Backpack question

I'm fairly new to backpacking, so yesterday I went out for a short overnighter. During the hike my pack kept sagging down. The waist strap would keep slipping down past my waist and over the top of my butt. I was carrying about 28 lbs of gear and it felt really heavy. While I'm not in perfect shape muscle wise, I'm not in poor overall physical shape. It just felt like I might have had too much weight on my shoulders. Turning my head left and right to look around put some strain on my neck.

In short, I know part of the problem is that I need to build some muscle, however that wouldn't fix the sagging issue. What could be wrong and how can I fix it?

Thanks guys/gals!

What backpack did you use? Make/Model.

How tightly did you pull the hipbelt, and where did you position it to start?

Ooops, did it again; I just clicked reply on the latest post, when I really meant to reply to the OP. Sorry, Glenn!

The belt is not for your waist, but to go around your hips. While there are many individual preferences, most buckle it over the iliac crest (look that up on google where you'll find a clearer explanation than I can give). If your pack is not transferring most of its weight to the hip belt, there are a number of explanations--the pack doesn't fit, you've packed it wrong, you don't have it adjusted right, and others.

In addition to answering the questions above, if you can get someone to take a nice clear photo of you wearing the loaded pack, preferably from the side, we might be able to tell you more.

These would be my top 3 reasons for your problems. With an emphasis on the the first two.

You have the belt too loose. There may be other reasons as mentioned by others - bad fit, packed wrong, etc. - but the belt should be tightened so the load rides in the proper place. If the belt doesn't tighten any more than you can get it and it still slides, it's too big for you. And, also, there should be compression straps on the pack itself to snug up the load against the frame to keep the weight on your hips and not bouncing around below them.

An easy way to initially put your pack on is to snug up the shoulder straps a bit, then shrug your shoulders, lifting the entire pack up "high", then tighten your waist belt, and when you let your shoulders fall back down, the pack will settle onto your hips. Kind of a word picture, but if you try it you will see/notice the difference with how it feels and where it rides. Your hips are supposed to carry the load, not your shoulders. Give it a try and see if it helps...