I recently sat next to a cardiologist on my flight home, and we ended up talking for most of the ride. Naturally, exercise came up. What stuck with me the most was when she said,
“Above all factors-sleep, diet, genetics-exercise is the single most important thing you can do for your health.”
From there, the conversation turned into a back-and-forth discussion about everything related to health, fitness, and different forms of exercise. Here are our most interesting topics that we discussed:
- Why run when you can bike?
- What’s the point of being exhausted during a workout?
- Doesn’t running burn muscle?
- And motivation…does anyone actually like working out?
In this post, I’m going to break down each of these questions.
What Are You Actually Burning When You Run?
One of the biggest myths around running is that it “burns muscle.” The truth is a little more complicated than that.
When you run, your body primarily uses carbohydrates (stored as glycogen) and fat for fuel. Muscle protein is not a preferred fuel source. Your body only starts breaking down significant muscle tissue under specific conditions:
- Extremely long-duration endurance work
- Severe calorie restriction
- Very low protein intake
- Excessive volume without recovery
Factors like body composition, training history, intensity, and whether you’re fasted or fed do matter, but not in a dramatic way.
A well-fed person who strength trains and runs intelligently is not “losing muscle” from a 20–30 minute run.
A 20-30 minute run will instead help to improve cardiovascular efficiency, insulin sensitivity, and overall work capacity.
To sum it up, running won’t burn muscle unless you’re under-fueling your body, under-recovering, and not lifting weights.
Why Run When You Can Bike?
This was a great question she posed: Why choose running when biking is lower impact?
The answer isn’t that one is “better,” it’s that they do different things.
I explained to her that what you choose to do depends on your fitness goals.
Biking is excellent for cardiovascular fitness with minimal joint stress.
Running, however, is a weight-bearing activity that improves bone density, tendon strength, and connective tissue resilience. Running also requires greater coordination, stiffness, and force absorption per step.
For the everyday person who wants to feel good, running in small doses is fine. Vary distances, times, and try to keep your runs under an hour unless you are training for a longer duration race.
Biking is a great option for the older population who need less stress on their joints.
Mix and match both of them to get the best of both worlds.
Why Would You Want to be Tired During a Workout?
Not everyone likes the feeling of being out-of-breath, dripping in sweat, and having their muscles tighten up. It is uncomfortable.
However, there’s a difference between being exhausted and being challenged. You don’t need to leave every workout on the floor, gasping for air. But you do need moments of discomfort if you want progress.
Your body adapts to stress. If you never push your limits—cardiovascularly, muscularly, mentally—you stay exactly where you are.
Every session should not be at your maximal effort, but there should be doses of intensity from lifting heavier weights, moving faster, or doing more repetitions than last week’s workout.
Some days are about building capacity. Some are about recovery. Some are about pushing the edge.
The majority of your “intense” workouts should feel like you’re pushing at 60-70% near maximal effort. There will be moments where you are in the 80-90% range, while occasionally testing a 100% effort through a 1-Rep Max lift or max effort sprint.
Final Thoughts on My Conversation With the Cardiologist
Our healthcare system is set up to take care of sick people. If you are sick, there’s probably a pill for that.
The cardiologist whom I spoke to, on the other hand, primarily works in preventive medicine to help people avoid heart disease.
Ultimately, you must take accountability for your health.
Train to be strong, live long, and not only take care of yourself, but earn the ability to take care of other people if and when they need it.