Plasma catecholamine and lactate relationship during graded exercise in men with spinal cord injury

Catecholamine and lactate responses to incremental exercise were examined in individuals with spinal cord injury (SCI). Three men with high-level (HINJ) and four with low-level (LINJ) SCI performed VO2peak exercise tests on an arm ergometer. Forearm venous blood samples taken at rest and at the end of each work stage were analyzed for norepinephrine (NE), epinephrine (EPI), and lactate (LA) content. Mann-Whitney tests revealed that peak LA, NE, and EPI responses were greater in LINJ compared with HINJ subjects (LA = 7.1 +/- 0.5 vs 3.2 +/- 0.4 mM; NE = 3.1 +/- 1.0 vs 0.4 +/- 0.1 ng.ml-1; EPI = 0.5 +/- 0.2 vs 0.1 +/- 0.01 ng.ml-1). Spearman rank correlations for LINJ and HINJ groups were NE-EPI, rs = 0.85 vs rs = 0.17; NE-LA, rs = 0.83 vs rs = 0.31; and EPI-LA, rs = 0.73 vs rs = 0.41. The strong relationships between NE, EPI, and LA in the LINJ group were similar to those previously reported in able-bodied athletes. However, the relatively weak association between these factors in the HINJ group indicates that, while some function exits, the sympathoadrenal response to exercise is significantly impaired in these individuals. These results suggest that mechanisms other than catecholamines are primarily responsible for muscle lactate production during incremental exercise in individuals with HINJ.