# What is the top speed of muscle contraction?

Currently I am looking into what muscles groups are most used during a football kick. I have a hypothesis that the quadriceps are not as used as most people think because the momentum the swing creates makes the knee extend to fast for the quadriceps to contract.

To prove this I need to know the speed the knee extends during a football kick and the time it takes for the quadriceps to contract. I know how fast the knee extends through my own research.

Does anyone have any information on the speed of muscle contraction? Quadriceps contraction time would be optimal, but any information relevant would be very helpful

Your question is a good one. The velocity of muscle contraction depends on the:

1. Initial length of the muscle
2. The Load on the muscle Source: Medical Physiology : a cellular and molecular approach by Walter F. Boron, Emile L. Boulpaep - 2nd ed. Page 248

From the above picture we can see that:

1. The velocity of muscle contraction is not constant. Initially it is zero and then it accelerates to reach a peak
2. The maximum velocity of muscle contraction is constant at any different initial muscle length
3. The lower the load the steeper the rise of velocity

So the velocity of muscle contraction should be calculated on a case by case basis.

## What can be calculated

What can be calculated is the displacement and frequency of actin myosin cross-bridging.

Under microscopically isotonic conditions, the quantal displacement of a single cross-bridge is ~11 nm.

The frequency of actin-myosin cross-bridging depends on atleast:

1. ATP concentration
2. Temperature

At an ATP concentration of 1 µM the frequency is 3.8 ± 0.4 M-1s-1

At 170C the mean time for single displacement was 15±20 ms. While at 250C the mean was 6.4±3.6 ms.

Source: Characterization of Single Actin-Myosin Interactions by Jeffrey T. Finer, Amit D. Mehta and James A. Spudich. Biophysical Journal, Volume 68, April 1995, p.291s-297s

Concerning your actual question regarding the quadriceps velocity and the velocity of the swing, you should keep the following in mind while calculating:

1. Quadriceps acts over a second order lever: The Knee is the fulcrum, the effort is put over the tibial tuberosity where the quadriceps is inserted and the load is the foot and whatever it hits/lifts...

2. The contraction of the quadriceps is calculated as linear velocity while the kicking action is circular - so what you actually observe is the angular velocity. So appropriate angular velocity to linear velocity conversion should be made.

All the best!