The Effect of Backpack Load on Muscle Activities of the Trunk and Lower Extremities and Plantar Foot Pressure in Flatfoot

Abstract

[Purpose] The purpose of this study was to investigate the changes in muscle activation of the trunk and lower extremities and plantar foot pressure due to backpack loads of 0, 10, 15, and 20% of body weight during level walking in individuals with flatfoot. [Methods] Fourteen young flatfoot subjects and 12 normal foot subjects participated in this study. In each session, the subjects were assigned to carry a backpack load, and there were four level walking modes: (1) unloaded walking (0%), (2) 10% body weight (BW) load, (3) 15% BW load, and (4) 20% BW load. Trunk and lower extremity muscle activities were recorded by surface EMG, and contact area and plantar foot pressure were determined using a RS scan system. [Results] The erector spinae, vastus medialis, tibialis anterior and gastrocnemius muscle activities, but not the rectus femoris and rectus abdominis muscle activities of flatfoot subjects significantly and progressively increased as load increased in flatfoot subjects. Contact area and pressure of the lateral and medial heel zones were significantly increased too. [Conclusion] Based on this data, the weight of a backpack could influence muscle activation and plantar foot pressure in flatfoot.

Correlations between Muscle Activities and Strap Length and Types of School Bag during Walking

“…Asymmetry in muscle activity may indicate a failure of trunk stabilization and contribute to the development of back pain 3 , 15 ) . Most studies of carriage load according to different types of bag, muscle activity of erector spinae was focused 10 , 13 , 15 ) . However, there is a paucity of study on the effects on the muscle activity of the trapezius caused by different types of bag.…”

“…All subjects walked on a treadmill with no bag, and while carrying a shoulder bag or backpack at the height of the iliac crest, 10 cm lower than the iliac crest, or 20 cm lower than the iliac crest 11 ) . The weight of the bag was set at 10% of the body weight of each subject 2 , 9 , 12 , 13 ) . The order of the tasks was carried out at random to prevent a carry over effect.…”

Effect of backpack shoulder straps length on cervical posture and upper trapezius pressure pain threshold

“…While carrying a bag and walking, the body is subjected to physical stress owing to the weight of the bag, and the body is either mechanically or physiologically influenced, which affects dynamic balance and changes the posture of the body2, 3 ) . Carrying a backpack in an incorrect manner can cause various biomechanical, physiological and neuromuscular disorders that may reduce physical performance4, 5 ) . An ideal bag weight and space between the shoulder straps have been recommended6, 7 ) .…”

“…If carrying weight on one side continues, the body involuntarily compensates by deviating the trunk in the opposite direction to correct the imbalance caused by an external force creating abnormal posture9 ) . Excessive weight will increase the load on the spine and shoulders and it may cause changes in the spine curvature4 ) . Scapular position1 ) and electromyogram activities of the trunk and lower extremities muscle3, 8 ) may be affected by a change in the space between the backpack shoulder straps.…”

Effects of orthotic insoles on adults with flexible flatfoot under different walking conditions

“…The contact area can be used to indicate the area of contact between various regions of the foot and the ground, and it is shown in square centimeters16 ) . The values for both of these variables are larger in the midfoot in individuals with flatfoot compared with those with normal feet17 ) . Because the arch of the foot is decreased in individuals with flatfoot in a weight-bearing position, the structure of the bones of the foot is further deformed, which makes both the contact area and load rate of the midfoot larger.…”