A lot of people seem take up cycling to get fit, and they'll talk about how light their bikes are.
However, as I understand it, a heavy bike uses more energy to pedal it. Should someone that wished to get fit find a very heavy bike?
I'm going to assume that your definition of "get fit" is to lose weight and develop aerobic fitness. I'm also going to assume that the person in question is rather unfit to begin with.
All in all, a person can get fit (or not) on either a heavy or light bike; it will really depend on how they go about their fitness program.
To achieve aerobic or cardiovascular fitness one needs to engage in an activity that elevates the heart rate to a target zone and keep it there for periods of time. To lose weight, one must burn more energy (calories) than one consumes. In order to do this the activity needs to be done on a regular basis.
On to the weight of the bike... Say a person can choose either a 15lb road bike, a 25lb mountain bike, or a 35lb commuter bike for their fitness program. It makes absolutely no difference which bike they choose in order to lose weight and develop aerobic fitness. The only thing that matters will be how they use the bike. So to get fit, the choice of bike would depend more on the type of use a person desires rather than the weight of the bike.
There are also drawbacks to choosing a heavier bike for the sake of it being heavier. One is that it would be harder on the knees of an unfit person, and even a fit person, if they have to climb hills. Another is that it's just plain harder to have to lug around. And also, it would be much less enjoyable once the person gets fit.
My second job is working as a fitness trainer. If a client came to me wanting to get fit with cycling, I would not recommend that they get a 'heavy' bike. I would recommend that they get the best bike they can reasonably afford, based on the type of riding that they prefer to do. I would also probably recommend that they start out with steady, regular riding and build up to interval training. The question is about getting a heavy bike for fitness; and I'd say no, don't get a heavy bike for fitness. Get a bike that will be frequently ridden.
As a trainer I've had several clients who turned to cycling for fitness reasons. One of them got an 'urban' bike decked out with fenders, rear rack, panniers, etc and proceeded to lose 30lbs and otherwise improve her fitness with a daily 16 mile RT commute, plus weekend fun rides. Another client went with an expensive, light road bike; he managed to burn off 25lbs, and 6 months later rode his first century. So, the weight of the bike shouldn't be the determining factor. Like others have said, it should be about the fun and enjoyment and finding a style of riding that'll be sustained.
A heavier bike may not handle as well as a lighter bike, and can be less enjoyable to ride. It's more fun to ride farther and faster, so a lighter bike is probably more likely to be used.
Also, you can make a bike heavier by hauling stuff on it, it's hard to make a bike lighter!
I'd suggest that someone who wanted to get in shape pedal further and faster on a lighter bike, and search out lots of hills!
To a large extent the comment by @wdypdx22 is correct. The primary exception being if you are working out in a hilly area.
The weight or mass of the bike and rider makes a big difference in the initial acceleration, but once moving on flat ground inertial effects take over. While most riders do all they can to keep from starting and stopping frequently, you can make your workout harder simply by doing repeated quick intervals. Slow to 5-8 mph, then sprint to 20 + for 30 seconds - lather, rinse, repeat.
Once rolling at a fairly consistent velocity you are primarily trying to overcome the frictional drag from the tires, and aerodynamic resistance from trying to push yourself through the air. That's why you can only expect a 2-3% gain in speed at the same effort when you switch from a mountain bike (with slicks) to a road bike.
So if you are cycling on the flats and want to make your workout harder, you can lower the pressure in your tires or use knobbies (watch for pinch flats) and wear loose, flapping clothes like a parachute.
If you are going uphill, the story changes significantly. The effort to lift you and your bike up a grade in watts is
Watts = M*g*[Sin(Arctan(grade))]*V where: V = Speed (Velocity) M = Mass (Weight of you and your bike in Kg) g = The gravitational acceleration constant (9.8) grade = % grade. A hill that rises 4.5 ft over 100 ft has a 4.5% grade
If we assume a mass of 87Kg (about 190 lbs) and a slope of 4.5 which feels steep for most people, riding at 200 watts your speed will be about 10 mph. Of the 200 watts, ~170 are expended in lifting your Mass upward, and ~30 watts are expended moving you forward. Increasing or decreasing the Mass can make a much bigger difference on the hills.
This article is a great explanation of the physics of a moving bicycle.
Echoing what others have said, anything that gets you riding trumps all else.
If you would ride to work, but not in the wet, fenders will help you get fit. If that's what it takes to get you riding, that's the most important thing to do.
Do you wear a suit at work? Drive your car 1 day / week, so you can keep fresh clothes at the office. Suddenly driving 1 day / week is the key to fitness.
