Background

Performance in cross-country skiing emerges from the interaction between the athlete, the equipment, and the environment. While physiological and biomechanical determinants of performance have been extensively studied, and ski–snow tribology has largely been investigated under static or simplified conditions, the dynamic interaction between skier movement and ski–snow contact mechanics remains insufficiently understood. In particular, it is unclear how time-varying loading during skiing influences contact mechanics and friction, and how variations in ski–snow friction, in turn, influence skier technique and movement patterns. 

Objectives

The overall aim of this doctoral thesis is to quantify and model the bidirectional interaction between ski–snow friction and skier biomechanics, thereby establishing a framework that integrates tribology and biomechanics in cross-country skiing. 

Methods

The thesis consists of two main parts. 

In the first part, plantar pressure distributions were measured during double poling on snow. Load magnitudes and load positions were used to predict ski camber deformation with an artificial neural network. These predictions were then used as input to a boundary element method-based contact mechanics solver to simulate time-resolved apparent contact length, pressure distribution, and load partitioning between the front and rear glide zones. In addition, controlled tribometer experiments were conducted to quantify the increase in dynamic coefficient of friction associated with thin and thick grip wax applications. 

In the second part, the influence of ski–snow friction on skier movement patterns was investigated in two complementary studies. In a field-based study, national-level skiers performed G3 skating under race-like conditions on both snow and asphalt, using two pairs of skis with distinct friction levels. A combined IMU–GNSS system was used to quantify cycle characteristics and movement patterns. In a laboratory-based study, national-level skiers performed double poling on a wide treadmill using roller skis with systematically varied rolling resistance and at different controlled velocities. Motion capture, pole force measurements, and plantar force measurements were used to quantify cycle characteristics and three-dimensional kinematics.

Results

The first part showed that dynamic variations in load position during the double poling cycle substantially modified the apparent contact area and local pressure, with direct implications for snow deformation, friction generation, and ski selection. The tribometer experiments further showed that both thin and thick grip wax applications increased the dynamic coefficient of friction, resulting in measurable increases in frictional power dissipation and estimated time losses during double poling.  

In the field study, G3 skating showed consistent cycle duration across friction levels, whereas increased friction reduced cycle length and velocity. This indicates that the temporal aspects of the technique are robust, while the spatial characteristics are friction dependent. The effects of friction were also context dependent, with larger effects on flatter terrain and smaller effects on steeper terrain. Despite substantial differences in measured friction, similar cycle characteristics were observed between snow and asphalt, suggesting that straight-line friction does not fully capture the effective friction during skating.  

In the laboratory study, cycle time tended to decrease with increasing rolling resistance, primarily because the recovery phase became shorter. Increased rolling resistance also consistently increased the magnitude of ski and body kinematics, including higher peak ski velocities, greater velocity ranges of motion, and larger vertical centre-of-mass dynamics. These findings indicate that increased friction increases propulsive demands and mechanical work within each cycle, whereas velocity primarily governs movement coordination.   

Conclusion

The thesis establishes a methodological framework that integrates tribology, contact mechanics, wearable sensing, and biomechanical analysis to study dynamic interactions between the skier, the skis, and the snow in cross-country skiing. Collectively, the findings demonstrate that ski–snow friction and skier biomechanics are tightly coupled through load redistribution, contact mechanics, and technique adaptation. Furthermore, friction does not merely act at the ski–snow interface, but strongly influences skier movement patterns, cycle characteristics, and propulsion. In this context, friction acts as a multi-scale constraint whose effects on performance are mediated by technique-dependent movement patterns and athlete-controlled adaptation. The results provide quantitative guidance for ski selection, grip wax application, and technique adaptation in the fluorine-free era, and they support future predictive modelling of performance under different environmental conditions. Beyond cross-country skiing, the thesis also contributes to a broader understanding of multi-scale friction systems in which human movement interacts dynamically with snow or ice surfaces.