Advanced footwear technology (AFT) shoes combine increased sole thickness with compliant midsole foams and stiffening elements, but it remains unclear how much of their biomechanical effect is caused specifically by sole thickness. Most previous studies have focused on level running, while uphill running has received little attention despite its relevance for trail and mountain running. Because uphill running has distinct mechanical demands, such as greater positive work, higher propulsive requirements, and altered joint mechanics, shoe effects may differ from level or downhill running. Therefore, this study investigates whether different shoe sole thicknesses influence running style and stability during uphill running.