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Back Strength and the Battle of the Sexes

Back pain is a common problem both for men and women. Often the exact cause of the pain is unknown. Trunk muscle function and strength are key factors. Researchers are gathering information about the muscles of normal adults. They hope to compare this data against the same information in patients with low back pain. This will help in treating back pain patients. It may even be useful in preventing back disorders.

Engineers at the University of Vermont studied the strength of trunk muscles in the standing and sitting positions. They used a special machine called a dynamometer. The dynamometer measures the strength of a muscle contraction. This machine was hooked up to a computer to gather and analyze the data.

Speed and muscle forces were measured through a range of motion while sitting and standing. Healthy men and women without back pain were measured and compared to each other. The men were stronger in all motions except back extension. The reasons for this were greater height, larger upper bodies, broader shoulders, and longer trunk length in men than in women.

The researchers went back and recalculated their findings. This time, they adjusted for differences in height and body mass. When all things are equal, no differences are found in back strength comparing men and women. This means that if men and women of the same height, breadth, and length were measured and compared, their strength would be the same. The only difference was in trunk extension. Women have stronger trunk extensor muscles than flexor muscles compared to men.

Scientists think this strength difference in trunk extensor muscles for women occurs naturally. Women need stronger extensor muscles because of the greater load some carry. In general, women need stronger back muscles to offset the weight of their breasts. Pregnancy requires a stronger back just to stay in an upright position.

This information about trunk strength for men and women can be used in several ways. Strength training can be done over the full range of motion and in different positions using normal values. Physical differences between men and women should be considered. This is important for training and measuring trunk muscle function.

References: Tony S. Keller and Amy L. Roy. Posture-Dependent Isometric Trunk Extension and Flexion Strength in Normal Male and Female Subjects. In Journal of Spinal Disorders. August 2002. Vol. 15. No. 4. Pp. 312-318.

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