It’s said that it can take 3000 or more repetitions to commit the simplest of movements to muscle memory, and up to 20,000 to make a complex skill "permanent." After learning a new skill – e.g. Mail Slot entry — with OverSwitch drills, and short, focused whole-stroke repeats, you commit it to muscle memory with thousands of strokes on which you visualize slipping your hand and forearm through the mail slot on entry. 

"Muscle memory" is a metaphor for a physiological change in your neuromuscular system. Entering the Mail Slot (the benefit of which is connecting your stroke to the effortless power produced by weight shifts) – rather than reaching farther on entry – requires a specific set of "motor units" in hand, arm and shoulder muscles to be turned on (and off) in a particular counter-intuitive pattern. With each stroke you take, an electrical signal travels from your brain over nerve pathways to instruct the motor units to contract or relax. If you think of your body as "hardware," these neuromuscular signals are the "software." Technique work is really about "debugging" the software.

Each time the signal crosses those nerve pathways, a bit more myelin — a fatty substance that acts like insulation on electrical wires – is secreted, strengthening the signal received by your muscles. A relatively faint signal is good enough to keep the movement constant while swimming slowly…for short distances…in a highly controlled environment. It takes a strong signal – i.e. a lot of myelin – to remain efficient when swimming a mile or two….at higher speeds…as fatigue accumulates…with waves smacking you….and someone climbing up your back.

"Seeing" Myelin 

Several scenes in the Outside the Box video illustrate myelin secretion in graphic terms: I need only a modest amount of myelin to swim in solitary fashion, at a leisurely pace, along the rope line in serene Lake Minnewaska. The TI campers swimming in a loose and fluid pack, at a relaxed pace, in Eleuthera, need a bit more. My  training buddies, Dave, Greg, and Willie practicing Paceline Swimming at Lake Minnewaska, at high speeds and inches apart, need yet more myelin. And in the scene from the World Masters Championships, as I pass through packs of swimmers from earlier waves, in rough water in San Francisco Bay, the main difference between me and those I’m passing is myelin secretion. Thicker insulation allows me to swim with virtually the same stroke as in the pool or a serene, non-racing setting. Lacking it, most others are left to swim with a "barely coping" stroke.

Making Choices 

Once you realize that muscle memory is physiological, you may be more mindful about how you practice. If inattention hurts your efficiency, myelin is now being deposited where you don’t want it. On many occasions, I’ve thought of little else. While swimming hundreds of unbroken strokes in a lake, thinking for instance about entering a Mail Slot, I smile to myself as I visualize electrical signals going to particular muscles, and the myelin sheath thickening.

And the deep concentration required to commit a more-efficient-but-counter-intuitive movement to muscle memory also builds "mental muscles" as I work on the physical ones. Mental endurance, along with "motor endurance" (the resistance of my movement patterns to breakdown) has proven as valuable to me as aerobic endurance in racing long distances in open water. 

In this video, I’m secreting myelin in the Endless Pool, lap pool and lake. I’m relying on it in the Masters World Championship race in San Francisco Bay.