The Shake in Movement: A Nervous System Solving the Problem

What is your body actually telling you when it shakes?

The shake is easy to mistake for failure. But movement is rarely that simple. Luke Khoury explores the nervous system, muscle physiology and motor control behind the tremor we experience in challenging Pilates positions – and why it may tell us more about how the body is learning than we realise.

A Nervous System Solving the Problem

If you’ve ever held a position in Pilates and felt your body begin to tremble, you’ve experienced

something often misunderstood. The immediate assumption is usually that the muscle is weak or fatigued. In reality, that shake is far more interesting. It is your nervous system working in real time to solve a movement problem it hasn’t yet fully mastered.

Every movement you perform is a coordination task. The brain is constantly deciding which muscles to recruit, in what sequence, at what intensity, and with what timing. When this system is efficient, movement appears smooth and controlled. When it isn’t, variability shows up. That variability is what we often see as shaking. It reflects a level of uncertainty in the system rather than simply a lack of strength.

A key contributor to this is the length–tension relationship of muscle. Muscles generate force most effectively at an optimal length where the overlap between actin and myosin is ideal. In many Pilates exercises, we intentionally move away from this optimal zone. We work in lengthened positions, shortened ranges, long lever arms, and isometric holds that challenge the system’s ability to maintain force under less favourable mechanical conditions. As a result, the nervous system must work harder to coordinate force output, and even small inefficiencies become more visible. The outcome is often a tremor.

At the level of the muscle, force production depends on motor unit recruitment. A motor unit consists of a motor neuron and the muscle fibres it controls. For smooth and stable movement, the nervous system recruits these units progressively and adjusts their firing rates with precision. When a task is unfamiliar, demanding, or placed in a mechanically disadvantaged position, this process becomes less refined. Motor units may be recruited inconsistently, their firing rates may fluctuate, and opposing muscle groups may co-contract in an attempt to create stability. This lack of coordination introduces noise into the system, which presents as shaking.

This process is also influenced by how the nervous system balances feedforward and feedback control. Feedforward control is predictive. It uses prior experience to anticipate the demands of a movement and prepare the body accordingly. Feedback control, on the other hand, relies on sensory information to make adjustments during the movement itself. When a task is well learned, feedforward mechanisms dominate, and movement appears smooth. When the system lacks confidence or familiarity, feedforward predictions are less accurate, and the body relies more heavily on feedback. Because feedback is slower, this creates a loop of constant correction, overshooting, adjusting, and correcting again. This oscillation is what we perceive as tremor.

In this environment, the nervous system cannot rely on familiar strategies and is forced to refine its coordination. This aligns closely with foundational ideas from Principles of Neural Science, particularly the concept that movement is an emergent property of distributed neural networks rather than a single command pathway. Variability is not simply error, it is part of how the system explores and refines solutions. The brain continuously updates its internal models through sensory input, comparing predicted outcomes with actual feedback. When there is a mismatch, the system adapts. Repetition strengthens synaptic connections, improving the timing and efficiency of recruitment, which is why movements that once felt unstable become more coordinated over time.

While much of the shake is neural, there is also a local muscular and metabolic contribution. Muscle contraction is powered by ATP, which is regenerated through different energy systems depending on the duration and intensity of the task. In short, high-intensity efforts, the phosphocreatine system provides rapid ATP resynthesis. As an isometric hold continues, there is a gradual shift toward glycolytic and oxidative pathways. In sustained contractions, particularly when muscles are held under tension without relaxation, local blood flow can be partially restricted. This limits oxygen delivery and metabolite clearance.

As a result, metabolites such as inorganic phosphate, hydrogen ions, and ADP begin to accumulate within the muscle. These changes can interfere with calcium handling and cross-bridge cycling, reducing the efficiency of force production at the fibre level. From a neural perspective, this metabolic state increases afferent feedback from group III and IV muscle receptors, which signal the central nervous system about the internal environment of the muscle. The brain responds by adjusting motor unit recruitment, often increasing drive or redistributing load across available fibres.

This interaction between metabolic stress and neural control adds another layer of variability. Motor units may cycle more rapidly, firing patterns may become less consistent, and the system may oscillate between recruitment strategies in an attempt to maintain output. What you experience as shaking, in this context, is not purely fatigue, but a combined effect of changing muscle chemistry and the nervous system’s ongoing attempt to stabilise performance under those conditions.

Pilates is particularly effective at exposing this because it removes many of the ways people typically compensate. It reduces momentum, demands control over load, challenges end ranges, and often removes external stability. In this environment, the nervous system cannot rely on familiar strategies and is forced to refine its coordination. The shake, in this context, is not failure. It is the system actively searching for a better solution while also responding to the physiological demands within the muscle itself.

Over time, with consistent exposure and improved sensory awareness, both the neural and metabolic systems adapt. Feedforward predictions improve, motor unit recruitment becomes more coordinated, and local muscular endurance increases through enhanced oxidative capacity and improved metabolite clearance. The need for constant correction decreases. The shake diminishes not because the exercise has become easier, but because the system (both neural and muscular) has become more efficient.

The key is not to chase the shake as a goal, but to understand what it represents. It is feedback. It tells you that the system is being challenged in a meaningful way, both from a coordination and an energy

The Body Is Always Learning

Movement isn’t fixed. Every challenge gives the nervous system information to work with, adapt to and learn from. What looks like instability can be part of that process — the body searching for a more efficient way to solve the problem.

The shake isn’t necessarily something to eliminate. It’s information. And when we learn to understand what the body is telling us, we can teach movement with greater clarity, curiosity and intention.