INTRODUCTION. Ski mountaineering (SkiMo) success in uphill segments depends on efficient push-offs of legs and poles with leg movements characterized by a complex alternation between push-off and glide phases [1]. The aim was to advance analysis by developing an algorithm to measure stride frequency and contact time on a treadmill using accelerometers. METHODS. The pilot study involved a well-trained recreational ski mountaineer, formerly an elite alpine skier. Uphill walking was performed on a Rodby treadmill at two vertical speeds: 680 and 1008 vm/h. Two Dytran accelerometers were mounted on the skis and connected to a Dewesoft Dewe-43 analog-to-digital converter while simultaneously recorded using a DS-CAM-1100m high-speed camera. Custom algorithms shown in the figure were developed in Matlab to measure stride frequency and contact time based on horizontal acceleration data. The algorithm's accuracy was validated through high-speed video analysis by an expert in motion analysis and SkiMo, using 200 strides from both the left and right legs. RESULTS. During uphill walking at 680 vm/h, the stride frequencies were 0.77 ± 0.018 Hz and 0.77 ± 0.011 Hz, with contact times of 0.86 ± 0.026 s and 0.85 ± 0.019 s for the left and right leg, respectively. This resulted in negligible differences in stride frequencies between the two systems (left: -0.00 ± 0.021 Hz, right: 0.00 ± 0.022 Hz), while contact times using a camera were shorter (left: -0.04 ± 0.030 s, right: -0.02 ± 0.030 s, average: -3.7%). At 1008 vm/h, the stride frequencies were 0.84 ± 0.017 Hz and 0.84 ± 0.027 Hz, with contact times of 0.76 ± 0.026 s, 0.76 ± 0.023 s, and 0.77 ± 0.028 s for the left and right leg, respectively. This also resulted in negligible stride frequency differences between the two systems (left: -0.00 ± 0.018 Hz, right: 0.00 ± 0.027 Hz) and shorter contact times using a camera (left: -0.02 ± 0.025 s, right: -0.03 ± 0.035 s, average: -2.8%). DISCUSSION AND CONCLUSIONS. The developed algorithm reliably assessed biomechanical characteristics for ski mountaineering with negligible differences in stride frequency and slightly longer contact times compared to cameras on a treadmill, and it is expected to perform similarly on snow due to the comparable movement patterns [2]. However, increased variability, such as differing snow conditions or turns, may affect its performance.
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