<p>&nbsp;&nbsp;&nbsp;&nbsp;In this study, we reviewed the literature on the gliding technique for diagonal-stride cross-country skiing from the perspectives of biomechanical and functional analysis; both of these assess cross-country skiing "externally". By comparing the results of these analyses, we identified the main focus areas of the gliding technique evaluation using motion analysis. <BR>&nbsp;&nbsp;&nbsp;&nbsp;1) The temporal order of the movement processes between the phases was different for the early deceleration phase of biomechanical analysis and the primary functional and preparatory secondary phases of functional analysis. <BR>&nbsp;&nbsp;&nbsp;&nbsp;2) The temporal order of the functional phase movement processes was the same in the late deceleration phase of biomechanical analysis and the transitional secondary phases of functional analysis; however, the movement tasks were different. <BR>&nbsp;&nbsp;&nbsp;&nbsp;3) The challenges identified in the actions associated with achieving the movement tasks were different in each of the phases. Biomechanical analysis was most important in the analysis of singular movements. On the other hand, functional analysis was more important in the analysis of multiple simultaneous movements. <BR>&nbsp;&nbsp;&nbsp;&nbsp;In this study, both biomechanical analysis and function analysis were found to have merits and demerits, however results that compared both analyses were found to be most beneficial. Functional analysis grasped the functional unit of movement, considering movement task as an important step in the movement process. Functional analysis provides important findings on movement affinity for the mastery of the movement. <BR>&nbsp;&nbsp;&nbsp;&nbsp;Therefore, functional analysis can be an important finding, as athletes and coaches are concerned with the practicalities of movement. Functional analysis is better than biomechanical analysis, as it can help in the practical aspects of coaching. <BR>&nbsp;&nbsp;&nbsp;&nbsp;These findings will make it easier to perform the technicalities of coaching cross-country skiing diagonal strides for both coaches and athletes.</p>

クロスカントリースキー競技において，競技パフォーマンスである滑走速度とサイクル特性との関係は深く，走法によって異なる関係性があることが知られている．本研究の目的は，競技現場で取得可能な用具の長さ情報を用いたサイクル特性の分析アプリケーションを開発し，その精度を検証したうえで，選手のサイクル特性を事例的に明らかにすることであった．その結果，１）簡単なマウス操作とキーボード操作によって，競技現場のコーチや選手が滑走速度，ストライド長，サイクル頻度，ポーリング時間およびスイング時間を容易に取得できること，２）開発したアプリケーションの精度について，従来の DLT 法と同程度であること，が示された．また，今回開発したアプリケーションを用いて日本代表選手と大学生選手のダブルポーリング走法中のサイクル特性を比較した結果，日本代表選手の滑走速度が高いこと，男子日本代表選手はストライド長を長くしてより高い滑走速度を獲得していること，女子日本代表選手はサイクル頻度を高くしてより高い滑走速度を獲得していることが示唆された．

The purpose of this study was to investigate the racing characteristics of elite roller speed skaters in a 300-m time trial race (300m TT). The subjects were 21 skaters who participated in the World Roller Speed Skating Championships in 2016. These included 9 skaters who qualified for the finals and 12 who ranked between the 25th and 45th places. Roller speed skaters glide while keeping their feet grounded for a short time in a curve: a movement known as "carrying". Nine finalists who performed carrying in C2 and C3 were classified as the top group (age 24.2 ± 2.4 years; height 1.8 ± 0.1 m; weight 73.2 ± 7.1 kg). Nine of 12 skaters who performed carrying in C2 and C3 were classified as the subgroup (age 24.0 ± 3.4 years; height 1.8 ± 0.1 m; weight 74.6 ± 7.1 kg), and 3 skaters were classified as the non-carrying group (age 25.0 ± 5.1 years; height 1.8 ± 0.0 m; weight 73.7 ± 2.4 kg). In this study, 300mTT was classified as 4 straight sections – Start, S1, S2, and Finish – and 3 curve sections – C1, C2, and C3. The investigated parameters included the 300mTT goal time (T300), the skating speed in each section, and the time during which carrying was performed (Tcar). In the subgroup and non-carrying group, the skating speeds in S1 were similar, but the skating speed of the non-carrying group in C2 was lower than that of the subgroup. The top group glided at a higher skating speed in every section expect C3. There was no significant difference in Tcar, and there was no significant correlation between T300 and Tcar in C2 and C3. There was a significant positive correlation between T300 and Tcar in C2. In the top group, there was a significant negative correlation between T300 and skating speed at C2. These results suggest that carrying in C2 is important for gliding at a higher skating speed in 300mTT, and that Tcar in C2 and C3 for elite roller skaters does not influence T300. Elite roller skaters had superior acceleration capacity in the Start, and obtained a higher skating speed until S1, after which they maintained a higher skating speed in C2. Furthermore, elite roller skaters were able to achieve a higher skating speed in spite of fatigue in their support legs.

