“The development of the HRIG”

It is now widely accepted that hamstring Injuries are on the increase, in the premier league, in soccer throughout the world and also in Gaelic football in Ireland (Sky Sports 2023; Ekstrand et al., 2022; Roe et al., 2018). These are sports in which players are generally expected to be mobile and proficient in terms of running capacity to implement particular game plans for tactical manoeuvring. The rate of HSI in Gaelic football is 1.5-2.6 times higher than the rate of HSI sustained in professional soccer (4.77 & 0.51 injuries per 1000h) (Ekstrand et al., 2016), rugby (5.6 & 0.27 injuries per 1000h) (Brooks et al., 2006) and American football (2.7 & 0.47 injuries per 1000h) (Elliott et al., 2011). Sports which involve both running and kicking placing players at increasing levels of risk.

Running in particular is the main mechanism of injury at high speed and accounts for 48%-81% of all hamstring injuries (Roe et al., 2018; Wilson et al., 2007; Askling et al., 2013). HSI during injury generally occurs in either late swing phase or early stance (Chumanov et al., 2011, Chumanov et al., 2012, Orchard et al., 2012, Schache et al., 2010, Yu et al., 2008, Heiderscheit et al., 2005, Schache et al., 2009) as this is where the greatest stress is placed on the hamstrings. The most commonly injured portion is the biceps femoris long head (BFlh) and it is required to tolerate between 10.5-26.4 N.Kg^-1(Kenneally-Dabrowski et al., 2019), reaches 110% of its maximum resting length and has the greatest excitation levels at this point (Thelen et al., 2005) (Table 1).

We know that there are a large number of rick factors predisposing players to various levels of HSI and one particular study as proposed a biomechanical model of HSI risk (Bramah et al., 2023). They outline a number of risk factors in relation to applied strain and hamstring capacity (Figure 1). Coupled with this some interesting research, as led to the development of a new product the, HRIG, which specifically assess’s the capacity of the hamstrings in relation to late swing and early stance.

Emanating originally from the start of a PhD some 7 years ago at Liverpool John Moores University and with some further research and product development from a sports engineering team at Sheffield Hallam University they have highlighted and researched the area around late swing and early stance. At the onset of the research it was concluded that nordic fall eccentric hamstring strength levels over the season were not predictive of hamstring injury occurrence in Gaelic football players and now this is widely accepted, this has limited value (Mc Intyre et al., 2021; Opar et al., 2021;Van Dyk et al., 2017). The research then delved into the area of the mechanism of injury (sprinting) and developed a test which simulated late swing and early stance (Figure 2).

They developed two test positions 1) a bilateral double leg test and 2) a unilateral single leg test. Bilateral Isometric strength assessment. Test 1 involved placing the knees of each leg against a pad, with the ankles (malleoli) directly below the mid-point of the knee and the feet were flat on the floor, but lifted slightly to ensure there is no ground contact during. The athlete is in a seated position to replicate the approximate limb posture observed in the late swing/early stance phase of running (30⁰ of knee flexion ). The test involves a upright trunk and isometric peak torque/force is defined and recorded as the highest recorded output across three repetitions between 3-5 seconds.

The second test again involved a upright posture however the un-tested limb/hip was extended into  20⁰ of hip extension. The test begins by instructing the participant to stay in a upright position, unweighting the body to perform a maximal repetition for 3-5 secs by pulling the ankle restraint horizontally for 3-5 secs. The opposite limb and the maximum score recorded. All data is relative to body weight and converted to torque to also normalise for limb lengths.

These test positions possess moderate to high levels of both intra and inter relater reliability. This is due to the isometric nature of the contraction and the repeatability and reliability of the setup and angles involved. Initially isometric testing showed a moderate to high reliability ICC (CI 95%) of 0.89 (CI 0.79-0.94) with the typical error of 7.7 % (6.9-9.7%) (Mc Intyre et al, 2022). Since then further research has indicated high reliability for both test positions. The bilateral testing on the HRig system has showed high inter-rater reliability ICC (CI 95%) of 0.86 (CI 0.74-0.92) with the typical error of 19N (14-27N). Unilateral isometric testing showed high Interrater reliability ICC (CI 95%) of 0.92 (CI 0.85-0.96) with the typical error of 23N (18-34N) (Mc Intyre, 2023)

Following on from this Bilateral testing on the HRig System also showed a high intra-rater reliability ICC (CI 95%) of 0.93 (CI 0.89-0.97) with the typical error of 20N (16-27N). While unilateral isometric testing showed high intra-rater reliability ICC (CI 95%) of 0.93 (CI 0.89-0.96) with the typical error of 22N (18-30N) (Mc Intyre et al., 2023).

These levels of reliability are important to minimise the measurement errors associated with testing and also increase the ability and sensitivity of the device for injury association, both from a prospective and retrospective injury perspective. These test positions have indicated that these positions of testing better identifies those with residual strength deficits following hamstring strain injury, compared to nordic fall eccentric strength testing (Mc Intyre et al., 2022). Furthermore they also identify deficits in players with previous HSI and those who sustain future HSI during the playing season (Tables 4 & 5) (Mc Intyre et al., 2024).

From a performance perspective the device has also been developed as a rehabilitative and strength training tool. Targeted isometric strength training can be achieved safely and progressively involving both pulling/pushing and quasi isometric muscle function. Sets with various repetitions of these modes of strength training can be applied whereby between 400-700N can be applied specific to late swing and early stance.

Moreover further research has indicated that pushing and quasi isometric EMG activity on the HRIG is similar to the EMG activity for the Biceps Femoris long head. These test positions elicit BFlh EMG activity of between 77%-100% of EMG experienced whilst running at 16 km/hr (Mc Intyre et al., 2023).

Finally some new research has now indicated from a performance point of view that targeted hamstring program significantly improves unilateral isometric strength (McIntyre et a., 2024). Given the device has previously been highly correlated with biceps femoris fascicle length this serves as useful measure of protecting and dosing players in terms of reducing prospective and future injury.

With the large volume of games in modern day and professional sport one of the challenging aspects of this high performance environment is identifying a window in which it is safe to dose players, from a strength perspective. The HRIG allows players to dose effectively (post training) and with a high degree of specificity in a time effective manner to positively affect the availability of a player or squad. Furthermore, isometrics are generally associated with low levels of delayed onset of muscle soreness which players prefer as a result. Finally, performance teams have limited contact time with players and again in this modern day environment, quick, effective and meaningful data in relation to hamstring injury is imperative to maximise player availability.

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REFERENCES

McIntyre M, Reilly C, Lake M, Baltzopoulos B. Eccentric hamstring strength in club Gaelic footballers. Proceedings Int Soc of Biomechanics in Sport 2021; 956-959

McIntyre M, Reilly C, Lake M, Baltzopoulos B. Reliability and bilateral strength imbalances of a new isometric test to identify previous hamstring strain compared to eccentric strength. Proceedings of Int Soc of Biomechanics in Sport 2022; 423-426

McIntyre M, Reilly C. Isometric strength deficits exist in players with previous and future hamstring strain injury. Proceedings Isokinetic conference 2024 (Under Review)

McIntyre M. Hamstring muscle strength assessment and the association with injury risk in Gaelic football. Unpublished Phd, Liverpool John Moores University 2022.

McIntyre M, Reilly C. Targeted hamstring program significantly improves unilateral isometric strength. Proceedings Isokinetic conference 2024 (Under Review)

McIntyre M, Reilly C. The HRIG, isometrics and EMG in hamstring rehabilitation. Proceedings Isokinetic conference 2023.

McIntyre M. The HRig manual. 2023; 3-4