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Use of the term overuse injury should be avoided until there is definite proof of the cause of the injury
Injuries are often categorised as being due to trauma or overuse. When no moment of trauma is recalled, then an assumption is made that an injury is the result of overuse. In this article, I will argue that there is insufficient evidence to support this extensive use of the term “overuse” and that there are problems associated with using it. Thus, we should avoid the term, which implies the cause of the injury, until we have proof of the cause.
WHAT IS MEANT BY OVERUSE
Overuse injury is now categorised in medical subject headings as “cumulative trauma disorder (CTD)”. This is a subcategory of sprains and strains. CTD is defined as a “Harmful and painful condition caused by overuse or overexertion of some part of the musculoskeletal system, often resulting from work-related physical activities. It is characterized by inflammation, pain, or dysfunction of the involved joints, bones, ligaments, and nerves.” The term includes overuse injury, overuse syndrome, repetition strain injury, repetitive strain injury, and repetitive motion disorders. As CTD is defined as being caused by overuse, this definition fails to clarify the meaning of overuse injury. Overuse probably implies there is an amount of use that is excessive, and if use reaches or exceeds that amount then injuries arise.
Consider now this term as used in sports medicine. Traumas, such as a fractured tibia caused by a tackle in soccer, are likely to be most common among players who play or train most. Yet, overuse is not said to be the cause of this injury. Injuries arising from obvious trauma are excluded from the category of overuse injuries. Such a trauma may be witnessed or may be felt as an acute moment of injury. An example of the latter is the sudden pain from a hamstring muscle strain when attempting to sprint. The cause of such an injury is sometimes called “macrotrauma”. There is speculation that there may be other damage to the body's tissues that does not manifest as immediate pain, loss of function, deformity, swelling, bruising, or bleeding. The cause of such damage is sometimes referred to as “microtrauma”. The accumulation of damage from microtrauma may eventually result in overt damage—that is, when someone feels pain, loses normal function, or notices swelling, deformity, etc. If it is the repeated physical activity of an athlete that has predisposed him or her to sufficient microtrauma to bring about such an injury, then it is reasonable to call it an overuse injury.
LOOKING FOR THE EVIDENCE
A Medline search (1966–2000) for overuse injury brought up 88 references. None of this research was designed to prove that injuries were due to overuse.
WHY IS THE TERM ACCEPTED READILY?
It is easy to accept that overuse causes injuries. We are all likely to be familiar with the negative sensations associated with a bout of unaccustomed exercises that leaves our muscles and tendons sore and tight. Those sensations are somewhat similar to some of those experienced after injuries caused by (macro) trauma. Fortunately the negative sensations wear off after a day or two. This phenomenon is called delayed onset muscle soreness and is not generally thought of as an injury. Now, when somebody starts to suffer similar sensations when there has been no obvious macrotrauma and no recent unaccustomed exercise, yet they are involved in some regular physical activity, it is understandable that they and their doctors blame their negative sensations on that physical activity.
In the clinic, sports physicians find that patients who have conditions that have been categorised as overuse injuries tend to be training or competing a lot. Thus, their experience seems to confirm that overuse causes these problems. However, there are factors that distort their experience. Sports physicians see a large proportion of physically active people in their clinics. They may therefore assume that the conditions seen are due to the activity. Non-active people may also suffer the same conditions, but would not present to sports physicians. Non-active people may be less inconvenienced by such conditions as their less active lifestyle puts fewer demands on their bodies. Hence, they may not present to doctors at all.
DOES IT MATTER?
The language used—overuse injury—may lead to responses that may not have a firm evidence base. One such response would be to tell any athlete with an overuse injury to rest. Rest can be absolute or may be more acceptable if activity modification is recommended. Telling the athlete to rest is an intervention. To be justified, we should know that it prevents further damage, works (brings about recovery), and that it is safe (no adverse affects). Another response is to impose limits on the physical activities of athletes to prevent overuse injuries—for example, fast bowlers in cricket. There should be evidence for effectiveness before a restriction becomes a regulation of the sport. A better approach would be to offer advice or guidelines where evidence is lacking.
