Impact of Digital School‐Based Personalized High‐Intensity Interval Training on Cardiorespiratory Fitness in French Adolescents: The <scp>METs</scp> ‐Up Programme

The aim of this study was to examine the impact of a short school-based personalized interval training program (METs-Up) using a smartphone application on cardiorespiratory fitness (CRF) in French adolescents. Secondary objective was to assess the effects of the program on body mass index (BMI). A total of 9021 adolescents (4428 boys and 4593 girls, age range: 10-14 years) were randomized to the experimental group (EXP) (n = 5845) or the control group (CON) (n = 3176). The EXP performed a personalized high-intensity interval training (HIIT) program ranging (95.5 to 102.5% dynamic maximal aerobic speed, MAS) integrated into physical education (PE) lessons over 6 weeks. HIIT consisted of approximately two 15-min sessions per week of high-intensity, intermittent-running exercises. The CON group followed conventional PE lessons. CRF (20-m Shuttle Run Test) and BMI were measured at baseline and after 6 weeks. After 6 weeks, both groups showed significant improvements in CRF compared to baseline value (p < 0.05). The increase in the EXP group (13.7% in laps completed) was significantly higher than in the CON group (4.8%) (p < 0.05). Additionally, a significant decrease in BMI was observed in the EXP (-0.8%), whereas no significant change was observed in the CON group. A short school-based personalized METs-Up HIIT program, utilizing an innovative smartphone application, significantly improved CRF in French adolescents, addressing the decline in CRF levels among youth.