Bruce used EMS (electrical muscle stimulation) to increase his fast-twitch response. Those have been pretty common with athletes and you've seen them in the Ab stimulator products.
The ems today is NOT what bruce was doing I the 70s
Been tased couple times and bit because i changed switches other electrical appliances hot .Don't try this at home unpleasant .Tesla yeah he understood . have a few of Clarks I built passed them around believe i have one stashed away some where from some time back fellow never claimed it
Bruce was very phukin near sighted btw .Elastic force can be learned really does a number just find a teacher .get outside of yourself nome sayin only way you can get it . Hey Stay Safe boys and girls .