Full course macro-kinematic analysis of a 10 km classical cross-country skiing competition.
ABSTRACT: In this study micro-sensors were employed to analyse macro-kinematic parameters during a classical cross-country skiing competition (10 km, 2-lap). Data were collected from eight male participants during the Australian championship competition wearing a single micro-sensor unit (MinimaxX™, S4) positioned on their upper back. Algorithms and visual classification were used to identify skiing sub-techniques and calculate velocities, cycle lengths (CL) and cycle rates (CR) over the entire course. Double poling (DP) was the predominant cyclical sub-technique utilised (43 ± 5% of total distance), followed by diagonal stride (DS, 16 ± 4%) and kick double poling (KDP, 5 ± 4%), with the non-propulsive Tuck technique accounting for 24 ± 4% of the course. Large within-athlete variances in CL and CR occurred, particularly for DS (CV% = 25 ± 2% and CV% = 15 ± 2%, respectively). For all sub-techniques the mean CR on both laps and for the slower and faster skiers were similar, while there was a trend for the mean velocities in all sub-techniques by the faster athletes to be higher. Overall velocity and mean DP-CL were significantly higher on Lap 1, with no significant change in KDP-CL or DS-CL between laps. Distinct individual velocity thresholds for transitions between sub-techniques were observed. Clearly, valuable insights into cross-country skiing performance can be gained through continuous macro-kinematic monitoring during competition.
Project description:In this study the pacing strategy, cycle characteristics and choice of technique of elite male cross-country (XC) skiers during a three-lap, 15-km classical race with interval start were measured. During the Norwegian Championships in 2016, fast (n = 18, age: 26±4 yr; height: 182±4 cm; body mass: 78±3 kg (means±SD)) and slow skiers (n = 18, age: 22±2 yr; height: 183±5 cm; body mass: 78±6 kg) were video recorded on flat (0°), intermediate (3.5°) and uphill sections (7.1°) of the first and final laps. All skiers adopted a positive pacing strategy, skiing more slowly (11.8%) with shorter cycles (11.7%) on the final than first lap (both p<0.001; p?2 = 0.93 and 0.87, respectively). The fast skiers were 7.0% faster overall (p<0.001, d = 4.20), and 6.1% (p<0.001, d = 3.32) and 7.0% (p<0.001, d = 3.68) faster on the first and final laps, respectively, compared to slower skiers. On all sections of both laps, the fast skiers exhibited 9.5% more rapid (p?2 = 0.74) and 8.9% (p?2 = 0.48) longer cycles (both p<0.001). On intermediate terrain, the fast skiers employed primarily double poling (DP, 38.9% on the first lap) and double poling with a kick (DPKICK, 50% on the final lap). In contrast, the slow skiers utilized for the most part DP alone (lap 1: 33.3%, lap 3: 38.9%) or in combination with other techniques (lap 1: 33.3%, lap 3: 38.9%) and decreased their usage of DPKICK from 27.8% on the first to 16.7% on the final lap. Skiing velocity on flat and intermediate terrain proved to be the best predictor of race performance (p<0.001). In conclusion, during a 15-km classical XC skiing race, velocity and cycle length decreased from the first to the final lap, most extensively on flat terrain and least uphill. Moreover, on the intermediate sections the fast and slow skiers chose to use different techniques.
Project description:Cross-country skiing is a popular Olympic winter sport, which is also used extensively as a recreational activity. While cross-country skiing primarily is regarded as a demanding endurance activity it is also technically challenging, as it contains two main styles (classical and skating) and many sub-techniques within these styles. To further understand the physiological demands and technical challenges of cross-country skiing it is imperative to identify sub-techniques and basic motion features during training and competitions. Therefore, this paper presents features for identification and assessment of the basic motion patterns used during classical-style cross-country skiing. The main motivation for this work is to contribute to the development of a more detailed platform for comparing and communicating results from technique analysis methods, to prevent unambiguous definitions and to allow more precise discussions and quality assessments of an athlete's technical ability. To achieve this, our paper proposes formal motion components and classical style technique definitions as well as sub-technique classifiers. This structure is general and can be used directly for other cyclic activities with clearly defined and distinguishable sub-techniques, such as the skating style in cross country skiing. The motion component features suggested in our approach are arm synchronization, leg kick, leg kick direction, leg kick rotation, foot/ski orientation and energy like measures of the arm, and leg motion. By direct measurement, estimation, and the combination of these components, the traditional sub-techniques of diagonal stride, double poling, double poling kick, herringbone, as well as turning techniques can be identified. By assuming that the proposed definitions of the classical XC skiing sub-techniques are accepted, the presented classifier is proven to map measures from the motion component definitions to a unique representation of the sub-techniques. This formalization and structure may be used on new motion components, measurement principles, and classifiers, and therefore provides a framework for comparing different methodologies. Pilot data from a group of high-level cross-country skiers employing inertial measurement sensors placed on the athlete's arms and skis are used to demonstrate the approach. The results show how detailed sub-technique information can be coupled with physical, track, and environmental data to analyze the effects of specific motion patterns, to develop useful debriefing tools for coaches and athletes in training and competition settings, and to explore new research hypotheses.
