Mission

Locomotion along non-straight trajectories

1. Changing direction while walking is a typical activity in daily life, necessary to perform basic functional activities such as turning around a table or walking a curved path along a footpath. A successful turn requires effective coordination between the movements of the lower limbs and those of the trunk and pelvis.
2. When walking along a curved trajectory, particularly with limited radii of curvature, asymmetric changes in the stride length of the two limbs occur (the stride of the leg towards the inside of the curve is shorter as a function of the angle of curvature, while the stride of the outer leg has a comparable length to when walking linearly at the same speed, see page 7) and ground reaction forces (which control the direction of the walk) are appropriate to orient the body in the new direction (Courtine and Schieppati, 2003; Turcato et al. , 2015).
3. Minimal but essential changes in postural reactions (such as mid-lateral trunk tilt) are also required to adjust walking speed when the turn is initiated (Turcato et al., 2015). These synergies lead to a critical body position tilted inwards in order to prevent the body from being ‘thrown’ outwards from the desired path by the centrifugal force caused by the execution of the curved trajectory.
4. Two important functions are therefore called upon: the control of posture and balance on the one hand (Brinkerhoff et al., 2023) and the control of the asymmetry of the steps of both legs on the other. The segment represented by the trunk and pelvis is the one that allows the execution of effective changes of direction while walking. Furthermore, rotation (intra- and extra-rotation of the legs) is possible thanks to the coxo-femoral joint on which numerous muscles insist (Figure 1 below).

Execution of curved trajectories is not trivial

5. It is well known that changing direction during walking is difficult in patients with Parkinson’s disease, who often stop or start taking small steps before changing direction (Guglielmetti et al., 2009; Turcato et al., 2018; Godi et al., 2019) or rotate slowly ‘en-bloc’ (Mellone et al., 2016). In Parkinson’s disease, prolonged exercise leads to greater mobility and allows the learning of strategies to control the body’s rotational movement and the necessary postural adjustments (Godi et al., 2017), including those affecting the trunk (Carpenter et al., 1999), controls that are progressively lost as the disease progresses. Turning slowly results in similar alterations in eye movements, rotation kinematics and gait characteristics in the group with PD and in healthy controls (Mancini et al., 2015). Training using different turning directions and speeds can improve coordination, as well as increase confidence and reduce the risk of falling (Khobkhun et al., 2022).
6. Stroke patients present walking disorders due to damage to motor and sensory pathways. Patients with hemiparesis due to a cerebral vascular accident also have incorrect postures and problems in walking in curved trajectories (Godi et al., 2010; Chisholm et al., 2015; Jin et al., 2023), as well as having obvious problems in foot positioning during even linear walking due to the general unstable gait pattern. These patients present asymmetry of the lower limbs due to the lack of control of muscle activation and cannot easily support their weight on the paretic leg inside the curvature. Disturbances in the synchronism of coordination between the lower limbs are indicators of stability control during walking (Singer et al., 2013).

Even young disabled people have problems changing direction

7. The strategy of changing direction during walking is also altered in children with infantile cerebral palsy (Dixon et al., 2014; Brégou-Bourgeois et al., 2014). Recently, differences in energy expenditure of walking with turns compared to a linear walk have been measured in children (Crossley et al., 2018). There are indications that (linear) walking in cerebral palsy patients can be partly improved if intensive coordination dynamics therapy is administered for 1 to 2 years (Schalow and Jaigma, 2005) including by means of exoskeletons (Patanè et al. 2017), but no effects on direction changes are known. For more details, see (Cappellini et al., 2020). Incorrect relationships of the bone anatomy cause a decrease in muscle power, because the corresponding muscles do not work in the plane for which they were designed. This makes the muscle less efficient and causes the patient to spend more energy walking (Novacheck and Gage, 2007; Böhm and Döderlein, 2012) and complicates coordination between motor synergies. Similarly, stepping exercises (stepping on and off a step) have been recommended for children with motor coordination disorders (Inacio et al., 2023), but these exercises appear to be very poor at promoting coordination of more common and more complex movements. Instead, exercises focused on the trunk seem to have a better effect (Pierret et al., 2023; van Dellen et al., 2023). It has recently been shown that dynamic postural stability does not fully mature until the age of 10 years or more (Mani et al., 2021), suggesting that an intervention such as the one described below (the rotating platform on which one walks in place, see Figure 2) may also work well in children with infantile cerebral palsy.

