1. Athletes who perform long sprint events displayed a significant asymmetry between right and left knee flexor strength.
2. Athletes with a previous injury displayed no significant difference in knee flexor strength compared to their previously uninjured colleagues.
3. When normalized to bodyweight, male and female track and field athletes displayed similar levels of eccentric knee flexor strength.

BACKGROUND AND OBJECTIVE
As in many sports, hamstring injury has been recorded as the number one cause of time loss in track and field athletes (1). Despite this knowledge, and also the knowledge that there is a correlation between decreased eccentric hamstring strength and increased risk of hamstring injury (2), there is not currently any published literature on eccentric hamstring strength in track and field athletes.

Therefore, the primary aim of this study was to compare peak and relative eccentric force and limb symmetry between different event groups and between genders. The secondary objective of the study was to establish if there were any peak force deficits among those previously injured.

METHODS
All athletes who completed this testing between 2016 and 2019 were eligible for the study.
A standardized method of testing was used throughout this time period, whereby the athletes completed testing prior to any fatiguing training following a standardized warm up involving the bike and single leg hamstring bridges.

All 44 athletes who were involved in the study had their injury records retrospectively collected and analyzed.

RESULTS
The male track and field athletes showed a significantly greater peak force than females (418N vs 318N), however once normalized to bodyweight there was no significant difference seen throughout the whole cohort of athletes.

When this data was then broken down into different events, the short sprints athletes displayed no significant right to left-sided asymmetry, and this was also the case in field event athletes. However there appeared to be

Hamstring injury has been recorded as the number one cause of time loss in track and field athletes.

As part of the athletes regular screening program, eccentric hamstring strength was measured using the NordBord device. In this test, players ankles are strapped into the device and load cells provide a measure of eccentric force production (see video).

Even very high levels of eccentric strength are not adequately protective against hamstring injury.

a significant difference between right and left limbs in athletes in the long sprint event group (200-400m).

Interestingly, the study also found that there was no significant difference in eccentric hamstring strength between injured and non-injured limbs.

LIMITATIONS
The key limitation of this study as acknowledged by the authors is that all testing was performed over a number of sites by a number of therapists. There is therefore a risk of poor inter-tester reliability, especially given that this variable has not been previously quantified in the literature (3).

CLINICAL IMPLICATIONS
This study revealed that when normalized according to body weight, track and field athletes displayed the greatest levels of eccentric hamstring strength compared to athletes from other sports. These relative force scores of 5.21N/kg and 4.91N/kg for male and female athletes respectively are higher than those previously reported in soccer, rugby union and Australian rules football.

This is an interesting finding as previous literature has suggested that greater levels of eccentric knee flexor strength are protective against hamstring injury. However, in this cohort of 44 athletes almost three-quarters had a history of hamstring injury. This highlights a fact that is true across all field-based sports – even very high levels of eccentric strength are not adequately protective against hamstring injury. It is vital to address all other proposed risk factors to try and maintain the training status of the athlete.

Another key finding from this paper is that the different events categorized within the study displayed different physical characteristics, with

Nordbord hamstring testing long sprint athletes demonstrating a profile of significant asymmetry between the right and left limbs. This was a profile not seen in field or short sprint athletes. Again, this highlights the importance of understanding the cohort of athletes that you are working with, as it could be argued that by trying to correct an asymmetry in long sprint athletes you are placing injury risk reduction ahead of performance maximization.

It could also be proposed that these athletes actually require an asymmetry to prevent against injury due to the asymmetrical nature of their sport (running a circular track). This is a fine balance and one that must be understood and fully discussed with the coach and the athlete. There may then be an agreement in place surrounding monitoring of what might be deemed an “acceptable” asymmetry.

The final key finding of this paper is that those athletes with a previous injury showed no significant difference in eccentric knee flexor strength compared to those without a hamstring injury history. This is an important finding as it demonstrates that with good quality rehabilitation and training athletes are able to restore desirable characteristics such as eccentric knee flexor strength. However, further work needs to be done to see if this is the same for other risk factors such as timing of muscle activation and fascicle length.

SUPPORTING REFERENCES
1. Eduoard, P., Branco, P. & Alonso, J-M. (2016). Muscle injury is the principle injury type and hamstring muscle injury is the first injury diagnosis during top-level international athletics championships between 2007 and 2015. British Journal of Sports Medicine,
2. Bourne, M.N., Opar, D.A., Williams, M.D. & Shield, A.J. (2015). Eccentric Knee Flexor Strength and Risk of Hamstring Injuries in Rugby Union: A Prospective Study. American Journal of Sports Medicine, 43(11), 2663-2670.
3. Opar, D.A., Williams, M.D., Timmins, R.G., Hickey, J., Duhig, S.J. & Shield, A.J. (2013). A novel device using the Nordic hamstring exercise to assess eccentric knee flexor strength: A reliability and retrospective injury study. Journal of Orthopaedic and Sports Physical Therapy, 43(9), 636-640.