We so far have a total of two studies which state that the risk of back injury is greater in the morning. The Snook, etal. study was done in 1998. The one above is even older, 1987.ChrisPBacon wrote:The library at the hospital my wife works at is looking for a copy of the 1998 article. If they find it, I'll post it.
Here is another article I found.
Spine (Phila Pa 1976). 1987 Mar;12(2):130-7.
Diurnal variations in the stresses on the lumbar spine.
Adams MA, Dolan P, Hutton WC.
Abstract
Millions of people exercise early in the morning. I would think that if activity at this time of day promotes back injury, there would be warnings all over the Internet concerning that so-called "danger". I believe the reason why there are none is that conclusion was reached by exactly two isolated studies, one 28 years old and the other done 17 years ago. I also wonder how many people were involved in those studies. As I said before, show me a lot more recent documentation confirming that fact and I'll listen. But if I have to rely on just those two, I can only assume they are nothing more than interesting curiosities.
I've read articles stating that early morning exercise for people with hypertension and diabetes may be a possible concern and they make a lot of sense. Another one concluded that exercising in the morning could possibly increase susceptibility to infection compared to an afternoon training session. I have no idea if that's true. But aside from the two studies above and Dr. McGill's comments, I have seen nothing else about the possibility of back injury arising from early morning workouts.
I think I found a reasonable solution as to what time of day is best to protect your back when exercising. If you exercise early in the morning and your back hurts and if you exercise later in the day and it doesn't hurt, don't exercise early in the morning.