Just off the top of my head... you could do a membership site with weekly interviews of experts in that niche, you could create a private forum, or you could create individualized training plans.

But the best way to know for sure is by surveying your list what they do, what goals they have and what kind of products they would be willing to pay you.

I'm in the muscle building/fitness niche too. What JanG said is correct. Survey your list on a regular basis. Also creating your own little 10-20 page reports that cost $7-$25 each can make you a surprising amount of money if you have a responsive list!

LOL! The muscle niche. Love it!

Bigger biceps.

"Add an inch to your arms in 24 hours."

Bigger bench press.

"Toss 315 around like a baby."

Washboard Abs

"They laughed when I said I had washboard abs, but when a chick came up with her wet laundry..."

Sell EVERYTHING around those 3 concepts and you will never go hungry.

Training, special reports, supplements, etc. Every muscle magazine covers those subjects in some for every issue. You can find PLR on the subject, plus are tons of Clickbank products.

Yeah I'm thinking that the easy road is Clickbank products- but a lot of people are tired of those long sales letters now.

If your list likes you, you might do better with short $7 or $17 reports that you write yourself (as previously mentioned). Or you can buy some good PLR and resell that to them.