November 14, 2012
I just got back from Kansas University to install our software technology with the force plate. The coaching staff is focused and cohesive, but the hardest concept to grasp for myself and these colleagues continues to be how more TIME on the ground can make you a faster athlete. After all, don’t we all want to be quicker and more explosive? Of course, but it is not that simple, especially in sports where timing and sequencing are more critical.
We have discussed this concept with Usain Bolt before, how he runs faster because he spends more TIME on the ground. Basically, his body type and technique leads to a longer stride length and less steps over a 100 meter race than his competitors. But, this post will go into more scientific explanations of his performance, specifically aligning the Force-Velocity curve with our Force-Time curves we use to analyze, train, and monitor athletes.
The Force-Velocity Curve Defined
Authors from the University of Essex in a 2010 study explained that Bolt’s slower muscle contractions allow him to optimize the force-velocity curve. This graph is shown to the right, with the y-axis representing muscle force and the x-axis representing muscle velocity.
The muscle force depends on the total number of attachments, contractile elements known as cross-bridges that slide past adjacent muscles to cause contraction, or shortening. As these contractile elements slide past one another faster and faster, the muscle contracts and shortens with increasing velocity. As you see to the right, increasing speed forces a decrease in muscle force production. This trade-off occurs because less cross-bridges can attach at higher speeds.
On the other hand, as this sliding velocity and muscle contraction rate decreases, more cross-bridges have time to attach and to generate force, and thus force increases.
Bolt is Actually Slower
This force-velocity curve can explain why more TIME on the ground can improve your performance. Bolt was found to spend more TIME on the ground than his competitors and take less steps, a track & field characteristic known as stride rate (see Sparta Point). This lower stride rate basically means a lower muscular contraction velocity.
Not only was Bolt able to generate 17% more force due to his SLOWER muscular velocity, but his efficiency was greater as well. So Bolt actually reduced stride rate and quickness, which allows him to increase his TIME on the ground, shown in this 2010 review by a larger impulse, which is the width of the force-time curves shown (see Sparta Point).
The relationship between the force-velocity curve and force-time curve are also more clear:
longer ground contact TIME = higher on the force-velocity curve = higher impulse = gold medal
You can also ignore TIME and focus on stride rate, the mile run is in the Olympics too.
References
Beneke R, Taylor MJ. What gives Bolt the edge-A.V. Hill knew it already! J Biomech. 2010 Aug 10;43(11):2241-3. Epub 2010 May 5.