I was thinking about parallels between running and rowing on my short training outing today. In a rowing boat (a racing shell with a sliding seat) the strokeman or person who sets the rhythm is probably the most important member of the crew. In rowing we talk of stroke rate in much the same way as we talk about cadence in running, but what is far more important, at least in rowing technique, is rhythm. The key is to maximize the ratio of the time spent gliding up the slide (the recovery) to the time spent pulling the oars through the water (the work). I should say optimize instead of maximize because, taken to an extreme, the boat slows down too much in between strokes, indicating that the stroke rate should be higher. Having a good feel for the optimum rhythm is something that one gains with experience but it certainly requires a "sharp catch" (placing the oar in the water and taking the weight of the boat rapidly) and a quick acceleration of the oars through the water, followed by a relaxed recovery. A rowing boat has the advantage of being able to tweak certain aspects like the length of the oars, size of the blades (paddles) and the ratio of the inboard length of the oar to the outboard (gearing).
In running, a good rhythm is one which optimizes the ratio of the flight (recovery) to the ground contact time (work). The best runners seem to be paradoxically both stiff and fluid. We can also feel it ourselves when we are running at our best.
I recently read an interesting article on Steve Magness' blog saying that one should aim to have a certain stiffness in the muscles prior to a race, the shorter (and faster) the race, the stiffer. With this goal in mind, running series of sprints the days before the race can increase stiffness while having a massage can reduce it. It's an interesting idea. I also read in the Science of Sports blog, in an article discussing Oscar Pistorius' advantage, that runners tend to take the same time to swing their legs forward into the landing position independently of the speed they run at and that this time rather determines their maximum running speed. Cadence also tends to be relatively independent of running speed. This implies that, the faster you run, the shorter and more explosive the ground contact must be. This would seem to support Steve Magness' claim.
What does "stiffness" mean? I understand it as the time it takes for the muscle action to ripple through the kinetic chain, like a whip cracking or a spring uncoiling. This stiffness can be lost either through fatigue or, equally important, through lack of mental concentration. Just as in rowing, as soon as you lose your rhythm you enter into a vicious circle: you get softer, the ratio of recovery to work goes down, you increase your cadence to maintain the same speed and get more tired, etc. Put another way, every millisecond you shave off the work phase becomes an extra millisecond in which to recover from this increase in power. For this reason I believe you have to be feeling the rhythm the whole time while you are running: if it slips you make an effort to stiffen up during the work phase and to relax during the recovery rather than increasing the cadence (or overstriding).
Normally I don't run with music because I like to hear the sounds around me, my breathing and the tapping of my shoes. If you can't hear your footfalls they have a tendency to become louder and heavier. But sometimes I like to listen to music, especially when I need an extra motivational boost, like today after a few days of feeling ill. Being a bit of a nerd, I have a playlist on my iPod of music which has 180 beats per minute, which is around the "optimal" cadence. (I put this in quotation marks because I think we are better at finding our own optimum cadence than running to a metronome as some running schools would have us do (for example, Chi Running) but many people do overstride and consequently run with too low a cadence.) As long as I don't abuse it, I think it is a good way of keeping my rhythm in check: by running in time with the music, if I slow down, I must improve my rhythm and avoid getting sloppy. Now I think of it, we did almost all our rowing training at a prescribed cadence that was not necessarily that at which we would compete for precisely this reason.