Partial body weight support (PBWS) training is an evidence-based approach for walking training of children with neuromotor disorders (Novak et al., 2020) that uses task-specific strategies, intensive practice, with variability and active participation of the child, and result in functional motor skills.
PBWS consists of reducing the load on lower limbs through a suspension system, allowing upright posture and facilitating walking movements. The fundamental principle of this strategy is to reduce the demand for muscle strength to overcome the gravitational force during walking. Based on this concept, the partial support of the body weight can be performed by different equipment, ranging from the swimming pool to harness systems and robotic devices.
The swimming pool was the first weight support system used as early as 1500BC by Hindus and Egyptians. The first “out of the water” PBWS system was developed in the 1980s with the evaluation of the motor behaviour of cats with spinal cord injury (Alaimo et al., 1984; Lovely et al., 1986). That system consisted of a vest fixed to a rod that stabilized the cat’s trunk and forelimbs, while the hindquarters were stabilized by the tail, during the animal’s walk on a treadmill. The explanation for the cat still being able to walk on the treadmill, even with spinal cord injury, was that there were structures in the spinal cord, called Central Pattern Generators (CPGs), capable of producing cyclic and rhythmic movements, such as walking movements, independently of brain control. Currently, with the advancement of PBWS training studies in human, we know that not only the CPGs of the spinal cord but also brain structures related to motivation, anticipation and motor adjustments that justify the great results on walking skill of individuals with different neurological conditions, including cerebral palsy and Down syndrome.

APPLYING PBWS TRAINING

There are several ways of applying PBWS in therapy that vary according to the basic elements of suspension systems. These elements include the way the suspension is applied, the stabilization to maintain the ideal posture, the way the individual’s body is attached to the system, the type of support surface on which the training is carried out and the amount of assistance the child needs to walk.

PBWS systems

The main element of PBWS is the way the suspension force is applied to the child. The suspension system has the function of complementing the muscle strength necessary to overcome gravity and keep the child standing, and to reduce joint compression in the lower limb joints and trunk as well. The child feels safe in the execution of the task, which motivates them to walk.
The suspension can be performed by a harness attached to a fixed point or rail, a counterweight system, a Spider cage elastic cable system, a thrust in hydrotherapy or with a robotic walking trainer. There is no protocol for the amount of bodyweight allowed, but it is applied according to the skills and therapeutic goal of each child. The suspension is gradually reduced as the walking training progresses, allowing the child to develop strategies and take on the task by supporting his/her own body weight. As the suspension is gradually decreased, the child has the opportunity to develop greater postural alignment, coordination of movements and balance in a safe and efficient way.
The child can actively maintain the ideal posture for walking maintained by using his/her own balance strategies or resting his/her hands on the parallel bars or the support bars of the electric treadmill. For children who need more assistance to keep their posture straight and stable, parallel cables or lateral stabilizers can be added.
The connection between the child’s body and the suspension system is commonly performed by a vest or belt fixation. Wearing the vest or belt makes walking training safe as it minimizes the child’s need for completely efficient posture adjustments.
The child’s posture, movement and stability when on a PBWS system are influenced by two factors: the part of the body in which the vest or belt is applied, such as the pelvis, abdomen, torso or lower limbs, and the anchorage point, i.e. the place where the suspension cables are placed, which can be on a fixed or mobile point, such as a rail, at the ceiling.
The most appropriate PBWS set varies for each patient, and the choice should be made aiming at the point of balance between stability and freedom of movement, as well as safety and comfort.

Overground versus Treadmill PBWS training

PWBS training can be applied on the ground or the treadmill depending on the child’s ability and therapeutic goal. The use of the floor as a support surface has the advantages of generating greater cognitive stimulation by continually changing the visual field and by the high specificity of training. On the other hand, the treadmill offers a controlled environment, suitable for the control of walking speed, adequacy of joint positions, and does not require large spaces for execution. Furthermore, with treadmill training, some children can be motivated to self-improve based on values such as speed and distance travelled.

Therapist handling versus Robotic devices

The therapist’s handling, the movement of the electric treadmill or the robotic walking trainer can be used to assist in the execution of the motor components of each phase of the walking cycle. The therapist can apply handling to facilitate passive or active-assisted weight transfer between the lower limbs and to lift the foot off the ground to take the step, while the conveyor belt of the treadmill is useful to facilitate ankle and foot movements by “dragging” the foot backwards.
The device commercially known as Lokomat, or similar equipment, is a robot developed for treadmill training, which also perform passive or active-assisted steps, but without the need for support by therapists. The mobility of the robotic legs is synchronized with the speed of the treadmill. The robot seems to provide symmetrical trunk balance, coordination, propulsion and step change. There are indications to improve walking speed, cadence and single-leg support time during walking. Children can start robot training only from the age of four. However, research is still inconclusive on these benefits in children with neuromotor dysfunctions and researchers suggest that more studies should be conducted to indicate the effects of this new therapeutic strategy for that population (Ammann-Reiffer, 2017).

BENEFITS AND INDICATIONS OF PBWS TRAINING

Based on the principle of motor learning, task-specific training with lots of repetition and active participation of the child, like training under PBWS systems, promotes the best performance of the essential aspects of the walking skill, as motor control, muscle strength, fatigue resistance, cardiopulmonary conditioning, motivation and emotional safety (Booth et al., 2018).
Non-walking children can benefit from better trunk control and maintenance of sitting and standing position (Damiano and DeJong, 2009). For children who are able to walk, even for short distances, PBWS treadmill training can improve endurance, speed, stride length (Booth et al., 2018). Activities like sitting, get up from sitting, going up and down steps, long-distance courses, standing without hand support, which influences the independent mobility in the day to day of the child and the caregiver, also may be improved (Emara et al., 2016).
Children with Down syndrome also benefit from this strategy to accelerate their development of independent walking (Wu et al., 2008).
Rare and minor adverse events can be related to PBWS treadmill training, such as leg discomfort off the treadmill, which resolve without intervention; and development of blisters on the feet if the socks, shoes or orthoses are not properly placed during the training (Booth et al., 2018). The hip dislocation has not been reported as an adverse event for this therapeutic strategy (Meyer-Heim et al., 2007), which is a good point to consider in a patient group that is at risk for hip subluxation or dislocation.

It is important to remember that PBWS training is only one of the physiotherapy strategies for walking acquisition and improvement of children with neuromotor dysfunctions. There are some points to consider before proceeding with PBWS training, such as core stability, postural control, joint range of movement and muscle strength in the lower limbs, coordination and balance. For this reason, each child must have their therapeutic plan individually designed.

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Sources:

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