According to the Motivational Intensity Theory (MIT) (Brehm and Self, 1989), internal states such as needs and motives influence the maximum effort individuals are willing to invest in a task, determining potential motivation. Simultaneously, social comparison theory (Festinger, 1954) suggests that in a performance context, others serve as a source of information for assessing one's abilities, creating an upward pressure to outperform (Munkes & Diehl, 2003 ; Rijsman, 1974). While playing against similar or slightly superior peers intensifies this upward pressure, weaker peers or alone play should not impact it. In the present experiment, we examined the link between social comparison and effort-related cardiovascular response. Participants engaged in 2D video games of unfixed difficulty for 5 minutes, with displayed scores of similar, slightly better, or weaker peers. A control condition featured no peer score display. Measurements, including initial systolic time interval (ISTI), systolic and diastolic blood pressure, heart rate, and task performance, were recorded each minute. A 4 (social comparison) x 5 (time) repeated-measures ANOVA was conducted and yielded a significant social comparison x time interaction. A planned contrast on the final task minute revealed higher ISTI reactivity for similar and slightly better peers, compared to weaker and alone conditions. These findings demonstrate that effort is influenced by social comparison, with similar and slightly better peers increasing effort intensity. This is attributed to the upward pressure effect on potential motivation, subsequently determining high effort intensity in unfixed task demands, expanding on previous research on social information and effort.