Project description:OBJECTIVES:We investigated sex-based differences in speed, sub-technique selection, and kinematic patterns during low- (LIT) and high-intensity training (HIT) for classical cross-country (XC) skiing across varying terrain. METHODS:Six male and six female elite XC skiers with an approximately 15% differences in VO2max (men: 68.9±2.9 mL·min-1·kg-1, women: 60.1±3.3 mL·min-1·kg-1) were monitored using a multi-sensor system to collect time-synchronised data of heart rate, speed, and multiple tri-axial inertial measurements units while XC skiing on a 5-km competition track. RESULTS:Men skied 21% faster than women during HIT (5.9±0.3 m·s-1 vs. 4.9±0.2 m·s-1, P < .001), with the greatest difference (26%) while skiing on flat terrain, whereas skiing speed did not significantly differ between men and women during LIT. At similar instructed intensity and rating of perceived effort, women exhibited significantly higher relative heart rate (85±2% vs. 71±3% of maximum) and blood lactate levels (4.0±1.3 vs. 1.2±0.2 mmol/L) during LIT (all P < .001) than men, whereas physiological responses did generally not differ between the sexes during HIT. During both intensities and among both sexes, double poling (DP) was the sub-technique most used relative to distance, followed by miscellaneous sub-techniques (MISC), diagonal stride (DIA), kick double poling (DK) and herringbone (HRB). In relation to distance women used DIA more than men during LIT (22% vs. 17%, P = .009) and HIT (23% vs. 12%, P = .001), whereas men used MISC, including tucking and turning, more than women during LIT (39% vs. 25%, P = .017) and HIT (41% vs. 30%, P = .064). In particular, men used DP more than women while skiing the uphill sections during both LIT (24% vs. 11%, P = .015) and HIT (39% vs. 13%, P = .002). CONCLUSIONS:Our findings provide novel insights into sex-based differences in speed, sub-technique selection, and kinematic patterns during LIT and HIT for classical skiing.
Project description:Leucine aminopeptidases (LAPs) are present in animals, plants, and microbes. In plants, there are two classes of LAPs. The neutral LAPs (LAP-N and its orthologs) are constitutively expressed and detected in all plants, whereas the stress-induced acidic LAPs (LAP-A) are expressed only in a subset of the Solanaceae. LAPs have a role in insect defense and act as a regulator of the late branch of wound signaling in Solanum lycopersicum (tomato). Although the mechanism of LAP-A action is unknown, it has been presumed that LAP peptidase activity is essential for regulating wound signaling. Here we show that plant LAPs are bifunctional. Using three assays to monitor protein protection from heat-induced damage, it was shown that the tomato LAP-A and LAP-N and the Arabidopsis thaliana LAP1 and LAP2 are molecular chaperones. Assays using LAP-A catalytic site mutants demonstrated that LAP-A chaperone activity was independent of its peptidase activity. Furthermore, disruption of the LAP-A hexameric structure increased chaperone activity. Together, these data identify a new class of molecular chaperones and a new function for the plant LAPs as well as suggesting new mechanisms for LAP action in the defense of solanaceous plants against stress.
