When the thoracic kyphosis and lumbar lordosis are within a normal range of angular values back pain is less likely to occur. Angular modifications in the physiological curvatures of this sagittal plane have been shown to indicate spinal disorders. For instance, increasing lumbar lordosis and thoracic kyphosis result in higher intradiscal pressure, tension in the spine's passive parts, and creep in the lumbar viscoelastic structures. One of the most important factors of human biomechanics, spinal curvatures provide optimal energy expenditure and movement capacity. Abnormal adaptations in thoracic and lumbar spine biomechanics can cause low back and back pain. Multiple spinal segments are covered by the lumbar erector spinae muscle (LES), which is regarded as a superficial back muscle. LES consists of two muscles, the longissimus thoracis and iliocostalis lumborum. To move the lumbar spine, the lumbar erector spinae muscle (LES) is recruited in a manner that depends on the applied force. It was suggested that patients used LES to compensate for laxity in passive ligamentous structures in an attempt to reduce excessive force on the lumbar spine. Excessive lumbopelvic movements and altered muscle activation patterns are common in patients with low back pain. Researchers have investigated the timing of each muscle's onset and the activity of the LES, and found that patients with low back pain had higher LES activation compared to healthy people. Exercises for strengthening the LES muscle have been performed trunk extension during prone position. Strenghening LES and thoracic extansors may lead to decrease or prevent painful spinal disorders, improve thoracic excessive kyphosis and other complications. Prone trunk extension exercises is used to clinically exercise approcah to activate weak and susceptible to fatigue LES muscle in patients with nonspecific low back pain. This exercise lead to not only strentghening but also lengthening and streching these muscles. To fully understand the effects and underliying the mechanism of this exercise, biomechanical changes in lumbopelvic movement patterns of individuals with kyphotic posture should be examined. Based on current evidence, it is not clear the mechanism that the prone trunk extension exercises is effective on different spinal alignment postures as excessive thoracic khyposis and compansation mechanism on lumbal lordosis. Thus findings from this research may guide clinicians to examine the effects of different prone trunk extension exercises on LES muscles activation. Mitani et al showed that different upper extremity postures effects the lumbal multifudis activations during standing. Brown et al indicated that sit-stand workstations do not change muscle activations of lumbar muscles. Muyor et al concluded that spinal aligment of cyclists affects core muscle activity during cyling. Wattananon et al demonstrated that clinicians should focus on muscle activation patterns rather than the amount of lumbopelvic motion during prone hip extension. Based on the current studies, and to optimally address the underlying mechanism that the main objective was to investigate and show the effects of lumbal lordosis and thoracic kyphosis angles on muscle activations during different low back exercises.

Inclusion Criteria:

• Individuals between the ages of 18-30
• Individuals who agreed to participate in the study

Exclusion Criteria:

• Individuals with congenital lumbar pathology
• Individuals who have previously had an operation on the back and waist region
• Individuals with scoliosis
• Individuals with a difference in length in the lower extremity

Individuals who agreed to participate in the study were determined as individuals between the ages of 18-30.