A closed loop fastening system for running and other shoes. The fastening system includes a harness, a strap, guides and a tension lock buckle. The harness includes strap portions which can tightly retain a user's foot inside the shoe. The guides are attached to the harness for guiding the strap. One end of the strap is attached to the harness and the other end of the strap is attached to the buckle. An effective length of the strap can be defined such that a shorter effective length yields a tighter harness and a fighter fit, and a longer effective length yields a looser harness and a looser fit. The tension lock buckle used in the closed loop fastening system is adaptable for use with numerous other products having a strap. The tension lock buckle includes a body, a pivotal locking member and a sliding bar. The sliding bar is mounted within the body for longitudinal movement therein. The pivotal locking member is pivotally attached to the body for relative pivotal motion. The pivotal locking member is movable between a locked position and an unlocked position. When the pivotal locking member is in the unlocked position, the tension lock buckle is movable along the strap to adjust the tension thereof. When the pivotal locking member is in the locked position, the strap is clamped against three surfaces of the sliding bar by three complementary surfaces, two located on the pivotal locking member and one located on the body.