When all is said and done our bodies are like accountants, but instead of tracking dollars, their currency is calories. It's funny how my personal opinion has morphed on this subject over the years. I used to be a staunch advocate that calories didn't really matter and as long as you made healthy choices consistently you could lose weight, gain muscle or maintain your weight -- whatever your goal. My current thoughts: The quality of what you put in your body is still of utmost importance for achieving optimal health, but calories have a large role in governing body composition. The more I learn about how our bodies work, the more I think that energy in vs energy out is a fairly irrefutable part of the deal.
There's a reason why sprinters, divers, and gymnists have some of the most incredible physiques in the world. They work on consistently building muscle and focus the majority of their workout energy on high intensity, explosive exercises. They train their bodies to be fat burning machines. I like to make the analogy of a Toyota vs a Ferrari. You can drive a Corolla from here to Edmonton on a tank of gas, no problem. The Ferrari burns up the same amount of fuel driving from one side of Calgary to the other. The reason is because it's got a more powerful engine.
Choosing to prioritize muscle building in your workouts is one of the savviest investments you can make. It's like the difference between linear and residual income. Invest in something that's going to keep paying you back down the road rather than something that only gives back exactly what you put in (yes I'm talking about you cardio).
Working out to build muscle can be pretty simple: Lift heavy when you can. Guys, try to incorporate 3 to 4 working sets and work in that 6 to 8 rep range. Girls, you can naturally handle a greater workload so make it the same 3 to 4 sets but up your reps to 10 to 12. Stick to the lifts that incorporate the most muscles at once, Deadlifts, Squats, Shoulder Press, push-ups and pull-ups. Work on continually getting stronger and you're going to build muscle, and as a result your metabolism!
This is probably all stuff you've heard before, and I'm sorry that there's no "advance to go and collect $200" card to flip over. No shortcuts, you just need to put in the work. A friend from work once told me this: In life you get out what you put in. It's true in so many different ways and it holds especially true with fitness and nutrition. Find a type of resistance training that you can enjoy and get better at consistently -- your future self will thank you for it. Make maintaining and growing muscle a priority and not only will you look better tomorrow but you'll feel better over a lifetime.
Live Your Best Life!