strength20%

Sessions completed

Full extension

0°

How it works

Range-of-motion (ROM) rehab follows a load–adapt curve: stretching a stiff joint just past its current comfortable maximum stimulates capsule/tendon remodeling and increases the achievable angle; stretching far beyond it tears newly formed tissue and triggers inflammation, which temporarily shrinks the achievable angle again.

overstretch = max(0, target − maxROM)
safe = min(overstretch, 12°)      // productive stretch zone
excess = max(0, overstretch − 12°) // re-injury zone

gain = modeFactor · repFactor · (0.4·safe + 1) · (1 − inflammation/140)
if excess > 0:
  inflammation += excess · (reps/10) · 1.8
  maxROM       −= excess · 0.25
  gain *= 0.3                        // setback, little net progress

maxROM      += gain
inflammation *= 0.8                  // rest between sessions
strength     += reps · (resisted ? 0.35·(1−inflammation/150) : 0.08)

Target angle — how far the knee is pushed toward flexion this session (goniometer reading).
Passive — therapist-driven stretch, gentle mode factor, lowest strength gain.
Active-assisted — patient contributes effort; best ROM-gain factor.
Resisted — adds load against the motion; smaller ROM gain but the only mode that meaningfully builds quad strength.
Staying within the green "safe" zone (target ≤ current max ROM + 12°) compounds gains session after session; repeatedly overshooting it stalls or reverses progress — exactly the clinical trade-off a physical therapist manages.

0.0°

Within safe ROM Stretch zone Re-injury zone

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