This study examined the effect of an external nasal dilator strip (ENDS) on three field tests of maximal performance and monitored the rating of perceived breathing effort (RPBE). Thirty male Chinese students (age 15.2 +/- 1.6 yrs) performed three maximal field tests: (a) short-term anaerobic power (SAnP: 40-m sprint); (b) long-term anaerobic power (LAnP: shuttle sprint); and (c) peak aerobic performance (AeP: multistage 20-m shuttle run) under three conditions: ENDS, placebo, and control. Students were randomly placed into 6 groups using a fully counterbalanced single-blind design. No significant differences were seen between conditions in the anaerobic performances measured by SAnP and LAnP. However, the ENDS produced a significant improvement in peak aerobic performance (p = 0.037) compared to the control condition of 3.2% (95% CI= 6.2-0.2; Cohen effect size = 0.2), and also compared to the placebo condition (p = 0.018) of 2.9% (95% CI = 5.1-0.2; Cohen effect size =0.2). The ENDS condition also significantly reduced RPBE during the AeP and LAnP tests by an average of 5.5% and 3.8%, respectively. Wearing an external nasal dilator can significantly reduce breathing effort and improve peak aerobic performance during field tests involving maximal running.