The problem with cadence, at least in cycling, is that there is both a motor-learning and a physiological component to it, and in practice these sometimes work against each other. Cadence is related to effort, and while one might be properly pedaling 80 rpm given a particular workload, a higher workload would require a higher cadence.
The next time you watch a cycling race on television, notice how the peleton is cruising through the countryside in the first couple of kilometers of a stage, talking about whatever it is they talk about before the hammer drops, they may well be riding along at 80 rpm. Later, on a flatter breakaway, a lone rider might be at 90 rpm, and in the final kilometer of an uphill finish the fastest climbers will be going at 95 rpm. In a field sprint, 120 rpm would be considered on the low side.
Having said that, cadence is one of the few areas in which it would not be proper for me to counsel you to ride at the most efficient rate for the level of effort at which you are working. That is because you might be in a particular part of your training that would require you to ride most of your miles at conversational pace, and the most efficient cadence for such a pace might be 80 rpm or even slower.
But there is that other element to cadence that I refer to as motor-learning and that others call its "neuromuscular" component. It is difficult to pedal a faster cadence. It will be harder for you to ride at 95 rpm in the beginning because you are simply not used to it. You'll be pretty sure that it is slower for you than riding at 75 rpm.
And you'll be right, on two counts. First, if you are not riding very hard on a particular day, 75 rpm might be a more efficient cadence for you. Second, if you're not used to riding 95 rpm, you'll not be very efficient at that pedaling rate regardless of your level of effort because you haven't made the motor-learning jump.
Fortunately, motor-learning is easy, and simple motor-learning procedures do not require the time that an increase in fitness takes. A few rides will make 90 or 95 rpm feel quite a bit easier for you.
The devilish part of this subject is that there will be a time when 85, 90 and even 95 rpm will be the appropriate cadence for maximum efficiency, and if you dont teach your muscles to pedal efficiently at that rate even when your training effort would dictate that pedaling at a slower cadence is more efficient - your muscles will not be able to do the cadence when it matters. The upshot is that you should be spending a lot of time pedaling at a cadence faster than you feel is comfortable.
My wife coaches quite a few athletes, and those with whom she's been working for a while have no problem with interval workouts - which are done on the trainer - in which they increase their effort and cadence at the same time. But the newer athletes have a problem maintaining that coordination because they are not used to working hard at a higher cadence. Like swimmers who are incorporating a new swim technique, they'll often be slow and clumsy until they get it down, although it's hard for them to imagine they'll be faster in the end.
Why is a cadence of 90 rpm better at a high work rate than a cadence of, say, 60 rpm? To be honest, I'm not entirely sure. What's more, I think it is hard to prove empirically.
One of my training partners is Pete Pennsyres, former winner of Race Across America, and an engineer by trade. He has found that at a certain speed and power output on hill repeats his pulse is lower at a slower cadence and is actually the lowest while standing and at an even lower cadence.
But he acknowledges several things. First, as he's been working on his hill repeats the delta between his efficiency readings is getting closer, especially as he works on seated climbing at a higher cadence. Also, he has a tremendous background as a very long distance rider, and so is more comfortable riding at a lower cadence. Pennsyres is also doing ten-minute hill repeats. This may not be a long enough time span to pick up other factors that might be going on during a race.
One such factor is venous return. Muscular contractions are what move blood and waste products out of your muscles, through your veins and back to your heart and lungs. When you're racing, you're bumping up against the upper limit of your body's ability to move de-oxygenated blood and blood lactate through your circulatory system, where lactate can be buffered and oxygen molecules can hop onto your heme groups and hitch a ride back to your muscles (and where carbon dioxide hops onto your heme groups to hitch a ride back out to your lungs to be exhaled).
A higher rate of muscle contraction and relaxation (i.e., a higher cadence) will move all this stuff around faster instead of keeping all the bad stuff locked up in your muscles for a longer period of time.
All this cadence stuff is exacerbated if you adopt a "tri position." This is not the power position that a rearward, seated, upright position is because you are not pulling on the "tops" with your hands and leveraging your body's power muscles against the pedals. On the other hand, you are in a position that is quite aerodynamic and your hip angle is open, creating the ability to product a nice, efficient pedal stroke.
Although you're not yanking on the tops the way you would during a seated climb on a road race bike, you are pulling up with your hands on the aero bars, and this allows a better recruitment of the hamstrings. So although you won't have quite the power you'd be able to apply ballistically from your quads, you'll have a more even application of power around the entire pedal stroke. You'll be better able to "turn" the cranks in a circle while riding in the aero position, and this will be much more efficient if done so at a relatively high cadence.
This is especially important while climbing. Normally, on a road race bike, you'd want to be able to develop the torque generated by the leverage you get from your quads. But in the aero position the worst thing you can do is sit up and try to acquire the seated climbing position that you'd get from your road bike. You're on a steep seat angle bike now, remember, and that position is gone for you. The best option for you is to stay in the aero position and just spin that up the hill. Keep that cadence up, maybe even over 100 rpms if need be to stay on top of the gear.
Runners also have an issue with cadence, but for different reasons. I, for one, believe a runner's cadence should never change (which is a departure from what I say above about cycling cadence). If you are running slowly, stride length should change, not cadence.
But the cadence should be relatively quick, because that is where your efficiency comes from. When your cadence or tempo is too slow, the result is an overstride. Your foot now falls in front of your knee instead of right below it, and you've got to wait for your body to catch up to your foot plant before you can apply the power that propels your body forward.
As is the case with cycling, you would do well to watch top-caliber runners run. They will almost certainly have a faster turnover than you. But I do have a super-secret foolproof way for you to acquire the proper footfall and quicken up your cadence. This is best done during a track workout but can be done during group runs of any sort.
Run right behind someone or, failing that, just off his shoulder so that your right leg would interfere with his left leg if you were running too close (or opposite if you are running on their opposite side). Run as close to his back as is comfortable for you. You'll find yourself occasionally in danger of running up your friend's back, and this will force you to chop your stride.
As you get comfortable with keeping just the right distance behind your friend, youll notice that your "chopped" stride is actually more economical and efficient. Your stride will quicken up and you'll be running more efficiently.
I am not going to talk about swimming because although certain principles apply, I could cause you more harm than good by lecturing about stroke turnover since your problems are almost certainly the reverse in the pool. What I mean is that you may well suffer from a "too complete" stride length when you run, but you almost certainly would not be lauded by your master's swim coach - were I to ask him - for having a substantially complete pull through the water.
If I tell you to quicken your cadence in the pool, you'll almost certainly make an already incomplete pull even more incomplete.
So I'm not going to broach the subject of cadence, or turnover, during the swim. But about cycling and running technique, what can I say? I know about that stuff.