I am not trying to jump on the bandwagon here; this is something I have been writing about and commenting on for years. Hamstring injuries have become a huge problem in sport. Just to be clear even though the Josey Altidore hamstring pull prompted this post I have no know knowledge of what the US Men’s National team does or does not do in terms of conditioning. I have had no contact with the US Men’s National Soccer team since I worked with the 1998 World Cup team. I do closely follow the tends the trends in training, injury prevention and rehab and the trends in regard to the hamstring have been quite alarming to me over the past ten years. I will state my premise up front: The more you train the hamstring to prevent hamstring injuries, the more hamstring injuries you will have. Introduction of the term “posterior chain” is part of the problem. It has caused us to focus more on one part of the body instead of thinking of the linkage, connection and coordination of the whole kinetic chain. Two years ago I visited a prominent DI football school. The Head Football S&C proudly told me about the extensive posterior chain work they were doing – last year they had eight hamstring pulls out of their 22 starters! Do you think there is any connection? I do!
Here is some food for thought from an article in Sports Coach, Volume 28 Number 4that Ico-authored with Dean Benton nine years ago.
- Poor timing-intermuscular coordination and eccentric strength in the short head of the biceps femoris muscle during the switch between late leg recovery and initial leg approach in the swing phase of sprinting (Woods et al. 2004).
- Lack of stiffness and eccentric strength in the short and long head of the biceps femoris muscle during the ground contact phase of running (Bosch and Klomp 2005). Stiffness refers to the ability of the muscle to absorb shock and rebound. Dropping a golf ball onto concrete is an example of stiffness, it immediately rebounds off the surface. The opposite would be would be sagging or a slight collapsing on contact.
- Previous strain — prior hamstring injury is a very good indicator of potential for future injury (Crosier 2004).
- Poor running mechanics — this consists primarily of overstriding which puts the hamstrings in a vulnerable position at ground contact. Also excessive sway or lateral deviations that force the synergistic stabilising muscles to overwork subsequently shifting more stress to the hamstrings. The hamstrings do not work alone, they need help. Poor technique when running curves and angles will put more stress on the hamstrings because of the work they have to do in the transverse plane.
- Improper warm-up or lack of warm-up — there is often confusion between stretching and warm-up. Stretching is not warm-up; the warm-up must be active and dynamic to prepare the muscles for the forces involved. Stretching is only one segment of warm-up.
- Inappropriate training loads — high speed work placed inappropriately in the workout will predispose the athlete to hamstring pulls. The hamstrings are primarily fast twitch Type II fibres that fatigue quickly. This demands that high speed work be done early in workout, as close to warm-up as possible to avoid fatigue. Higher intensity speed endurance work must be gradually built into the program to allow for adaptation. This type of work must be built on a sound foundation of running mechanics.
- Fatigue (neural and local muscle) — because the hamstrings are primarily fast twitch Type II fibre, all activities that occur in the course of a game must be taken into consideration, for example, in AFL fatigue arising from running then sprinting and kicking.
- Lower back pathology — abnormalities of the lumbar spine that potentially could cause nerve dysfunction, which in turn lead to muscle weakness.
- Playing surfaces — a wet slippery surface will put more strain on the hamstring due to slipping.
In order to select effective exercises to prevent hamstring injuries and optimize sprinting performance, it is necessary to understand hamstring function. The nature of the injury and the phase of the stride cycle where the injury commonly occurs provide a major indication of hamstring function as well as insights into the mechanism of injury. Despite this clear evidence of hamstring function and the biarticular nature of the hamstrings there is a continued search for ways to isolate the hamstrings in order to strengthen them. With the understanding of the eccentric role the hamstrings play in the stride cycle, some people (the authors included) searched for ways to strengthen the hamstrings eccentrically. Unfortunately, most of those methods still relied on single joint movements, for example:
- Hamstring curl (regardless of the position of the body)
- Ham/gluteal raise — this is an exercise that has gained much favor, but it still isolates the hamstring in a position of mechanical disadvantage
- Kneeling Russian (Nordic) hamstring exercise — executed from a kneeling position with a partner securing the ankles. Slowly lower, extending the knees. This puts undue stress on the distal hamstring. In the authors’ experience this has caused many hamstring problems.
