Developments in the use of the hamstring/quadriceps ratio for the assessment of muscle balance

Isokinetic moment ratios of the hamstrings (H) and quadriceps (Q) muscle groups, and their implication in muscle imbalance, have been investigated for more than three decades. The conventional concentric H/Q ratio with its normative value of 0.6 has been at the forefront of the discussion. This does not account for the joint angle at which moment occurs and the type of muscle action involved. Advances towards more functional analyses have occurred such that previous protocols are being re-examined raising questions about their ability to demonstrate a relationship between thigh muscle imbalance and increased incidence or risk of knee injury. This article addresses the function of the hamstring-quadriceps ratio in the interpretation of this relationship using the ratios Hecc/Qcon (ratio of eccentric hamstring strength to concentric quadriceps strength, representative of isolated knee extension) and Hcon/Qecc (ratio of concentric hamstring strength to eccentric quadriceps strength, representative of isolated knee flexion).