Laboratory tests are commonly performed by cross-country (XC) skiers due to the challenges of obtaining reliable performance indicators on snow. However, only a few studies have reported reliability data for ski-specific test protocols. Therefore, this study examined the test-retest reliability of ski-specific aerobic, sprint, and neuromuscular performance tests.; Thirty-nine highly trained XC skiers (26 men and 13 women, age: 22 ± 4 years, V̇O; 2max; : 70.1 ± 4.5 and 58.8 ± 4.4 mL·kg; -1; ·min; -1; , respectively) performed two test trials within 6 days of a diagonal V̇O; 2max; test, n = 27; skating graded exercise test to assess the second lactate threshold (LT; 2; ), n = 27; 24-min double poling time trial (24-min DP, n = 25), double poling sprint test (Sprint; DP1; , n = 27), and 1-min self-paced skating sprint test (Sprint; 1-min; , n = 26) using roller skis on a treadmill, and an upper-body strength test (UB-ST, n = 27) to assess peak power (P; peak; ) with light, medium, and heavy loads. For each test, the coefficient of variation (CV), intraclass correlation coefficient (ICC), and minimal detectable change (MDC) were calculated.; V̇O; 2max; demonstrated good-to-excellent reliability (CV = 1.4%; ICC = 0.99; MDC = 112 mL·min; -1; ), whereas moderate-to-excellent reliability was found for LT; 2; (CV = 3.1%; ICC = 0.95). Performance during 24-min DP, Sprint; DP1; , and Sprint; 1-min; showed good-to-excellent reliability (CV = 1.0%-2.3%; ICC = 0.96-0.99). Absolute reliability for UB-ST P; peak; was poor (CV = 4.9%-7.8%), while relative reliability was excellent (ICC = 0.93-0.97) across the loads.; In highly trained XC skiers, sport-specific aerobic and sprint performance tests demonstrated high test-retest reliability, while neuromuscular performance for the upper body was less reliable. Using the presented protocols, practitioners can assess within- and between-season changes in relevant performance indicators.
When exercising in the cold, optimizing thermoregulation is essential to maintain performance. However, no study has investigated thermal parameters with wearable-based measurements in a field setting among elite Nordic skiers. Therefore, this study aimed to assess the thermal response and sensation measured at different body parts during exercise in a cold environment in biathletes.; Thirteen Swiss national team biathletes (6 females, 7 males) performed two skiing bouts in the skating technique on two consecutive days (ambient temperature: -3.74 ± 2.32 °C) at 78 ± 4% of maximal heart rate. Heat flux (HF), core (T; core; ) and skin (T; skin; ) temperature were measured with sensors placed on the thigh, back, anterior and lateral thorax. Thermal sensation (TS) was assessed three times for different body parts: in protective winter clothing, in a race suit before (PRE) and after exercise (POST).; HF demonstrated differences (; p; < 0.001) between sensor locations, with the thigh showing the highest heat loss (344 ± 37 kJ/m; 2; ), followed by the back (269 ± 6 kJ/m; 2; ), the lateral thorax (220 ± 47 kJ/m; 2; ), and the anterior thorax (192 ± 37 kJ/m; 2; ). T; core; increased (; p; < 0.001). T; skin; decreased for all body parts (; p; < 0.001). Thigh T; skin; decreased more than for other body parts (; p; < 0.001). From PRE to POST, TS of the hands decreased (; p; < 0.01).; Biathletes skiing in a race suit at moderate intensity experience significant heat loss and a large drop in T; skin; , particularly at the quadriceps muscle. To support the optimal functioning of working muscles, body-part dependent differences in the thermal response should be considered for clothing strategy and for race suit design.
