Leg and core strength as we approach ages where muscle mass is in decline remain as important as cardio health.

Skip upper body if you want but skipping leg, back, and core days is done at your own risk.

At least do walking lunges a few times a week. Or squats once a week. They suck! But not being able to do them as you grow older is worse.

(I'm your age too, and am also trying to balance weight work with riding)

I am 70 and lift three days a week and ride or use my elliptical. The amount of muscle loss when I do not lift is dramatic and at this age it does not come back very easily. I would strongly suggest that you get into a three day a week lifting program that hits the major muscle groups and core. Your bone density is also at risk and no amount of bike riding will compensate for not doing resistance work. You might want to do higher reps, 12-15 for two sets with lighter weights as you build up your strength. I can not stress enough how difficult it is as you get older to retain much less build mass. Do what you wish but you will be very happy you did some weight training when you get in your 60's. Just my .02.
Frank.

Give an example of the weight program you've been doing.

IME there's nothing really better out there for cyclists than what's in Friel's Cyclist's Training Bible. Simple, quick, no injuries, no excess strain. I know a lot of folks love their deadlift, but it's a huge metabolic strain. Overheads and chins aren't useful for cycling. Really it's just squats or sled, rows, and benches, enough reps so it's not too much weight to exhaustion. Other exercises flesh it out a bit, but that's the basics. You could try the Friel. I always ride for an hour or so before my 1 hour gym session. Works fine. Hill sprints were always my strong point. Long competitive group rides on the weekends. I only lift twice a week, Tuesday and Thursday. So like:

Sunday - long hard ride, preferably group
Monday - off or hike or snowshoe or something non-bike depending on how I feel and the season and weather
Tuesday - 1 hour, usually with a long very high cadence interval, moderate intensity, then gym, 1 hour
Wednesday - usually run, just to keep everything working properly. I'd hate it if I got so weak I couldn't run. But off I I'm going to do intervals on Thursday
Thursday - 1 hour moderate steady-state or maybe with intervals, depending on season and fitness. Then gym, 1 hour
Friday - maybe another hour of steady-state or a run or off, depending on how I feel and how hard the Sunday ride is going to be.
Saturday - usually off, but if I've missed weekday workouts I'll do 1/2 hour of zone 1 with a full-gas 3' interval in it. During base, sometimes I'll ride moderate on both Saturday and Sunday, 60-100 miles total.

I'm 53 and, as I got older, I cut back on the heavy weights and keep my lifting workouts to 45 min or so and only 2-3 days a week. I don't work the quads as much because they tend to gain size during riding season but I do work the hamstrings and calves. For the upper body it's a general workout with some emphasis on shoulders and upper back/traps to help the neck while riding. After reading a study that cyclist tend to lose bone mass as we age I decided keeping weights in my workout program was important. I definitely went lighter with weights (and more repetitions) as I've gotten older as years of heavy weights and their effects on my joints became a little more apparent.

It might not be enough: https://bmjopensem.bmj.com/content/b...00449.full.pdf

It does sound like what you are doing is working for you, but have you given consideration to having another day in between weight training sessions?

Hate weights. Any core and leg strength I need that is not built on the bike, I can get skiing or hiking. Over the past few years I've been doing a fair bit of construction, which also helps. Once a week or so, I mix in a run or elliptical session to what is usually 7 days a week of some type of cardio. Then again, I'm not at 62 looking to improve, just to slow the decline.

The hardest part of aging is coming to terms with the fact that you can't do some of the things you used to.

Hard indeed. A willing mind and uncooperative body is a tough pill to swallow.

53 here and still lifting weights often(4 days/week) but the heavy days are over. I'd like to be faster on the bike but dont want to stop lifting and lose the hard earned gains in a matter of one season. Not to mention what it would do to my endomorphic appearance. I need all the upper body I can get to offset a fat ass and large quads most of which are covered with a nice layer of adipose.

One thing I have noticed since crossing the half century mark is my ability to react to training. It seems my body is resistant to training and improvements through the Summer months are very minimal.

In the words of a dear friend who passed of cancer at the young age of 35, "never quit man, never quit"

I have a 2nd job at a big box home improvement store in their lumber/building materials dept. lugging bags of sand & concrete, wielding & cutting giant sheets of pressure treated plywood, MDF & Melamine. then there's the lumber I cut at the radial arm saw & up to 24,000 steps. after a full shift, I'm absolutely sore head to toe. at age 59.8 it takes a good 24 hrs to recover. sometimes I need a muscle relaxer for my lower back. none of that holds a candle to precision weight training for muscle development tho. for a time, I was also swimming & running in addition to the cycling & weight training with some occasional racquetball. for a while there, between 49 & 51 I was in the best shape of my life w no injuries. it was a long duration body transformation that started 10 years prior with just walking at lunch. the key for me was timing. timing for the various efforts & nutrition. meaning run today, cycle tomorrow & weight train the day after. occasionally did more than one in a single 24hrs day, like biking 44 miles round trip to do upper body weight training, but that was rare. my mantra was "do no harm". following an emotional trauma Sept/Oct 2010, I lost all motivation but I kept that 2nd job. by August 2011 I was back at the gym & on the bike regularly. it takes a lot of motivation to do it all. I'll likely never have that again but it's no sweat working in some weight training & cycling despite working 6 days a week with about a dozen 7 day work weeks a year (spring & summer). we do what we can, & not what we can't. reminds me realizing some days I was not at my best, like a poor performance or weak run. then out of nowhere, I'd have a run & didn't recognize the legs under my body as I propelled myself around the track at blistering speeds. would love to feel that surge again some day. pardon the wobbling rant. stay true to what's important to you. that's all that matters

recently asked my 91+ yr old Dad what's the point, to anything we do. he smiled & said: "if it makes you happy"

I can sympathise with that. I started keeping track this year and the last time I moved weights was weeks ago. I'm running 3-4 hours per week and biking 7 or 8 hours, but for some reason just balk at the weights.

I had time to experiment with almost everything. Sure, 2 days between strength workouts would be better for the strength workouts, but worse for cycling. My Big Deal of the week is my Sunday group ride and sufferfest. I need 2 days after a strength workout to hit my numbers on the ride. No point in it if I can't hit my numbers. OTOH, doing strength and working almost to failure, the weight used almost doesn't matter.

Perhaps my best results from strength training came from doing 3 sets of 30, circuit style, using the same weight for all 3 sets, the weight calibrated so that I couldn't quite complete the 3rd set. I used these exercises in this order: leg sled, horizontal rows, hyperextension machine, barbell squats, bench press, one legged calf raises (no weights), knee raises in Roman chair, lat pulldowns. I did this for a few years, but changed it because it took too long and the gym had to be sparsely populated. Really good results, though. I got pretty strong on the bike. Highly recommended if you have the time or use a home gym.

At 59, with a few good crashes to my name; there are strength training exercises that I HAVE to do 6 days a week if I want to ride my bicycles.