Impact induced muscle damage: Performance implications and associated timeline

Mitchell Naughton

doi:10.25907/00356

For contact-sport athletes, performance is often impaired following exposure to match-play or high-intensity training conditions. This has previously been ascribed to the negative influence of exercise induced muscle damage (EIMD) which occurs following unaccustomed or strenuous exercise and results in skeletal muscle ultrastructural damage and delayed onset muscle soreness (DOMS). However, athletes involved in contact-sports are exposed to repetitive collisions that have the potential to also result in impact induced muscle damage (IIMD). Previous research has noted that the EIMD theory may not be applicable to other forms of muscle damage including that occurring from blunt force trauma. This supports the contention that IIMD is distinct from EIMD, with an independent time course of potential changes in symptomology and associated functional capacity which remains to be elucidated. Previous studies investigating IIMD have yet to distinguish between EIMD and IIMD and as such findings may be confounded by the presence of EIMD. From the wider literature, it appears that EIMD and IIMD may be divergent with differing aetiologies, effects on functional capacity, adaptations, and interventions that may attenuate or mitigate the damage based on their mechanism of action. Therefore, the aim of the present research was to generate IIMD in the absence of EIMD and characterise the implications on performance, markers of muscle damage and inflammation, and perceptual measures in a cohort of contact-sport participants. To do so, a novel collision simulator was developed and a protocol implemented based on an amalgamation of published animal contusion research and contact-sport match-play data. A cohort of 18 healthy contact-sport athletes completed a single-group time series with measures assessed at baseline (PRE) and immediately following (POST) the IIMD protocol, with repeat testing 24, 48, and 72 h following the IIMD protocol. The collision protocol exposed the participants to 26 collisions over 80 min with an 80 kg load, which the frequency and intensity prescribed based on published match-based research. Biochemical indices of muscle damage (myoglobin [Mb]) and inflammation (high-sensitivity C-reactive protein [hs-CRP]), ultrasound assessment of oedema, 15 m sprint performance, squat jump peak power (SJ-PP), perceived mood, subjective function and soreness were assessed. Five, 10, and 15 m speed and SJ-PP were impaired for 48 h following the IIMD protocol (P < 0.01). IIMD significantly altered perceived function and mood for 24 and 48 h, respectively (P < 0.01), whilst subjective soreness was elevated from baseline for 72 h (P < 0.01) following the IIMD protocol. No change in ultrasound-derived oedema, [CRP] or [Mb] was observed (P > 0.01), primarily due to high interindividual variability. For the first time, the present research has shown that IIMD generated in the absence of exercise results in impaired performance including the ability to produce power and speed. Additionally, IIMD produced changes in systemic markers of muscle inflammation but not muscle damage, with the effect being highly variable between participants. Further, IIMD negatively influenced perceived mood, function, and subjective soreness. These changes were most pronounced in the 48 h following the IIMD protocol. In conclusion, the results of the present study suggest that symptomology and functional capacity impairment commonly attributed to EIMD amongst contact-sport participants is at least in part due to IIMD. Furthermore, the experimental protocol implemented in the present study was successful in inducing IIMD in the absence of EIMD and therefore may be a valuable model to further investigate broader aspects of IIMD, including recovery and mitigation strategies. A number of potential future research streams based on this research and the model described are discussed herein.

Impact induced muscle damage: Performance implications and associated timeline

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