Bruce Lee himself was more than willing to do away with katas, but definitely not sparring. He also referred to shadow boxing as "homework for sparring". I am certain that a lot of coaches and instructors will also tell you that you can't expect to be a competent fighter without sparring. I agree to a certain extent- as you will need to have some data on what to expect in a real fight.
One training tool I wish to introducein this post is the imagination. I did give a short reference to it in a post of a couple of years ago, but never spoke about how to use it in a way that works.
I have left our Shotokan dojo in 1998. From this time I have been practicing by myself. The first things I have discarded were the katas that were always the same pattern of techniques, but not quite the stuff that would get me out of trouble. From that point on I began imagining attacks of all kinds against me during practice. I'd feel the panic of being cornered, the quiet anticipation of a coming attack and the clash of limb against limb. My visualisations were real enough to actually train fast reflexes and quick movements.
The first time I have put this training to the test was in 2002. I found myself actually blocking attacks without thinking and seizing openings without trying. Well- after all- I had lots of practice.
Today- being back at the dojo, and in the first jiu kumite session after more than a decade, I saw again that this training has paid off.
If you have no choice but to train alone, don't think it silly to have imaginary opponents. Bear in mind that physical conditioning is necessary too when practicing alone as being accustomed to physical pain is what sets any fighter apart from a non-fighter.
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