Loprinzi, PD, Cardinal, BJ, Karp, JR, and Brodowicz, GR. Group training in adolescent runners: influence on V̇o2max and 5-km race performance. J Strength Cond Res 25(10): 2696–2703, 2011—The aims of this study were to (a) examine the interrelationships between training intensity, V̇o2max, and race performance in adolescent crosscountry runners and (b) determine if adolescent runners participating in a group crosscountry training program differ in the amount of training time at various intensities. In this study, 7 adolescent runners performed a laboratory-based V̇o2max test before and after a 9-week high-school crosscountry season. Heart rate (HR) and ventilatory threshold (VT) were used to identify 3 training zones for each runner based on the HR at ventilator threshold (HRVT): zone 1: >15 b·min−1 below HRVT; zone 2: between zone 1 and HRVT; zone 3: >HRVT. During each training session throughout the season, HR was measured to quantify the amount of training time in each of these 3 intensity zones. Results showed that the time in each of the 3 zones was not significantly associated with 5-km race performance. Zone 3 training time was positively associated with postseason V̇o2max (r = 0.73, p = 0.06); V̇o2max was significantly inversely associated with 5-km race performance (r = −0.77, p = 0.04). Each week, the amount of training time at, above, and below the VT was significantly different among the participants even though the training prescription for the group was standardized. The results suggest that, among adolescent crosscountry runners, training above the VT may be important in increasing V̇o2max and ultimately, race performance. Given the between-participant differences in the amount of training time in each HR zone, coaches should apply individual, rather than group, training programs.