Intermittent locomotion by terrestrial crustaceans may under specific circumstances increase walking distance and may allow partial re-oxidization of anaerobic products, and replenishment of ATP and arginine phosphate. The Christmas Island red crab G. natalis undertakes a substantial breeding migration each year. The leg muscles of G. natalis subjected to bouts of 2.5 min walking and 2.5 min rest were severely anaerobic. Adenylate energy charge and the large arginine phosphate stores were greatly reduced. Walking for 4 min with pauses of only 1 min exacerbated the anaerobiosis and utilised 50% of the endogenous muscle glycogen. Post-exercise, the adenylate energy charge recovered before the arginine phosphate charge and a large and persistent hyperglycaemia accompanied the restoration of glycogen. Arginine phosphate functioned as a large, longer term, energy reservoir-almost as part of the adenylate pool. Gluconeogenesis is yet to be generally substantiated in decapod crustaceans but G. natalis appears to remove lactate slowly and to reincorporate exogenous glucose into muscle glycogen in the same time frame as lactate removal from the haemolymph. The 4:1 exercise/pause regimen facilitated access to energy stores and increased walking distance, and it allowed L-lactate and H(+) efflux from the muscle during pausing. These responses are similar to those of G. natalis in the field, except during the migration when walking was entirely aerobic. Determinations of adenylate, fuel and arginine phosphate reserves and usage during the migration are required together with more detailed behavioral analysis to resolve the dichotomy in metabolic response.