Beyond the Mechanics Part 2: The Bucket Principle in Biology and Physical Health

By Duke Autret, Myotherapist

The bucket theory, a metaphor for the reserve principle in biology, helps explain why symptoms or dysfunctions can emerge, not with any single or sudden event, but rather when the body's capacity for handling stressors is overwhelmed. It conceptualizes the body's resilience as a bucket with a finite capacity. Stressors of all kinds e.g. biomechanical, systemic, or psychosocial, add "water" to the bucket. Overflowing represents the point at which reserves are depleted, and symptoms arise. This model is especially relevant in understanding unexplained musculoskeletal (MSK) pain, where symptoms can appear without a clear mechanical cause.

​The Bucket and MSK Pain: More Than Just Biomechanics
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Stress Accumulation Beyond the Physical
While biomechanical factors like poor posture, repetitive strain, or acute injury are traditional contributors to MSK pain, the bucket metaphor illustrates how other stressors can also fill the bucket:

• Systemic Stress: Chronic inflammation, poor nutrition, or inadequate recovery can tax reserves. For instance, poor glycemic control in diabetes or unresolved inflammation such as in metabolic diseases and autoimmune conditions may amplify sensitivity to physical stress. Important to note that chronic inflammation can exist too even when there is no clinical diagnosis of a particular condition associated.
• Psychosocial Stress: Anxiety, poor sleep, and life challenges can trigger central sensitization, reducing the threshold for pain perception.
• Environmental Stress: Factors like temperature, air quality, toxins in food and other household products, or prolonged exposure to light at night can indirectly heighten the load on the system.

These non-biomechanical factors may not cause MSK pain directly but add to the cumulative load, leaving the body more vulnerable to biomechanical stressors.

Overflow Without an Event
A common experience with unexplained MSK pain is its seemingly spontaneous onset—pain arises without an obvious injury or change in activity. This can happen when the bucket overflows, even if the last "drop" appears insignificant.

Examples include:

• Pain after a poor night's sleep or heightened emotional stress, despite no physical trauma.
• Onset of pain in a previously pain-free region due to systemic stressors, like illness, nutritional deficiencies or psychological and emotional stress triggered but an experience or interaction with colleagues, friends, family or even a stranger for example.
• Central sensitization, where the nervous system amplifies signals, creating pain even in the absence of tissue damage.

The bucket metaphor reframes the idea that MSK pain must have a direct biomechanical cause, highlighting how cumulative, unseen factors play a role.

Physical Therapy and the Bucket Principle
Physical therapy is uniquely positioned to address MSK pain by both managing the current bucket load and building capacity to prevent future overflows.

Reducing the Load
Therapists can help patients identify and alleviate stressors:

• Biomechanical Adjustments: Improving posture, ergonomics, and movement patterns.
• Systemic Interventions: Guiding recovery strategies like adequate hydration, sleep hygiene, and anti-inflammatory approaches such as basic dietary advice for example.
• Psychosocial Support: Encouraging stress management techniques such as mindfulness, breathing and progressive relaxation exercises.

Expanding the Bucket
Therapeutic interventions can enhance the body’s resilience by building reserves:

• Graded Exercise Therapy: Gradually strengthening muscles and tissues to improve tolerance to stress.
• Education on Energy Conservation: Teaching pacing strategies for chronic conditions like ME/CFS or fibromyalgia.
• Improving Recovery: Incorporating tools like foam rolling, stretching, or hydrotherapy to optimise tissue health.

Unexplained MSK Pain: A Systems Perspective
Unexplained pain doesn’t arise out of nowhere, it reflects a system under strain. By acknowledging the interplay of biomechanical, systemic, and psychosocial factors within the bucket principle, therapists can move beyond symptom-focused treatments.

​Key Takeaways:

• Pain is Multifactorial: Unexplained MSK pain often results from cumulative stressors rather than a single event.
• Systemic and Psychosocial Factors Matter: They influence pain perception and tissue resilience, even in the absence of clear physical damage.
• Prevention is Key: Managing stressors and building reserves reduces the risk of overflow and chronic pain.

By applying the bucket principle, physical therapists can provide more holistic care, empowering patients to navigate and balance their stress loads for long-term health. Don’t hesitate to come and see one of our experienced therapists at Simple Wellness Myotherapy and Osteopathy and find out how we can help you today, book your appointment today.