Hamstring injuries (especially the biceps femoris) are the most common sports injuries in sports such as football, rugby, athletics, etc. These sports are characterized by sprinting and high-speed actions, which suppose a great demand of the hip extensor muscles (gluteals and hamstrings), with the hamstrings being the most affected in this situation (1-3).
Hamstring injuries account for 6-29% of total injuries recorded in Australian football, rugby, football, basketball, cricket, and sprinters. In addition, it has high recidivism rates, between 12-31% (2, 4, 5).
Most hamstring injuries occur in a sprint or high-speed actions, and also in muscle over-stretching actions (2, 3).
It is estimated that in a team of 25 players, they suffer an average of 5-6 hamstring injuries throughout the season, equivalent to more than 80 days of competition lost due to the injury. In addition, injury rates show an annual increase of 4.1%, year after year (study period since 2001, duration of 13 years) (6). So we can see that something failed in the “preventive programs” or “reduction of the injury incidence”.
In the following graph, we can see how hamstring injuries are the most prevalent over a season in professional soccer players (study between 2001 and 2008) (figure 1) (7).
HOW TO WORK OUR SPRINT STRENGTH-SPEED PROFILE?
If you have not read the first part yet, there you have the bases on the horizontal profile, the theory of force vectors, determining aspects and orientation of the training to optimize it. Here, we will clarify a couple of concepts in relation to the previous article.
Within the different parts to work, in the previous article, we divided it into:
– Force exercises in horizontal vector. In this case, we highlight the application of exercises such as hip thrust, bridge gluteus, horizontal jumps, kettlebell swing, etc (8-10). Since it has been seen that this type of exercises have a greater transfer to determinants of performance such as sprinting, changes of direction and horizontal jumps (8)
– Weathered sprint and sprint exercises. In the previous work, we could see that the optimum load to produce the maximum power during the rested sprint is between 69-96% of the PC (depending on the friction conditions) (11). In addition, it was observed that the application of resisted sprints with heavy loads (80% PC) have a greater effect on the mechanical properties of the sprint, improving the levels of FH (FO, Pmax, and RFmax) (12).
To all the above, I would like to add new work from the same research group. In this case, we present a graph that refers to the load used in a resisted sprint based on the loss of speed associated with this load, and its influence on the sprint properties (FO and VO) (Figure 2). All this must be individualized according to the needs of the athlete based on a prior assessment of his sprint profile (13).
In addition, the work of the race technique and the quality of movement can be other positive aspects to work to improve our performance in sprint, due to a greater efficiency in the race (3, 5, 15, 16), since it has been seen that they are key aspects within the rehabilitation of hamstrings since the beginning of the recovery along with the work of race and sprint (3).
ISQUIOTIBLES – MULTIFACTORIAL APPROACH
Within a preventive program for the hamstring musculature, we observe how they have usually isolated work protocols or that they only take into account a single factor. The most common of these is the work of force with the Nordic Curl. With this, I do not want to demonize the Nordic Curl, but we must have a broader vision, beyond the strength of the hamstrings as a single factor to work (4).
And observed as in most clubs bet on this work, and hamstring injuries continue to increase, are we sure that only with the Nordic Curl we will prevent hamstring injuries? The evidence suggests that no, and we should give it another approach or point of view to make it more effective (4, 6).
With all this, the multifactorial approach to hamstring injury arises, and it is nothing more than the interrelation of the various risk factors of it (Figure 2), associated with the most common mechanisms of injury (sprint and over-stretching). In this way, we bet on a more global approach that seems more appropriate, both in the prevention and in the rehabilitation of injuries (4, 5).
A recent review includes several associated risk factors (in addition to the general ones already mentioned), and among them, we can highlight weekly sprint exhibitions / high-speed actions, load ratios, psychosocial factors, recovery strategies and movement quality ( 5).
Therefore, we observed that we can not attribute a hamstring (or other) injury to a single factor and we must have a more global view of the process.
