Isotonic

[Sarah]

Having or indicating, equal tones, or tension. Isotonic system(Mus.), a system consisting of intervals, in which each concord isalike tempered, and in which there are twelve equal semitones.

[Sarah]

Isotonic is a popular recently developed type of sports drink, usually with Glucose or Fructose flavouring. Its mostly known as a cheap alternative to branded sports drinks such as 'Lucozade' or 'Powerade'.

[Sommer]

(of muscle action) taking place with normal contraction.