Recently, a new automated carbon monoxide (CO) rebreathing method (aCO) to estimate haemoglobin mass (Hb; mass; ) was introduced. The aCO method uses the same CO dilution principle as the widely used optimised CO rebreathing method (oCO). The two methods differ in terms of CO administration, body position, and rebreathing time. Whereas with aCO, CO is administered automatically by the system in a supine position of the subject, with oCO, CO is administered manually by an experienced operator with the subject sitting. Therefore, the aim of this study was to quantify possible differences in Hb; mass; estimated with the two methods. Hb; mass; was estimated in 18 subjects (9 females, 9 males) with oCO using capillary blood samples (oCOc) and aCO taking simultaneously venous blood samples (aCOv) and capillary blood samples (aCOc). Overall, Hb; mass; was different between the three measurement procedures (; F; = 57.55,; p;
We recently measured the development of hemoglobin mass (Hbmass) in 10 Swiss national team endurance athletes between ages 16-19. Level of Hbmass at age 16 was an important predictor for Hbmass and endurance performance at age 19. The aim was to determine how many of these young athletes were still members of Swiss national teams (NT) at age 25, how many already terminated their career (TC), and whether Hbmass at ages 16 and 19 was different between the NT and TC group. We measured Hbmass using the optimized carbon monoxide re-breathing technique in 10 high-performing endurance athletes every 0.5 years beginning at age 16 and ending at age 19. At age 25, two athletes were in the NT group and eight athletes in the TC group. Mean absolute, body weight-, and lean body mass (LBM) related Hbmass at age 16 was 833 +/- 61 g, 13.7 +/- 0.2 g/kg and 14.2 +/- 0.2 g/kg LBM in the NT group and 742 +/- 83 g, 12.2 +/- 0.7 g/kg and 12.8 +/- 0.8 g/kg LBM in the TC group. At age 19, Hbmass was 1,042 +/- 89 g, 14.6 +/- 0.2 g/kg and 15.4 +/- 0.2 g/kg LBM in the NT group and 863 +/- 109 g, 12.7 +/- 1.1 g/kg and 13.5 +/- 1.1 g/kg LBM in the TC group. Body weight- and LBM related Hbmass were higher in the NT group than in the TC group at ages 16 and 19 (p < 0.05). These results indicate, that Hbmass at ages 16 and 19 possibly could be an important predictor for later national team membership in endurance disciplines.
During early parenthood, walking and/or running while pushing a stroller is a common form of endurance exercise among both recreationally active individuals and athletes. Here, we investigate how pushing a stroller influences the energetic cost, gross efficiency (GE), and kinematic behavior of well-trained men and women while walking or running on flat and uphill incline. Eight men and nine women, all recreationally active, performed three 5-min submaximal tests of walking or running during four different testing sessions, in randomized order: with and without pushing a 24.3-kg stroller on a flat (1%; 6, 8/9, and 11/12 km/h for women/men) and uphill (10%; 5, 6.5/7.5, and 7.5/8.5 km/h for women/men) incline. Respiratory parameters, heart rate (HR), blood lactate concentration, and rating of perceived exertion (RPE) were determined and video-based kinematic analysis was performed in connection with all these tests. Except while walking on the flat incline, pushing a stroller increased the energetic cost of walking/running under all conditions (all; p; < 0.05). This was associated with shorter and more rapid strides on both inclines (all; p; < 0.05); however, GE was higher when pushing the stroller (; p; < 0.05). The increase in energetic cost of pushing the stroller was approximately threefold higher uphill than on the flat incline, and women were influenced more than men when running uphill at the highest speed (all; p; < 0.05). Here, we provide novel insights on the energetic cost and kinematic behavior of pushing a stroller while walking or running on flat and uphill inclines. The energetic cost of pushing a stroller was clearly higher than for unloaded exercise, coincided by shorter and more rapid strides, and especially pronounced on uphill terrain where also women were more influenced than men.
