If you're a runner you may not have completely developed cycling muscle groups and techniques yet. Try this on the next ride. Leave the HR monitor at home and quit trying to be so scientific about the rides. Just enjoy yourself. When the group hits a hill and you start to lag behind, stand up and pedal at a smooth cadence of maybe 60. Concentrate on a smooth technique but also putting out power.
You probably haven't learned how to use your quads climbing while seated. That's okay but for now use your quads and glutes and stand more.
Last edited by StanSeven; 06-24-14 at 07:20 PM.