Yifang Fan

The influence of gait speed on the stability of walking among the elderly

Walking speed is a basic factor to consider when walking exercises are prescribed as part of a training programme. Although associations between walking speed, step length and falling risk have been identified, the relationship between spontaneous walking pattern and falling risk remains unclear. The present study, therefore, examined the stability of spontaneous walking at normal, fast and slow speed among elderly (67.5±3.23) and young (21.4±1.31) individuals. In all, 55 participants undertook a test that involved walking on a plantar pressure platform. Foot-ground contact data were used to calculate walking speed, step length, pressure impulse along the plantar-impulse principal axis and pressure record of time series along the plantar-impulse principal axis. A forward dynamics method was used to calculate acceleration, velocity and displacement of the centre of mass in the vertical direction. The results showed that when the elderly walked at different speeds, their average step length was smaller than that observed among the young (p=0.000), whereas their anterior/posterior variability and lateral variability had no significant difference. When walking was performed at normal or slow speed, no significant between-group difference in cadence was found. When walking at a fast speed, the elderly increased their stride length moderately and their cadence greatly (p=0.012). In summary, the present study found no correlation between fast walking speed and instability among the elderly, which indicates that healthy elderly individuals might safely perform fast-speed walking exercises.

Bone Surface Mapping Method

Bone shape is an important factor to determine the bones structural function. For the asymmetrically shaped and anisotropically distributed bone in vivo, a surface mapping method is proposed on the bases of its geometric transformation invariance and its uniqueness of the principal axes of inertia. Using spiral CT scanning, we can make precise measurements to bone in vivo. The coordinate transformations lead to the principal axes of inertia, with which the prime meridian and the contour can be set. Methods such as tomographic reconstruction and boundary development are employed so that the surface of bone in vivo can be mapped. Experimental results show that the surface mapping method can reflect the shape features and help study the surface changes of bone in vivo. This method can be applied to research into the surface characteristics and changes of organ, tissue or cell whenever its digitalized surface is obtained.Bone in vivo: Surface mapping technique Yifang Fan, Yubo Fan, Zhiyu Li, Changsheng Lv 1 Center for Scientific Research, Guangzhou Institute of Physical Education, Guangzhou 510500, P.R. China 2 Bioengineering Department, Beijing University of Aeronautics and Astronautics, Beijing 100191, P.R. China 3 College of Foreign Languages, Jinan University, Guangzhou 510632, P.R. China ∗ E-mail: tfyf@gipe.edu.cn

Optimal principle of bone structure.

This paper studies foot bone geometrical shape and its mass distribution and establishes an assessment method of bone strength. Using spiral CT scanning, with an accuracy of sub-millimeter, we analyze the data of 384 pieces of foot bones in vivo and investigate the relationship between the bone’s external shape and internal structure. This analysis is explored on the bases of the bone’s center of mass and its centroid of shape. We observe the phenomenon of superposition of center of mass and centroid of shape fairly precisely, indicating a possible appearance of biomechanical organism. We investigate two aspects of the geometrical shape, (i) distance between compact bone’s centroid of shape and that of the bone and (ii) the mean radius of the same density bone issue relative to the bone’s centroid of shape. These quantities are used to interpret the influence of different physical exercises imposed on bone strength, thereby contributing to an alternate assessment technique to bone strength. Introduction The structure and function of bone largely depends on its mechanical and biological environments [1– 5]. When bone is bearing external force, bone tissue undergoes adaptive changes such as physiological activities of remodeling and reconstruction [6]. These changes emerge as those of external shape and internal structure so as to maximize its potential to bear external load [7–9]. Bone’s adaptive changes to the external force are regarded as an optimization process [4, 10, 11] which observes some special law. Current research results, however, did not provide us with convincing explanations to this special law. Bone strength is an important index to diagnose osteoporosis [12]. That justifies why bone strength has always been an issue in biomechanical research. Bone strength is determined by factors such as bone external shape and internal structure. How to measure bone shape and structure accurately largely depends on equipment. As a result, the advanced measurement equipment affects bone biomechanical research. With the development of CT scanning technology, more reliable modeling methods emerged. Many mechanical models, both macroscopically and microcosmically, depict the relationship between bone density, geometric shape, internal structure and bone strength [13–16]. This has made a quantitative assessment of bone strength more reliable. But in clinical medicine, no other quantitative assessment index has been more widely used than bone mineral density, which actually cannot objectively reflect the real condition of bone strength [14, 16, 17]. It is imperative to explore a quantitative and practical bone strength assessment index. External force can change bone shape and structure [18] and in turn, bone shape and structure affect the result of external force. When we do research on the interaction of one body with another, bone’s centroid of shape (COS) and center of mass (COM) have been considered as two basic physical quantities. Concerning the above-mentioned two issues, this paper focuses on selecting COS (shape) and COM (structure) to study the variation laws of bone in its adaptation process to external force and based upon these two quantities, we propose a couple of bone strength assessment indexes.Bone modeling and remodeling is an optimization process where no agreement has been reached regarding a unified theory or model. We measured 384 pieces of bone in vivo by 64-slice CT and discovered that the bones center of mass approximately superposes its centroid of shape. This phenomenon indicates that the optimization process of non-homogeneous materials such as bone follows the same law of superposition of center of mass and centroid of shape as that of homogeneous materials. Based upon this principle, an index revealing the relationship between the center of mass and centroid of shape of the compact bone is proposed. Another index revealing the relationship between tissue density and distribution radius is followed. Applying these indexes to evaluate the strength of bone, we have some new findings.

