This study investigated whether low-intensity isometric training would elicit a greater improvement in maximum voluntary contraction (MVC) at the same fascicle length, rather than the joint angle, adopted during training. Sixteen healthy women (21.8 +/- 1.5 years) were randomly divided into an intervention group and a control group. Before (Pre) and after (Post) training, isometric plantarflexion MVCs were measured every 10 degrees through the range of ankle joint position from 20 degrees dorsiflexion to 30 degrees plantarflexion (i.e., 6 ankle angles). Medial gastrocnemius fascicle length was also measured at each position, using B-mode ultrasound under 3 conditions of muscle activation: at rest, 30% MVC at respective angles, and MVC. Plantarflexion resistance training at an angle of 20 degrees plantarflexion was performed 3 days a week for 4 weeks at 30% MVC using 3 sets of twenty 3-second isometric contractions. Maximum voluntary contraction in the intervention group increased at 0 and 10 degrees plantarflexion (0 degrees; Pre: 81.2 +/- 26.5 N.m, Post: 105.0 +/- 21.6 N.m, 10 degrees; Pre: 63.0 6 23.6 N.m, Post: 81.3 +/- 20.3 N.m), which was not the angle used in training (20 degrees). However, the fascicle length adopted in training at 20 degrees plantarflexion and 30% MVC was similar to the value at 0 or 10 degrees plantarflexion at MVC. Low-intensity isometric training at a shortened muscle length may be effective for improving MVC at a lengthened muscle length because of specificity of the fascicle length than the joint angle.