We sought to investigate arterial baroreflex (ABR) control of muscle sympathetic nerve activity (MSNA) in the transition from rest to steady-state dynamic exercise. This was accomplished by assessing the relationship between spontaneous variations in diastolic blood pressure (DBP) and MSNA at rest and during the time course of reaching steady-state arm cycling at 50% peak oxygen uptake (VO_2peak). Specifically, DBP-MSNA relations were examined in 8 subjects (25±1 yrs) at the start of unloaded arm cycling, and then during the initial and a later period of arm cycling once the 50% VO_2peak work rate was achieved. Heart rate and arterial blood pressure were progressively increased throughout exercise. Although MSNA at rest (16±2 burst/min; 181±36 (au) total activity) was unchanged during unloaded cycling, MSNA burst frequency and total activity were significantly elevated during the initial (27±4 burst/min; 367±76 (au); P<0.05) and later (36±7 burst/min; 444±91 (au); P<0.05) period of exercise. The relationships between DBP and burst incidence, burst strength, and total MSNA, were progressively shifted rightward from unloaded to the initial to the later period of 50% VO_2peak arm cycling without any changes in the slopes of the linear regressions (i.e., ABR sensitivity). Thus, a continuous and dynamic resetting of the ABR control of MSNA occurred during the transition from rest to steady-state dynamic exercise. These findings indicate that the ABR control of MSNA was well maintained throughout dynamic exercise in humans progressively being reset to operate around the exercise-induced elevations in blood pressure and MSNA without any changes in sensitivity.