This Japanese technique is written using two Chinese and one Japanese ideogram - with all three ideograms being routinely used in the Japanese written language - and two ideograms ('1' and '2') being used in the Chinese written language:
腰 - Japanese - Koshi (Chinese: yao1) = waist, hips and midsection
投 - Japanese - Na (Chinese: tou2) = throw, blend, redirect and reject
げ - Japanese - Ge = down, low, depth and ground
Interestingly, with regards the ideogram '腰' (Koshi) - both the Japanese and Chinese language dictionaries give an identical (and exact) physical location. Therefore, 'Koshi' represents the 'waist' (or the anatomical 'space' between the hips) situated toward the front of the body - whilst the back of the body corresponds 'Koshi' to the 'small of the back' or the 'lumbar' region. Although neither dictionary mentions the centre of gravity of the body - or the 'lower dantian' (both situated three-inches below the naval) it seems clear that such a 'special' area is implied. I think this assumption receives support as 'Koshi' is also used to refer to the 'kidney' area - perhaps slightly higher than the lumbar a 'cold' area significant within traditional Japanese and Chinese medicine.
Although 腰 (yao1) is prevalent within Chinese martial arts (used to counter an opponent through penetrating their technique, blending with it and redirecting it) - 'Koshinage (腰投げ)' is a 'distinct' Japanese physical interpretation not found in China. When the Chinese government took Sō Dōshin (宗道臣) [1911-1980] to a Japanese Court in the early 1970s (an event covered in one of Donn F. Draeger's books on 'Modern Budo') - part of the evidence accepted by this Court that his style of 'Shorinji Kempo' ('Shaolin Gongfu') was NOT of Chinese origin - is that nearly all of its techniques include 'Koshinage' (the BBC chose to omit this Court verdict in its 1980 'Way of Warrior' series). Cooperation of this type is a Japanese cultural development - and is not found in China's traditional arts - even though the concept is present (and used in a different manner). However, I would note that the use of squat-kicks is found in Chinese arts and are used in exactly the same manner as this documentary suggests - although our Hakka style places a great deal on toughening the legs to take continuous impact (similar to Muay Thai fighters in Thailand) and keep effectively moving. The only Karate-Do style I have encountered that has squat-kicks is Goju Ryu.
I have been looking through the Chinese language internet for 'Ju Jitsu' (or 'Jiu Jitsu') information and found a very good historical article which I have fed through a universal translator:
The early history of Ju Jitsu (Rou Shu) - or 'Giving-Way Art' is described as follows (I have translated this extract exactly):
'The origins of Ju-Jitsu can be traced back to around 2000 BCE (in Egypt). There are hundreds of murals in the famous Khufu Pyramid in Egypt depicting Ju Jitsu-type combat techniques. These North African martial arts techniques appear very similar to modern-day Brazilian Ju-Jitsu. The combat techniques that define Ju Jitsu are found (today) throughout the world within the traditional fighting systems of China, Japan, India, Greece, Egypt, Russia and Mesopotamian, etc. Some scholars speculate that Asian Ju-Jitsu developed separately (and parallel) to its African variant - and is a martial art that originated in ancient India. This Indian martial art then spread to China - where it was consolidated - before being spread across the world by migrating monks and soldiers. It is currently unknown whether there is a direct link between the Egyptian and Asian variants.'
Watching this (and all the excellrnt videos you have forwarded) - Ju jitsu looks like Qinna - or an element of Qinna. Qinna - or 'Joint Relocation' as Master Chan referred to it in Hakka - emphasises breaking bones, dislocating and/or snapping joints, but only in its highest or most deadliest aspect. The Chinese language instructional texts talk of the 'grip' being developed so that 'skin' is torn-off and 'bones' shattered like glass!
a) Ju Jitsu (柔術) = 'Rou Shu' - or 'Soft Expertise/Art'. An ethnic Chinese speaker once explained the underlying concept behind the 'Rou' (柔) ideogram to me as 'to ride in another person's rickshaw' - which I thought was superb! Not just 'borrowing' - but if need be - 'stealing' another person's vehicle of transportation (or mode of 'movement') certainly with their knowledge (after-all, they are 'present'), but equally 'without their consent' (as the resulting outcome is often contrary to that desired by the opponent)!
b) Qin Na (擒拿) = 'Catch Relocate' (Probably 'Kin Na' in the Japanese language).
Working down from that level of destruction, there is the well-known 'controlling' of the opponent through 'light' joint relocation designed to 'move' the body around (from an 'inconvenient' place to a 'convenient' place), or to 'disarm' or 'subdue' whilst leaving the opponent or assailent relatively 'unharmed'. Indeed, what makes genuine Taijiquan so effective is its inner core of guiding Qinna. Coupled, of course, with the mastering of the dropped bodyweight through an aligned bone structure - and the efficient directing of the resulting 'rebounding' force from the ground to the extremities - a process which allows for the generation of tremendous 'breaking' force with apparently 'little' effort!
Shifu Adrian Chan-Wyles (b. 1967) - Lineage (Generational) Inheritor of the Ch'an Dao Hakka Gongfu System.