Updated: Sep 20, 2021
Continuing from our previous blog, Injury Prevention in Young Elite Footballers | Part 1 - Growth Spurt, this blog explores the importance of muscle strength in young elite footballers, especially the hamstring and quads, for prevention of injury.
What are the muscles?
The hamstring and quadriceps (quads) muscles are in fact different muscles combined and named under a collective term. The quadriceps muscle consists of 4 muscles and the hamstring muscles consists of 3 muscles. The quadriceps are located at the front of the thigh and have the primary function of straightening the knee. The hamstring muscles on the other hand are the exact opposite of the quadriceps, they are located at the back of the thigh and primarily function to bend the knee.
The hamstring and quadriceps muscles work in tandem to create stability for the knee and form an important part of an athlete’s functional capacity and lower limb movement and performance. If one or both muscle groups are affected, these potentially may cause knee injuries for the athlete. Particularly, a deficit in hamstring muscle strength in comparison to the quadriceps muscle has found to be an early warning sign of the potential for a lower extremity injury. (For more about hamstring conditions, you can read our blogs on hamstring injury and prevention and hamstring tendinopathy).
What is H/Q ratio and why is it important?
H/Q ratio is an abbreviation of Hamstring to Quadriceps ratio, and this is defined as the ratio of strength between the hamstrings and quad muscles. Before we begin to talk more about the H/Q ratio, we need to explain what concentric and eccentric muscle contractions are. An eccentric muscle contraction involves the process of the muscle lengthening under load whilst concentric is the opposite, muscle length shortening under load.
A good example to understand how this contraction works is to relate it to kicking a soccer ball. When a player kicks a soccer ball, during the moment that the foot hits the soccer ball the hamstring muscles is forced to contract in a lengthened position (straight leg) with a force (the ball), this is known as an eccentric hamstring contraction. At the same time, the quadriceps muscles are contracting whilst shortening (remember that quadriceps primary function is to straighten the knee) with a force and this is known as a concentric quadriceps contraction. Therefore, due to the opposing relationship of the quadriceps and hamstring muscles, that ratio of strength between them is important as they affect the function of the knee joint as well as the risk of injury.
How to measure H/Q ratio?
An isokinetic dynamometer is usually used to measure H/Q ratio. This equipment can be used to calculate various things which include, forces applied at certain speeds and at different angles of the knee joint. It provides the most accurate result in determining H/Q ratio; however, gaining access to the equipment might not be easy. Therefore, an alternative option would be to use a leg extension and leg curl machine to measure 1RM for quadriceps and hamstrings. 1RM is maximum weight you can perform at 1 repetition. Although, this will not give as detailed data as the isokinetic dynamometer, the results can still be used to identify any strength deficits. Talk to your trusted physio about making an assessment of your H/Q ratio!
What is the normative value?
The general consensus in research suggests that a ratio of 0.5-0.8 is accepted in a normal healthy population, although a ratio greater than 0.6 is more preferable. What this means is that if the quadriceps can do a maximum lift of 60kg through a full range of movement (straighten the knee completely) than the hamstrings should be able to lift 36kg also through a full range of movement (for a 0.6 ratio). It is also understood that if the velocity of the movement increases, the H/Q ratio also increases.
As the ratio nears 1 (hamstring strength equals quad strength) then the hamstrings have an increased capacity functionally to provide more support and stability for the knee. This knee stability may also be able to help reduce the risk of injury, especially an ACL injury, in the sporting population. The ratio of 1 is also much more preferred in the football population.
What can happen if my H/Q ratio is small?
Footballers generally are required to perform very explosive and powerful movements during their matches. During a jump, the quadriceps muscles contract and shorten to extend the knee. The hamstrings then contract by lengthening to counteract the quadriceps force and slow down the power required in a jump to extend the knee. The ACL and hamstrings also have a role in stabilising the knee when performing pivoting movements such as landing from a jump and a sudden change in direction.
Soccer injury usually occurs in two ways, contact or non-contact injury. Research has shown that more than 50% of soccer injuries occur from non-contact injury. Most of the injuries occur in athletes with a H/Q ratio of less than 0.6 and often occurred in the hamstring muscle group where the muscle itself is stretched beyond its normal capacity to stretch.
Another common injury soccer players experience can be partially faulted to low H/Q ratio are ACL injuries. As mentioned before, the ACL and hamstring work in tandem to stabilise the knee by preventing it from shifting forwards as the knee straightens when jumping, kicking, or pivoting. If the hamstring muscles are lacking in strength, this forces more stress on the ACL to prevent the shifting motion of the knee, which over time may cause an injury to the ACL. Therefore, for the athlete population, hamstring strengthening is important in both ACL rehab and prevention of injury.
Prevention of injury vs. rehab after injury
Following an injury to the knee, it is important to do exercises that involve using the hamstring and quadriceps muscles simultaneously. This is especially so in the early rehab phases in order to promote better muscle control during the later stages of rehab in preparation to return to sport.
A good exercise to do after injury is to squeeze the muscles feeling the contraction between the hamstring and quads (holding for 5-10s).
Some simple exercises to do in mid- to late stages of rehab following injury are:
single leg Romanian deadlift (shown below)
sideways and forward hopping
single leg squats (shown below)
When doing the above exercises, allow the knee to bend to approximately 60 degrees, this was found to be the most optimal position to allow equal amounts of strength used between the hamstring and quads.
Moving onto exercises in order to aid in prevention of injury, in most cases it would be good to focus on strengthening of the hamstring muscles. Although strengthening of the quads are important as well, most athletes present with weaker hamstrings and optimal hamstring to quad ratio is when they are equal. Exercises that are beneficial include nordic curls and hamstring curls (see below).
These exercises target the hamstring more specifically and should be done slowly at first before being progressed to being done at various speed to improve H/Q ratio.
Eventually you would also want to incorporate more functional exercises like squat jumps
The exercises above are all just some examples of possible exercises to do to prevent injury. However, it is important to remember that not everyone is suited for a type of exercise and talking to your coach or a physiotherapist would be a good way to go whether you are aiming for some conditioning to prevent injury prior to a season start or are in your rehab phase, a tailored exercise program that is suitable for you would optimally place you in a better position on your sporting journey.
Blog and videos by UQ Physiotherapy student undertaking clinical placement, supervised by principal physiotherapist, Winnie Lu.
Souths United Football Club Physiotherapist
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