I'm sure a lot of you remember the scene in the movie "The Presidio" were Sean Connery's character decimates the jackass in the bar with nothing more than his thumb!
Some of you may remember Andy Adam's book on Ninjutsu highlighting Hatsumi. Several photos showed the intense conditioning of natural weapons including the 'boshiken" or thumb fist. One photo in particular impressed me. That showed a small flat stone being broken by a "thumb" jab.
Sykes, it has been reported, had a tremendous amount of grip and hand strength. He was apparently quite fond of the "thumb" jab. Though NOT a basic method, since conditioning over a period of time is mandatory, it still was a favored "personal" weapon of his.
Allowing the thumb to jut out along the side of the fist was a "street" tactic shown to me when I was a kid by my father and uncles. Aimed at the eyes it made that left jab a really potent weapon.
The thumb as a weapon can be used to strike, gouge and/or apply tremendous concentrated force. It is also used in many Judo/Jujutsu "shimewaza" of the "combat" variety.
Many methods employ this type of strike. The problem is CONFIDENCE in its use! Here's a method of toughening and strengthening the "thumb" that is specific to its use in hand to hand combat:
Grab your palm sized "crushing" rock. Keep the flattest side UP. If the rock you use is TOO round, find a flatter one.
Get a THICK DENSE piece of foam as used in upholstery.
Place the rock in the middle form your "thumb jab" fist, place the pad of the thumb on the rock and PUSH. Try to push/press the rock right THRU the foam. DON'T STRIKE IT YET! Just numerous repetitions of the FORCEFUL push! Repeat it over and over. Over time you will be able to strike the rock and ram it right down fully to the bottom of the thick foam pad.
Other good exercises such as the "thumb" hook push up on bricks or cinderblocks can also be added as well as any other personal favorites, BUT the exercise as described above is about as specific to USING the "thumb" jab as you can get.
I train the thumb in several uses:
Boshiken - Thumb tip jab
Boshiken - Thumb knuckle Uechi style
Oyayubiken - Thumb knuckle fist
Tohote - Sword tip hand (thumb hook)
Dim Jeang - Palm strike with thumb jab. From Fushan Wing Chun as taught by Sifu Chong.
Ying Jow - Eagle claw with thumb crush/gouge
In Dr. Ernst Jokl's excellent treatise on the scientific and medical aspects of boxing blows, he describes the "old" street fighter