Patellofemoral joint loading in females during back squats of varying depth, weight load, and stance width

Abstract

As a repetitive and loaded exercise, the back squat can lead to tissue injury. One concern is patellofemoral pain syndrome, a common knee diagnoses over twice as prevalent in females as in males. Patellofemoral joint stress is cited as a cause of the syndrome. To manage the syndrome, quadriceps strength is important. Although the back squat is a good exercise for quadricep strength, modifications to squat technique may be necessary to decrease patellofemoral joint stress. Two studies on female recreational athletes are addressed here: 1) how patellofemoral joint loading changes with squat depth and load and 2) how it changes with squat load and stance width. Depth-specific 1-repetition maximums were measured, and weight loads were based on percentages of the maximum. Peak knee extensor moments, patellofemoral joint reaction forces, and patellofemoral joint stresses were calculated using inverse dynamics and previously reported equations. First, participants squatted to 90°, ~°110, and ~135° of knee flexion with loads of 0%, 50%, and 85% of 1RM. A depth-by-load interaction was found such that within each depth, moments increased as load increased, while decreasing with increased depth. Patellofemoral joint reaction force had main effects of load and depth such that as load increased or depth decreased, reaction force increased. Another depth-by-load interaction was found such that within each depth, as load increased the stress increased, while increasing with increased depth. From these results, squats to full depth or loaded squats to less than 90° of knee flexion are recommended to minimize patellofemoral joint stress. Second, when squatting to ~110° with loads of 35% and 85% and stance widths of 90%, 100%, 110%, and 120% of natural stance, there was a main effect of load for knee extensor moment, patellofemoral joint reaction force, and patellofemoral joint stress. Although altering stance width does not appear to change joint loading, some research suggests that there may be a relationship between foot turnout and joint loading. Continuing relatively simple studies, like these, reveal trends which more individualized approaches can later use, accounting for individuals' anatomy to fully understand patellofemoral joint loading during the back squat.