floppiness       
noun [ U ] uk/ˈflɒp.i.nəs/ us/ˈflɑː.pi.nəs/
 松懈,下垂
the quality of being soft and not able to keep a firm shape or position
  With decreased muscle tone there is floppiness of the limbs and trunk. 随着肌肉张力的降低,四肢和躯干会变得松弛。 
 The baby was vomiting and showing signs of floppiness. 婴儿呕吐并出现软弱无力的迹象。 
 See: floppy
 - More examples
 - The dancer melted into floppiness, then lifted a leg sky-high.
 - The operation tightens up tissue at the opening of the throat, eliminating the floppiness and vibration that cause snoring.
 - She had an increased heart rate and a sudden feeling of floppiness.