INTRODUCTION: The cross-country ski sprint prologue involves a 2 – 4 minute long effort on varying terrain with only the top 30 skiers advancing to the subsequent heats. Qualification success not only depends on physiological and technical capacity, but also on optimal pacing strategy and appropriate relative efforts in the various terrains (Sandbakk et al., 2011). METHODS: During the U23 Cross-Country Ski World Championships 2018 freestyle sprint prologue in Ulrichen (SUI), skiing performance in flat, uphill and downhill terrain was analyzed for female (N = 43) and male (N = 64) skiers using time-synchronized video recordings. Relative performance indices for the three different terrains were calculated (Vterrain / Vaverage). A Spearman’s rank order correlation for the terrain indices ranking and overall prologue ranking was calculated and potential sex differences regarding performance in the various terrains were analyzed by ANOVA. Table 1. Spearman’s rank correlation coefficients for terrain index rank and overall prologue performance and corresponding level of statistical significance. Overall prologue rank Women Men Flat index rank -0.42** -0.24 Uphill index rank 0.59*** 0.57*** Downhill index rank -0.39* -0.50*** *p < .05; **p < .01; ***p < .001 RESULTS: Terrain index rank correlations are shown in Table 1. Male skiers demonstrated higher uphill indices than females 0.62 ± 0.01 vs. 0.57 ± 0.02 (p < .001), with no significant differences found for flat and downhill terrain indices (both p > .05). DISCUSSION: A higher relative skiing effort for uphill terrain appeared to be correlated to overall rank in the investigated cross-country ski sprint prologue for both female and male skiers. At the same time, relative skiing performance in flat and downhill sections were negatively correlated to overall rank in the prologue, indicating a smaller relative effort and/or significance. Furthermore, male skiers demonstrated higher relative skiing velocities in the uphill track sections compared to female skiers, which was not observed regarding relative flat and downhill terrain efforts. CONCLUSION: The current study identified higher relative velocities invested during uphill terrain in faster skiers compared to slower skiers at an international freestyle sprint skiing competition, supporting the importance of performance indicators for uphill terrain. In addition, the difference in the relative effort investment between female and male skiers appeared to be only present in uphill terrain, indicating a sex differences in performance concerning uphill relevant performance factors and/or pacing strategy. REFERENCES Sandbakk, O., Ettema, G., Leirdal, S., Jakobsen, V., Holmberg, HC. (2011) Analysis of a sprint ski race and associated laboratory determinants of world-class performance. European Journal of Applied Physiology 111:947-957.
It is unknown, whether endurance training stimulates hemoglobin mass (Hbmass) and maximal oxygen uptake (V˙O2max) increases during late adolescence. Therefore, this study assessed the influence of endurance training on Hbmass, blood volume parameters, and V˙O2max in endurance athletes and control subjects from age 16 to 19 yr.; Hemoglobin mass, blood volume parameters, V˙O2max and anthropometric parameters were measured in male elite endurance athletes from age 16 to 19 yr in 6-month intervals (n = 10), as well as in age-matched male controls (n = 12).; Neither the level of Hbmass per lean body mass (LBM) (P = 0.80) nor the development of Hbmass during the 3 yr (P = 0.97) differed between athletes and controls. Hbmass at age 16 yr was 13.24 ± 0.89 g·kg LBM and increased by 0.74 ± 0.58 g·kg LBM (P < 0.01) from age 16 to 19 yr. There was a high correlation between Hbmass at age 16 and 19 yr (r = 0.77; P < 0.001). Plasma volume, blood volume, and V˙O2max were higher in athletes compared to controls (P < 0.05). Blood volume and V˙O2max increased with age (P < 0.01, similarly in both groups).; Endurance training volumes do not explain individual differences in Hbmass levels nor Hbmass and V˙O2max development in the age period from 16 to 19 yr. The higher V˙O2max levels of athletes may be partially explained by training-induced higher plasma and blood volumes, as well as other training adaptations. Since Hbmass at age 16 yr varies substantially and the development of Hbmass in late adolescence is comparably small and not influenced by endurance training, Hbmass at age 16 yr is an important predictor for Hbmass at adult age and possibly for the aptitude for high-level endurance performance.
The rim width of cross-country mountain bike wheel sets has increased in recent years, but the effect of this increase on performance remains unknown. The aim of this study was to analyse the influence of rim width on rolling resistance and off-road speed. We compared 3 tubeless wheel sets: 25 mm inner width as baseline, 30 mm width with the same tyre stiffness, and 30 mm width with the same tyre pressure. Three riders conducted 75 rolling resistance tests for each wheel set on a cross-country course. We determined rolling resistance using the virtual elevation method and calculated off-road speeds for flat and uphill conditions using a mathematical model. Baseline rolling resistance (C; r; ) was 0.0298, 90% CI [0.0286, 0.0310], which decreased by 1.4%, [0.7, 2.2] with the wider rim and the same tyre stiffness and increased by 0.9%, [0.1, 1.6] with the wider rim and the same tyre pressure. The corresponding effects on off-road speed were most likely trivial (0.0% to 0.7% faster and 0.1% to 0.6% slower, respectively). Because the effect of rim width on off-road speed seems negligible, athletes should choose the rim width that offers the best bike handling and should experiment with low tyre pressures.
