The therapists will propose the orthotic wedges after examining the foot angles following the foot assessment from the study of Root, the forefoot angle will be determined for both the forefoot and rearfoot wedges. Previous studies recommended the posting at 60% of the measured forefoot angle, up to a maximum of 8 degrees, for extrinsic forefoot varus wedge and the posting at 50% of the measured forefoot angle, up to a maximum of 6 degrees, for extrinsic rearfoot varus wedge. After the posting, all participants will be asked to test the provided foot orthoses within their footwear. If any disturbance has been found during testing, the adjustment will be performed.

The therapists will propose the orthotic wedges after examining the foot angles following the foot assessment from the study of Monaghan et al., the forefoot will be posted at 50% of the measured forefoot angle, and the rearfoot will be posted at 20% of the measured rearfoot angle. After the posting, all participants will be asked to test the provided foot orthoses within their footwear. If any disturbance has been found during testing, the adjustment will be performed.

The 3-quarter-length CFO will be made from thermoplastic material (rigid foot orthoses) which consists of four layers i.e. two layers of 0.5-mm polyvinyl chloride (PVC), one layer of 1.5-mm thick fiber to increase strength of foot orthoses in the bottom layers as well as one layer of 1.2-mm genuine leather in the upper layer to increase comfort. It incorporates a heat-molding process to adjust individual foot shape in prone position. The materials will be set within approximately three minutes.

The orthotic wedges with a full length of 3-mm soft foam layer will be provided to each participant under the molded orthoses; the amount of wedge angle will depend on the rearfoot and forefoot angles of the participants. The present study developed 3-degree, 6-degree, and 8-degree wedges for the rearfoot and forefoot. It was made from solid rubber with a cover of thin fabric. There are three sizes for these products which include small (S), medium (M), and large (L) sizes, according to the foot length of participants.

Pain intensity during the last week will be assessed using the visual analog scale (VAS) which is the high-reliability measurement (ICC = 0.88). The highest pain level is 10 and the lowest pain level is 0. In addition, the foot function will be assessed by the 23-item foot function index (FFI). The present study will use the Thai version of FFI that has been translated forward and backward from the English version. The previous study showed high internal consistency (Cronbach alpha = 0.98) and high test-retest reliability (ICC = 0.86). It is appropriate to use among patients with PHP.

Plantar fascia thickness will be assessed by a portable digital Ultrasound (US) diagnosis imaging system, D-6600 (Mindray, China) with a 10 MHz wideband linear array probe. Intra-rater reliability from the assessment showed an ICC(3,1) of 0.97. To evaluate the plantar fascia thickness, scan depth will be set at 4 cm. The measurement protocol will follow the recommendation from the European Society of Musculoskeletal Radiology.

A gait analysis system (Zebris FDM, Isny, Germany) will be used to collect the gait parameters at a sampling frequency of 100 Hz over a 3-m force distribution platform. The participants will be asked to walk with a self-selected speed to the other end of the platform for 3 trials. Data will be averaged and used in further analysis. The gait parameters include stance time (s), double support time (%), stride time (s), step length (cm), step width (cm), stride length (cm), cadence (steps/min), and walking velocity (km/h).

A gait analysis system (Zebris FDM, Isny, Germany) will be used to collect the balance parameters at a sampling frequency of 100 Hz over a 3-m pressure distribution platform. The participants will be asked to stand with both legs on the firm and foam surface in two conditions i.e. eye closed and eye open, for 20 s in each condition. And then, they will be asked to walk at a self-selected speed to the other end of the platform. Each condition will be tested for 3 trials and averaged data will be used in further analysis. The following parameters from the platform will be acquired:

1. Sway path length of center of pressure (COP) (mm) is the total length of the path marked by COP
2. Average velocity of COP (mm/s) is the speed of changes in the COP location
3. COP area (mm2) is the size of the area marked by COP

LBP during the last week will be assessed using the Thai version of the Roland-Morris disability questionnaire. The previous study showed high internal consistency (Cronbach alpha = 0.83), which is a reliable tool to assess functional disability of LBP in Thai persons. In addition, hip pain during the last week will be assessed using the Thai version of the hip disability and osteoarthritis outcome (HOOS). The previous study showed high internal consistency for the pain subscale (Cronbach alpha = 0.89) and high test-retest reliability (ICC = 0.94). Regarding the assessment of knee pain during last week, the Thai version of the knee osteoarthritis outcome score (KOOS) will be used. The previous study showed high internal consistency (Cronbach alpha = 0.90) and moderate test-retest reliability for the pain subscale (ICC = 0.78).

A self-reported questionnaire will be divided into 4 parts, including individual information (i.e. sex, age, gender, dominant side, body mass index, job, average time during standing and walking), general health information (i.e. characteristics of heel pain, history of injury and fracture at the lower extremity, falling history, types of footwear), foot pain and function, low back pain and lower-extremity pain.