By Ashley Arnold

Hydration has plagued me since I started running trails. Coming from a track and cross-country background, the idea of carrying something to drink water while running was annoying. (I still remember my college cross-country coach asking me to stop during a long run and drink water. I refused).

The transition from 5K to 100-miler, as you might imagine, was difficult for me ... until I found a pack that fit. Not surprisingly (since I am writing this blog for Nathan Sports), that pack was a Nathan Women's VaporAiress Hydration Pack. And truth be told, that was the only hydration unit I used for a long time. I tried others over the years. I liked a few and detested a lot more ... but never really found anything else that quite compared to that original vest. (Today I admittedly wear exclusively Nathan products.)

As my training increased in intensity and length so did my races and so did the demands I had for my hydration pack. There were several questions I had to answer before any training run or race: How much water will I need given the temperature and my run length? How much food do I need to carry? Will I need a change of clothes? What sort of emergency gear do I need? What about technology (i.e. iPhone and/or iPod)?

And so, while my exact pack contents tend to vary from run to run and race to race, each concern weighs into my pack choice, as it should yours. So what are the basics for finding your pack sweet spot?

Let's start with fit:

I think the term "pack" is perhaps the wrong term. When I think of a pack, I can't help but be reminded of my LandsEnd backpack from middle school ... not anything I would ever want to lug around the trails! The better term, I believe, is vest. And that's how all Nathan's packs (er, vests) fit.

You want a unit that sits closely and comfortably to your body. I like to think of my vest just being an extension of my clothing. It's just there. It just works. Plus, during the later stages of an ultra when I've lost some water weight and I'm still sweating, I find I always need to synch my pack tighter to prevent slosh. Nathan's vests (I now wear the VaporHowe) have always allowed me to do this. Too much slosh = blistered painful back. And I don't want to go down that path and trust me, neither do you. Body Glide will only go so far.

OK, so you found a pack that fits close and comfortably to your body, right? Then next up is storage:

I've worn the VaporHowe for two-hour runs synched as tightly as possible with a half-liter of water and a fourth of a granola bar. I've worn the same vest filled to the brim with water, gear and food. I guess the point I'm making is that it's nice to have storage. It's nice to have options. Some ultras have very specific gear requirements. It's important that your unit have enough pockets and enough pockets in easily accessible places. No one wants to take off his/her pack mid-run just to eat a gel (especially during a race).

So, find a pack with the right amount of pockets for your running style, in the best places (I like chest pockets for nutrition) and with enough back storage room for extra layers (if you need them). I often bring a wind layer with me into the mountains and I prefer having a bungee to strap it in so that I can reach back and pull it out without even removing my pack. And, when I'm out for a long time, I want the full big pocket on the back for a change of clothes and extra food I may or may not need (emergency food!).

Storage leads us to fluid capacity, which is, of course, one of the biggest reasons for carrying a hydration pack in the first place. I always recommend a pack with at least a liter of bladder space. My preference is a two-liter bladder. I rarely fill it all the way up, but at least I have the option if I need to. I've run enough races in the desert-and run out of water enough times in the desert-to be thankful for the extra H20 room when I have it!

And then, because I have a thing with colors, the way it looks actually matters to me. (Yes, I know. I am one of those people that won't buy shoes if I don't like the color [GASP!]) The brighter the pack, the better. 

What do you think?