What, how much, and when do you eat before, during, and after a bike ride? What is your normal diet? What's your guess at the distribution of the 3 macros: protein, carbs, and fat?

I assume you've read the wiki on Fasciculation and have, working with your doctor, eliminated all but the benign causes, including CPT2.

Depending the answer to those questions, it could still be a training problem. This has nothing to do with age, believe me. That's BS from someone who's not worked with older athletes. I'm 71 and still ride double centuries, etc. at a good pace.

I'll make a couple recommendations.

If you aren't riding at least 100 miles/week try increasing your volume. I find that 150 miles/week is a good number for reliable cycling performance.

Do strength training if you don't already. Read this thread: http://www.bikeforums.net/training-n...e-athlete.html

Do first ventilation threshold (VT1) training. This is easier to do and very effective. It's best if you have a trainer or rollers or access to a lot of flat road with no stops. On a geared road bike, warm up gradually and then add power until you start to breathe deep and fast. Then back off until the fast breathing ceases and you are only breathing deeply and at a rate which allows you to easily recite the alphabet in one out-breath.

Play around with this, gradually increasing effort until faster breathing starts and then backing off until it eases back to the alphabet ("conversational") pace. You'll find that the pace (VT1) just below faster breathing is very distinct. If you have a heart rate monitor or power meter, note that HR and/or power. That number will be fairly consistent at the VT1 pace.

Once you have your VT1 figured out, ride for at least an hour at that steady pace, trying really hard not to go over it. Don't eat during that period. If you start to feel light-headed like you need to eat, or if your HR increases or power or speed decreases at that VT1 pace during the hour, you need a lot more training at that level. If you can hold that pace for over an hour without changes to your HR, speed, or power, that's not the problem! If you can't, train at that level for at least 3 hours/week for 2-3 months. If you can hold it easily, on to the next idea:

Start doing zone 5 intervals once or twice a week. If you're racing or doing group rides on the weekend, then only once/week. Find a long relatively steady hill and, after warming up, climb at a zone 5 pace* for 8 minutes. If you can't hold 8 minutes, then for as long as you can hold it. You should do 3-4 repeats of the same duration, but watch how high you climb each time. When you can't climb as high as you did the last time, quit and go home at an endurance (VT1) pace.

*Zone 5 pace is above VT2, about the same as lactate threshold or FTP. To find your second ventilation threshold (VT2), on a long climb gradually increase your pace through deep breathing, through deep, fast breathing, through really fast deep breathing, until all you can do is pant. When you start to pant, that's above VT2 and just where you want to be for these intervals.

And no matter how the rest of it goes, the zone 5 training is always a good idea. For most folks it eliminates cramping on long hard rides.

I did notice that you asked about supplements. One of my standard sayings is "Supplements are a feather. Training is the hammer." Not to say they don't work. Your reply to the diet question might shed light on whether and what supplements might help.