WHAT HAPPENS AFTER AN INJURY OF ISQUIOTIBLES IN THE SPRINT MECHANICAL PROPERTIES?
In a work done with soccer players (17), we could observe how those who returned to compete after a recent hamstring injury, had a worse performance in the sprint and a decrease in the production of horizontal force compared to healthy players. In addition, they needed approximately 2 months of regular training to significantly improve sprint speed, with an increase in horizontal force production (obtaining similar values to the group of healthy athletes).
In another similar study, this time with rugby players (18), the same research group shows similar results. When performing the RTP after the hamstring injury, there was a significant decrease in the levels of FH (from 8.3 to 6.6 N / kg, ↓ 20.5%), while there were no changes in the levels of VO (8.7 and 8.7 ms) (figure 4).
Recently (19), it has been observed that after a hamstring injury there is a greater decrease in the application of horizontal force (13% lower) in the injured leg vs the healthy leg. To assess it, they compared soccer players with a previous hamstring injury to healthy players. All of them completed 10 series of 6 seconds of the repeated sprint (RSA) to evaluate it.
These asymmetries between legs can be considered as a risk factor and, above all, should be taken into account when deciding the RTP of the athlete, minimize the risk of relapse. Knowing that the performance in RSA is also a factor of performance in football, that asymmetry between legs can produce a decrease in the performance of the athlete (19).
KEY ASPECT IN THE PREVENTION AND REHABILITATION OF ISQUIOTIBLES, SPRINT, “WIN-WIN” STRATEGY
For all the contributions made in the previous points, we can see how both the preventive and sports rehabilitation approach must see the hamstring injury with a multifactorial approach, in which the various risk factors are interrelated (strength, flexibility, fatigue, previous injury, etc) along with the most common injury mechanisms (sprint and/or high speed, and over-stretching). All this, with the nuance of the differences and individual needs of the athlete (3-5, 16).
Within all the pieces of the puzzle of the process, sprint training becomes part of the solution to all this. It would be mandatory to include it in our work, both preventive and in the process of readaptation, since it is the most common mechanism, and due to the alterations that occur in its mechanical properties (especially, the decrease in FH) (3-5, 17, 18).
In the previous work, we could observe the importance of hip extensor muscles (glutes and hamstrings) in the production of horizontal force (FH), being the hamstring activation a determining factor in that application of force (20). Recently, the same research group has published a paper on the mechanical properties of sprinting in a situation of fatigue (2). For this, they subjected 14 experienced athletes with sprint training to a repeated sprint test of 6 seconds, with a rest of 44 seconds between each repetition.
The results indicate a significant decrease in Pmax (-17.5 ± 8.9%) and in the production of FH (-8.6 ± 8.4%). The determining musculature of the FH also had a significant decrease in force, with a greater decrease in the strength of the hamstring muscles compared to the gluteal muscles. According to the data obtained, the production of horizontal force in a situation of fatigue seems to be more dependent on the gluteus than the hamstrings. Therefore, it is hypothesized that this compensatory role of the gluteus could be an adaptation to maintain performance and have a protective function in hamstring injuries in a situation of fatigue. The recommendations of the study suggest work on the gluteus maximus as a strategy for both performance improvement and injury prevention (2).
Finally, weekly sprint exhibitions and/or high-speed actions seem to be another effective strategy for the prevention of hamstrings (21, 22).
– Hamstring injuries are one of the most common injuries, and injury rates are increasing.
– Focus our preventive work on a single factor does not seem to be the most successful. It is recommended to bet on a multifactorial approach.
-After a hamstring injury, our sprint profile is affected, above all, in the production of FH. Therefore, we will have to work it during the re-adaptation process and evaluate it at the moment of the RTP of the athlete.
– A specific work of gluteus maximus, sprint and/or high-speed exposures, and individualization of work according to the athlete, seem to be the most effective strategies (“Win-Win” strategy).