Defining a Training Target : Max Strength or Rate of Force Development ?


In a recent article, I wrote about the link between Strength and time of movement,introducing Rate of Force Development and defining Explosive Strength as the ability to exert maximal forces in minimal time.

The key concept is that for many movements, the time it takes to develop full range of motion may not be enough to also express maximal force.

Let’s define the Time to Peak as the time needed to reach one’s Maximum or Absolute Strength in a determined movement.

Let’s define the Time of Motion as the time needed or available to complete a determined movement.

V. Zatsiorksy and W. Kraemer give a good display for time typically required to perform several motions in “Science and Practice of Strength Training”, a must have book for athletes and coaches who are looking for advanced training techniques. Typically the Time to Peak is longer than 0.4″ and drops below 0.4″ only when Strength is isometrically displayed.

Screen Shot 2015-07-30 at 17.14.15

Table 1 displaying Time of Motions for main movements in track and field

It is easy to see that the Time of Motion is less than Time to Peak in all the situations described. The duration is simply too short for any athlete to display absolute strength during the movement.

When the external resistance decreases the motion time becomes shorter, meaning a faster movement. The faster the movement, the greater the difference between the Peak Force reached in the given condition and the Absolute Strength

The difference between Peak Force and Absolute Strength is named Strength Margin (or Explosive Strength Deficit, as described on “Science and Practice of Strength Training” by Zatsiorsky and Kraemer).

By definition :

Strength Margin (ESD) = 100 x (Absolute Strength – Peak Force)/Absolute Strength

Strength Margin Definition on a Force - Time Graph

Strength Margin Definition on a Force – Time Graph

Strength Margin shows the percentage of an athlete’s strength potential that was not used in a given repetition.

This happens every time you set a maximum time for your movements! Let’s take for example a Deadlift.

Once you’re trying to max out close to or with your 1RM, you will be expressing Absolute Strength. There is no Time-related issues for the lift, you just have to complete it. Instead, once you’re asked to work on a specific time trait, like Speed Strength or Strength Speed, the total range of motion of the movement is linked to the speed necessary for the execution, resulting in a specific time for the execution. Let’s say the movement requires 1 m and your target speed is 1 m/s, that makes 1s to complete the concentric part of the lift.

Now, how much Strength can you express in that time compared to your max? How much are you leaving in the tank? This is exactly what the Strength Margin tells you. By tracking it, you may discover very interesting things! For example, you could be a great Max Effort Lifter, with a strong 1RM,  but when lifting for Speed, your load (therefore your Peak Strength) for the 1m/s could drop like crazy!

Or it could be the reverse situation, when you are very explosive and your load for the speed deadlifts is very high, but your 1RM sucks (this is when Strength Margin is very low instead).

Now don’t get desperate about these situations, you can easily assess the problem just by tracking Strength Margin.

There are two ways to increase the force output in explosive motions :

1 – Increase Absolute Strength, this is the best way when Strength Margin of Speed Exercises is low

2 – Decrease Strength Margin by increasing Rate Of Force Development, therefore developing more Strength in the same time. This is the best way when Strength Margin of Speed Exercises is over 60% and training with light loads


Low Strength Margin

Low Strength Margin

If you tracked any rep with very heavy load or if you ever tried lifting close to your 1RM, Beast has your Absolute Strength tracked. Once you record any further repetition, the app will automatically compare it to the Strongest rep for that exercise, displaying Strength Margin in the Pause View. Remember, the key is to track Strength Margin during Explosive Movements!!

The first method usually brings good results at the beginning of sports preparation when a young sprinter improves his achievements in the squat from 50 to 150kg. This is not necessary valid for a squat gain from 200 to 300kg. In spite of efforts devoted to making such a tremendous increase in Absolute Strength, the sprint performance may not improve. The reason for this is the very short duration of the ground contact time during each step. The athlete simply has no time to develop maximal force. In such a situation the second factor, explosive strength is the critical factor.

Strength Margin with Explosive Reps

Strength Margin with Explosive Reps

Training of maximal Strength cannot help the athlete improve performance if the motion is in the time-deficit zone.

Time Deficit Zone

Time Deficit Zone

When programming for Explosive Strength gains, always give a look to your Strength Margin in key exercises like Squats, Deadlift and Bench Press. It may tell you the right direction whether to improve Absolute Strenght or to look for increase in the Rate of Force Development.




by Ingtommy

Founder, President and CTO of Beast Technologies Aerospace Engineer turned Certified Strength Coach Wide Receiver for Parma Panthers and Italian National Football Team "Lifting is mathematics, physics and biomechanics" cit. Louie Simmons

  • John

    Where can I see my strength deficit in my beast sensor app? I can’t find it.