Theories come and go. For example, 18th-century chemists thought phlogiston was a substance that was released when something burned ... and breathing removed it from your body so you wouldn't spontaneously ignite.

It's long been said that the best way to get into a new exercise routine is to start slowly. But a study published in JAMA Cardiology shows that if you design your own exercise routine, chances are it will be something that you can actually do, and when you couple that with doing it from day one you may actually stick to it and increase the time you spend exercising.

With that in mind, here are some tips on how to set up your own exercise routine and get going pronto.

• Write out your goal(s). Want better balance? More endurance? Increased muscle tone? Better breathing? Weight management? Improved sleep? Write down what you want to achieve. That way, you’ll be able to target your exercise to meet your goal.

• Write out a list of activities that appeal to you in different areas of exercise. For instance, aerobic exercise: interval walking, cycling — as many as you like. Then write out a list of strength-building activities you will enjoy: Using stretchy bands? Push-ups? Lunges? Squats?

• Decide how much time you're going to spend exercising every week. Write down the days and times of day you'll exercise. And you don’t have to do any one exercise at maximum effort — just do it from beginning to end; and increase intensity each week.

These are some ways to go from couch to self-coach. You'll live longer and better.