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.

Background: Keirin races are often decided by the "makuri," a final-lap sprint in which a racer from the rear overtakes the leader at approximately 75 km/h. Because direct measurement during races is extremely difficult, its mechanisms remain unclear. This exploratory, hypothesis-generating study used musculoskeletal simulation to examine how pedaling posture may reduce its metabolic cost. Methods: A modified AnyBody BikeModel was checked for plausibility against one professional racer's pedaling force (approximately 150 rpm, 1,000 W). Model-estimated metabolic power–cadence curves were simulated at constant mechanical loads, and only relative differences were interpreted. On these curves, a racer in the group (Point A: seated, 1,200 W, 147 rpm, 73 km/h) changes posture at the same load and cadence (Point A′), then accelerates (Point B: 1,255 W, 151 rpm, 75 km/h). Results: At Point A′, a non-seated posture with the hips anterior to the bottom bracket increased ankle dorsiflexion (possibly promoting stretch-shortening cycle utilization) and reduced metabolic power by 67 W (4%); it also raised the optimal cadence but recruited more fatigue-prone muscles. At Point B, despite a 55 W higher load, metabolic power remained comparable to that at Point A, assuming a slightly smaller drag area; under idealized conditions, the resulting speed difference (0.55 m/s) would close a 5 m gap in approximately 9 s. A seated "makuri" with deliberate ankle dorsiflexion reduced metabolic power by 59 W (4%). Idealized trunk stabilization representing strong core stability (relative pelvic rotation restricted from 5° to 0.5°) reduced it by a further 86–109 W (5–7%). These differences changed little when the scaling factor of the metabolic model was reduced from 1.5 to 1.0. Conclusions: Hip position, deliberate ankle dorsiflexion, and trunk stabilization are experimentally testable candidates for an energy-saving "makuri." Drawing on previous studies, we also discuss hybrid training, in which voluntary agonist contraction is resisted by electrically stimulated antagonists, and the potential of this simulation framework as a "digital trainer" for individualized training and bicycle configuration.