Despite there being little general consensus on how to perform stretching effectively, the bulk of arguments are in fact not to resolve the matter but rather to look at a problem further down the line. The most hotly contested and sexiest debate in the world of flexibility training is not "how to do it" but the impact of stretching on injury prevention and injury manifestation. This is interesting because there is an insufficient amount of advice on how and when to stretch, but plenty of people have their opinions on why stretching will cause an injury. Hmm... surely if we don’t know how and when to stretch, we can’t be so confident about the effects? Indeed, we seem more confident about the effects of stretching than we are of how to perform stretches in the first place. With the growing interest in the need for physical activity, it is certainly appropriate now to consider the need to prevent injuries, for an individual's own best interests (health and economic). What we need to do is marry our knowledge of correct flexibility training with current conceptions regarding injury prevention.
And what about the scientific papers that have been produced on the subject of stretching and injury prevention? Well, as a scientist, I must suggest that the grand majority are inappropriate. If I take 100 subjects and get them all to perform a 20-kilometre run every other day for two months, with half stretching before and half not, will I have performed a useful test? What about the results? If there was no difference, does that mean that stretching is useless? Well, there are some questions to ask first. What about the fitness of the participants? Some might find the load too much and develop overtraining injuries because, even if they were stretching, it was not enough because muscle imbalances caused some areas to be overworked, which consequently led to an injury. Secondly, what if there were, for example, 20 participants in each group that were equally fit and healthy, yet they developed very different injuries? The injuries may well have been the result of microtrauma that developed over several years and happened to manifest itself during the trials. Unless each participant was tested for microtraumas and previous injuries first, and then given a specific flexibility program to stretch that area, that individual was probably predisposed to injury before the trials began.
To turn this into a useful test, the scientist would need to have 100 people with exactly the same predisposition to exactly the same injury and then have half of the group perform exactly the same specific flexibility routine prior to each run. Finally, you would need to be certain that each participant ran exactly the same route on exactly the same surface. If the tests were performed outside, then one participant might run on a more uneven surface than someone else, again predisposing them to injury. And this is before we even consider how the flexibility and warm-up sessions should be undertaken. In fact, it is almost impossible to perform an accurate test with a large group. Flexibility needs to be thought of as specific in the full sense of the word. Flexibility is specific to a given joint, side, speed and within sports as well as the frequency and uniqueness of joint movements and their immediate influence on the other joints of the body. This being the case, suggesting a relationship between flexibility training and injury frequency is a particularly challenging task.
So until those perfect - or near perfect - tests emerge, we are left with only a theoretical debate based on what studies do tell us about how to perform flexibility sessions. The purpose of this article, the final part in the series, is to examine what causes muscular, or musculotendinous injury, and what the exercise specialist can do to minimize the client’s risk. Voluntary muscle is the largest human organ system. The musculotendinous contractile unit maintains the body’s posture and, in conjunction with the nervous system, facilitates movement. Muscle strain injury is recognized as one of the most frequent injuries in sports. Musculoskeletal injuries can occur following single or recurrent bouts of biomechanical overloading.
To design an injury-prevention program, it is necessary to first look at the underlying causes of musculoskeletal disorders (MSD). Injured muscles are often abnormally shortened with increased tone and tension due to varied states of over-contraction. It is important to consider that, although we can assess tightness in an injured muscle, we should also be aware that muscle tightness could be a warning in an apparently healthy muscle that a future injury may occur. The exercise specialist should ensure that s/he carries out flexibility tests regularly with clients to assess for any developing muscle tightness. Even though the cause of the muscle tightness might not be determined, an apparently healthy muscle that has become shortened could be indicative of microtrauma at the musculotendinous junction, and future recurring injuries may develop at this site. It is therefore appropriate for the exercise specialist to take steps to stretch this area and then strengthen it to help prevent future injuries from occurring.
Flexibility assessments should include screening for muscular imbalances as well as for individual muscle tightness. A muscle imbalance may be the cause of an overuse or chronic injury. Where one muscle is particularly tight and painful, the muscle on the opposite side may be stretched out and weakened. Muscle imbalances may be the result of a previous injury in the tightened muscle, an imbalance across a number of muscles due to preference in lifting and carrying activities or a similar imbalance caused by sustained poor posture. To be proactive, in terms of really assessing all likely possibilities for future injury, it is necessary to test the muscles as they act in movement through a movement analysis such as gait and/or a squat, then independently check force couples (the muscles which work in pairs during movements) and assess not just the agonists and antagonists but the stabilizing muscles as well. Once an assessment of flexibility has been carried out, the next stage is to decide whether any limitations in joint range of motion (ROM) are the result of the muscle or the joint capsule. Any limitations caused by the joint capsule need to be investigated to ensure an appropriate treatment program. Any limitations that are muscular can be treated with an appropriate flexibility program.
