Summary

We live in a time of plenty. During evolution, periods of hunger and simultaneously high activity levels would combine giving a stimulus which is absent from modern lifestyles. This is potentially connected with abnormal glucose metabolism. It was hypothesised that simultaneous fasting and aggressive aerobic neuromuscular electrical stimulation (NMES) exercise, until metabolic exhaustion, may be an acceptable modern equivalent. A healthy subject fasted for 44 h (water allowed) during which he undertook three aerobic NMES sessions at >50%VO_2max; heart rate >160 bpm. Metabolic gas analysis of a comparable session in the non-fasting state showed 100% carbohydrate substrate utilisation. With fasting the NMES exercise consumed mostly fat–up to 100% fat utilisation at 42 h. This clear shift away from using carbohydrate as a substrate and hypoglycaemia may indicate that carbohydrate stores are nearly depleted. The authors postulate that this may constitute a metabolic super stimulus mimicking the famine-activity periods of our ancestors.