Objectives: To analyse stroke rate (SR) and stroke length (SL) combinations among elite swimmers to better understand stroke strategies across all race distances of freestyle events.Design: We analysed SR and SL data from 324 male and female swimmers competing in all individual freestyle events (50 m to 1,500 m) at the 2019 European Short-Course Championships using video-based kinematic analysis.Methods: Two-dimensional kernel density estimation (2D KDE) was applied to visualise SR–SL combinations. Spearman correlations quantified relationships between stroke parameters and speed by sex and race distance.Results: In the 50 m sprint, SL showed the strongest positive correlation with speed (men: ρ = 0.57; women: ρ = 0.50), while SR correlations were trivial. As race distance increased, SR correlations with speed strengthened, reaching moderate levels in long-distance events (men's 1,500 m: ρ = 0.37; women's 800 m: ρ = 0.45), whereas SL correlations weakened. The 2D KDE heatmaps revealed an inverse SR–SL relationship, with medallists often employing stroke strategies distinct from finalists and the broader field. Gold medallists in sprint events favoured above-average SR without compromising SL, while in middle- and long-distance races, a shift toward higher SR and reduced SL was observed, particularly among women.Conclusions: These findings highlight the complexity and individuality of stroke mechanics at elite levels and suggest that superior conditioning and technique enable medallists to sustain elevated SR without compromising SL. The application of 2D KDE provides a novel, intuitive method to capture nuanced biomechanical strategies, offering valuable insights for coaching and performance optimisation.

PlayerLoad™ is the most widely used accelerometer-derived metric for quantifying external demands in sport. Its normalized variant, PlayerLoad·min ⁻¹ , is also commonly used as a marker of exercise intensity. However, recent literature has raised concerns regarding its scientific foundation, including inconsistent definitions, arbitrary units, opaque filtering methods, questionable theoretical underpinnings, and imprecise mechanical terminology. The construct validity of PlayerLoad™ remains unverified, and emerging evidence suggests weak dose–response relationships with performance outcomes. Although widely adopted in practice, these concerns warrant critical scientific scrutiny. This review critically evaluates the validity and reliability of the PlayerLoad™ metric, highlighting the need for greater transparency and theoretical rigor in wearable athlete monitoring. Furthermore, we present alternative accelerometer-derived metrics, developed from clearer biomechanical and physiological principles, which may offer more robust and interpretable measures for researchers and practitioners.

To permit the collection of quantitative data on start, turn and clean swimming performances in any swimming pool, the aims of the present study were to (1) validate a mobile in-field performance analysis system (PAS) against the Kistler starting block equipped with force plates and synchronized to a 2D camera system (KiSwim, Kistler, Winterthur, Switzerland), (2) assess the PAS’s interrater reliability and (3) provide percentiles as reference values for elite junior and adult swimmers. Members of the Swiss junior and adult national swimming teams including medalists at Olympic Games, World and European Championships volunteered for the present study (n = 47; age: 17 ± 4 [range: 13–29] years; World Aquatics Points: 747 ± 100 [range: 527–994]). All start and turn trials were video-recorded and analyzed using two methods: PAS and KiSwim. The PAS involves one fixed view camera recording overwater start footage and a sport action camera that is moved underwater along the side of the pool perpendicular to the swimming lane on a 1.55 m long monostand. From a total of 25 parameters determined with the PAS, 16 are also measurable with the KiSwim, of which 7 parameters showed satisfactory validity (r = 0.95–1.00, p < 0.001, %-difference < 1%). Interrater reliability was determined for all 25 parameters of the PAS and reliability was accepted for 21 of those start, turn and swimming parameters (ICC = 0.78–1.00). The percentiles for all valid and reliable parameters provide reference values for assessment of start, turn and swimming performance for junior and adult national team swimmers. The in-field PAS provides a mobile method to assess start, turn and clean swimming performance with high validity and reliability. The analysis template and manual included in the present article aid the practical application of the PAS in research and development projects as well as academic works.

