Why Do Muscles Shake During Pilates?
Muscle shaking is a common and fascinating phenomenon experienced during Pilates exercises, especially on the Reformer. Understanding the science behind these shakes not only demystifies the process but also highlights the unique benefits of Pilates for clients of all fitness levels. Here's a deeper dive into how this phenomenon relates to Pilates Reformer exercises, clients, and their fitness journeys.
1. Muscle Fatigue and Reformer Pilates
Reformer exercises, such as leg presses or bridge work with resistance springs, emphasize endurance and control. The slow, sustained movements target slow-twitch muscle fibers, which are designed for prolonged activity. However, as these fibers fatigue during exercises like a controlled leg extension or plank variations on the carriage, the body begins recruiting fast-twitch muscle fibers to maintain the movement.
This transition creates a temporary imbalance, which manifests as muscle shaking.
For clients: This is a sign that the muscles are working hard and adapting to the demands of the exercise, leading to greater strength and endurance over time.
2. Motor Unit Recruitment and the Reformer
On the Reformer, the interplay between resistance and instability forces the body to recruit motor units efficiently.
Motor units (a motor neuron and its associated muscle fibers) are activated in a progressive manner to sustain the effort.
As smaller motor units fatigue, larger and more powerful units take over, causing the "shakes."
Exercises like leg circles or single-leg presses amplify this effect due to the combination of precise movements and the instability of the Reformer carriage.
For clients, this shaking reflects the nervous system’s adaptation to progressively complex challenges, improving coordination and muscle recruitment patterns.
3. Stabilizer Muscle Fatigue in Reformer Work
Reformer Pilates uniquely targets deep stabilizing muscles such as the transversus abdominis, multifidus, and the muscles of the pelvic floor.
These muscles are smaller and fatigue more quickly than larger muscle groups like the quadriceps or glutes.
Exercises such as planks on the Reformer, single-leg stretches, or side-lying glute work heavily recruit stabilizers, which can lead to early onset shaking.
For clients recovering from injury: This fatigue is especially evident, as stabilizers around the injury site may be weakened and need retraining.
Shaking during these exercises indicates that the stabilizing system is working to its capacity, a critical step in improving posture, core strength, and overall functional stability.
4. Post-Injury Muscle Shakes
Reformer Pilates is widely used for post-rehabilitation clients due to its low-impact nature and focus on controlled movement. However, clients recovering from back, neck, or other injuries often experience more pronounced muscle shaking due to:
Weakened stabilizers: Muscles such as the transversus abdominis may be underactive post-injury.
Protective compensation: Larger, global muscles (e.g., erector spinae) compensate for weakened stabilizers, leading to quicker fatigue.
Proprioception retraining: The nervous system is "relearning" how to stabilize the body and coordinate movement, resulting in shakiness.
This shaking, though challenging, is a sign of progress in neuromuscular retraining and improved functional stability for these clients.
5. Autonomic Nervous System Activation on the Reformer
Reformer Pilates often pushes clients into a state of physical stress due to the added resistance and instability.
The sympathetic nervous system (fight or flight) becomes activated, especially during demanding exercises like pikes, plank holds, or jumpboard work.
This heightened state increases motor unit responsiveness, contributing to the shaking sensation.
For clients, this is an opportunity to build both physical resilience and mental focus, as they learn to perform under controlled stress.
How to Support Clients Experiencing Muscle Shakes
Normalize the Shaking: Educate clients that shaking is a positive sign of strength and neuromuscular adaptation. Reassure them it’s a normal part of the process, not a sign of weakness.
Encourage Rest: For clients recovering from injury or those new to Pilates, pausing briefly can prevent overfatigue. This ensures safe and effective progression.
Modify Exercises: Adjust the resistance, range of motion, or duration to match the client’s capabilities. For instance:
Reduce the spring tension for Reformer exercises.
Shorten the hold time for planks or core-focused movements.
Focus on Form: Shaking is most beneficial when it occurs with proper alignment and technique. Emphasize control over speed during every movement.
Key Takeaway for Reformer Pilates
The muscle shakes clients experience during Reformer Pilates are a scientific marker of progress, reflecting adaptations in muscle strength, endurance, and neuromuscular coordination. Whether holding a deep lunge or performing a dynamic core sequence, these tremors highlight the effectiveness of Pilates in challenging and transforming the body.
For clients, embracing the shakes as a sign of growth makes each session not only rewarding but also a step closer to improved strength, stability, and movement efficiency. As instructors, we celebrate these moments as tangible evidence of the body’s incredible ability to adapt and grow.
Aimee Liddington is a New Zealand–registered senior physiotherapist, clinical Pilates instructor, and rehabilitation specialist with over a decade of experience in sports medicine, orthopaedics, neurological rehabilitation, and performance physiotherapy. With a BSc in Human Nutrition and Sports Science, she has worked in leading hospitals, with elite sports teams, and in concussion care and mountain rescue. As founder of FORM Pilates Studio, Aimee combines clinical expertise with a passion for intelligent movement, helping clients recover fully, move well, and build lasting strength.