Nice improvement MinnMan!

When you are "trying to do a difficult bridge" are you attempting to do very hard 30 - 45 second efforts up the steep end of the bridge? If so that is a different power that you are asking your muscles to do. One good workout to develop those muscles is "power force intervals". You do those by riding along at a slower pace, and then put the bike in the biggest gear and pedal very, very hard for 20 to 25 complete pedal revolutions using the entire pedal stroke to up the cadence by pedaling in circles and pulling on the bars to stay on the saddle. The cadence at first may be 45 - 50 rpm and will slowly ramp up. Do about 7- 10 of those reps with a 4 minute recovery. Beware; you may get cramps in some of your weaker muscles the first few times you do these.