Immovable Root, or Root like a Mountain is basically done only in practice. You train it disperse or expel force by pushing from the ground up and breathing out upon impact...
You train when you intecept a hard blow or kick you sink and breath out upon impact to absorb the force. But this is momentarily. You do not stand in Yee Gee Kim Yeung Ma while fighting or any other stance. In a fight you should be fluid and flowing. From one horse to the next, one technique to next.
The horse aka root aka structure aka what ever else you wanna place with it gives you the connection you need to utilize the whole body upon absorbtion or expulsion of energy. With out a strong horse you wont have a root. With out a strong root you wont have a strong structure. I digress. Yip man lineages have a wider horse thus they will have stronger root but be less mobile as someone with a shorter horse. A YKS has a narrower horse therefore their movement will be more agile and quicker and they will be able to send more force via momentum through their horse while in motion. YKS has skill in movement while YM has skill in stillness.
Hendrik brings up four elements. I would argue there are more but I will stay on topic?
Whick are
1. JlNG。勁。jing path 勁路.
2.勢 momentum . 勢力 momentum depth.
3. 弓 bows, 弓位 bows alignment.
4. 氣 breathing. 脈 medirians flow.
All Four of these deal with structure and root and issuance of force and the expulsion of chi. All four allow you to generate power when you are striking. You need Jing and Momentum...either the momentum of your fist alone or also the momentum of your body and fist together strikin in unison amassing on your target. Jing is the issuance of force. With out Jing your strike will lack power. When you train Jing or Fajin you can explode into your opponent. Accompanied with momentum which is traveling at a linear pathway you increase the force. Breathing out upon impact allows for the release of chi into the impact. Giving you extra force. Try holding your breath while hitting a punching bag as hard as you can. Now breath out upon impact...Can you feel the difference? As for Bows Alingment I guess he means your body, structure and horse. When they are alignment you will deliver who body force via your mass and weight upon impact...All four items together is basically delivering a rooted solid strike upon impact while in motion...Meaning stepping into the opponent while you strike.
No root as hendrik means is not just standing there throwing your arms around...but this is my opinion!
The Flow is relentless like a raging ocean with crashing waves devasting anything in its path.
"Kick Like Thunder, Strike Like Lighting, Fist Hard as Stones."
"Wing Chun flows around overwhelming force and finds openings with its constant flow of forward energy."
"Always Attack, Be Aggressive always Attack first, Be Relentless. Continue with out ceasing. Flow Like Water, Move like the wind, Attack Like Fire. Consume and overwhelm your Adversary until he is No More"