There's more to horse stances than keeping still.

Practically every martial art movie training montage starts with horse stances. We've all seen tons of kung fu movies where the protagonists are forced into horse stances while their faces contort from pain and their legs shake violently. 

Another martial art concept twisted by the entertainment industry.  

If all you measure in your kung fu progess is how long you can stay in a deep stance, you're only a quarter there.

Here are the stance training concepts I impose for each stance. I use the elements to name them since it's cooler and sticks to students' brains better.

1. Earth - Core training builds power and endurance. This training is to train your core for sustained resistance against impact, but it gradually became the only way to train your stances because its what can be done while being by yourself. Going slowly from high (one legged stances) to low and deep stances are necessary in combat.
2. Water - Elasticity and Impact adjustment training. Many arts practice this in a convuluted way, such as 2-man forms and drills like "Push-hands." Simply pushing and pulling the student from side to side, up and down while in horse stances suffices. This also helps to train what I call the "train" effect. It teaches you how to build powerful momentum for striking or throwing. A bit like how a train takes time to get to speed but once moving it's difficult to stop.
3. Wind - Agility and flow training. Transitioning from stance to stance and instant adjustment without thought. This is what you must master first to achieve the state of the "Null Mind" when in combat. In other words, this practice lets you punch, kick, throw, and grapple while your feet does quick and automatic adjustments to your footwork. Even if you trip or lose your footing, your body naturally recovers.
4. Fire - Elasticity and explosive strength training. This is much like doing jumps and lunges but while in your stances. This is what develops explosive strength and natural elasticity. In street-combat, the fastest to move from an inert position usually has a large advantage, meaning the first strike.

Horse stances are the icon that represents foundational training for all combative martial arts today. So make sure to do all 4 elements to each stance you practice.  

--------------- Added notes from Master Ron.

We are a strange species compared to most species in this earth. We are upright and are literally on bone stilts. Most of our biological kin in this world walk or run on 4 or more appendages. This posture natually protect their chests and bellies. This is why many martial arts trainers tell students to armor yourself by pointing one shoulder towards your opponent and always strike in-line with your back foot for power and stability.

A sure way to know the source of your stance's power and stability is to punch something heavy while in a particular stance. If you fall back, it's the wrong way to strike. Test this out and enjoy.

Stance training is a large part of your fundamentals. Every martial art has stance training, from boxing to Capoeira. If you don't get constant stance training in your Kung Fu school then do it on your own since stances are your vitamins in martial art. If a technique is not working, look to adjust your stance first.