Strength Training
A well written and perform Strength Training Program enhances Judo performance.
"Beating your body up" from Strength Training, any sport or activity is due to Overtraining: not allowing our body to recover..
The same applies to Kettlebell Training.
Power
Judo is a Power Sport. The foundation of Power is build on Maximum Strength.
"Power = Force x Distance/Time
Since the terms force and strength are often used interchangeably and distance divided by time is the same thing as speed, power can more simply be defined as strength multiplied by speed. Therefore,
Strength x Speed = POWER.
Since
strength and speed are components of power,
increasing one while neglecting the other limits total power development. ... Because
strength and speed have a multiplicative impact on power,
athletes can make greater gains if they develop both components. For
example, if an arbitrary strength score for an athlete was 2, and the athlete's arbitrary speed score also was 2, the hypothetical power rating would be:
2 x 2 = 4
Doubling strength without altering speed would double power:
4 x 2 = 8
If the same athlete made only a 50 percent gain in strength and an equal gain
in speed, the power rating would be:
3 x 3 = 9" (Brittenham, 1997)"
Source:
Plyometric bench training for 1rm increases
Initially, increasing Strength translates to an increase in Power. However, at some point, Power Training needs to integrated in a program for maximizing Power.
The Deadlift
The Deadlift is primarily a Strength Training Movement. It or similar posterior chain exercise to the Deadlift are necessary for increasing Power.
Personal Note
I am a Powerlfiter. I spent two years in Judo.
Due to my Deadlift Strength, I was able to overpower some Brown Belts and a few Black Belts had a hard time with me.
A Pulling Sport
Also, Judo is reliant more on Pulling Movements. The Deadlift is a Strength Pulling Movement.
Kettlebell Swings are a great Power Movement for the posterior chain; rather than a Strength Training Movement.
Kettlebell Swing will increase Strength to some degree. However, not to the same degree that a Deadlift or similar posterior chain movement will.
Summary
To optimize Power in Judo, any sport, some Strength Training is necessary.