The Role of the Nervous System in Strength Training

Strength training is often associated with the physical transformation of muscles—bigger, stronger, and more defined. However, beneath the surface, the nervous system plays a pivotal role in driving these changes. From controlling muscle activation to coordinating adaptations, the nervous system is the unsung hero of resistance training. In this article, we’ll explore how the nervous system influences muscle function, motor unit recruitment, and long-term adaptations to resistance training.

The Nervous System: An Overview

The nervous system can be divided into two main components [1]:

• Central Nervous System (CNS): Composing the brain and spinal cord, the CNS processes information and sends signals to the rest of the body.

• Peripheral Nervous System (PNS): Includes all the nerves outside the CNS. Within the PNS, the somatic nervous system controls voluntary movements, such as those performed during strength training.

During resistance training, the CNS and PNS work together to communicate with muscles, enabling them to contract and generate force. This coordination relies on a network of motor neurons, sensory inputs, and feedback mechanisms that ensure the body moves efficiently and effectively under load.

Muscle Activation and the Role of Motor Neurons 

Every voluntary movement begins in the brain. When you decide to lift a weight, the brain sends an electrical signal through the spinal cord and peripheral nerves to the muscles involved in the action. This signal activates motor neurons, which are specialized nerve cells that control muscle fibers.

Each motor neuron connects to multiple muscle fibers, forming a motor unit. When a motor neuron is activated, all the muscle fibers within its motor unit contract simultaneously. The number of muscle fibers in a motor unit varies depending on the muscle’s function:

• Small motor units (fewer muscle fibers per neuron) control fine, precise movements, such as those in the fingers.
• Large motor units (hundreds or thousands of fibers per neuron) generate more force and are found in muscles like the quadriceps.

Motor Unit Recruitment and Strength Training 

Motor unit recruitment refers to the process by which the nervous system activates motor units to produce force. The recruitment follows the size principle, which states that smaller motor units are recruited first, followed by larger ones as the demand for force increases [2].

During light resistance exercises, only the smaller motor units, which are more fatigue-resistant, are activated. However, as the intensity of the exercise increases—such as during heavy lifting—the nervous system recruits larger, more powerful motor units. This progressive recruitment ensures that the appropriate amount of force is generated for the task at hand.

In strength training, repeated exposure to high-intensity loads teaches the nervous system to recruit motor units more efficiently and effectively. This process, often referred to as neuromuscular adaptation, is a critical component of early strength gains, even before significant muscle hypertrophy (growth) occurs.

Rate Coding: The Role of Firing Frequency

In addition to recruiting more motor units, the nervous system can increase the firing frequency of motor neurons, a process known as rate coding. Higher firing frequencies cause muscle fibers to contract more forcefully, enhancing overall strength output.

For example, during maximal lifts, the nervous system increases both motor unit recruitment and firing frequency to generate peak force. Over time, resistance training improves the nervous system’s ability to synchronize these actions, resulting in greater strength.

Coordination and Intermuscular Efficiency

Strength training doesn’t just make individual muscles stronger—it also improves the coordination between different muscles. This is known as intermuscular coordination and is governed by the nervous system.

When performing a compound movement like a squat, multiple muscles (e.g., quadriceps, hamstrings, glutes, and calves) must work together. The nervous system orchestrates this collaboration by activating the prime movers, stabilizers, and synergists in the correct sequence and intensity.

With practice, the nervous system refines these movement patterns, making them more efficient. This is why beginners often see rapid strength improvements as their nervous system learns to optimize movement mechanics.

The Stretch Reflex and Muscle Activation 

The nervous system also uses reflexes to enhance performance during strength training. One key reflex is the stretch reflex, which is mediated by muscle spindles—sensory receptors within muscles that detect changes in length.

When a muscle is rapidly stretched, such as during the eccentric phase of a squat, the muscle spindles send signals to the spinal cord, triggering an automatic contraction of the stretched muscle. This reflexive response helps stabilize the body and generate additional force, contributing to improved performance.