<p>&nbsp;&nbsp;&nbsp;&nbsp;The study aimed to investigate the kinematics of curve skating among national-level Japanese roller speed skaters and world-class skaters in the 300-m time-trial race. The subjects were 12 finalists who were classified as world-class skaters (age, 24.9±4.1 years, height, 177.0±6.0 cm, weight, 73.0±5.2 kg) and 3 Japanese skaters (age, 18.7±0.5 years, height, 169.0±0.0 cm, weight, 64.3±3.1 kg) in the World Roller Speed Skating Championships in 2016. Data on the three-dimensional coordinates were calculated using the direct linear transformation technique. Parameters included the displacement of distance between the center of curvature and the center of body mass at the end and start of stroke, the skating length, speed, the stroke frequency, time in the one- and dual-leg supporting phase, side tilt angle, and segment angle. This study found the following: Japanese skaters (1) glided while climbing the incline owing to their low stroke frequency; therefore, their skating velocity additionally decreased; (2) were unable to control their center of body mass (COM) because they tilted their left shank less inward in the first half of the left stroke, (3) performed larger push-off movements in the duration of the dual-leg supporting phase in both strokes; and (4) restrained their COM as they tilted their shank less forward after tilting backward in both strokes; therefore, their skating velocity in the skating direction was lower.</p>

Cross-country skiers perform over a long distance using poles and skis. Physical fitness, in terms of factors such as VO₂max and muscle strength, skiing technique and race strategy are important for winning competitions. To plan the race strategy, investigations of the course profile and race analysis are needed. The purposes of this study were to investigate cross-country skiing course profiles which were planned for the Winter Olympic Games at Peyongchang, and to analyze the men's 15km+15km World Cup skiathlon race (SA) as a pre-competition event. A cross-country skier followed the classical and skating courses using a GNSS (Global Navigation Satellite System) antenna. The antenna instantly measured the latitude, longitude and height of the skier on the courses. The coordinate values on a plane were calculated from latitude and longitude, after the inclination was then calculated from the coordinate values and height every 10 m. The overall finish time and transit time at 24 points for 12 skiers in SA were retrieved from the Official Home Page of the International Ski Federation (FIS), and the segment times among the various points were calculated. Three segment times formed a lap, and each segment speed was calculated by dividing the segment distance by the segment time. For the classical course profile, the distance was 3819 m and the maximum inclination was 18.6%. In contrast, for the skating course, the distance was 3777 m and the maximum inclination was 20.6%. No correlation was found between the overall finish time and the segment times for the classical course. This result was attributable to small variations in the lap times for the classical course because of the skiers' use strategy, checking among competitors, and the mass-start. On the other hand, positive correlations were found between the overall finish time and the segment times on skating. In skating, the segment speeds from the final phase of the 2nd lap to the middle phase of the 3rd lap indicated deceleration relative to the 1st lap. These results suggest that gliding on a skating course in a short time is important for shortening the overall finish-time. Especially, it is important to minimize the deceleration of the 2nd and 3rd lap segment speed. The race pattern for the Olympic Games was similar to that of pre-competition, except for the time taken. These results indicate that pre-competition race analysis is useful for devising a strategy for target competition.

The motion capture of alpine skiing is technically challenging. Motion capture systems using inertial sensors such as gyroscopes and accelerometers have begun to be used in sport. The capture volume of the system can be large enough to cover the whole area of a particular sporting event, because sensors are affixed to the human body itself. The current study developed a method of tracking the pose of an alpine skier using gyroscopes for 3 min with a tracking error of 2° (RMSE). The technical significance of the presented method, which uses one common simple algorithm to improve measurement of pose, applies to many experimental conditions. The adoption of a high resolution (24 bit) analog-to-digital converter and high sampling rate (1 kHz) also contribute to the improvement of measurement time.

