When you go to the gym you can simply flap your arms about. After a long time you may gain some extra muscle. Or you could use some weights. That makes it harder but results come faster. You can increase the weights over time and your results get better. Swimming fully clothed is the fun alternative with less risk of muscle injury.

Required clothing: T-shirt, tracksuit top and bottoms.

Tracksuits are versatile and give you a harder work-out. They should be unlined, as the space between the outer and inner layer traps air which can get in the way.

Begin with just the bottoms and a T-shirt. Swim a fair distance to get used to the extra resistance on the legs.

Then put on a jacket or pullover and begin some serious resistance training.