Strength and Specificity: Optimizing Performance with Technology-Driven Training

Discover how technology-driven training tools like Gymaware RS and FLEX optimize muscle fiber recruitment and performance. Learn about the role of Henneman’s size principle and specificity in maximizing strength gains.

By Valerio Esposi to

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Introduction
Is Henneman’s Size Principle Always Valid?
Difference Between Intramuscular and Intermuscular Coordination
Strength and Specificity

Introduction

Muscle fibers contract and exert tension (force) due to stimuli that travel from the Central Nervous System to the fibers via a motor neuron. The group of fibers innervated by the same motor neuron forms a motor unit.

Strength and Specificity How to Optimize Performance with Technology

In the previous article, we discussed how muscle fiber recruitment is explained by Henneman’s size principle (1965), which states that slow fibers are recruited before fast fibers. To summarize, this principle highlights that slow fibers are recruited for light loads, intermediate fibers for medium loads, and only fast fibers are activated for heavy loads.

Is Henneman’s Size Principle Always Valid?

Henneman’s size principle has been questioned in relation to ballistic movements. In these types of movements, as shown in the following image, fast motor units are recruited without the prior activation of slow fibers.

The hypothetical recruitment model developed by Stuart and Enoka in 1983 suggests that Henneman’s size principle remains valid only if light-load movements occur at low speeds.

Studies conducted by Bosco and Komi have shown that individuals with a high proportion of fast fibers in their lower limb muscles achieved better results in vertical jumps. This suggests that, even with very low force outputs (30-40% of maximum isometric force), the activation of fast motor units dominates over slow ones.

GymAware FLEX allows us to determine the speed of load displacement, enabling “selective” work on the fast fibers of boxers. Furthermore, this tool provides real-time percentage increases and decreases for each repetition, which is crucial information for achieving the training session’s objective.

Difference Between Intramuscular and Intermuscular Coordination

Intramuscular coordination is the ability of the muscle fibers within a single muscle to contract efficiently. It is primarily relevant in maximum strength training, as it represents the capacity of the individual muscle fibers to generate high force.

Intermuscular coordination is the nervous system’s ability to efficiently recruit the muscles involved in a movement to achieve the desired outcome. It plays a crucial role in strength improvement.

Strength and Specificity

Many studies demonstrate that strength improvement is specific, meaning that progress in one exercise, such as the squat, is not always accompanied by strength gains in another exercise. This implies that strength increases are partly due to the coordination of specific muscles involved in that particular exercise.

This aspect leads us to one of the core principles of sports training: the principle of specificity.

In their renowned book “Supertraining” Yuri Verkhoshansky and Siff discuss the “Dynamic Correspondence Principle“, or S.A.I.D. (Specific Adaptation to Imposed Demand), which states that the first law of training is specificity. Each training program should be specific to the sport in question, ensuring the best correlation with a precise athletic movement.

According to the SAID principle, specificity involves adaptations in:

Biomechanical aspects
Metabolic aspects
Psychological aspects

These adaptations always relate to a specific characteristic of the task an athlete is required to perform. In particular, correspondence involves:

Movement amplitude and direction
Force production region
Effort dynamics
Rate and time of force production for that movement or aspect of it
Muscle work regime (type of muscle contraction)

In practice, this means finding similarities in three main aspects:

Movement/motor pattern (jump, push, pull, etc.)
Kinetic aspects (direction of force production, vertical and/or horizontal, Rate of Force Development, Time to Peak Force, Rate of Loading, Power Output (Peak and Average), Impulse, Ground Contact Time, movement/contraction speed)
Neurophysiological aspects (Heart Rate, VO2, Metabolic Power, Blood Lactate Concentration, motor unit recruitment rate)

To ensure that the exercises we propose to our athletes have similarities with the aspects listed above, the use of GymAware technological instrumentation is invaluable. It facilitates a truly difficult and complex task through the collection and monitoring of numerous data points.

Bibliography

Bosco C, La forza muscolare. Aspetti fisiologici ed applicazioni pratiche, Società Stampa Sportiva1997
Henneman E, Somjen G, Carpenter D.O. Functional significance of cell size in spinal motoneurons. J. Neurophysiol. 1965
Verkhoshansky Y, Siff M, Supertraining, 2009