Meaning of たたみのうえのすいれん in Japanese

It seems that your search contains the following:

Definition of たたみのうえのすいれん

たたみのうえのすいれん(tataminouenosuiren) 【畳の上の水練】

(exp) practising swimming on land; dry swimming exercise
コンピューターのマニュアルを読むだけでは所詮畳の上の水練だ。
Just reading a computer manual is like practicing swimming on dry land.