By Jason S Davis, BSc. M.Chiro
When discussing hamstring injuries, attention is often focused on the management and rehabilitation of acute injuries such as grade one biceps femoris tear. However, many times hamstring soreness and poor sprint performance resulting from hamstring problems can persist long after an initial acute injury or multiple acute tears. In some cases, soreness develops even without an initial tear taking place. Most coaches and athletes are aware that the hamstrings are under tremendous forces during sprinting.
The forces appear highest during the terminal recovery phase of the foot just prior to ground contact, as well as during the support phase working to create stiffness in conjunction with the quadriceps and gluteal muscles. This occurs in around 0.03 seconds in elite sprinters, meaning the rate of forces is tremendous. The literature would suggest that overly ambitious and unmanaged training and competition volumes are the major culprits for the development of hamstring injuries. Chronic pain is handled extremely badly with athletes, often because the wrong things are blamed for the problem, and the wrong recommendations are perpetuated because coaches and athletes think they can fix the problem the same way you manage an acute injury. As we will see this is not the case.
With chronic hamstring soreness, athletes tend to complain more of stiffness and soreness that persists long after exercise and is especially prevalent when warming up. They note that the pain often goes away after warming up and can often compete or train well, but the soreness gets worse the following few days. This process continues for a while until it suddenly seems to get worse and more persistent. This also tends to lead them towards more massage therapy and more stretching. Unfortunately, if these measures are aimed at the wrong things, such as attempts to break up scar tissue, adhesions, or trigger points they may perpetuate the issue, increasing anxiety and frustration.
This article will discuss the causes and implications of chronic hamstring soreness and dysfunction and what the best management approach would be.
What Causes Chronic Hamstring Soreness and Weakness?
It seems that following a hamstring injury, the nervous system sets in place inhibitory mechanisms to avoid injury again, literally turning the contractile power down. This neural inhibition can often persist long after the structural integrity has returned. The brain is likely not to allow all the powerful, fast-twitch motor units to fire when the same discipline that caused the injury is implemented again. Unfortunately, due to the rate that high muscle forces occur at during fast running, the nervous system’s protective role can remain persistent for some time specifically in relation to that activity. If fast running is forced during this period, the forces experienced are likely to be absorbed less by the contractile muscular structures and more from the passive connective tissues in the muscle and tendon. Commonly, this leads to chronic tendon soreness, further inhibition and lack of speed that can occur long after a muscular injury. Athletes and coaches underestimate how long this process may persist for, and commonly with complete rest the problem resurfaces quickly because of general relative deconditioning.
The brain responds to unmanaged or unrelenting tissue stress in an interesting way. The central nervous system and brain receive information back from the tissues via receptors that travel up through tracts in the spinal cord. The brain takes this information and together with previous experience as well as the athlete’s beliefs about the meaning of them, determines the significance of that information. Brain outputs such as pain and excessive muscle tightness are determined by how the brain responds in light of this information. However, in the case where pain and connective tissue strain has been exacerbated for some time, the brain begins to output pain messages much more readily. This is known as central sensitization that, in essence, is a lowering of the threshold to which a stimulus in the tissue receptors triggers a pain response. This is a very important point. Pain is not experienced in the tissues; it is experienced in the brain over the area that maps that region of the body (it’s much more complex than that but for the purpose of this article it will do).
Interestingly, the experience of tightness and stiffness can also be considered expressions of the brain. My experience working closely with patients in a clinical setting has made clear over time that a person’s complaint of stiffness and tightness has little to do with the actual flexibility that they possess. I was shocked when examining a top soccer player from Nigeria once when looking at his limited hamstring flexibility. When I asked him “does that feel stiff or tight?” he experienced no stiffness or tightness at all which made me question the assumption of tightness and flexibility, and what is considered normal. I concluded that his degree of flexibility was normal for him, and importantly his brain also told him that it was normal. Indeed, he did not have a hamstring problem, and he was very fast. On the other end of the spectrum, I have had examined experienced yoga attendees who complain of tightness in a hamstring with 120 degrees of range. Tightness is a perception brought on by particular sensations towards a muscles end range.
Chronic hamstring problems can build slowly over the length of a competitive season; however, very often in the initial stages they do not cause a significant decrease in performance. Commonly, a young athlete will have a breakthrough year and compete week in week out from indoor to outdoor ignoring the increasing hamstring soreness because they are still improving. They figure that with a few weeks of rest at the end of the season it should go away, only to find that when they return to training it is worse than when the season finished. Why would this be so? It seems likely that following a period of rest the general strength of the muscles may be reduced, the muscles feel well rested and relaxed but the brain has become more vigilant and remembers the stress it experienced. The brain also senses that things, in general, are a bit weaker in combination and with a state of low training arousal the brain will take precedence over the need to avoid the activity you are forcing it to do in favour of more recovery. However, it is likely that the tissue injury has healed well.
