A Scientific Perspective on Reducing Ski-Snow Friction to Improve Performance in Olympic Cross-Country Skiing, the Biathlon and Nordic Combined.

Of the medals awarded at the 2022 Winter Olympics in Beijing, 24% were for events involving cross-country skiing, the biathlon and Nordic combined. Although much research has focused on physiological and biomechanical characteristics that determine success in these sports, considerably less is yet known about the resistive forces. Here, we specifically describe what is presently known about ski-snow friction, one of the major resistive forces. Today, elite ski races take place on natural and/or machine-made snow. Prior to each race, several pairs of skis with different grinding and waxing of the base are tested against one another with respect to key parameters, such as how rapidly and for how long the ski glides, which is dependent on ski-snow friction. This friction arises from a combination of factors, including compaction, plowing, adhesion, viscous drag, and water bridging, as well as contaminants and dirt on the surface of and within the snow. In this context the stiffness of the ski, shape of its camber, and material composition and topography of the base exert a major influence. An understanding of the interactions between these factors, in combination with information concerning the temperature and humidity of both the air and snow, as well as the nature of the snow, provides a basis for designing specific strategies to minimize ski-snow friction. In conclusion, although performance on "narrow skis" has improved considerably in recent decades, future insights into how best to reduce ski-snow friction offer great promise for even further advances.

Preparing for snow-sport events at the Paralympic Games in Beijing in 2022: recommendations and remaining questions.

During the 2022 Winter Paralympic Games in Beijing, the Para snow-sport events will be held at high altitudes and in possibly cold conditions while also requiring adjustment to several time zones. Furthermore, the ongoing COVID-19 pandemic may lead to suboptimal preparations. Another concern is the high rate of injuries that have been reported in the Para alpine and snowboard events. In addition to these challenges, Para athletes various impairments may affect both sports-specific demands and athlete health. However, the group of Para snow-sport athletes is an understudied population. Accordingly, this perspective paper summarises current knowledge to consider when preparing for the Paralympic Games in Beijing and point out important unanswered questions. We here focus specifically on how sport-specific demands and impairment-related considerations are influenced by altitude acclimatisation, cold conditions, travel fatigue and jetlag, complications due to the COVID-19 pandemic, and injury prevention and sports safety considerations. As Para athletes with spinal cord injury, limb deficiency, cerebral palsy and visual impairment account for the majority of the Para snow-sport athletes, the focus is mainly on these impairment groups. In brief, we highlight the extra caution required to ensure athlete health, performance and sports safety among Para athletes participating in the snow-sport events in the 2022 Beijing Paralympic Games. Although there is an urgent need for more high-quality research focusing on Para winter athletes, we hope these non-consensus recommendations will help prepare for the 2022 Beijing Paralympic Winter Games.

Waist Circumference is not Superior to Body Mass Index in Predicting Groin Hernia Repair in Either Men or Women.

BACKGROUND AND AIMS: A high body mass index (BMI) is considered a risk factor for ventral abdominal wall hernias but protective for the development of groin hernias. The reason for this is unclear. The surrounding abdominal fat in obesity might "protect" and limit the passage through the inguinal canal. The aim was to compare two different methods used for obesity registration in groin hernia patients and to investigate the hypothesis of high BMI/low groin hernia risk phenomenon. METHODS: This was a population-based observational study comparing BMI to waist circumference (WC) as well as their correlations to the quantity of groin hernia repair performed in either sex. Two national registers were crosslinked to a large regional register including information on WC. RESULTS: A larger WC and a higher BMI were associated with a lower risk of having groin hernia repair in both sexes. There was no difference using either WC or BMI as a risk factor for groin hernia repair in either sex. There was no advantage to using body composition based on WC rather than BMI for surgery indication. CONCLUSIONS: Overweight patients, both men and women, have a lower risk of undergoing groin hernia repair regardless of fat distribution. BMI is a well-established method for obesity registration and is recommended in the evaluation of hernia patients.

Is the Effect of a High-Intensity Functional Exercise Program on Functional Balance Influenced by Applicability and Motivation among Older People with Dementia in Nursing Homes?