Purpose: This study introduces two-dimensional (2D) Kernel Density Estimation (KDE) plots as a novel tool for visualising Training Intensity Distribution (TID) in biathlon. The goal was to assess how KDE plots, alongside traditional training metrics, might provide a more detailed understanding of heart rate (HR) intensity patterns, aiding in the evaluation of training quality and compliance.Methods: Fifteen elite-level youth biathletes from two national academy programmes were monitored over 5–6 weeks using HR monitors. Training sessions were measured via time-in-zone (TIZ) within a five-zone HR model with any time accumulated below the threshold for Zone 1, considered Zone 0. Sessions were dichotomised into those planned as low-intensity training (LIT) or those planned with high-intensity training (HIT). KDE analyses were conducted in MATLAB (Version R2020b) using the “ksdensity” function to create 2D KDE plots that visualise HR intensity accumulation across each programme, session type (e.g., Low-intensity training: LIT; High-intensity training: HIT), and individual athlete responses. Traditional histogram plots and grouped bar charts were also used for comparison.Results: For LIT sessions, athletes performed less time in Zone 1 than planned, while performed time exceeded planned time in Zone 2. For HIT sessions, performed time in Zone 5 was lower than planned. All sessions contained unplanned time in Zone 0. The 2D KDE plots provided a continuous and detailed representation of HR intensity accumulation throughout training sessions, revealing patterns and intensity fluctuations that complement traditional TIZ analyses.Conclusions: 2D KDE plots might serve as a valuable complementary tool for assessing TID in biathlon, offering a more nuanced and continuous view of HR intensity. By identifying discrepancies between planned and performed training intensity, coaches can refine strategies and provide individualised feedback. Incorporating KDE plots into training monitoring could improve training alignment, helping reduce overtraining or undertraining risks and optimising athlete development.

Purpose: This study examined tactical positioning and pacing in short-distance (100 m), middle-distance (200 m, 400 m) and long-distance (800 m, 1,500 m) freestyle events, focusing on the influence of race distance, competition round (HEAT vs. FINAL), and sex.Methods: Race data from multiple World Championships (2013–2023) were analyzed. Spearman's rank correlations (ρ) were calculated to examine rank stability across race distances, competition rounds, and sex. Additionally, lane distributions of Top3 finishers were analyzed to assess the impact of lane position on race outcomes.Results: Rank correlations increased progressively from the first to the final lap across all race distances (p < 0.05). Long-distance events exhibited earlier rank stabilization, with correlations reaching ρ ≥ 0.90 by 50% race completion, whereas middle-distance events showed greater positional variability throughout. Rank correlations were lower in FINALS than in HEATS (p < 0.05), indicating greater positional shifts in high-stakes races. No significant sex-based differences were observed (p > 0.05). Central lanes (4 and 5) were associated with the highest Top3 finish rates, while outer lanes (0, 1, 8, and 9) had the lowest, particularly in long-distance events.Conclusion: Finals foster more dynamic race strategies, with increased positional changes. Rank stability was achieved at a relatively earlier proportion of the race in long-distance events compared to middle-distance events. By the final lap, rank stability converged across all distances, suggesting that race order was largely set before the last lap, emphasizing early tactical positioning over late-race surges. These findings offer insights into optimizing race tactics and pacing in elite swimming.

Purpose: Biathlon is an endurance sport that combines high-intensity cross-country skiing with precision shooting, requiring athletes to carry a rifle while skiing. This study examined the effect of rifle carriage on angular kinematics involving hip and knee range of motion (ROM) in on-snow biathlon skiing. Methods: 29 tier 3 level biathletes (11 F; 18 M) skied two maximal effort time trials (2300 m), once with and once without carrying the biathlon rifle. A 3D motion analysis system, comprising of twelve inertial measurement units, was used to measure hip and knee ROM in the sagittal plane. Multilevel linear models, considering slope, stance (dominant/non-dominant), and side (leading/lagging, left/right), were employed to analyze the effects of rifle carriage on knee and hip ROM in gears 2 and 3. Results: In gear 2, rifle carriage was associated with reduced knee ( p < .001) and hip ROM. ( p < .001). In gear 3, rifle carriage was associated with reduced knee ROM ( p < .001) but greater hip ROM ( p = .003). Conclusion: Biathletes change their skiing kinematics when carrying a rifle during on-snow skiing. Rifle carriage was associated with decreased knee and hip ROM in gear 2, and reduced knee but increased hip ROM in gear 3. Future research should determine the relationships between rifle-induced changes to skiing kinematics with performance.