Compensatory acceleration training (CAT) is a strength training technique whereby the lifter attempts to impart maximal acceleration to a loaded barbell. Dr. Frederick C. Hatfield (aka Dr. Squat) introduced the concept of CAT in early 1980’s and described it as “pushing as hard as possible throughout the movement”. The lifter’s goal is to achieve the highest level of velocity possible during the concentric portion of the lift. The result is a high degree of muscular tension. During the eccentric phase, the resistance is lowered in a controlled manner.
CAT is a viable strategy because it enables a lifter to recruit powerful high threshold motor units even with submaximal weights. The science behind this lies in the Size Principle of motor unit recruitment.
A motor unit is defined as a motor neuron and all of the muscle fibers it innervates. The number of muscle fibers per motor unit varies throughout the body. Motor units responsible for intricate movements, such as those controlling the eyes, possess far fewer muscle fibers than motor units associated with larger more powerful muscles. Motor units also vary based on the contractile properties of the muscle fibers they contain. In general, motor units can be divided into two categories: slow-twitch and fast-twitch. In reality, there are subtypes in each category, especially fast-twitch, and the divisions are based on the characteristics of the motor unit. These characteristics include twitch rate, capillary density, type of energy metabolism, and resistance to fatigue.
Slow-twitch motor units have a high resistance to fatigue and are therefore suited for long duration, slow velocity activities. They are designed for aerobic oriented activities and their high capillary densities ensure they have a constant supply of nutrient rich blood in order to maintain recruitment for extended periods of time. Slow-twitch motor units also have a low threshold for recruitment due to their smaller motor neuron size. Fast-twitch motor units, on the other hand, are highly fatigueable but capable of producing high rates of force development, fast velocities, and large power outputs. Their recruitment threshold is higher than that of slow-twitch motor units meaning that it takes a stronger stimulus for them to become active.
Slow-twitch motor units, because of the small size of their motor neurons, are called upon first to contract to produce force. As more force is needed, larger motor neurons activate higher force producing motor units. The largest fast-twitch motor units capable of producing the most force are recruited last, should they be needed. This pattern is referred to as the Size Principle. Recruitment begins with slow motor units and adds faster ones based on the amount of force that needs to be generated.
High threshold fast-twitch motor units are responsible for success in speed, power, and strength sports due to the tremendous forces they are capable of generating. Therefore, they need to be the focus of training in any successful athletic enhancement program.
Force is the product of mass and acceleration as stated in Newton’s second law of motion. In the context of strength training, force is increased by either lifting a heavier weight (increasing mass) or lifting a given weight faster (increasing acceleration). Applying this concept to neuromuscular activation, the level of motor unit recruitment is a result of the interaction between the magnitude of muscle tension, determined by the amount of weight lifted, and the velocity of movement. By combining compensatory acceleration training with heavy weight training, fast-twitch motor unit recruitment is enhanced greatly.
Utilizing velocity-based strength training, a lifter begins a set recruiting the powerful fast-twitch motor units because the loaded barbell is being moved as fast as possible, requiring a high degree of force. When the fastest-twitch motor units are active so are all of the other available motor units. As the lifter progresses through the set, fatigue accumulates and barbell velocity begins to decrease. The reduction in velocity signals a reduction in motor unit recruitment. The fastest most fatigueable motor units drop off first, followed in order by others of lesser speed. As a result, the fast motor units that are the focus of training are no longer being overloaded and the set should be stopped. The smaller less powerful motor units are the only ones remaining active.
Velocity-based strength training combines compensatory acceleration training with heavy weight training to create an objective and measurable periodization strategy. It is designed to minimize unnecessary fatigue and maximize results.
Zatsiorsky, V. M., & Kraemer, W. J. (2006). Science and Practice of Strength Training. (Second Edition). Champaign, IL: Human Kinetics.