Thermal behaviour of ski-boot liners: effect of materials on thermal comfort in real and simulated skiing conditions

The choice of the appropriate material for the construction of ski-boot liners is of fundamental importance in order to achieve ergonomic comfort and high thermal insulation. In this work the effect on thermal comfort of different materials used for commercial ski-boot liners has been analysed. The thermal insulation and the moisture management of liners made of different materials have been tested both in a climatic chamber and in outdoor conditions using wireless sensors combined with infrared thermography. The results obtained show substantial differences in terms of thermal comfort between the liners in the same environmental conditions, showing that closed cell ethylene vinyl acetate foams provide the best thermal comfor

Talent development in young cross-country skiers: longitudinal analysis of anthropometric and physiological characteristics

Introduction: Very little is known about talent development and selection processes in young cross-country skiers. Aim: (1) to analyze the effect of age on anthropometric and physiological parameters in medium-to-high level cross-country skiers during the late teenage period; (2) to describe parameters' trend in selected talents after the late teenage period; (3) to define which characteristics during the late teenage period could discriminate against further talent selection. Method: We found 14 male (M) and nine (F) athletes in our database, identified as talents by regional teams during the late teenage period, who performed the same diagonal-stride roller-skiing incremental test to exhaustion at 17 and 18 years old. Of these, four M and three F teenagers performed four further evaluations, and were selected by the national team. Age effect during the late teenage period was verified on anthropometric and physiological parameters measured at maximal intensity (MAX), first (VT1), and second (VT2) ventilatory thresholds, and 3\ub0 and 6\ub0 of treadmill incline. An observational analysis allowed to evaluate parameters' trend after the late teenage period in selected athletes, and to determine possible characteristics early discriminating further selection. Results: During the late teenage period, height, weight, and BMI was still raising in M as well as V'O2 at VT2 and 6\ub0 of treadmill incline (all P > 0.05). In F, mass-scaled V'O2 MAX increased while heart rate (HR) at MAX and VT2 decreased (all P > 0.05). Since the late teenage period, all selected males showed maximal ventilation volumes, absolute V'O2 at MAX, VT1, and VT2 that were within or above the 75th percentile of their group; the same was found in selected females for mass-scaled V'O2 MAX, VT1, and VT2 time. After the late teenage period, all selected athletes showed an increasing trend for VT2 time, while a decreasing trend for sub-maximal energetic cost, %V'O2 and HR. Discussion: During the late teenage period, males are still completing their maturation process. Since the late teenage period, some physiological parameters seem good indicators to early discriminate for further talents. A progressive increase in skiing efficiency was demonstrated in developing talents of both sexes after the late teenage period

Thermal behaviour of ski-boot liners: effect of materials on thermal comfort in real and simulated skiing conditions

The choice of the appropriate material for the construction of ski-boot liners is of fundamental importance in order to achieve ergonomic comfort and high thermal insulation. In this work the effect on thermal comfort of different materials used for commercial ski-boot liners has been analysed. The thermal insulation and the moisture management of liners made of different materials have been tested both in a climatic chamber and in outdoor conditions using wireless sensors combined with infrared thermography. The results obtained show substantial differences in terms of thermal comfort between the liners in the same environmental conditions, showing that closed cell ethylene vinyl acetate foams provide the best thermal comfort

Exploring muscle activation during nordic walking: a comparison between conventional and uphill walking

Nordic Walking (NW) owes much of its popularity to the benefits of greater energy expenditure and upper body engagement than found in conventional walking (W). Muscle activation during NW is still understudied, however. The aim of the present study was to assess differences in muscle activation and physiological responses between NW and W in level and uphill walking conditions. Nine expert Nordic Walkers (mean age 36.8\ub111.9 years; BMI 24.2\ub11.8 kg/m2) performed 5-minute treadmill trials of W and NW at 4 km/h on inclines of 0% and 15%. The electromyographic activity of seven upper body and five leg muscles and oxygen consumption (VO2) were recorded and pole force during NW was measured. VO2 during NW was 22.3% higher at 0% and only 6.9% higher at 15% than during W, while upper body muscle activation was 2- to 15-fold higher under both conditions. Lower body muscle activation was similarly increased during NW and W in the uphill condition, whereas the increase in erector spinae muscle activity was lower during NW than W. The lack of a significant increase in pole force during uphill walking may explain the lower extra energy expenditure of NW, indicating less upper body muscle activation to lift the body against gravity. NW seemed to reduce lower back muscle contraction in the uphill condition, suggesting that walking with poles may reduce effort to control trunk oscillations and could contribute to work production during NW. Although the difference in extra energy expenditure between NW and W was smaller in the uphill walking condition, the increased upper body muscle involvement during exercising with NW may confer additional benefit compared to conventional walking also on uphill terrains. Furthermore, people with low back pain may gain benefit from pole use when walking uphill

COVID-19-associated Guillain-Barré syndrome in the early pandemic experience in Lombardia (Italy)

Objective To estimate the incidence and describe clinical characteristics and outcome of GBS in COVID-19 patients (COVID19-GBS) in one of the most hit regions during the frst pandemic wave, Lombardia. Methods Adult patients admitted to 20 Neurological Units between 1/3–30/4/2020 with COVID19-GBS were included as part of a multi-center study organized by the Italian society of Hospital Neuroscience (SNO). Results Thirty-eight COVID19-GBS patients had a mean age of 60.7 years and male frequency of 86.8%. CSF albuminocytological dissociation was detected in 71.4%, and PCR for SARS-CoV-2 was negative in 19 tested patients. Based on neurophysiology, 81.8% of patients had a diagnosis of AIDP, 12.1% of AMSAN, and 6.1% of AMAN. The course was favorable in 76.3% of patients, stable in 10.5%, while 13.2% worsened, of which 3 died. The estimated occurrence rate in Lombardia ranges from 0.5 to 0.05 GBS cases per 1000 COVID-19 infections depending on whether you consider positive cases or estimated seropositive cases. When we compared GBS cases with the pre-pandemic period, we found a reduction of cases from 165 to 135 cases in the 2-month study period in Lombardia. Conclusions We detected an increased incidence of GBS in COVID-19 patients which can refect a higher risk of GBS in COVID-19 patients and a reduction of GBS events during the pandemic period possibly due to a lower spread of more common respiratory infectious diseases determined by an increased use of preventive measures

Assessment of the reliability of a custon built Nordic Ski Ergometer for cross-country skiing power test.

