What God says is always true (Rom. 3:4). The wisdom of man is of this earth, by definition earthly, sensual and devilish (James 3:15). Exercise and eating the right kind of foods in moderate amounts can make one’s life better in terms of health. The problem is when man tells us what exercises, food and how much in order to preserve our lives. The wisdom of man has always been that man himself can solve all his problems. The NFL and other groups strive to speak about exercise for children to make their lives better. The same NFL puts their teams on the field by advertising products which children are not allowed to drink. The wisdom of the world remains dangerous.
Was Paul, therefore, condemning taking care of our bodies? The Holy Spirit, through Paul, states that we nourish or cherish our bodies (Eph. 5:29). So, Paul was not condemning taking care of our bodies. As Christians, we walk by faith and not by the wisdom of this world (2 Cor. 5:7). Giving power to government or any other group allows them to set the standard. The danger here is that if the group says that “salt” is bad for you can also say that reading the Bible is bad for you. If you need an example consider what happened to Daniel regarding prayer (Daniel chapter 6). Stop and think who has decreed that we cannot end prayers in public in Jesus’ name in certain places?
What Paul was teaching in I Tim. 4:8 is that bodily exercise in comparison to the exercise of godliness, would not be as important. Spiritual exercise as in righteous development has the blessing of making our lives here better and gives us the hope of eternal life with God. Bodily exercise may help us to have a better quality of life here but it can do nothing for eternity. When making a decision about what to do, either physical or spiritual be sure to go to the right source. God cannot lie, whereas the wisdom of man can often have hidden agendas.