Take an Olympic swimmer and an Olympic runner and stand them next to each other—both will look lean, powerful and undeniably fit. And yes, both will have world-class cardiovascular conditioning. So it’s fair to ask: is swimming truly a cardio workout, especially if it doesn’t feel as intense as pounding the pavement?
The short answer: absolutely. Swimming raises your heart rate and boosts the amount of oxygen your body uses—two hallmarks of cardiovascular training.
Swimming vs Running: Which Is Better for Cardio?
This debate isn’t new. In fact, it helped inspire the very first triathlon—an all-out contest between a swimmer, a cyclist and a runner to see which discipline delivered the fittest athlete.
While swimming and running offer different physiological benefits, both strengthen the heart and improve endurance. They just go about it differently.
READ MORE: 17 Running Clubs in South Africa You Need to Know About
A study published in Frontiers in Physiology compared the hearts of elite swimmers and elite runners and found that both had stronger, more efficient hearts—particularly the left ventricle, which pumps oxygenated blood through the body. However, the runners had even larger left ventricles than the swimmers. That’s likely because running forces the heart to work against gravity, while swimming in a horizontal position places slightly less demand on the cardiovascular system.
But it’s not about one being “better” than the other—both are excellent for heart health.
How to Maximise the Cardio Benefits of Swimming
If you’re an experienced runner who can crush a 5K at pace, jumping into the pool might feel frustrating at first. Without strong swimming technique, you’ll struggle to swim continuously, meaning your heart rate won’t stay elevated for long.
But once you build enough skill to swim several lengths at a steady clip, you’ll unlock serious cardio gains. Think of swimming as a full-body, low-impact form of interval training—if you keep the intensity up, the benefits will follow.
Calories Burned: Swimming vs Running
How do they compare when it comes to kilojoules burned? Pretty closely. According to data from ACE Fitness in the US, here’s what a 73kg guy would burn in 30 minutes:
- Running at a 6:00/km pace: ±1,548 kJ (370 calories)
- Running at a 3:45/km pace: ±2,295 kJ (548 calories)
- Swimming fast (±70m per minute): ±1,582 kJ (378 calories)
- Swimming moderately (±45m per minute): ±1,306 kJ (312 calories)
So yes, you might need to swim for a bit longer to match a tough run, but you’ll get there—and spare your joints in the process.
Other Key Differences
Swimming and running place different demands on the body. Runners tend to have stiffer ankles, which help with propulsion and efficiency on land. Swimmers, on the other hand, often develop greater ankle flexibility, which improves their kick in the water.
READ MORE: 3 Drills That Will Definitely Boost Your Cardio Fitness
There’s even a hybrid endurance challenge like the Ironman, which is held in South Africa and combines swimming, cycling and running in one brutal test of overall fitness. It pushes athletes to master multiple disciplines—so neither natural swimmers nor natural runners hold an advantage for long. Completing one requires serious cardio conditioning, mental toughness and balanced training across all three sports.
Can You Build Muscle in the Pool?
You can tone muscle with swimming alone, but if you want to build noticeable mass, you’ll need to go beyond laps. That means incorporating pool-based resistance exercises or water workouts using gear like paddles, fins or aqua dumbbells.
This article was originally published on Men’s Health US – additional reporting and products added by the Men’s Health SA team.
