OBJECTIVE: In this study, structure, blood flow and thickness in the Achilles tendon related to tendon-loading activity were investigated. DESIGN: Examination by ultrasound (US) and colour Doppler (CD) immediately before and after 1 h of floor-ball matchplay. SETTING: Sports Medicine Unit, Umeå University, Sweden. PARTICIPANTS: 36 Achilles tendons in 18 middle-aged (mean 39 years) recreational male floor-ball players. MAIN OUTCOME MEASUREMENTS: Structure and high blood flow (HBF)/neovessels (NV) in the tendons were registered. Tendon thickness was measured 3 and 4.5 cm above the upper calcaneus and at the thickest part of the tendon. RESULTS: The US examination showed that 11/36 tendons (30.5%) in nine individuals had structural changes before and after the floor-ball match. In 7/36 tendons (five with structural changes), there were HBF/NV before, and after, the match. In six of these seven tendons, the blood flow was higher after than before the match. In three more tendons (two with structural changes), there were HBF/NV after, but not before, the match. After the match, mean tendon thickness had decreased significantly in both normal tendons and tendons with structural changes at the 3-cm level (6.0 (1.0) mm to 5.8 (0.9) mm; p<0.019), at the 4.5-cm level (5.7 (1.1) mm to 5.5 (1.0) mm; p<0.044), and at the thickest part (6.6 (1.1) mm to 6.3 (1.2) mm; p<0.000). CONCLUSIONS: In about 1/3 of the tendons, there were structural changes, about half of those tendons also had HBF/NV, which was higher after, than before, the match. Mean tendon thickness in both normal tendons and tendons with structural changes had decreased significantly after a 1-h floor-ball match.