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

Abstract

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).

Keywords: Muscle contraction; isokinetic; muscle balance; thigh.

Figure 1.

Moment of force of the concentric quadriceps (Qcon), eccentric hamstrings (Hecc) and concentric hamstrings (Hcon) as a function of knee joint angle. Moments are representative of 60°/s^-1 in a seated position. 0° represents full knee extension. Adapted from Coombs et al. (2002).

Figure 2.

Hecc/Qcon and Hcon/Qcon ratios as a function of knee joint angle at 60°/s^-1 (unpublished data). 0° represents full knee extension. Arrow represents point of equality between Hecc and Qcon. Data was collected from a continuous knee extension-flexion protocol, with Qcon-Hcon separate to Hecc-Qecc.