H. Sasaki, N. Hotta and T. Ishiko (1991). Comparison of sympatho-adrenal activity during endurance exercise performed under high- and low-carbohydrate diet conditions. The Journal of sports medicine and physical fitness, 31(3), 407-12.

PubMed 1798313

[Abstract]
Effects of varied carbohydrate (CHO) content in the diet on sympatho-adrenal activity to endurance exercise during which blood sugar was kept over a preexercise level were studied in five male physical education students. The CHO loading was used and consisted of a 7-day low CHO diet (30% CHO, 50% fat, 20% protein) followed by a 7-day high CHO diet (70% CHO, 20% fat, 10% protein). The results obtained from the present study were as follows: (1) plasma epinephrine (E) was almost the same between the low and the high CHO diets before and at 30 min of the exercise, while plasma norepinephrine (NE) level at 30 min of the exercise was significantly higher in the low (959 +/- 98 pg/ml) than in the high CHO diet (679 +/- 64 pg/ml) (p less than 0.05); (2) serum free fatty acid (FFA) level was significantly higher in the low than in the high CHO diet before (p less than 0.05) and at 30 min of the exercise (p less than 0.01); (3) a negative correlation was found between muscle glycogen and plasma NE (p less than 0.05). In all the subjects, increase in serum FFA accompanied by increase in plasma NE was detected in the low CHO diet. In conclusion, sympathetic activity to endurance exercise during which blood sugar was kept over a preexercise level was elevated more in the low than in the high CHO diet. It was suggested that the more elevated sympathetic nervous activity would have resulted from glycogen depletion in the working muscle due to the low CHO diet and would have increased FFA mobilization from the adipose tissue.