BACKGROUND AND OBJECTIVES: Exercise can be an important way of maintaining balance function in people with dementia, but further investigation is needed to determine the optimal way of exercising. The objective was to evaluate whether exercise applicability (i.e., attendance, exercise intensity, and adverse events) and motivation were associated with the effect on functional balance of a high-intensity functional exercise program for older people with dementia in nursing homes. DESIGN, SETTING AND PARTICIPANTS: Exercise intervention participants (n = 81; 60 women, 21 men) from a randomized controlled trial (UMDEX) were included. Their mean age was 84 and mean Mini-Mental State Examination score was 15. INTERVENTION: Groups of 3-8 participants participated in the High-Intensity Functional Exercise (HIFE) Program, with 5 sessions per 2-week period, for 4 months (total, 40 sessions). MEASUREMENTS: Outcome was the Berg Balance Scale (BBS), assessed at baseline and follow up, and the score difference, dichotomized to classify participants into two groups: responders (≥5-point increase) and non-responders (<5-point increase). Target variables were measures of applicability and motivation. Associations between each target variable and the outcome were analyzed using multivariable logistic regression. Baseline characteristics and new medical conditions developing during the intervention period were compared between responders and non-responders and included in the analyses when p < 0.10. RESULTS: The BBS score was 28.6 ± 14.3 at baseline and 31.2 ± 15.3 at follow up, with the difference between follow-up and baseline scores ranging from -35 to 24. Twenty-nine (35.8%) participants were responders. The multivariable models showed no significant association between responders vs. non-responders and any target variable. CONCLUSION: Participation in a 4-month high-intensity functional exercise program can improve balance in many individuals with dementia in nursing homes, despite the progressiveness of dementia disorders and several co-existing medical conditions. Predicting balance exercise response based on applicability and motivation seem not to be possible, which lends no support for excluding this group from functional exercise, even when exercise intensity or motivation is not high.

Recent Kinematic and Kinetic Advances in Olympic Alpine Skiing: Pyeongchang and Beyond.

Alpine skiing has been an Olympic event since the first Winter Games in 1936. Nowadays, skiers compete in four main events: slalom, giant slalom, super-G and downhill. Here, we present an update on the biomechanics of alpine ski racers and their equipment. The technical and tactical ability of today's world-class skiers have adapted substantially to changes in equipment, snow conditions and courses. The wide variety of terrain, slopes, gate setups and snow conditions involved in alpine skiing requires skiers to continuously adapt, alternating between the carving and skidding turning techniques. The technical complexity places a premium on minimizing energy dissipation, employing strategies and ski equipment that minimize ski-snow friction and aerodynamic drag. Access to multiple split times along the racing course, in combination with analysis of the trajectory and speed provide information that can be utilized to enhance performance. Peak ground reaction forces, which can be as high as five times body weight, serve as a measure of the external load on the skier and equipment. Although the biomechanics of alpine skiing have significantly improved, several questions concerning optimization of skiers' performance remain to be investigated. Recent advances in sensor technology that allow kinematics and kinetics to be monitored can provide detailed information about the biomechanical factors related to success in competitions. Moreover, collection of data during training and actual competitions will enhance the quality of guidelines for training future Olympic champions. At the same time, the need to individualize training and skiing equipment for each unique skier will motivate innovative scientific research for years to come.

Patient-reported rates of chronic pain and recurrence after groin hernia repair.

BACKGROUND: The effectiveness of different procedures in routine surgical practice for hernia repair with respect to chronic postoperative pain and reoperation rates is not clear. METHODS: This was prospective cohort study based on a unique combination of patient-reported outcomes and national registry data. Virtually all patients with a groin hernia repair in Sweden between September 2012 and April 2015 were sent a questionnaire 1 year after surgery. Persistent pain, defined as at least 'pain present, cannot be ignored, and interferes with concentration on everyday activities' in the past week was the primary outcome. Reoperation for recurrence recorded in the register was the secondary outcome. RESULTS: In total, 22 917 patients (response rate 75·5 per cent) who had an elective unilateral groin hernia repair were analysed. Persistent pain present 1 year after hernia repair was reported by 15·2 per cent of patients. The risk was least for endoscopic total extraperitoneal (TEP) repair (adjusted odds ratio (OR) 0·84, 95 per cent c.i. 0·74 to 0·96), compared with open anterior mesh repair. TEP repair had an increased risk of reoperation for recurrence (adjusted OR 2·14, 1·52 to 2·98), as did open preperitoneal mesh repair (adjusted OR 2·34, 1·42 to 3·71) at 2·5-year follow-up. No other methods of repair differed significantly from open anterior mesh repair. CONCLUSION: The risk of significant pain 1 year after groin hernia repair in routine surgical practice was 15·2 per cent. This figure was lower in patients who had surgery by an endoscopic technique, but at the price of a significantly higher risk of reoperation for recurrence.

