Changes in roller skiing economy among Nordic combined athletes leading up to the competition season.

The purpose of this study was to compare roller skiing economy during different training phases in Nordic combined (NC) athletes and determine the aerobic and anaerobic factors responsible for changes in skiing economy. Seven elite NC athletes underwent incremental load tests on a large buried treadmill in both spring and autumn using roller skis. Measurements included oxygen uptake, respiratory exchange ratio, and blood lactate concentration. Roller skiing economy was calculated from aerobic and anaerobic energy system contributions, and overall roller skiing economy was determined by combining the two. Comparisons were made between the skiing economies obtained in the two measurement sessions. Physical characteristics and incremental test performance remained consistent between the two measurement sessions. The overall skiing economy at each speed significantly improved toward the competition season (p < 0.05). Similarly, the contribution of anaerobic energy system at each speed showed significant improvement (p < 0.05). In contrast, the contribution of aerobic energy system did not change between the two measurement sessions. This study reveals that NC athletes enhance their skiing economy at the same speed during submaximal efforts in preparation for the competition season. This improvement is predominantly associated with an improvement in the contribution of anaerobic energy system.

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.

Development of the Rope-Climbing Ergometer for Physical Training and Testing.

The purpose of this study was to develop and characterize a rope-climbing ergometer. A custom-made loading device that has an eddy current brake with an electrical current control circuit was developed to impose resistive load on the rope. A calibration test was first performed using a three-phase induction motor to associate the scale of the load-level setting (100 levels) with the resultant traction force. The calibration test yielded criteria values of loads (123 N at Level 0 and 1064 N at Level 100). The human test was carried out by 14 male subjects. The participants performed eight sets of 10-second maximal-effort exercises at different levels. Presumable trajectories of force, velocity, and power were obtained. The mean force increased by 161% (from 147.5 N at Level 0 to 383.7 N at Level 18), whereas the mean velocity decreased by 64.7% (from 1.87 m/s at Level 0 to 0.66 m/s at Level 18). The mean power reached its peak at Level 9 (320 W). The new rope ergometer for physical training and testing was successfully developed and characterized in this study. However, it remains to be seen whether its concurrent validity and reliability are qualifiable.

Automatic Identification of Subtechniques in Skating-Style Roller Skiing Using Inertial Sensors.

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.

Automated identification and evaluation of subtechniques in classical-style roller skiing.

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 classical-style 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° and 5.5° uphill, respectively. In addition, male and female skiers selected diagonal stride above 0.7° and 2.5° 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. Key PointsThe automatic identification method, which utilizes data obtained by small and light inertial sensors, could be used to recognize subtechniques of classical-style roller skiing with a high accuracy of 98.5%.The skiing velocity was measured using a small DGNSS module at all over the course, which made it possible to evaluate the technical features of skiers together with the results of the automatic identification.However, there were limitations in the automatic identification during the start phase, the downhill, and the transition period between subtechniques.

Effectiveness of a lumbar support continuous passive motion device in the prevention of low back pain during prolonged sitting.

STUDY DESIGN: Subjective ratings of discomfort were compared between a fixed lumbar support and lumbar support continuous passive motion (CPM) device. OBJECTIVE: To compare a fixed lumbar support with a lumbar support CPM device during prolonged sitting. SUMMARY OF BACKGROUND DATA: To prevent low back pain during prolonged sitting, an inflatable lumbar support CPM has been developed. There are no studies that compare static lumbar support with lumbar CPM using the same pressure in the cushions. METHODS: A total of 31 male volunteers without low back pain sat in the same chair for a 2-hour period on each of 3 consecutive days under 3 randomized test methods: 1, no lumbar support; 2, static lumbar support; and 3, lumbar support CPM. Each subject rated low back pain, stiffness, fatigue, and buttock numbness on a visual analog scale (VAS). Fixed lumbar support and CPM device were compared with a same inflation pressure in the cushion. For 10 subjects, the whole body posture and the pressure distribution changes of the human-seat interface during CPM were evaluated. RESULTS: Compared with no lumbar support, a significant improvement in VAS scores for low back pain, stiffness, and fatigue was obtained with both static lumbar support and with lumbar support CPM (P < 0.005). A significant (P < 0.005) improvement for buttock numbness was obtained only with lumbar support CPM. There were no statistical differences in all VAS scores between the fixed lumbar support and the CPM device. A forward rotation of the pelvic region was obtained during inflation of the cushion during CPM. Significant differences (P < 0.05) were found between cushion inflation and deflation periods both in contact areas and in the peak pressures at the human-seat interface. CONCLUSION: There were no statistical differences in the subjective ratings of discomfort between the fixed lumbar support and the CPM device.

Primary factors affecting maximum torsional loading of the tibia in running.

The purpose of this study was to determine primary factors that contribute to the magnitude of the maximum torsional moment on the tibia during running based on information from three-dimensional shank kinematics and ground reaction forces. Eight male subjects were asked to run along a straight track at 5.0 m s-1. Data were collected using two high-speed cameras and a force platform. Each subject's left foot and tibia were modelled as a system of coupled rigid bodies. First, net axial moments acting at both ends of the tibia were calculated using inverse dynamics. Then the tibial torsional moment was determined from the quasi-equilibrium balance of the net tibial axial moments. Our results showed considerable inter-individual variations for the tibial torsional moment during the stance phase of running. The maximum torsional moment reflecting external rotational loading of the proximal tibia was significantly correlated with the outward tilt angle of the shank in the frontal plane (r = 0.78, p < 0.05) and with the vertical force of ground reaction (r = 0.70, p < 0.05). In conclusion, lowering tibial torsional loading by interventions based on the present findings may lead to the reduction of running injuries that occur in athletes' tibiae.