The public health problem

8. Steps occurring during turning represent approximately 35-40% of all steps in a typical day for a normal adult subject; the daily number of steps in turning increases when in confined spaces such as in a flat. Aging people change direction less efficiently, as evidenced by the degradation of kinematics and neuro-muscular modulation (Baird and Van Emmerik, 2009; Robinovitch et al., 2013; Asmidawati et al., 2014). In the elderly, systematic reviews of the literature have established that exercise reduces falls, but the most effective types of exercise are unknown (Lord and Close, 2018; Sibley et al., 2021). The frequency of falls increases in the elderly with rotation impairment. Falls during rotation are responsible for eight times more hip fractures than during walking along a straight path (Cumming and Klineberg, 1994; Thigpen et al., 2000; Almajid et al., 2020). It has been suggested that measures of turn-based gait production efficacy predict (and may prevent) recurrent falls in community-dwelling older adults (Leach et al., 2018). It is worth mentioning the enormous social and economic cost of fall-related fractures (Veronese and Maggi, 2018). There is a recent paper on ‘Frailty in Italy’ (Vetrano, 2022) and another equally recent one by the World Health Organisation on the need for rehabilitation in Europe, which highlight the problems related to these needs (Health Workforce and Service Delivery, 2022).

Physiology of curved walking

9. The muscles responsible for the rotation of the lower limb along the longitudinal axis are the pelvic muscles, which rotate the femur in its coxo-femoral joint (Figure 1, A and B). These muscles are numerous and require special coordination (Ventura et al., 2015). The pelvis in turn pivots on the supporting leg and the trunk pivots on the pelvis, causing the body, including the neck and head, to be properly oriented to the walking trajectory to be executed.
10. Coordination between the neural commands directed to the pelvic muscles (which are asymmetrically active during the walk between the right and left leg) and to the muscles of the spine is critical for the correct execution of the curved trajectory.
11. The weight of the body, whose centre of mass is approximately on the vertical of the trajectory of the inside foot (or even towards the centre of the curve, outside the distance between the foot supports) requires that the pelvis and spine muscles are able to produce adequate forces to maintain dynamic balance during the execution of the path along a curved trajectory.

Prevention and Rehabilitation

12. It therefore seems appropriate to design a physical treatment capable of exercising the intra- and extra-rotator muscles of the leg on the pelvis in a manner consistent with their function during curved walking.
13. This activity is aimed at stimulating neuro-muscular coordination and at the same time strength development in the aforementioned muscles. Indeed, it is known that sensory information about the ongoing movement from intramuscular receptors provides an important input for learning and reinforcing the execution of a certain movement (Ziemann et al., 2001; Rosenkranz and Rothwell, 2012). The ability to ‘learn’ appropriate co-ordination through the use of the rotating platform is evidenced by the persistence of turning on oneself while walking in place with eyes closed (i.e. without visual spatial reference) after the rotating platform has stopped (Sozzi and Schieppati, 2016).
14. It is necessary to address the issue of strengthening and coordination of the muscles responsible for intra- and extra-rotation of the lower limbs, both for a) preventive purposes i.e. to reduce the likelihood of falls due to insufficient strength development in sedentary elderly and frail subjects (Álvarez-Millán et al, 2023), for b) rehabilitative purposes (rehabilitation of impaired or slow gait for problems related to neurodegenerative diseases) or c) therapeutic purposes (restoration of locomotor function along non-linear paths after hip or pelvic fractures (Fox et al., 1998; Damm et al., 2018). Incidentally, muscle and coordination strengthening is also appropriate prior to hip replacement surgery (Fairhall et al., 2022).
15. Despite the wealth of known physiotherapeutic exercises and the use of the corresponding equipment, which are offered in a hospital or community setting or at home (independently or guided), there is no simple instrument on the market that a) can stress activities normally neglected during conventional rehabilitation treatment, b) can be used by the healthy or elderly or frail individual with the ease and safety with which he or she uses an exercise bike or a simple treadmill.
16. Until now, a frequently used device has been the normal linear treadmill. An evolution of the normal treadmill is the so-called ‘split-belt’ treadmill, in which the bands move at different speeds, producing an asymmetrical path – but always in a straight line. For example, in Parkinson’s disease, the ‘split-belt’ treadmill has been used but did not produce appreciable results in post-treatment walking (Hulzinga et al., 2023).
17. There are also complex, wearable, motorised exoskeletons, which are innovative devices that can aid activities of daily living – but the production of curved gait is not envisaged (Wright et al., 2023). Furthermore, they are not widely adopted in clinical settings due to the ‘disconnect’ between the needs of exoskeleton users and the needs of the engineers designing the devices (Morris et al., 2023), as well as entailing a number of risks that are not always evaluated (Massardi et al., 2023). They may be considered as aids rather than re-enabling devices, but they still do not address the problem of coordinating movements to promote or produce gait rotation when turning (Ivanenko et al., 2023), a problem that is instead specifically addressed by the device proposed here. Several exoskeletons fix the pelvis and limit mediolateral movements. However, mediolateral displacements of the centre of mass towards the supporting leg are a crucial component of normal gait. In physiological gait, this is achieved with a sinusoidal trajectory of the pelvis, while the thorax is kept relatively stable above it.
18. In none of the above cases is it possible to intervene on the intra- and extra-rotation of the legs, let alone the complex control of posture and balance that necessarily accompanies the production of turns or walking on curved trajectories. Walking on the spot rotating on oneself along the vertical axis of the body represents a specific condition that favours dynamic control of posture and coordination between the legs and trunk. Furthermore, it represents a way to foster coordination between pelvis and trunk in the most natural way possible (van Dellen et al., 2023). The rotating platform on which one walks in place with the centre of mass placed approximately along the vertical of the body and the feet marching around the centre of curvature allows intra- and extra-rotation of the legs avoiding any head rotation and vestibular stimulation that causes disorientation, dizziness, imbalance and falls.

