Effect of Trunk Stabilization on Pronated Feet

Pronation is the simultaneous calcaneal eversion with foot abduction and dorsiflexion. The range of motion (ROM) for subtalar joint during pronation was around 5 ° to 10°. Pronation is important for stabilization in standing and walking, but excessive ROM for this motion can lead to over pronation.

Foot pronation is a natural movement, necessary for the normal development of gait, since it contributes to the absorption of the ground reaction forces .

However, overpronation causes the collapse of the medial longitudinal arch of the foot, thus causing more tension in certain muscles of the foot and leg, i.e., posterior tibialis. Pronated feet present rearfoot eversion and dorsiflexion with abduction of the forefoot in a static position, and in addition, have a strong relationship with the medial longitudinal arch (MLA). It is suggested that maintaining the integrity of the MLA can prevent numerous musculoskeletal injuries .

Pronated foot posture is common in adulthood, with a prevalence of around 21%, and it may be related to deformities of the first ray of the foot, such as the hallux valgus. Furthermore, this biomechanical alteration can also affect other areas, such as the knee .Thus, pronation influences the time and intensity of lumbopelvic muscle activation, giving rise to low back pain or other dysfunctions at that level.

There are several methods to treat the pronated foot, such as custom foot orthoses, external modifications of the footwear, exercises to strength the muscles involved or even surgery .Strength exercises are a highly recommended method in the treatment of childhood flat foot, since muscle enhancement plays very important role in the development of the lower limbs in the growth of the child. The lack of treatment can often lead to short- and long-term problems with deformities in adolescence and adulthood .

In adults, exercising the intrinsic foot musculature (short-foot exercises) has been shown to be effective in reducing the height of the internal arch or pronation in healthy subjects and sportspersons .Recently Pabón-Carrasco et al. demonstrated that foot posture could be modified with shot foot exercises, with a decrease in navicular drop measurements.

The main Intrinsic foot muscles (IFMs) are abductor hallucis (ABH), flexor digitorum brevis (FDB) and quadratus plantae (QP). Their principal function is to provide foot stability and flexibility for shock absorption ; improve dynamic alignment; stiffen the foot arches and stimulate proprioceptors on the sole of the feet . IFMs are also categorised as active subsystems in the foot core system and play an important role in static posture and dynamic activities .

Hence, strengthening of the IFM is logical as a possible intervention to help prevent pronation-related injuries. Common methods used to strengthen the IFM have previously involved toe-flexion exercises (e.g. towel crunches or marble pickups). However, Isolation of the IFM using the short-feet exercise could potentially be a more effective method to reinforce the MLA.

The muscle thicknesses and cross-sectional areas (CSAs) of the abductor hallucis (AbH), flexor hallucis brevis (FHB), flexor hallucis longus (FHL), and flexor digitorum longus (FDL) change in feet with reduced MLA ,under weight-bearing conditions. (4).

The core trunk musculature is comprised of abdominals, paraspinal, hip joint muscles and pelvic floor muscles. Co-contraction of transverses abdominis and multifidus is essential for the stability of the spine in static and dynamic balance. During inspiration, the diaphragm creates intra-abdominal pressure which creates spinal stability. This intra-abdominal pressure activates pelvic floor muscles and eccentrically abdominals to provide spinal stabilization and posture is improved .