In the late 1990s, world records in speed skating were suddenly shat-tered on virtually all distances. Race times fell by as much as 4 percent
at once, a huge amount for a sport in which improvements are usually measured in hundredths of a second. The reason was the arrival of a new kind of skate, the klapskate. Some skaters who had been barely known before became acclaimed record holders because of their wise decision to make the switch from conventional skates.
The klapskate is a simple but effective improvement over the con-ventional speed skate. It has a hinge on the front fixture of the blade and there is no attachment at the back, so the boot can tilt forward while the blade remains in full contact with the ice. The new design enables the leg to provide a longer push without increasing the ice friction on the blade. It didn't take long before puzzled sport scientists took a close look at the klapskate to see how it affected skating. They found that the added foot flexibility allows the leg to generate more power not only at the ankle but also at the hip. This simple improve-ment increased the athlete's power output by as much as 10 percent.
One may wonder why hockey hasn't made use of this speed skat-ing technology. Wouldn't players become faster and therefore better? While it is true that, with some training, athletes can attain greater speed on a linear stretch with speed skates, we should not forget that hockey is as much about mobility as it is about speed. As mentioned earlier, the unavoidable sharp turns and quick responses to a change of play make the rounded blade a necessity. We will see in the next chapter that when a player makes a slap shot, there is a transfer of body weight from the back leg to the front, in the direction of the shot. This is accompanied by a quick rotation of the skates. Without the quick foot positioning made possible by the rounded blade, such a move would be awkward.
It is not yet certain whether new design features such as the klap-skate will eventually appear in the hockey rink, but it is almost certain that a hinged blade would not have the impact it had in speed skating. For one thing, because the hockey blade is not flat, it would not stay parallel to the ice as the boot is tilted forward, thereby defeating the purpose of the design.
In the simplest case, when you are skating with the help of your hip muscles without bending your knees, most of the push-off force is oriented along the ice, and R is simply that pushing force. On the other hand, when you propel yourself by bending your knees and leaning forward, the push-off force has a large vertical and horizontal component. If we suppose you're pushing with a force F from your leg and you're leaning at an angle f3 relative to the ice (f3 = 90° if you are standing upright), then the reaction force along the ice is R = F cos f3, and the forward component of that force becomes R = F cos f3 sin e. Now that we know the force in the forward direction, we can deduce the acceleration from Newton's second law: it is a = Rim, where m is your mass.
These equations relate the skating acceleration to the push-off force and the orientation of the skates. What is to be learned here? How can we use this to improve our skating? First of all, if your skates are straight (e = 0°), you will not move forward, only side-to-side.
The greatest acceleration is achieved at the largest angle e. When speed skaters or hockey players want to accelerate quickly from rest, their stakes are really sticking out to the left and right. The second lesson is that leaning forward (keeping f3 small) is very important. This is why speed skaters bend forward at the beginning of a race and hockey players crouch forward as they try to gain speed. Last, the push-off force is proportional to, well, the force you push with! Therefore, you need strong legs to accelerate quickly.
The push-off and the reaction forces are not constant in time, of course, but change substantially within the stride. Scientists have measured this force experimentally using sensitive electronic devices sandwiched between the blade and the skate boot. 5 Results of their experiments are graphed in Fig. 2.5. It shows a typical push-off force on one skate over a period of time totaling four strokes. Notice that the force is largest at the beginning of each stroke, when the sharp edge of the blade penetrates the ice, and at the end, when the leg is almost fully extended and can exert a greater force.
But is pushing side-to-side the only way to move on ice? Not really. Figure skates, for example, have jagged picks at the front that can grip the ice and allow a skater to move ahead by a walking-type motion. But pushing sideways is the technique that produces the greatest velocities, allowing skaters to reach speeds even faster than they can move their feet-estimated to be around 7 m/ s. 6 The fastest runners, for instance, move their feet at 12 m/s. So it is impossible for a skater to push against a fixed point on the ice if he or she is moving faster than that. Hence, speeds greater than this limit would not be possible without the push-and-glide technique. Even though the side forces cause the body's center of gravity to follow a sinuous trajectory (with an amplitude observed to vary between 25 and 50 cm), the gliding technique enables skaters to reach speeds exceeding
50 km/h, far more than what could be achieved through simple running.
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