Project description:The benefits of using longer than self-selected poles have been shown in double poling, but these potential benefits have not been examined in the gear 3 ski skating sub-technique (G3), during which the poling movement is very similar to double poling. The aim of this study was to examine the effect of longer than self-selected poles on physiological and perceptual responses in the G3 sub-technique. Ten cross-country skiers and biathletes (VO2max 72.4 ± 3.0 ml?min-1?kg-1, age 20.1 ± 2.8 years, height 1.81 ± 0.03 m and weight 73.1 ± 4.6 kg) completed two tests, each with three different submaximal intensities, during roller skiing using the G3 technique. The first test was carried out at a fixed speed (10 km?h-1) and the skiers performed two intervals of 5 min at 7, 9 and 11% inclination on a roller ski treadmill with self-selected poles (SSP) and 7.5 cm longer poles (LP) at each step. The second test had a fixed inclination of 4% and speeds of 14, 17 and 20 km?h-1, also performed with SSP and LP at each step. At fixed speed, the oxygen uptake was 2.7% lower (P = 0.005) and the gross efficiency (GE) 2.1% higher (P = 0.01) with LP than with SSP at the steepest inclination of 11%. At fixed inclination, the oxygen uptake was 2.1% lower (P = 0.01) and the GE was 4.1% higher (P = 0.03) with LP than with SSP at the highest speed of 20 km?h-1. At 14 km?h-1, the oxygen uptake was 3.0% lower (P = 0.05) and GE was 3.8% higher (P = 0.03) with LP than with SSP. Our novel findings show that longer poles in the G3 technique may enhance the efficiency of skiing.
Project description:Introduction:Long-distance cross-country skiing (XCS) has gained increased popularity within the past decades. However, research about long-distance XCS is limited; therefore, the aim of this study was to analyze the intensity distribution, technique application, and pacing strategies during long-distance XCS racing. Methods:Heart rate (HR) and section skiing speeds of 9 elite (ranked 1-100) and 10 amateur skiers (ranked 101-1,500) during the 90-km Vasaloppet race were collected. In addition, during the first uphill, the first 1,000 skiers were video-recorded to analyze the applied skiing strategy (e.g. grip-waxed skis versus exclusive double poling). Results:Mean race intensity was 82% of maximal HR and was not different between performance groups even though elite skiers skied ?15% faster than amateurs. There was an interaction effect of section × group with a pronounced decrease in HR in amateurs compared with more even pacing in elite skiers (0.13 vs. 0.04% decrease/km) and skiing at higher percentage in the high-intensity zones in elite compared with amateurs (46 vs. 24%). Ninety-eight percent of the top 100 skiers and 59% of the first 1,000 skiers used exclusively double poling. Conclusion:Elite and amateur skiers ski at comparable mean race exercise intensity, but they have clear differences in skiing speed. The difference in the pacing profiles between elite and amateur skiers (more even vs. distinct positive pacing) demonstrate the greater capacity of the former with respect to physiological capacity and highlights that amateurs seem to start too fast according to their capacities. The exclusive application of the double poling technique is no longer a phenomenon of elite skiers but is widely used among the top 1,000 ranked skiers.
Project description:This study compared the effects of adding upper-body sprint-intervals or continuous double poling endurance training to the normal training on maximal upper-body strength and endurance capacity in female cross-country skiers. In total, 17 female skiers (age: 18.1±0.8yr, body mass: 60±7 kg, maximal oxygen uptake (VO2max): 3.30±0.37 L.min-1) performed an 8-week training intervention. Here, either two weekly sessions of six to eight 30-s maximal upper-body double poling sprint-intervals (SIG, n = 8) or 45-75 min of continuous low-to-moderate intensity double poling on roller skis (CG, n = 9) were added to their training. Before and after the intervention, the participants were tested for physiological and kinematical responses during submaximal and maximal diagonal and double poling treadmill roller skiing. Additionally, we measured maximal upper-body strength (1RM) and average power at 40% 1RM in a poling-specific strength exercise. SIG improved absolute VO2max in diagonal skiing more than CG (8% vs 2%, p<0.05), and showed a tendency towards higher body-mass normalized VO2max (7% vs 2%, p = 0.07). Both groups had an overall improvement in double poling peak oxygen uptake (10% vs 6% for SIG and CG) (both p<0.01), but no group-difference was observed. SIG improved 1RM strength more than CG (18% vs 10%, p<0.05), while there was a tendency for difference in average power at 40% 1RM (20% vs 14%, p = 0.06). Oxygen cost and kinematics (cycle length and rate) in double poling and diagonal remained unchanged in both groups. In conclusion, our study demonstrates that adding upper-body sprint-interval training is more effective than continuous endurance training in improving upper-body maximal strength and VO2max.
