Background/Objectives: Skeletal muscle functions as an endocrine organ by secreting myokines in response to exercise, with interleukin-6 (IL-6) recognized as a representative intensity-dependent biomarker that rapidly increases immediately after exercise and is strongly dependent on exercise intensity. However, it is unclear how changes in mechanical stress affect the response of myokines after exercise. This randomized crossover study aimed to investigate the effect of mechanical stress on acute myokine secretion during matched metabolic exercise under different mechanical stress. Methods: Ten healthy adult males performed 30 min of cycling at 60% of peak $\stackrel{·}{\mathrm{V}}$O₂ in both semi-recumbent position and side-lying positions. Blood samples were collected before, immediately after, and at 30 and 60 min post-exercise to evaluate IL-6, brain-derived neurotrophic factor (BDNF), and lactate. Results: BDNF and lactate levels peaked immediately after exercise, and IL-6 reached its peak at 30 min post-exercise in both the semi-recumbent position and side-lying positions. All markers showed significant elevations in response to exercise. However, no significant differences were found between the two postures in any of the measured variables. Conclusions: These findings suggest that reduced mechanical load does not impair endocrine responses when the intensity of metabolic stress is maintained. This study provides scientific evidence that, regardless of posture or environment, sufficient exercise intensity can induce adequate IL-6 and BDNF secretion, through which the beneficial effects of exercise may be expected.