Prior studies suggest that moderate whole-body heating (WBH), which raises internal temperature (Tcore) ~0.6-1.0 deg C, alters the exercise pressor reflex. It is speculated that elevated muscle temperature (Tmuscle) alters the sensitivity of muscle afferents. However, less is known about the effects of passive WBH on the limb Tmuscle during exercise. PURPOSE: To determine limb Tmuscle during exercise under passive WBH and limb heating conditions. METHODS:Forearm Tmuscle was measured with a needle probe (thermocouple) in 8 healthy subjects (57 +- 3 yrs). Mean skin temperature (Tsk), Tcore (telemetric pill), the arm skin temperature (Tarmskin, not covered by suits), blood pressure (BP) and heart rate (HR) were measured during WBH with water perfused suits. After Tcore rose ~0.6 deg C, subjects performed a fatiguing handgrip exercise followed by post exercise circulatory occlusion (PECO). In a separate visit, the forearm was heated with a water perfused sleeve. After the Tmuscle rose ~1 deg C (i.e. similar to that seen during WBH), the exercise paradigm was repeated. RESULTS: Passive WBH significantly raised Tsk (3.2 +- 0.3 deg C), Tarmskin (1.9 +- 1.0 deg C), Tmuscle (0.96 +- 0.15 deg C) and HR. The increases in Tmuscle were positively correlated with the increases in Tcore (R = 0.75, P < 0.05). Limb heating raised Tmuscle (0.98 +- 0.11 deg C), Tarmskin (2.3 +- 0.6 deg C), and did not alter Tsk, Tcore or HR. There was no significant difference in the grip force, grip time, or the change in HR with handgrip between the trials. The increases in Tmuscle during the last min of grip (0.37 +- 0.07 vs. 0.92 +- 0.17 deg C, P < 0.03) and PECO (P = 0.01) were significantly lower during WBH than during the limb heating trial. CONCLUSION: Although local limb heating and WBH induced similar elevations in Tmuscle, the responses in Tmuscle to exercise were different between these two heating conditions. Supported by NIH R01 HL141198 (Li and Cui) and UL1 TR002014 (Sinoway), and AHA Award #15GRNT24480051 (Cui).