The Frustration Begins
Commonly, the athlete will seek out an answer for the soreness and see a sports professional. Often, MRI or ultrasound examination will show no abnormalities such as inflammation or distinct tears; however, it can be important to rule out. Clinical examination will demonstrate normal flexibility, strength testing in a clinical setting will appear normal, and the muscle feels no different to palpation in comparison to the other opposite muscle. At this point, many therapists will attempt to give the athlete a structural reason to rationalize some therapy. These may or may not be relevant, but, unfortunately, the relevance can be overstated, and a lot of false positives can be blamed which can build on the athlete’s anxieties if not put into perspective. Common diagnoses for chronic hamstring soreness includes tendinitis/tendinopathy, grade one tear, sciatica, and piriformis syndrome. With common treatment aimed at soft tissue joint manipulation, stretching and strengthening which if not utilized appropriately can perpetuate the belief that a structural problem is predominant and ignore a higher brain involvement.
To overcome chronic soreness in hamstring muscles, the athlete needs reassurance that there is not a structural tissue problem, or it is at least minimal. If this is not managed well, this can lead to disability reinforcement. If the athlete can understand early on that their brain might be playing a role in their sensations, it can give them a sense of power over it. This is vital, it tells them there is a problem, and it is real, but it is not because they have a structural muscle problem. I often tell patients that your brain will do what it wants to do, but your thoughts and perceptions about the sensations can either make it better quicker or make it worse. Encouraging positive reinforcement, building confidence, and time are important factors that will help remarkably. This may require more time with the athlete talking about their feelings, taking every opportunity to reassure. Secondly it may require a break from normal training on track and avoiding speed endurance work for a focus on slower resistance training.
Mistakes in the management of chronic pain can be summed up in one sentence; excessive treatment and attention to the problem area without enough consideration of an overall approach can lead to disability reinforcement. I suggest that in most cases taking a more general or global approach to chronic injury management and therapy, as well as appropriate counselling that includes reassurance to rebuild confidence will be more effective.
I will outline what I think can perpetuate the problem with different treatment modalities, as well as rehabilitation attempts and suggest a better overall management approach.
Joint and Muscle Therapy
Manipulation of the soft tissues and articular structures can play a role in hamstring injury management. Unfortunately, this can be overdone and can lead to disability reinforcement often through confirmation bias. For example, athletes and coaches will seek out therapy and certain therapists with the impression that they need excessive treatment for muscular adhesions, scar tissue, poor flexibility, joint misalignment, poor core strength and a huge array of other things that may only be a fraction of the problem. Low down on the list is how the brain might be affecting the dysfunction and that their thoughts and beliefs may be reinforcing the problem. Many therapists do their job well by fixing these subtle problems; however, they fail to counsel the athlete well enough by placing these problems into perspective.
As a Chiropractor, I often consult athletes with chronic hamstring injuries/pain, and they come on the referral of their coach who tells them maybe you should go to the Chiropractor because I think your back is causing the problem. When I examine them, they often are suffering from some lower back/pelvic strain/dysfunction. However, it is often clear that these issues are likely another product of an excessive volume of training/competition and protective brain output. In essence, they often accompany a hamstring strain rather than directly cause it. Asymmetry of mobility in the sacroiliac joints has been associated with acute and chronic hamstring strains and a look at the training regime highlights two things when we find this pattern. The proportion of block starts and high-intensity bend running is too high, so I would advise that these two factors be limited in volume, especially early in the season. However, before considering joint and muscle therapy, I make sure the athlete and coach understand that this may only be a very small part of the problem and that it is likely an associated factor that is being caused by protective brain output, and not the entire cause of the hamstring injury.