What is the central question of this study? It has been assumed that athletes embarking on an 'live high-train low' (LHTL) camp with already high initial haemoglobin mass (Hb; mass; ) have a limited ability to increase their Hb; mass; further post-intervention. Therefore, the relationship between initial Hb; mass; and post-intervention increase was tested with duplicate Hb; mass; measures and comparable hypoxic doses in male athletes. What is the main finding and its importance? There were trivial to moderate inverse relationships between initial Hb; mass; and percentage Hb; mass; increase in endurance and team-sport athletes after the LHTL camp, indicating that even athletes with higher initial Hb; mass; can reasonably expect Hb; mass; gains post-LHTL. It has been proposed that athletes with high initial values of haemoglobin mass (Hb; mass; ) will have a smaller Hb; mass; increase in response to 'live high-train low' (LHTL) altitude training. To verify this assumption, the relationship between initial absolute and relative Hb; mass; values and their respective Hb; mass; increase following LHTL in male endurance and team-sport athletes was investigated. Overall, 58 male athletes (35 well-trained endurance athletes and 23 elite male field hockey players) undertook an LHTL training camp with similar hypoxic doses (200-230 h). The Hb; mass; was measured in duplicate pre- and post-LHTL by the carbon monoxide rebreathing method. Although there was no relationship (r = 0.02, P = 0.91) between initial absolute Hb; mass; (in grams) and the percentage increase in absolute Hb; mass; , a moderate relationship (r = -0.31, P = 0.02) between initial relative Hb; mass; (in grams per kilogram) and the percentage increase in relative Hb; mass; was detected. Mean absolute and relative Hb; mass; increased to a similar extent (P ≥ 0.81) in endurance (from 916 ± 88 to 951 ± 96 g, +3.8%, P < 0.001 and from 13.1 ± 1.2 to 13.6 ± 1.1 g kg; -1; , +4.1%, P < 0.001, respectively) and team-sport athletes (from 920 ± 120 to 957 ± 127 g, +4.0%, P < 0.001 and from 11.9 ± 0.9 to 12.3 ± 0.9 g kg; -1; , +4.0%, P < 0.001, respectively) after LHTL. The direct comparison study using individual data of male endurance and team-sport athletes and strict methodological control (duplicate Hb; mass; measures and matched hypoxic dose) indicated that even athletes with higher initial Hb; mass; can reasonably expect Hb; mass; gain post-LHTL.
Although a low rolling resistance is advantageous in mountain bike cross-country racing, no studies have used the virtual elevation method to compare tyres from different manufacturers as used in international competitions so far. The aims of this study were to assess the reliability of this method, to compare the off-road rolling resistance between tyres and to calculate the influence on off-road speed. Nine 29-in. mountain bike cross-country tyres were tested on a course representing typical ground surface conditions 5 or 6 times. The coefficient of rolling resistance was estimated with the virtual elevation method by 3 investigators and corresponding off-road speeds were calculated. The virtual elevation method was highly reliable (typical error = 0.0006, 2.8%; limits of agreement
Hemoglobin mass does not change over years in Swiss male elite endurance athletes Theoretical background In aerobic sport disciplines – such as cross-country skiing or mountainbiking - a main important factor determining aerobic performance is the total amount of hemoglobin, hemoglobin mass (Hbmass). Since endurance athletes are characterized by an about 35% higher Hbmass than untrained subjects, the question arise if this is due to endurance training over years or other factors like genetic predisposition. Very little is known about the Hbmass changes with training over years. From cross sectional data from athletes at age 23 and age 28 (2) as well as Hbmass data measured over one training year (1), it can be hypothesized there is no relevant Hbmass increase over years (3). Research question Does Hbmass in Swiss national team endurance athletes change with several years of endurance training? Methods We retrospectively filtered body weight related Hbmass values (CO-rebreathing), measured during standard performance testing of the Swiss national cross-country and mountain bike teams twice a year, with the athlete inclusion criteria: male, age > 23 yrs, minimum measurement duration three years and/or at least six measurements. 22 Athletes fulfilled the criteria and were included in the analyses. The average number of measurements was 10.8 ± 4.5 over a period of 5.1 ± 2.1 years. For every athlete mean of the two first and mean of two last measurements were compared and an individual linear model for the development of Hbmass with age was fitted. Individual models were combined to one linear model by averaging all individual slopes and axis sections. All values are mean ± SD. Results There was no difference in mean absolute Hbmass (1058 ± 93 vs 1069 ± 93g; p=0.48) and mean relative Hbmass (14.49 ± 0.88 vs 14.64 ± 0.97g/kg bodyweight; p=0.32) between pre- and post-measurements. The mean linear model was: Hbmass = 0.009 (± 0.12) · age + 14.3 (± 3.2). Discussion Our results show, that for elite endurance athletes older than 23 years no substantial increase in Hbmass can be expected with sea-level training over the years despite high training loads usually accomplished by these athletes. References Prommer N, Sottas PE, Schoch C, Schumacher YO, and Schmidt W. Total Hemoglobin Mass - A New Parameter to Detect Blood Doping? Med Sci Sport Exerc 40: 2112-2118, 2008. Steiner T, and Wehrlin JP. Does Hemoglobin Mass Increase from Age 16 to 21 and 28 in Elite Endurance Athletes. Med Sci Sport Exerc 43: 1735-1743, 2011. Wehrlin JP, Marti B, and Hallén J. Hemoglobin Mass and Aerobic Performance at Moderate Altitude in Athletes. Adv Exp Med Biol 357-375, 2016.
