This study will randomize healthy adults who regularly perform resistance training exercises for the lower extremities (2x a week) to one of three groups: a blood flow restriction (BFR) exercise group that trains 2x a week, a BFR exercise group that trains 5x a week, and a control group that does not perform any additional BFR exercise. Those randomized to the BFR groups will perform the unilateral 90-0 knee extension exercise followed by the bilateral squat. Subjects will have the BFR applied to their dominant lower extremity and will perform 4 sets (30/15/15/15 reps) per exercise. Training will initial start at 30% of 1RM with training intensity increased by 5% every 2 weeks. The training program will last 8 weeks.

Pre- and posttests include ultrasound imaging of the dominant leg rectus femoris and strength testing via hand held dynamometry.

Inclusion Criteria: healthy adults 18 years of age who currently perform weight-lifting (i.e., resistance training) exercise 2x a week.

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Exclusion Criteria: current musculoskeletal injury; surgery to the low back or lower extremities during the prior year; one or more contraindications to blood flow restriction training.

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The outcomes assessors are blinded to group allocation.