what would be a good supplemental excercise that could be done at the gym that would have good carry over for useful cycling leg strength? maybe leg extensions, hamstring curls, calf raises, etc.....?

None of those will do you any good except for short term distances like track sprinting. Weight training is good for overall conditioning and maybe avoiding injuries but lifting won't translate to better cycling to any degree.

yoga.

squats and deadlifts will give you the most overall benefit if you plan on lifting weights.

This has come up many times. While weight training might not be the best use of time you could spend actually riding, my experience with strength training (not weight lifting) is that it has made me a better athlete, hence a better cyclist.

I have found that the older I get, the more benefit I seem to derive from my strength training in terms of more stamina, less injury etc. It just seems to me that I have more stamina in a lot of things. And I attribute it to my strength training program.

Oh, I forgot to mention that my stamina, sex-wise, also benefited. No kidding!

https://www.bicycling.com/training-nu...ling-body-ever

If you could only do one then it's deadlifts. Generally speaking it won't make you faster but it will strengthen most of the same muscles used on the bike. Upper back, lower back, glutes, hams, quads, forearms, and many supporting muscles.

https://epicidiot.com/sports/weights_cycling.htm

Push ups, and weights.

I started doing old fashioned sit ups, to strengthen the hip flexors. No idea if that's working but I can do almost 50 sit ups at a rapid pace versus 20 before

Seriously though I think that working the lats, the pull up muscles in the arm (biceps? but not really, if your hand is holding a bar like the drops of a bike), lower back, etc help with out of saddle sprinting efforts.

And another observation. Usually when I lift I immediately feel some benefit, even just the pumped muscles right after the workout. I feel energetic, strong, etc. I usually see some reasonable strength gain at first (plateaus to known levels). This year is the first year where I've lifted and such and my muscles feel downright flabby, even after a couple weeks of work. It's really annoying. Same weights, curling (bar pointing forward, like the way the drops are) 22-23 lbs, but without the snap I used to have. Is this called "getting old"?

Running. It has made me a better rider for so many reasons. Chief among them being core strength and balance. It also works back and shoulder muscles like you wouldn't believe.

ball squats, burpees, plyometrics, power cleans

Squats, seated rows and calf raises. To get more benefit you really need to figure out where you strengths and weaknesses are and work around that.
Or do what Stanseven says.

lots of core to help keep the upper body stable and keep form for longer distances

cycling uses a lot of core but doesn't really strengthen it much

Cycling is primarily an aerobic sport. Your legs are likely more than strong enough. What makes you think they need to be stronger? It's not like you have to push very hard on the pedals.

except when you're climbing, or sprinting, or taking pulls, or time trialing...

seriously? how did this post take off with lots of ideas when mine went straight to page 2?
https://www.bikeforums.net/showthread...dination-power

If you're TTing correctly, you should be spinning fluidly 95+ rpm, not mashing the pedals.

Cycling is ore about neuromuscular coordination, metabolic adaptations, and aerobic adaptation, not muscular strength. Aside from light upper body workouts you're far better riding more/harder when you ride and doing less/more rest when you're off.

Because once CDR posted there was nothing left to be said...

Since the weakest part of many cyclists' spin is from the 11:00 to 2:00 position at the top, one good muscle group to work on is the hip-flexor.
Nate Loyal recommended this one to me, and my FTP immediately picked up 21 watts, and my spin is MUCH more fluid.

Yes. Makes you appreciate the speed of some old guys now doesn't it.

My other two regimes are TRX training and Plyometrics. TRX is great core training and plyometrics helps maintain the fast twitch muscle fiber.

Running, yoga, pushups.

I'll let you do the calculations for the force required to TT or take pulls or climb at 350-400W.

Weight training can be useful for sprinting, or old farts, but my original statement stands.

Anything that operates on 2+ planes of motion, twisting, various planks and that works the stabilizer muscles (hint, the weights will be small). If that's too hard to remember just look around at everyone in the gym and don't do what they do. GL