The plasma norepinephrine (NE) and epinephrine (E) responses to a variety of stressors are influenced by age, adiposity, and exercise training status. The objectives of this study were to 1) compare basal levels as well as posture- and exercise-induced changes in plasma NE and E concentrations in young [25 +/- 1 (SE) yr; n = 24] and older (64 +/- 1 yr; n = 106) people and examine the associations of the responses with adiposity and maximal O2 uptake (VO2max) and 2) determine the extent to which the NE and E responses are altered by exercise training in older people. We found no significant differences in basal NE and E levels between young and older subjects. However, the NE response to standing was exaggerated in older people (696 +/- 39 vs. 512 +/- 61 pg/ml; P < 0.05), whereas NE and E responses to exercise requiring approximately 78% of VO2max were attenuated in older people (NE: 1,444 +/- 74 vs. 1,983 +/- 222 pg/ml; E: 109 +/- 10 vs. 228 +/- 29 pg/ml; both P < 0.01). Increments in NE and E during exercise were more closely associated with age (NE: r = -0.38; E: r = -0.46; both P < 0.05) and VO2max (NE: r = 0.43; E: r = 0.52; both P < 0.05) than with adiposity (NE: r = -0.29; E: r = -0.25; both P < 0.05). In 48 older subjects who completed 9 mo of exercise training, the increases in NE and E during exercise at the same absolute intensity were 39 and 57% lower, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)