本研究の目的は，クロスカントリースキー競技中のダイアゴナル走法を対象に競技パフォーマンスに優れた選手のキネマティクス的特徴を明らかにすることであった．15 kmクラシカル競技に参加した成人男子クロスカントリースキー選手を6度の上り坂の地点で撮影した．被験者は，競技成績によって上位群と下位群に分類した．比較の結果，競技パフォーマンスに優れた選手は，（１）大きいストライド長を獲得していること，（２）スキーを離地させてからポールを接地させるまでの滑走時間が長いこと，（３）ポールを接地してから比較的早い段階で肘を伸展させていること，（４）プッシュオフ動作時にスキーと雪面とをすばやくグリップさせ，その後，膝関節をすばやくかつ大きく伸展させていることが明らかとなった．

<p>&nbsp;&nbsp;&nbsp;&nbsp;The purpose of this study was to investigate the technical factors in curve skating in inline speed skating on a flat track by comparing between an elite skater (n＝1) and a trained skater (n＝1) in flat track. Data on the three dimensional coordinates of the skaters who participated in the 60th East Japan Roller Speed Skating Championship were collected to calculate kinematic parameters such as the trajectory of the center of body mass, joint and segment angles of the support leg, and tilt angles of the body and shank of the support leg during the curve skating using the direct linear transformation technique. In the left leg stroke of the top skater, the forward rotation of the thigh was greater than the forward bent of the shank and the forward movement of the center of the body mass was greater than that in the left leg stroke of the trained skater. The tilt angles of the body and the shank of the support leg to the inside of the curve of the top skater were greater than those of the trained skater. The top skater tilted the body and the shank of the support leg sideward largely during the right and left leg strokes. These results suggest that high degrees of rotation of the thigh of the support leg, and tilting of the body and the shank of the support leg to the inside of the curve were good technical factors in curve skating among Japanese inline speed skaters.</p>

This study aims to develop and validate an automated system for identifying skating-style cross-country subtechniques using inertial sensors. In the first experiment, the performance of a male cross-country skier was used to develop an automated identification system. In the second, eight male and seven female college cross-country skiers participated to validate the developed identification system. Each subject wore inertial sensors on both wrists and both roller skis, and a small video camera on a backpack. All subjects skied through a 3450 m roller ski course using a skating style at their maximum speed. The adopted subtechniques were identified by the automated method based on the data obtained from the sensors, as well as by visual observations from a video recording of the same ski run. The system correctly identified 6418 subtechniques from a total of 6768 cycles, which indicates an accuracy of 94.8%. The precisions of the automatic system for identifying the V1R, V1L, V2R, V2L, V2AR, and V2AL subtechniques were 87.6%, 87.0%, 97.5%, 97.8%, 92.1%, and 92.0%, respectively. Most incorrect identification cases occurred during a subtechnique identification that included a transition and turn event. Identification accuracy can be improved by separately identifying transition and turn events. This system could be used to evaluate each skier's subtechniques in course conditions.

The purpose of this study was to identify differences in (1) total skiing time and (2) lap time for different course situations in cross-country skiing (uphill, flat and downhill) between classical-style sub-techniques using classical skis and double poling and herringbone sub-techniques using skating skis. The subjects were 5 college cross-country skiers who performed at maximal effort in 2 different trials: classical-style sub-techniques while wearing classical-style skis (CL), and double poling and herringbone sub-techniques while wearing skating-style skis (DP). Skiing velocity was measured with a global navigation satellite system module and mobile PDA. The sub-techniques employed were recorded with a small video camera. It was found that a strategy using DP (1) significantly increased the skiing time, (2) increased the skiing velocity on downhill and decreased it on uphill, and (3) was associated with a tendency to use double poling on uphill.

