Speaking only for myself (oblgatory disclaimer), the main reason I've tended to avoid any training other than riding and running is because... I just wanna hop on my bike and ride, or lace up my shoes and run. Like I could when I was younger. Like, 40 years ago.
But the reality is that the older I get, the longer it takes my body to warm up, loosen up and get ready to do anything.
Over Christmas weekend, Friday-Sunday, I tried three days in a row to go for a "real" run -- either a short speed workout (intervals, strides) or longer run of 7 miles or so, to prep for a solo unofficial half-marathon by the end of the year. Just a goal I've had for a couple of years that was delayed in winter 2021 by a long bout with the Super Cooties or some other upper respiratory bug. I did a continuous 10 mile run/jog/walk in late 2020, but knew I'd need more training to do a half marathon.
But the legs just didn't want to cooperate. And the weather was much colder than usual for Texas, with highs in the teens and lows in single digits. So I waited until afternoon Every day to start.
I didn't do much of a warmup, just a few stretches, squats, lunges, etc., maybe 5-10 minutes worth. In reality, the past few years I need a full hour warmup just to get ready for a "real" workout, bike ride or run.
I started out jogging slowly, walking when I got a bit winded, figuring I'd warm up within a mile to be ready to run. Nope. Never happened. Same Friday, Saturday and Sunday. Legs felt dead. Hips and knees ached, and I don't have any particular injuries or joint problems in my hips and knees, just uncooperative muscles. For years I've had more aches and pains with sudden, drastic barometric pressure shifts up or down, so it's nothing new to me.
I was so disappointed after yet another sluggish 3 mile jog Sunday that I decided to regard that as my warmup. Then I hopped on the indoor trainer for about 45 minutes, hoping to loosen up the legs. An hour afterward I felt better and decided to try a real running workout doing intervals, with full length strides for 30-60 seconds, interspersed with walking or slow jogging until my breath and heart rate slowed, etc. Felt much better, hit most of my usual best peak speeds for this kind of workout.
And afterward I did another 45 minute cool-down spin on the indoor trainer. Legs felt better than usual.
But it irks me that I need to plan on at least an hour warmup, and possibly another hour cool-down, scheduled around any exercise more vigorous than a walk or very leisurely bike ride. In that regard, it's like being back in my teens and 20s, training for amateur boxing, and spending almost all of my free time - apart from school or work - in the gym or doing roadwork. After awhile it dominates your life and seems impossible to juggle amid work, school, family, and just needing time to depressurize.
The older I get the more I can see why so many people my age just give up, become sedentary and obese. It's literally a pain just to limit the inevitable decline, let alone indulge in wishful thinking about improving fitness.