Rate of Force Development (RFD) - how quickly athletes generate force - offers valuable insights into explosive abilities and athletic performance. In this blog post, we'll delve into the significance of RFD, explore how it is calculated, and discuss its practical applications.
Introduction to Rate of Force Development
Rate of Force Development (RFD) describes the speed with which an individual can produce force.
Typically, achieving peak force takes a few seconds. However, the ability to enhance RFD can allow athletes to reach high levels of force more swiftly, thereby impacting performance positively. RFD has been linked to greater sprinting and jumping performance.
Technologies like handheld dynamometers (such as VALD's DynaMo) and force plates (like ForceDecks), enable the evaluation of RFD in various tests, particularly isometric tests like the mid-thigh pull or ASH shoulder test.
Understanding the Force-Time Curve
The force-time curve is integral to understanding RFD. It shows us that force generation isn't instantaneous; instead, it's a gradual process. Increasing RFD means athletes can achieve greater force within shorter time frames. This is especially beneficial in sports where time to exert maximum force is limited. The curve helps us to comprehend how quickly force is generated and is often used in assessing isometric exercises.
The isometric mid-thigh pull (IMTP) is a prevalent test for analysing RFD. An example force-time curve from an IMTP is shown below in the figure taken from Brady et al., (2018). Key insights can be drawn by examining the curve's slope during force generation. While it might seem most obvious to explore peak and average RFD measures, rates of force within set time frames often yields more reliable results...
Analysing RFD Measures
To calculate RFD we divide the change in force over the change in time, to give us RFD in Newtons per second:
RFD [N/s] = Change in Force [N] / Change in Time [s]
RFD measures are often calculated between two specific time points, like 50 to 150 milliseconds, as these provide higher reliability than an overall peak or average (Haff et al., 2015). Utilising specific timeframes allows for precise assessments of how force production evolves over such brief periods.
RFD is frequently associated with other early phase measures, such as Force at 100ms. Remember that RFD represents the rate i.e. how quickly this changes, as opposed to the actual measure of force. Using an absolute force at 100ms will also include the individual's body mass from the force plate, but we can view the net force which will remove body mass.
For examples of analysing RFD data, have a watch of the video below.
Reliability of RFD Measurements
Reliability in measuring RFD can sometimes be questionable. As well as selecting the most suitable timeframes and calculation methods as described above, we can improve reliability via consistent testing protocols, standardised warm-ups, familiarisation with the test, and appropriate cueing.
How you cue the test is critical for RFD. If you are keen to explore RFD, you need to cue your athletes to conduct the test (e.g., pull the bar) "HARD AND FAST". This will allow them to express their maximum RFD capabilities, as opposed to gradually increasing force.
Coefficient of variation (CV) is commonly used to assess reliability, with less than 10% variation often indicating acceptable reliability in the literature. This metric helps ensure consistent and accurate RFD assessments. In the video above we compare and contrast two athletes with RFD measures of 5 and 25% CV, respectively.
Practical Applications of RFD Data
Understanding RFD aids in performance profiling and programming guidance. Maximum strength training can elevate peak force capabilities, while explosive training enhances rapid force generation. The figure below, by Haff and Nimphius (2012), illustrates how particular training approaches can shift the force-time curve.
These insights are also invaluable in rehabilitation, where RFD is often slower to recover compared to peak force. Tracking RFD can thus be critical in rehabilitation settings, helping athletes return to pre-injury performance levels.
Frequently Asked Questions (FAQs) About Rate of Force Development
What is Rate of Force Development (RFD)?
RFD refers to how quickly an individual can generate force. It is a critical factor in evaluating an athlete's explosive capacity.
How is RFD measured?
RFD is measured by analysing the rate of change in force over time, typically using force plates. The rate is expressed in Newtons per second.
Why is RFD important in sports?
RFD is crucial because most athletic movements do not allow time to reach peak force. Improving RFD can lead to better performance by increasing force output rapidly.
Can RFD be improved through training?
Yes, both maximum strength and explosive training can enhance RFD. These training methods allow athletes to generate greater force in shorter periods or reach peak force faster.
How can RFD be used in rehabilitation?
In rehabilitation, RFD is often slower to recover than peak force. Thus, tracking RFD can provide insights into an athlete's recovery and readiness to return to competition.
This article is support by VALD Performance. For more information, about their technology, visit their website.
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