How many times have you heard
skater's or coaches say things like "you've got to sit lower, get your bum
down"? How many of you have heard that the thigh position during speedskating
should be parallel to the ground with a 90 degree bend in the knee? Has anyone
ever questioned this? Is such an extreme knee bend really necessary? This
article explores this query by looking to specific research for the answers.
Squatting low is important. Doing so allows the muscles of the knee and hip to contract powerfully by developing force over a broad range of motion. The ability of any muscle to generate force depends in large part to it's momentary length, and angle of the joint on which it acts. Therefore, as the knee extends during push-off, the force generating capacity of the muscles also changes. In the case of the quadriceps muscles, maximum force can be developed around knee joint angles between 105 and 115 degrees. It is therefore important to ensure that the pre-extension knee angle will be deep enough to take the joint muscles through their most powerful functional range. But, it is really necessary to sit so low that the thigh is horizontal?
Equally important as developing maximal force, deeply bending the knees leads to a greater push displacement, that is the amount of lateral distance that the skate travels from the beginning to end of the push. One of the best ways to go faster is to sit lower and increase the distance the skate travels. John Banks, in a previous article in SST, explored this concept further and pointed out that even a slightly lower knee angle has significant effects on increasing push displacement.
So far everything sounds groovy, right? Sitting low appears to make prefect sense. But, are there any negative consequences to doing so? You better believe there are. In fact, squatting too low can be extremely detrimental to performance. One reason is mechanical while the other is physiologically based.
Mechanical
As mentioned, the quadriceps
can generate the most force around a knee angle of 110 degrees. A deeper knee
bend of 90 degrees actually places the muscles in a relatively poor position
to do their job. Because the push-off should occur in an accelerated fashion
with most of the force developed within the first one-third of the extension,
squatting too low makes things a little difficult. Not only does squatting too
low detract from the efficiency of the push-off by initiating the extension
from a poor biomechanical position, but doing so gobbles up an enormous amount
of energy during the static glide phase.
Research
by Dutch physiologist van Ingen Schenau determined that during skating,
bending the knees at 115 degrees versus 100 degrees results in very little
increase in external power output (7%). However, the static force needed to
maintain this position increases a whopping 23%. This same researcher
concluded that because the increase in static force requires significantly
more metabolic energy, skating at knee angles lower than about 105-110 degrees
lowers the mechanical efficiency of the movement and should therefore be
avoided. Since power output is also dependent upon stroke frequency, skating
with a higher cadence is preferable to bending the knees excessively.
Physiological
During the speedskating movement pattern, the muscles of the hip and knee are engaged in static (isometric) contraction during the glide phase. With such static contractions, blood flow through the working muscles can be seriously reduced. Not only does reduced blood flow diminish the amount of oxygen-rich blood reaching the muscles tissue, but restricts the outflow of metabolic waste products such as lactic acid, potassium, and inorganic phosphate. As such, high blood lactate concentrations are found in speedskating. Restricted blood flow is also believed to induce early muscle fatigue by raising the levels of by-products which interfere with the excitation-contraction coupling of muscle fibres, and by prematurely shifting energy metabolism towards anaerobic pathways. In further research, van Ingen Schenau stated his belief that the ability of a skater to resist such lactate-induced muscle fatigue seems to dictate the extent to which the athlete can fully utilize aerobic capacity. As such he concluded that because a deeper knee bend requires a larger anaerobic contribution, performance ability is likely related highly to the muscle force level that corresponds to the onset of anaerobic energy production. In a study that examined the differences between novice and elite skaters, the latter group proved to be inexplicably superior in this regard.
What makes this discussion interesting is that the degree of blood flow restriction is highly related to the absolute static force level in the muscles. Research into repeated static contraction indicates that blood flow restrictions can become significant above 15-20% of maximum voluntary contraction (MVC). Swedish researcher Eckblom determined that the force levels in the quadriceps muscles of speedskaters appears to be on the order of 25-35%. It is safe to say that during speedskating, blood flow is reduced during the glide, which accounts for roughly 50% of the stride, and temporarily restored during the stroke recovery. As mentioned, we also know that the static force of the quadriceps muscles increases when the knees are flexed deeper. What this means is that pre-extension knee angle should not be so low that blood flow restriction is unnecessarily elevated or mechanical efficiency is compromised.
So, how low should one sit? There appears to be a trade-off between positive outcomes and negative consequences. Sitting low is required to have the quadriceps work with maximum efficiency and to achieve a long stroke displacement, but squatting excessively hinders blood flow to a point where lactic acid builds up rapidly and anaerobic energy metabolism accelerates. How low is low enough? To answer this question, we can look to actual observations of the sport's finest during competition. What follows are results from a study by van Ingen Schenau that examined body position during four metric distances.
Table 1: Mean knee and trunk angles during four metric speedskating distances
(Note: Data from van Ingen Schenau, G.J. and K. Bakker, 1980.)
| Distance | Knee Joint Angle | Trunk angle |
| 500 m | 101.0 | 52.2 |
| 1,500 m | 110.7 | 54.0 |
| 5,000 m | 112.6 | 58.5 |
| 10,000 m | 115.7 | 60.4 |
We see that from the above results that skaters do not display a knee bend as low as 90 degrees, even in the 500m event. It is clear, however, that knee joint angle becomes progressively more upright for increasing distance. The reasons for this are undoubtedly linked to the desire to decrease the amount of energy committed to static contraction and the resulting blood flow restriction, to delay the onset of lactate-induced muscle fatigue, and minimize the shift toward energy production in the absence of oxygen i.e. anaerobic.
So if all of this is true, then why do many coaches tell their skaters to assume a 90 degree bend? It would be a little presumptuous of me to answer for everyone, but my guess is there are two reasons. For starters, what most coaches are trying to do is get their skaters to over-exaggerate the knee bend. This common teaching technique involves getting an athlete to perform a movement to an extreme limit so that following the process of resistance and accommodation where the skaters sits progressively higher, the new adjusted knee bend is now appropriate. Since even the most dedicated skaters will sit higher than instructed, teaching athletes to squat lower makes practical sense.
The second likely reason that coaches often emphasize a 90 degree knee bend is simply because this is what has been done for decades. It is possible that practicing in an extremely low position helps to increase one's tolerance for being in the down position, trains the muscles to function in a high-tension, acidic environment, helps the energy systems resist a shift towards anaerobic energy production. Perhaps it is the continual badgering of coaches towards elite athletes to always sit lower that has helped them to be superior just as van Ingen Schenau pointed out.
It has not been my intent to tell you that coaches ill-advised or incorrect to be preaching about a 90 degree knee bend. This method has produced some fine speedskaters, and will likely not ever change. However, I think it is important for skaters of all ability levels to realize that it just isn't practical to skate at such an extreme low knee position, and that even the top sprinters in the world only lower the knees to about 100 degrees. What I think is most important is that skaters assume a knee bend that is as low as possible, but only so low that it can be maintained for the duration of the event. This way, the emphasis shifts away from setting a low point, but to the ability to sustain body position, and therefore speed, throughout the course of the race.
References
Eckblom, B., L. Hermansen, and B. Saltin. 1967 Hastighetsakning pa skrisko. Idrottsfyiology, nr. 5, Stockholm.
van Ingen Schenau, G.J., and K. Bakker. 1980. A Biomechanical Model of Speedskating. Journal of Human Movement Studies. 6:1-18.
van Ingen Schenau, G.J., G. de Groot, and A.P. Holander. 1983. Some Technical, Physiological and Anthropometrical Aspects of Speedskating. European Journal of Applied Physiology. 50:343-54.