Gregory W. King

Classification of body movements based on posturographic data

The human body, standing on two feet, produces a continuous sway pattern. Intended movements, sensory cues, emotional states, and illnesses can all lead to subtle changes in sway appearing as alterations in ground reaction forces and the bodys center of pressure (COP). The purpose of this study is to demonstrate that carefully selected COP parameters and classification methods can differentiate among specific body movements while standing, providing new prospects in camera-free motion identification. Force platform data were collected from participants performing 11 choreographed postural and gestural movements. Twenty-three different displacement- and frequency-based features were extracted from COP time series, and supplied to classification-guided feature extraction modules. For identification of movement type, several linear and nonlinear classifiers were explored; including linear discriminants, nearest neighbor classifiers, and support vector machines. The average classification rates on previously unseen test sets ranged from 67% to 100%. Within the context of this experiment, no single method was able to uniformly outperform the others for all movement types, and therefore a set of movement-specific features and classifiers is recommended.

Age-related differences in kinetic measures of landing phase lateral stability during a balance-restoring forward step

Lateral stability during stepping is critical to successful balance recovery, and has been previously studied from a kinematics perspective. However, relatively little is known about the kinetic aspects of lateral stability. The purpose of this paper is to investigate age-related changes in laterally directed landing phase ground and joint reactions during a balance-restoring step response. 12 young and 13 older male adults were released from a static forward leaning position and were instructed to take a single step with the dominant leg. Laterally directed landing phase ground and ankle reactions, foot kinematics, and center of mass movement were compared across age groups. No age-related differences were observed in step width or center of mass behavior during step landing. Older adults, compared to young, demonstrated larger laterally directed landing phase ground and ankle reaction forces. The findings demonstrate an age-related increase in kinetic, but not kinematic or stability measures, suggesting that older adults do not minimize strength when maintaining stability during a single step balance recovery maneuver.

A multimodal assessment of balance in elderly and young adults

Falling is a significant health issue among elderly adults. Given the multifactorial nature of falls, effective balance and fall risk assessment must take into account factors from multiple sources. Here we investigate the relationship between fall risk and a diverse set of biochemical and biomechanical variables including: skeletal muscle-specific troponin T (sTnT), maximal strength measures derived from isometric grip and leg extension tasks, and postural sway captured from a force platform during a quiet stance task. These measures were performed in eight young and eleven elderly adults, along with estimates of fall risk derived from the Tinetti Balance Assessment. We observed age-related effects in all measurements, including a trend toward increased sTnT levels, increased postural sway, reduced upper and lower extremity strength, and reduced balance scores. We observed a negative correlation between balance scores and sTnT levels, suggesting its use as a biomarker for fall risk. We observed a significant positive correlation between balance scores and strength measures, adding support to the notion that muscle strength plays a significant role in postural control. We observed a significant negative correlation between balance scores and postural sway, suggesting that fall risk is associated with more loosely controlled center of mass regulation.

Machine learning methods for credibility assessment of interviewees based on posturographic data.

This paper discusses the advantages of using posturographic signals from force plates for non-invasive credibility assessment. The contributions of our work are two fold: first, the proposed method is highly efficient and non invasive. Second, feasibility for creating an autonomous credibility assessment system using machine-learning algorithms is studied. This study employs an interview paradigm that includes subjects responding with truthful and deceptive intent while their center of pressure (COP) signal is being recorded. Classification models utilizing sets of COP features for deceptive responses are derived and best accuracy of 93.5% for test interval is reported.

Age Differences in Landing Phase Ankle Dynamics During a Balance-Restoring Step Response

Falls are a significant health concern among older adults. The rate of falls increases with age [1], and often leads to fall-related injuries such as fractures and head injuries. These lead to loss of independence, morbidity and fear of falling [2]. There are many strategies used to prevent falls, including those used to regain balance following a slip or trip. One such balance recovery maneuver is the step response, which involves respositioning the body’s base of support to recapture its moving center of mass [3]. Age-related performance declines in the step response may contribute to fall risk, especially during the step response landing phase where biomechanical strength requirements are largest [4]. Such age-related declines likely manifest themselves as alterations in lower extremity joint dynamics. While these effects are likely present in all lower extremity joints (hips, knees, and ankles), the purpose of this preliminary study was to investigate age effects in stepping leg ankle dynamics during a balance-restoring step response.Copyright

The Role of Knee Extensor Strength in Balance-Restoring Step Initiation and Execution

A stepping response is often used to restore balance following a fall. Using laboratory-induced balance perturbations, various researchers have reported age-related alterations in balance recovery step characteristics including earlier step liftoff time [1; 2], shorter step length [1; 3], and longer step duration [2]. Such age-related changes in the step response may be related to older adults’ reduced strength reserve, which is prominent in the lower extremities [4] and therefore likely plays an important role in balance recovery.Copyright