Modulation of the activated protein C pathway in severe haemophilia A patients: The effects of thrombomodulin and a factor V-stabilizing fab.

INTRODUCTION: The thrombomodulin (TM)/activated protein C (APC) system is a key regulator of haemostasis, limiting amplification and propagation of the formed blood clot to the injury site. Dampening APC's inhibition of factor V (FV) and factor VIII (FVIII) may be a future strategy in developing next-generation therapeutic targets for haemophilia treatment. AIMS: To determine ex vivo the respective concentration-dependent effects of TM and a FV-stabilizing Fab on the APC regulatory pathway in severe FVIII-deficient blood and plasma. METHODS: Ten severe haemophilia A subjects and one healthy control were enrolled. Blood was spiked with TM (0, 1, 2.5, 5, 10, 20.0 nmol/L) and FV-stabilizing Fab (0, 3, 15, 65, 300 nmol/L). The respective effects were compared to FVIII concentrations of 3- and 10% using rotational thromboelastometry clotting time (CT) and thrombin generation analysis (TGA). RESULTS: With 1 and 2.5 nmol/L TM, 5% FVIII resulted in CT similar to the absence of TM, suggesting it completely reversed the effect of APC. Increasing TM concentrations also reduced peak thrombin generation and ETP. The addition of 300 nmol/L FV-stabilizing Fab returned CT to nearly baseline, but for most subjects was less than the effects of 3- or 10% FVIII. The FV-stabilizing Fab produced similar or greater thrombin generation compared to samples with 3- or 10% FVIII. CONCLUSIONS: The FV-stabilizing Fab resulted in enhanced CT and TGA parameters consistent with FVIII levels of 3- and 10%. Additional studies need to further characterize how modulating the APC pathway may prove beneficial in developing new haemophilia drug targets.

Tobacco use is not associated with groin hernia repair, a population-based study.

PURPOSE: The pathogenesis of groin hernia is not fully understood and some suggested risk factors are debatable. This population-based study evaluates the association between groin hernia repair and tobacco use. METHOD: An observational study based on register linkage between the Swedish Hernia Register and the Västerbotten Intervention Program (VIP). All primary groin hernia repairs performed from 2001 to 2013 in the county of Västerbotten, Sweden, were included. RESULTS: VIP provided data on the use of tobacco in 102,857 individuals. Neither smoking nor the use of snus, increased the risk for requiring a groin hernia repair. On the contrary, heavy smoking decreased the risk for men, HR 0.75 (95% CI 0.58-0.96), as did having a BMI over 30 kg/m2 HR (men) 0.33 (95% CI 0.27-0.40). CONCLUSION: Tobacco use is not a risk factor for requiring a groin hernia repair, whereas having a low BMI significantly increases the risk.

Risk factors for injuries associated with damage claims following groin hernia repair.

PURPOSE: Surgical repair of groin hernia should be carried out with minimal complication rates, and it is important to have regular quality control and accurate means of assessment. The Swedish healthcare system has a mutual insurance company (LÖF) that receives claims from patients who have suffered healthcare-related damage or malpractice. The Swedish Hernia Register (SHR) currently covers around 98% of all Swedish groin hernia operations. The aim of this study was to analyse damage claims following groin hernia repair surgery and link these with entries in the SHR, in order to identify risk factors and causes of injuries and malpractice associated with hernia repair. METHODS: Data on all 48,574 groin hernia operations registered in the SHR between 2008 and 2010 were compared and linked with data on claims made to the Swedish National Patient Injury Insurance (LÖF). RESULTS: Of the 130 damage claims received by LÖF, 26 dealt with bleeding, 20 with testicular injury and 7 with intestinal lesions. Eighty (62%) of the complications were considered malpractice according to the Swedish Patient Injury Act. Acute and recurrent surgery, sutured repair and general anaesthesia were associated with a significantly increased risk for a damage claim independently the patients were compensated or not. Females filed claims in greater proportion than males. There was no significant difference in background factors between claims accepted by LÖF and compensated and those who were rejected compensation. CONCLUSION: Risk factors for filing a damage claim included acute surgery, operation for recurrence, sutured repair and general anaesthesia, whereas local anaesthesia reduced the risk.

Energy system contributions and determinants of performance in sprint cross-country skiing.

