Purpose: The purpose of this study was to investigate the impact on health-related fitness resulting from COVID-19 lockdowns on male high school students in Melbourne, Australia. Method: A total of 146 students completed fitness testing in February and retesting in November following 7 months of remote learning. Fitness tests conducted were 20-m shuttle run (Beep Test), flexed arm hang, body mass index, push-ups, sit-ups, and sit and reach. Results: The mean fitness levels of this cohort decreased across the health-related fitness components. Decreases were varying in magnitude, body composition (d = 0.3), flexibility (d = 0.56), muscular strength (d = 0.64), muscular endurance (d = 0.39 and d = 0.26), and cardiovascular endurance (d = 0.96). Discussion: The impact on students' fitness levels was noteworthy, and the long-term impacts of this decrease are yet to be seen. This research brings focus to what can be done to maintain adolescent fitness when their usual exercise opportunities are not available.