Biomedical subjects

Toshimasa Yanai

Publications and source records attributed to Toshimasa Yanai.

4 recordsLinked to original sources

PubMed2006

In vivo measurements of subacromial impingement: substantial compression develops in abduction with large internal rotation.

BACKGROUND: Subacromial impingement is a widely recognized mechanism of chronic shoulder pain. The magnitudes of the compressive forces that impinge the subacromial structures were often measured from cadaveric specimens, but it is questionable to use this data as a sole basis to determine the shoulder motions and/or shoulder configurations that induce impingement in live subjects performing active motion. The purpose of the present study was to determine in vivo the magnitude of the compressive force at selected shoulder configurations. METHODS: The subacromial structures may be impinged by the downward-directed forces exerted by the coraco-acromial ligament. The reactions of these forces push the ligament upwards and deform it into a curved shape. A single resultant of these reaction forces was determined with an inverse approach to quantify the magnitude of the impingement force. An ultrasound unit was used to visualize the deformed shape of the coraco-acromial ligament for thirteen subjects with no symptomatic shoulder problem actively holding their shoulders in five configurations. FINDINGS: The impingement force in 90 degrees abduction+maximum internal rotation (mean=21.3N) and that in the Hawkins test position (mean=18.3N) were significantly greater than those in 90 degrees abduction+neutral and external rotation (means < or = 3N). INTERPRETATION: For young asymptomatic shoulders, the motions that induce impingement are not any arm abduction, but the arm abduction with a large internal rotation. Further study is indicated to examine the impingement force among various age groups.

Acromioclavicular Joint↗

PubMed2004

A non-invasive technique for assessing innominate bone motion.

OBJECTIVE: To determine the suitability of a magnetic tracking device to measure pelvic bone range of motion based on palpated and digitized pelvic landmarks. DESIGN: A repeated measures study was conducted in two experiments to determine the reliability and validity of innominate bone range of motion measured with a magnetic tracking device in healthy subjects through passive hip abduction and external rotation. BACKGROUND: Because of the anatomical position of the pelvic joints, kinematic analysis of joint motion is difficult. Accurate and precise measurements typically require highly invasive techniques involving implantation of titanium markers and exposing the subject to multiple radiographs. There is a need for a practical and accurate measurement method that will allow researchers and clinicians to accurately and reliably evaluate motion in the pelvis. METHODS: Innominate bone angles were measured for two static hip postures from the 3D spatial coordinates of the pelvic landmarks. By palpating and subsequently digitizing pelvic landmarks using an electro-magnetic tracking device the 3D coordinates were obtained. Palpated results were validated using CT scans and a metallic bead attached to the palpated landmarks. RESULTS: The mean range of innominate bone motion was between 3 degrees and 4 degrees (transverse plane) for each side with large variability across the subjects in the range of motion. Despite this variability, the measurements were found to be reliable and valid.

Biomechanical Phenomena↗

PubMed2004

Buoyancy is the primary source of generating bodyroll in front-crawl swimming.

The present study was conducted to determine the contribution of the turning effect of buoyant force for generating bodyroll and its relationship with the subjects' variability in swimming speed at distance pace and sub-maximal sprinting pace. The performances of front crawl swimming performed by 11 skilled swimmers were recorded with two panning periscopes for three-dimensional analysis. The bodyroll (BR) exhibited by each of the 11 male competitive swimmers was determined for every given instant as the time-integral of the conceptual angular velocity of the entire body about the long-axis, which was computed from the angular momentum and the moment of inertia of entire body. The part of BR generated by the buoyancy torque (BR(BT)) was determined from the moment of inertia of the entire body and the double time-integral of the buoyancy torque. The mean value for the peak-to-peak amplitude of the buoyancy torque was 15 Nm at distance pace and 19 Nm at sub-maximum sprinting speed. The contribution of buoyancy to BR was significantly greater ( P < 0.01) than that of the hydrodynamic forces. The individual swimming speed at sub-maximal sprinting pace was positively correlated ( P < 0.04) with the contribution of buoyancy to BR. These results showed that the skilled swimmers used buoyant force as the primary source of generating BR, and that faster swimmers used buoyant force more effectively to generate BR than slower swimmers. Based on the results and subsequent theoretical analysis, possible patterns of arm-BR coordination that may increase the effectiveness of using buoyant force for BR are discussed.

Computer Simulation↗

PubMed2003

Stroke frequency in front crawl: its mechanical link to the fluid forces required in non-propulsive directions.

Two hypotheses were tested: (a) stroke frequency is predictable from the amplitudes of bodyroll and the turning effect around the body's long-axis generated by the non-propulsive fluid forces (that is, the torque driving bodyroll), and (b) swimmers exhibit at least one alteration in the factors influencing the bodyroll cycle as they increase the stroke frequency for faster swimming, so that they can reduce the fluid forces "wasted" in non-propulsive directions. The mechanical formula that links stroke frequency and the kinetics of bodyroll was derived on the basis of Euler's equation of motion. Experimental data were collected from competitive swimmers to validate the derived mechanical relations and to examine the strategy that skilled swimmers would use to change the stroke frequency as they swam faster. A strong correlation (slow: r = 0.70 and fast: r = 0.85) and a non-significant difference between the observed stroke frequency and the formula-based estimates supported the first hypothesis. As the subjects increased stroke frequency (38%) for faster swimming, bodyroll decreased (19%) and the trunk twist increased (40%). The combined alterations resulted in a small reduction in the shoulder roll (12%), enabling the swimmers to gain the benefits associated with a large rolling action of the upper trunk, while limiting the amount of increase in the turning effect of fluid forces in non-propulsive directions (40%). The second hypothesis was, therefore, supported. The derived mechanical formula provides a theoretical basis to explore mechanisms underlying the interrelations among stroke frequency, stroke length and swimming speed, and sheds light on a possible reason that swimmers generally adopt six-beat kicks.

Computer Simulation↗