Can you please explain about the hamstrings:quadriceps ratio? what is is for? what are the normal values?

Quadriceps and hamstrings strength can be reliably assessed using isokinetic dynamometry. Isokinetic strength testing can be performed to test concentric or eccentric muscle strength at fixed angular velocities. The recorded strength is a measure of the net effect of the force developed by the quadriceps and hamstrings muscles to move the lower leg into extension and flexion.

For optimal and reproducible results when testing knee strength, the knee joint is aligned with the axis of the rotating arm and the pad for the rotating arm is secured just above the malleolus of the ankle joint. Straps around the chest, waist and thigh are tightened to limit bodily motion other than knee flexion or extension. Concentric exertions are often preferred over eccentric exertions for feasibility and safety reasons. However, maximal eccentric exertions may be measured as well (see Fig 1).

During the test, the subject is instructed to kick and pull back as hard and as fast as possible against the resistance provided by the machine (which has been set to move at a pre-defined speed).

One of the most common outcome measures of interest when assessing knee strength is the hamstrings : quadriceps ratio (H/Q ratio). H/Q ratio is calculated as the peak torque of the hamstrings divided by the peak torque of the quadriceps within the same limb. Depending on the speed of the test, the hamstring/quadriceps ratio is normally between 50% (i.e. 1:2) and 60% (i.e. 1.8:3). However, as the speed of isokinetic testing increases, the ratio approaches 1 : 1 or 100%.

The H/Q ratio provides important information about the relative strength of different muscle groups and helps identify muscle imbalances where present. It is useful for strength comparisons between subjects without the need for normalization for individula body weights. Finally, a reduced H/Q ratio (which may be indicative of quadriceps dominance ) may put athletes at a higher risk for lower extremity injury.

Ref 1. Keading CC, Borchers JR. Hamstrings and Quadriceps Injuries in Athletes : A Clinical Guide. 2014. Springer Publishers. Chapter 2. Quadriceps and Hamstrings Strength in Athletes. Pgs 15 – 17.

Ref 2. Magee DJ. Orthopedic Physical Assessment. 2014. 6th Edition. Elsevier Saunders Publishers. Chapter 12. knee. Isokinetic Test Parameters Commonly Used For the Knee. Pg 786.