Not if the 5 safety rules are followed.  If blood in deep veins is brought to a standstill for a prolonged period of time, the blood can begin to form clots.  If this happens and the clots move into the lungs, they will cause what is called a pulmonary embolis.  If big enough, pulmonary emboli can be fatal.  Fortunately, the B Strong Training SystemTM Bands are designed so that when the safety rules are followed, they cannot make the blood stand still long enough to clot, and thus, B STRONG Training does not increase the risk of blood clots or pulmonary emboli.  Millions of BFR sessions have been performed world wide over the last 50 years and where it has been studied, the individuals who practice BFR have less blood clots detected than a matched group of individuals who don’t do BFR training.
Some individuals are genetically predisposed to clotting.  By the time these individuals are adults, they know whether they or others in their families have this condition.  Often they are on anticoagulants.  B Strong Training is safe even for these individuals.
Sometimes, after particular types of surgery (e.g. various orthopedic procedures on the lower extremities), one may have formed clots in the veins while anesthetized.  These clots may go unrecognized and cause a pulmonary embolus in the days following the surgery.  Thus, we recommend waiting a week after surgery to resume or start a B STRONG training program.
Some individuals are genetically predisposed to clotting. By the time these individuals are adults, they know whether they or others in their families have this condition. Often they are on anticoagulants. B Strong Training is safe even for these individuals.
Sometimes, after particular types of surgery (e.g. various orthopedic procedures on the lower extremities), one may have formed clots in the veins while anesthetized. These clots may go unrecognized and cause a pulmonary embolus in the days following the surgery. Thus, we recommend waiting a week after surgery to resume or start a B Strong training program.