Project description:Leucine aminopeptidase (LAP) is found in all kingdoms of life and catalyzes the metal-dependent hydrolysis of the N-terminal amino acid residue of peptide or amino acyl substrates. LAPs have been shown to participate in the N-terminal processing of certain proteins in mammalian cells and in homologous recombination and transcription regulation in bacteria, while in parasites, they are involved in host cell invasion and provision of essential amino acids for growth. The enzyme is essential for survival in Plasmodium falciparum, where its drug target potential has been suggested. We report here the X-ray structures of three kinetoplastid acidic LAPs (LAP-As from Trypanosoma brucei, Trypanosoma cruzi, and Leishmania major) which were solved in the metal-free and unliganded forms, as well as in a number of ligand complexes, providing insight into ligand binding, metal ion requirements, and oligomeric state. In addition, we analyzed mutant cells defective in LAP-A in Trypanosoma brucei, strongly suggesting that the enzyme is not required for the growth of this parasite either in vitro or in vivo. In procyclic cells, LAP-A was equally distributed throughout the cytoplasm, yet upon starvation, it relocalizes in particles that concentrate in the perinuclear region. Overexpression of the enzyme conferred a growth advantage when parasites were grown in leucine-deficient medium. Overall, the results suggest that in T. brucei, LAP-A may participate in protein degradation associated with nutrient depletion. IMPORTANCE Leucine aminopeptidases (LAPs) catalyze the hydrolysis of the N-terminal amino acid of peptides and are considered potential drug targets. They are involved in multiple functions ranging from host cell invasion and provision of essential amino acids to site-specific homologous recombination and transcription regulation. In kinetoplastid parasites, there are at least three distinct LAPs. The availability of the crystal structures provides important information for drug design. Here we report the structure of the acidic LAPs from three kinetoplastids in complex with different inhibitors and explore their role in Trypanosoma brucei survival under various nutrient conditions. Importantly, the acidic LAP is dispensable for growth both in vitro and in vivo, an observation that questions its use as a specific drug target. While LAP-A is not essential, leucine depletion and subcellular localization studies performed under starvation conditions suggest a possible function of LAP-A in the response to nutrient restriction.
Project description:Flow-cytometric detection of minimal residual disease (MRD) has proven in several single-institute studies to have an independent prognostic impact. We studied whether this relatively complex approach could be performed in a multicenter clinical setting. Five centers developed common protocols to accurately define leukemia-associated (immuno)phenotypes (LAPs) at diagnosis required to establish MRD during/after treatment. List mode data files were exchanged, and LAPs were designed by each center. One center, with extensive MRD experience, served as the reference center and coordinator. In quarterly meetings, consensus LAPs were defined, with the performance of centers compared with these. In a learning (29 patients) and a test phase (35 patients), a mean of 2.2 aberrancies/patient was detected, and only 1/63 patients (1.6%) had no consensus LAP(s). For the four centers without (extensive) MRD experience, clear improvement could be shown: in the learning phase, 39-63% of all consensus LAPs were missed, resulting in a median 30% of patients (range 21-33%) for whom no consensus LAP was reported; in the test phase, 27-40% missed consensus LAPs, resulting in a median 16% (range 7-18%) of 'missed' patients. The quality of LAPs was extensively described. Immunophenotypic MRD assessment in its current setting needs extensive experience and should be limited to experienced centers.
Project description:The automatic classification of sub-techniques in classical cross-country skiing provides unique possibilities for analyzing the biomechanical aspects of outdoor skiing. This is currently possible due to the miniaturization and flexibility of wearable inertial measurement units (IMUs) that allow researchers to bring the laboratory to the field. In this study, we aimed to optimize the accuracy of the automatic classification of classical cross-country skiing sub-techniques by using two IMUs attached to the skier's arm and chest together with a machine learning algorithm. The novelty of our approach is the reliable detection of individual cycles using a gyroscope on the skier's arm, while a neural network machine learning algorithm robustly classifies each cycle to a sub-technique using sensor data from an accelerometer on the chest. In this study, 24 datasets from 10 different participants were separated into the categories training-, validation- and test-data. Overall, we achieved a classification accuracy of 93.9% on the test-data. Furthermore, we illustrate how an accurate classification of sub-techniques can be combined with data from standard sports equipment including position, altitude, speed and heart rate measuring systems. Combining this information has the potential to provide novel insight into physiological and biomechanical aspects valuable to coaches, athletes and researchers.