Search

PurposeThis study aimed to differentiate external and internal training loads during on-snow biathlon training by adding an accelerometer-derived metric.MethodsEleven adolescent athletes were fitted with a combined heart rate (HR) and accelerometer to be worn during all training sessions. Duration, HR, training impulse (TRIMP), and average net force (AvFNet) were used as training variables. All training was divided into either low-intensity training (LIT), or high-intensity training (HIT) based on reported intensity. The training was further categorized as training without any shooting practice (NS) or as a combination of skiing and shooting (COMB). Duration, HR, TRIMP, and AvFNet were analyzed in a linear mixed model for the different training modalities.ResultsAll training was similar in duration for LIT and HIT sessions (p = .0521) and NS and COMB sessions (p = .988). TRIMP did not differentiate between LIT or HIT training (p = .350) or for NS compared to COMB (p = .298). While AvFNet decreased during COMB compared to NS during LIT sessions (p

Objective: To investigate the relationship between head impact characteristics and the levels of blood biomarkers associated with brain injury, neurofilament light (NfL) and glial fibrillary acidic protein (GFAP). Methods: Four elite amateur Muay Thai athletes were equipped with impact monitoring mouthguards, collecting linear and rotational acceleration data during a period of eight weeks. Capillary blood samples were collected after each period of sparring sessions to analyse the levels of NfL and GFAP. Results: On a group level, mean GFAP levels were negatively correlated to mean impacts per session (p ​

The aim of this study was to determine the impact of runs 1 and 2 on overall rank in Giant Slalom. Data from 15 seasons (2005/2006–2019/2020) including and unique starts for women (n = 2,294) and men (n = 2,328) were analyzed. Skiers were grouped based on final ranks 1–3 (G3), 4–10 (G10), and 11–20 (G20) and separately analyzed for women and men. A Wilcoxon-signed rank test was used for comparisons between runs 1 and 2, while a multi-nominal logistic regression was used to identify odds ratios (OR) associated with group rank. Women had similar run times for runs 1 and 2 (p = 0.734), while men had faster times on run 2 (p < 0.001). The strongest association to G3 was during run 1 for run time (men: OR 1.06–1.12; women: OR 1.06–1.11, all p < 0.01) and gate-to-gate times (men: OR 33–475; women: OR 81–2,301, all p < 0.001). Overall, this study demonstrates the importance of a fast first run for improving the final ranking group and the need to increase the tempo going from the first to the second run for men.

The purpose of the study was to investigate whether there are energy-efficiency differences between the execution of the old-fashioned double-poling technique (DPOLD) and the modern double-poling technique (DPMOD) at a submaximal work intensity among elite male cross-country skiers. Fifteen elite male cross-country skiers completed two 4-min tests at a constant mechanical work rate (MWR) using the DPMOD and DPOLD. During the last minute of each test, the mean oxygen uptake (VO2) and respiratory exchange ratio (RER) were analyzed, from which the metabolic rate (MR) and gross efficiency (GE) were calculated. In addition, the difference between pretest and posttest blood-lactate concentrations (BLadiff) was determined. For each technique, skiers' joint angles (i.e., heel, ankle, knee, hip, shoulder, and elbow) were analyzed at the highest and lowest positions during the double-poling cycle. Paired-samples t-tests were used to investigate differences between DPMOD and DPOLD outcomes. There were no significant differences in either VO2mean, MR, GE, or BLadiff (all P > 0.05) between the DPMOD and DPOLD tests. DPMOD execution was associated with a higher RER (P < 0.05). Significant technique-specific differences were found in either the highest and/or the lowest position for all six analyzed joint angles (all P < 0.001). Hence, despite decades of double-poling technique development, which is reflected in the significant biomechanical differences between DPOLD and DPMOD execution, at submaximal work intensity, the modern technique is not more energy efficient than the old-fashioned technique.

This study examined the micro-pacing strategies during a distance freestyle cross-country (XC) skiing competition. Nine female and 10 male highly trained XC skiers wore a GNSS device during a FIS-sanctioned race. The course was ~4900 m; women completed two-laps; men completed three-laps. The course was divided into uphill (S1, S3, S5, S7), downhill (S2, S4, S6, S8), and flat (S9) sections for analyses. Statistical parametric mapping was used to determine the course positions (clusters) where total race time or section time was significantly associated with instantaneous skiing speed. Total race time was associated with instantaneous skiing speed during a cluster in S1 on lap 2 for both sexes (t ≥ 5.899, p ≤ 0.008). The two longest uphill sections (S1; S5) and the flat section (S9) contained clusters where section times were related to instantaneous skiing speed for both sexes (p < 0.05). The fastest woman gained 6.9 s on the slowest woman during a cluster in S1 on lap 1 and 7.3 s during a cluster in S9 on lap 1. The fastest man gained 51.7 s on the slowest man over all clusters in S5 over the 3 laps combined. Compared to skiers with longer total race times, skiers with shorter race times skied with faster instantaneous speeds in some clusters of the uphill sections, as well as on the flat section of the course. This study also identified different relative micro-pacing strategies for women and men during freestyle distance XC skiing races. Finally, statistical parametric mapping analyses can help to identify individual strengths and weaknesses for guiding training programs and optimise competition pacing strategies.

