Just like Mohagen said. Use straps and load the weight.The exercise is as follows:
* you should warm up your traps with conventional methods or deadlift before starting jump shrugs.*
Use a squat rack or power rack with safety bars with settings a little higher than knee level. Use a double overhand grip( with straps when heavy). Start the movement like a rackpull to get the bar off the rack. Bend the knees slightly and then explode upwards as fast as you can like you are going to jump-but a super shrug.Try to move your shoulders as high and close to your ears as possible.
You should be on your tip-toes when you shrug is at it's hightest.Try not to bend your elbows too much but they will bend when you get heavy.Try to control the weight on the way back down. you dont have to reset on the rack every rep. After the first rep treat it like a normal set.Hope this helps.