Purpose To compare acute hemoglobin responses during bench press (BP) exercise among bodybuilders (BB), powerlifters (PL), Paralympic powerlifters (PP), and untrained controls (CON), with emphasis on relative load and sport background. Methods Thirty-eight participants (BB, n = 10; PL, n = 10; PP, n = 8; CON, n = 10) performed ten BP repetitions at 20%, 40%, and 60% of one-repetition maximum (1RM). Multichannel functional near-infrared spectroscopy (fNIRS) was used to assess oxygenated hemoglobin (O₂Hb), deoxygenated hemoglobin (HHb), and total hemoglobin (tHb) responses over the C3–Cz–C4 region. Linear mixed models were used to test the effects of group, condition, and their interactions. Results The main effect of condition was significant for ΔO₂Hb in nine of ten channels and for ΔtHb in one channel (p_FDR_channel textless 0.05). No group effects or group × condition interactions were observed for ΔO₂Hb, ΔHHb, or ΔtHb. Within-group post hoc analyses showed that ΔO₂Hb differences were observed mainly between 20 and 40% of 1RM (p_FDR_slice textless 0.05), with fewer additional differences involving 60% of 1RM. Conclusion Acute hemoglobin responses during BP were expressed primarily as ΔO₂Hb changes and were associated with relative load under the present low-to-moderate load conditions. Because group effects and group × condition interactions were not supported, these findings should be regarded as preliminary and descriptive rather than evidence of sport-specific adaptation or between-group differences in response magnitude. Observed O₂Hb changes represent regional hemodynamic responses, not direct measures of cortical activation or motor control processes.