The aims of the present study were (1) the development of an automated system for identifying classical-style ski subtechniques using angular rate sensors, and (2) the determination of the relationships among skiing velocity, ski course conditions, and ski subtechniques using a global navigation satellite system (GNSS) and the developed automated identification system. In the first experiment, the performance of a male cross-country skier was used to develop an automated system for identifying classical-style ski subtechniques. In the second one, the performances of five male and five female college cross-country skiers were used to validate the developed identification system. Each subject wore inertial sensors on both wrists and both roller skis, a small video camera on the helmet, and a GNSS receiver. All subjects skied a 6,900-m roller ski course using the classicalstyle at their maximum speed. The adopted subtechniques were identified by the automated method based on the data obtained from the sensors, and also by visual count from a video recording of the same ski run. The results showed that the automated identification method could be definitively used to recognize various subtechniques. Specifically, the system correctly identified 9,307 subtechnique cycles out of a total of 9,444 counted visually, which indicated an accuracy of 98.5%. We also measured the skiing velocity and the course slope using the GNSS module. The data was then used to determine the subtechnique distributions as a function of the inclination and skiing velocity. It was observed that male and female skiers selected double poling below 6.7 degrees and 5.5 degrees uphill, respectively. In addition, male and female skiers selected diagonal stride above 0.7 degrees and 2.5 degrees uphill, and below 5.4 m/s and 4.5 m/s velocity, respectively. These results implied that the subtechnique distribution plot could be used to analyze the technical characteristics of each skier.

The purpose of this study was to evaluate the relationships between race performance and cycle characteristics in a 10-km classic-style men's cross-country ski competition. The subjects were competitors in the 89th Japan National Ski Championships. Skiing motions of the subjects on flat stretches (1.5 km and 6.5 km) and uphill slopes (1.7 km and 6.7 km) were videotaped using two high-speed cameras. Cycle characteristics were calculated based on measurement of hip displacement and cycle time. It was revealed that elite competitors (1) performed at high velocity at all measurement points, (2) reduced their velocity in the last half of the race, (3) achieved a high velocity in double poling and diagonal stride, (4) increased their cycle length and cycle rate when employing the double poling technique, and (5) increased their cycle length when employing the diagonal stride technique.

The purpose of this study was to identify relationships between the skiing velocity and each axial force components on the ski during V2-skate technique. Fifteen elite cross-country skiers performed at their maximal efforts. Ski reaction forces were measured using specific ski sensors, the A/D converter, the transmitter, and the personal computer. The skiing
velocity was recorded by the laser distance meter. Skiers exerted the skier generated force on downward in vertical, medial, and posterior directions
in the coordinate system of the ski during the push-off phase. The peak force on downward in the vertical direction of the ski positively correlated with the skiing velocity. In contrast, the peak force on the medial
direction of the ski negatively correlated with the skiing velocity. Those results suggested that cross-country skiers increased the skiing velocity
by increasing the force on downward in the vertical direction and decreasing the force on the medial direction of the ski during the push-off
phase in the V2-skate technique.

記述分析法に関してプレー重心は散布したプレー回数の代表値を示す尺度として妥当であること，また，記述分析法がデジタル測定法と同等の精度を持つことが明らかとなった．

Purpose: This study aims to clarify the biomechanical changes in double poling performance in a sprint race of cross-country skiing caused by fatigue. Methods: Five cross-country skiers including those representing Japan national team performed double poling for 3 min in a flat ski circuit (320 m long), and their movement and force at around 30 m and 670 m were compared. Results: Because of fatigue, (1) the velocity significantly decreased because of a decrease in the cycle rate during 1 cycle, (2) the cycle rate decreased because of the slowly change in the upper body movement, (3) while body became to erect standing position and (4) the leg motion supported the upper body motion, and it was controlled together with upper body motion. These results show that in order to maintain the velocity of double poling in the second half of a race, it is important to maintain the movement of the upper body.

This study aims to quantify the degree of contribution of arms and legs during V2 skate in cross-country skiing from the viewpoint of the force along the direction of acceleration. Method: Six male cross-country skiers performed V2 skate at a speed of 6 m/s, and the pole and ski reaction forces were measured. In addition, using a high-speed camera, the three-dimensional coordinates of each part
of the body were obtained, and the velocity, the pole, and ski angles were calculated, which were then
converted to the force along the direction of movement. Results: The peak and mean forces along the direction of movement were 100 ± 20 and 63 ± 12 N, respectively, for the pole (one side) and 202 ± 48
and 106 ± 18 N, respectively, for the ski (one side). Those suggested that in V2 skate at a speed of 6
m/s, the degree of contribution of the force due to arms（push of both poles）and leg（push-off of right
or left ski）are approximately the same. Furthermore, when pushing off with the ski, although the force component perpendicular to the ski comprises a large proportion, it was shown that the force can be
divided into lateral and horizontal directions by converting it to a global coordinate system using the
ski edge and orientation angle. In addition, ski edge angle was changed depending on abduction of hip
joint. Ski force propulsion was generated by bduction of hip joint and extension of hip and knee joint.
Hence, this implies that in order to increase the force of push-off for hip abduction and extension and
knee extension movement, it is important to point the force along the direction of movement while exerting a force perpendicular to the ski.

