3. Shoes used within the trials.

Study ID	Control shoe	Comparator shoes
Asymptomatic flat feet
Wenger 1989	usual shoes	corrective shoes, usual shoes + Helfet heel cups, usual shoes + UCBL CFO
Gould 1989	straight last shoes	‐ straight last shoes plus longitudinal arch cookies ‐ orthopaedic shoes with long counters, solid shanks, Thomas heels, and 0.312 cm inside heel wedges ‐ orthopaedic shoes with long counters, solid shanks, Thomas heels, and 0.312 cm inside heel wedges, with supplemental thin longitudinal arch support
Whitford 2007	usual shoes	none (PFO, CFO)
Asgaonkar 2012	usual shoes	none (valgus insole)
Kanatli 2016	usual shoes	corrective shoes, i.e. custom‐made orthopaedic shoes that had 0.5 to 0.9cm longitudinal arch support and 3 to 4 mm heel wedges
Ahn 2017	usual shoes	none (2 CFO types)
Khamooshi 2017	usual shoes	none (foot, core exercises)
Jafarnezhadgero 2018	New Balance 759 (trainers)	New Balance 759 (trainers)
Solanki 2020	not stated	not stated
Abd‐Elmonem 2021	not stated	not stated
Symptomatic flat feet
Hsieh 2018	usual shoes (encouraged to wear at least 5 hours daily)	usual shoes (encouraged to wear at least 5 hours daily)
JIA
Powell 2005	new supportive athletic shoes with a medial longitudinal arch support and shock absorbing soles (cross‐training type shoes)	all children, regardless of intervention, received new athletic shoes at beginning of the study
Coda 2014	usual shoes	none (PFO, CPFO)
DCD
Morrison 2013	usual shoes	none (CFO)
Immediate effects studies
Bok 2016	usual shoes	none (3 inverted CFOs)
Aboutorabi 2013	no shoes (bare feet)	medical shoes, regular shoes (with FO)

CFO:customised foot orthoses, CPFO: customised prefabricated foot orthoses; DCD: developmental co‐ordination disorder; FO: foot orthoses; JIA: juvenile idiopathic arthritis; PFO: prefabricated foot orthoses; UCBL: University of California Biomechanics Laboratory heel cup orthosis