The Influence of Trunk Impairment Level on the Kinematic Characteristics of Alpine Sit-Skiing: A Case Study of Paralympic Medalists.

This study aimed to examine the relationship between the trunk impairment level and the trunk kinematic characteristics during alpine sit-skiing from a classification perspective. Three Paralympic medalists in sitting classes (LW10-2, LW11, and LW12-2) participated in the present study. To simulate the racing conditions, giant slalom gates were set. To measure the kinematics of the skier and sit-ski during skiing, a motion capture method with inertial measurement units was used. The muscle activities of the trunk muscles were evaluated using electromyography. Chest lateral flexion, chest flexion, and hip flexion/extension angle during sit-skiing were reduced due to impairment. Additionally, the insufficient lateral flexion (angulation) caused a decrease in edging angle, and that the insufficient chest and hip flexion/extension caused a lower loading in the latter half of the turn through smaller vertical movement. Since edging angle and loading are key factors in ski control, the three joint motions could be measures of sport-specific activity limitation in sit-skiing classification. Between the LW10-2 and LW11 skiers, no distinct differences in trunk kinematics were found. Assuming the scaling factor of race time as a measure of skiing performance, one possible reason is that the difference in skiing performance the LW10-2 and LW11 skiers is considerably smaller relative to differences between the LW11 and LW12-2 skiers. There were no distinct differences among classes in the results of muscle activity, and therefore, this information appears to play a minimal role for classification.

Muscle Activity and Morphology in Slalom Skiing by a Single-Leg Amputee Ski Racer: A Case Study of a Paralympic Athlete.

The aim of this study was to clarify the characteristics of skiing by a single-leg amputee ski racer from the viewpoints of muscle activity, morphology, and the relationship between both elements through comparisons with those of a non-disabled ski racer. One elite athlete, classified as LW2 (left thigh amputation), and one non-disabled athlete, as a control, participated in this study. The cross-sectional area of thigh muscles was measured through magnetic resonance imaging. Additionally, muscle activities and joint and segment kinematics during slalom skiing were measured using electromyography and inertial measurement units, respectively. The muscle activities and joint kinematics of the amputee racer in the turn in which he performed with the inside edge of the ski were similar to those of the outside leg of the non-disabled racer over a turn. In contrast, at the turn in which the amputee racer performed with the outside edge (more difficult side), the amputee racer largely activated the biceps femoris (BF) in the first half of the turn compared to the non-disabled racer. The reason could be to control the angular momentum of the trunk during the forward tilting motion. This is because a greater activity of the BF was observed during the period in which the forward tilt of the trunk was increased, and the mean activity of the BF was the greatest during the first half of the right turn in which the range of the motion of the forward tilt was the greatest. In terms of muscle morphology of the amputee racer, a significant hypertrophy of the BF and vastus lateralis was observed compared to the non-disabled racers. The well-developed BF was considered to be related to the large activity during the turn performed with the outside edge of the ski.

Case Report: Countermeasures Against Heat and Coronavirus for Japanese Athletes at the Tokyo 2020 Olympics and Paralympic Games.

The Tokyo 2020 Olympics and Paralympic Games were held in the hottest environment in the history of the games. Additionally, the worldwide coronavirus disease 2019 (COVID-19) pandemic necessitated daily polymerase chain reaction (PCR) testing during the games, wearing a mask became mandatory publicly, and it was an unheard and unique Olympic with no spectators. Heat acclimation, hydration, and body cooling are essential for safe and high-performance activities in hot environments. In 2015, the Japan Institute of Sports Sciences launched the "Heat Countermeasure Project" to conduct experiments and practical research on heat countermeasures and investigate issues related to heat countermeasures in each athletic event. The results obtained were proposed to various Japan national sports teams, and support for heat countermeasures for the Tokyo 2020 games was promoted in consultation with national federations. Furthermore, due to the COVID-19 pandemic, infectious disease countermeasures for the Tokyo 2020 Games during support were a must. Moreover, athletes, coaches, and team staff could not avoid implementing heat countermeasures while adopting measures against infectious diseases. This study aimed to clarify the issues faced with heat countermeasures and report on heat acclimation training and cooling support efforts, considering measures against infectious diseases.

Kinematics and joints moments profile during straight arm press to handstand in male gymnasts.

Biomechanical features of the handstand, one of the most fundamental skills required for artistic gymnastics events, have not been well documented. The purpose of this study was to clarify the kinematics and joint moment profiles during straight arm press to handstand in different highly skilled male gymnasts. Fifty-nine male gymnasts performed a straight arm press to handstand on a force platform and were judged on their performance by experienced certified judges. Subjects were divided into two groups (highly-skilled and less-skilled). Kinematic data were obtained using a video camera synchronized with force platform. Joint moments (wrist, shoulder, hip) during each straight arm press to handstand were calculated using the inverse dynamics solution. Larger shoulder flexion moments were observed in less-skilled compared with highly- skilled performers (at 3-59%, p < 0.001) while larger hip flexion moments were observed in highly- skilled performers at 52% (p = 0.045) and 56% (p = 0.048) and normalized time of straight arm press to handstand. Major differences between highly-skilled and less-skilled performers were observed in hip joint moment production as it shifted from extension to flexion from the leg horizontal position to the handstand position in highly-skilled gymnasts. Successful straight arm press to handstand techniques observed in highly-skilled performers were characterized as a more acute pike position at toe-off as well as hip flexor moments at latter phase of the straight arm press to handstand.