Effects of adding high-intensity training during an 8-week period on maximal oxygen uptake in 12-year-old youth athletes.

Purpose: Maximal oxygen uptake (V̇O ) increases during adolescence parallel to the increase in fat-free mass (FFM). How much endurance training adds to this effect is still controversial. Our aim was to investigate if inclusion of high-intensity training (HIT) during an 8-week training period was superior to low-intensity strength and coordination training in 12-year-old youth athletes concerning the effect on V̇O .

Methods: Thirty-five cross-country skiers were randomized into a HIT group (ET) and a strength and coordination group (SC), while 29 less active peers served as controls for growth and maturation (C). Anthropometrics and V̇O were assessed before and after the training period, and level of physical activity and training were monitored with accelerometers, training logs and a questionnaire.

Results: The number of weekly training sessions were higher for ET (4.6 ± 1.2) and SC (4.1 ± 1.0) compared with C (1.8 ± 2.0) (p < 0.01), with only ET conducting HIT sessions (1.9 ± 0.2 per week). C spent more time sedentary and less time in moderate and vigorous activity compared with ET (p < 0.05). All groups had a similar %-change pre-post in absolute V̇O (mL min ) of 6% ± 6% for ET (p < 0.01), 5% ± 7 for SC (p = 0.14), and 5% ± 13% for C (p = 0.03), with no significant differences between groups. V̇O relative to FFM did not change significantly for any groups.

Conclusion: The change in V̇O paralleled the change in FFM for all groups, questioning the effect of HIT on V̇O over an 8-week period in youth athletes.