Background: High school sports participation has increased in the past decade, notably in multiple sport participation and sport specialization by adolescent athletes. Stressful circumstances during training and competition can predispose athletes to overtraining syndrome and athlete burnout. Others have used a mental toughness training program to determine how athletes handle stressors during training and competition, and whether the training positively affects factors associated with illness and injury. Objective: This study is an extension of previous research on mental toughness.1 This study measured the effect of a mental toughness intervention on mental toughness, somatic manifestation, athlete burnout, stress recognition, stress response, coping aptitude, and athletic performance. Participants: Six Caucasian male varsity track athletes from a rural public high school participated in this study. Methods: The participants completed instruments assessing mental toughness, athlete burnout, somatic manifestations, stress recognition, and stress response prior to, during, and at the conclusion of a 4-wk mental toughness intervention. The Mental, Emotional, and Bodily Toughness Inventory (MeBTough) was used for assessing mental toughness. Spearman rho correlation coefficients (r) assessed the relationships between mental toughness, athlete burnout, somatic manifestations, stress response, stress recognition, and coping aptitude. A related sample Wilcoxon signed rank test was used to determine if the MeBTough, Athlete Burnout Questionnaire (ABQ), Cohen-Hoberman Inventory of Physical Symptoms (CHIPS), Stress Response Scale for Adolescents (SRSA), Brief Cope Inventory (BriefCOPE) and Perceived Stress Scale (PSS) scores after the intervention were significantly different than baseline scores. Results: At baseline, mental toughness displayed a negative relationship with athlete burnout (r = -0.07), somatic manifestations (r = -0.46), and stress recognition (r = -0.17). There was a decrease in somatic manifestations (P = 0.04) and athlete burnout (P = 0.04) following the intervention. Active coping (P = 0.04), use of emotional support (P = 0.04), and planning (P = 0.04) subscale scores of the BriefCOPE increased from pre- to postintervention. No significant change in mental toughness (P = 0.17), stress recognition (P = 0.34), or stress response (P = 0.71) from pre- to postintervention was observed. Increases in mental toughness resulted in enhanced performance, most noticeably by a decrease in the team’s 4 x 800 m event time by 1 min. Conclusion: Though mental toughness was inversely related to athlete burnout and somatic manifestations in these 6 rural high school track athletes, a 4-wk mental toughness intervention did not improve their mental toughness. Future studies, including a longer intervention in a larger sample of a variety of athletes, are needed to assess the true impact of the online intervention on mental toughness scores and the factors associated with overtraining injury and illness.