Would you do grocery trips by bike? Set yourself up with removable panniers. Carry them in to the store with you, and put the groceries directly in them at the register.
Do you have young kids? Get a tandem-style trailer or a sitting-style trailer.
Do you live in a hilly area? If that stops you from riding, get an electric-assist bike, preferably one that requires you to pedal.
A bike that is built to be super-light might be exhilarating to ride, until your carbon fiber forks collapse, or your radial-spoked wheel tacos. As a Clydesdale, most frames flex under me so much that I don't enjoy riding them.
Forcing yourself to ride when it's not fun only works for a short time. Soon you'll undermine yourself. For me, at least, this is why "exercise programs" and "diets" don't work.
Figure out what it takes for you to ride, and do that.
There's already a cacophony of answers, but their detail obscures the simple response to your question: no, a heavier bike will not help you get fit easier than a light bike.
Simply put, you will output the same amount of power independent of the weight of the bike you are riding. On a heavier bike, you will just go slower than you would have otherwise on a lighter bike.
Update: The one counterexample to this is if you participate in group training rides. If you ride on a heavier bike than the rest of your group, assuming you keep up with them, you're (probably) getting a better workout than you would had you been riding on a lighter bike. However, the difference isn't as much as advancing to a more strenuous route with a faster-paced group.
A person might burn more calories per km with a heavy bike, but the lighter and possibly more fun bike will make the ride enjoyable. If the person has fun, it will help for developing an active life-style which will be better in the end.
And burning calories is nice, but you want to get that heart pumping. The same person might reach his target bpm at 15 km/h on the heavy bike and at 25 km/h on the light one. In the end it's all good cardiovascular exercise.
Someone wanting to get fit by cycling should just get on a bike and start cycling. Heavier or lighter doesn't make a difference with the getting fit part.
The reason for the lightness part is:
You need the bike that you will ride. You should make your choice based upon how much of an impact it will have in how often you ride.
If you are heavy (220lbs or more), you might want a heavier, more solid bike. Something that you can feel a bit more secure on and something which will creak less.
You don't mention what types of rides you like. I rode for a couple years in and around a small down. I was constantly hopping up on curbs, bunny hopping potholes crossing railroad tracks. I went for a steel frame bike without regard to weight. A hybrid would have worked just as well probably, but I got double duty out of mine on weekend rides.
If you only plan to go out on the road, a good light bike seems to make things more effortless, and that might encourage you to ride more.
As far as energy used up, it really doesn't matter. Gearing will allow you to put forth the same effort just a slightly different speeds depending on the bike weight.
I'm a firm believer of "The easiest way to take a half pound off your bike is to lose half a pound." I don't buy light and expensive anything until it is race time.
A light bike is so much more fun to ride than a heavy one that you'll be more likely to ride the light one. Also, I find that on my lighter bike, since it's easier to go faster, I'm always pushing to go as fast as I can (because fast is fun). On the heavy bike, it's so much work that I end up going slow and ultimately not working as hard. An hour on the heavy bike and I'll not even be tired. An hour on the light bike and I'm exhausted and the muscles are burning and will be sore for a day or 2! :-)
You don't need a heavier bike to get fit, you need to ride the right technique and observe the right discipline (well designed workout plan) and commitment.
I think the wrong argument around bike weight lies in ignoring inertia. Obviously, it takes more energy to accelerate a 32 lb bike from 0 to 20 mph than to accelerate a 15 lb bike to the same speed. However, once that speed is achieved, keeping at that speed needs almost the same energy, due to inertia. At that point, friction and drag are more likely to make you burn more or less energy.
Nonetheless, you can modify the amount of energy spent during a ride, much like you can change the way you drive to save fuel. The same principles apply. If you drive restlessly, in a sporty fashion, accelerating and braking heavily, you'll end spending a lot more fuel than if driving in a more controlled manner. With multi-speed bikes you have that alternative to modify the purpose of your riding, especially in hilly terrain.
You can climb up the same hill by doing two extremes: Use the biggest cog you can put up with, pedaling a lot faster but riding slow, that will be cardiovascular exercise, will make your heart beat faster and will keep your breath fast and light, doing this regularly is great for for burning body fat, but must be done several times a week and for at least 40 minutes (aprox) each time.
Or you can climb on the hardest gear combination, pedaling slowly, but exerting much more force in every pedal stroke. You will the build muscle strength. Doing this regularly even only two times a week will quickly build muscular strength, but mostly in the legs only.
