Doesn't your competent? doctor already have the EXACT rehab protocols to fix your dorsiflexion problems? After they have objectively defined the damage that caused the dorsiflexion problems? Oh, they didn't do an objective damage diagnosis either?
The ankle dorsiflexion kinetics demand to increase swing phase foot-ground clearance: implications for assistive device design and energy demands
Journal of NeuroEngineering and Rehabilitation volume 21, Article number: 105 (2024)
Abstract
Background
The ankle is usually highly effective in modulating the swing foot’s trajectory to ensure safe ground clearance but there are few reports of ankle kinetics and mechanical energy exchange during the gait cycle swing phase. Previous work has investigated ankle swing mechanics during normal walking but with developments in devices providing dorsiflexion assistance, it is now essential to understand the minimal kinetic requirements for increasing ankle dorsiflexion, particularly for devices employing energy harvesting or utilizing lighter and lower power energy sources or actuators.
Methods
Using a real-time treadmill-walking biofeedback technique, swing phase ankle dorsiflexion was experimentally controlled to increase foot-ground clearance by 4 cm achieved via increased ankle dorsiflexion. Swing phase ankle moments and dorsiflexor muscle forces were estimated using AnyBody modeling system. It was hypothesized that increasing foot-ground clearance by 4 cm, employing only the ankle joint, would require significantly higher dorsiflexion moments and muscle forces than a normal walking control condition.
Results
Results did not confirm significantly increased ankle moments with augmented dorsiflexion, with 0.02 N.m/kg at toe-off reducing to zero by the end of swing. Tibialis Anterior muscle force incremented significantly from 2 to 4 N/kg after toe-off, due to coactivation with the Soleus. To ensure an additional 4 cm mid swing foot-ground clearance, an estimated additional 0.003 Joules/kg is required to be released immediately after toe-off.
Conclusion
This study highlights the interplay between ankle moments, muscle forces, and energy demands during swing phase ankle dorsiflexion, offering insights for the design of ankle assistive technologies. External devices do not need to deliver significantly greater ankle moments to increase ankle dorsiflexion but, they should offer higher mechanical power to provide rapid bursts of energy to facilitate quick dorsiflexion transitions before reaching Minimum Foot Clearance event. Additionally, for ankle-related bio-inspired devices incorporating artificial muscles or humanoid robots that aim to replicate natural ankle biomechanics, the inclusion of supplementary Tibialis Anterior forces is crucial due to Tibialis Anterior and Soleus co-activation. These design strategies ensures that ankle assistive technologies are both effective and aligned with the biomechanical realities of human movement.
Background
Gait impairments that increase the risk of tripping-related falls are one of the most serious consequences of ageing, stroke and many neurological and muscular conditions such as spinal cord injury, multiple sclerosis, muscular dystrophy or cerebral palsy [1,2,3]. In normal gait, the swing phase is shaped by two events, ‘Mx1’ and ‘Mx2’, representing two vertical foot displacements maxima that frame a critical moment of Minimum Toe Clearance (MTC) or Minimum Foot Clearance (MFC) (Fig. 1). MTC refers to the toe’s clearance above ground, while MFC measures the lowest part of the forefoot or shoe’s clearance from the ground. Avoiding contact with walking surface irregularities requires precisely modulated vertical displacement of the foot, especially at the swing phase Minimum Foot Clearance (MFC) event [4,5,6].
Ankle dorsiflexion is crucial for elevating the foot during swing by enabling substantial adjustments to ground clearance with relatively minor changes in ankle angles and minimal disruption to overall gait control [6,7,8]. The development of assistive technology for ankle joint dorsiflexion could play an important role in maintaining safe ground clearance and preventing tripping-related falls. Rapid progress has been observed in the development of ankle orthoses, employing advanced actuators to apply moments that can effectively assist impaired ankle dorsiflexion [9,10,11]. An essential requirement of these devices is to deliver sufficient mechanical power to ensure the necessary magnitude of ankle assistive moments. Understanding the kinetics demands of ankle joint dorsiflexion is, therefore, particularly useful for devices employing energy harvesting or utilizing lighter but also less power-demanding actuators. This understanding is the foundation for designing assistive technologies that harmonize the required ankle moments with required energy inputs.
