My last note on cross training missed my intended point, when I started talking about how easy it is to get into a rut and not cross train enough. I started out with the goal of saying how important it is to train for your specific sport. Every time we go to the internet or open a magazine, we are inundated with the importance of cross training and magic formulas about how standing on a Bosu ball will help us run faster.
A Bosu ball will not make you a better runner. Running will make you make you a better runner. Cross training will certainly help by making your supporting muscles strong. When you are worn out from a long training session, a strong body will help you get through it. Part of my weak body realization came when I was out on a long run and choked on a payday bar after I was out running for about 3 hours. The coughing hurt my stomach. Some work on the abs solved the problem. Good abs help when you are choking while running. They did not help me be able to run for 3 hours. Running did.
I was out for a swim last week and ran into a young guy training for a big swim event. He was really ripped. He told me he spent a lot of time getting into shape to be ready for the swim. I was thinking he would win, if the competition included standing at the end of the pool posing. I told him that pool time was very valuable and the time should be spent on swimming. When you are in the pool, it is not a good idea to waste pool time doing pushups on the pool deck. Public pools can get very crowded and people will get mad if someone wastes a lane by doing calisthenics at the end of the pool. A lot of people will sit on the bench and seethe, if someone hogs a lane. People like me, who are used to swimming in crowds, will jump right in and make you suck it up and share.
The biggest benefit I get from cycling is that I have an elevated heart rate for hours. Having an elevated heart rate for a long time burns a lot of calories. Burning calories is good for weight control. Weight loss for some and weight maintenance for others. Stopping to do pushups and sit ups on the side of the road, help burn calories and build strength but it will also build fatigue which will cut your ride short. The best way to be good a climbing hills on a bike is to go climb hills.
At the end of the day, it is better to get out and do something than to sit on the couch all day. Both cross training and sport specific training are good. Use some sense and think about your situation. Try not to trade a long run in for a session of squats.