There are two things that are going on. Muscle groups become tight while others become ..well...lazy. I'm a good example. My pecs are over developed and tend to round my shoulders forward while my back muscles are stretched due to the pecs being over tight. So when you look at muscle imbalances you have to address the tight muscles as well as the weak muscles. The only way to do this is with dynamic assessments.

There is a whole way of approaching it but what what it comes down to is that cyclists need to spend time hitting the weights (or doing some type of strength training that includes core and balance training) to help keep everything in check.

I'm a good example. I thought that mtn biking and commuting would be enough. I should know better. It's not. I now have a muscle imbalance that came to light after an injury and won't heal right. Guess what I'm now doing? Yep, calf strengthening. I was pretty surprised but then I compared what my calves look like now compared to last year and it's pretty obvious. I have much less defined calves and last year I weight trained twice per week.

Balance is really important too, I was pretty surprised how much I was lacking in that area as well. I am spending alot of time on the bike but I need to take my own advice at some point and spend some time training off of it too.