Manual therapies can a have a great effect on chronic pain when the athlete is treated in a more general way. Massage and joint manipulation can stimulate pressure and movement receptors which can have the effect of altering pain processing in the brain over time. If, however, treatment is directed too much at the region of the injury, eventually we may begin to add to the sensitization. People are often confused as to why I would treat the upper back, neck or ankle with a hamstring problem; the goal is the effect on the brain and spinal cords pain processing pathways via leveraged movement stimuli. We are trying to alter wiring through very novel stimulus. I believe massage can work in a similar way as long as attention is not excessively given to a problem area and I would limit attempts to repeatedly “break up scar tissue in the muscle”. Stretching the hamstring statically or dynamically is also unlikely to have any beneficial effect on an athlete’s chronic hamstring soreness and may even perpetuate the problem as end-range stimulus is often associated with a reciprocal protective response. The muscle feels looser for about 10 minutes but subsequently it tightens up again. In addition, stretching can then become an obsessive habitual desire and continues a low-grade stimulus that triggers the brain’s protective reflexes.
Workouts to Enhance Recovery
Performing low-intensity workouts between high-intensity speed training or competition such as tempo may seem like a good idea on the surface. However, I would question the rationale behind this approach, especially with an athlete suffering chronic pain. Firstly, the intensity is relative to the degree of effort, so a workout of 10 x 100m at 75% of top speed may feel like a low-intensity session one week, but performed following a high-intensity session can become moderate to high intensity regarding effort that is the real measure of intensity. For an athlete with chronic pain, rather than providing recovery these sessions gradually create more irritation as well as slowing the rate of neuromuscular output. I would recommend that for an athlete with chronic soreness, that more days of complete rest be implemented and resist the temptation for too much active recovery. The risk of too much low intensity is that the overall ability to produce high intensity may become reduced. The rationale behind recovery sessions and tempo are that it will increase blood flow to the area and provide a gentle stimulus to the muscles to stimulate recovery and beneficial cardiovascular changes to provide better recovery systems over time, more so than high-intensity sprint training and competition can. However, there is no strong evidence that recovery can be improved this way (other than restricting intensity) or that long term adaptations will occur to enhance recovery systems. I would suggest that the main effect on some athletes may be psychological.
Strength Protocols That Excessively Focus on Strengthening the Problem Area but Fail to Create General High-intensity Muscle Effort
The longer that an athlete has suffered chronic hamstring pain and stiffness the more likely they have lost the ability to absorb load through the muscle, and they tend to remain in a shortened position to protect them. The research literature regarding hamstring injuries often focuses on which exercises activate the hamstrings the most. The argument being that high EMG activity must mean that it is a better choice to strengthen the muscle, and this will rebuild structural integrity as well as high neuromuscular output. Coaches and athletes, however, must be careful how quickly and how much volume of direct and isolated hamstring training they implement, as this plus track work may serve to overload the hamstring (and the brains response) even more. The idea of the “weak link” is an attractive one, and this type of thinking often leads to excessively working the area rather than giving it a rest and considering an overall strength approach. Indeed, the injured muscle may be a compensation for weakness in other areas, and there is a tendency over time for the athlete to develop overall lower body weakness if attention is focused on only isolated areas rather than the whole muscular chain. Certainly the hamstring to quadriceps strength ratio may be less important than once thought. Instead, one should consider strength in all muscles. Exercises that are often prescribed by health professionals tend to be generic low-intensity movements that aim to work the hamstrings in multiple ranges. The frequency of recommendation is also often far too high for daily exercise programs common that may reinforce a disability complex and simply overwork the muscle in a less than biomechanically sound fashion.
Hence with chronic hamstring injury I would suggest compound exercises can be a better initial option that involves the hamstrings as part of a team rather than in isolation. High neuromuscular output and recruitment of fast twitch motor units is accomplished well through key compound exercises such as the squat and deadlift. These exercises work the muscles and the hamstrings in their strong ranges and avoid forced or vulnerable end-range movements and forced positions in active or passive insufficiency. A lying leg curl, for instance, often places the biceps femoris in a position of active insufficiency and then it gets forced further into active insufficiency and tends to overwork the medial hamstrings, as a result, which potentiates a groin strain. The Glute-ham raise and Nordic hamstring exercise may also be limited in these regards, and I would suggest that the best and healthiest hamstring exercises produce high tension when the hip is not maintained in an extended position. Better options to isolate the hamstrings would be the Romanian or stiff leg deadlift, with both double or single leg, glute ham raise or even a seated leg curl.
Eccentric exercises have been suggested as a good means of chronic muscular and tendon pain management and have demonstrated good results in subjective pain improvements, objective intramuscular and tendon changes as well as greater strength output. However, it is not clear that omitting the concentric portion of the exercises is necessary for optimal results. I would suggest that with some exercises, avoiding forced contractions in a shortened muscle position may be the added benefit of eccentric only protocols. There is also suggestion that long-term exposure to eccentric exercise will increase fascicle length and possibly provide an advantages length-tension relationship for greater power generation in sports. This is interesting and needs more research to examine whether this can be transferred over to sporting disciplines or it is a temporary and exercise specific change.
