Yep, that's his law all right! The last 4 or 5 tiimes my back has gone it has been due to me turning awkwardly or reaching across for something or bending over awkwardly, never through doing heavy deadlifts or other strength exercises. Aside from the first time it went, which was during me stupidly doing at set of Superman back exercises without a warm up, the only times I've aggrevated it working out, have been when it has already been giving me a bit of pain and I've ignored it!