The aim was to evaluate the energy turnover in the forearm during isometric submaximal exercise. Eight subjects performed isometric handgrip contractions until exhaustion at 10%, 25% and 40% of maximal voluntary contraction (MVC). Blood samples were drawn frequently from the cubital vein of the exercising arm during exercise and a 60 minutes recovery period, and forearm blood flow (plethysmography) was monitored during the same periods. Oxygen uptake and lactate release were used to quantify aerobic and anaerobic energy expenditure. Electromyography (frequency analysis) was monitored during exercise. Anaerobic glycolysis contributed 4%, 31% and 37% of the ATP production in the three experiments, respectively, but total ATP production from anaerobic glycolysis was the same, suggesting a maximal anaerobic glycolytic capacity (MAGC). MAGC may be a limiting factor for muscle performance at 25 and 40% MVC, but not at 10% MVC. Judging from the match between oxygen debt or estimated oxygen deficit vs the anaerobic energy production, the muscles recovered during 60 min rest after 10% MVC and 40% MVC. However, recovery after 25% MVC may have been incomplete.