Introduction to the Windlass Mechanism and Its Role in Gait
Phases of Gait: Contextualising the Windlass Mechanism
To fully appreciate the Windlass Mechanism, it is essential to understand its role within the gait cycle. The gait cycle consists of two main phases: the stance phase (when the foot is in contact with the ground) and the swing phase (when the foot moves through the air to prepare for the next step). The Windlass Mechanism plays its most active role during the stance phase.
The Windlass Mechanism is a critical biomechanical process in the foot, first described by John Hicks in 1954, that plays an essential role in effective locomotion during walking and running. It involves the tightening of the plantar fascia, a fibrous band running along the sole of the foot, as the toes dorsiflex (bend upwards). This tightening causes the arch of the foot to rise and the foot to stiffen, converting it into a rigid lever for efficient push-off. The Windlass Mechanism is crucial in the later phases of the gait cycle, particularly in creating stability and propulsion, making it a vital aspect of human movement mechanics.
1. Stance Phase (60% of the Gait Cycle)
The stance phase, which occupies about 60% of the gait cycle, begins at heel strike (initial contact) and continues until toe-off. This phase is where the Windlass Mechanism is most engaged, especially during the transition from mid-stance to toe-off.
• Heel Strike (Initial Contact): The foot initially strikes the ground, and the body’s weight begins to transfer onto it. At this early point, the plantar fascia begins to preload, though the Windlass Mechanism is not fully engaged yet. This preloading is critical, as it prepares the fascia to handle the increasing forces it will encounter as the body moves forward.
• Loading Response: As the body’s weight shifts further onto the tripod in the foot, the plantar fascia elongates, absorbing the force. Although the Windlass Mechanism remains relatively inactive during this part of the stance phase, tension continues to build in the plantar fascia. This is when the foot is absorbing the load in loading response.
2. Midstance to Toe-Off
The Windlass Mechanism becomes fully engaged as the foot moves from midstance to toe-off.
• Midstance: At midstance, the body’s weight is fully supported by the foot. The plantar fascia elongates to its maximum length, absorbing the ground reaction forces and distributing them through the foot. The MTP (metatarsophalangeal) joint remains relatively neutral, but as the body moves forward, this joint begins to plantar flex from a dorsiflexed position.
• Terminal Stance and Pre-Swing (Toe-Off): As the digits dorsiflex, the Windlass Mechanism is activated. The metatarsophalangeal joints (MTP) plantar flex, causing the plantar fascia to tighten. This action raises the arch of the foot and turns the foot into a rigid lever, preparing it for the propulsion required during toe-off. The foot becomes supinated, allowing for efficient energy transfer as the body pushes off the ground.
3. Swing Phase (40% of the Gait Cycle)
The swing phase, during which the foot is off the ground, accounts for the remaining 40% of the gait cycle. The Windlass Mechanism is largely inactive during this phase since the foot is no longer bearing weight or engaging in ground contact. The plantar fascia returns to a more relaxed state, preparing to engage again in the next stance phase.
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Kinetic and Kinematic Contributions of the Windlass Mechanism
The Windlass Mechanism plays a crucial role in not only stabilizing the foot but also influencing the entire kinetic chain of the lower limb. The plantar fascia acts like a spring, storing and releasing energy as the foot moves through the gait cycle. During the push-off phase, the tightening of the fascia and the subsequent rise of the arch increase foot rigidity, allowing for efficient propulsion.
This spring-like action contributes to energy efficiency in walking and running. By enhancing foot rigidity during push-off, the Windlass Mechanism minimizes the muscular effort required to move forward. Studies have demonstrated that a properly functioning Windlass Mechanism allows the body to recycle energy stored in the plantar fascia, reducing the overall metabolic cost of walking and running (Hicks, 1954). This energy efficiency is particularly evident during prolonged activities like running, where the body’s ability to conserve energy becomes crucial.
Clinical Relevance: Pathologies and Windlass Dysfunction
Understanding the Windlass Mechanism’s role in gait is critical for diagnosing and treating various foot pathologies. Dysfunction in this mechanism can lead to a range of issues, including:
• Plantar Fasciitis: One of the most common foot pathologies, plantar fasciitis is often associated with improper activation of the Windlass Mechanism. When the plantar fascia is overworked or fails to engage properly during the stance phase, it can become inflamed, leading to heel pain, particularly after periods of rest or inactivity.
• Metatarsalgia: Improper foot mechanics that disrupt the Windlass Mechanism can also cause strain on the metatarsals (the bones in the midfoot), leading to pain and inflammation in the ball of the foot.
• Achilles Tendinopathy: Dysfunction in the Windlass Mechanism can also result in excessive strain on the Achilles tendon, as the foot’s inability to become rigid during push-off forces the tendon to compensate.
Windlass Test
The Windlass Test: Diagnostic Tool
The Windlass Test is a clinical diagnostic tool used to assess the functionality of the Windlass Mechanism. The test involves passively dorsiflexing the toes while observing the arch of the foot. A positive test, indicated by pain or an absence of the expected arch rise, external rotation of the ankle suggests issues with the Windlass Mechanism, such as plantar fasciitis or other structural abnormalities in the foot (McPoil & Hunt, 1995).
Recent Research and Advanced Theories
Recent studies have deepened our understanding of the Windlass Mechanism. Some research has suggested that the plantar fascia may begin to preload earlier than previously thought, even during heel strike. This challenges the long-standing belief that the Windlass Mechanism is only activated during toe-off. Studies also highlight that the Windlass Mechanism is not solely responsible for foot rigidity—active muscle contraction also contributes significantly, particularly during high-impact activities like running (Pataky et al., 2008).
Interventions for Windlass Dysfunction
Several interventions can be employed to restore proper function of the Windlass Mechanism:
• Strengthening Exercises: Strengthening the plantar fascia and surrounding muscles is critical for enhancing the foot’s ability to engage the Windlass Mechanism effectively.
• Gait Retraining: Modifying foot posture and movement patterns during walking can help ensure that the Windlass Mechanism engages at the appropriate time during the stance phase.
• Orthotic Devices: Temporary orthotic devices can provide support to the arch and plantar fascia, redistributing forces and aiding in the restoration of normal foot mechanics. But temporary is the key here.
Conclusion
The Windlass Mechanism is a vital component of foot biomechanics, playing a central role in stabilising the foot and enabling efficient propulsion during walking and running. By converting the foot into a rigid lever during the latter stages of the stance phase, it contributes to overall energy efficiency and movement effectiveness. Understanding how the Windlass Mechanism functions, as well as recognising the clinical implications of its dysfunction, is essential for diagnosing and treating foot pathologies. As research continues to evolve, health professionals are gaining new insights into how this mechanism interacts with other elements of gait, enhancing the ability to provide targeted treatments for improved mobility and reduced pain.
References
• Hicks, J. H. (1954). The mechanics of the foot. II. The plantar aponeurosis and the arch. Journal of Anatomy, 88(1), 25-30.
• McPoil, T. G., & Hunt, G. C. (1995). Evaluation and management of foot and ankle disorders: Present problems and future directions. Journal of Orthopaedic & Sports Physical Therapy, 21(6), 381-388.
• Pataky, T. C., Caravaggi, P., & Savage, R. (2008). Regional peak plantar pressures during gait. Journal of Biomechanics, 41(9), 2036-2039.
• Richie, D. H., & Keeley, J. A. (2021). Advances in understanding the mechanics of the Windlass mechanism. Foot and Ankle International.