Adenosine triphosphate production rates, metabolic economy calculations, pH, phosphomonoesters, phosphodiesters, and force output during short-duration maximal isometric plantar flexion exercises and repeated maximal isometric plantar flexion exercises.

Measurements of adenosine triphosphate (ATP) production rates, metabolic economy, intracellular pH, phosphodiesters, and phosphomonoesters along with the force output were used to study 90-s maximum voluntary contractions and two new exercise protocols (20-10 and 30-16 exercises). The 20-10 exercise consisted of thirty-one 20-s maximal voluntary contractions separated by 10-s rest periods. The 30-16 exercise consisted of twenty 30-s maximal voluntary contractions separated by 16-s rest periods. There were no differences in ATP production rates, metabolic economy, intracellular pH, or force output between the 20-10 and 30-16 exercises. The 20-10 exercises accumulated more phosphomonoesters than the 30-16 exercises. These increases in phosphomonoesters may be attributed to increased accumulations of glucose-6-phosphate and/or inosine monophosphate. The increased perception of effort reported during and after the 20-10 exercises was not present during the 30-16 or 90-s exercises. This increased perception of effort may be related to increases in lactate, glucose-6-phosphate, inosine monophosphate, and/or NH3.