Article by Emanuel Giordano

Often when we talk about hojo undo (auxiliary exercises) strengthening exercises with all kinds of equipment, be it traditional or modern, immediately come to mind. Here then in our mind images of chiishi, ishisashi, nigirigame, tetsugeta, etc. are crowded. In reality hojo undo is not just weight lifting, and so also thought a great teacher of the past, Kyan Chotoku sensei:
Some people believe that chiishi and sashi are part of Karate, but this is completely wrong. Chiishi and sashi are used to strengthen muscles and bones, and to develop a strong grip. Weights, nigirigame, rubber or iron bars, and various other training items are also used to strengthen muscles and bones. However, you cannot develop the full power of Karate in the body simply by strengthening muscles and bones. The makiwara must be hit to forge all the body power of the attack.
I truly believe that makiwara is a very special training feature, not only for Okinawan Karate, but for all martial arts. Matsumura sensei and Itosu sensei still hit the makiwara when they were already over eighty. All Karate instructors and students should realize that training with makiwara is just as important as training with kata” 
Karate no omoide (full article in Italian available in "Karate no buyuden 2 - la storia eroica del Karate, parte seconda")
What Kyan sensei, as well as other masters, wanted to specify is that the generic strengthening of the body, obtained through weight training, does not correspond to the specific strengthening of the techniques, obtainable only through the practice of makiwara.
It being understood that the use of the aforementioned tools was and is strongly recommended to strengthen the body, but the makiwara remains the fundamental tool for developing the power of the attacks! In the photo we can easily see a chiishi and testugeta (red circle), proof of the fact that Funakoshi sensei also introduced these practices in his courses; but also a makiwara (green circle), that is a roll of straw (makiwara 巻 藁 means roll of straw) to be used as padding for the tool of the same name.
There are various types of makiwara suitable for training in Karate, but they all have in common the ability to absorb and return the force with which you hit them, in such a way as to allow the practitioner to also learn the correct use of the technique and of the body. These characteristics make the makiwara the only tool a karateka should never do without, so much so that a famous Okinawan master of the past claimed that there was no karateka who did not use this tool.
However, it should be stated that although the main purposes of makiwara training are those mentioned above, training with this tool also involves conditioning the hands and wrists, accustoming them to impact. But that doesn't have to be the purpose of such exercises! Practicing makiwara training for the sole purpose of growing calluses on the knuckles means not having understood how to use "the karateka's best friend"!
  • "Shorin-ryu Karate: kata 2" (here)
  • "Shorin-ryu Karate: kata" (here)
  • "Shorin-ryu Karate: The legacy of the bodyguards of the king of Okinawa" (here)
  • "The legend of the masters of Okinawan Karate: Biographies, curiosities and mysteries"  (here)