Fitness, training, sport rehabilitation

19. In sports, it is relevant to consider that the exercise imposed by the rotating platform can last for an indefinite period of time decided by the coach or the athlete himself, leading to optimal development of the muscles involved and optimal coordination of the pelvic musculature with the trunk and lower limb musculature. An instrument capable of imposing rotations at different speeds while walking on the spot appears essential for training Repeated Sprint Ability in football, for example. Examples of other sports activities that involve rotational movements on oneself are basketball, discus and hammer throwing, skiing, dancing, golf, and tennis (Wang et al., 2022).
20. The rehabilitation of various sports-related injuries can be addressed with the specific exercises permitted by the use of the rotating platform. One example is the complicated and prolonged rehabilitation of knee ligament injuries, which makes it possible to transmit rotation of the femur to the leg. This rehabilitation to date follows less than complete protocols (Rodriguez et al., 2020; Kasmi et al., 2021; Lin, 2023).

The proposed device

21. It is therefore appropriate to provide a machine capable of stimulating the rotation of the legs on the trunk. The device consists of a rotating horizontal disc on which the subject ‘walks in place’ with head and trunk stabilised in space by the grip of a fixed handrail. This device is able to train the rotational movements of the lower limbs that normally occur when walking in curved trajectories and allow the learning (or re-learning) of the underlying neuromuscular coordination (Figure 2). A European patent application was filed on 26 Apr 2023 under No. 23169980.2 for: DEVICE FOR PHYSIOTHERAPY TREATMENTS).
22. Briefly, the action of the device can be described as follows. When the right foot rests on the rotating disc in a clockwise direction, the right foot and leg are passively extra-rotated (the rotation of the tibia on the foot and that of the femur on the knee are of minimum amplitude while that at hip level is maximum). During the next phase of lifting the rotated limb (as the subject continues to march in place), while the other limb is on the ground (resting on the platform), the subject actively and naturally brings the lower limb back to a ‘straight’ position and then places it back on the rotating disc and so on. A similar sequence occurs for the left limb, which will instead be intra-rotated by the rotating disc. A sequence of intra- and extra-rotation will then occur for clockwise rotations. The same sequence of leg rotations will occur in the opposite direction when the turntable rotates anti-clockwise. Other movements are provided, such as short, rapid impulsive rotations of the platform (see below). Although the use of postural perturbations has shown positive results in various areas of posture and gait rehabilitation (Ribeiro de Souza et al., 2023), there is to date no dedicated system for rotator muscle perturbations.
23. It is sufficient for the rotating disc to have a diameter of 50 cm in order to easily perform its function. The subject will be leaning with the upper limbs against a support that allows the primary position (looking forward without head-neck rotation) of the upper torso and head to be maintained. The primary position of the upper body, with the head virtually fixed in space, avoids any vestibular rotatory stimulation that could cause dizzy episodes and falls (as when the subject rotates on itself for a few seconds on fixed ground). The subject walks in place with its vertical axis passing through the centre of mass of the body, which is projected onto a point on the platform that forms the pivot of the rotation.