AIM: Despite the recent development of cross-country ski technique having led to an increase in the importance of upper body power, there is a substantial lack of specific equipment for upper body force and power evaluation. In order to achieve good reproducibility of the skiing motion, a new upper body ergometer has been developed in our lab and tested by elite cross-country skiers. In this study, the reliability of this device was assessed comparing upper body power measurements with double poling ski performance in the field. METHODS: The new apparatus consists of an electric motor acting as load and actively controlled by a personal computer on the basis of force and velocity data. Nine cross-country skiers (age: 21.7+/-3.12 years; body weight: 72.2+/-3.8 kg), competing at international level, performed a ski test on a 1.2 km long sprint track and a 50 s exercise on the Nordic Ski Ergometer. The velocity of the last section (180 m, slope 1.37%) of the track, performed using the double poling technique at maximal voluntary intensity, was related to the upper body power measured at the ergometer. RESULTS: Mean upper body power was 9.22+/-2.29 W kg(-1), while average velocity on the section considered was 6.66+/-0.67 m s(-1). A high correlation (R(2)=0.871) was found between upper body power and ski velocity. CONCLUSION: In addition to overcoming the main limitations that affect traditionally used equipment, the strong relationship between the parameters obtained with the new ergometer and ski velocity indicates their ability to assess athletes performance. The new apparatus could therefore be considered a ski specific testing equipment for cross-country skiers which is useful for reproducing upper body involvement in cross-country ski-ing in a laboratory setting

From front to back-load ergometer: muscular and biomechanical differences

The relevance of double poling ski technique is already underlined by a lot of authors. Double poling technique involves massively upper body (Holmberg, 2005).To achieve high specificity of indoor double poling force training, different ergometers are developed. The aim of this preliminary study was to compare biomechanical and neuromuscular differences between standard pull-down ergometer and a new idea of back-load ergometer to better emulate double poling technique during maximal force training

Double poling kinematic changes during the course of a long-distance race: effect of performance level

We aimed to evaluate the changes in double poling (DP) kinematics due to a long-distance cross-country skiing race in athletes with different performance levels. A total of 100 cross-country skiers, belonging to 10 different performance groups, were filmed on flat terrain 7 and 55 km after the start line, during a 58-km classical race. Cycle velocity, frequency and length decreased from the best to the lower-ranked group, while duty cycle increased (all P <.001). Between track sections, cycle velocity and length decreased, duty cycles increased (all P <.001) while frequency was unaltered (P =.782). Group*section interactions resulted for cycle velocity (P =.005). Considering all the participants together, % change in cycle velocity between sections correlated with % change in length and duty cycle (all P <.001). Thus i) skiers in better groups showed longer and more frequent cycles as well as shorter duty cycles than skiers in slower groups; ii) throughout the race all the groups maintained the same cycle frequency while decreasing cycle velocity and length; iii) better groups showed a lower reduction in cycle velocity. Individually, a low reduction in cycle velocity during the race related to the capacity to maintain long cycles and short duty cycles

Effect of training on specific power expression in elite cross country skiers

Cross country skiing is characterized by many techniques which differ in contribution offered by upper and lower limbs to propulsion. In diagonal stride technique upper and lower body are fully involved in the movement. The aim of this study is to analyze upper body contribution in diagonal stride and the effect of training on specific power expression in elite cross country skiers

Energetics and biomechanics of double poling in regional and high-level cross-country skiers.

Purpose:The aim of this study was to evaluate the energetics and the biomechanics of double poling technique (DP) in two groups of cross-country skiers.Methods:Eight high-level (HLG) and eight regional-level (RLG) skiers performed a 5-min sub-maximal DP trial, roller skiing on a treadmill at 14 km h 121 and 2\ub0. Energetic cost (ECDP), center of mass (COM) vertical displacement range, body inclination (\u3b8, i.e., the angle between the vertical line and the line passing through COM and a fixed pivot point identified at feet level) and mechanical work associated to COM motion were analyzed. Pole and joint kinematics, poling forces and cycle timing were also considered.Results:HLG showed lower ECDP than RLG, smaller COM vertical displacement range and mechanical work, whereas higher \u3b8 during the early part of the poling phase (P < 0.05). In HLG, pole inclination was higher, poling forces greater and cycle duration longer (P < 0.05). Considering all skiers, a forward multiple regression revealed that the maximum value of \u3b8 (\u3b8 max) and the minimum value of COM vertical displacement resulted the COM-related parameters that better predict ECDP (AdjR 2 = 0.734; P < 0.001). Moreover, \u3b8 max positively related to poling force integrals and cycle duration (P < 0.05).Conclusions:A pronounced body inclination during the early poling phase and a reduced COM vertical displacement range concur in explaining the differences in ECDP found between the groups and among the skiers. A mechanically advantageous motion of COM during DP improves poling effectiveness, reduces cycle frequency and the mechanical work sustained