it could be.....
that you should also do some work on your abs to complete the picture. You are doing a good job on your legs/thighs/butt which is just natural for cycling.
Doing additional ab work will not only strengthen your stomach muscles but will also strengthen the muscles in your back which help with overall posture on and off the bike. Having a good posture on the bike helps fatigue especially back and neck fatigue.
It's good to develope upper body strength which can make cycling easier by increasing power for pulling on the handlebar when accelerating out of the saddle, sprinting and pedaling uphill.
The winter months are great for getting in the gym and working on strength training.
Hope this helps........I just joined a gym today, ugh!
Kate
Life is like a 10 speed bike, we all have gears we never use.
Charles Schultz
"The bicycle is just as good company as most husbands and, when it gets old and shabby, a woman can dispose of it and get a new one without shocking the entire community." — Ann Strong, Minneapolis Tribune, 1895