ThePSUDon,
Welcome, here are a few quick and dirty tips to get you started off on the right foot. Starting with the "Off Season", which you are now officially in. This is the toughest part of the cycle for most triathletes as it is generally a time to de-condition, gain a few pounds and recover from what is usaully a brutal season. Most importantly it is the time to relax you mind from the rigors of training as well as let your body recover. That said, here we go. Start a weight training regimen, if you want to progress in this sport you have to be strong as well as fast, so start building that core, that will help with your back pain. What will fix your back pain is setting up the stationary bike correclty, here a few major tweaks to make on the bike: 1.) adujst the saddle height high enough so that when your heel is down and you are in the 6 oclockl pedal position, your leg is slighty bent. 2.) adjust the fore/aft position of the saddle so that when you are in the 3 oclock pedal position your knee directly intersects(while looking straight down) the ball of you foot as well as the pedal axle. The part of the knee I am referring to is the bony prominence that sticks out slighty on each knee, you know the one. 3.) Start with a conservative height for the bars and try not to hunch over to much on the bike when you are riding for long periods of time. These are basics, there is much greater detail you will need to research as far as bio-mechanics and form goes. You mentioned brick workouts(bike to run sessions), stop them immediately, these DO NOT need to be performed in the off season, the off season is to build a good aerobic base/foundation as well as to work on form to set the stage for the new season in 08.
Conclusion: Start weight training, work on form, take is easy and keep your workouts purely aerobic till you begin training for next season. Remember too that nutrition and recovery are key components as well as training, good luck!
-Anthony
