A faked prolongation of an endurance target time does not affect muscle fatigue but increases perceived exertion

While psychological factors are known to influence physical performance, responses to unexpectedly extended endurance tasks remain unclear.

In a crossover-randomized study, 37 participants performed an isometric endurance task twice, with a 14-day interval, compensating for 50% of upper body weight for 10 min. Muscular fatigue was measured via EMG of the back muscles, and perceived exertion (RPE; Borg scale 6-20) was recorded every minute (Real). In the experimental condition (Fake), RPE was recorded every 50 s without participants' awareness. After the tenth query, participants were told a technical error occurred and were asked to continue for two additional minutes with two extra RPE queries. Participants were grouped by RPE and Fatigue Index (FI) into "good-end" and "bad-end" groups. FI and RPE were compared between Real and Fake conditions.

RPE-based grouping showed no significant FI differences. FI-based grouping revealed significantly higher RPE in the "good-end" group during the Fake condition (+0.9 at 540/550 s; +1.0 at 600 s). No significant differences were found in the "bad-end" group.

Extending a task beyond its expected endpoint increases perceived exertion, which may lead to task termination despite unchanged muscular fatigue.