This study aimed to determine whether orthotic insoles can improve upper extremity muscle strength by correcting foot alignment in patients with flat feet.
The study involved 18 male patients diagnosed with bilateral flat feet. Foot alignment and upper extremity muscle strength were measured with and without the use of orthotic insoles. Foot alignment was assessed by measuring the medial longitudinal arch height and the external rotation angle of the subtalar joint in both feet. Upper extremity muscle strength was measured in the elbow flexion, shoulder abduction, and shoulder internal and external rotation on the dominant side. Muscle strength testing used a handheld dynamometer (μTas F-1 by Anima Co., Ltd.).
The positions for muscle strength measurement were as follows: elbow flexion was tested with the elbow bent to 90° and the forearm supinated; shoulder abduction was tested with the arm at 90° abduction in the scapular plane; and internal and external rotation strength were measured in the 1st position, with the arm in neutral rotation.
Before using the orthotic insoles, the medial longitudinal arch height ratio averaged 11.6% (right) and 11.8% (left), while the external rotation angle of the subtalar joint averaged 7.3° (right) and 7.2° (left). After using the insoles, the medial longitudinal arch height increased to 16.3% on both sides, and the subtalar joint’s external rotation angle decreased to 1.0° (right) and 1.1° (left).
In terms of muscle strength, prior to wearing the insoles, elbow flexion averaged 173.7N, shoulder abduction 120.4N, external rotation 78.9N, and internal rotation 80.8N. After wearing the insoles, these values improved to 191.4N, 139.8N, 90.1N, and 93.3N, respectively.
Wearing orthotic insoles significantly improved upper limb muscle strength and foot alignment compared to not wearing the insoles. The improved foot alignment provided better stability and increased the ability to generate floor reaction force. This led to secondary improvements in the alignment of the lower limbs, pelvis, spine, thorax, and scapula, resulting in better posture and enhanced upper limb function. These findings suggest that orthotic insoles may benefit individuals with flat feet by improving both foot and upper limb mechanics.
The finding that a decrease in foot arch function due to conditions such as flat feet can affect upper limb strength has important implications for the prevention of shoulder joint disorders, including rotator cuff injuries. Correcting the foot arch with insoles can improve upper limb strength, highlighting the significance of foot function in physiotherapy research.
flat feet
upper extremity muscle strength
