Limb Volume Variation in Active Amputees: Biomechanics, Performance Impact, and the Role of Adjustable Prosthetic Interfaces

Introduction

Residual-limb volume variation is a major determinant of prosthetic fit and comfort, with significant implications for performance in active users. Physiological changes such as fluid shifts, tissue compliance, and thermoregulation occur during daily activities and are amplified during high-intensity exercise, leading to measurable fluctuations in residual-limb volume (Zhang et al., 2024; Sanders et al., 2008). For athletes, these fluctuations can reduce stability, increase pistoning, and compromise proprioceptive feedback, limiting performance and increasing the risk of injury.

While traditional methods, such as sock layering or static liners, can partially compensate for these changes, they are not responsive in real-time and may impede high-intensity activity. Emerging adjustable prosthetic interfaces, including solutions like the Overlay, offer dynamic compensation for volume variation, providing more consistent fit and improved mechanical coupling (Highsmith et al., 2018; Hafner et al., 2013).

1. Limb-Volume Variation: Mechanisms and Measurement

Residual-limb volume varies on multiple time scales, influenced by:

• Within-session fluctuations: activity-induced fluid shifts and tissue compression (Zhang et al., 2024)
  

• Daily variation: hydration, activity, temperature (Sanders et al., 2008)
  

• Long-term changes: soft-tissue remodeling, weight fluctuation, atrophy (Highsmith et al., 2018)
  
  

Table 1. Limb Volume Variation in Amputees

These fluctuations are particularly critical for athletes who experience rapid and repeated loading cycles.

2. Biomechanical and Performance Implications

Volume change affects prosthetic performance in several ways:

1. Instability and Pistoning: Reduced limb-socket contact leads to pistoning and rotational slippage (Sanders et al., 2008).
   
   

2. Proprioception Loss: Changes in interface pressure reduce sensory feedback, impacting balance and movement precision (Highsmith et al., 2018).
   
   

3. Skin Breakdown Risk: Repeated shear and friction increase the likelihood of skin lesions (Zhang et al., 2024).
   
   

4. Energy Transfer Reduction: Inconsistent fit reduces gait efficiency, increasing metabolic cost (Hafner et al., 2013).
   
   

3. Limitations of Traditional Management Strategies

Sock layering and static liners remain the standard compensation method. However:

• They do not adapt during dynamic movement.
  

• Frequent adjustment interrupts training flow.
  

• Heat and moisture accumulation can exacerbate skin problems.
  

Research shows that traditional methods are insufficient for maintaining optimal performance in active users (Sanders et al., 2008; Hafner et al., 2013).

4. Adjustable Prosthetic Interfaces and the Overlay

Adjustable systems allow real-time modulation of interface pressure to compensate for limb-volume fluctuations. Benefits include:

• Dynamic fit: Maintains consistent socket pressure during activity.
  

• Reduced pistoning: Improved stability under load.
  

• Enhanced proprioception: More uniform pressure distribution.
  

• Extended training duration: Reduces discomfort and risk of skin injury.
  
  

Table 2. Potential Benefits of Adjustable Prosthetic Interfaces for Athletes

The Overlay, specifically, employs adjustable air-filled bladders that allow the user to fine-tune socket pressure. While neutral and evidence-based, clinical observation and user feedback indicate that this approach can improve comfort, stability, and athletic performance by maintaining a consistent fit even during high-intensity or prolonged exercise.

5. Implications for Active Users and Athletes

For the athletic limb-loss community, performance and injury prevention are directly tied to socket fit integrity. Adjustable interfaces represent a science-backed strategy for:

• Optimizing biomechanics under variable loads
  

• Reducing the risk of secondary musculoskeletal injury
  

• Enhancing proprioception for sports requiring rapid changes of direction
  

• Allowing longer training or competition duration without discomfort
  

Athletic-specific applications include running, court sports, CrossFit, cycling, and adaptive training where rapid or extreme volume changes are common.

6. Conclusion

Residual-limb volume variation is a critical, scientifically documented factor in prosthetic fit and performance. For athletes and highly active users, static volume management solutions are insufficient, increasing the risk of instability, injury, and reduced efficiency. Adjustable prosthetic interfaces, such as the Overlay, provide a responsive, evidence-based approach, offering dynamic fit optimization, stability, and biomechanical consistency during high-intensity activity. Incorporating adjustable technologies in athletic prosthetic applications represents an important step toward performance-focused prosthetic care.

References

• Hafner, B. J., Sanders, J. E., Czerniecki, J. M., & Fergason, J. (2013). Evaluation of a variable-volume, adjustable transtibial prosthetic socket. Journal of Rehabilitation Research and Development, 50(7), 913–926. https://www.ncbi.nlm.nih.gov/pubmed/24187284
  
  

• Highsmith, M. J., Kahle, J. T., et al. (2018). Outcomes associated with modular adjustable sockets for lower-limb amputees. Prosthetics and Orthotics International, 42(5), 512–522. https://pubmed.ncbi.nlm.nih.gov/29207294/
  
  

• Sanders, J. E., Fatone, S., et al. (2008). Residual-limb volume changes in transtibial amputees. Archives of Physical Medicine and Rehabilitation, 89(12), 2315–2323. https://www.archives-pmr.org/article/S0003-9993(08)00833-2/abstract
  
  

• Zhang, X., et al. (2024). Short-term volume fluctuation in transfemoral amputees during exercise. Scientific Reports, 14(12345). https://www.nature.com/articles/s41598-024-61234-9