Some athletes may have too great a range of motion at a particular joint, possibly coupled with an increase in joint laxity. If this is the case, the specific muscles that have allowed this movement should not be stretched. Instead, a specific strengthening program should be prescribed in order to increase the stability of the joint and to prevent future injuries in that area. In most cases, a little extra mobility is not likely to lead to injury, but for contact sports in particular, it would be worthwhile promoting a strengthening program and avoiding flexibility work on the specific area.
The previous point actually suggests that injury prevention is not solely down to flexibility training. Indeed, injury prevention is about the balance of flexibility, mobility, strength and cardiovascular training. This range of training should allow the musculotendinous unit to work effectively throughout it’s range of motion, under various levels of stress and for various numbers of repetitions.
Cardiovascular warm-up periods, followed by counteractive stretching exercises, are vital components to any effective MSD management and prevention program. If a muscle’s contractile ability has been impaired through previous injury, microtrauma or tightness, then that muscle is susceptible to (further) injury, as it’s ability to absorb energy has also been impaired. This initial impairment may then lead to recurring and more severe injuries to the same area. Effective stretching programs can decrease the resistance on structures across the length of a muscle-tendon unit, including at the musculotendinous junction itself, which is where many muscle strain injuries are thought to occur.
What this tells us is that, in individuals with areas of muscle tightness or with previous injuries, there is an increased susceptibility to muscular (or musculotendinous) injury. Stretching can then be used to release some of the tension within the muscle and reduce the risk of injury. Studies have found that flexibility training, such as the four sets of 30+ seconds of static (including PNF) stretching recommended in this series, are effective only up to an hour. This means that for exercise sessions lasting longer than one hour, it is important to stretch during any rest periods.
But what if stretching actually increases the risk of injury or decreases performance? If a muscle has been effectively stretched, then it has been relaxed, meaning that it’s contractile ability has been reduced. Furthermore, because the sarcomeres and muscle proteins have been stretched out, so too have the muscle’s proprioceptors. This is why studies may find a greater injury occurrence amongst stretching athletes during the first 10 minutes or so of activity. But here we can find the solution within the problem. It takes approximately 10 minutes for proprioception to be returned to a stretched muscle. This means that following stretching, a further 10 minutes of cardiovascular exercise is required prior to an event. For most general exercisers, this can be a gentler introduction to a cardiovascular exercise, such as walking and jogging prior to running. It may seem an onerous task, especially as stretching is most beneficial following a light cardiovascular warm-up, but really it can be introduced with a minimum of inconvenience into any general program. The real difference may be in introducing this system into an athlete’s program prior to activity. It is particularly important for athletes that might be running on uneven surfaces and therefore requiring effective proprioception.
The other difficulty in prescribing a stretching routine to prevent injury is that, by relaxing a muscle, it will not be as powerful. This suggests that sprinters should not stretch their legs before sprinting. But how many sprinters have we seen limp off the track with hamstring or calf injuries? The key point to make here is that the athlete should not be competing with muscles in such a dire state! This may seem harsh, but as has been discussed earlier in this series, long-term benefits of stretching can be achieved through effective stretching programs performed three times a week for four weeks. Stretching before competition can certainly be recommended for many athletes, but for those requiring high levels of power (such as strength athletes, sprinters and field athletes), it may be more appropriate to ensure that stretching is up to standard in training sessions and that, by the time of the event, there are no injury risks still evident. If there were, then increased mobility work and the gentlest of stretching would be advisable.
To conclude, stretching should be used over the long-term to reduce tension in tightened muscles. Further, stretching should be used to correct muscle imbalances and bring shortened muscles back to their desired length. Any muscles with previous injuries should be rehabilitated with a combination of flexibility, mobility, strengthening and cardiovascular programs. Any athletes with hypermobility through one or more ranges of motion around a joint should avoid stretching through that particular range of motion. A flexibility program should be balanced to target the muscles and the ranges of motion used in an athlete’s particular sport and position within it. Stretching of specific areas can be undertaken prior to activity provided that the person participates in at least 10 minutes of further cardiovascular warming up prior to the main activity or event. The exception to this last point is for sprinters, strength and field athletes prior to competition. In this case, the decrease in performance associated with decreased tension and power available in the muscle(s) may outweigh the perceived risks of a musculotendinous injury during the event.
The recommendation for all clients, including athletes, is to prescribe an effective flexibility routine to be practiced throughout the week to correct any appropriate areas. When proper preparation is impossible in the weeks prior to an event, then there is a trade-off between injury risk and performance ability if stretching immediately prior to competition. This may not be an issue for most people, or for training sessions, but for actual events, you would have to trust that preparation up to the day of the competition was sufficient to prevent injury and then let them go out and compete in the best possible state of health and mind. This article is not supposed to prescribe the best possible flexibility or injury-prevention program but rather the best program that is supported by the current science on the subject to date. Over time, this may be adapted, but I believe it is the best recommendation we have to work with for the time being.
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