What is clear, however, is that higher motor unit recruitment is beneficial in most cases of rehabilitation. And when it comes to sprinting, the central nervous system will only ALLOW fast sprinting to occur if it has confidence that the muscular tensile capability is very high. It would make sense that developing maximum strength capacity would be very beneficial in the whole system. The squat and deadlift, while being valuable overall leg strength developers, can also build athlete confidence as well as alter the focus away from an injury that may be valuable in the athlete that has chronic soreness. The rate of muscle tension is a lot slower than that of sprinting, so it is likely not to irritate the muscle and tendons as much. It is important, however, that the goal doesn’t become to see how much the athlete can lift, and they will need to be reduced or eliminated before speed work and competition, as a chronic hamstring problem will be much more susceptible when being forced to perform vastly different disciplines. Importantly the squat or deadlift should be taken to the point of momentary muscle failure (as long as the technique is sound) once per week to ensure fast twitch muscle fibre involvement. Staying away from running may allow the nervous system to re-learn what the muscles are capable of and change the wiring.
Hence, for an athlete coming back from a chronic hamstring problem, I would recommend a break from all running and prior to the start of competition for a 6 to 8 week period of strength training, two to three days per week, alternating between low bar squats to parallel and the conventional deadlift setting the bar down between reps. This will build general core and lower body strength output and should over some weeks let some chronic hamstring pain and stiffness reduce. After about four weeks, they should be able to challenge the hamstrings more directly by loading with the semi-stiff leg deadlift in either double leg with a wider stance that tends to target the medial hamstrings more, or in a single leg stance that appears to target the biceps femoris to a greater extent. However, I would still be mindful of the frequency of these exercises as well as the loads used. Indeed, it may be better to use them as a good gauge of strength rather than a regular exercise. The Nordic hamstring exercise may also be a good gauge of progress. Importantly are the principles of progressive overload and recovery, if the athlete can see they are getting stronger in a few key exercises confidence will soar. In cases of long-term chronic hamstring problems, the athlete may not be strong enough for the semi-stiff leg deadlift initially, and even very moderate weights can be quite aggravating and perpetuate the soreness if not careful, especially if the end-range position is not controlled well, and the passive structures of the tendon and muscle are loaded too rapidly. I would make sure that the athlete can do continuous tension normal style deadlifts (reps without putting the bar down in between) before attempting a stiff leg deadlift in the same fashion.
Speed work and Competition
It would be prudent for the athlete to build gradually up to speed work but being mindful not to make the error to push for endurance. Keeping volume relatively low with easy not forced repetitions of a distance that allows a comfortable rhythm, and encourages the athlete to ease into it. Staying away from the excitement of the track and finding a long straight and flat running strip of 200-400m would be ideal, always finishing on a faster run and avoiding the build up of fatigue. It is alluring to push into fatigue and think that the athlete will adapt, but the goal is not fitness but smooth, relaxed running that will allow a smooth transition back to top speed.
Once they are ready to get back on track and work on speed in spikes, it would be beneficial for the athlete to aim to stay fresh and maintain short high-intensity sessions, and being careful to avoid too much bend work, speed endurance and block work. Keeping the athlete’s top speed ability over a short range high will be somewhat protective over the injury. Leaving speed endurance efforts to competition would be a good strategy due to the high states of psychological arousal as it will stimulate high-quality movement, tune the nervous system and build confidence. However, they should avoid the desire to get in lots of speed work before or between competitions as they might find that they will break down fast. The athlete needs time at high intensity without exacerbation. This means high quality with long recoveries in between. If the athlete does not have access to high-quality competition a timing system such as Freelap is very valuable in keeping them from doing too much and working on mechanics at top speed, however, be mindful not to strain more and more for better times, especially no more than once per week.
Chronic hamstring soreness is common in sprinters and the approach to the injury must be different to that of acute tears. Their origins lie in prolonged high intensity over a period of time and are perpetuated by altered brain output. Many measures aimed at the injury often continue to aggravate the injury and over time this becomes manifested as reduced neuromuscular output. The athlete’s coaches and therapists have a crucial role in counselling the athlete in the complexity of these problems and a collaborative approach with communication can be essential. While passive manual therapy can be useful, the keys to rehab training are building strength capacity in the entire muscular system and a gradual, graded return to fast running. With the correct approach outlined in this article, over time these chronic problems will disappear; with the wrong approach promising careers can be finished.
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