Document Type : Full Research Paper


1 MSc. Graduated, Orthotics and Prosthetics Group, School of Rehabilitation Science, Medical University of Iran

2 Associate Professor, Physiotherapy Group, Health Science School, University of Sharjeh

3 Assistant Professor, School of Electrical and Computer Engineering, Tehran University

4 Instructor, Biomechanic Group, School of Mechanical Engineering, Sharif University of Technology



CNS applies Anticipatory Postural Adjustments (APA) strategy to reject or minimize perturbation during different voluntary movements. The postural control mechanisms associated with voluntary arm movement (rapid arm rising) in below knee amputees (BKA) was investigated and the results were compared with the normal subjects. Biomechanical variables including ground reaction forces and displacements of the center of pressure were used to investigate the APA in BKA. Six below knee amputees and six control subjects stood on a force plate under three conditions: 1. with both feet on the platform, 2. with right foot (prosthetic foot) and 3. with left foot on the plate. For each condition, the task was repeated 10 times. At the same time, a camera recorded the task performance. The recorded data were used to determine the start moment of the movement. The instant at which, for the first time before starting the movement, any one of the recorded biomechanical variables deviated from its initial value was considered as the beginning of the APA. To increase the validity of the test, efforts were made to match the subjects with regards to their age, gender, cause of amputation and prosthesis types. Our results indicated that the center of pressure in the BKA participants showed greater displacements in medial-lateral and anterior-posterior directions. It was also observed that the vertical components of the ground reaction forces, when the right foot was on the plate, were increased. There were no significant differences in other biomechanical variables between the two groups. We may conclude that the voluntary arm movement perturbs the posture in the BKA participants more than in the control group. The BKA participants shifted their weight to the intact limb by the anticipation of the disturbance to avoid balance loosing. Therefore, in our study the intact limb in below knee amputee subjects played an important role in the balance control. Based on our results, we suggest considering the role of the intact limb in the rehabilitation programs and strengthening the muscles of both limbs as a major part of theses programs.


Main Subjects

[1]     Shomway C., Wollacott M., Motor Control. 2nd edition. Lippincott Williams&Wilkins, 2000.
[2]     Massion J., Movement, Posture and Equilibrium: Interaction and Coordination, Progress in neurobiology, 1991; 38, 35-56.
[3]     Winter D.A. Human Balance and Posture Control during Standing and Walking, Gait & Posture, 1995; 3: 193-214.
[4]     Belenkii V.YE., Gureinkei V.S., and Pal'tsev YE.L., Elements of Control of Voluntary Movements. Biofizika, 1966; 12(1): 135-141.
[5]     Bouisset S., Zattara M., Biomechanical Study of the Programming of Anticipatory Postural Adjustments Associated With Voluntary Movement, J. Biomechanics, 1987; 20 (8): 735 – 742.
[6]     Aruin A.S., Nicholas J.J., Latash M. L., Anticipatory Postural Adjustments during Standing in Below-the-Knee Amputees, Clinical Biomechanics, 1997; 12 (1): 52-56.
[7]     Aruin A.S., The Organization of Anticipatory Postural Adjaustments, Journal of Automatic Control, University of Belgerad, 2002; 12: 31-37.
[8]     Geurts A., Mulder T. Reorganization of Postural Control Following Lower Limb Amputation. Theoretical Considerations and Implications for Rehabilitation, Physiother Theor Prac, 1992; 8: 145-157.
[9]     Isakov E., Mizrahi J., Ring H., Susak Z, Hakim N. Standing Sway and Weight- Bearing Distribution in People Whit Below  Knee Amputation, Arch Phys Med Rehabil , 1992; 53: 174-178.
[10] Geurts A., Mulder T.,Neinhuis S.B., Rijken R., Postural Reorganization Following Lower Limb Amputation, Scand J Rehab Med, 1992; 24: 83-90.
[11] Atlas of Limb Prosthetics: Surgical, Prosthetics, and Rehabilitation Principles.(1992) American Academy of Orthopedic Surgeons, 2nd edition
[12] Riach C.L., Hayees K.C., Lucy S. D., Changes in Center of Peresure of Ground Reaction Forces prior to Rapid Arm Movements in normal Subjects and Patients With Cerebellar Ataxia , Clinic Biomech , 1992; 7: 208-214.
[13] Clark L.A., Zenicke R.F., Balance in Lower Limb Child Amputees, Prosth Orhto Intern, 1981; 5: 11-18.
[14] Latash M.L., Aruin A.S., Neyman I., Nicholas J.J., Anticipatory Postural Adjaustments during Self Infilicted and Predictable Perturbations in Parkinson's Disease,Neural Neurosurgery Psychiatry, 1995; 58: 326-334.
[15] Hay L., Rendon C., Development of Postural Adaptation to Arm Rising, Exp Brain Res, 2001; 139: 224-232.