24. For clinical use in critically ill patients, a lightweight sling is provided (Figure 2). It is attached to support the subject vertically, and the platform does not move unless the ‘seat belt’ is fastened (as in cars). This function is optional if the training is supervised. It is just worth mentioning that since the subject is leaning and with his feet around the centre of the platform, the vertical of the body corresponds to the centre of rotation. Therefore, since its centre of mass is not stressed by transverse perturbations, the risk of falling is negligible. The necessary safety precautions are provided. Supporting the handrail will be compulsory, on pain of stopping the platform. Any failure of the legs will also cause the rotation to stop. A lock button will be available.
25. The angular speed of the rotating disc can vary in order to adapt the speed of rotation of the body while walking on the platform to the subject’s abilities (from slow to progressively faster speed both during one treatment and in repeated treatment sessions). The speed and duration of rotation can be pre-set by the subject at home, or in the clinical setting by the physiotherapist. The rotation period may last several minutes. The rotation may have constant or variable angular velocity. It can be continuous clockwise or continuous counterclockwise or have periods with increasing and decreasing angular velocities and with reversal of the direction of rotation. Several rotation patterns are pre-set and retrievable by the subject (or physiotherapist) through interaction with an accessible tablet. Other patterns can be easily implemented off-line and then incorporated into the pre-set options. Another rotation pattern consists of very rapid rotations of a few degrees (< 5°) (impulsive rotations with subsequent slow return of the platform to the initial position). This stimulus produces reflexes in the intra- and extra-rotator muscles (to the right and left with clockwise rotations or vice versa, respectively), simulating the muscular stretch and its effects that occur during a sudden rotation of the trunk on the legs. Other patterns can be easily implemented. The duration of the platform rotation can also be very prolonged, configuring a ‘gait endurance’ type of training (Petrini, 2023).
26. The rotating ‘system’ (rotating platform and marching subject) is equipped with a simple accelerometer that records the cadence of the footstrike and a heart rate monitor.
27. A tablet collects platform rotation data and foot strike cadence and creates an excel table of these variables, which can be accessed and downloaded to a PC for later off-line analysis. An acoustic and/or visual metronome can be set from the tablet, so that the ‘imposed’ rhythm can be compared with the actual rhythm.
28. At this early stage of the device’s development, there are no plans to implement other functions, such as the vibration of the trunk muscles, which has been shown to be capable by itself of causing deviations in the locomotion trajectory (Bove et al., 2001; Courtine et al., 2007) and inducing body rotations during walking in place (Sozzi et al., 2019).
29. The ease of use is safe: the person simply walks in place (with or without a sling, depending on the conditions), at the pace they prefer (or at the pace set by a metronome) while holding onto a handrail. The angular speed of the platform is set through the use of buttons on the tablet (which limits the choices to non-threatening rotations).
30. End-user acceptance of the adoption and use of a prototype of the new system was evaluated and proved to be positive. Although some minimal effort may be required to use the system during prolonged treatment, the effort is perceived as worthwhile as users expect that the device will improve their walking performance and influence their social life.
31. The device is movable and transportable because it has a modest weight (≈ 20 kg) and can be disassembled into a few pieces with negligible bulk. When assembled, it occupies an area of no more than one square metre, allowing it to be placed even in small rooms or to locate several in the same room. It is safe, both mechanically and electrically. The cost for the healthcare facility or private individual who will be equipped with it will be low (depending on the characteristics of mass production).

The characteristics of the training (see an animation at the end of this page)

