The purpose of this study was to examine the upper-limb muscle strength of 8 weightlifters (aged 18.75±1.13 years old) in 6 directions during maximal voluntary contraction (MVC). The average number of years that the subjects had been practicing weightlifting was 5.25±1.77 years. A Biodex isokinetic measurement instrument was used to compare the differences in 6 directions of 6 100% MVCs measured using muscle electromyography (EMG). Data collection was performed using EMG electrodes attached to the skin overlying 6 upper limb muscles, and data were processed using a Biovision system, with DASY lab software as the filter. Root-mean-square (RMS) EMG values were used to represent the 6 upper limb muscles tested in 6 different directions of isometric MVC. A repeated 1-way analysis of variance (ANOVA; direction, muscle) was performed. SPSS 10.0 was used for the statistical analysis. In the different directions of upper-limb muscle motor unit recruitment (MUR), shoulder extension showed greater MUR than the other muscles. In elbow extension, MUR was less than that for other muscles. In shoulder flexion, RMS for the pectoralis major and middle deltoid was significantly greater than that for other muscles, indicating that weightlifters have stronger MUR in the anterior deltoid, pectoralis major, and middle deltoid. This result may be attributed to increased MUR, which generates more power to resist weight, due to muscle adaptation occurring over long periods of high-strength training. In the different directions of upper limb activity, elbow flexion in weightlifters was significantly greater than the other directions tested. The force produced by pectoralis major was significantly greater than that produced by other upper limb muscles.