IMPLICATION FOR STUDY DESIGN
If we are to accept that the term overuse is valid for certain injuries, then we need proof that these injuries arise when a certain level of use is exceeded. To provide evidence that overuse causes a particular injury, a study design will need to include several groups exercising at different levels of activity. These groups need to be matched, so we will need to know the contribution of all confounding factors. Ideally, the groups and investigators need to be blinded to the activity level, but this may be impossible. Compliance with the exercise regimen would need to be confirmed. There may be ethical problems in asking a group to be inactive when there is evidence to suggest this is harmful to health.
Observational studies may be required, bearing in mind the difficulties outlined for prospective trials. Yet, evidence for causality is less convincing from such cohorts. The design would have to allow for the change in activity level that a serious injury may bring, otherwise the injury rate in the less active groups would be distorted. In this respect, a retrospective study that measured activity level leading up to injury may provide more useful data, but would such a study have reliable activity data?
INTERPRETING RESEARCH DATA
Let us consider a type of injury that is caused by macrotrauma and obviously not overuse. Road runners may be hit by cars. Let us make the reasonable assumption that the risk of injury from such a road traffic accident when road running is proportional to the distance run in training. Figure 1 presents these hypothetical data.
Risk of injury from a road traffic accident (RTA) when running.
This would be the appearance of the chart for any type of injury that was related to use and not overuse. The example given above of tibial fractures in football may look similar.
If we are to accept the notion of an injury being caused by overuse, we must see that the relation of injury to activity is not one of proportionality. At some point on the curve that relates injury risk to activity level, the risk must exceed the risk predicted if it continued to rise proportionally with activity.
If we are to accept the notion of an injury being caused by overuse, we must see that the relation of injury to activity is not one of proportionality.
Figure 2 provides further hypothetical data. In this, the risk of plantar fasciitis rises proportionally to activity, and this is compatible with a traumatic causation. Achilles tendinitis, however, only occurs above a threshold activity level and so is compatible with the notion of overuse as cause. The examples are clearly simplified relative to data that may realistically be collected. The influence of contributory factors would distort the relation in real charts.
Risk of injury in runners.
HOW MIGHT SPORTS PHYSICIANS MISINTERPRET THEIR EXPERIENCE IN CLINIC?
If a type of injury was due to overt trauma and that trauma was equally likely for each unit of activity, the relation between number of injuries and level of activity would mirror the example of road traffic accidents in runners given above. If all runners presented to a sports physician, he/she would see four runners with this type of injury from the highest mileage group to every one from the lowest mileage group. If the moment of injury is not obvious, yet the pattern of occurrence the same, then the sports physician will blame the one thing that appears to have brought most athletes to the consulting room with this problem: the amount of running. There appears to be no other explanation, and so the injury is blamed on running too much and categorised as overuse. This experience could be repeated time and time again for various types of problems and each experience compounds the sports physician's opinion that overuse causes many injuries that he/she is called upon to treat. Only carefully conducted and interpreted research could show whether he/she is right.
ALTERNATIVE THEORY
If overuse is not the cause of some or all of the injuries thus categorised, what is? We need to consider the possibility that there may be an acute injury that was not apparent by obvious trauma with pain and or loss of function occurring at the time. It is reasonable to speculate that the pain may not start at the moment that the pathological process starts. Such an injury, like all sports injuries, would relate to use not overuse. There may be another explanation for these injuries.
CONCLUSION
This all highlights the challenge for those researching the cause of sports injuries to prove whether the concept of overuse as a causal factor is correct. I propose that, until this proof is available, we stop using the term overuse injuries. We will then be less inclined to fall into the trap of assuming that rest will be therapeutic and that restriction of activity is a justified preventive measure.
My apologies to Slocum and James1 who coined the phrase overuse injury.
Use of the term overuse injury should be avoided until there is definite proof of the cause of the injury