Muscle Glycogen Depletion And Body Water Status Assessed With Segmental Bioimpedance Spectroscopy

Abstract

Glycogen is stored in combination with 3-5 g/g of water in muscle tissue, and carbohydrate (CHO) loading is accompanied by an increase in body water content, especially intracellular water. Therefore, body water status may be useful as an indicator of muscle glycogen level. However, body water status under conditions of glycogen depletion has not been investigated. PURPOSE: To determine the effect of muscle glycogen depletion on body water distribution using segmental bioimpedance spectroscopy (S-BIS). METHODS: Twelve healthy men performed cycling exercise aimed at muscle glycogen depletion, and 24 hours later consumed a high- (HIGH group; CHO, 7 g/kg/day) or low- (LOW group; CHO, <1 g/kg/day) CHO diet. Thigh muscle glycogen content was measured at baseline, immediately after, and 24 hours after exercise using 13C-magnetic resonance spectroscopy. Intra- and extracellular water content (ICW and ECW) in the leg was assessed using S-BIS; measurement was performed at baseline and 24 hours after exercise to avoid the effect of exercise-induced acute changes in blood flow and metabolite concentration, but not glycogen, on body electrical properties. RESULTS: Muscle glycogen content decreased after exercise in both groups (HIGH, 76.2 ± 16.4 to 28.1 ± 16.8 mmol/kg w.w.; LOW, 71.6 ± 12.1 to 25.5 ± 10.1 mmol/kg w.w.; both p < 0.05 vs. baseline). At 24 hours after exercise, muscle glycogen content recovered in the HIGH group, but not in the LOW group (HIGH, 72.7 ± 21.2 mmol/kg w.w.; LOW, 33.2 ± 12.6 mmol/kg w.w.; p < 0.05 between groups). ICW and ECW in the leg were unchanged from baseline in both groups (ICW; HIGH, 7.70 ± 1.43 to 7.59 ± 1.37; LOW, 7.53 ± 1.24 to 7.58 ± 1.35: ECW; HIGH, 4.73 ± 0.50 to 4.69 ± 0.54; LOW, 4.66 ± 0.67 to 4.49 ± 0.53). CONCLUSION: Muscle glycogen was obviously decreased in thigh muscles, but ICW and ECW in the leg were unchanged. We conclude that muscle glycogen depletion per se does not alter body water status assessed with S-BIS.