The aim of this study was to clarify how coaching in the V2 skate technique, intentionally including the flight phase, affects the skating velocity of female cross-country skiers. First, seven female skiers performed the V2 skate technique at maximal effort. Next, five subjects who did not have any flight phase in their V2 skate technique were trained to perform it along with the flight phase for about 10 minutes, and were then asked to execute the flight phase. In this test, the subjects used poles and skis equipped with force sensors, and their velocity was recorded. After the test, each subject was interviewed about her subjective experience of the V2 skate including the flight phase. It was found that the training caused all of the subjects to change the V2 skate so that it included the flight phase. Moreover, during skating attempts with the flight phase, both the skating velocity and the peak and average forces of the pole and ski increased significantly. The interviews revealed that three subjects felt a sense of fear when they were airborne, and that four subjects felt close to loss of balance. These results suggest that training in the V2 skate with a flight phase was effective for increasing the skating velocity of the female skiers. Moreover, it was evidently difficult for the female skiers to learn to skate with flight phases through a normal training method because of the sense of fear they experienced during the maneuver.

本研究は，クロスカントリースキー競技クラシカル種目のスタート局面におけるダブルポーリング走法およびダイアゴナル走法をキネマティクス的手法を用いて解析し，それぞれの走法の特徴を明らかにすることで，加速局面においてより高い滑走速度を得るための示唆を得ることを目的とした．被験者は，日本代表を含む大学クロスカントリースキー競技者 5 名とした．被験者には，雪上での 50m の直線コースにおいて，ダブルポーリング走法およびダイアゴナル走法，さらに被験者が最も滑走速度が高くなるように前述の 2 走法を自由に組み合わせた試技(以下，コンビネーション試技)を用いて静止した状態から最大努力で滑走させた．被験者の実施をレーザー瞬時速度測定器と高速度ビデオカメラを用いて記録し，50m の所要時間，10m 毎の平均速度および最高速度，総サイクル数，ピッチおよびストライドを算出した．その結果，(1) 50m の所要時間に差はみられなかった，(2) 最高速度はダブルポーリング走法がダイアゴナル走法と比較して有意に高値を示した，(3) 滑走速度は，10-20m 区間においてはダイアゴナル走法がダブルポーリング走法より有意に高値を示し，(4) 30-50m 区間においてはダブルポーリング走法がダイアゴナル走法より有意に高値を示した，(5) コンビネーション試技は，スタート直後にダイアゴナル走法を実施し，その後ダブルポーリング走法に切り替えて実施されていた．以上の結果から，クラシカル種目におけるスタート局面では，まずスタート直後の加速に優れるダイアゴナル走法を用いて，次にダイアゴナル走法より最高速度の高いダブルポーリング走法に切り替えるというコンビネーション技術が，高い滑走速度を得るために重要となることが示唆された．

Two types of profiles of ski reaction forces during V2 skating have been reported by previous investigations. One of the differences between these two profiles is in the existence of the “flight phase,” i.e., the phase in between gliding and kicking off, in which the skis float above the snow while skiing. It has been suggested that the difference is caused by the skating velocity. The purpose of this study is to clarify whether or not there is a relationship between the occurrence of the flight phase and the increase in velocity during V2 skating. Seven elite male cross-country skiers performed two types of trials at different velocities (high and medium speeds). The high and medium speeds correspond to the competitive pace for a sprint race and a 10-km race, respectively. The kinematics was measured for each trial using two video cameras and a panning direct linear transformation technique. The flight phase was determined by the ski load data obtained from a sensor attached to the ski. No flight phase was confirmed during medium-speed skating, but a flight phase was confirmed during high-speed skating, indicating the existence of the flight phase is related to an increase in skating velocity. However, the hip- and knee-joint angles and the vertical displacement of the center of mass were not changed by an increase in skating velocity. These results suggested that the flight phase was a small change from the standpoint of kinematics, but it may cause changes in muscle activity since the leg muscle groups experience no ground reaction force.