What is Rate of Force Development?

>> October 08, 2014

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

Look at 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 quick can you jump from one point (position) to another point? Note that we are not talking about jump height or distance, but "how quick" ... That is depend on your RFD as well.

How good you are at the execution of "weak or slowest" part of an explosive activity, e.g. initial part of a sprint race (which is the slowest right?) ... Depend on your RFD.

There are many movements that occur very quickly, i.e. below 200 milliseconds. Ground contact in elite sprinters is around 0.100 s, javelin throw release takes about 0.180 s, and so on. These movements are largely influenced by your "ability", or the more specific term is "RFD".

Further enlightenment.

In a sprint race ...
a) your toughest opponent and yourself reacted very quickly (both at 0.13 s)
b) but he makes a gap very quickly
c) about 20 metres into the race, you found he was a metre in front
d) you managed to catch him at the end
e) both crosses the finish line together, you won by 0.001
... regardless the story of your race, he was superior than you at the start. How was it happen? he has a more efficient force application (because he has higher rate of force development) which ensured faster ground contact times at each step.

RED - World class sprinter
BLACK - National class sprinter
BLUE - University class sprinter

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

How do you measure Rate of Force Development?

This is not as simple as measuring your 1RM bench press. You need to have an extra careful with the method of  measurement of RFD, including instruction (to ask performer to contract "as fast as possible" (during a 5-sec max voluntary contraction test) . Measurement is highly sensitive. When you use the isometric mid-thigh pull (with force plateform), the sampling rate can influence the "actual illustration" of force-time curve (the change in force with time). Thus, a sampling frequency of at least 500 hz may be required. However you can always have alternative. Field test such as movement time assessment can be applied, for instance the 5 m sprint time (although not that accurate, but still is very helpful). Other assessment such as bounding test can give a more representation for activities involving fast stretch shortening cycle (i.e. below 250 ms). Following is the illustration of 30 m bounding test.

1. Ready position on a box (30cm or 40cm).
2. Start by landing on the pre-determined start line (slightly in front, 50cm, of the box).
3. The time must start from first touch, stopped when body crosses line.
4. Determine the number of contact. If the last step involved only "half" step, you can say 0.5 (or 0.2 or 0.8 depend on your judgement).
5. Divide the number of contact with the time.
6. The higher ratio means the better.

The most important to remember in the bounding test is "consistency of measurement". You can also use electronic timing gate to reduce measurement errors, thus increases test sensitivity. Weight bag throw and vertical jump may also be used for RFD assessment. They have quite strong correlation with RFD value from the mid-thigh pull.

Final thought (but no way a final wrap-up of this particular topic!)

You can be very strong ... but this is not the quality that determine how quick you can move, or how fast you can accelerate ... it is how do you use the strength to move, sprint, jump or throw faster. Strength is the ability to produce force. Muscular strength must be further trained in order to become more powerful ... so one of the keys is to develop the explosive strength.

Explosive strength training ... the use of light to moderate equipment/tool or means (e.g. weightlifting snatch, plyometric, throwing exercises).

RFD assessment via the mid-thigh pull can also be used for training monitoring, diagnosis of muscular preparedness, fitness management, and so on.

Regardless of assessment means, please pay attention on consistency and test sensitivity.

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