If you want to know where Ignatius is coming from in his letter to Polycarp, consider this text from Paul. I'm in the middle of a base building period doing very, very low intensity exercise, with minimal hard efforts. But I know that when you are getting ready for competition, or building strength, you do close to maximum effort lifts, sprint, and sustained anaerobic threshold efforts.
All these things hurt. Athletes learn to embrace this.
2 You then, my child, be strengthened by the grace that is in Christ Jesus, 2 and what you have heard from me in the presence of many witnesses entrust to faithful men who will be able to teach others also. 3 Share in suffering as a good soldier of Christ Jesus. 4 No soldier gets entangled in civilian pursuits, since his aim is to please the one who enlisted him. 5 An athlete is not crowned unless he competes according to the rules. 6 It is the hard-working farmer who ought to have the first share of the crops. 7 Think over what I say, for the Lord will give you understanding in everything.
We need to accept the psychological pain that comes with a change of habits, turning from that which holds us back. This requires effort. It does not come merely by existing. But the rewards of right living are there: the pain is only for a moment. Victory is forever.