The best replacement for rigidity is spasticity.

The best alternatives to rigidity are rated as following:
★★★★★  spasticity
★★  stiffness
★★  voluntary guarding
★★  flexibility
★★  hypertonia
★★  contracture
★  spasticity difference
★  guarding
★  dystonia
★  rigidness
★  modulus of elasticity
★  decerebrate
  rebound
  decorticate
  decerebrate rigidity
  neck stiffness
  torsional rigidity

Your alternative for rigidity is not listed? Suggest!
Speaking about rigidity, one probably shouldn't forget about parkinson's.

Other search terms related to rigidity and their ratings are:
★★★★★ parkinson's
★★ cerebral palsy
★ meningitis
★ parkinson
parkinsons
You have in mind a companion for rigidity and it is not yet here? Propose!



Google Trends

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rigidity
spasticity
stiffness