I have a lot of friends and know a lot of people who are heavy riders, this meaning they ride in a regular basis, but they are all doing slow uphill pedaling, they all have very strong and muscular legs but a lot of abdominal fat. (I personally am a little bit into this category).
Other riders who climb the same routes as we do, use lower gears and a faster cadence, we can ride side by side, so ground speed is almost the same. They have a better general physical shape, or at least they look so.
Comparing this two "climbing techniques" i can say that: I usually look more tired than they do while climbing, my breathing is slower and deeper than theirs, and my pulse is also slower and deeper (not measured, just felt finger on the wrist). BUT, in the other hand, I can usually keep going further and stay pedaling for a longer period of time.
I also do sporadic commute in a very hilly city, and I have tested both techniques and I can say, pedaling hard with slow cadence works best for me.
Because of this, I have come to the conclusion that slow cadence burns less energy "per minute", so I guess this is the less effective for loosing weight.
I wrote about my experience as a mountain bike rider, riding kind of "all mountain" style. I cannot speak for route riding, but it seems to me that it is a lot more cardiovascular.
Depends on the person.
Answer: what do you like most on the gym?
If your answer is aerobics, get the lightest bike and increase the commute ride each day.
if your answer is weights, get the heaviest bike and add cargo/pedal faster each day.
I was 10Kg above my regular weight. i loath cardio. and love weight lifting. So i got a 12yr old mountain bike, with wide tires. restored it just enough. carry a lot of stuff and a heavy chain. started doing 12km/h avarage, jumped on the first week to 21km/h on a 6+km comute. now i am doing almost 26km/h average. it's nothing for someone who like to ride the bike. i hate to :) got back to my weight in some 12days.
bottom line is, the efficiency of the activity is NOTHING compared to your willingness to progress on it. So if the worse method has more changes of you sticking to it, go with the worse method.
Late to this party but some good reading here!
There are a couple of jewels in this thread. The math guy proving the weight of the bike might help 2-3% is priceless. As an overweight cyclist, when someone passes me going up a hill and they do frequently, a 10% increase in my speed wouldn't help me keep up. I'm doing 7, their doing 12, you figure it out.
Then there is that comment by Lance saying it is easier to lighten the rider than the bike. So true. When I hit my goal later in the year, I'll have lost more than the weight of the heaviest bicycle out there.
But here is the rub, newbies and guys like me trying to get fit and lose a few pounds are going to get messed up with this light is right stuff. Almost every light bike I've looked at drops the 1st chain ring and has little tiny tires and many even have missing spokes. My Surly LHT is a heavy bike and the reason I got this bike was for the gearing, it has a MTB crank set and cassette. I'm pretty sure it will climb a phone pole if you can keep the tires stuck to it. I ride in the 3rd ring most of the time but when I need to dump down, I need to dump down. We all agree, hills make the man (person).
That leaves me with the tires and wheels, going from 26x2.2 to 700.37 indeed rolls easier, but those tiny racing tires are not something I'm ready for. Perhaps it is more between my ears than real, but my Continentals ride just fine, thank you on chipped granite, something we see around here. I cannot imagine hitting a pot hole with those little tires and half the spokes.
While heavy, my LHT is a very smooth ride and having being professionally fitted, I am comfortable on 25 mile rides. You all agree the bike has to be fun to ride and for the new guy struggling to get fit, he needs to be fitted to the bike and he needs low gears if he is going to ride hills and overpasses or the bike will not be fun.
You should get as light a bike as possible.
They tend to go faster. When you go fast, cycling is more fun. When it's fun, you will do it more. When you do it more, you get fit faster.
It's also more expensive to get a light bike. When people spend lots of money, they tend to use their bikes more. And you'll look so much more awesome when you get fit if you have an awesome bike. That's theory. The practice is that you'll buy something less spectacular and save some cash.
The math formula somewhere is nice and very correct, but you know what it really says: if you have a light bike and do the same amount of work as someone with a heavy bike, you'll fly past him and humiliate him with your awesome climbing powers. If that's not a reason to get on that awesome carbon fibre wonder (and get very fit), I don't know what is.
If you have got a spare 4 hours every day, then get a light fancy pantsy road bike that weighs 20 grams. If you have a short fixed commute and a life though, you want to waste as much energy as possible so find a heavy high- friction beast with the brakes stuck half on that someone is throwing away, take the hilly path covered in pedestrians that force you to keep burning energy off on the brakes, and drag an old car tyre around behind you. Personally I think riding for speed on a new expensive light weight bike in a large group where you barely ever have to pedal may be good for social health but is useless for physical health and is just plain dangerous. Methinks there has been some clever marketing and that there is some pride at stake ...