The Strength Deficit

The strength deficit can be interpreted as the difference between the actual capacity of a muscle or group of muscles, and the individual’s ability to express that capacity in a given task. All individuals possess a strength deficit, but some are limited more so than others by their ability to utilize their actual strength.

In strength & conditioning bible, Supertraining, Verkhoshansky explains that an approximate measure of strength deficit may be made in measuring a vertical jump, firstly with a static start in a fixed position with flexed knees and hips, and then with a vertical jump preceded by a sudden dip. In the first case the stretch reflex has been completely removed, and in the second case the stretch reflex is activated by the counter movement. The strength deficit is calculated by finding the difference between these two jumps. For example:

Static Jump = 22inches

Countermovement Jump = 30inches

Difference = 8inches

Deficit = 27%

Verkhoshansky goes on to explain that if the strength deficit is large, an increase in speed-strength may be produced by maximal neuromuscular stimulation and ballistic methods such as Olympic lifting, plyometrics, or med ball exercises. And if the strength deficit is small, the athlete will require submaximal efforts to induce hypertrophy followed by maximal efforts against heavy loads.

Strength deficit large = train using ballistic methods

Strength deficit small = train using traditional strength training methods

Initially, this could be confusing. The static jump involves a concentric only muscle action. If an individual is able to jump significantly higher when using a countermovement than they are when jumping from a static position, it may seem logical to assume that the athlete is weak and would benefit from traditional strength training methods. And if an individual is able to jump close to as high with a static jump as they are with a countermovement jump, it may seem logical to assume that the athlete is not “reactive” or “springy” and would benefit from ballistic training methods. However, the opposite is true.

A countermovement jump utilizes the slow stretch shortening cycle, as well as the ability of the muscle and the connective tissue to use elastic energy to generate force through a stretch reflex. A static jump does not utilize the stretch shortening cycle, and instead utilizes the athlete’s central nervous system, and more specifically the ability to produce force rapidly and in a concentric manner only.

Greater jump heights are achieved in countermovement jumps because the countermovement itself provides more time for the athlete to develop the force needed to propel themselves off the ground, like in traditional strength training. So if the stretch shortening cycle is a function of the muscle, then training the muscle through traditional strength training methods would improve this function. Athletes who have a small strength deficit would therefore benefit from this type of training.

Lesser jump heights are achieved in static jumps because less time is available to display the force needed, like in ballistic exercises. So, if the demand to jump from a static position is a function of the central nervous system, then training the system through ballistic training methods would improve this function. Athletes who have a large strength deficit would therefore benefit from this type of training.

Verkhoshansky does not outline a threshold at which we should deem an individual’s strength deficit too large or too small, but we can draw some obvious conclusions. A difference of 20% seems to be an agreed upon figure for a strength deficit that is too large, and a sign that an athlete could benefit from improved CNS efficiency. On the other hand, an individual who produces a static jump height very close to their countermovement jump height could likely benefit from improved muscular strength. And finally, most athletes are likely to fall somewhere in the middle ground, where they would see benefits from performing both training methods consistently.