Quote: "Muscle fatigue, due to glycogen depletion within the muscles and liver, cause a relative deficit of ATP and thus a resultant inability of crossbridges to detach, causing contractures (McArdle et al., 2001)."

If this were true, then it would make sense that Creatine, which acts as an ATP energy substrate in cells would offset the relative deficity of ATP. This would indicate that in fact cellular substrate manipulation could indeed influence muscle contracture/cramps. The study cited appears to support this statement.

However, although certain food or nutritional materials are quite obviously necessary (K+/Na+ for example vital for muscle contraction), it is likely that the effects of this are augmented by appropriate muscle work, as you mentioned.

I think it is important even as physiotherapists to understand how cellular mechanisms influence physical presentation of symptoms. Hypokalemia/hyperkalemia, as an example