PURPOSE: Knee injuries are widespread in athletes, and despite efforts to return to pre-injury status, deficiencies can remain. This research explores the connection between the hamstring-toquadricep strength ratio, fatigue in lower extremity muscles following multi-modal exercise, and their roles in potential knee re-injury. METHODS: Healthy individuals with a prior knee injury will be compared to those without one. Day 1: Measurements of a subject's hamstring and quadricep endurance will be measured using tri-axial accelerometry during neuromuscular electrical stimulation at 5Hz. Stimulation will elicit a vigorous contraction for 5 minutes with electrodes placed on the subject's hamstring and quadricep muscles. The tri-axial accelerometer is placed between the two electrodes on the subject's skin. The decline in contraction acceleration will allow for the calculation of the endurance index. The leg with the lower hamstring endurance index will be used for Day 2 strength testing. Near-Infrared Spectroscopy will measure muscle mitochondrial capacity to compare to the muscular endurance data. Day 2: Before the exercise protocol, strength will be measured by the peak isometric knee extension repetition for the quadriceps and the peak isometric knee flexion repetition for the hamstrings using a Biodex ergometer. Subjects will undergo a 45-minute multi-modal exercise protocol incorporating intervals of jogging, running, and walking with intermittent sprints, agility drills, and plyometric movements leading to variations in speed and direction. Throughout the protocol, heart rate and overall distance will be measured. Following the protocol, there will be a second round of Biodex strength testing. RESULTS/CONCLUSION: We hypothesize both the hamstrings and quadriceps will show losses in strength following exercise, with the hamstrings showing a greater degree of fatigue. We believe those with prior knee injury will display decrease in hamstring strength following the protocol compared to their non-injured counterparts. Combining strength and endurance data collected on Day 1, we also hypothesize the lower the muscle endurance index, the more the muscle will fatigue. This data could shift rehabilitation protocols, placing additional focus on restoring muscular endurance in the hamstrings. [ABSTRACT FROM AUTHOR]