Hemoglobin mass response to normobaric and hypobaric altitude training in senior male athletesTheoretical BackgroundOne main physiological adaptation to altitude training is an increase in hemoglobin mass (Hbmass). Recently, a meta-analysis has calculated that an increase in Hbmass of ~1.1%/100 h of hypoxic exposure at ≥2100 m can be expected (1). During the last decades, several types of altitude training have been developed, which can be performed under either hypobaric hy-poxia (HH) or normobaric hypoxia (NH). Whether NH and HH can be used equally for an alti-tude training camp on Hbmass adaptations is still unclear.Research QuestionsDoes normobaric and hypobaric altitude training evoke similar Hbmass responses and is there a substantial inter-individual variability in Hbmass response?MethodsTo compare mean and individual Hbmass responses during an 18-day live high-train low (LHTL) altitude training camp in either NH or HH, we designed a randomized matched con-trolled (n=28) (2) and a crossover (n=15) (3) study with endurance athletes. To more precisely quantify the individual Hbmass response to altitude training, we implemented error-reducing duplicate Hbmass measures. Furthermore, the hypothesis that athletes with a high initial Hbmass starting an altitude sojourn will have a limited ability to further increase their post-altitude Hbmass in endurance and team-sport athletes (n=58) was tested (4).ResultsHbmass increased similarly in HH (+4.4% and +4.5%, p
Hemoglobin mass and endurance performance in elite sportPerformance and maximal oxygen uptake (VO2max) in endurance sports is mainly limited by the oxygen supply to active muscle. Since total amount of hemoglobin (Hbmass) determines in large part the oxygen transport capacity of the blood, Hbmass is a main limiting factor for endurance performance. The importance of a high Hbmass in endurance athletes is also shown by the problem of blood doping in elite sport. It is well known, that senior elite endurance athletes are characterized by about 35% higher Hbmass than untrained individuals. From a sport practical point of view, therefore several key-questions arise: 1) Does Hbmass in senior endurance athletes incresase with endurance training over years? 2) Does Hbmass increase more in adolescent endurance athletes with a high load of endurance training than in control subjects between age 16 and 18.5 yrs? 3) Does normobaric and hypobaric altitude training in senior athletes evoke similar Hbmass responses and is there a substantial inter-individual var-iability in Hbmass response? In the three presentations of our session, these key-questions will be answered and an outlook for further investigations in this relevant field for endurance performance will be addressed.
PURPOSE: To examine the effects of exercise-induced trunk fatigue on double poling performance, physiological responses and trunk strength in cross-country skiers. METHODS: Sixteen well-trained male cross-country skiers completed two identical pre- and post-performance tests, separated by either a 25-min trunk fatiguing exercise sequence or rest period in a randomized, controlled cross-over design. Performance tests consisted of a maximal trunk flexion and extension test, followed by a 3-min double poling (DP) test on a ski ergometer. RESULTS: Peak torque during isometric trunk flexion (- 66%, p < .001) and extension (- 7.4%, p = .03) decreased in the fatigue relative to the control condition. Mean external power output during DP decreased by 14% (p < .001) and could be attributed both to reduced work per cycle (- 9%, p = .019) and a reduced cycle rate (- 6%, p = .06). Coinciding physiological changes in peak oxygen uptake (- 6%, p < .001) and peak ventilation (- 7%, p < .001) could be observed. Skiers chose a more even-pacing strategy when fatigued, with the performance difference between fatigue and control condition being most prominent during the first 2 min of the post-test. CONCLUSIONS: In well-trained cross-country skiers, exercise-induced trunk fatigue led to a substantial decrease in DP performance, caused by both decreased work per cycle and cycle rate and accompanied by reduced aerobic power. Hence, improved fatigue resistance of the trunk may therefore be of importance for high-intensity DP in cross-country skiing.
