How does pole length affect lower back muscle activity at different inclines and skiing intensities during double poling?

Marie Lund Ohlsson ¹ Marcus Nilsson ¹ Mikael Swarén ^2*

• ¹ Swedish Winter Sports Research Centre, Faculty of Human Sciences, Mid Sweden University, Östersund, Sweden
• ² Dalarna University, Falun, Sweden

Purpose: This study aimed to investigate how pole length, incline, and skiing intensity affect lower back muscle activation in elite cross-country skiers. This addressing a critical gap in understanding the biomechanical demands and risk of low back pain of double poling (DP). Method: Eleven elite crosscountry skiers performed skiing trials on a treadmill, varying in incline (flat vs. 6°), intensity (two selfselected speeds, training speed and racing speed), and pole lengths. Muscle activity was measured by surface electromyography on the erector spinae thoracic and lumbar muscles, on the left and right side. A motion capture system was used for kinematic analysis of the lower back-pole moment arm and the hip angle during the DP cycle. Results: Compared to men, female skiers had a significantly higher (p < 0.001), overall muscle activation for the m. erector spinae lumbar on both the left and right side (26% of MVC vs, 15% of MVC, and 28% of MVC vs. 22% of MVC, for the left and right side, respectively). No correlations were found, neither between muscle activation to the lower back-pole moment arm, or to the hip angle. Conclusion: The findings suggest that female skiers experience significantly higher lumbar erector spinae activation during DP, potentially indicating greater susceptibility to back-related issues. The results also highlight the need to tailor training and right adapted equipment to mitigate lower back stress, especially in flat terrain high-intensity conditions. The asymmetrical muscle activity and gender differences underscores the need for further investigation into biomechanical factors influencing back muscle engagement in cross-country skiing.