When patients with cerebrovascular disorder-associated hemiplegia and orthopedic diseases walk using a cane made necessary by a functional disorder on the paralyzed side of the affected leg, they tend to load excessive weight on the cane. In such patients, the latissimus dorsi on the side using the cane is hyperactive, and this hyperactivity promotes a vicious cycle leading to dysfunction of the abdominal muscles. Aiming to clarify the association of weight loading on a cane by the upper limbs with activities of the latissimus dorsi and trunk muscles, we investigated the influence of changes in unilateral upper limb weight loading on a cane, by adopting a one-legged standing position, on electromyographic integrals of the upper and lower fibers of the bilateral latissimus dorsi, obliquus abdominis, and low back muscles. The subjects were 8 healthy males. While the subjects maintained a resting standing position on 2 scales, loading equivalent weights on the bilateral legs, electromyograms of the muscles were recorded, and the integrals were determined. The subjects then held a 4-point cane with their right hand in this position. The weight loaded on the cane was adjusted to 0% of the body weight, and each subject lifted the heel on the cane side to a level at which the anterior sole lightly touched the scale, maintained this position supported by the leg on the non-cane side, and electromyograms were recorded. The weight loaded on the cane was randomly changed to 5%, 10%, 15%, and 20% of the body weight, electromyograms were measured, and the integrals were determined. The load on the cane was then set to 0% of the body weight, the subject lifted the heel on the non-cane side to a level at which the anterior sole lightly touched the scale, maintained this position supported by the leg on the cane side, and electromyograms were recorded. The load on the cane was again randomly changed to 5%, 10%, 15%, and 20% of the body weight, electromyograms were recorded, and the integrals were determined. The relative electromyographic integrals of the upper and lower fibers of the latissimus dorsi on the cane side increased with an increase in the load (at 15% and 20% of the body weight) on the cane in both tasks, that of the obliquus abdominis on the cane side also increased, and that of the upper fibers of the latissimus dorsi on the non-cane side tended to increase. In contrast, no marked changes were noted in the low back muscles on the cane side, lower fibers of the latissimus dorsi, or obliquus abdominis and low back muscles on the non-cane side. These results suggest that long-term excess loading on the cane causes hypertonus and muscle shortening of the lower and upper fibers of the latissimus dorsi on the cane side, for which consideration of weight loading on the cane in necessary during clinical gait training.