Shooting in biathlon competitions substantially influences final rankings, but the predictability of hits and misses is unknown. The aims of the current study were A) to explore factors influencing biathlon shooting performance and B) to predict future hits and misses. We explored data from 118,300 shots from 4 seasons and trained various machine learning models before predicting 34,340 future shots (in the subsequent season). A) Lower hit rates were discovered in the sprint and pursuit disciplines compared to individual and mass start (P < 0.01, h = 0.14), in standing compared to prone shooting (P < 0.01, h = 0.15) and in the 1; st; prone and 5; th; standing shot (P < 0.01, h = 0.08 and P < 0.05, h = 0.05). B) A tree-based boosting model predicted future shots with an area under the ROC curve of 0.62, 95% CI [0.60, 0.63], slightly outperforming a simple logistic regression model and an artificial neural network (P < 0.01). The dominant predictor was an athlete's preceding mode-specific hit rate, but a high degree of randomness persisted, which complex models could not substantially reduce. Athletes should focus on overall mode-specific hit rates which epitomise shooting skill, while other influences seem minor.
Effect of endurance training on the development of hemoglobin mass in male adolescent endurance athletesIt is well known, that adult elite endurance athletes are characterized by about 30-40% higher hemoglobin mass (Hbmass) than untrained subjects (1). However, it is unclear, whether this is due to endurance training, a better genetic predisposition of the athletes combined with a selection process, or other factors (2). Interestingly, Hbmass at age 16 years (yrs) is reported to be not different between endurance athletes and untrained subjects (3).Research QuestionDoes Hbmass increase more in adolescent endurance athletes with a high load of endurance training than in control subjects between age 16 and 18.5yrs?Methods:We measured Hbmass (CO-rebreathing) in 10 Swiss National Team endurance athletes (AG: cross-country skiers and triathletes) as well as in 12 age matched non endurance training controls (CG) every 0.5 yrs six times from age 16 to age 18.5yrs (T1 - T6) with the optimized carbon monoxide re-breathing technique.ResultsHbmass increased (p
Vorhersage von Treffern in Biathlonwettkämpfen mit maschinellem LernenTheoretischer HintergrundSchiessfehler in Biathlonwettkämpfen wirken sich bedeutend auf das Schlussklassement aus. Der erschwerende Effekt der vorangehenden körperlichen Belastung sowie biomechanische Einflussfaktoren auf die Trefferquote wurden bereits untersucht (Hoffman, Gilson, Westenburg, & Spencer, 1992; Sattlecker, Buchecker, Gressenbauer, Müller, & Lindinger, 2017). Al-lerdings ist bisher unbekannt, ob und wie genau sich einzelne Treffer und Fehlschüsse vorhersagen lassen. Für automatische Vorhersagen eignen sich Algorithmen aus dem maschi-nellen Lernen, welche komplexe Zusammenhänge aus gegebenen Daten generalisieren, um Vorhersagen für neue Fälle zu berechnen (Bauer & Kohavi, 1999).FragestellungenA) Welche Faktoren beeinflussen die Trefferquoten in Biathlonwettkämpfen?B) Wie gut lassen sich zukünftige Treffer und Fehlschüsse mit maschinellem Lernen vorhersagen?MethodeWir aggregierten und untersuchten Daten von 118‘300 Schüssen aus vier Wettkampfsaisons (2012/13 bis 2015/16) mittels explorativer Datenanalyse und trainierten verschiedene Vorher-sagemodelle aus dem maschinellen Lernen mittels zeitsegmentierter Kreuzvalidierung. Als Basismodell diente eine logistische Regression mit einer Eingangsvariablen. Zusätzlich wurden zwei komplexe Modelle verwendet: ein Boosting-Modell basierend auf Entscheidungsbäumen und ein künstliches neuronales Netzwerk. Mit den finalen Modellen berechneten wir Vorhersagen für 34‘340 zukünftige Schüsse der nächsten Wettkampfsaison (2016/17). ErgebnisseA) Tiefere Trefferquoten zeigten sich in den Disziplinen Sprint und Verfolgung verglichen mit den Disziplinen Einzel und Massenstart (p < 0.01, Cohen‘s h = 0.14). Im Stehendschiessen war die Trefferquote tiefer als im Liegendschiessen (p < 0.01, h = 0.15). Im Vergleich zu den anderen Schüssen in der gleichen Position zeigte der erste Liegendschuss und der fünfte Stehendschuss eine tiefere Trefferquote (p < 0.01, h = 0.08 und p < 0.05, h = 0.05). B) Das