Intervals and pacing, a general and vague term you might think, since everything we swim is an interval with a corresponding pace/speed. There has to be a reason, right? So here comes a classic SwimGym explanation.
Swimming requires great technique, as we keep reminding you, and moving through the water requires a large amount of energy due to the density of water (754 times that of air). The best example is walking 25m to collect your snorkel or aqua-jogging, 25m in the water and compare how you feel after both activities. The water’s resistance to our movements and the inefficient way of moving in the water takes a lot of energy from our muscles. The enormous density of water means that for a little more speed we need a lot more energy. The energy needed increases by the power of three. If you want to swim 2% quicker, your body has to deliver 2x2x2% more energy. Knowing what speed to swim at and how to sustain that speed is very important for your physical conditioning and training goals within swimming. Know how to pace your effort is the motto!
If you think of the energy needed to swim, you will rightly think of the energy being used to move your arms and legs, pump your heart and make your lungs work. However, one system that is working very hard and is under extreme stress while swimming is your nervous system. Neurons are continually firing, orchestrating the complicated set of movements in the muscles. The nervous system also gets tired. You might have noticed it while swimming, that all at once you struggle to finish the stroke or can’t make the catch as smooth. This is not because of tired muscles, but because the control centre needs a time out. To limit the tiredness of our nervous system or to let it recover, we need to stop and rest. This is called a passive recovery. Taking a rest at the wall is good for your technique as it allows the nervous system to recuperate, but not for too long, as you probably understand ;-)
This is the reason why in swimming we almost always choose for intervals with passive rest. That is different to say cycling, where you could quite happily cycle for an hour without stopping and maintain the same speed. In swimming, however, our technique deteriorates the longer we swim and as a result we swim with less efficiency and more resistance which requires more energy to keep us moving forward. We saw the result of this with the stroke length. The longer we swim, for instance over 300m continuously, it becomes difficult to hold our stroke length, especially if we have chosen the incorrect pace to swim at in the first place.
Choose the correct gear and there be can no fear.