Self-control exertion leads to performance decrements during tasks demanding of muscular and cardiovascular systems (Bray et al., 2008; Marcora et al., 2009). Several reviews have also implicated self-control depletion with the psychobiological state of fatigue (Hagger et al., 2010; Van Cutsem et al., 2017). In this state, individuals have also been noted to report higher levels of perceived exertion when exercising at vigorous intensities (MacMahon et al., 2014; Marcora et al., 2009; Wagstaff et al., 2014). The purpose of this study was to investigate physical performance and ratings of perceived exertion during a self-paced maximum distance cycling trial (MDT) following a short bout of mentally-fatiguing cognitive activity (thought-suppression). Recreationally active participants (N = 16, Mage = 20.94) completed one familiarization session and two testing sessions. All visits were separated by ≥ 72-hours. Control and experimental trials were counterbalanced, with either a 6-minute bout of thought-logging (control) or a 6-minute bout of thought-suppression (experimental) being performed prior to each respective MDT. Ratings of perceived exertion (RPE) were solicited from participants across three sensory domains relevant to MDT task performance (Leg-muscle, Respiration, Mental). Thought-suppression was perceived to be significantly more demanding than the control task, which resulted in significantly higher ratings of mental fatigue (p = 0.04, 2 = 0.26). Distance travelled on the MDT was not significantly different following thought suppression, relative to control trials (p = 0.84, 2 = 0.00). Similarly, a repeated-measures ANOVA showed no differences in HR between conditions (p = 0.95, 2 = 0.00). Despite these similarities, ratings of perceived leg-muscle exertion (RPE-L) were significantly higher during the MDT following thought-suppression (p = 0.05, 2 = 0.24). RPE-R (respiration) and RPE-M (mental) ratings also trended towards higher scores following the experimental manipulation, although they did not differ significantly. RPE-L was perceived to be significantly higher than both RPE-R and RPE-M in both conditions on the MDT (ps < 0.05). RPE-M was rated significantly lower than RPE-L and RPE-R during MDTs in both conditions (ps < 0.05). Results indicate that performing a demanding self-control exertion task for a short duration leads to increased feelings of mental fatigue. The observed levels of fatigue were also associated with higher than normal ratings of perceived exertion during cycling tasks of equal demands and performance. / Thesis / Master of Science (MSc) / Any thought, emotion or behaviour that an individual modifies in order to better suit their goals occurs as a result of self-control exertion. Research indicates that just like the exertion of muscular strength, exerting self-control impacts subsequent attempts to do so. Using a mentally-demanding task, we induced states of self-control depletion which left individuals feeling mentally-fatigued. As a result of this state, participants needed to exert themselves harder in order to complete a task that was perceived less demanding, when non-fatigued.