I coached a dedicated group of boys for two years. Their dedication was such that, even though I introduced some new techniques which were difficult for them; taught and held them accountable in ways that were different from what they were used to, they showed up to play anyway. At the end of my time with them, we won the tournament held in our backyard for the first time. A look back to those days...
Their dedication also extended to wanting to play, even when they were injured. One practice, one of my midfielders showed up with roadburn down his side- he fallen off his skateboard and slid a few yards. Another one was involved in a crunching tackle. We had to lift him off the pitch in the second of three games at a tournament for which we had woken up before dawn to make. two minutes later, he was doing his best impression of courtesy while demanding that I put him back on the field. There were many of these in the time I was with them; but this is not the impetuous spirit of 14- and 15-year-olds. I managed significant trauma to my own hamstrings during a match and insisted on playing the next match. It was six days from the first injury. Plenty of time to rehab- or so I thought. It was not until the 6 months had gone by, and the next season was under way before I was confident enough to sprint the like I used to. The hamstrings were well and healed, but I kept thinking, "What if it happened again?"
Without reservation, this is an issue faced at the highest level, where players need to play to keep their spots on the team, and managers need them to play to win championships. The result is players and managers who have to deal with the frustration of injury and re-injury.
Function vs. Time- When Can I play...
While research shows that regeneration would still be ongoing up to and over 3 weeks since the initial injury, early return to sport is often proposed when players have suffered a hamstring injury. It is no wonder that the recurrence rate for hamstring injuries is so high. Part of the issue is that hamstrings have been shown to be most susceptible during the late swing phase of high speed running/sprinting. Jogging with barely a burst of speed constitutes most of the 'tests' that athletes have to pass before being allowed to return to play. However, the eccentric capacity of the hamstrings is not tested under these conditions. Team practices are very controlled with less competitiveness, speed and the kind of muscular fatigue that players experience during actual match play. Therefore, even when players 'successfully' navigate practice, they may still be unprepared for the rigors of first team play. Indeed, complete recovery could still be months away. Peterson at al, (2010) suggested that a player with a recent hamstring has 15 times the risk of injury in a match as he or she does a training session. According to Askling et al., (2006) Isometric hamstring muscle strength in sprinters was 70% (2 weeks), 85% (3 weeks) and 90% (6 weeks) that of the uninjured limb after an initial hamstring muscle injury. A range of 6-50 weeks was observed before the same set of players felt they were back to the level they were before getting injured. Both athletes and managers report reduced performance when players return to play early, both in a physical and mental capacity.
Specific criteria need to be established before players can return to play, measures that can help determine the readiness of players to resume play, and thereby reducing the risk of re-injury. These will measure how well the hamstrings perform in a fashion akin to that of competition (function) rather than being based on the question of how long its been since the incidence of injury (time). The following have been proposed:
- Hamstring strength recovery
- Hamstring flexibility
- H:Q ratio
- self-reported insecurity/pain during ballistic hamstring flexibility movements (Askling's H-test)
- high-intensity running performance
Other tests certainly exist at the highest levels where teams have physiotherapists, athletic trainers, fancy equipment etc, which are not readily available to coaches like I was at U14/15. For those coaching at grassroots, the Nordic hamstring exercise is all but the holy grail. It requires no equipment, can be taught easily, and when used appropriately, has produced some spectacular results.
Can One exercise really make a difference?
The effects of the exercise on acute hamstring injury as well as on re-injury were investigated (Petersen et al, 2011) with 924 soccer players. In a carefully structured, progressively overloaded 10-week program, injuries both new and recurrences were reduced by 70% and 85% respectively. The investigators concluded that this preventive effect was solely due to the Nordic hamstring exercise. (Petersen et al, 2011) Moreover, the study showed that in order to prevent one re-injury, only three players at high risk (players with a hamstring injury in the previous year) had to perform the program. Thus, the number needed to treat (NNT), is much lower than the threshold considered acceptable in cardiovascular diseases or cancer where 10–100 or more is often celebrated (Slider et al., 2008) and around 90 athletes for ACL injury training programs, including neuromuscular work. (Grindstaff et al., 2006)
These findings concur with Arnason et al., (2008) whose own 10-week intervention produced a 65% lower injury incidence in soccer players. This intervention consisted of warm-up stretching, flexibility training and the Nordic hamstring exercise program, compared with a group performing warm-up stretching and flexibility training alone.
A 2002 paper by Croisier et al., reported a 100% success rate (no re-injury the following year) after introducing progressive isokinetic strength training (including both concentric and eccentric contractions), performed thrice weekly. This was continued until hamstring strength and eccentric strength deficits normalised from 4 to 10 weeks.
Why it works... briefly.
The Nordic hamstring exercise addresses the eccentric strength deficits which are undoubtedly present following injury, if not the cause of the initial injury. Recall that most injuries occur when the hamstrings are in their lengthened state (during eccentric contraction).
Taken together with Petersen et al's data, systematic and progressive eccentric strengthening has a large hamstring re-conditioning capability, most likely addressing eccentric strength deficits, (Crosier et al., 2002) muscle-tendinous atrophy and scar tissue, (Artalejo et al., 1998) certainly changing the injury risk profile of the athlete with a previous hamstring strain, even when addressed after a significant time period following the initial injury and rehab. (Peterson et al., 2011)
Bold summary
"It is thus incontrovertible that the Nordic hamstring exercise program reduces hamstring injuries. It could almost be considered negligent not to provide eccentric hamstring strengthening in this form for athletes with a history of previous hamstring injury (i.e, athletes at high risk of re-injury)."
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Reference
Thorborg K. (2012) Why hamstring eccentrics are hamstring essentials. Br J Sports Med Vol 46:463-465
Artalejo FR, Banegas JR, Artalejo AR, et al. (1998) Number-needed-to-treat to prevent one death. Lancet 351:1365.
Askling C, Karlsson J, Thorstensson A. Hamstring injury occurrence in elite soccer players after preseason strength training with eccentric overload. Scand J Med Sci Sports 3:244–50.
Croisier JL, Forthomme B, Namurois MH, et al. (2002) Hamstring muscle strain recurrence and strength performance disorders. Am J Sports Med 30:199–203.
Grindstaff TL, Hammill RR, Tuzson AE, et al (2006). Neuromuscular control training programs and noncontact anterior cruciate ligament injury rates in female athletes: a numbers-needed-to-treat analysis. J Athl Train 41:450–6.
Petersen J, Thorborg K, Nielsen MB, et al. (2011). Preventive effect of eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized controlled trial. Am J Sports Med 39:2296–303.
Silder A, Heiderscheit BC, Thelen DG, et al. MR observations of long-term musculotendon remodeling following a hamstring strain injury. Skeletal Radiol 37:1101–9.
