Traces of this system are found in Sanskrit and, to a much lesser extent, in Greek. There were two types of paradigm with a mobile accent. The o-stems which formed the largest class of nouns in IE had a fixed accent although they may show the effects of ablaut. However, there was no ablaut alternation throughout the paradigm as there was in consonant stems. Only Sanskrit preserves a clear relationship between stress and ablaut in athematic verbs.
Athematic verbs have a full grade root under stress, but a zero grade when the ending is stressed.
In Greek, the accent on finite verbs was assigned as far back as possible suggesting the same thing. That is, in Greek at one stage verbs were accentless. When the language required that all lexical items should be stressed, the old verbal accent had been forgotten, hence the new system of assigning stress as far back as possible was applied.