The aim of the study was to investigate the exercise intensity and energy expenditure during four types of on-court tennis drills. Five female and five male tennis players participated in the study (age: 17 ± 2 years; V∙O2max: 54 ± 6 ml·kg−1·min−1). Anthropometric measures were taken for each player and, on separate days, each player performed (i) treadmill running to determine V∙O2max and (ii) four different tennis drills (Drill1-4) during which V∙O2, blood lactate concentration, ratings of perceived exertion (RPE 6–20), and displacement of center of mass (m) using 3D kinematics were recorded. The drills were designed to simulate match play with 90 s of rest between each drill. A repeated two-way ANOVA was used for physiological and biomechanical data and Friedman's test for RPE using < α 0.05. Fractional utilization of V∙O2max was greatest during Drill1 81.8 ± 7.0% and lowest during Drill4 72.4 ± 5.2% (p < 0.001) with no difference between sexes (p > 0.05). The highest energy expenditure was during Drill1 and lowest during Drill4 (77 ± 15 and 49 ± 11 kcal, respectively, p < 0.05). Energy expenditure per meter for Drill1–Drill4 was subsequently reduced for each drill with 10.5 ± 2.1, 9.9 ± 2.2, 7.6 ± 1.7, and 8.0 ± 1.6 J·kg−1·m−1 (p < 0.01). There were no interaction effects for any of these variables. RPE (6–20) and blood lactate concentration post Drill1–Drill4 were 17.5, 15.5, and 13.0 (overall, legs and arms, p < 0.001) and 5.9 ± 2.0, 4.9 ± 1.9, 5.6 ± 2.0, and 5.0 ± 2.2 mmol·l−1 (p < 0.05). The findings of this study demonstrate that the on-court tennis drills performed here are suitable for high intensity training in junior tennis players. The energy expenditure per minute is comparable to similar sports whereas the energy expenditure per meter is notably greater.

IntroductionLong-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.MethodsHeart 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).ResultsMean 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.ConclusionElite 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.

Our aims were to measure anthropometric and oxygen uptake (V˙O2) variables in the laboratory, to measure kinetic and stride characteristics during a trail running time trial, and then analyse the data for correlations with trail running performance. Runners (13 men, 4 women: mean age: 29 ± 5 years; stature: 179.5 ± 0.8 cm; body mass: 69.1 ± 7.4 kg) performed laboratory tests to determine V˙O2 max, running economy (RE), and anthropometric characteristics. On a separate day they performed an outdoor trail running time trial (two 3.5 km laps, total climb: 486 m) while we collected kinetic and time data. Comparing lap 2 with lap 1 (19:40 ± 1:57 min vs. 21:08 ± 2:09 min, P < 0.001), runners lost most time on the uphill sections and least on technical downhills (-2.5 ± 9.1 s). Inter-individual performance varied most for the downhills (CV > 25%) and least on flat terrain (CV < 10%). Overall stride cycle and ground contact time (GCT) were shorter in downhill than uphill sections (0.64 ± 0.03 vs. 0.84 ± 0.09 s; 0.26 ± 0.03 vs. 0.46 ± 0.90 s, both P < 0.001). Force impulse was greatest on uphill (248 ± 46 vs. 175 ± 24 Ns, P < 0.001) and related to GCT (r = 0.904, P < 0.001). Peak force was greater during downhill than during uphill running (1106 ± 135 vs. 959 ± 104 N, P < 0.01). Performance was related to absolute and relative V˙O2 max (P < 0.01), vertical uphill treadmill speed (P < 0.001) and fat percent (P < 0.01). Running uphill involved the greatest impulse per step due to longer GCT while downhill running generated the highest peak forces. V˙O2 max, vertical running speed and fat percent are important predictors for trail running performance. Performance between runners varied the most on downhills throughout the course, while pacing resembled a reversed J pattern. Future studies should focus on longer competition distances to verify these findings and with application of measures of 3D kinematics.

Although today's ski waxing chemicals and micro-machining techniques of the ski base are highly sophisticated, objective procedures for testing and verification of the results have not yet been developed and evaluation is based on comparison of subjective experience. The purpose of the present study was thus to compare different setups for testing the glide of cross-country skis. Two differently waxed ski pairs were tested for glide inside a ski tunnel. Inertial measurement units (IMUs) were attached to each ski; instantaneous velocities monitored by three different speed-traps; the velocities during the acceleration phase determined by Doppler radar. Kinetic, potential and total energy, giving the energy dissipation, were calculated for four representative trials during the acceleration phase. No reliable data were obtained from the IMUs due to high drift. The mean maximal velocity for the two ski pairs were 6.97,s = 0.09 and 6.70,s = 0.09 m·s − 1, respectively. Higher differences between the skis were identified during the retardation phase compared to the acceleration phase. The mean difference between the velocities determined by the speed-trap and Doppler radar was 0.6,s = 1%, demonstrating that the latter provides accurate data for evaluation of gliding characteristics and performance. However, theoretical confirmation of the friction coefficient, on the basis of data provided by Doppler radar and energy calculations requires exact measurements of the inclination and topography of the track in question. [ABSTRACT FROM PUBLISHER]

The article presents a study which examines the difference between expanded polystyrene (EPS) and expanded polypropylene (EPP) cores in helmets used in alpine ski racing and their repetitive impact at alpine slalom gates. It finds that EPP cores may be more suitable for absorbing multiple low impacts caused by alpine gates. It implies that repeated violence and multiple impacts are relevant parameters to consider when constructing alpine ski race helmets.

