Author: Leo Bell (Physical Performance Coach)
Hamstring strains are one of the most common sports injuries, with lots of time and money lost in the wake of a hamstring strain incident. The AFL have seen over 65 hamstring strain injuries (as of Round 11) so far in 2018, and you could only expect this tally to increase as the season progresses.
The pinch of hamstring strains has also been felt at local level sport, but recreational participants are at a greater disadvantage without the resources and treatment that a professional athlete may receive. Therefore, the reason for this blog is to discuss hamstring strain injury mechanisms, risks, and potential preventative strategies that we can employ to reduce their occurrence.
Whats the cause of a Hamstring strain?
A hamstring strain is caused as a result of a rapid eccentric (lengthening) contraction that exceeds the strain capacity of the muscle, resulting in damage to the muscle and/or neurovascular tissues (think of an elastic band stretching too far that it causes a tear in the band). This typically occurs during high speed running at the terminal swing phase, where the hamstrings are stretched over the hip and knee joints. Additionally, it is not unusual to see a hamstring strain occur during kicking or quick changes of direction. Whilst these movements are the mechanism of injury, they’re unavoidable. Additionally, risk factors predispose certain people to an increased chance of incurring a hamstring strain. So let us look at the risks…
There are two types of risk factors that we should concern ourselves with when discussing hamstring strain injuries – non-modifiable, and modifiable risk factors.
Non-modifiable risk factors – are those that are inherently beyond our control. The athletes age, race, muscle fibre type and injury history are examples of non-modifiable risks that increase the chances of experiencing a hamstring strain injury. Athletes aged older than 25 years are seemingly more at risk of injury. There are several theories as to why the age-related difference in hamstring injury risk exists, however none have been substantiated by clinical research. It is suggested that a loss of muscle flexibility and mobility of the lumbo-pelvic-hip complex is problematic for the length-tension relationship and ultimately exposes the hamstrings to greater strain. Moreover, research has indicated that athletes of African or Aboriginal descent also experience hamstring strains more often than Caucasians. The reason for this can be simply explained by their predominant muscle fibre type, as type 2 muscle fibres are more prone to strain than type 1 muscle fibres, due to their greater rate of force production and fatigue-ability. Whilst we know there is nothing we can do to change these risk factors, greater emphasis can be placed on negating the modifiable-risk factors and implementing preventative strategies.
Modifiable risk factors – are those that we can effectively change. Modifiable risk factors include muscle temperature, shortened optimal muscle length, reduced muscle strength and flexibility, and training-load factors such as speed exposures and fatigue. Due to early observations of hamstring strains occurring early in training and competition, it was declared that muscles were not in a prepared state for physical activity. Hence, the introduction of a well-structured warm-up was used to increase muscle temperature and improve the muscles pliability under stress. In addition to cold muscles, short muscle-fascicle length demonstrably increases the risk of future hamstring-strain injuries. If you can imagine, your muscle fascicles are made of up tiny cross-bridges that clasp onto each other and shorten during contraction. If these cross-bridges are clasped too tightly and the fascicle length is chronically shortened, there is a reduced capacity to stretch and therefore the yield point of the strain will be much sooner (resulting in a tear). Furthermore, shorter muscle-fascicles result in a sub-optimal length-tension relationship, effectively reducing the strength capabilities of the muscle and its capacity to withstand forces during running or kicking. Simply put, short and weak hamstrings significantly increase the risk of hamstring strain injury.
With the development of GPS technology and research monitoring the physical demands of training and competition, we now know that a well-balanced approach to training is important to mitigate injury risk. Athletes are at a greater danger of hamstring strain injury due to the significant forces endured during high intensity efforts such as accelerations, decelerations and sprinting. The greater the forces produced during these activities, the greater the energy demands are on the hamstrings. The fatigue and muscle-damage induced by these high intensity efforts add to the danger of a hamstring strain. Because the muscle is fatigued, it loses the capacity to contract in a coordinated and timely response to ground reaction forces and is in a weakened state. A sharp increase in weekly training load compared to the preceding four weeks dramatically increases the risk of hamstring strain injury. Additionally, athletes who experience a spike in high intensity running loads greater than their average output of the previous 2 years are also at a heightened risk.
As you can see there a number of contributing factors that impact on why the injury occurred. An important thing to remember is that when you are pushing your body to the absolute limits and pushing the boundaries there is going to be an increased risk to injury.
We just want to make sure we do all we can to build strong robust athletes that are resilient to injury.
Stay tuned, with our following hamstring series posts going into detail on how to bullet proof your hamstrings and then providing an insight to hamstring injury rehabilitation.