With any exercise program if you set the bar too high you’ll likely quit. Set the bar lower and you are more likely stick to it and see more results in the long run.
One way to do sprint training that I have seen recommended and I have tried: Warm up on an exercise bike or other aerobic equipment. Then go as fast as you can for 30 seconds. Recover at much slower RPMs for 90 seconds then repeat the cycle for a total of eight sprints. If you are truly going as fast as you can it will take a long time to acheive eight all-out sprints. It is grueling. It took me months to build up to eight sprints. I hadgreat results, but I absolutely hated it. I had a sense of dread whenever I would go into the gym to do it. I eventually quit.
Trying to go as fast as you can is a euphemism for trying to withstand as much pain as you can. These sprints are difficult. Approaching spring training in this manner was, for me, a prescription for quitting.
After a three-month hiatus I finally had enough gumption to go back to this type of training, but I took a different approach. Instead of seeing how much I could withstand I set the bar lower. Instead of working up to a total of eight as-hard-as-you-can sprints I started at eight not-nearly-as-hard-as-you-can sprints. When I was done I said, “That's not so bad”. I kind of looked forward to the next session instead of dreading it.
Instead of going to 95% of my maximum heart rate I went between 85% to 90% of my max, and instead of taking 90 seconds to recover, I waited for my pulse to come down before doing another sprint. At first doing a total of eight sprints took me 29 minutes, as the recovery periods were longer. With each session I patiently waited for my pulse to come back down and over a series of weeks my pulse came down quicker. After a couple of months I was still doing sprints. But instead of taking 29 minutes it only took me 21 minutes. I was very happy with this quantifiable improvement, and I did not dread the next sprint session.