The sandals straps have velcro and loops to adjust them, but in the place most would need that extra room (on the middle strap at the widest part of your foot), they have put the smallest adjustable strap. These are adjustable! The main problem is that they didn?t come with different size earbuds and because they are too small for my ear canal they keep falling out when running unless I wear a headband over them. The comfort is perfection, but the sizing is much larger than usual. Oh and yes these are a upgrade to the original zs10 and well worth the price difference! Well I finally pulled the plug and bought these. I was contacted by their customer service and the issues was resolved quickly. Be sure to follow directions and it will work amazingly well. It is fun for fans, but is very limited to what it can do. Ive suffered with plantar fasciitis & heel spurs on both feet for many years, despite orthotic insoles, tendon stretches, & compression foot sleeves.