Thursday, August 28, 2008

Insight in Usian Bolt sprint

I watched spectacular 100m run in 9.69 sec by sprinter Usian Bolt. I became curious in sprint techniques and training. I got several doubts like, what is humanly achievable target (As Green did 12m/s for a 10m split, so can it be done in 8s for all 100m), why are women always behind men in sprint, why do they say hight is negative point in sprint, why is that all short distance runners are strong built, but all long distance runners are lean people, and why can not runners can get all medals on track compared to swimmers winning six to eight gold medals etc.

Stride rate vs. Stride length: Speed is stride rate multiplied by stride length. Improving either one of them makes a runner faster. Usian bolt is taller and is able to finish the 100m in 41 strides (41 right leg steps and 40 left leg steps). That is around 2.5m per stride and 4.2 strides per seconds. Silver medal winner took 45 strides and completed in 9.89 seconds. His stride frequency is 4.5 strides per second. His frequency is faster, but could not match the Usian Bolt because his stride length compensated him much more.

Impluse and strength: Runner has to hit the ground harder and to rebound and run faster. However that strength also reates backward friction on the ground and reduces the speed. Trick is to use more force, but less impulse. Impulse is calculated physically as force multiplied by time the force is applied. So the player has to hit the ground for shorter duration and contact time.

Disadvantages of tall person in sprint: Starting position will be uncomfortable. Pickup from stand still and balancing takes some time. Taller person tends to have more weight and so ground and air resistance will be more. So Usian bolt had to use more power to succeed.

Advantages of strength in sprint: Extensors in hip, knee and ankle are helpful to get long stride. The more force the sprinter can hit the ground with, the more faster he can move. The more faster the muscles can recover, the less fatigue sprinter faces. It is difficult to keep the speed achieved without strength.

Sprinter needs the following and training improves each of them.
- good posture and fast pickup
- able to accelerate till the maximum speed is achieved.
- fast leg speed
- large stride like raising knees higher
- fast and equal in flight and ground contact time.
- speed endurance for the last 30m.
- less energy consumption like keeping torso straight, reducing ground contact time.

Phases of sprinting: Startup speed for fast sprinter is around 3mps. It reaches around 5mps after 10m split, 8mps after second split, and reaches 11mps after 50m. Some sprinters are able to increase speed up to 70m, and some could not. Most sprinters after this de-accelerate, but only few can manage with the same speed. The last portion needs speed endurance.

Short distance runners for 100m or 200m need quicker speed acceleration capacity, and long distance runners for 400m, 800m or more need more speed endurance.
Long distance runner needs
- Larger oxygen intake - VO2
- Larger lactate threshold - 80% of VO2
- Exercise economy - less amount of oxygen need for same speed.
A taller or huge runner has hard time to achieve all of these qualities needed for endurance.

More details later.

Reference books:
* Physiology of sports
* Physiological aspects of sport

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