Strength training has a potent effect on a number of health outcomes, whether it be muscular size and strength, or reduction in chronic disease risk. In recent years many research articles have suggested that strength training IS medicine.
Just like any good medicine, strength training has a dose-response relationship; meaning that if you strength train infrequently enough you won’t see any benefits from it, and if you strength train too frequently there will actually be a negative response and we’ll see people actually start to get weaker.
Why is it that we get weaker by doing very frequent weight lifting? Well think about; each time you do a workout you are breaking your muscle tissue down, and it is only after a few days of rest that your body has fully recovered. Now imagine you go and lift before your body has rebuilt, and imagine that you are doing this chronically. You are putting yourself in a constant state of muscle tissue breakdown, and when you never give yourself a chance to rest you end up seeing muscle disappear because it was constantly being broken down and never given the chance to rebuild. This is termed overtraining.
So while training more frequently can be of great benefit (training twice a week instead of once), it is important to remember that there comes a point of diminishing returns and more is not always better when it comes to strength training.