I'm swimming twice a week. My biggest issue is breathing and stamina, so I asked the teacher if running on the weekends would help. She told me that they are different kind of aerobic exercises, that a person may be able to swim one hour straight but not able to run a block, and vice-versa.
Maybe she exaggerated, but I found her answer interesting. Is that so? Let's say, if I were a runner, would doing 1 hour spinning (a different aerobic exercise) not help me as much?
Your teacher is correct: aerobic conditioning is specific and practice running will make you a better runner, but won't necessarily do much for your swimming. For one thing, running doesn't help you adapt more efficiently to the movements required by swimming. Furthermore, cardiovascular fitness is specific at the cellular level; it's not a systemic thing per conventional wisdom.
Body By Science (p. 40) reports on one salient study:
An elegant study was performed in 1976 in which the experimenters recruited thirteen subjects and trained them on a stationary bike. However, they had them train only one leg; the other leg wasn't trained at all. The trained leg employed a sprint and/or an endurance (steady-state) protocol. The subjects performed four or five such workouts per week for four weeks. After the study, when the researchers tested the subjects' VO2 max by having them exercise with the trained limb, they noted an increase in VO2 max of 23 percent. This low-intensity, steady-state exercise was supposed to produce a central cardiovascular adaptation, but when the experimenters tested the subjects' untrained legs, they discovered that the untrained limbs showed no improvement in VO2 max at all.
(Study: B. Saltin, et al., "The Nature of the Training Response: Peripheral and Central Adaptations of One-Legged Exercise," Acta Physiologica Scandinavica 96, no. 3 (March 1976): 289-305.)
This also speaks to the fact that if you choose running as your exercise, any improvement in your VO2 max will be restricted to your legs for the activity of running. It's not having a central adaptation, as the muscles in your trunk and arms will be largely unaffected, and the effect will not be transferable to any other exercise modality.
My advice to you: if you want to build endurance swimming, then swim more.
If you are only swimming twice a week, cross training by running can help because it can improve your general fitness and aerobic capability. I highly recommend it. I only swim 1-2 times per week and my breaststroke sprint speed and distance freestyle endurance are improving month to month because of my cross-training (running, pushups, weights). She is correct that the specific muscles and how they are used is quite different between the two exercises. I am more tuned to swim, and it took me 8 weeks to train up to a relatively comfortable 4.4 mile swim last spring, and 14 weeks to train up to a rough 3.1 mile five-fingers run.
While improving your general fitness will help, your issues of breathing and stamina suggest to me that you should – like all swimmers – be working quite a bit on your balance. Leaning forward hard will prevent your legs from dragging and make it easier to rotate to breathe, but while the concept is simple it is a difficult skill to master. I often recommend the popular book Total Immersion Swimming for working on this and other skills.
I would recommend including some weight training, stronger and more effective muscles help reduce the overall aerobic drain during your activity. Here's a link to a good article.
I would recommend the big 4 exercises: squats, deadlifts, bench press and overhead/military press.
I think that running could help, but sincerly it really depends on how much time you spend swimming....
I run about 300km/month and when I go to swim (once every 2/3 months) I barerly finish 4 lap straight (25mt), a big improvement I noticed from the run is that I recover very very fast my breath and stamina...
