Characterization of the training load in trail runners and its associations with exposure to injury risk

Resumen

Trail running is a recent sport with particular characteristics that increased in number of athletes and competitions. Given this growth and in the same way as in other sports, athletes want to improve performance through the training process. For this to happen, it becomes necessary to understand the sport's demands and the predominant performance variables in trail running. This work aimed: (i) to compare the variations of weekly workload indices of internal and external load measures across the three weeks prior to injury occurrences in trail runners; (ii) to analyze trail runners’ weekly load variations in the four weeks leading up to a trail running competition, and to determine the relationship between the runners’ pacing in competitions and their physical fitness and workload parameters; (iii) to analyze fitness level variations during different times of the season and establish a relationship between changes in fitness levels and accumulated load. Twenty-five male trail runners (age: 36.23   8.30 years old; body mass: 67.24   5.97 kg; height: 172.12   5.12 cm; minimum International Trail Running Association performance index: 600) were monitored daily for 52 weeks. Three periods of assessment were implemented, while load between those periods was calculated. Athletes were monitored daily by global positioning systems. The collected data included distance covered, duration, and rate of perceived exertion (RPE), which were used to obtain session-RPE. The accumulated load (AL), acute:chronic workload ratio (ACWR), training monotony (TM), and training strain (TS) indices were calculated weekly for each runner. Additionally, anthropometric composition, maximal aerobic speed, vertical jump, and dynamic balance were tested periodically (every four months). During the period of analysis, the injury occurrences were recorded. The differences were observed in AL and ACWR for sRPE and training time were significantly greater during the injury week when compared to the previous weeks. Similar evidence was found in TM and TS indices for sRPE, training time, and total distance. Furthermore, no meaningful differences were observed in AL and ACWR for total distance in the weeks prior to injury occurrence. Also, no significant differences in workload measures (p > 0.05) were observed in the four weeks leading up to each short trail competition; however, leading up to the long trail, ultra-trail medium, and ultra-trail long/extra-long competitions, the differences in the runners’ workload measures were significant (p < 0.05). Concerning the pace, in the short trail, pace was found to be moderately correlated with the ACWR of total distance (r = -0.334) and with training monotony of rate of perceived exertion (RPE) (r = -0.303). In the ultra-trail, a large correlation was observed between pace and elevation accumulated (r = 0.677). In the assessments, moderate inverse correlations were found between assessment 1 and 2 for total sRPE and vertical jump: countermovement jump (VJ: CMJ) (r = -0.349), and Y balance test: left posterolateral (YBT: LPL) (r = -0.494). Similar correlations were found between assessment 2 and 3 for total sRPE and VJ: CMJ (r = -0.397), and vertical jump: drop jump (VJ: DJ) (r = -0.395). The results suggest that athletes and coaches should pay special attention to the training periodization and the monitoring of workloads, causing the necessary stimulus to improve performance and avoid the injury risk. It is also worth highlighting the variables that correlate with the pace for each type of competition, constituting an essential tool in preparing the trail running events. Also, possible earlier asymmetries of dynamic balance performance should be considered in trail running athletes.