1 Corinthians 9:27 AMPC
But [like a boxer] I buffet my body [handle it roughly, discipline it by hardships] and subdue it…

Paul, that great runner who finished his own race, compares his walk with the runner and the boxer, and makes his life purpose as disciplined as the athlete. His trials were evidence of his inner strength and physical condition. Paul was fit!

You do not know what lies ahead of you tomorrow. Your race is not a seen course, a clear path. Health and strength are your responsibility of obedience.

There are private disciplines that are crucial to your stamina and well-being. Health is a responsibility; your body is a temple of the Holy Spirit. I myself am weak in this. I’ve been very healthy in my life, yet I have also often treated my body with awful neglect.

Some years ago the Lord came into our midst as a church and entirely changed our ways of eating. It wasn’t difficult because His power was present somehow to accomplish it for us, in spite of us. Because we eat the same healthy ways, it is easier and less tempting. We are not legalistic, we can enjoy things outside our natural foods but we have a standard the Lord as Master established that is easy to live with and very satisfying.

As for exercise, John began to swim and I joined him several years ago. My best exercise, though, is gardening.

If you want to be disciplined, then pray. If you need healing so that you can live in discipline, then pray for healing for the purpose of serving God fully and unencumbered. If you want to have the motivation to be healthy, then pray and pray fervently. God will “accomplish what concerns you” to the extent you ask Him. 

Christ will infuse you with the gift of His own life of self-discipline.