What is Rate of Force Development?

In short, the Rate of Force Development (RFD) is the maximal rate of rise in muscle force, which refers to the speed of force production or how quickly you can reach peak levels of force.  

Consider these situations:

How fast can you move from 0.00 m to 3.00 m distance? The time taken can be heavily dependent on your RFD.  

How quickly can you jump from one point (position) to another? Note that we are not talking about jump height or distance, but rather "how quickly" you can do it. This also depends on your RFD.  

How good are you at executing the "slowest" part of an explosive activity, e.g., the initial part of a sprint race (which is the slowest part; overcoming inertia)? This depends on your RFD as well.  

Many movements occur very quickly, i.e., in less than 200 milliseconds. Ground contact in elite sprinters is around 0.100 s, and the release in a javelin throw takes about 0.180 s. These movements are largely influenced by your "ability," or more specifically, your RFD.

Further enlightenment:

In a sprint race: 

a) Your toughest opponent and yourself reacted very quickly (both at 0.13 s). 

b) However, he created a gap very quickly. 

c) About 20 meters into the race, you found he was a meter in front. 

d) You managed to catch him at the end. 

e) Both of you crossed the finish line together, and you won by 0.001 s.

Regardless of the story of your race, he was superior to you at the start. How did this happen? He had a more efficient force application (because he had a higher rate of force development), which ensured faster ground contact times with each step.

RED - World class sprinter

BLACK - National class sprinter

BLUE - University class sprinter

The world-class sprinter (figure above) is able to produce a high amount of force within 200 milliseconds compared to both national and university sprinters. As a result, the world-class sprinter has the capacity to explode and create a gap in the next few meters (for sprint 100m context). We can also say that the national sprinter (black dot) will be slightly ahead of the university sprinter in the next few meters because he can produce higher force at the start of the movement (in this case, 200 ms) than the university sprinter.

How do you measure the Rate of Force Development? 

Measuring RFD is not as simple as measuring your 1RM bench press. 

Basically, RFD measurement relies on the force time data (change in force production over time) from force plate (>500 Hz). This can be done using the isometric mid-thigh pull assessment.

However, there might be some alternatives (field test). Field tests, such as movement time assessment, can be considered. For instance, a 5-meter sprint time, although not as accurate (ie, without force-time data), but might be helpful. This test requires an athlete to produce high force within short period to be able to move fast.

Other assessments, such as speed bounding test, can provide a measure of reactive strength ie, explosive movement (require high force generation in short time), for activities involving a fast stretch-shortening cycle (i.e., below 250 ms). 

Below is an illustration of speed bounding test (named reactive bounding or reactivity index), 10 bounds (need to be videotaped).

Ready position: 

Begin by standing on a track with shoe (front leg) behind a pre-determined start line.

Testing (with timing and distance measurement):

Begin by bounding forward with one leg, followed by another leg (alternate) and so on. The timing must start from the last seen contact of shoe's edge with ground, and then stopped after 10 bounds exactly at the first contact (last bound) seen on the ground.

Calculation:

You need to have the following:

- distance (m) for the 10 bounds.

- time (s) to complete the 10 bounds.

- leg length (m)

(i) Calculate average velocity by dividing distance by time.
(ii) Divide by 10 to get the single-bound average (1Tread).
(iii) Divide 1Tread by leg length.
(iv) Multiply by 10 to get the relative reactive bounding value.

Interpretation: 

A higher value indicates better performance.

Next, weight bag throws and vertical jumps may also be used for explosive strength assessment. They have a strong correlation with RFD values from the mid-thigh pull.

Final thought...
An athlete can be very strong, but this is not the quality that determines how quickly you can move or how fast you can accelerate. It is how you use the "strength" to move, sprint, jump, or throw faster.

Strength is the ability to produce force. This can be characterized as maximal (e.g., with heavy squats - longer time in force generation) or explosive (e.g., jumping - short available time to generate force). Explosive strength exercises can improve RDF. Activities using light to moderate loads (e.g., weightlifting snatch, plyometrics, throwing exercises) can be helpful in enhancing RFD.