The human foot is a highly specialized structure that must be both flexible and stable during gait. One of the most important biomechanical features contributing to this dual role is the windlass mechanism, a process by which dorsiflexion of the hallux tightens the plantar fascia, elevates the medial longitudinal arch, and assists with foot rigidity during propulsion. Jack’s test, also known as the Hubscher manoeuvre, is a clinical assessment designed to observe this mechanism in action. By passively dorsiflexing the hallux and watching for an increase in arch height, the examiner can gain insight into the integrity of the plantar fascia, first metatarsophalangeal joint function, and the overall flexibility of the foot.
The windlass mechanism is fundamental to normal foot biomechanics. When the hallux dorsiflexes, the plantar fascia wraps around the metatarsal head like a rope around a windlass, shortening the distance between the calcaneus and the metatarsal heads and tightening the plantar aponeurosis. This tension raises the medial arch and increases foot stiffness, which is especially important during the push-off phase of gait. In this way, the foot transitions from a mobile adaptor during early stance to a rigid lever during propulsion. Without an effective windlass mechanism, the foot may remain overly compliant, potentially impairing efficient load transfer and increasing strain on soft tissues.
Jack’s test is commonly performed in a weight-bearing position, though variations exist in the literature and clinical practice. Typically, the examiner asks the patient to stand while dorsiflexing the hallux at the first metatarsophalangeal joint. In a normal response, the medial longitudinal arch rises as the hallux is lifted, reflecting activation of the windlass mechanism. A delayed, absent, or limited arch rise may suggest reduced plantar fascial tensioning, first ray dysfunction, or altered foot mechanics. Clinicians may also use the test to observe rearfoot behaviour, subtalar joint alignment, and the relationship between hallux motion and arch function.
One of the principal clinical uses of Jack’s test is the assessment of flatfoot deformity. In individuals with pes planus, the manoeuvre may help distinguish a flexible flatfoot from a rigid one. If the arch rises normally during hallux dorsiflexion, the deformity is more likely flexible, suggesting that the foot still retains functional support through passive structures. If the arch remains collapsed despite hallux extension, the foot may be rigid or structurally constrained, which can indicate more significant pathology. This distinction matters because flexible and rigid deformities have different prognoses and management strategies.
The test is also useful in the broader examination of arch mechanics and foot posture. Some authors describe Jack’s test as a way to estimate the efficacy and integrity of the windlass mechanism rather than as a definitive diagnostic tool. It can be used to observe how much force is required to initiate arch rise, and this varies considerably among individuals. In some feet, the arch rises with minimal hallux dorsiflexion, while in others a greater degree of motion or force is needed. This variability reflects differences in plantar fascia compliance, first MTP joint mobility, foot type, and possibly the influence of footwear or orthotic support.
From a biomechanical perspective, Jack’s test is attractive because it is simple, quick, and visually intuitive. It provides immediate feedback about how hallux dorsiflexion influences the arch and can help the clinician explain foot function to patients or parents. It is especially useful in paediatric practice, where visual demonstration of arch mechanics may improve understanding and engagement. However, the test should be interpreted cautiously. It reflects static or quasi-static mechanics, not the full complexity of dynamic gait. A foot may appear to respond normally in Jack’s test yet behave differently during walking or running, when muscle activity, load magnitude, speed, and timing all influence function.
Another important limitation is that Jack’s test does not isolate a single structure. Although it is often framed as a test of the plantar fascia, the observed response is shaped by the first MTP joint, first ray mobility, midfoot stiffness, rearfoot position, and neuromuscular control. For example, reduced dorsiflexion at the first MTP joint may alter the apparent response, and excessive midfoot mobility may blur the distinction between normal and abnormal arch elevation. As a result, the test should be used as part of a broader biomechanical assessment rather than in isolation.
Recent research continues to explore the mechanics and measurement of the windlass phenomenon. A 2024 biomechanical study examined Jack’s test in barefoot standing and confirmed that hallux dorsiflexion is closely linked to windlass activation, arch height change, and rearfoot behaviour. Other clinical commentary notes that the amount of force needed to establish the windlass can vary substantially and may be altered by interventions such as orthoses or biomechanical socks. These findings reinforce the idea that Jack’s test is not simply a yes-or-no assessment, but a window into the dynamic behaviour of the foot’s passive support system.
In clinical practice, Jack’s test has value because it links anatomy, function, and observation in a single manoeuvre. It can support the assessment of flatfoot, hallux-related mechanics, plantar fascia behaviour, and propulsion efficiency. When interpreted thoughtfully, it helps clinicians understand whether the medial arch can tighten appropriately when the hallux is dorsiflexed, which is central to the windlass mechanism. At the same time, its findings must be integrated with history, observation, range of motion testing, and gait analysis to avoid overinterpreting a single static sign.
Jack’s test remains a valuable and widely recognised clinical assessment of the windlass mechanism in the foot. Its strength lies in its simplicity and its ability to demonstrate the functional link between hallux dorsiflexion and arch elevation. Its main limitation is that it represents only one part of a complex biomechanical system, so it should be interpreted as part of a comprehensive foot and lower-limb examination. Used well, Jack’s test offers important insight into foot flexibility, plantar fascial function, and the mechanics that support efficient human gait.