The potential for assessing performance and acute fatigue in uphill trail running (UTR) through acceleration time series remains underexplored. For this purpose, time-variability of body acceleration and covariation among limb acceleration were studied in UTR. Twenty competitive and young trail runners participated in a simulation UTR test covering a distance of 4758 meters, with a total elevation gain of 575 meters and an average slope of 13.6%. Four sections with clear slope differences were identified. Detrended Fluctuation Analysis of upper back acceleration and Principal Component Analysis among wrists and ankle acceleration were performed for the whole test and for each section. The outcomes were correlated with performance and standardized effect size was used to compare sections. The main findings suggest that (a) runners with higher performance showed less persistence in body acceleration fluctuations and greater interlimb diversity, and (b) the steepest parts, particularly the final and effortful section, showed increased persistence in body acceleration and some runners lost interlimb covariation. In conclusion, time-variability and coordination analyses of acceleration time series seem to be sensitive to performance and acute fatigue in UTR, which opens further possibilities for providing more integrative, dynamic, and practical assessment tools.
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