The aim of this study was to investigate how physical fitness performance, which is related to the strength and power of the lower extremities and core, as well as lateral agility, changes across 20 weeks of in-season training in youth female and male padel players. This study was conducted using a prospective cohort design on 16 Swedish high school padel players aged between 15 and 18 years old. The players were assessed at baseline with five tests of their physical fitness and followed prospectively, with the registration of their training load for 20 weeks, and then assessed at a follow-up, approximately five months later. The players increased their performance in all tests (p ≤ 0.02). The mean improvement in their Isometric squat test performance was 20% for peak force, 18% for relative strength value and 69% for average rate of force development. Their improvement in the squat jump test performance was 9%, whereas the improvement in their countermovement jump test was 6%. For the 30 second sit-up test, an improvement of 14% was observed. Improvements were also noted for the 30 second side hop test performance on both the right (9%) and left leg (11%). The effect size ranged from 0.31 to 1, respectively, for the tests, representing a small to large effect. The data from this study suggest that an improvement in physical fitness performance can be obtained during 20 weeks of padel training. © 2024 by the authors.