Muscles for Athletes: The Science of High-Threshold Motor Recruitment for Hypertrophy in High School and Collegiate Athletes

This article is for athletes who want to add muscle mass while improving their performance on the field. Adding muscle doesn’t automatically make you a better athlete. While a bigger muscle can be stronger and more powerful, this isn’t always the case. Muscle mass can sometimes impair athletic performance, especially if the added bulk doesn’t come with a proportional increase in strength. This is known as “non-functional hypertrophy” – an increase in muscle mass without a performance improvement.

Building Functional Muscle for Athletes

Athletes need muscle like a car needs an engine. Without muscle, movement is impossible. Athletes require strength, power, and speed, meaning they need an engine with a lot of horsepower! The size of a muscle determines its strength and power potential. However, without the proper neural adaptations, a big muscle won’t necessarily be super strong. Similarly, an efficient nervous system without the proper muscle mass won’t be very powerful either.

Athletes need to increase their muscle mass in a way that also boosts physical performance. This means focusing on stimulating high-threshold motor units (HTMUs), increasing strength and efficiency in all types of muscle actions (concentric, isometric, and eccentric), and improving the three main force production factors: muscular, elastic, and reflexive.

1. Focus on Stimulating High-Threshold Motor Units (HTMUs)

Success in strength and power events, as well as actions requiring high strength and power (sprinting, jumping, changing direction), is highly correlated with the proportion of fast-twitch fibers in muscles. While our muscle fiber types are largely genetic, compensatory hypertrophy (selective hypertrophy of fast-twitch fibers) can help. This means even if you have fewer fast-twitch fibers, increasing the size of these fibers can enhance your power and strength.

2. Increase Strength and Efficiency in All Types of Muscle Actions

Most athletes have sufficient concentric (lifting) strength but often lack eccentric (lowering or absorbing) and isometric (holding, static) strength. These types of strength are crucial as they enable athletes to absorb and stop force before projecting or moving it. Training should focus on:

  • Concentric Strength: Overcoming resistance.
  • Eccentric Strength: Absorbing and controlling resistance.
  • Isometric Strength: Holding and stabilizing resistance.

Athletes should devote at least 30% of their training volume to eccentric and isometric training, with a greater percentage for those lagging in these areas.

3. Improve the Three Main Force Production Factors

To maximize HTMU recruitment and stimulation, athletes must produce as much force as possible in training. Three main factors contribute to force production:

  • Muscular Factor: The force produced by muscle contraction.
  • Elastic Factor: The elastic properties of muscles and tendons enhancing force production.
  • Reflexive Factor: The myotatic stretch reflex facilitating muscle shortening and increasing force production.

Athletes should use exercises that place the muscle in a stretched position at the end of the eccentric phase, maximizing force production in the subsequent concentric phase.

Training Methods for Hypertrophy

Athletes should train every type of muscle contraction (isometric, concentric, and eccentric) and the three components of force production (muscular, elastic, and reflexive). Here are some methods:

Concentric-Muscular Method (Heavy Emphasis): Use heavy weights (at least 80% of max) with exercises like bench press, squats, and deadlifts.

Concentric-Muscular Method (Explosive Emphasis): Use explosive exercises like Olympic lifts from a static start to create peak force and power.

Eccentric-Muscular Method (Heavy Emphasis): Use slow lowering of heavy weights to stimulate eccentric strength.

Isometric-Muscular Method (High Intensity): Perform maximal contractions over short durations (5-7 seconds) using exercises like squats and bench presses with safety pins.


Building functional muscle for athletes involves more than just lifting heavy weights. It requires a strategic approach that includes training all types of muscle actions and maximizing force production through various methods. By focusing on high-threshold motor units and using a mix of concentric, eccentric, and isometric exercises, athletes can improve their muscle size and performance on the field.

Stay tuned for the next installment, where we’ll detail how to design a training plan that incorporates these methods!