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Background & aim: One of the most common causes of trunk deviations is a change in the curvature of the spine in the lumbar region. Physiotherapy is one of the most common treatments for hyperlordosis and low back pain. In the field of corrective exercises, the comparison of the findings of Williams and McKinsey's research is small and contradictory. The aim of the present study was to determine and compare the effects of two types of corrective exercise program on lumbar muscle strength in girls with hyperlordosis.
 
Methods: In the present quasi-experimental study conducted in 2019, 30 females with lumbar lordosis beyond normal degrees (Hyperlordotic) in lumbar curve were selected as the study sample and were randomly divided into Williams and McKenzie’s exercise groups. Training protocols were done for eight weeks, three times a week. The lumbar lordosis was measured using a flexible ruler, isometric strength of trunk and hip muscles were measured by using digital dynamometer and precieved pain was measured using Copeck Pain Questionnaire. Data was analyzed using independent and paired t-testes.
 
Results: The results indicated that both types of exercises lead to a significant increase in the strength of the lumbar, extensor and pelvic flexor muscles as well as the strength of the abdominal muscles. Exercises in both groups correspondingly significantly reduced the subjects' low back pain (p <0.001), nonetheless, no significant difference was observed between the results of the two types of exercises in any of the study variables (p> 0.05).
 
Conclusions: The results indicated that the administration of Williams and Mackenzie corrective movements can lead to a significant improvement in lumbar arch angle and isometric strength of trunk muscles; however, in terms of effectiveness, no significant difference was observed between the two training methods.