Does Even Mild Knee Swelling Switch Off Your Quads While Jogging?

In a landmark 2005 study, Torry et al. injected 20 cc of saline into the knees of 13 healthy adults (with no prior knee problems) to simulate mild knee swelling. Participants then jogged while researchers measured quadriceps EMG activity and knee movement.

Results showed clear quadriceps inhibition: vastus medialis EMG dropped 8.5% and vastus lateralis dropped 5%. Surprisingly, there was no change in knee joint motion or running form. The study proves that even mild knee effusion can silently weaken key thigh muscles during jogging.