To improve current understanding of energy contributions and determinants of sprint-skiing performance, 11 well-trained male cross-country skiers were tested in the laboratory for VO2max , submaximal gross efficiency (GE), maximal roller skiing velocity, and sprint time-trial (STT) performance. The STT was repeated four times on a 1300-m simulated sprint course including three flat (1°) double poling (DP) sections interspersed with two uphill (7°) diagonal stride (DS) sections. Treadmill velocity and VO2 were monitored continuously during the four STTs and data were averaged. Supramaximal GE during the STT was predicted from the submaximal relationships for GE against velocity and incline, allowing computation of metabolic rate and O2 deficit. The skiers completed the STT in 232 ± 10 s (distributed as 55 ± 3% DP and 45 ± 3% DS) with a mean power output of 324 ± 26 W. The anaerobic energy contribution was 18 ± 5%, with an accumulated O2 deficit of 45 ± 13 mL/kg. Block-wise multiple regression revealed that VO2 , O2 deficit, and GE explained 30%, 15%, and 53% of the variance in STT time, respectively (all P < 0.05). This novel GE-based method of estimating the O2 deficit in simulated sprint-skiing has demonstrated an anaerobic energy contribution of 18%, with GE being the strongest predictor of performance.

Location of recurrent groin hernias at TEP after Lichtenstein repair: a study based on the Swedish Hernia Register.

PURPOSE: To investigate which type of hernia that has the highest risk of a recurrence after a primary Lichtenstein repair. METHODS: Male patients operated on with a Lichtenstein repair for a primary direct or indirect inguinal hernia and with a TEP for a later recurrence, with both operations recorded in the Swedish Hernia Register (SHR), were included in the study. The study period was 1994-2014. RESULTS: Under the study period, 130,037 male patients with a primary indirect or direct inguinal hernia were operated on with a Lichtenstein repair. A second operation in the SHR was registered in 2236 of these patients (reoperation rate 1.7 %). TEP was the chosen operation in 737 in this latter cohort. The most likely location for a recurrence was the same as the primary location. If the recurrences change location from the primary place, we recognized that direct hernias had a RR of 1.51 to having a recurrent indirect hernia compared to having a direct recurrence after an indirect primary hernia repair. CONCLUSIONS: Recurrent hernias after Lichtenstein are more common on the same location as the primary one, compared to changing the location.

Exposure to a combination of heat and hyperoxia during cycling at submaximal intensity does not alter thermoregulatory responses.

In this study, we tested the hypothesis that breathing hyperoxic air (FinO2 = 0.40) while exercising in a hot environment exerts negative effects on the total tissue level of haemoglobin concentration (tHb); core (Tcore) and skin (Tskin) temperatures; muscle activity; heart rate; blood concentration of lactate; pH; partial pressure of oxygen (PaO2) and carbon dioxide; arterial oxygen saturation (SaO2); and perceptual responses. Ten well-trained male athletes cycled at submaximal intensity at 21°C or 33°C in randomized order: first for 20 min while breathing normal air (FinO2 = 0.21) and then 10 min with FinO2 = 0.40 (HOX). At both temperatures, SaO2 and PaO2, but not tHb, were increased by HOX. Tskin and perception of exertion and thermal discomfort were higher at 33°C than 21°C (p < 0.01), but independent of FinO2. Tcore and muscle activity were the same under all conditions (p > 0.07). Blood lactate and heart rate were higher at 33°C than 21°C. In conclusion, during 30 min of submaximal cycling at 21°C or 33°C, Tcore, Tskin and Tbody, tHb, muscle activity and ratings of perceived exertion and thermal discomfort were the same under normoxic and hyperoxic conditions. Accordingly, breathing hyperoxic air (FinO2 = 0.40) did not affect thermoregulation under these conditions.

Repeated high-intensity exercise modulates Ca(2+) sensitivity of human skeletal muscle fibers.

The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations in the redox balance. Eleven elite cross-country skiers performed four maximal bouts of 1300 m treadmill skiing with 45 min recovery. Contractile function of chemically skinned single fibers from triceps brachii was examined before the first and following the fourth sprint with respect to Ca(2+) sensitivity and maximal Ca(2+) -activated force. To investigate the oxidative effects of exercise on single fiber contractile function, a subset of fibers was incubated with dithiothreitol (DTT) before analysis. Ca(2+) sensitivity was enhanced by exercise in both MHC I (17%, P < 0.05) and MHC II (15%, P < 0.05) fibers. This potentiation was not present after incubation of fibers with DTT. Specific force of both MHC I and MHC II fibers was unaffected by exercise. In conclusion, repeated high-intensity exercise increased Ca(2+) sensitivity in both MHC I and MHC II fibers. This effect was not observed in a reducing environment indicative of an exercise-induced oxidation of the human contractile apparatus.

