Knee Bend Is King

by barbaragarn

​From Andy Blaylock of Competitive Edge (located at Hat Trick Hockey in St. Louis Park)

In the previous segment of Hockey Skating and Physics, we looked at a skating technique adjustment that led to more speed, a slightly shorter stride length, and a greater stride rate.  While extolling the virtues of this adjustment we knocked stride length off of its metaphorical pedestal as the key metric in excellent skating technique.  While, the rumors of stride length’s demise may have been greatly exaggerated (as stride length is still a hugely important concept that skaters should value in many ways), dethroning it does leave room for the true king of hockey skating concepts.  All hail knee bend!  Long live the king.
Readers of last week’s article would remember discussion about how, in the forward stride, forward horizontal force production is what it all boils down to.  Wouldn’t that make that the king?  It would… if we were looking to focus on the result that we are trying to produce.  But, what we are talking about here is a question of how we can generate that result (how we can produce maximum forward horizontal force).  Knee bend is the single most important variable that helps us achieve that goal.  And knee bend is so important, it makes the abbreviated recovery strategy from the previous “Hockey Skating and Physics” segment seem downright trivial.   
Increased knee bend has an effect on two key stride metrics which lead to speed.  This dual effect is what makes deep knee bend such an important component of the high-performance skating stride.  We will delve into both the increased extension length and flatter extension force direction that deeper knee bend leads to. 
To understand extension length, it helps to use the skater’s body as a reference point from which to take our measurements.   
When we measure stride length we are talking about the distance down the ice that a player moves during each stride.  To take this measurement, it requires us to use the rink to establish a baseline from which we take our measurements.  In other words we are measuring relative to the rink.  But using this, it is hard to learn much about the effects of knee bend.  For that we should use the skater’s body as the central point that we measure from even though the skater would be moving around the rink.
Using a perspective that treats the body as stationary, we can talk about extension length in the simplest terms.   Extension length is the distance along the skating surface that the player pushes the skate away from the body.  At the beginning of this extension, the skater’s leg is at a maximally bent position and his skate is very nearly underneath the body.  At the end of extension, the leg is (ideally) straight and the skate is out away from the body.  In between, as the skate moves away from the body during extension, the skater’s muscles are applying the propulsive force that we so covet to push the body forward.  Extension is the part of the stride where we push ourselves forward so it stands to reason that more extension length would lead to more force and more speed. 
What does deeper knee bend mean for extension length?  
Imagine a person standing straight up with both knees locked straight.  How far to the side along the ground can that person reach with one leg with all of their weight on the other leg and neither knee bent?  If you don’t allow the pointing of the toe, the answer is zero distance.  The only place that foot can touch the ground would be right next to the other foot because with both legs straight, bringing one leg to the side means you can no longer touch the ground with that foot.  This ultimately means that with zero knee bend you can achieve zero extension length.
Now, if we allow the knee to bend on the support leg and then reach out to the side with the other leg, how far out can we tap the ground with the leg that is reaching out?  We assume that the leg that is reaching out is locked straight as this gives the maximum outward reach.  Now the answer is, “it depends”.  You may ask, “it depends on what?”.
It depends on the height of the hips.  The closer the hips are to the ground, the further out along the ground the foot on the extended leg reaches.  This spot along the ground where the foot touches is the point of maximum extension and the bigger that maximum the greater extension length we can have.  So one huge benefit of greater knee bend (and the lowering of the hip joints that it creates) is an increased extension length.
Flattening our Extension Force  
When we flatten something, one way to define that is to say that we minimize the difference in height from its highest point to its lowest point.  Our extension force by nature will always have a vertical component and a horizontal component to it.  This means that it is directed upwards 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.  Lets look at how it does this.
As we extend our leg and produce force to drive ourselves forward, our leg straightens out (which is obvious).  This results in a force that is on a line starting 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 it is simply 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.
Andy Blaylock and Competitive Edge provide hockey skill development training in a facility setting and on-ice for players of all ages and abilities.