This study aimed to examine the effects of 6 weeks of high-intensity interval training (HIIT) vs. 6 weeks of on-court tennis training (OTT) on the psychophysiological responses, performance responses, and technical scores of young tennis players. Twenty-nine young male tennis players (aged 13.8 ± 0.4 years) were divided into HIIT (n = 14) and OTT …