This involves rapid alternation of lengthening and shortening of muscle fibers against resistance. Isometrics, muscle lengthening and muscle shortening exercises were studied and compared. There is evidence of both vowel shortening and lengthening. The incremental daily increases result in a considerable lengthening of the limb over time. A promising therapy involves eccentric loading exercises involving lengthening muscular contractions. External fixation is also used in limb lengthening. Lenited stops generally disappear before sonorants , with compensatory lengthening of the preceding vowel. It is accompanied by allophonic lengthening of the vowel. Some symmetry was restored by open syllable lengthening, which restored a long low vowel . Another pathway for which P70 has proposed involvement is in muscle lengthening and growing. The lengthening of the urethra is where most complications occur. Loss of the fricatives was accompanied by some compensatory lengthening or diphthongization of preceding vowels. Also unaffected was long that arose by compensatory lengthening of short . In the process of lengthening, the high vowels were lowered. The Fitbone is a fully implantable, motorized, lengthening and correction nail.