Is it like riding a horse, where you really have to use your legs (not to mention your abdomen, back, etc.) to do it right? Or is it more like driving a car, where you can just sit there, push the gas pedal, and aim?
(Mods, I’m assuming that the answer is going to be as much opinion as a simple statement of fact. If this belongs in GQ, please move the thread. Thanks.)
Not an expert by any stretch of the imagination but I would have to assume the riding position makes a huge difference. I’ve really only ridden lightweight, cruiser type cycles and they were comfortable for me for extended rides (up to four hours).
Your own experience is the only way to answer this. If you can, rent or borrow a few different types of cycles to see what you think.
There’s not much to do except sit, for the most part. You don’t need to transfer bodyweight much on most bikes - you can efficiently steer with counter-steering, which barely needs a touch on the bars. If you’re hustling, especially on an unfaired bike, you may need to brace yourself against a strong wind-blast, but relaxed riding, or even blasting along on a properly designed sportsbike, is relatively undemanding.
–Mal, rider since 1979 with many, many thousands of miles behind him.
Do you mean gentle walking all day kind of riding or more like Kentucky Derby kind of riding?
With or without a windshield and fairings*? My bike doesn’t have a windshield or fairings. While still not all that demanding, at higher speeds you are taking all that wind against your body, so you do have to hold on which takes a bit more effort then if you have something to deflect it for you.
I’d say the most physically demanding part, after you really get a hang of riding (and lets assume we aren’t talking about getting your self into bad situations) is probably when you’re sitting at a red light and it’s either really really windy or really really hot out.
*FYI, fairings are the plastic parts you see on the front of the bike under the windshield, in front of the hands and legs etc… They dress up the bike and deflect air/bugs/rocks etc.
Riding position counts for a lot. I’ve never ridden a cruiser, but it looks uncomfortable with the feet-forward position. Obviously it isn’t, based on the percentage of cruisers I see on the roads.
My 1994 Yamaha XJ600 is a Standard, I’ve ridden it hundreds of miles in a day, getting off only to refuel. I could get over 200 miles on a tank. I’ve also taken long rides on the '79 Honda CX500 I used to have. It’s a small Touring bike, and it was comfortable. On both of these bikes you are, as others said, just sitting. Not physically demanding at all.
My 2002 Yamaha YZF-R1 is a Sportbike-class, so it is ridden in a ‘tucked’ position. Many people who have not ridden a Sport assume it’s hard on the arms because the rider supports his weight with them. Not really. The riding position is self-supporting, so you don’t need to use your arms to keep yourself up. But I destroyed both of my knees, and the tucked position is hard on them. The bike is very comfortable for me for up to 80 miles. After that it starts to get painful and I want to get off after 100 miles. I’m looking for fuel after 120 miles or so anyway. Were it not for my physical condition it would not get uncomfortable at all. Incidentally, you may think the windscreen is very small. That’s because it’s not there to block the wind, but to redirect it over the rider’s head. Anyway, a Sport isn’t really ‘physically demanding’ either – but it can be if you like to ride aggressively. 
Good question. I was thinking of something in the middle. Perhaps mixed open country/trail riding - mixed walk/trot/canter, with enough obstacles that you have to steer the horse, but no jumping, high-level dressage-type movements, or extended gallops.
I know you covered it in your post, but we cruiser people think sport bikes look uncomfortable, leaning so far forward, your legs behind you etc. My MSF teacher, a big leather covered, unshaven guy surprised us all when he showed up on his rocket one day (know idea what kind it was, but it was huge). He said he’s ridden all the way to Florida and back, and he’d rather spend 15 hours at a shot with his weight on his shoulders then his butt.
It always seemed like such an odd riding position, I want to take one around the block someday.
I don’t think you can compare it to riding a horse at all. No up and down movements to speak of (no more then in a car with stiff shocks anyways), and you have handlebars, so you aren’t using your core muscles to keep yourself balanced.
If only I’d said so, eh?
I now ride a BMW F800S, before that it was an F650GS - a street trailie. The switch to the much more forward crouch on a sports bike was odd to begin with, but after the first few miles you don’t notice it. You’d rather the weight wasn’t on your coccyx anyway, and on the F800S it’s divided between arms and thighs, and you have some freedom to adjust the balance. Also, the wind on the upper body partly counterbalances the weight on the wrists.
It will take a little more than just around the block. The stance is sufficiently different from a Standard to require some adjustment. I imagine the change would be greater from a Cruiser. And a Sportbike handles much differently from other rides.
But do get some saddle time.
Maybe your answer, maybe confirmation bias, but there sure are a lot of fat people riding Harleys.
It largely depends upon the weather.
Even if you are riding at legel speeds, when you have a wind against you, it can be hard work on a run of a couple hundred miles.
Add in cold and wet, it can make things quite demanding.
If you start to add in things such as not having a fairing, it becomes harder work, and God help you if you are taking a trail bike at speed over any distance, the riding position holds you out to the wind like a sail.
Also, worth noting, if you go on a longish ride and visit some place, you then have to walk around, and if that means in your leathers and carrying a crash hat, it all adds to the experience.
When you go offroading, you can multiply the physical demands by a factor of 10 or 20.
For short runs you still have to kit up, get the bike out of the garage, lug security chains about, etc, there is quite a lot of ordinary mundane work to do if you are a regular bike rider.
If you decide to take a sports bike on a few track days, you’d be surprised at the physical forces involved in hard braking and the acceleration pulling out of hairpins
You get used to it.
I rode from the LA area to San Diego and back once (about 250 miles total) on my '97 Concours (a sport tourer, leaned forward but not nearly as much as a true sports bike). On my way back, I was having an awful lot of issues with cramping, but I think that had more to do with me than with the riding being uncomfortable.
I remember being sore in my thighs after the first day of the MSF course, but never had that kind of soreness again. I think one uses different muscles riding a motorcycle than one might otherwise (similar to riding a horse, I’m guessing), but that it doesn’t take much riding to get used to that.
On road, as long as the weather is comfortable, is just fine. Off road can be very demanding if you are pushing it. I assume a track day would also be very demanding.
When I ride my bike (Kawasaki Vulcan 900 cruiser) in-city, it’s generally not too bad, although the stock seat is not quite ergonomic such that it starts to get tiresome after half an hour or so of riding. The one long trip I took, about 100-120 miles, was physically demanding as I don’t have a windshield and there’s pretty much just one stop in the middle, so for nearly two hours I was fighting the wind while clamping my hand down on the throttle to maintain 80 mph. Toward the end I ran into some rain, and even a light drizzle stings like heck at 80 mph.
Really, general riding is far more mentally taxing than physically. As heightened as your senses need to be while driving a car, they need to be double that on a bike due to the higher risk.
I’ve taken a few 1000 mile round trips on my FZ6 and was probably as comfortable as you can be with no AC in July in Texas. I will say I did manage to fall asleep on it one time, so it’s not that physically demanding.
Am I the only one that cringed at this?
No. No you are not.
I heard an interesting quote from the movie On Any Sunday saying (this is from recollection, may have details wrong…) that dirt biking is the most physically demanding sport second only to soccer (?).
Street riding is nothing like that, of course. My most grueling trip was last fall and consisted of 2,200 miles over 5 days. I ride a Suzuki V-Strom that has a straight up riding style with some weight on my butt, knees and hands. I routinely do 200+ mile rides and often those three areas are the parts that hurt, and that mostly due to lack of movement.