All of the above exercises certainly do work the hamstrings eccentrically, but the problem is that they all isolate the hamstrings by working at one joint, the knee. None of the exercises contribute to intermuscular coordination nor do they work the hamstrings at anywhere near the speed necessary to transfer to performance. Furthermore, the Kneeling Russian Hamstring exercise in particular excessively loads the hamstring distally. All these exercises are contraindicated.
Location of injury
Injury data indicates that around 80 per cent of hamstring strains occur in the biceps femoris muscle (Koulouris and Connell 2003). There is some disagreement in the sports medicine literature whether hamstring strains occur at the switch between late leg recovery and initial leg approach in the swing phase of sprinting, or during the early to mid phase ground contact phase of sprinting. However, when consideration is given to EMG (electromyography) research, biceps femoris activity is at its highest just prior to and during the ground contact phase (Kyrolainen 1999). Furthermore, most of the hamstring strains that occur in the biceps femoris muscle occur in the long head of the muscle (Koulouris and Connell 2003).
Criteria for prevention exercise selection
Hamstring injury prevention and performance enhancement exercises should be multiple joint, closed kinetic chain and eccentric in nature. The emphasis should be on exercises that enhance intermuscular coordination. The training of timing and coordination is essential. Timing and coordination has not received much emphasis because it is difficult to measure. Timing and coordination demand a clear understanding of sprint mechanics and the adaptation of those mechanics to multidirectional field sports where the incidence of hamstring injuries is so high. It is imperative to examine the plethora of ‘sprint type’ exercises in order to determine their transfer to the skill of sprinting. The goal should not be more drills, but finding drills that work. The drill must not be an end unto itself, it should contribute to coordinating the hamstrings in patterns that transfer to the demands of the activity. Also, in order to withstand the large eccentric load that must be attenuated during ground contact, exercises that train muscular stiffness and reactivity need to be included as part of a comprehensive injury prevention and performance enhancement program.
Another prevalent thought in sports medicine circles is that hamstring injuries are due to a lack of stretching, or improper stretching in warm-up. There is nothing in the literature to support this belief. In fact, recent research has shown that static stretching in warm-ups plays little or no role in injury prevention. This area warrants further research to refute or verify what the practitioners have experienced. There is no doubt that the lack of an active and dynamic warm-up is a contributing factor to many hamstring muscle strains.
Based on Lieber’s (2002) work on muscle architecture and what we know of muscle function from biomechanical studies there are certain exercises that are contraindicated. They are:
- Hamstring curl - regardless of the position of the body (Bosch and Klomp 2005)
- Roman chair hamstring/gluteal raise
- Kneeling Russian (Nordic) hamstring exercise
- Swiss ball bridging exercises.
These exercises are contraindicated because of the non functional position of the body and the fact that they all work the hamstrings at one joint. These exercises are often used because you can 'feel the burn' during execution. That is a poor reason to choose an exercise. The burn is felt because the hamstring is at a mechanical disadvantage.
Contraindicated training modalities
- Treadmill sprinting – treadmill sprinting and overground sprinting are different activities. The treadmill allows the athlete to place the foot farther in front of the centre of gravity than would be possible in overground running because the ground is not moving under the athlete, the athlete is moving over the ground. Empirical evidence based on the authors’ experience is that athletes who make extensive use of treadmill training are more prone to hamstring strains.
- Overspeed sprinting with elastic tubing - this method, regardless of the modality, is trying to get the athlete to run faster than they are capable of running of their own volition. There is a tendency, especially with the elastic cord, to ‘reach’ and ‘break’ to alleviate the fear of falling. This obviously reinforces overstriding which predisposes the athlete to hamstring pulls.
Fallacious training modalities
- Backward sprinting (running) – this has assumed almost mythological status as a hamstring strengthening and preventive exercise. EMG studies have shown that during backward running the hamstrings are essentially silent; they are along for the ride. Backward running works the quadriceps, most specifically the VMO and the gastro/soleus complex. So it is not a waste of time, but it doesn’t help the hamstrings directly. The work on the gastroc/soleus may help train that group to be stiffer at ground contact which contributes indirectly to helping the hamstrings.
- Butt kicks – this is a classic misunderstanding of the difference between similar and same. It appears to mimic what happens in the stride cycle, but in reality the legs flex as a result of ground reaction forces and momentum, the hamstrings contribute minimally immediately after toe off in the running stride (Kyrolainen, Komi and Belli 1999). Remember that the hamstrings’ primary job is not to flex the knee. The butt kick is telling the hamstring to flex the knee, in essence creating neural confusion. It is not an exercise worth spending time on.