A Scientific Perspective on Reducing Ski-Snow Friction to Improve Performance in Olympic Cross-Country Skiing, the Biathlon and Nordic Combined

Energy expenditure during physical work in cold environments: physiology and performance considerations for military service members

Effective execution of military missions in cold environments requires highly trained, well-equipped, and operationally ready service members. Understanding the metabolic energetic demands of performing physical work in extreme cold conditions is critical for individual medical readiness of service members. In this narrative review, we describe 1) the extreme energy costs of performing militarily relevant physical work in cold environments, 2) key factors specific to cold environments that explain these additional energy costs, 3) additional environmental factors that modulate the metabolic burden, 4) medical readiness consequences associated with these circumstances, and 5) potential countermeasures to be developed to aid future military personnel. Key characteristics of the cold operational environment that cause excessive energy expenditure in military personnel include thermoregulatory mechanisms, winter apparel, inspiration of cold air, inclement weather, and activities specific to cold weather. The combination of cold temperatures with other environmental stressors, including altitude, wind, and wet environments, exacerbates the overall metabolic strain on military service members. The high energy cost of working in these environments increases the risk of undesirable consequences, including negative energy balance, dehydration, and subsequent decrements in physical and cognitive performance. Such consequences may be mitigated by the application of enhanced clothing and equipment design, wearable technologies for biomechanical assistance and localized heating, thermogenic pharmaceuticals, and cold habituation and training guidance. Altogether, the reduction in energy expenditure of modern military personnel during physical work in cold environments would promote desirable operational outcomes and optimize the health and performance of service members.

Respiratory Exposure to Highly Fluorinated Chemicals via Application of Ski Wax and Related Health Effects

PURPOSE

Waxes containing per- and polyfluoroalkyl substances (PFAS) are applied to the base of skis and snowboards ("skis") to reduce friction with the snow surface and improve glide. PFAS exposure can adversely impact cardiometabolic, thyroid, liver, kidney, reproductive, and immune health and are associated with increased risk of certain cancers. In the present review, we summarize the state of the science on PFAS exposure from fluorinated ski wax use, including acute respiratory health effects and PFAS concentrations in biological and environmental media collected from ski waxing settings.

RECENT FINDINGS

Perfluoroalkyl carboxylic acid (PFCA) concentrations in serum and air collected from professional wax technicians and the rooms where waxes are applied are among the highest of any occupation investigated to date, including the fluorochemical industry. High airborne concentrations of fluorotelomer alcohols contribute to high body burdens of certain PFCAs among ski waxers. Fluorinated ski waxes are a significant source of PFAS exposure for people waxing skis and/or spending time in areas where waxing occurs. We highlight recommendations for future research, policy, and technologies needed to address PFAS exposures from fluorinated wax use.

Sliding friction on ice

We study the friction when rectangular blocks made from rubber, polyethylene, and silica glass are sliding on ice surfaces at different temperatures ranging from -40 to 0 °C, and sliding speeds ranging from 3 μm/s to 1 cm s-1. We consider a winter tire rubber compound both in the form of a compact block and as a foam with ∼10% void volume. We find that both rubber compounds exhibit a similar friction on ice for all studied temperatures. As in a previous study at low temperatures and low sliding speeds, we propose that an important contribution to the friction force is due to slip between the ice surface and ice fragments attached to the rubber surface. At temperatures around 0 °C (or for high enough sliding speeds), a thin pre-melted water film will occur at the rubber-ice interface, and the contribution to the friction from shearing the area of real contact is small. In this case, the dominant contribution to the friction force is due to viscoelastic deformations of the rubber by the ice asperities. The sliding friction for polyethylene (PE) and silica glass (SG) blocks on ice differs strongly from that of rubber. The friction coefficient for PE is ∼0.04-0.15 and is relatively weakly velocity dependent except close to the ice melting temperature where the friction coefficient increases toward low sliding speeds. Silica glass exhibits a similarly low friction as PE for T > -10 °C but very large friction coefficients (of order unity) at low temperatures. For both PE and SG, unless the ice track is very smooth, the friction force depends on the position x along the sliding track. This is due to bumps on the ice surface, which are sheared off by the elastically stiff PE and SG blocks, resulting in a plowing-type of contribution to the friction force. This results in friction coefficients, which locally can be very large ∼1, and visual inspection of the ice surface after the sliding acts show ice wear particles (white powder) in regions where ice bumps occur. Similar effects can be expected for rubber blocks below the rubber glass transition temperature, and the rubber is in the (elastically stiff) glassy state.

Effect of Polydimethylsiloxane Oil Lubrication on the Friction of Cross-Country UHMWPE Ski Bases on Snow

Silicone oils are known for their excellent lubricating properties, low toxicity and are ice-, snow-, and hydrophobic. With the upcoming ban on fluorine-containing glide products imposed by the International Ski Federation (FIS), novel glide enhancers for skis are desperately needed. Here, the effect of four silicone oil viscosities (10, 20, 50, and 100 cSt) have been evaluated at three temperatures and snow conditions ranging from −10 °C dry snow to +5 °C wet snow. In dry snow conditions, the shear forces introduced by the silicone oil film increased friction significantly compared to a ski without any treatment. On wet snow, the increased hydrophobicity from the silicone oils reduced the friction by 10%. While commercial glide wax outperformed the silicone oils, this study reports the silicone oils do have desirable friction reducing properties for wet conditions.