In advanced lifters, the nervous system learns to harness the stretch reflex more effectively, enhancing power output in movements like plyometrics or Olympic lifts.

Long-Term Adaptations: Neural Plasticity in Strength Training

The nervous system is highly adaptable, and strength training induces significant changes over time. These adaptations, often referred to as neural plasticity, are critical for sustained strength improvements [3].

1. Increased Neural Drive

Neural drive refers to the strength and frequency of signals sent from the brain to the muscles. Resistance training increases neural drive, enabling muscles to contract with greater force. This adaptation is especially important for maximizing strength in high-intensity lifts.

2. Improved Motor Unit Synchronization

As lifters gain experience, the nervous system becomes better at synchronizing the activation of motor units. This improved coordination enhances force production, particularly during explosive movements like deadlifts or clean-and-jerks.

3. Reduced Neural Inhibition

The nervous system includes mechanisms, such as the Golgi tendon organs (GTOs), that prevent excessive force generation to protect muscles and tendons from injury. With consistent training, the sensitivity of these protective mechanisms decreases, allowing the muscles to generate higher levels of force safely.

The Nervous System and Fatigue

While the nervous system is key to strength, it is also a limiting factor. During intense training, the nervous system can become fatigued, leading to reduced performance. Central fatigue occurs when the brain’s ability to send strong signals to the muscles diminishes, while peripheral fatigue involves the reduced responsiveness of motor neurons or muscle fibers [4].

To optimize recovery and performance:

• Ensure adequate rest between heavy training sessions.
• Incorporate deload weeks to prevent overtraining.
• Focus on sleep, nutrition, and stress management to support nervous system health.

Practical Applications for Strength Training

Understanding the role of the nervous system can help athletes and coaches design more effective training programs. Here are some key strategies:

1. Prioritize Progressive Overload

Gradually increasing the intensity of exercises forces the nervous system to adapt, improving motor unit recruitment and firing frequency.

2. Incorporate High-Intensity Training

Maximal effort lifts and explosive movements (e.g., plyometrics, Olympic lifts) are particularly effective at stimulating the nervous system.

3. Emphasize Movement Quality

Perfecting technique ensures efficient motor unit recruitment and reduces the risk of injury. Use lighter weights to master form before progressing to heavier loads.

4. Utilize Specificity

Train with exercises that closely mimic the target activity to develop the specific neural adaptations required for optimal performance.

5. Include Variability

While specificity is important, introducing new exercises periodically challenges the nervous system to adapt to different movement patterns, enhancing overall strength and coordination.

6. Manage Fatigue

Avoid overtraining by balancing high-intensity sessions with lower-intensity work and recovery days. Tools like heart rate variability (HRV) can help monitor nervous system readiness.

Conclusion

Strength training is as much a neurological endeavor as it is a physical one. The nervous system orchestrates every aspect of muscle activation, from motor unit recruitment to firing frequency and reflexive responses. It adapts to resistance training by becoming more efficient and effective, enabling lifters to lift heavier loads and perform complex movements with precision.

By understanding the nervous system’s role, athletes can train smarter, optimize performance, and achieve long-term success in their strength training journey.

Please Note: The information provided in this article are the opinions and professional experience of the author and not all activities are recommended for the beginner or participants with underlying health conditions. Before following any advice or starting any fitness, health and wellbeing journey please consult with an Allied Health Professional and / or General Practitioner.

References

1. Nervous System
2. Motor Unit
3. Long-Term Neurophysiological Adaptations to Strength Training
4. Neural Contributions to Muscle Fatigue: From the Brain to the Muscle and Back Again

• Bio

Steve Irwin

Steve has spent the last 19 years in the Australian Fitness Industry as a Group Fitness Instructor, 1-1 Coach, State Manager, Business Owner and is currently an Educator for the Australian Institute of Fitness. A lifelong fitness enthusiast he started his working life in the Military which guided him into the fitness industry where his passion for helping others on their health and fitness journey has been realised. Steve believes that for anyone thinking about getting fit or healthy they should “just get started” as “doing something is better than doing nothing”.