A School-Based Progressive Muscle Relaxation Program for Female Adolescents: Development and the Effectiveness on Physiological and Psychological Evidence

(1) Background: A variety of stressors may be potentially harmful to adolescents’ health and well-being. Relaxation techniques have been recognized as a valid method for stress release, but the challenge is to apply them practically in schools to produce the desired effects. (2) Methods: This feasibility study used the Perceived Stress Scale (PSS) and hair cortisol concentration (HCC) to test the effects of an abbreviated progressive muscle relaxation (APMR) program on female adolescents. The participants were recruited from a high school and assigned by class cluster to either the experimental group (EG, n = 40) or the control group (CG, n = 35). Both received 4 weeks of stress-related lessons. The EG received 60 additional sessions of APMR over 12 weeks. (3) Results: The program dropout rate of the participants was 1.3%. The EG’s program adhesion rate was 99.1%, and nearly half felt satisfied with the program. After adjusting for the BMI and the pretest in the ANCOVA, it was found that the CG had a greater change in HCC between the pre- and post-tests than the EG, while the PSS did not change significantly in either group. (4) Conclusion: APMR is a valid practice for physiological homeostasis of HCC for female adolescents, but it has no significant effect on perceived stress.