Background:Although subjective exercise intensity is widely used to monitor training load in athletes, the reliability of subjective effort (SE) during high-intensity sprint running has not yet been established. Objectives:This study aimed to examine the intra-individual and inter-individual variability in sprint running performance at different SE levels. Methods:Eighteen male collegiate sprinters participated in the study. We measured 60 m sprint running performance at four SE levels (60% SE, 80% SE, 90% SE, and 100% SE) every day for 5 days. The coefficient of variation (CV) of each participant`s 5-day performance (60 m sprint time (60T) and 40 - 50 m interval average speed (SP)) was calculated to assess the intra-individual variability of SE. A repeated measures ANOVA was used to compare 60 T, SP, and the CVs of 60 T and SP across the different SE levels. Results:The SP ratios of each submaximal sprint (60% SE, 80% SE, 90% SE) to the maximal sprint (100% SE) were 89.72 ± 1.62%, 95.50 ± 1.08%, and 98.11 ± 0.56%, respectively. The inter-individual variation at each SE level for 60T was inversely related to the SE level (60% SE: 3.25%, 80% SE: 2.31%, 90% SE: 2.06%, and 100% SE: 1.54%). Significant differences were found in the intra-individual variability (CV) of 60 T between 60% SE (2.22 ± 0.35%) and 90% SE (1.42 ± 0.22%), 60% SE and 100% SE (1.40 ± 0.30%), 80% SE (1.95 ± 0.32%) and 90% SE, and between 80% SE and 100% SE (P < 0.05). Conclusions:Intra- and inter-individual variation at all SE levels were below 5%, indicating that SE is a reliable indicator of sprint running intensity. However, the lower the SE, the greater the variability, suggesting SE is most suitable for higher-intensity sprint running.
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