During a sprint, a strike, a sudden change in running direction or even during a physical contact, the simultaneous contraction of the quadriceps femoris and the hamstrings stabilizes the knee joint. Fatigue alters the capacity to rapidly produce force to protect the joints.
A deficit in muscle activation during the first 100 milliseconds after a physical contact is key and associated with a potential increase in injury.
Frequent cruciate ligaments and hamstrings injuries
Our previous articles introduced the problem, the cruciate ligaments and hamstrings injuries are the most prevalent and the most serious in professional soccer players (2). During a sprint, a strike, a sudden change in running direction or even during a physical contact, the simultaneous contraction of the quadriceps femoris and the hamstrings stabilizes the knee joint and prevent the excessive constraints that could be applied on it. The cruciate ligaments and hamstrings injuries are associated to a misbalance between the force produced by the quadriceps femoris and the hamstrings (3).
Fatigue induces a decrease in knee stability
Fatigue induces a deficit in muscle force which in turn induces a decrease in knee stability. The quadriceps femoris, via the quadriceps tendon, the patella and the patellar tendon, stabilizes the knee on its anterior side, while the hamstrings and the gastrocnemius (calf muscles) stabilize on the posterior side. The lateral (internal and external) and cruciate (anterior and posterior) ligaments contribute to the knee stability in a structural manner. A decrease in muscle force increases the constraints imposed to the ligaments and cartilage in the knee.
The capacity to rapidly produce force: a key factor
This study confirms that fatigue induces a decrease in force, but the novelty is that, for knee stability, the deficit of force in the first 100 milliseconds is key because associated with the increase in injury risk. During landing, sudden change in direction or physical contact, it is precisely the muscle contraction during the first 100 milliseconds after the impact that determines whether there is an injury and how serious it is.
How to measure fatigue ?
It is obviously unthinkable to repeat this experimental protocol, cumbersome and complex, on each player before each match or training, to assess his risk of injury in order to adjust his physical preparation or to replace him. This is why inCORPUS® is today the only technology capable of assessing this risk, in the short and medium term (from a few days to a few months), thanks to a rapid, non-invasive and immediate method making it possible to obtain five profiles of fatigue (and three in good shape) for more informed decision making.
(1) Zhang, Q.; Morel, B.; Trama, R.; Hautier, C. A. Influence of Fatigue on the Rapid Hamstring/Quadriceps Force Capacity in Soccer Players. Front. Physiol. 2021, 12, 627674. https://doi.org/10.3389/fphys.2021.627674.
(2) Ekstrand, J.; Spreco, A.; Bengtsson, H.; Bahr, R. Injury Rates Decreased in Men’s Professional Football: An 18-Year Prospective Cohort Study of Almost 12 000 Injuries Sustained during 1.8 Million Hours of Play. Br. J. Sports Med. 2021. https://doi.org/10.1136/bjsports-2020-103159.
(3) Baroni, B. M.; Ruas, C. V.; Ribeiro-Alvares, J. B.; Pinto, R. S. Hamstring-to-Quadriceps Torque Ratios of Professional Male Soccer Players: A Systematic Review. J. Strength Cond. Res. 2020, 34 (1), 281–293. https://doi.org/10.1519/JSC.0000000000002609.