Cross-training is a valuable part of running program. It allows you to work on physiological attributes (such as aerobic energy production) while avoiding the specific loading of running itself. This means you can work on improving your aerobic capacity while avoiding the impact of running and reducing the possibility of overuse injuries that are common with high volume running programs.
All aerobic activity will have positive benefits on lung volume, blood volume and the body’s ability to exchange and utilise oxygen and carbon dioxide, both at the blood/lung interface and the blood/tissue interface (where your muscles are).
When deciding what kind of cross-training would be suitable for you, first consider how much rest your legs need within your current running schedule. If they’re generally handling the workload alright, something that still works the legs, but avoids repeated impact such as cycling or boxing would work well. If you think your legs need all the rest they can get, perhaps something like swimming might be a better option for you to add into your schedule.
Importantly though, we should point out that there’s no substitute for specificity. By that we mean, if your main aim is to run faster or further, then running has to be a large part of your training routine. To add to that, if your running schedule is sporadic and unorganised, work on getting that efficient, consistent and aimed towards your specific running goal before adding extra activities to work on your aerobic capacity. And as always…don’t forget your running specific strength training!!