Kinesiology of Muscle Force and Its Impact on the Spine

Overview

• Importance of posture and muscle force on spine health
• Encouragement to maintain good posture

Neck and Head Positioning

Upright Position

• Neutral head position is a first class lever system
• Minimal muscle force needed to maintain position

45° Neck Flexion

• Common position when using cell phones
• Increased moment arm and external torque
• Greater muscle force required from neck extensors
• Prolonged flexion can lead to spinal stress, disc herniation, or rupture

Neural and Muscular Impact

• Poor coordination of bilateral sternocleidomastoid muscles
• Difficulty in chewing and swallowing due to coupled muscles

Recommendations

• Maintain an upright head position
• Take frequent breaks
• Stretch neck in flexion, extension, or both

Trunk and Lifting Mechanics

Lifting Heavy Boxes

• Longer moment arm with larger, heavier boxes
• Closer lifting reduces torque and required muscle force
• Incorrect posture (leaning back) increases spine stress

Everyday Activities

• Bending over (e.g., drinking from a fountain) increases moment arm
• Increased stress on lower spine (L4, L5)

Common Posture Issues

Using Laptops and Cell Phones

• Kyphosis with posterior pelvic tilt
• Cervical lordosis to compensate
• Adds stress to lumbar and cervical spine

Long-Term Effects

• Chronic spine pain
• Responsibility to correct posture in occupational therapy (OT)
• Introduction to future discussions on improving posture for better spine health

Conclusion

• Impact of posture on spine health
• Responsibility to maintain good posture and correct it where possible