I havent heard anyone using this but i do it to try and get my fretting hand more endurance. 
It also gives my plucking hand a workout by increasing its speed. Its wroks really good 
for new bass players. I have only been playing for 4 months and my plucking and fretting 
hands have good endurance before cramping up.TRY IT!!!

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Do it until your hand is exhausted to get a good workout. Ill post more wokrouts as i discover 
them.