Neck pain is one of the most common issues I deal with when bike fitting. It can occur whether you’re on a road bike in the road position, on a road bike in the TT position or on a TT bike in the TT position.
More often than not, if riding in the upright road position, neck pain is caused by the rider being stretched out. You’ll know you’re stretched if you can’t comfortably position your hands into the hoods – an important place to get to as the hoods act as an anchor (to stop you going off the front of the bike) and they (should) provide easy access to the brakes.
The simple fix for this is to move your saddle forward, or to find a saddle that allows you to come forward (there’s a lot that don’t), but make this change at the rear of the bike before you start shortening the stem.
If you’re riding in a TT position, whether that’s on a road or a TT bike, and you’re getting neck pain it’s likely that you’re either stretched out, don’t have your elbows on the pads or a combination of the two. It’s in this scenario that the choice of aero bars become so important and here’s why.
Not all aero bars allow for independent adjustment of the extensions and pads but, in my opinion, they should. When you mount your triathlon bike there are a number of things which should happen – 1) you plant your butt on the saddle 2) you clip in 3) you place your ELBOWS on the arm pads and 4) your hands at the end of the extensions.
The pads are designed to provide skeletal support and that is best delivered when your elbows are placed upon them. This is why fore/aft movement of the pads is so important for comfort in the time trial position. The ability to adjust the arm pad stack is also desirable (to lift the rider and open up their hip and back angle if necessary). As is being able to set the length of the extension so that the rider can change gear with their elbow still on the pad, without having to reach or shuffle back with the hand. The hands themselves should be placed higher than the elbows, for two primary reasons – 1) to lock the rider into position and 2) to reduce frontal surface area thus saving both watts and time.
If I’m fitting a client with a road bike and they want to get into a TT position I use Profile clip-on aero bars, without exception. The Profile bars have all of the adjustments mentioned above and at $230 they are great value for money. I favour ski bends so the T1, T3 and T4 options in my opinion are best.
If you’re riding a TT bike and are unable to move the pads it’s worthwhile looking to see whether you can fit a set of the Profile F-19 arm 
rests. I use these pretty much every time I fit a client with a Giant Trinity (the older models in particular). But I’ve also used these on a wide variety of other bikes. As well as having a great range of fore/aft movement they’re super comfy, provide significantly more real estate for your elbows than most other pads and at $75 per set are much cheaper than massage and physio.