[sn9]

Have you read The Power of Habit?

The focus on willpower is almost inherently demoralizing and absolutely not the best strategy. You should focus on building habits, even one at a time, so that you can let the habits take over without expending much in the way of willpower.

The building of habits is what takes energy, but once they've been built, they almost run on autopilot.

And on a different note, there's a difference between exercise and training. Training for a goal can be a much more productive use of your time and will probably get you better results in terms of fitness and body composition depending on the goal chosen.