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=Volume 12 - 2021

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=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 VO2Max (r=0.68) and gross efficiency (r=0.70) measured on separate days, as well as the ability to ski on a lower relative intensity (i.e. %HRMax (r=0.87), %VO2Max (r=0.89) and RPE (r=0.73)) during the initial 21-min of the simulated mass-start (all p-values <0.05). Accordingly, the ability to increase HR (r=0.76) and VO2 (r=0.72), beyond the corresponding values achieved during the initial 21-min, in the AOS correlated positively with performance (both p<0.05). In addition, greater utilization of the G3 sub-technique in the steepest uphill (r=0.69, p<0.05), as well as a trend for longer cycle lengths during the AOS (r=0.52, p=0.07), were associated with performance. 
In conclusion, VO2Max 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 cycle lengths and higher speed during the AOS.