Vital Statistics? 6', 200lbs, 67 y/o. Gearing is 50-39-30, 12-30. Have ridden approx. 3000 miles/year over the last 5 years majority of which was on a tandem. I'm mostly riding my single now and looking to get stronger at 100K distance and simply able to ride a typical Century around here (Northern California). Over the last 4-5 months I've only been able to do about 300 miles/month with only 3 rides longer than 60 miles; most of my long rides are 45 miles or so. Typical long ride might have 50'/mile climbing.

My Marin 100K is my most recent effort. I felt pretty good up until the 40 mile point, but was definitely uncomfortable on the bike and experienced muscle fatigue during the last climb. I was bearing more weight on my arms and found it more difficult to hold my position: almost seemed like a loss of core strength was causing my pelvis to rotate forward. I didn't cramp during the ride but experienced some cramping of the small inner thigh muscles in the car on the way back. I believe I was adequately hydrated. A few weeks prior I had ridden an easy 100K, only 2000' of climbing, and averaged 16.0 mph so the additional 1800' of climbing really took its toll.

Here's what I think I've learned:

1. I need to do more than 75 miles/week. On weeks without business travel I could easily ride >100 miles, but travel has been a bit of a problem. My longest ride should be closer to my current target ride, 100K.
2. I need to go harder on my hard training rides. When I look at my average HR on this recent ride and the Strava Watts estimate on the climbs, I actually was going harder on this ride than a typical 30-40 mile training ride. This was also evident in the VAM which was 10% higher than I typically see.
3. I need to think about how climbing is incorporated into my current rides. I've got one tough training climb that is 3000', but I don't think that represents the sort of stress that doing 3-4 medium tough climbs over 60 miles represents. I would like to avoid climbing intervals if I could, but I recognize the potential value
4. I need to probably do some exercises to increase my core strength. My sense is that even if the legs are still capable, when the core goes the back. arms, neck and backside start to hurt.
5. Normally, I drop Nuun tablets in my Gatorade, but I failed to do this. I don't know if it helps, but I'm going to try Endurolytes (again) on my next long, hard ride.
6. Loosing weight wouldn't hurt

I don't know if this ride would have benefited from a lower gear. There were a few brief periods when my cadence got down to 70 or slightly below. I would definitely put an 11-36 on the back if I were attempting a Century with 6000+' of climbing in my current condition.

Any suggestions, observations, etc. would be greatly appreciated.