UNDERSTANDING STRENGTH AND POWER

It’s time to take another look at strength training.   Strength in our sport is tested in many different ways.  Sometimes it’s a 1RM, other times it’s 30 reps as fast as possible.   Some strength tests are squeezed between other skills.   Your training must prepare you for any of these challenges, while minimizing mass gain.  Many of the popular strength programs are inadequate for fitness athletes.

In this sport, we do almost everything against a clock, even 1RMs.  When the clock is running, power is the parameter being measured.  Sometimes we call it work capacity.  In Physics, power is also defined as force * velocity.

Although force and velocity are the components of power, maximum force and maximum velocity cannot appear simultaneously.  A 1RM deadlift expresses maximum force, but the bar will move slowly.  High force, low velocity.  Likewise, a PVC-pipe snatch, no matter how fast, will not result in high force development.  High velocity, low force.  Maximum power output occurs away from the extremes of force and velocity.   

Most “strength programs” miss the mark on both strength and power. Power is developed by

  • Increasing strength
  • Increasing the rate of force development
  • Enhancing the contribution of the stretch shortening cycle
  • Learning and perfecting movement patterns

 

HOW STRENGTH WORKS: MOTOR UNITS

The basic force production mechanism is the motor unit: a neuron (nerve cell) and the muscle fibers connected to it.  Groups of motor units work together to contract a muscle, as follows:

Performing a physical task activates motor units according to the size principle: the smallest and slowest are recruited first, then larger, faster motor units are recruited as needed, increasing force production.

Within a single motor unit, force production is governed by the firing rate, which is the rate of arrival of nerve impulses.  Demand for additional force increases the firing rate of activated motor units

Under normal conditions, the brain cycles motor units on and off to prevent fatigue and the ensure smooth, consistent movement.   As the need for force becomes very high, motor units can be more closely synchronized for very short-duration maximal efforts.   

   Motor Units are activated by size, based on the amount of force production required. 

Motor Units are activated by size, based on the amount of force production required. 

Any training intended to increase strength and enhance power must activate the larger motor units regularly, increase the firing rate, and develop synchronized force output during maximal or near-maximal efforts.

 

HOW STRENGTH WORKS: LEVERAGE

The body is a series of levers and fulcrums.    As with any lever, force production and transmission depend on positioning.  Squat just six inches deep, and you can move weight well in excess of your 1RM.  This has nothing to do with motor units; the reason is leverage.   The key mechanical idea is a moment arm: the horizontal distance from the load to the axis of rotation.     

A simple example helps:  While standing, perform a dumbbell side raise until your arm is extended horizontally.   Now lower your arm until it’s about 2 inches away from normal position at your side.   You can control much more weight in the lower position, because the horizontal distance from the dumbbell to your shoulder is much shorter.

If you only squat six inches deep, your hips and knees are barely flexed.  The moment arms are very short and you can produce tremendous force.   (This is also the “power position” in weightlifting; that's not a coincidence). 

As you descend into a squat. your hips go back and knees go forward.   Moment arms lengthen.  This is why people with shorter femurs can squat more: the moment arms created when they squat are shorter. 

Longer moment arms give gravity more leverage against you.  

 

Rate of force development

Developing maximum force happens fast but not instantaneously; it takes around 0.4 seconds to activate sufficient motor units to approach maximal force production.  Some tasks in our sport do not allow that much time.  When a time component is introduced to force production, it is called explosive strength.   Explosive strength is the rate at which an athlete can produce force.

The difference between your absolute max and the max you can achieve in a constrained time is called an explosive strength deficit.   In general, shorter available time for force production increases the deficit.   Top powerlifters are incredibly strong, but weightlifters are far better trained in explosive strength.  

For the Olympic lifts, heavier weight means less time to generate a powerful extension, because you fatigue sooner under a heavy load and cannot maintain optimal position.  Therefore, you have to increase the rate of force development to be successful with heavier weights.   Other than training the snatch and clean and jerk, most strength programs spend little time on the rate of force development.

 

The stretch shortening cycle

The stretch-shortening cycle is a mechanism by which the body stores and releases energy. 

When force is applied to the body, muscles and tendons stretch, capturing energy (like a rubber band).   This stretch corrects itself and the energy is transferred from the muscles and tendons to the joints.   This mechanism is crucial to maintaining walking and running speed.   The SSC increases force and power while reducing energy demands. 

The bounce at the bottom of a clean is the SSC, and it’s a lot easier than a dead-stop front squat. This type of movement is also called reversible muscle action and appears all over our sport.   Reversible muscle action is a motor skill and should be trained often as part of a strength and power program.

The SSC is substantially governed by two reflexes.  The first increases muscle tension (and energy capture) when the stretch occurs.  The second prevents injury by “shutting off” muscle tension if excessive force is applied to a muscle.   These two reflexes, plus voluntary muscle action, determine the amount of force applied during reversible muscle action, such as the bottom of a squat or clean.

When the SSC is trained, muscles can withstand greater “stretch” before shortening, and the inhibitory reflex is diminished.   For this reason, a track athlete like a triple jumper will outperform even the strongest weightlifter on exercises like a drop jump or bounding hops.   While our training should not mirror the track athlete’s focus on explosiveness, the SSC is integral to maximizing power output for fitness athletes. 

 

THE CORRIDOR EFFECT

Increasing strength requires increasing the activation, firing rate and synchronization of motor units.   Effective strength training focuses on activating the biggest and fastest motor units.   Most programs spend a lot of time in the 65-80% range, which can create several problems: 

The biggest motor units are not activated.   Instead, the motor units in the middle of the spectrum are trained.   This produces some strength gains, but leaves a lot on the table. This also exhausts some of the motor units you need for your MetCons.   

Movement patterns transfer poorly.  A 97% squat requires high force production throughout the entire lift.   At ~75%, production surges at the bottom of the lift and then diminishes throughout the rep.   This diminishment reduces the stimulus and suppresses your gains.  This is an unhelpful motor pattern for competition lifts.

Even those crazy “volume” programs may miss the mark.  By focusing on total work, rather than intensity, they’re likely to promote hypertrophy alongside strength gains.   Increased mass is rarely desirable for fitness athletes. 

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Summary

Strength training for fitness athletes should develop power.  Force production is the foundational ingredient in power, and force production increases when motor units are activated and stressed.   However, strength programs often under-activate the biggest and fastest motor units, leaving substantial force production gains on the table.   Training in this manner also trains unproductive movement patterns, because force production is overly biased toward the start of the exercise and then decreases throughout the rep.

The conversion of strength into power requires emphasis on the rate of force development as well as training the stretch-shortening complex.   Training these motor skills enable the expression of increased power without increases in mass.  These motor skills are often ignored in conventional programs, resulting in athletes spending an enormous amount of time for modest strength and power increases.  To see how we attack Strength and Power, click here.