What's your favourite off season activity to stay fit for skiing?

How do you stay fit for skiing in the off season? So many options of things to do in the summer that help us all stay fit for skiing. Here are a few of the options we see around the Kootenays. Let us know which you roll with.
Mountain biking. With legendary trails scattered throughout the Kootenays, some consider this to be the first of adrenaline sports in this area. For those of us that prefer the winter, the ability to do Enduro style laps is helpful in keeping the ski touring fitness high. The two compliment each other in that the fitness needed to get to the great downhills is similar, as is the speed of thought and precision for the downs.
Trail running. For fitness and getting out into nature in the same quiet and contemplative way, some say trail running is the perfect foil to ski touring in the winter. Certainly a case can be made for the fitness component, as trail runs often cover 20km or more of rough ground, both up and down.
Stand up Paddling. Having been rediscovered by Hawaiian surfers, this sport has taken the lakes by storm of the last few years. It can be as simple as sitting on a board and padding in the sun. However,when taken further down the road, there are some benefits for fitness and balance that can help in the off season. The core strength needed to balance and drive the board through the water is one obvious benefit. Also, the small movements of the foot needed can be beneficial, as they increase the strength and control of your feet.
These are just a few of the off season sports we find beneficial. Let us know what we've missed that you love on the off season.