Background Salivary secretory immunoglobulin A (sIgA) is a non-invasive biological marker that may be used to monitor an athlete’s response to training and to identify athletes at risk for upper respiratory tract infection. However, its usefulness in elite athletes is unclear.

Objective To determine the variation of sIgA in male Olympic athletes during the preparation period and the Olympic football tournament.

Design Prospective observational study.

Setting Preparation period and the Olympic football tournament in Rio2016 (from July 18 to August 11, 2016).

Participants Twenty male elite football players (aged 22 ± 2 years) called up to the Olympic team.

Intervention Over 27 days, athletes had 19 training days, 2 traveling days, 2 days with friendly matches, and 4 days with official games.

Main Outcome Measurements sIgA was analysed using a real-time lateral flow device. Training and match internal loads were assessed using the session rating of perceived exertion (sRPE) method.

Results During the first 3 days of training, sRPE (p < 0.001), but not sIgA (p > 0.05), varied significantly; however, sIgA had a moderate negative within-subjects correlation with sRPE (r = -0.39; confidence interval 95%: -0.62 to -0.09). During the whole study period, daily sIgA ranged from 350 ± 242 to 517 ± 238 µg.mL^-1 (p > 0.05). The between-subjects coefficient of variation of sIgA ranged from 44.5% to 69.2%, whereas its within-subjects coefficient of variation ranged from 17.3% to 74.7%. Daily sRPE varied significantly throughout the whole study period (p < 0.001). No upper respiratory tract infection was reported.

Conclusions sIgA showed a high between- and within-subjects variation in male elite football players, which may limit its usefulness as a valid biological marker for response to training and risk of upper respiratory tract infection.