“So if someone wants to start exercising… I would ask: What are you trying to accomplish? And why? There seem to be three principal reasons for exercising, and what is needed for one goal is not necessarily what is needed for another.
If your goal is to improve your health, studies in recent years have consistently indicated that you get the most benefit when you go from no exercise at all to exercising moderately. Starting with Steve Blair’s classic study ‘Physical Fitness and All-Cause Mortality’ (1989), a convincing body of research has emerged in support of the observation that most of the health benefit probably occurs from just mild exercise, not necessarily from the most arduous workouts… Most health benefits seem to accrue if you simply walk briskly for about 20 to 30 minutes a day, covering a mile in 15 to 20 minutes, or ride a bike at a modest pace. You can take three 10-minute walks a day, or you can ride a bike for 20 minutes and walk for 10. Or you can swim at a comfortable pace for all or a part of your exercise program. Almost any physical activity will suffice, and there is no need to push yourself till you’re out of breath, gasping for air. You don’t have to return from your session soaked in sweat. Yes, you do get a slight extra benefit from exercising a little harder or a little longer, but that extra benefit is small compared to the benefit you apparently get from just doing moderate exercise.
When it comes to the benefits of strength training, the extensive body of evidence in the position paper written by the American College of Sports Medicine documents that it can improve muscle strength, make everyday life easier, and prevent falls. Decades of research by exercise physiologists show that resistance exercise can change the muscle cells in positive ways. As Claude Bouchard, for example, confirmed in his large study of inherited differences in the ability to train, muscle that is developed with exercise is more efficient, has more mitochondria, and is better at using fat for fuel and at allowing cells to use insulin to utilize blood sugar, thus making diabetes less likely…
The second reason to exercise is to improve your appearance and your performance. You may want to be thinner or stronger. In this case, moderate exercise is unlikely to be enough. Whether you lose weight may depend on how hard you exercise, how long, what you eat, and what your genetics are… Whether you grow stronger or reshape your body depends on a lot of factors, including your genes, but also including how often you lift weights, whether the weights are heavy enough to stress your muscles, and whether you stay within your program. The exercise that will make you… more muscular, the sort that will allow you to run faster or swim for longer distances, requires not just consistency but effort. Or, as exercise physiologist Donald Kirkendall says: ‘If you want to push performance, you’ve got to push intensity. The biggest way to gain fitness is to push intensity.’
The third reason for exercise is almost never the impetus for starting. Instead, it is one that tends to creep up on people, taking them by surprise. Yet it is the one that often accounts for them staying with an exercise program. Time and again, when I ask people why they keep exercising, year in and year out, they tell me that they started exercising to lose weight, or to help their hearts, or to firm up their bodies, and kept at it because they discovered that they loved physical exertion…
One day, I get an email from Richard Friedman, the avid swimmer and psychopharmacologist at the Cornell medical school. He knows I’m writing this book and he has a question: ‘Are you planning to tell the truth about exercise?’ he asks me.
I write back. What, I ask, is the truth?
‘Ah, the truth about exercise?’ he replies. ‘Well, I suspect that exercise is more often a marker of health than it’s cause — healthy people like to exercise more than unhealthy people to start with.’”
– Gina Kolata, Ultimate Fitness: The Quest for Truth About Exercise and Health, pg. 262-67.
My guess is that it’s best to focus on the third reason for exercise, and let the first two fall into place naturally over time. Become the sort of person who enjoys exercise (if you can), lean into that transformation, let it wash over every aspect of your personality and change how you think. If you do that, you’re both more likely to stick with exercise for life and you’re also more likely to accrue the ancillary health benefits that come, not from exercising, but from being the sort of person who exercises regularly.