I have an exercise bike (recumbent, though I don’t think that matters) that has multiple settings for how difficult it is to pedal. I have been on the third-hardest but wanted to increase to the second-hardest. When I was on the third-hardest, I was able to go for about 45-50 minutes. On the second I can only go 30 minutes. So my question is: Which one is burning more calories? Going longer at an easier pace, or shorter at a more difficult?
IAMNAexercise specialist or doctor or anything. But from what I’ve been repeatedly told and read about fitness is:
you need at least 30 minutes for your body to switch from an-aerobic (the natural, but ineffecient mode, which also produces milk acid, which may be partly responsible for muscle cramps the next day) to aerobic burning. This is when you will properly loose fat (instead of burning mostly carbohydrates as earlier). So if you barely manage 30 min. in the higher settings, you’ll probably burn less fat than doing 40 min. in the lower setting.
Also, at least 30 min. of aerobic exercise such as running or biking (as opposed to strenthg building exercises like weight lifting or crunches) should be done every day to get fitness and burn muscles (while crunches and similar will then build the muscles under the fat layer you want to show, if you want that.)
Plus, the general recommendation is to start slowly and increase instead of starting strong and risking muscle damage overfatigue etc., and loosing motivation (continuing on weak).
So I’d start with the slower setting until you can do it comfortable for 30 min. and only then after some weeks of building endurance and fitness to raise to the harder setting.
Also, there’s an old saying “It’s not the speed [itself during the exercise], but the [time of ] recovery [after the exercise] that proves the fitness” - whether you are wheezing out of breath for 5 or for 20 minutes is as much an indicator as your pulse during the exercise.
Doctors and physiologists recommend that your pulse during the exercise - at least for jogging - shouldn’t be too high: 180 minus life in years is the thumb rule. They say that with jogging, too many people are running too fast, that you should be able to talk comfortably while jogging, otherwise you’re doing it too hard instead of building up slowly and steadly.
Constanze has it basically right.
Your muscle cells have two forms of energy available to them: Glucagon and Glucose. Glucagon is stored in the muscle cells themselves, while glucose comes from the foods you eat and from the liver as a break-down product of the fat in your fat cells.
Glucagon can be turned into energy without the use of oxygen from the blood stream. This is important when you get surprised by a bear and have to run away all of a sudden and your blood stream hasn’t had a chance to re-route more blood and oxygen to your muscles. Glucagon is used for short bursts of energy. Your muscle cells get energy from the glucagon by breaking it down chop shop style into other products, the last of which is Lactic Acid (not found in milk, but I can see how Constanze would be confused by the similar names). That burn you feel in your muscles when you pick up something really heavy is the lactic acid, building up as your muscle cells break down glucagon. You put down the heavy thing, and your muscles burn for a little bit, but then feel normal again. The lactic acid has been carried away by your blood stream to be processed elsewhere (the lungs, if I recall correctly). So, glucagon, stored in the muscle cells, is broken down to lactic acid to produce a short burst of energy when oxygen is not available.
Conversely, glucose needs oxygen to be chop shopped into energy for the muscle cells. The trade off is that glucose produces more energy than glucagon in the process of being broken down and it doesn’t make stingy lactic acid. When you go for a walk, your blood system has a chance to shift more blood to your leg muscles, and you aren’t squeezing your muscles so hard that you are transiently squeezing the blood vessels shut, so your muscles have lots of blood and oxygen and can use glucose for energy. Since glucose isn’t stored in the muscle cells, your muscles will first use some of the glucose that is floating in your blood stream. But, your blood glucose levels have to stay above a certain threshold for your brain and blood cells to work, so as the muscles make the levels drop, the liver kicks into gear, requesting the fat cells to release their stores of fat and then converting the fat into glucose, thereby keeping the level of glucose in the blood constant. That’s why the excercise specialists will tell you to do long sessions of moderate exercise if your goal is to burn fat.
Here is where it gets more complicated:
When you go and really exercise and you are sore the next day, what you have done is cause microscopic tears in your muscle cells and they are now telling you to calm the F down so they can fix things. But, these tears can be a good thing. The muscle cells respond to the damage by filling themselves with more contractile proteins, making them stronger. It takes energy to maintain these contractile proteins, even when they aren’t being used. So, muscle cells that are full of proteins will use up more glucose while they are resting than thinner muscle cells. That’s why muscly people have a higher metabolism and can seem to eat whatever they want, even if they aren’t exercising regularly. The trouble is, muscle cells will get rid of extra contractile proteins if they aren’t being used periodically. Without proteins to maintain, less glucose gets used, the metabolic rate drops, and the athlete who could eat whatever and still be fit balloons to sumo sizes.
But, while some muscle damage to encourage the production of contractile proteins is good, Constanze is correct in that many people overdo exercise and hurt themselves. Slow and steady is the course.
Are you sure you didn’t mean glycogen, not glucagon? Glucagon is used to mediate blood glucose levels; glycogen is a polysaccharide of glucose that is stored in the muscle cells and is used to meet the body’s short term energy needs.
Son of a bitch. :smack:
Sorry. I have too much stuff crammed into my brain and it’s all getting jumbled. 
Thanks for the quick and detailed responses! I re-set the bike to the third-highest setting last night, since that seems to be the way to go. (My knees thank you also.)
About the being able to talk while exercising–in another thread recently, someone said the opposite–that if you can talk while running/jogging/etc., you’re not working hard enough. I’ve been running for years now, so I don’t think it’s a matter of being used to it for me, and I can’t really imagine ever being able to say much while doing it.
Well, the last part is the key: if your knees hurt then you should go to a lower (easier) gear. That’s always true, whether on an exercise bike or on the road.
Latest research in exercise/weight loss indicates that interval training is the most efficient way of burning calories. IIRC the studies found that doing 10 seconds flat out then 50 seconds at a comfortable pace, for 20 minutes had twice the benefits of doing 30 minutes at a medium pace.
Personal anecdote: I started doing HIIT (high intensity interval training), as opposed to longer, less intense forms of cardio, and I can see a difference in my body. Per my heart rate monitor, I burn about the same amount of calories for both exercises, though, often more during the longer workouts.
As for being able to talk during workouts, I’ve mostly heard that as a judgement of intensity. If you can sing while working out, it’s low intensity. If you can talk, but not sing, it’s moderate. If you can’t speak more than a few words at a time, it’s high.