The extracellular matrix (ECM) plays an essential role in the development, growth and repair of skeletal muscles and serves to transmit contractile force. However, its regulation is poorly understood. This study investigates the age‐specificity of the effects of acute resistance exercise on ECM gene expression. To this purpose, five young (YM, 23.8 ± 2.2 yrs.) and 5 elderly (EM, 66.8 ± 4.1 yrs.) men performed one session of unilateral leg press and leg extension exercises. Six hours post‐exercise, biopsies were taken from the vastus lateralis muscles of both legs. A PCR array was used to profile the expression of 84 ECM‐related genes, of which 6 were validated by qPCR. The PCR array found 9 and 4 ECM‐associated genes to be selectively altered (>1.5‐fold change) in YM or EM only. Four further genes were upregulated in YM but downregulated in EM. Of the 6 genes validated on individual samples MMP9 expression increased in YM (9.7‐fold) and decreased (0.2‐fold) in EM. MMP15 was downregulated in EM only (0.6‐fold). A significant correlation between leg extension 1 RM and changes in COL7A1 expression (ρ = 0.71) suggests a potential influence of fitness levels. In conclusion, acute resistance exercise affects ECM gene expression at least partly in an age‐specific manner. The altered expression of genes encoding matrix metalloproteinases (MMP3, MMP9, MMP15) highlights the role of remodelling processes in the response to an acute bout of resistance exercise. Larger studies are required to verify the age‐associated differences in gene expression profiles and establish their functional implications.

The coefficient of friction of skis on snow appears to be influenced by several factors, for example, speed, contact area, snow type, and ski properties. The purpose of this study was to determine simultaneously the coefficient of kinetic friction and the drag area in straight running on a slope with varying inclination and in traversing on an inclined plane. Experimental measurements were taken using photo cells for straight running and by film analysis for traversing. The skier was modeled as a particle that moves on the surface of a slope. The equation of motion with the algebraic constraints of the track of the skier represents a differential-algebraic equation which was solved numerically. The coefficient of friction and the drag area were calculated by minimizing the sum of the square errors between computed and measured time data. For straight running, the computed coefficient of friction and the drag area were in the same range as obtained by other methods. For traversing, the coefficient of friction could be determined but not the drag area. The skier traversed in an upright position at a speed from 0 to 17 m/s. In this range of velocity the drag area is not constant. It corresponds to critical Reynolds numbers where a sudden drop in the drag coefficient occurs if the body segments are approximated by cylinders. The results indicate that in both cases the applied method is adequate for determining simultaneously the coefficient of kinetic friction and the drag area if these parameters are independent of the velocity.

Competitive skiers encounter a high risk of sustaining an ACL injury during jump‐landing in downhill ski racing. Facing an injury‐prone landing manoeuvre, there is a lack of knowledge regarding optimum control strategies. So, the purpose of the present study was to investigate possible neuromuscular control patterns to avoid injury during injury‐prone jump‐landing manoeuvres. A computational approach was used to generate a series of 190 injury‐prone jump‐landing manoeuvres based on a 25‐degree‐of‐freedom sagittal plane musculoskeletal skier model. Using a dynamic optimization framework, each injury‐prone landing manoeuvre was resolved to identify muscle activation patterns of the lower limbs and corresponding kinematic changes that reduce peak ACL force. In the 190 injury‐prone jump‐landing simulations, ACL forces peaked during the first 50 ms after ground contact. Optimized muscle activation patterns, that reduced peak ACL forces, showed increased activation of the monoarticular hip flexors, ankle dorsi‐ and plantar flexors as well as hamstrings prior to or during the early impact phase (<50 ms). The corresponding kinematic changes were characterized by increased hip and knee flexion and less backward lean of the skier at initial ground contact and the following impact phase. Injury prevention strategies should focus on increased activation of the monoarticular hip flexors, ankle plantar flexors and rapid and increased activation of the hamstrings in combination with a flexed landing position and decreased backward lean to reduce ACL injury risk during the early impact phase (<50 ms) of jump landing.Highlights First study investigating advantageous control strategies during injury‐prone jump‐landing manoeuvres in downhill skiing using a musculoskeletal simulation model and dynamic optimization framework. The simulation results predicted high injury risk during the first 50 ms after initial ground contact. Optimized neuromuscular control patterns showed adapted activation patterns (timing and amplitude) of muscles crossing the knee as well as the hip and ankle joints prior to and after initial ground contact, respectively. An optimized control strategy during an injury‐prone landing manoeuvre was characterized kinematically by increasing hip and knee flexion and less backward lean of the skier at initial ground contact and the following impact phase.