Force estimations and theoretical calculations for the biarticular muscles during squatting

Abstract

Although the role of biarticular muscles during squatting and its variations have received considerable attention, the function of these muscles during squatting is not well understood. Closed kinetic chain exercises like squats are commonly preferred for knee rehabilitation and strength training for athletes. Squat exercises require both the hip and knee extensors, such as the gluteus maximus, hamstrings, and quadriceps femoris. For the hip extension strategy, the gluteus maximus and hamstrings have an important role, while the hamstrings and quadriceps co-contract at the knee. The same co-contraction occurs at the hip, between the rectus femoris and the hip extensors. These co-contractions do not seem to be effective, in terms of minimum energy expenditure, minimum muscle fatigue, and minimum sense of effort. However, muscular co-contraction is often seen in human movement, and the co-contractions were measured using electromyography (EMG). Although muscle co-contraction is important to modulate joint stability, the co-contraction cannot be predicted in simulations using a musculoskeletal model where the sum of the muscle activations or metabolic energies is minimized. Thus, the activations of those biarticular muscles are clearly underestimated. In this study, EMG were measured during squatting, and interpretations to understand biarticular muscles activations are discussed.