AUTHOR=Seeberg Trine M. , Kocbach Jan , Danielsen Jørgen , Noordhof Dionne A. , Skovereng Knut , Haugnes Pål , Tjønnås Johannes , Sandbakk Øyvind 

TITLE=Physiological and Biomechanical Determinants of Sprint Ability Following Variable Intensity Exercise When Roller Ski Skating

JOURNAL=Frontiers in Physiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.638499

DOI=10.3389/fphys.2021.638499

ISSN=1664-042X

ABSTRACT=<p>The most common race format in cross-country (XC) skiing is the mass-start event, which is under-explored in the scientific literature. To explore factors important for XC skiing mass-starts, the main purpose of this study was to investigate physiological and biomechanical determinants of sprint ability following variable intensity exercise when roller ski skating. Thirteen elite male XC skiers performed a simulated mass-start competition while roller ski skating on a treadmill. The protocol consisted of an initial 21-min bout with a varying track profile, designed as a competition track with preset inclines and speeds, directly followed by an all-out sprint (AOS) with gradually increased speed to rank their performance. The initial part was projected to simulate the “stay-in-the-group” condition during a mass-start, while the AOS was designed to assess the residual physiological capacities required to perform well during the final part of a mass-start race. Cardiorespiratory variables, kinematics and pole forces were measured continuously, and the cycles were automatically detected and classified into skating sub-techniques through a machine learning model. Better performance ranking was associated with higher VO<sub>2<italic>Max</italic></sub> (<italic>r</italic> = 0.68) and gross efficiency (<italic>r</italic> = 0.70) measured on separate days, as well as the ability to ski on a lower relative intensity [i.e., %HR<sub><italic>Max</italic></sub> (<italic>r</italic> = 0.87), %VO<sub>2<italic>Max</italic></sub> (<italic>r</italic> = 0.89), and rating of perceived exertion (<italic>r</italic> = 0.73)] during the initial 21-min of the simulated mass-start (all <italic>p</italic>-values &lt; 0.05). Accordingly, the ability to increase HR (<italic>r</italic> = 0.76) and VO<sub>2</sub> (<italic>r</italic> = 0.72), beyond the corresponding values achieved during the initial 21-min, in the AOS correlated positively with performance (both <italic>p</italic> &lt; 0.05). In addition, greater utilization of the G3 sub-technique in the steepest uphill (<italic>r</italic> = 0.69, <italic>p</italic> &lt; 0.05), as well as a trend for longer cycle lengths (CLs) during the AOS (<italic>r</italic> = 0.52, <italic>p</italic> = 0.07), were associated with performance. In conclusion, VO<sub>2<italic>Max</italic></sub> and gross efficiency were the most significant performance-determining variables of simulated mass-start performance, enabling lower relative intensity and less accumulation of fatigue before entering the final AOS. Subsequently, better performance ranking was associated with more utilization of the demanding G3 sub-technique in the steepest uphill, and physiological reserves allowing better-performing skiers to utilize a larger portion of their aerobic potential and achieve longer CLs and higher speed during the AOS.</p>