The aim of this study was to determine the optimal intensity for isometric strength training. Isometric elbow flexor strength of 51 subjects was measured before and after a six-week training period. Subjects were randomly assigned to target training intensities between 0 and 100 per cent of a maximal voluntary contraction, and undertook supervised isometric elbow flexor training at the allocated target intensity three times each week for six weeks. Strength increases at the trained angle of the trained limb were linearly or near linearly related to training intensity, with the greatest increases in strength occurring at maximal or near-maximal intensities. These findings suggest that the optimal intensity for isometric strength training is maximal or near maximal.