33. This type of exercise frees the central nervous system from the ‘effort’ to maintain balance, critical activity during the nomal walk in patients with problems of locomotion of different nature, thanks to the fact that the upper body of the subjects (the head, the shoulder girdle and the trunk) is practically stationary (or rather little mobile) because they hold with their hands to a support while marching on the place.
34. This allows you to perform with ‘tranquility’ and for a long time the movements imposed by the platform. The rotation along the major axis of the lower limb during the stepping in place is both passive, during the support of the foot, and active during the lifting; in both cases does not involve any unusual or ‘strange’ movement or the deliberate learning of an unusual motor sequence. It can detect the observation that an acoustic cueing given by the metronome, and a long-lasting path help patients with PD to maintain a constant running rate despite the ‘virtual’ curvature of the path trajectory, helping them to overcome conditions that normally lead to destabilization, rhythm alterations and gear freezing (Spildooren et al., 2010; Rutz and Benninger, 2020).
35. As for the mentioned rapid rotations of small amplitude, it is known that exercises based on postural disturbances are able to prevent falls in the elderly. Perturbation-based balance training (PBT) can have several characteristics (Brüll et al., 2023). The movements of this platform are able to propose an activity that summarizes the salient aspects of PBT and at the same time causes stress on the posture and muscles that generate the rotations of the lower limbs. The advantages of this procedure have so far only been described in the linear path (Castano, 2023).
36. The many features offered by this training are in line with recent indications relating to reablement programs or restorative treatments in elderly patients admitted to the community (see the recent review article by Lewis et al., 2021). In particular, reference is made here to function-focused treatments that aim to improve degraded motor functions (for reduced coordination or sarcopenia or other common conditions related to hypo-mobility in the elderly) and thus prevent serious problems such as falls. The proposed exercise is a typical ‘proprioceptive’ exercise (Sherrington et al., 2019) suitable to prevent falls in the elderly.
37. It is important to note that the articulated options of the control of the movement of the platform offer the physiotherapist the freedom to act both on the duration and speed of the rotation of the platform according to his experience during the treatment of a particular old and fragile patient or subject.
38. It is worth mentioning that on-site running on the rotating platform does not cause high impact on the foot support base (as is the case with the ‘normal’ treadmill) because it lacks the ‘forward thrust’ imposed by the treadmill, and even less it produces excessive pressure on the joints of the leg and pelvis, thus eliminating any risk of injury from impact.
39. In the first part of this text some characteristics of the path along curved paths have been summarized. It is evident that the march in place simulates the intra- and extra-rotation of the lower limbs with respect to the pelvis, but not the inclination of the body towards the center of the curvature of the trajectory to generate the centripetal force.
40. On the other hand, the march on the spot has the advantage of minimizing the movements of the head, making negligible the vestibular stimulation and the effects of opto-kinetic stimulation. Even the center of mass of the body, which during the journey moves with considerable kinetic energy remains practically in situ, as well as the support base does not require the generation of the displacement of the feet of several tens of centimeters in the sagittal plane as it happens in the walk (straight and on linear treadmill).
41. Detects that on the rotating platform there is no load on the hip produced by the ‘normal’ walk on linear treadmill due to the foot support (heel strike) (for references see Palmowski et al., 2021). Since the body is always aligned vertically, as already mentioned, the foot support during the march on the spot configures a negligible load (Kuster 2002). In this way, the training can last even for long periods in the absence of the activation of the muscles that stop the fall of the body during the step (Honeine et al., 2013).
42. Note here that this type of exercise can also be performed wearing an ankle-foot orthosis (AFO) or knee, ankle, foot (KAFO) (Zancan et al., 2004), which could be regularly worn even by patients with spastic paresis (or in young people with CP) (Bayón et al., 2023). In addition, various tests are available to assess the ability to rotate (see below). The Route 8 test (Zancan et al., 2021) mentioned below (Figure 3) can be used together with the platform for preventive purposes, evaluative or rehabilitative when you want to solicit the mechanisms of production of anticipatory and compensator adjustments during the walk along curvilinear trajectories (unlike the walk on the spot) and measure the effects of treatment.

Outcome Tests

1. There is a range of (pre-post) tests suitable for assessing the treatment outcome. The ‘after’ time can be set after a single treatment and/or after each of the subsequent treatments and at the end of the planned treatment.
2. The 360° rotation test is a measure of dynamic balance. The person undergoing the test rotates at least 360 degrees while the completion time and/or number of steps taken to complete the turn are recorded. See …
3. The Freezing of Gait questionnaire. See in Giladi et al. (2000).
4. The Timed-Up-and-Go (TUG) test. The results correlate with the risk of falling.
5. The Figure-of-8 test. See Odonkor et al. (2013), Zancan et al. (2021), and Lowry et al. (2022). Figure 3 below (Zancan et al. 2021) shows the 20-metre path, printed on a large, thin but robust plastic sheet. The subject travels along a linear section, followed by a sharp right turn and a complete counterclockwise circle. The latter continues in another circle to walk clockwise, the route ends with another linear section.
6. The L-test. See Cetin and Erel (2022).
7. The use of some relevant measurement scales (e.g. the Falls Efficacy Scale-International and the modified Elderly Mobility Scale) is briefly summarised in Hasebe et al. (2022) and Saito et al. (2023).

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