Courtesy of Gary Hall Sr., 10-time World Record Holder, 3-time Olympian, 1976 Olympic Games US Flagbearer and The Race Club co-founder.
At The Race Club, inertia is the third fundamental law we teach our swimmers. Although Newton is often credited for this law (his first law of motion), it was actually Galileo that was the first to conceptualize inertia.
A Moving Body Resists Changing Its Speed
The definition of inertia is a body in motion tends to want to stay in motion. In other words, a moving body resists changing its speed. The same holds true for a car on the freeway as it does for a body swimming down the pool. The frontal drag forces are working to slow us down whenever we are moving, so to maintain a more constant speed requires that we maintain a near-constant propulsion. Although this takes work, it actually requires a lot less work than if we were to stop or slow down appreciably and try to regain the original speed. A good example is when you completely misjudge the wall on a flip turn, pushing against nothing but water. The result is a total loss of speed and the effort to get back to race speed from this dead stop is overwhelming.
The Freeway Strokes
There are really only two inertia strokes; freestyle and backstroke. I call them the freeway strokes. Because of the way in which we generate propulsion in fly and breast, abrupt changes in body speed are unavoidable. Consequently, these two stop-and-go strokes are both difficult and inefficient. Yet, even in those strokes, the law of inertia still applies.
There are only three things I can think of one can do to comply with this law of inertia in freestyle and backstroke, in order to keep the body speed more constant. The first is to kick with a six-beat kick, trying to generate some propulsive force on both the down and the up kick.
The second is to increase the pulling stroke rate (decrease the cycle time). For a freestyle sprinter with a stroke rate of 120 strokes per minute (60 right arms and 60 left arms), the cycle time is one second. The propulsive phase (when the hand is actually moving backward) in front and back quadrants is about .35 seconds. For both hands that means that .7 seconds of the one-second cycle time (70%) is spent actually propelling the body forward. The rest of the time the hand is either lifting the body or recovering. Either way, it is in propulsive ‘down time’. The faster the stroke rate, the less propulsive ‘down time’ and the more constant the speed.
Distance Swimmers Must Have a Strong 6-Beat Kick
For distance swimmers, like Sun Yang, who use a stroke rate in the middle of the 1500 of 60 (cycle time 2 seconds), the time in propulsive phase is still .7 seconds, but that represents only 35% of the total cycle time. That does not bode well for the law of inertia. For this reason, hip-driven (slow stroke rate) freestylers must have strong six-beat kicks to obey this law.
Reduce Frontal Drag
Finally, the third way to abide by this fundamental law of maintaining constant speed is to reduce frontal drag as much as possible. This is accomplished by keeping the head in alignment with the body and getting the head underwater at the crucial time of hand entry, keeping the body and legs in as straight a line as possible and by pulling under water with a high elbow position. In testing myself with the velocity meter using arms-only freestyle, with a deep pull, the body speed dropped by nearly 40% from hand entry to the initiation of the propulsive phase (.3 seconds in a sprint). With the high elbow pull, the body speed dropped by 30% during the same phase. While that may not seem like a huge difference, when it comes to inertia, every bit helps.
George Bovell demonstrates some creative drills for fast swimming: http://www.theraceclub.com/videos/swimming-technique-videos/
Yours in swimming,
Gary Hall Sr.
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Swim Training / Swimming News courtesy of The Race Club / Gary Hall Sr.