The clinical use of beta-lactam antibiotics combined with beta-lactamase inactivators, such as clavulanate, has resulted in selection of beta-lactamases that are insensitive to inactivation by these molecules. Therefore, therapeutic combinations of an enzyme inactivator and a penicillin are harmless for bacteria harboring such an enzyme. The TEM beta-lactamase variants are the most frequently encountered enzymes of this type, and presently, 20 variants are designated as inhibitor-resistant TEM ("IRT") enzymes. Three mutations appear to account for the phenotype of the majority of IRT enzymes, one of them being the Asn276Asp substitution. In this study, we have characterized the kinetic properties of the inhibition process of the wild-type TEM-1 beta-lactamase and of its Asn276Asp variant with the three clinically used inactivators, clavulanic acid (clavulanate), sulbactam, and tazobactam, and we report the X-ray structure for the mutant variant at 2.3 A resolution. The changes in kinetic parameters for the interactions of the inhibitors with the wild-type and the mutant enzymes were more pronounced for clavulanate, and relatively inconsequential for sulbactam and tazobactam. The structure of the Asn276Asp mutant enzyme revealed a significant movement of Asp276 and the formation of a salt bridge of its side chain with the guanidinium group of Arg244, the counterion of the inhibitor carboxylate. A water molecule critical for the inactivation chemistry by clavulanate, which is observed in the wild-type enzyme structure, is not present in the crystal structure of the mutant variant. Such structural changes favor the turnover process over the inactivation chemistry for clavulanate, with profound phenotypic consequences. The report herein represents the best studied example of inhibitor-resistant beta-lactamases.

The cdc2 kinase subunit (cks) proteins play an essential function in the control of mitosis through their molecular complexes with the cdc2 kinase. In this work, we characterize the conformational state(s) in solution of the cks proteins p13suc1 from Schizosaccharomyces pombe and p9cksphy from Physarum polycephalum. Monomers of p13suc1 and p9cksphy were found to be markedly nonglobular, presumably with a long, nonfolded C-terminal moiety. This was in contrast to the previously published structure of p13suc1, derived from crystallographic studies on a zinc-promoted p13suc1 dimer, in which the individual p13suc1 subunits had a globular conformation. This disparity was resolved when we found that the globular p13suc1 fold undergoes a conformational transition into nonglobular monomers upon dissociation of the dimers following chelation of the zinc ions by ethylenediaminetetraacetic acid (EDTA). We also found that p13suc1, but not p9cksphy, forms stable dimers in the absence of metal ions. The topology of these EDTA-insensitive dimers likely resembles that of the human p9ckshs2 protein, characterized by beta 4 strand exchange from each nonglobular monomer.

Background: Escherichia coli TEM1 is a penicillinase and belongs to class A beta-lactamases. Its naturally occurring mutants are responsible for bacterial resistance to beta-lactamin-based antibiotics. X-ray structure determinations show that all class A beta-lactamases are similar, but, despite the numerous kinetic investigations, the reaction mechanism of these enzymes is still debated. We address the questions of what the molecular contexts during the acylation and deacylation steps are and how they contribute to the efficiency of these penicillinases., Results: Electrostatic analysis of the 1.8 A resolution refined X-ray structure of the wild-type enzyme, and of its modelled Michaelis and acyl-enzyme complexes, showed that substrate binding induces an upward shift in the pKa of the unprotonated Lys73 by 6.4 pH units. The amine group of Lys73 can then abstract the Ser70 hydroxyl group proton and promote acylation. In the acyl-enzyme complex, the deacylating water is situated between the carboxylate group of Glu166, within the enzyme, and the estercarbonyl carbon of the acyl-enzyme complex, in an electrostatic potential gradient amounting to 30 kTe-1 A-1. Other residues, not directly involved in catalysis, also contribute to the formation of this gradient. The deacylation rate is related to the magnitude of the gradient. The kinetic behavior of site-directed mutants that affect the protonation state of residue 73 cannot be explained on the basis of the wild-type enzyme mechanism., Conclusions: In the wild-type enzyme, the very high rates of acylation and deacylation of class A beta-lactamases arise from an optimal chemical setup in which the acylation reaction seems triggered by substrate binding that changes the general base property of Lys73. In site-directed mutants where Lys73 is protonated, acylation may proceed through activation of a water molecule by Glu166, and Lys73 contributes as a proton shuffle partner in this pathway.