Boosting-Modell prognostizierte zukünftige Treffer und Fehlschüsse mit einer Fläche unter der ROC-Kurve von 0.62, 95% VI [0.60, 0.63], leicht besser als das künstliche neuronale Netzwerk (0.61, [0.60, 0.62], p < 0.01) und die logistische Regression (0.60, [0.59, 0.61], p < 0.01, Eingangsvariable: vorgängige positionsspezifische Trefferquote).DiskussionDie Trefferquote im Biathlon variiert zwischen den Disziplinen, den Schiesspositionen und den Schussnummern einer Serie. Die vorgängige positionsspezifische Trefferquote eines Athleten oder einer Athletin ist aber der wichtigste Faktor, um einzelne Treffer vorherzusagen. Ein gros-ser Zufallseffekt bleibt bestehen, den auch komplexe Modelle nicht relevant verringern können: Die Anzahl der Fehlschüsse eines Athleten oder einer Athletin pro Wettkampf variiert zufällig um ca. 1-2 Schüsse.Im Training sollte somit primär die allgemeine Trefferquote in beiden Schiesspositionen unter wettkampfnahen Bedingungen optimiert werden, evtl. mit einem besonderen Fokus auf dem ersten Liegendschuss und dem letzten Stehendschuss. Echtzeitvorhersagen der Trefferwahr-scheinlichkeiten einzelner Schüsse könnten zudem Wettkampfübertragungen bereichern.ReferenzenBauer, E., & Kohavi, R. (1999). An empirical comparison of voting classification algorithms: Bagging, boosting, and variants. Machine Learning, 36(1), 105-139.Hoffman, M. D., Gilson, P. M., Westenburg, T. M., & Spencer, W. A. (1992). Biathlon shooting performance after exercise of different intensities. International Journal of Sports Medicine, 13(3), 270-273.Sattlecker, G., Buchecker, M., Gressenbauer, C., Müller, E., & Lindinger, S. J. (2017). Factors discriminating high from low score performance in biathlon shooting. International Journal of Sports Physiology and Performance, 12(3), 377-384.
Effect of competition-compatible precooling on distance running in humid heatTheoretical Background:The next two major competitions in athletics will be held in Doha, Qatar (World Championships 2019) and in Tokyo, Japan (Olympic Games 2020). On both occasions, extreme environmental conditions are expected: A wet bulb globe temperature (WBGT) of ~28°C in Doha and of ~30°C in Tokyo (Murata et al., 2016), indicating “high” and “excessive” temperatures, respectively (Racinais et al., 2015). High WBGT cause a fast increase of body core temperature (CT) during exercise and therefore impair endurance performance (Nybo et al., 2014).One commonly used means against the reduction of endurance performance induced by the rise of CT is “precooling”. It aims to delay the point where critically high CT is reached by lowering CT before the onset of exercise (Ross et al., 2013). Positive effects of precooling on endurance performance have been found, especially where different cooling modalities such as cold water immersion, cooling vests and ice slurries were combined (Racinais et al., 2015).However, most of the existing studies on precooling have executed precooling directly before exercise-onset. They are thus hardly compatible with the regulatory restrictions before major athletics competitions. For example, long distance runners competing in track events (most importantly the 5000 m event) are obliged to arrive in the “call-room” ~30 min before the start of their race. In the call-room, no personal precooling instruments like cooling vests or baths are allowed. Before entering the call room, athletes typically are transferred from their hotel to the competition stadium. Also during transfer and subsequent warm-up, precooling is not pos-sible without practical and regulatory restrictions. In order to implement precooling into the predetermined schedule, it would be necessary to extend the duration between precooling and the start of the race. This would likely reduce the chance of a performance benefit, as the effect of precooling could be “washed out” before the start. However, no study has investigated the effects of best-practice precooling compatible with the schedule before major athletics compe-titions on physiological parameters and on distance running performance so far.Research Question:What are the effects of competition-compatible precooling on A) body core temperature, B) heart rate, oxygen consumption and thermal perception as well as C) performance during dis-tance running in humid heat?....
