On the contrary I agree Fa Jin is explosive power. An all you have said is correct. But I started the thread to hear others points and views. I didn't want to bogged it down with my Sifu's teachings. But to me the Fa Jin is much more than just an explosive punch. But what you said is good and true. I do not want to take away from that. On the contrary let me add to it. Now Sil Lim Tao trains Internal Energy and Short Power. You are correct that movements at the end train Fa Jin along with some other aspects.
My Sifu taught me to practice Sil Lim Tao different ways.
1.Once Really Slow, With Soft Power.
2.Once Medium Speed With Hard Power.
3.Once Extremely Fast with medium Power.
4.Once with Explosive power medium speed all the way through.
5.Once with with medium speed and soft power.
6.Once Fast with hard Power.
7.Once Extremely Slow with Fa Jin(Explosive Power).
8.One One leg alternating legs.
9.Meditating on the techniques.
10.Meditationg on energy or Chi and dispersing it at the end of fist.
These are basic ways I practice Sil Lim Tau. Now lets take Medium Speed with Fa Jin. Now the only place I do not use Fa Jin or medium speed is where you do your Wu Sau Fok Sau Motion. The reason being is this is a Chi Kung Exercise with in Sil Lim Tao. So I always do it soft and slow. But the movements before and after that sequence I do with Fa Jin at medium or slow speeds. Or Fast speeds. Depending on which number I am on. But I do other exercises with Fa Jin. I practice punches in the air using my hips, waist and joints and stance along with a snap at the end of punch. I practice the forms using the Breath along with meditating on Chi traveling through my body and out my fist. I practice punching the Air concentrating on Chi as well coming from Tan Tien.
In my humble opinion
Fa Jin is much more than the snap at end of your punch or the extra power you place into the punch. But it is a total connection of your stance and waist generating power from the ground to your feet, ankles, knees, hips waist chest shoulders elbows wrist and out through the knuckles. This is my opinion others may disagree. I look at Fa Jin as whole body power. Using your Structure to give you power in your punch over mere phyiscal strength.
Wikipedia says: "
A famous application of nèi jìn is the "fā jìn" (發勁) used by practitioners of the internal martial arts to generate relaxed but explosive force. A key aspect of fa jin is the recruitment of the body's sinews (tendons, ligaments, and other connective tissues) to release force rather than relying on muscular tension."
I believe the key to increasing it would be to practice with a heavy bag like 200lbs to 400lbs. An practicing punching or kicking the bag using your entire body. Concetrate on your Chi and release the breath upon impact. Envision your Energy going through the bag and out the other side. I practice Punches while using foot work to generate more power. As well practicing stepping forward and palm striking a tree. Shaking the tree gives me a gauge on how much whole body force I am using in my palm strike. I also stand in front of tree and practice rotating palm strikes using my stance and waist to generate power.
In my opinion a good practice for the wall bag would be train each part of the hand tediously and then the arm and then the entire body behind the punch.
1.Start off with just punching with just the wrist with your entire arm extended.
2.Secondly punch with just wrist and elbow
3. Third punch with just Wrist elbow and shoulder
4.Fourth punch with Wrist, Shoulder Elbow and Chest or Curl.
5. Fifth Punch with Wrist Shoulder Elbow Chest and Waist.
6 and 7 begin use your stance and then footwork.
Do each fifty times on each hand then switch.
But this is my humble opinion on ways to train Fa Jing. There are others including Chi Kung and Tai Chi one can practice and adding Fa Jing to all Wing Chun forms as well as some one man drills. But I will stop here...Because again my purpose is not for me to share all my thoughts and opinions on what I have been taught but to listen and inquire and learn how other lineages train and develop their Wing Chun. This is my reasoning for asking questions.
So do not take my questioning as demeaning or be littling in anyway.
That's an odd question! Practising running fast develops your ability to run fast. In the same way, repeating the execution of a jik jeung (or a punch etc) with all the power concentrated at the end of the movement develops fa jing. My understanding is that the 'explosive power' at the end of the movement is the fa jing. If you practise that then you develop your ability to do it.
But how do you understand fa jing, Yoshiyahu, and how do you develop it? Your perspective might be different to mine. I'm guessing from all the questions that you've been taught differently?