Dynamic Principles of Center of Mass in Human Walking

We present results of an analytic and numerical calculation that studies the relationship between the time of initial foot contact and the ground reaction force of human gait and explores the dynamic principle of center of mass. Assuming the ground reaction force of both feet to be the same in the same phase of a stride cycle, we establish the relationships between the time of initial foot contact and the ground reaction force, acceleration, velocity, displacement and average kinetic energy of center of mass. We employ the dispersion to analyze the effect of the time of the initial foot contact that imposes upon these physical quantities. Our study reveals that when the time of one foots initial contact falls right in the middle of the other foots stride cycle, these physical quantities reach extrema. An action function has been identified as the dispersion of the physical quantities and optimized analysis used to prove the least-action principle in gait. In addition to being very significant to the research domains such as clinical diagnosis, biped robots gait control, the exploration of this principle can simplify our understanding of the basic properties of gait.

Screening Method Based on Walking Plantar Impulse for Detecting Musculoskeletal Senescence and Injury

No consensus has been reached on how musculoskeletal system injuries or aging can be explained by a walking plantar impulse. We standardize the plantar impulse by defining a principal axis of plantar impulse. Based upon this standardized plantar impulse, two indexes are presented: plantar pressure record time series and plantar-impulse distribution along the principal axis of plantar impulse. These indexes are applied to analyze the plantar impulse collected by plantar pressure plates from three sources: Achilles tendon ruptures; elderly people (ages 62–71); and young people (ages 19–23). Our findings reveal that plantar impulse distribution curves for Achilles tendon ruptures change irregularly with subjects’ walking speed changes. When comparing distribution curves of the young, we see a significant difference in the elderly subjects’ phalanges plantar pressure record time series. This verifies our hypothesis that a plantar impulse can function as a means to assess and evaluate musculoskeletal system injuries and aging.

Standing footprint diagnostic method

Center of pressure is commonly used to evaluate standing balance. Even though it is incomplete, no better evaluation method has been presented. We designed our experiment with three standing postures: standing with feet together, standing with feet shoulder width apart, and standing with feet slightly wider than shoulder width. Our platform-based pressure system collected the instantaneous plantar pressure (standing footprint). A physical quantity of instantaneous standing footprint principal axis was defined, and it was used to construct an index to evaluate standing balance. Comparison between results from our newly established index and those from the center of pressure index to evaluate the stability of different standing postures revealed that the standing footprint principal axis index could better respond to the standing posture change than the existing one. Analysis indicated that the insensitive response to the relative position between feet and to the standing posture change from the center of p...

Calculation of Center of Mass and Inertia Moment of Human Body in Motion by Means of Transformation Matrix

Aim of research: Human body segment inertial parameters are the basic physical quantities in the study of human body in motion. Through careful calculation, inertial parameters such as the position of center of mass and moment of inertia of the total and segmental human body in motion in random postures have been obtained. Research method: Based upon the basic inertial parameters derived from Hanavan human body model and from Barter regression equation, upon position vector, moment and moment of inertia of the human body and segment relative to inertial reference frame by means of transformation matrix, and upon the resultant moment theorem and the parallel-axis theorem, inertial parameters such as the position of center of mass and moment of inertia of human body in random posture in motion are thus obtained. Result and conclusion: The research findings are in accordance with those of the balance plate and trilinear pendulum. The characteristics of individual and random posture of human body inertial parameter in motion are presented in this paper.