When you speak about strength or being strong, what do you imagine? An athlete hoisting a barbell loaded with heavy weight in a Squat or Bench Press? How about an Olympic weightlifter explosively moving 400 pounds from the floor to over his head in a single movement?

These types of things are often considered “strong,” but what about other sporting actions? How about sprinting at full speed, jumping high, or throwing and kicking?  Most people become unsure whether or how strength is part of these movements.

Defining Strength

What is strength in general and specifically for athletes?  Strength is all about physics, and we are talking about Newton’s 2nd Law of Motion: in a nutshell, Force is equal to Mass multiplied by Acceleration.

Strength is a way of talking about the application of force. An athlete can apply force to the ground, to an opponent, to a ball or other piece of sports equipment, or even internally to his or her own body.

Mass & Magnitude

The mass in this equation is what’s being moved—everything from a ball or stick in your hands, to your own body weight (jumping, sprinting and cutting), to a 300-pound linemen or 500 pounds on a barbell.

Acceleration and Time

One thing most people recognize is that in sports, doing things quicker is usually an advantage. Athletes don’t have unlimited time to apply force.

Acceleration is how fast something increases its speed. The faster the acceleration, and thus the speed, the shorter the time.

In sprinting or agility, your foot is in contact with the ground for a limited time. In jumping, there is limited time, and doing it faster than your opponent can be key.  When throwing or kicking a ball or swinging a racket, bat or stick, you want it moving as fast as possible.

Speed of movement matters.

Muscle Action

In terms of physics, force is what we call a “vector.” This means it has a magnitude (how much?) and a direction (which way?). Direction matters because forces can be applied in different directions for different effects.

One thing to consider about direction is whether the muscle is lengthening or shortening during the contraction. When it’s contracting and getting shorter (e.g., bringing the bar up in a Bicep Curl), it’s called a “concentric” action.

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If you’re applying force while the muscle lengthens (e.g., while slowly lowering the bar in the 2nd half of the Bicep Curl), it’s called an “eccentric” action.

Even though the same muscles may be used, with the same structure and contractile proteins, eccentric and concentric strength are not the same. The brain uses different motor control strategies for the same action concentrically and eccentrically.

Physiology & Motor Control

Another important thing to understand about strength for athletes is where it comes from.  Often people equate strength with bigger muscles. This is for good reason, because they are related, although not perfectly and not for all types.

Generating force with your body is a combination of the structure of your muscles (size and biological content) and your neuromuscular control. The muscle may be your engine to develop horsepower, but your brain is the driver that decides how hard you push the pedal.

Sport-Specific Strength

When we analyze an athlete in his or her sport, we observe various forms of movement. Speed, agility, jumping, throwing, kicking, hitting, twisting, landing and so on are movement caused by how an athlete generates force.

It follows that all types of athletic movement are based on how you generate and apply strength.  Still, how can everything be about strength if what your muscles do squatting a full barbell is different from what they do when you throw a baseball that only weighs ounces?

The answer to understanding strength is actually composed of different combinations of Newton’s 2nd Law.

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Playing with the Equation

If we manipulate the 3 parts of the equation—Force, Mass and Acceleration (Speed & Time)—and consider direction of contraction (eccentric or concentric), we now have a way to analyze sports movements and strength types.

We use a movement-based approach to simplify complex biomechanics into 6 specific strength types.

6 Types of Strength

Max Strength 

The basic capability of the muscle to produce a forceful contraction and coordinate multiple muscle groups across multiple joints is part of strength. How much force that can be generated regardless of the time it takes to develop and apply it is called max strength. This is what we call strength when the athlete is expressing it, even when he or she is under sub-maximal loads.

To go back to our car analogy, imagine a big industrial dump truck. It may not move fast, but it can move big loads.

Eccentric Strength

As mentioned before, motor control is different if the action is concentric or eccentric, so eccentric strength is important. The capacity to develop high levels of eccentric force is key in sports actions such as landing from a jump, stopping, changing direction, winding up to throw a ball and swinging a bat. When we come to cars, think brakes.  Eccentric strength is like having great brakes on a car to handle those high speeds. An F1 racer has to have great brakes so he or she can go into turns as fast as possible before braking.

Strength-Speed Power

Most sports applications of force involves doing it quickly. Faster is usually better. Whenan athlete applies force rapidly to a larger load (e.g., blocking another lineman or pushing a bobsled), it’s what we term Strength-Speed Power. “Strength” is listed first because it’s the bigger component in generating the power. This is like a NASCAR racer who can apply a lot of torque (force), moving the car even at high speeds.

Speed-Strength Power

Here it’s the “speed” of movement (or short time of force application) that is the larger factor in generating the power. Think of an athlete swinging a bat, throwing a ball, or applying force to the ground during maximum velocity sprinting. The racing equivalent is more akin to motorcycle racing—still applying force at high speeds (like NASCAR), but against much lighter loads.

Rate of Force Development

This is the drag racer. In a drag race, the goal is to go from 0 mph to full speed in as little time as possible. This is the same quality that creates quickness in an athlete. Rapid movement of the limbs, a quick release of the ball throwing or a shot in hockey, fast feet for soccer. Being able to rapidly generate force, regardless of whether the force level is high is known as Rate of Force Development.

Reactive Strength

This one’s a combo. It’s a fast eccentric action coupled with a high RFD force. Think rapid footwork, or a quick step to change direction and juke an opponent, or the second quick jump when a basketball player comes down and goes back up quickly to get a rebound. We use a motocross bike as the analogy, because it has high Rate of Force Development with eccentric-type landings of bumps that gives it that “springy” quality.

Strength that’s Functional

At the end of the day, athletes want the type of strength that will help them perform at the highest level and gives them the resilience to stay healthy. Every athlete needs a base across all six types of strength. As you progress in your development and level of competition, you begin to focus on the specific qualities more important to your sport, your position and even your individual genetics and style of play.

Strength is much more than how much you can lift on the barbell.