The regular N&A typically feature one male and one female in a 21-day challenge somewhere in the world eg. Africa, Amazon, Swampsville USA etc. It's generally fairly brutal as they're only allowed one survival item each, which tends to be a pot or fire-starter, although occasionally these items are provided so they can choose a knife, insect net etc.
XL is usually an All-Stars kind of arrangement, where there will be four groups of three survivalists (often 3 females, 3 males, 2-male-1-female, 2-females-1-male) in slightly different encampments for anything between 40-60 days. The smaller groups will often find one another and become larger groups, whittled away by inevitable taps and med-taps.
There's been some seriously hairy situations over the years in XLs, including an emergency evac due to a herd of elephants stampeding through a campsite. The combination of extreme cold, heat, hunger, sleep dep, insects, wild creatures, putrid water supplies and general discomfort really sort out who's fair dinkum - any single one of these factors would sort me out.
These XL challenges are for the best survivalists only. Matt Savage, who's largely considered to be the best primitive survivalist on the planet, has done about 260 days in total on about 8 or 9 challenges. Whereas the regular N&A often have fans of the show doing a 14-day challenge, and usually pretty poorly.
Don't let the nudity thing put you off. It's sort of irrelevant from a viewer perspective, but makes the survivalists totally vulnerable in extreme elements.
