A snowboard having curved sides（sidecuts）maintains a certain angle between the board and the snow plane （edging angle）during descent. The width of the snowboard was measured after descent. The sidecut radius of curvature was calculated using half the value of the measured snowboard width. After the descent of the snowboard, a clear track was left on the snow plane. The inclination angle of the descending snowboard with respect to the horizontal plane（horizontal edging angle, β0）was obtained by measuring the inclination angle of the track on the snow plane． The sidecut of the snowboard was deformed in accordance with the change of the edging angle. The radius of curvature of the sidecut deformed during descent, R3, was calculated by the cylinder approximation. We photographed the track of the descending snowboard and drew the locus of the descent on paper by using the "method for drawing the locus of a sliding ski as observed from the direction perpendicular to the snow surface". The radius of curvature of the track left by the snowboard descending the snow plane, R, was obtained from this locus. When the relationship between R3 and R was examined, R did not always agree with R3. However, the sign of β0 measured on the snow plane corresponded to differences in the descent direction of the snowboard. That is, we reached a finding similar to that for sliding skis; "β0＝0 indicates a straight descent and β0≠0 indicates a turning descent."

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The first alpine ski racing event in Japan was held on January 21, 1912 at a 4-kilometer course from Asahiyama to Haizuka（later called Lerch course）with 20 red flags set along the course. Forty-four skiers, divided into three groups, took part in the event. The race was won by Kosaburo Kogure with a time of 25 minutes. The weather was fine on the day of the race and the course conditions were good. Lieutenant colonel Lerch, who was the starter as well as the sweeper, praised the skiers for their good performance. There are five original articles on the race and errors can be found in all of them. Some examples of erroneous statements in past articles are that 1）the race was held on February 11, 1911, 2）fifty skiers took part in the race, 3）there was 3-shaku of fresh snow, 4）the skiers were divided into two groups or into four groups, 5）the winning time was 26 minutes and 50 seconds, and 6）red beech wood was used for the poles.

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A telemarker turns with a telemark posture in which the inside ski trails the outside ski. In contrast, a skier however turns with a traverse posture in which the outside ski trails the inside one. Moreover, at the same time the heel of a telemarker on the inside ski is lifted up from the ski surface. The joint motion mechanism in a telemark turn is a significant point of interest in any analysis of telemarkers. What requires further explanation is how--and in what order--the telemarker enables heel-freedom, performs edging, and modifies the edging of the skis during the performance of a sequential parallel turn. We have developed a model capable of both flexion and extension of the knee joints which can parallel turn like a telemarker. The ankle joints are fixed. A hinge is put on the bottom of shoes and the surface of a ski. Then, from a straight down-hill running posture, by flexion (backward) of the left knee joint and extension (forward) of the right knee joint (or vice versa, i. e., flexion of the right knee joint and extension of the left knee joint), this model configuration can achieve the heel-free posture and the inward-leaning posture of a turn. Two servomotors were attached to the flexion and extension of knee joints. This model inclines to the heel-free side and the inside ski runs behind the outside ski. A parallel turn can be performed by using a side-cut telemark-ski. This model can perform techniques characteristic of telemark skiing, such as a sequential parallel turn with heelfreedom by flexion and extension of the knee joints from the straight down-hill running posture.

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This paper proposes the motion measurement system and analysis method of snowboarder to reveal characteristics of snowboarding turn on an outside actual snowfield. This motion measurement system that consists of 3D gyro sensor, 3-axis acceleration sensor and 3-axis magnetic field sensor can be used easily to the experiment because this system is directly attached to the body of snowboarder and the binding of snowboard. As a result of experiment on the carving turn by the snowboarder installed this system to upper body, lumber, femur and lower thigh and binding, we could obtain angular velocity, acceleration and magnetic field in the parts of body. Furthermore, we calculated joint angle of lumber, hip, knee and ankle based on the measurement information in order to analyze the motion of snowboarding turn. The joint angle indicated the characteristics of motion, that is, the internal-external motion of hip to twist lower limb and the flexion- extension motion of hip and the plantar flexion-dorsal flexion motion of ankle to generate edging angle in snowboarding turn. Therefore, the effectiveness and the validity of this motion measurement system and analysis method were proved. This motion measurement system can analyze the major features of snowboarding turn and this analysis method is able to quantitatively evaluate the skill of snowboarders.

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