The Inman Mile is a great exercise; effectively a supersized version of a Farmers' Walk. Although there are several variations (see below), the most common versions are :
1.5 x bodyweight, barbell across shoulders : This is the version recognised by the USAWA, and occasionally appears at USAWA sanctioned events. Their definition is :
The lifter will have loaded onto his/her shoulders a weight equal to 150% of bodyweight. The lifter will then carry the weight a distance of one mile. Gait is optional. Resting is allowed, but neither the lifter nor the weight may be supported. Records will be kept in both pounds and time. Should the weight be touched by any aide once the lift has begun, the event is terminated. The lifter may be handed refreshments during the lift.
For obvious reasons, this is usually performed outdoors.
1.0 x bodyweight, dumbbells or Farmers' Walk handles : This is the same as above, with the major difference being the position of the weight. Not only is it much closer to the ground (although as my lawn will attest, it still carves out a chunk of dirt when you drop the bells), but there's a much greater emphasis on grip.
For this reason alone, the 1 x bodyweight is usually more than enough.
As with most exercises, there are a number of ways to vary things a little. A few suggestions :
Reduce the load : 1.5 x bodyweight is a lot heavier than it sounds - particularly over that distance. And if you're doing an 'Inman Stroll' (same thing, over a distance of 1.5 miles); it'll get old in a hurry.
Try cutting back the load a bit - especially when you're just getting used to it. Your traps will still be acutely aware of the exercise.
Reduce the distance : the other obvious change is simply to reduce the distance. After all, a mile is an exceptionally long way to carry that sort of weight.
Work up to it.
Allow the weight to be put down during rest breaks : this one makes a big difference. When it comes time for a pause, put the weight down. It'll still be there when you start up again.
Use a Strongman Yoke : if you've got access to one, use a Strongman Yoke. This is a great piece of equipment, and is perfect for exercises like this.
Try the dumbbell version before considering the barbell : although the weight doesn't sound too bad - particularly if you're used to performing Farmers' Walks - it's the distance that will get you. A mile or a mile and a half is a long way when you're loaded up.
When you try this for the first time, use dumbbells or Farmers' Walk handles. Although this really brings your forearms into play, it keeps the weight nice and close to the ground. Much safer when it comes to setting them down, and taking a few deep breaths.
Leave the equipment outside (covered) : At the start of each workout, you probably won't mind the time you spend carrying everything up the stairs from your basement, and setting up outside. The same goes for the lap after lap of the workout itself - adrenalin will keep you going.
When it comes to the end of the session, however, you won't exactly feel like carrying everything back inside. If possible, leave it outdoors - covered, and set up ready for next time.
This is a great exercise, whether you make the full distance or not. Oh, and it's also the perfect time to try out that Manta Ray you got a while ago.