Perhaps the greatest challenge in the realm of training and rehabilitation is separating our assumptions from science. Just as eating fat does not make you fat, having greater peak force does not make you a better athlete. In fact, often times such larger maximum forces hinder your abilities. So we often create value behind the expressions of force (strength, speed, power, explosiveness) because such measurements allow us to…
Yet force is a relatively misunderstood term, particularly critical for those individuals who are measured by their performance in their sport or military mission.
Average Force is a Solution for Athletic Expression of Strength
When people think about increasing force, the number one thought is how to increase the amount of weight we lift. By squatting heavier, we move more mass. And if we have the ability to move more mass, force will be higher. While this is a correct assumption, mass is only one part of the equation. When an athlete sprints, jumps, and lands they can produce and absorb up to 5 times their body weight. I have yet to see an athlete squat 5x their body weight as the ability to create, absorb, and apply force has more to do with timing than mass or weight.
Image from Paul A., et al. “A biomechanical comparison of the traditional squat, powerlifting squat, and box squat.” The Journal of Strength & Conditioning Research 26.7 (2012): 1805-1816.
Perhaps the best example of such timing is the situation of peak force versus average force. Peak force is a measure at a specific moment in time, and research has shown this metric can be accurate (reliable) using quality measurement tools such as force plates. So the question becomes whether or not this metric is valid. Peak force does not take into consideration time, which forces the measurement to be very specific and invalid. The specificity refers to the type of athlete and the type of test. For example, a shorter athlete with strong Olympic lifting experience will outshine others in an isometric mid thigh pull. How much force you create is just as important as how and when that force is created.
The average force allows us to look at the ability to produce this force over a period of time. Does an athlete produce a large amount of force in an extremely short amount of time, or do they take much longer to produce that high amount of force?
Both athletes can have similar readings when looking at peak force, but will go about achieving that goal in a much different way. This contrast is particularly evident when differentiating levels of athleticism. A recent study showed collegiate soccer athletes had greater vertical jumping VELOCITIES than recreational soccer athletes, but no differences in peak power output or peak forces (1).
Physics Calculations not Opinions make Time most Important
All sports rely on timing. Whether this is offensive or defensive, reactive or calculated, timing matters. As strong coaches we have all seen the “strong and slow” and the “weak and quick” athletes subjectively for years. How does the athlete who cannot squat his own body weight jump out of the gym? He uses timing differently to produce larger amounts of force by decreasing time not increasing mass. The physics calculation of force clearly shows the superiority of time.
Force= mass *multiplied* by acceleration (F=ma)
a=velocity *divided* by time (a=v/t)
v=distance *divided* by time (v=d/t)
So F= m*(d/t²)
To increase force by itself we must increase mass, increase distance or decrease time. In athletics, mass is relatively unchanged, as most sports are playing only with their bodyweight and any number of implements with a standardized weight. Mass is most often utilized as a training tool. Increases in distance can be achieved by utilizing longer ranges of motion, however most strength training demands a strong relationship between range of motion and time so the intent of increasing distance traveled will increase time as well, keeping the ratio a constant. But time, not to mention the fact that it is squared in the calculation heavily favors quicker movements to boost force production.
Time is often Integrated with Force…Again
Time is so valuable that once force is measured, the aspect is often included again by dividing or multiply force by the value. Perhaps the simplest example is Rate of Force Development (rFD) which divides the Force by time required to produce it. Impulse on the other hand is Force multiplied by time required to produce it. Certainly we can all picture the value of rFD, producing force quickly is the heart of explosiveness, particularly in reactive sports. But what if I am a baseball pitcher or an outside hitter in volleyball where the goal is to impart velocity on a ball. These situations require precise timing to prolong force production, transferring energy to the ball for maximum speed.
Image from Haff, G. Gregory, and Sophia Nimphius. “Training principles for power.” Strength & Conditioning Journal 34.6 (2012): 2-12.
Now many recent studies and sports organizations are examining force plates and their outputs. There are hundreds if not thousands of different force related measurements to analyze, this pursuit is justified by broad spectrums of raw value printouts which poses several problems. The largest of which is our working memory’s ability to only process 3-4 items at a time. Keyboard warriors within sports organizations feel that they are infallible and can process 20+ variables at a time amongst their GPS pivotal tables. Yet such data gatekeepers often miss the goal that sports science and technology is not about them. It is about aligning an organization together around a common goal.
So what 3-4 variables can everyone understand and remember? Always start with reliability when looking at the variables, find the consistent variables as anything that randomly fluctuates can erode the trust from your coaches, peers, and athletes.
Avoid the assumption that peak force means stronger, as a higher peak force only means better, but better at what?