I found this article that offers a study underpinning something I’ve been saying for twenty years; “Every day is kidney day.”
This is for the guys who train frequently with the maxim, ‘yesterday was arms, today is chest and back, and tomorrow is legs.‘ It’s easy to fall into this trap when you never take objective measurements of your actual performance.
By contrast, when you have Power Factor, Power Index or Static Contraction numbers to compare every exercise on every workout you quickly discover the fallacy of training with the premise that every muscle group is independent.
Nottingham Trent University in Britain has determined that arm training diminishes leg training. Their hypothesis is “Unlike muscle energy stores, whose effects are local, increasing the level of metabolites in the blood affects the whole body.” Hmmm. Arm day is kidney day. (So is chest and back day. So is leg day.)
The test subjects did the arm and leg exercises the same day. But once you establish that the arm training diminishes the power of other muscle groups the next question is, ‘For how long does this effect last?’ Well, without using objective measurements how the hell would you know? I can tell you it lasts for days and it varies between individuals. Thousands of other people who train my way can tell you the same thing. Plus it varies according to where you are in your training in terms of beginning, intermediate and advanced levels of strength.
I’m sure the scientists will further investigate and debate the actual causes right down to the molecular details. But anybody with a stopwatch and a pencil could determine the same thing using the measurements I’ve been talking about since 1993. (All the “Monday, Wednesday and Friday” guys will never talk about this. They want you in the gym regardless of whether it’s productive.)
If you don’t measure it ain’t a science. Train Smart.