Risk factors for hip fracture in very old people: a population-based study.

SUMMARY: Knowledge of risk factors for hip fracture among very old people is limited. Walking indoors with help from ≤1 person, Parkinson's disease, currently smoking, delirium in the previous month, underweight, and age were associated with increased risk of hip fracture and could be important for preventive strategy development. INTRODUCTION: The purpose of this study is to investigate risk factors for hip fracture among a representative sample of very old people. METHODS: In total, 953 participants from the Umeå 85+/Gerontological Regional Database population-based cohort study were interviewed and assessed during home visits. Associations of baseline characteristics with hip fracture during the maximum 5-year follow-up period were analyzed using Cox proportional hazards regression. RESULTS: Participants had a mean age of 89.3 ± 4.7 years; 65.8% were women, 36.8% lived in residential care facilities, 33.6% had dementia, and 20.4% had histories of hip fracture. During a mean follow-up period of 2.7 years, 96 (10.1%) individuals sustained hip fracture. Walking indoors with help from no more than one person (hazard ratio [HR] = 8.57; 95% confidence interval [CI], 1.90-38.71), Parkinson's disease (HR = 5.12; 95% CI, 1.82-14.44), currently smoking (HR = 4.38; 95% CI 2.06-9.33), delirium in the previous month (HR = 2.01; 95% CI, 1.15-3.49), underweight (body mass index <22; HR = 1.74, 95% CI, 1.09-2.77), and age (HR = 1.09; 95% CI, 1.04-1.14) were associated independently with an increased risk of hip fracture. Hip prosthesis at baseline decreased the risk of hip fracture (HR = 0.37; 95% CI, 0.15-0.91), but only for those with bilateral hip prostheses. CONCLUSIONS: Seven factors were associated independently with incident hip fracture during follow-up in this sample of very old people. These factors could have important clinical implications in identifying persons at high risk of hip fracture, as well as in the development of effective preventive strategies.

The elite cross-country skier provides unique insights into human exercise physiology.

Successful cross-country skiing, one of the most demanding of endurance sports, involves considerable physiological challenges posed by the combined upper- and lower-body effort of varying intensity and duration, on hilly terrain, often at moderate altitude and in a cold environment. Over the years, this unique sport has helped physiologists gain novel insights into the limits of human performance and regulatory capacity. There is a long-standing tradition of researchers in this field working together with coaches and athletes to improve training routines, monitor progress, and refine skiing techniques. This review summarizes research on elite cross-country skiers, with special emphasis on the studies initiated by Professor Bengt Saltin. He often employed exercise as a means to learn more about the human body, successfully engaging elite endurance athletes to improve our understanding of the demands, characteristics, and specific effects associated with different types of exercise.

The effect of incline on sprint and bounding performance in cross-country skiers.

AIM: Aim of the present study was to investigate performance and kinematics of cross-country skiers during sprint running and bounding on different inclines, in relationship to maximal strength, power and skiing performance. METHODS: On day one, the maximal strength of 14 elite skiers was tested using a mid-thigh isometric pull and maximal relative leg power determined using squat and countermovement jumps. Day two involved 15-m maximal sprints and 5-step bounding at 0º, 7.5° and 15º inclines. From video recordings sprint, step, contact and flight times; step length and frequency; total number of sprint steps and average bounding velocity were determined. Skiing performance was assessed using International Ski Federation (FIS) points from the preceding season and compared to strength, power, bounding and sprint performance, and kinematics. RESULTS: On steeper inclines sprint time was higher and bounding distance shorter (both P<0.001), and step frequency during sprinting and bounding, reduced and increased respectively (P<0.001). Isometric maximal strength correlated strongly with bounding distance on the two steeper inclines (r=0.76 and 0.83). Squat and countermovement jump heights correlated moderately with sprint performance at both 7° and 15°, and bounding performance on all three inclines (r=0.55-0.65). The distance bounded uphill correlated moderately with FIS points (r=-0.55 and -0.67). CONCLUSION: Incline influenced sprinting and bounding performance and kinematics. Maximal leg power is important for both sprinting and bounding uphill, while maximal strength is important for the latter. The skiers with better FIS rankings bounded farther on steeper inclines, suggesting that this capacity is beneficial for cross-country skiing performance.