I’ve never been a fan of oi-tsuki (追い突き) – the lunge punch so ubiquitous that it is synonymous with Karatedo in the public’s eyes. One of the main reasons for my dislike of this punch is that it is not found in classical Nahate kata. Sure it can be found in Geki-sai I & II, but those are relatively modern creations made along the same lines as Pinan series, but in the classical forms we predominately see gyaku-tsuki (逆突き) or reverse punch as its commonly referred to. The rather tragic English translation of gyaku-tsuki aside (or oi-tsuki for that matter) the punch takes its name from the “flipped” position of the punching arm and lead leg.
What makes gykau-tsuki such a valuable punch in Nahate is its destructive power that stems from linking the lower and upper body, and then transmitting that force into the target. This consists of five main components that I’d like to talk very briefly about and how a Karateka can strengthen each component outside of classical methods. For an excellent description of what classical methods can be used, see Mike Clarke’s book on Hojo Undo.
(1) Driving with the rear leg to start the kinetic chain
I think exercise that strengthens the hamstrings, and quadriceps would be best and should include squats and dead lifts.
(2) Stabilization of the lead leg to ground the punch
For stabilizing the knee the exercises should naturally aim to strengthen and stabilize the knee. These might include the torturous Bulgarian split squat, or the simpler forward lunge. Plyometrics might also be an option but can be pretty hard / dangerous if not done properly.
(3) Rotation of the trunk to transfer energy from legs
The koshi have become a bit of a gimmick in some Karate-do teachers and styles, and outside of kata or basic body mechanics, provide few methods for developing them. So exercises that strengthen the abdomen and obliques dynamically might include medicine ball throws and slams as well as cable wood chopper
(4) Extension of the arm from trunk rotation
This isn’t critically important but if you do, a few exercises will suffice. General strengthening exercises for the shoulders and triceps to aid in delivering the punch could include military press, dumb bell press, triceps extensions, skull crushers
(5) Contact with target with fist
The hand decompresses when it strikes its target and no amount of kata can help you understand this – you need to hit something. There really isn’t a modern tool or method that is superior to the makiwara IMHO. But if that is not available then some heavy bag or pad work would suffice.
How often should do these exercises? I would say once a week to start for the large muscles at 3×5 as some of them are quite draining and your body needs time to recover. The smaller muscles also once a week to start but higher volume, maybe 3×8-10. As you get stronger you can increase the frequency and the load.
Remember to always talk to your physician before doing any physical activity like weight lifting, and if possible talk to a trainer.
All this said, there’s no substitute for regular Karate-do training, just remember that there are also other methods that you can adopt, traditional and modern, that may help you improve your punch.