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Definition

adjective

1. Having equal tension.

2. Pertains to a muscular contraction in which the muscle remains to be in a relatively constant tension while its length changes, as in isotonic muscle.

3. Isoosmotic, i.e. having the same (or equal) osmotic pressure and same water potential since the two solutions have an equal concentration of water molecules.

4. Pertaining to a solution that has the same tonicity as some other solution with which it is compared. For example, blood serum is isotonic to a physiologic salt solution. Solutions that have same tonicity will result in no net flow of water across the cell membrane.

Supplement

Word origin: ISO– + Greek tonos, tension; see tone + –IC.

Related forms: isotonically (adverb), isotonicity (noun).
Related phrases: isotonic exercise, isotonic contraction, isotonic solution.

Compare: hypotonic, hypertonic.
See also: solute, solution, osmotic pressure.