The effects of glycerol ingestion on body water distribution and exercise performance

Water movement in the body is determined by the osmotic forces acting on the cell membrane. Ingestion of a highly-hypertonic glycerol solution resulting in high extracellular osmolality could drive water out of the intracellular space into the vascular space resulting in reduced muscle hydration and increased blood volume. The aim of this thesis was to study the effects of altered body water distribution during exercise. In chapter 3, ingestion of a 400 ml glycerol solution (1 g·kg-1 body mass) increased serum osmolality (309 mosmol·kg-1) which was associated with a 4.0% increase in blood volume due to a 7.2% increase in plasma volume, attributed to a shift of water from the intracellular space, resulting presumably in tissue dehydration. Glycerol ingestion was then used as a means of altering body water distribution in the other studies described in this thesis. Altered body water distribution had no acute effect on force production during quadriceps muscle isometric exercise (chapter 4), or handgrip strength (chapter 5). Regarding chronic effects (chapter 5), two groups of participants exercised handgrip and initiated recovery after ingestion of either a glycerol solution or placebo over a period of 8 weeks. Maximum handgrip strength increased in both groups and there was no statistically significant difference between the two groups. In chapters 6 and 7, the subjects performed a cycling exercise protocol to fatigue. In the glycerol trial, time to fatigue decreased compared with the iso-osmotic trial during an incremental VO2max test (chapter 6) and during cycling against a constant load at 100% VO2max intensity (chapter 7). In the glycerol trial, there was an accelerated increase in blood lactate and an accelerated increase in serum potassium (chapter 7), indicating altered muscle metabolism which may have contributed to the early development of fatigue.