Exercises are commonly recommended for chronic neck pain, but evidence-based guidelines do not explain what types of exercise. The aim of this randomized study was to evaluate the rate of change in neck strength following high- and low-intensity neck muscle training and their effects on pain and disability. One hundred eighty women with chronic neck pain were randomized into a high-intensity strength training group (STG), local muscle endurance training group (ETG), or control group (CG). The neck training consisted of isometric exercises in the STG and dynamic exercises in the ETG. Both groups performed dynamic exercises for the upper extremities. Strength tests, neck pain, and disability indices were evaluated at the baseline, at the follow-ups after 2 and 6 months in the training groups, and after 12 months in all groups. In both groups the greatest gains in neck strength, as well as decrease in neck pain and disability, were achieved during the first 2 months. However, the improvements continued up to 12 months. The STG achieved the greatest strength gains at all follow-ups. The CG showed only minor changes, and significant differences were found in favor of the training groups in all measures. The change in neck pain and disability indices correlated with the isometric neck strength (r = -0.22 [-0.36 to - 0.08] to -0.36 [-0.49 to -0.23]). Neck and shoulder muscle training was shown to be an effective therapy for chronic neck pain, resulting in early improvement in both the strength tests and subjective measures. The results can be maintained and even improved with long-term training.