Swimming can be brilliant for expanding the lungs. You can put some real pressure on your breathing and response to lack of recovery with water as you simply cannot breathe through it. It may not push the heart rate as you said but in a pool if you do a 3/5/7 stack for 50-100m that'll test your lungs good an proper. Freestyle, 3 strokes, breathe, 5 strokes, breathe, 7 strokes, breathe. No pussying out, go at a solid pace, but not full gas. And dont come up early until you grey out... there be dragons in the greying out area.The comedian was correct.
Cycling allows you to get your HR much higher than swimming. With swimming, I struggle to maintain 120bpm but with cycling I'm pretty comfortable in the 130s and on big hills it's over 150, even in a low gear. Plus the countryside is so much more motivating than 100 lengths of a 25m pool.
I like swimming for mobility. I get to move my body in all sorts of ways due to effectively being in zero gravity. I can move all of my joints through a good ROM. But for cardio, cycling trumps it. Looking at my HR profile, I think it trumps running, too.
Helped me improve my lung capacity (perhaps not physically but that mental barrier or taking larger breaths) and my ability to withstand fatigue in a sprint scenario.
Due to some very sensitive to touch achillies tendons post serious injury I cant really do combat sports any more without serious risk. So I play Squash, this type of conditioning is perfect for that type of game.
You can increase the stack too, go 5/7/9 if you wanna really push yourself. Or sprint it in on the 3/5/7.
Cycling is fannnnyyytastic for getting your grind on. Hill intervals on a road bike will kick yo ass. I know this thread is bashing expensive bike owners but to get the most out of road biking I would recommend a road bike with drop bars. You can push the envelope so much futher and for longer. They just simply go faster. That hill that's 30k away isnt an issue just to nip over to, 5 sets of killer sprints, back again. On a hybrid of mountain bike... that is a long day in the saddle.
Passionate cyclist in all disciplines here, swimmer when I can, runner when I aint training squash. Triathlete once a year...