Evaluation of the biomechanical strategies of standing balance

• Main Author: Haideri, Nasreen F
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2004
• Subjects: Biomedical engineering; Biomedical research; Kinesiology; Sports medicine
• ISBN: 0496721879; 9780496721870

The ability to maintain upright standing balance is fundamental to activities of daily living, locomotion, and injury prevention. The purpose of this work was to improve understanding of the multifarious strategies that humans use to maintain standing balance. Forward dynamic simulation techniques were employed to thoroughly explore the domain of sagittal plane dynamic balance maintenance strategies (“DBMSs”) in a two joint (mobile ankle and hip, with a locked knee) system in which the feet remain still and on the floor. Utility of the model was demonstrated through experimental verification. A comprehensive field search was conducted across parameterizations of ankle and hip net joint moments to define and identify strategies capable of maintaining balance during forward fall simulations. Strategy effectiveness was determined by the dynamic limit of stability, the maximum initial forward center of mass velocity from which the strategy could prevent the model center of mass from exiting the base of support, and by a “COST” index comprised of four components: effort, dynamic magnitude, risk, and final posture. Four distinct DBMSs were identified in this paradigm; three of which generated comparable kinematic results, highlighting the importance of defining DBMSs using net joint moments. A hierarchy of strategy effectiveness was established that was maintained over a range of postural and anthropometric values. Results revealed that a DBMS involving ankle plantarflexor moments was four times more effective than a bimodal hip flexor/extensor strategy, the net effect of which was relatively small over the entire simulation. Addition of hip moments to the ankle strategy did not greatly influence strategy effectiveness. Strategy effectiveness was increased through passive hip flexion. Applying bimodal hip moments to an elderly female model severely limited the ability to maintain balance. Contrary to previous belief, results from this work indicate that net moments acting at the ankle joint are of primary importance in maintaining upright balance under increased dynamic conditions. Net joint moments at the hip are required primarily for control of upper body posture. Comparison of dynamic limits and COST provided insight as to why, and under what conditions, some balance strategies can be successfully utilized and others fail.