Background Although climbing is an increasingly popular sport, there is a lack of scientific evaluation of suitable training methods for climbers, especially with a view to prevention and rehabilitation. A specific rehabilitation program, Adjunct Compensatory Training (ACT), has recently been presented, but it has not been evaluated scientifically to date. Objective To investigate the effects of Adjunct Compensatory Training on climbing-specific overstrain syndromes of the shoulder. Methods Twenty active boulderers and climbers with an average age of 28.9 (± 7.4) years performed a guided shoulder program of six specific exercises from the ACT program over a period of four weeks. They were examined before and after the intervention. Pre- and post-interventional measurements included the Constant-Murley Score, the QuickDASH Score and the measurement of shoulder ROM (range of motion). Results The Constant-Murley Score increased from 82 (± 10.0) to 104.1 (± 8.2) at follow-up (p < 0.001). The VAS value for bouldering and climbing decreased from 5.25 (± 1.4) before to 2.4 (± 1.6) after the intervention (p < 0.001). Shoulder flexion increased from 167.5 (± 14.9) to 173.1 (± 7.7) after the intervention (p < 0.05), abduction from 172.5 (± 14.9) to 179.6 (± 5.9) (n. s.), external rotation from neutral zero position from 77.6 (± 16.8) to 86.3 ± (8.3) (p < 0.05). Feasibility and acceptance of the intervention were good. Ninety-five percent of the participants continued to exercise, and 100 percent recommended the program to others. Conclusion The ACT led to an improvement in pain, activities of daily living, range of motion and strength in boulderers and climbers with overstrain symptoms of the shoulder. It is also classified as a realistically feasible workout. The extent to which this effect will continue, and whether or not the program can prevent injuries, remains to be seen. It can only be presumed that regular exercises prevent shoulder injuries in the climbing population.