Vrije Universiteit Brussel

ALTACRO - Step Rehabilitation Robot

The ALTACRO Project

ALTACRO is a multidisciplinary research project that aims at the development and clinical testing of a step rehabilitation robot powered by compliant actuators. The ALTACRO project is a contribution to the synergy between robotics and rehabilitation. The acronym stands for Automated Locomotion Training using an Actuated Compliant Robotic Orthosis. Our primary goals are to improve the quality of step rehabilitation therapy both for patients and therapists and increasing the availability of automated step rehabilitation training.

Find more information on the ALTACRO website.

Contact information

Contact Persons:
Prof. dr. ir. Dirk Lefeber
E-mail: dirk.lefeber@vub.be

Vrije Universiteit Brussel
Faculty of Engineering Sciences
Department of Mechanical Engineering
Building Z - Room ZT
Pleinlaan , 2
B-1050 Brussels

Phone: +32 2 6292862
Fax: +32 2 6292865

Research Team

Behind the ALTACRO project is a multidisciplinary research team, the Advanced Rehabilitation Technology & Science research group (ARTS), involving six research groups of the Vrije Universiteit Brussel (VUB). Four groups are part of the faculty of Physical Education and Physiotherapy, one group is part of the faculty of Medicine and one of the faculty of Engineering.


Gait training proves to be an effective approach to help patients with neurological disorders (e.g. stroke, multiple sclerosis) or neurological injuries (e.g. incomplete spinal cord injury) regain functional walking abilities. Intensive walking training appears to be vital to the activity triggered learning process of the sensorimotor system. For people who will probably never walk again, for instance due to complete spinal cord injury, assisted gait training diminishes the negative effects resulting from being bound to a wheelchair.

In one of the existing practices, body-weight supported treadmill training (BWSTT), the patient's body weight is partially supported by an overhead harness while his/her lower limb movements are assisted by one up to four physiotherapists. The strenuous physical effort encumbering the therapists and the resulting short training session duration was one of the main reasons for introducing robotics into gait rehabilitation. The envisaged benefits were:

  • Longer and more intensive training sessions, enhancing rehabilitation outcome.

  • A reduction of the number of therapists per patient.

  • Accurate, quantifiable assistance and/or movements.

  • The ability to monitor and steer the patient's rehabilitation process.

Repeatability, accuracy and quantification are features easily associated with robotics. However, a robot operating in close physical contact with an impaired human requires an approach to robot performance that differs significantly from the viewpoint of industrial robotics. Accurate repeated motion imposed by a position controlled robot is considered contraproductive for several reasons: a lack of adaptable and function specific assistance, a limitation of the learning environment, reduced motivation and effort by the patient, and a risk of unsafe human-robot interaction. Nowadays, the field of rehabilitation robotics is increasingly convinced by a human-centered approach in which robot performance is focused on how the robot physically responds to and interacts with the patient.

Research project

In the ALTACRO concerted research action project a multidisciplinary team of doctors, engineers and physiotherapists at Vrije Universiteit Brussel conducts research into four identified challenges in robot-assisted gait rehabilitation:

  • Active assistance of the ankle joint, which is lacking in the gait rehabilitation devices currently on the market.

  • A more natural load distribution in the body, allowing for balance training. A robotic exoskeleton capable of providing full body weight support without any additional suspension system could open up possibilities.

  • More functional gait kinematics. Introducing threedimensional movements in a rehabilitation robot should improve recovery of coordination and equilibrium.

  • Improved physical human-robot interaction. The device should be capable of adaptable, compliant behaviour both for reasons of safety and functionality.

One of the main project goals is the development of a novel full lower body exoskeleton powered by compliant actuators and the clinical evaluation of its concepts aimed at improving robot-assisted gait rehabilitation in the four aforementioned areas.

ALTACRO is a 5-year project (2008-2012) funded by the university research council of Vrije Universiteit Brussel. ALTACRO stands for Automated Locomotion Training using an Actuated Compliant Robotic Orthosis.

Project Goals

The primary objective is to enhance the quality of automated step rehabilitation training both for patients and therapists, in this way increasing its availability.

Integrating the expertise of neurological rehabilitation, functional anatomy, biomechanics, physiology and robotics, the project aims to develop and assess an original robotic rehabilitation system, providing the capacity to substantially enhance the prognostic health profile of the patient.

In addition, the research outcomes will contribute to the synergy between robotics and rehabilitation and to the development of related applications in the emerging fields of rehabilitation robotics and assistive robotics.

Research tasks

The key objective of the project is the development and clinical study of a novel step rehabilitation robot prototype. Research activities are clustered according to the four research challenges to be addressed.

Active ankle assistance

  • Integrating a powered ankle-foot structure into the gait rehabilitation exoskeleton prototype design that is capable of fully supporting the ankle joint.

  • Clinical assessment of active ankle support. Study of the influence on gait (kinematics, kinetics, muscle activity) and on gait rehabilitation outcome.

Natural load distribution
  • Design the exoskeleton prototype for full body weight supporting capacity without relying on a supension system.

  • Studying the effects of overhead and exoskeleton body weight support on gait kinematics and physiology.

Functional gait movements
  • Incorporating three dimensional mobility into the exoskeleton prototype design.

  • Evaluating the effects of three dimensional movement support on balance, gait kinematics and physiology.

Compliant human-robot interaction
  • Applying "adaptable compliance" concepts both in the exoskeleton hardware (compliant actuators) and software (dedicated control strategies). Studying and evaluating the benefits of intrinsic and controlled adaptable compliance in view of safety, interaction-oriented assistance and "soft" interaction.

  • Identifying and evaluating the clinical effects of human-robot interaction in different interaction scenarios, e.g. spasticity, voluntary muscle activity.

Project status


  • Construction of a bilateral lower body exoskeleton
  • Sensing and control of pelvis actuation and body-weight supporting structure
  • Design of integrated control hardware and real-time system
  • Design of high performant force sensors for pelvis actuation


  • Design of a bilateral lower body exoskeleton
  • Design and construction of pelvis actuation and body-weight supporting structure
  • Design of integrated control hardware


  • Design of a bilateral lower body exoskeleton
  • Performance evaluation of KNEXO in impaired subjects
  • Body-weight support study in unimpaired-subjects


  • Performance evaluation of KNEXO in unimpaired subjects
  • Trunk balance study in unimpaired subjects
  • Biomechanical study of the ankle foot complex
  • Design and evaluation of a proof-of-concept MACCEPA powered exoskeleton joint


  • Design and construction of KNEXO, a knee exoskeleton powered by pleated pneumatic artificial muscles (PPAMs)
  • Feasibility and conceptual design study of a compliant bilateral lower body exoskeleton


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