Is it possible to increase cardiovascular fitness through strength training?

An idea dawned on me a couple weeks ago about that has stayed in my head like a “thorn in the mind”.

My question is, “Could it be possible that having stronger legs will force the cardiovascular system to also get stronger?”.

I’ve noticed a big improvement in my cycling from working on my main weakness which is strength. When I used to do my threshold efforts before it would be my legs that where burning and failing that slowed me down. Granted my heart rate was sky high as I was riding at threshold, I felt like when it came down to it, I could have kept pushing harder, but my legs just wouldn’t do it, they where spent.  Another big clue was that after doing a short time trial and riding until failure then recovering my legs felt like butter, they where done, even riding slow my legs would feel weak for the rest of the training session. It’s like once I pushed my leg muscles past a certain point, that was it, there was not coming back, the muscle had failed not my cardio system.

The biggest thing to improve with cardiovascular improvement is your heart muscle and it’s stroke volume. But you can’t lift weight with your heart muscle, you can’t make your heart muscle do squats or bench presses. So what is the best way to work the heart muscle? Is it through riding miles and miles of  riding? Or riding intervals? Almost everyone that I asked in a recent survey I did agrees that intervals are one the best known ways to get faster, but why? Did you every stop to wonder how intervals change your body?

1. they make your leg muscles stronger
2. they make your heart muscle stronger
3. they also cause other adaptions but I think the first two are the main improvements

Now it would seem to me that the heart and your legs would have to be somewhat balance to match each other’s ability. It would seem strange to me that someone with skinny little legs that can barely sustain 15mph pace would need or have, or be able to develop a big strong heart with a large stroke volume. You’re body’s muscles don’t have the ability to build up enough demand to stress out your heart enough to make it burn and want to grow bigger and stronger.

I guess it would be possible with a lot of effort, maybe by running or doing something that used more then just your legs muscles, maybe like running or swimming or cross country skiing, to force your “fuel pump” to work overtime and get stronger. But from what I’ve experienced in cycling training is that it’s easier to blow your leg muscles out before your cardio system is exhausted. I think running is “better” for cardio then cycling for a lot of people because the muscular strength demand is less and spread across the whole body, both the legs and the upper body, so the demand for the heart to feed all the those muscles and to feed your legs which are moving fast but with little resistance cause you’re heart to work hard. I think to get an equally hard cardio workout on the bike requires leg muscles that are fairly strong, but more importantly have strength endurance, the ability to pedal hard for long periods of time.

Another thought too is that spinning at a faster RPM can also help target the heart muscle and cardio system better. But when riding for maximum speed I find that the effort is balanced over the cardio and leg muscles for the most part, and depending on the rider they may be riding at a faster RPM easier gear and using more cardio, or using more muscular strength by riding a lower rpm harder gear. 

I guess the counter arguments would be that

1. because of your weak cardio system, it’s making your legs fail prematurely, if you had a stronger cardio system it would be able to feed your legs more fuel and oxygen and not cause you to go anaerobic.
   I was a fast runner at one point, and got into racing MTB, it wasn’t until I increased my intensity and started doing hard hill climbs and put on some leg muscle did my riding improve greatly, also my running improved a lot as well.
   We use to do intervals running etc, but nothing seemed to push me to the puke level like charging up steep hills on my bike, esp. when my legs got stronger and I could ride harder longer, this I think really forced my heart to catch up in strength as well.
2. Strength training doesn’t help cycling it’s not specific
   If you train wrong that could be possible, but I’ve seen with my very own eyes what a huge improvement strength can make in cycling and other sports. I’m a strong advocate of strength training for cycling, and almost any sport, and in life in general. I also believe in doing cardiovascular training as well of course. I think for athletes with a lot of natural strength, it might be possible that they don’t get as much benfit. But I am very suspcious of any serious athletic coach that doesn’t recommend at least some strength training for their athletes. I’m not alone on this either, there’s a reason why Lance’s coach has him hitting the weights in the winter.
3. You can still push your heart muscle hard by doing full body aerobic sports, even if your leg muscles are failing to push you to the limit in cycling.
   This I could see as a valid point and perhaps why two of the greatest cyclists Eddie Merckx and Greg Lemond both did cross country skiining in the offseason.
   But for many cyclists, they don’t do much cross training, so I question their ability to train their cardio system hard enough if they’re riding with legs that aren’t very strong.

These are all my crazy theories, but I just wanted to write them down so I dont’ forget what I’m thinking.