The Thoknia instep-strap is an additional strap that fits over your instep and provides a greater degree of fixation. It connects to the heel strap as an extra measure to fixate the strap securely above your heel bone. It also prevents the foot from sliding forward on the sandal when descending steep inclines. We recommend it as an additional fixation for terrain with steep inclines, large rocks, or muddy trails. People tend to use them most often with our trail-blazing sandals to effectively transfer the extra traction of the deep sole tread from your feet to the ground. For road running most people don't use an instep-strap, but if you start using them in other terrain you usually end up using them everywhere. Available in red or blue to match your sandals.