In Part 3 we saw how deeper knee bend allowed for greater extension length resulting in more forward horizontal force and thus, more speed. Now we will consider how deeper knee bend also allows us to flatten our propulsive force vector making it closer to horizontal.

Let’s take a moment to get specific about what is meant by “flatten” here. A good way to see what we mean is to say that in this “flattening” of the force vector we minimize the difference in height from its highest point to its lowest point. 

Our extension force by nature will always have an upward vertical component to it in addition to a horizontal component. This means that it is directed up and across at an angle. 

To flatten this force would be to diminish the vertical component and increase the horizontal, or get it closer to the horizontal. Greater knee bend accomplishes this for us. Let’s look at how it does this.

As we extend our leg and produce force to drive ourselves forward, our leg straightens out (which is clear just by the meaning of “extension” in biomechanics). This results in a force that is on a line that starts at the point where our skate blade edge interfaces with the ice and goes through the hip of the same leg. 

If we extend our leg when our foot is directly below our body, this force is essentially all vertical. Do this with enough explosion and you will jump. But jumping does nothing for us in terms of building speed in hockey. It is horizontal, not vertical, motion that we need.

Consider the final moments of extension (just before the leg gets fully straight during a hockey stride). In these moments, a violent push of the skate into the ice would drive the player's body away from that push (as was the case before). 

But, since the foot is now way out to the side of the body, and since the force of such a push would go on a line from the place where the blade edge interfaces with the ice through the hip joint of the same leg, this force would drive the body not straight vertical, not straight horizontal, but a diagonal in between.

Now consider this same final moments of extension with greater knee bend. The hips would be lower and this force would be directed closer to the horizontal. 

Since we are looking to maximize horizontal force this is huge for our ability to achieve speed. Within the same body, if we get in the habit of skating with deeper knee bend, we can produce the same force and yet achieve greater horizontal force.  

Combine the two effects of knee bend to understand its importance.

With greater knee bend we can increase our extension length AND improve our horizontal force production even without training the body to produce more force. 

By combining those two effects we see that deeper knee bend is plainly a huge factor in our ability to produce horizontal force and to get from place to place on the ice more quickly, efficiently, and effectively.

So far we have looked at the impact of knee bend in terms of the forward stride and horizontal force production. In crossovers, increased extension length and horizontal force add to speed and lateral acceleration which are the goals there. 

In the backward stride, increased knee bend helps us produce more rearward horizontal force.  Knee bend also helps with performance on stops, starts, and tight turns. 

All of these effects of knee bend in all these areas of skating are related to one or both of the effects discussed above (increased extension length and/or flattening of the extension force).  

The effects and benefits of knee bend in high tempo skating remain present regardless of what on-ice maneuver or stride technique we are attempting. And if it wasn't so critical in all facets of skating... well then it wouldn't be the king.

A final nugget to consider with respect to knee bend is that we are actually advocating a deeper knee bend than what is considered ideal in speed skating. Why would this be?  In a sport where speed is the only thing, if knee bend is so important, wouldn’t extremely deep knee bend show up there? No. It should not. Let me explain.

The simple act of maintaining a deep knee bend position comes at a very high cost in terms of energy output, even before considering applying a propulsive force (consider a wall sit). A deep knee bend position is a poor “leverage” position. 

Avoiding an overly detailed explanation of why that is, from a simplified perspective, it boils down to the thighs being very parallel to the ice. This forces our muscles to work extra hard in the face of this lack of leverage and this results in a rapid depletion of muscle resources.  

This cannot be tolerated in speed skating where the goal is to be fast over a pretty long distance of 500 meters or more. In hockey we need to be fast over some burst, typically of a few seconds. The success or failure of that burst in terms of winning the puck, winning an uncontested shooting opportunity, or some other big difference in winning or losing a game, is huge. 

So, in hockey, it is worth spending a ton of energy fast to win short races where in speed skating it is not because energy must be spent relatively evenly over the full race.

Look for Part 5 of this article series where we will go into the dynamics of push direction and consider why we need a lateral component to our push in the forward stride for skating and we do not when we are running.