Why are rapid gains in strength often not accompanied by increased muscle mass? It has been widely accepted that changes in the central nervous system (CNS) must happen before changes in muscle mass are noticeable. In this article, we explain what role the CNS plays in weight training and what part of the CNS dominates it.
The central nervous system (CNS) plays a key role in coordinating voluntary movements.
Signals are sent from the brain to the muscles via motor pathways.
Feedback is sent back to the brain from the muscles.
The cerebellum reviews this feedback and sends revised instructions back to the muscles.
New research suggests that area of the CNS largely responsible for coordinating all this activity may be the reticulospinal tract.
It has been widely accepted that strength training requires adaptations to the central nervous system (CNS) in the early phases of training. This assumption is based on research showing that early stages of training often achieve marked increases in force production without accompanying changes in muscle mass. Until recently, though, the strength training literature has not conclusively pinpointed the portion of the CNS most responsible for these adaptations.
A study published in the Journal of Neuroscience in 2020 evaluated two female macaque monkeys as they learned to pull a handle with one arm. The researchers measured nerve signals in three motor pathways before and after resistance training. The investigators suggest that the neural adaptations triggered by weight training may be primarily due to changes in the reticulospinal tract.
Work to understand the various pathways of the CNS have wide-ranging implications beyond strength training, such as recovery from stroke and spinal cord injury. They may also provide insights regarding your own strength training program, why learning and practicing good form matters, and perhaps a renewed appreciation for the complexity of the human body.
What is the central nervous system?
The CNS comprises the brain and spinal cord. The CNS is connected to the peripheral nervous system (PNS) which is the network of nerves coursing throughout the rest of the body. The PNS includes your sensory and motor nerves. These nerves carry impulses to the brain (sensory) and directions from the brain (motor) to the muscles. The CNS coordinates movements by processing sensory inputs and motor outputs.
CNS and muscle fibers – the connection:
The somatic nervous system controls the skeletal muscles. Information from the external environment is carried to the brain via the sensory pathways and interpreted. The voluntary response is a planned movement. However, autonomic movements such as breathing are under unconscious control unless we need to direct our attention to our breath, such as during yoga or lifting.
Motor nerve planning areas in the brain
You may have heard about the prefrontal cortex and its role in managing executive function. Also located in the frontal lobe of the brain is the primary motor cortex, which controls the movement of the core muscles. The motor cortex helps manage movement, especially that of learned movements such as performing a squat or deadlift.
How signals travel from the brain to the muscles
The Betz cells are large neurons that synapse with motor neurons in the spinal cord. Signals travel from these Betz cells down two pathways — the corticospinal tract and the corticobulbar tract — and control movements on opposite sides of the body as pictured below.
Other connections between the CNS and the muscles
Control over movement, posture, and balance is managed by several different descending connections of neurons. The tectospinal tract supports posture, the reticulospinal tract influences trunk movements and limb (arm and leg) muscles close to the trunk, and the vestibulospinal tract integrates information from the vestibular system to coordinate posture, movement, and balance.
CNS role in weightlifting
While it is perhaps easy to conceptualize a message being sent from the brain to the muscles via the motor nerves, the reality is much more complex. The brain and muscles are in constant communication during voluntary movement. The muscles send information to the brain, and revised instructions are fired back. Where this all comes together in lifting is proprioception: the perception and awareness of the position and movement of the body.
The cerebellum plays a role in comparing the signals sent by the brain to the muscles with proprioceptive feedback about body position and movement. When conflicting messages are detected, the red nucleus of the midbrain is stimulated to send a correction through the spinal cord along yet another pathway — the rubrospinal tract.
Training your CNS for lifting
Learning proper technique is an important part of training the CNS to ensure good form on every lift. It takes time for these pathways to develop and mature. Much of the CNS research has focused on the role of the corticospinal tract, with equivocal results.
One study of recreational lifters working on their squat technique found that participants increased their max squat by 35% and spinal nerve excitability, but no changes were found in muscle thickness. In addition, no extra excitability was found in the corticospinal tract. This suggests that the RST may be doing the “heavy lifting” of directing movement complexity and generating high force. The study of female macaques offered the first real evidence in favor of this hypothesis.
Working with an experienced coach or personal trainer can help you train your brain to automatically detect and correct deviations in form. Even Olympic athletes can benefit from a periodic review and revision process to improve efficiency and power. If you are getting back in the game after an injury, take the time to revisit your technique and allow your brain to relearn proper form to help avoid injury in the future.
- Journal of Neuroscience. Cortical, Corticospinal, and Reticulospinal Contributions to Strength Training.
- Journal of Applied Physiology. Does the reticulospinal tract mediate adaptation to resistance training in humans?
- Oregon State University, Anatomy and Physiology. 14.5 Sensory and Motor Pathways – Anatomy & Physiology.
- Experimental Physiology. Task‐specific strength increases after lower‐limb compound resistance training occurred in the absence of corticospinal changes in vastus lateralis.