​Training for a trekking trip can get tedious.  There is lots of uphill walking involved, which can get old if you live in a flat area.  To account for the effort you’ll exert at altitude, you may add a weighted pack and some strength training.  All of these training components are necessary to build your lungs and legs for your trip.   But how do you ensure that your training will help you move efficiently as you race weather changes, gain elevation, and get into higher altitudes?  One technique that endurance athletes use to gain fitness is employing “fartleks” into their training.  “Fartlek” is Swedish for “speed play” and has been used for decades in coaching programs for endurance athletes.