The full-body swimsuits used in Beijing in 2008 are the real deal. I researched their effects, did some number crunching, and found that all things equal the suits, on average, boosted swim times by 1.3 to 2.2 percent. Lets think about this, consider a 100m freestyle time of around 48 seconds, which happens to be around the world record as of 2000, before the super suits came of age. Simply by donning the suit that time of 48 seconds should be expected to fall by around 2 percent – 2 percent of 48 seconds is around 1 second. In swimming, 1 second is sometimes all you need. The world record for the 100m was 47.05s in 2008..
The 1500m freestyle was the only race in which the suits didn't help performance, which makes sense, since the suits both decrease mobility and drag, and constrict the muscles. For the shorter events (50, 100, 200m), drag reduction is key. So is muscle constriction, which allows for a quick burst of speed. But for the longer events (400, 1500), mobility rules. And muscle constriction does not help with long distances; it might actually even hurt.
So the mystery is solved, which helps explain why after 2009, every single world record achieved before 2008, barring the 1500 meter freestyle, had been beaten. Michael Phelps also crushed 8 events while wearing the suit (the Speedo LZR), which is now banned from competition. So his legacy is probably going to survive for some time.
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