During my stay in Hong Kong I had the honour of meeting and training with Kwok Wan Ping, who many would say was the top disciple of grandmaster Sum Nung. Master Kwok was really easy going and had a good sense of humour. He seemed to always wear just a pair of shorts and sandals, and his figure was in top condition, even for a 70 odd year old man he was still covered in muscles. The first day I met with him, I was invited to dinner and his wife cooked traditional Cantonese food which was really nice. Then after our food had digested, we went on to the rooftop to train. The rooftop of his apartment had been the sight of many Beimo (illegal challenge matches, popular amoung kung fu students in the 60s) and he told me that when he fled mainland China for Hong Kong all the people were practicing Yip Man Wing Chun. So in order to start teaching Yuen Kay San lineage he had to prove himself and fought and beat several of Yip Mans students.
His style of Wing Chun was a fairly hard style in comparison to the other stuff ive seen. Chi Sau with master Kwok was very tiring, his arms felt immovable and really heavy, but they werent tense. He also put a lot of emphasis on arm conditioning drills, which I did so much with him that my arms were swollen next day! He was critical of many people who are too soft, which is good in theory, but it doesnt work in real fights. And if you doubt that is true, Im sure he would invite you to test your skills on him! He said that his tremendous internal power came from a lot of Tai Chi and Ba Gua Zhuang training. He had even created some training drills which combined Wing Chun with Tai Chi principles.
In the Yuen Kay San lineage, there is 12 basic excercises called San Sik, which means free excercise. These can be done with a partner, or alone and are a good way of developing a strong foundation in Wing Chun. They are a condensed way of demonstrating the basic principles of the art.