Ankle dorsiflexion moments have been determined experimentally but more commonly in static conditions, rather than when walking. Takaiwa & Noritsugu (2008) [12] determined that 2 N.m ankle moment was required to achieve 20 degrees of ankle dorsiflexion, i.e. from − 15 degrees plantar flexion to + 5 degrees dorsiflexion. A University of Illinois design team adopted Perry and Burnfield’s (1993) [13] data to calibrate their powered AFO, employing a constant 3 N.m ankle torque throughout swing [11, 14,15,16]. Such time-dependent ankle moment measurements recorded dynamically are anticipated to be more useful in designing ankle assistive devices to more closely mimic natural gait. Kao and Ferris, (2009) [17] and Sawicki and Ferris, (2009) [18] used inverse dynamics to estimate ankle dorsiflexion moments at 1.25 m/s. They found a maximum ankle moment following toe-off of 0.016 N.m/Kg which decreased gradually until end of swing; with an ankle power range of -0.08 W/Kg to 0.05 W/Kg. Their study did not include ankle moment and power changes with increasing ankle dorsiflexion but this control feature may be useful in revealing the kinetics of high ankle dorsiflexion rotation to determine the required adequate mechanical energy input.
Consistent with the traditional focus on stance kinetics there are limited data to show ankle joint energy exchanges during swing, possibly because swing phase energy requirements are often considered less important components of lower limb joint kinetics [19, 20]. More recently it has, however, been argued that the energy consumed during swing is non-trivial, with research by Doke et al. (2005) [21] concluding that swing phase muscle activity consumes between one-quarter to one-third of total gait energy. Exploring joint work is important for understanding the mechanical energy demands of walking because joint mechanical energy is associated with the ability to perform work [22,23,24]. Ankle work can, therefore, be calculated to indicate the maximum energy demands of swing phase ankle dorsiflexion. In the study reported here we sought to determine the kinetic requirements of increasing swing phase ankle dorsiflexion by incorporating a treadmill-walking condition in which foot-ground clearance was manipulated via a continuous foot trajectory display. Subsequently, we derived the swing-phase profile of ankle joint moments and the power demands of augmenting ankle dorsiflexion.
Previous investigators have often described three swing sub-phases representing approximately 0–35%, 35–65%, and 65–100% of the swing cycle, corresponding to Initial, Mid, and Terminal swing, respectively (Fig. 1) [13, 25]. Unusual or pathological gaits may not, however, always be described adequately using these sub-phases [26] and investigation of time-dependent variables such as joint power may also require a more fine-grained analysis [27].
To explore functional variations in ankle energy demands with greater specificity, in this study we introduced three new event-dependent swing sub-phases and also calculated the time and power demands of each (Fig. 1).
In addition to determining ankle joint mechanics, foot-ankle computational modelling has been used to quantify force and power of the Tibialis Anterior (TA) as the primary dorsiflexor. A systematic review of twelve studies indicated maximum swing TA forces ranging from 1 to 4 N/kg at preferred walking speed [28] but there are important variations within sub-phases. Błażkiewicz (2013) [29] found a maximum TA force of 2 N/kg following toe-off and TA power computed by Bogey et al. (2010) [30] reached an initial negative peak of almost − 2 Watts, followed by a positive maximum of 12 Watts; those data were, however, time-normalized to the swing cycle, precluding a post-hoc work calculation. Possibly because the TA is the primary dorsiflexor, less research attention given to other ankle dorsiflexor muscles, i.e., Extensor Digitorum Longus (EDL) and Extensor Hallucis Longus (EHL). In addition to providing a more complete description of dorsiflexor kinetic contributions to ankle swing phase control, in this experiment the kinetic contributions of these three muscles were also derived.
Our objective in this study was to investigate ankle joint moments, dorsiflexor muscle forces and mechanical energy requirements of increasing swing phase ankle dorsiflexion, specifically at the high-risk Minimum Foot Clearance (MFC) event. By experimentally manipulating foot-ground clearance using a continuous feedback display, the timing and magnitude of ankle dorsiflexor moments, forces and work were modelled in response to a controlled increment in ankle dorsiflexion. It was hypothesized that relative to an unconstrained-walking control condition, greater ankle dorsiflexion would require higher ankle moments and power with increased dorsiflexor muscle forces and work.
Our findings on ankle joint and dorsiflexor muscle kinetics offer critical insights for enhancing ankle assistive technologies. Rather than increasing ankle moments, our study suggests that assistive devices should focus on providing higher mechanical energy for effective dorsiflexion. This is particularly vital for bio-inspired devices incorporating artificial muscles, where accommodating the co-activation of Tibialis Anterior and Soleus at higher dorsiflexion angles is key. These insights aim to guide the development of more efficient ankle orthoses and exoskeletons.
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