Sympathetic neural regulation in endurance-trained humans: fitness vs. fatness.
We tested the hypothesis that muscle sympathetic nerve activity (MSNA) would be higher in endurance-trained (ET) compared with sedentary (Sed) men with similar levels of total body and abdominal adiposity. We further hypothesized that sympathetic baroreflex gain would be augmented in ET compared with Sed men independent of the level of adiposity. To address this, we measured MSNA (via microneurography), sympathetic and vagal baroreflex responses (the modified Oxford technique), body composition (dual-energy X-ray absorptiometry), and waist circumference (Gulick tape) in Sed (n = 22) and ET men (n = 8). The ET men were also compared with a subgroup of Sed men (n = 6) with similar levels of total body and abdominal adiposity. Basal MSNA was greater in the ET compared with Sed men with similar levels of total body and abdominal adiposity (28 +/- 2.0 vs. 21 +/- 2.0 bursts/min; P < 0.05) but similar to the larger group of Sed men (n = 22) with higher total body and abdominal adiposity (vs. 26 +/- 3 bursts/min; P > 0.05). In contrast to our hypothesis, sympathetic baroreflex gain was lower in the ET compared with Sed men (-6.4 +/- 0.8 vs. -8.4 +/- 0.4 arbitrary integrative units x beat(-1) x mmHg(-1); P < 0.05) regardless of the level of adiposity. Taken together, the results of the present study suggest that MSNA is higher in ET compared with Sed men with similar levels of total body and abdominal adiposity. In addition, sympathetic baroreflex gain is lower in ET compared with Sed men. That sympathetic baroreflex gain was lower in ET compared with Sed men regardless of the level of adiposity suggests an influence of the ET state per se.
Human Integrative Physiology Laboratory, Department of Human Nutrition, Foods, and Exercise, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
Guy E
GE
Alvarez
John R
JR
Halliwill
Tasha P
TP
Ballard
Stacy D
SD
Beske
Kevin P
KP
Davy
D000273:Adipose Tissue / Q000502:physiology*; D000328:Adult; D017704:Baroreflex / Q000502:physiology; D001824:Body Constitution / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology*; D010806:Physical Education and Training / Q000379:methods; D010807:Physical Endurance / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology*; D013223:Statistics as Topic; D013564:Sympathetic Nervous System / Q000502:physiology*