Previous posts discussed the physiology behind muscle contraction and the role of neuromuscular recruitment. With the fundamentals under our belts we’ll discuss the current evidence for nordic curls contributing to injury mitigation. This has been mostly studied in soccer players and hamstring strains. However hamstring strengthening in general is key for optimal performance in most sports and is crucial in rehabilitation of knee injuries. In this post we will focus specifically on hamstring muscle injuries.
While hamstring force production is a key consideration in a variety of knee injuries and rehabilitation scenarios, the most obvious is the injury to the hamstring itself. A quick (I promise) pathophysiology review follows. Muscle strains occur when muscles are stressed beyond their ability to stretch and contract. They can be categorized into grade I, II, and III strains which indicate increasing amounts of injury and location of injury.1 These injuries can theoretically occur at any site in the muscle but generally occur at the musculotendinous junction. That is, they occur where the muscle tissue blends into the tendon which anchors that muscle to the bone. A grade III strain is a muscle rupture and not good news because they usually require surgery.
Hamstring injuries occur most frequently in sports involving sprinting when the hamstring contracts to decelerate the leg. As outlined in a previous post, this is where the muscle is most vulnerable biomechanically due to the relatively high strain placed on the muscle fibers in this position combined with the powerful eccentric contraction. Other injury mechanisms are possible and more prevalent depending on the sport but running injuries are what we will focus on today. These injuries are very common, frustrating, and even with a relatively short recovery time, they can still derail a season. Because of their impact on sports participation, these injuries have been studied extensively and it just so happens that the nordic curl has been a big part of the literature on this topic. So, with the solemn understanding that there is no way to truly guarantee injury prevention, we are going to briefly wade hamstring-deep into the literature on hamstring injury prevention and nordic curls.
Hamstring injury “prevention” has been studied extensively in running, sprinting sports but particularly in soccer players. Part of this led to the development of the FIFA 11+ injury prevention program. Though it sucks to admit, we really don’t have a complete understanding of how to prevent injuries. Lots of study has been devoted to establishing causation between use of specific strategies and reduction of hamstring injuries but ultimately there are many factors predictive of hamstring injury. Quadriceps:hamstring torque ratio of less than 60% may predict injury, as may significant interlimb differences in eccentric or concentric hamstring strength. Some data suggests that a greater than 15% difference in hamstring strength between legs was associated with injury and that for every 10% improvement in eccentric hamstring strength there was an 8.9% reduction in injury rates.1 Interestingly several studies have used the nordic hamstring curl as a test of eccentric hamstring strength. So how does the nordic curl fit into prevention of hamstring injuries?
In 2017 the British Journal of Sports Medicine published a systematic review and meta-analysis (a big study that pools and analyzes the data from many other studies) proclaiming that the Nordic hamstring exercise halved the rate of hamstring injuries when used in injury prevention programs.2 Another 2017 systematic review and meta-analysis in the journal Sports Medicine reported similar findings.3 This ushered in what might be called the “nordics for everyone” era. With such powerful findings, why would we not utilize nordics for injury prevention? As it turned out, when researchers went back and scrutinized the studies included in the meta-analysis, they found that the quality of the studies used to draw the conclusion that nordic curls halve the rate of hamstring injuries, was in fact insufficient to draw those conclusions.4 So what does this all mean? Unfortunately, we can’t just use nordic curls and say with certainty that they cut hamstring injury rates in half, but that doesn’t mean they aren’t useful, or for that matter an awesome exercise. This also, doesn’t mean that hamstring strength or mobility deficits aren’t contributing factors to hamstring injury. Part of what is currently unclear is whether nordic curls specifically, were responsible for injury reduction rates since they were often utilized in conjunction with other exercises. That doesn’t mean that getting the hamstrings stronger in a properly implemented program for athletes who need it won’t help reduce injury risk, we just can’t say how much or guarantee “injury prevention”.
If we identify hamstring weakness as a limiting factor in someone’s performance or rehabilitation, nordic curls can be a great tool to remedy that under certain circumstances. “What are those circumstances?” you ask, great question! If someone wants to get their hamstrings stronger and be a badass who impresses all of their friends, then nordics are a great option (Seriously, who isn’t impressed by a full nordic?). Part of what makes nordics a great choice comes down to how they get people stronger overall because they provide such good bang for buck per rep. Like we covered in another post, high central drive is needed throughout the entire exercise and, unless you are freakishly strong, you generally have to work really hard using the hamstring and entire posterior chain to complete even just a single rep to your end-point. This high relative difficulty makes nordic curls rather taxing but good at promoting the strength adaptations we are often looking for. Additionally nordics are an eccentric-type exercise, typically maximal or near maximal for most people, especially untrained individuals. Assuming you are routinely hitting that end range failure point frequently enough and without correct form, you can be pretty sure that if it feels hard, it is hard enough to make you stronger. All that said, effective programming of nordics is vital for success and that means respecting the inherent difficulty of the exercise and therefore programming it properly.
So while we shouldn’t consider nordic curls the end-all-be-all of hamstring injury prevention, or any injury prevention for that matter, they do have their place in a well designed strength and conditioning or rehabilitation program. Proper use of the nordic curl will definitely get you stronger, with the nordstick they are low cost, and psychologically it is just so rewarding when you hit your first full range of motion repetition. Next up, some nordic programming considerations. Until then, happy curling!
-Dr. Devin Cervani
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Wing, Chris MSc1; Bishop, Chris MSc2. Hamstring Strain Injuries: Incidence, Mechanisms, Risk Factors, and Training Recommendations. Strength and Conditioning Journal: June 2020 - Volume 42 - Issue 3 - p 40-57 doi: 10.1519/SSC.0000000000000538
Van Dyk N, Behan FP, Whiteley R. Including the Nordic hamstring exercise in injury prevention programmes halves the rate of hamstring injuries: a systematic review and meta-analysis of 8459 athletes. Br J Sports Med. 2019 Nov;53(21):1362-1370. doi: 10.1136/bjsports-2018-100045. Epub 2019 Feb 26. PMID: 30808663.
Al Attar WSA, Soomro N, Sinclair PJ, Pappas E, Sanders RH. Effect of Injury Prevention Programs that Include the Nordic Hamstring Exercise on Hamstring Injury Rates in Soccer Players: A Systematic Review and Meta-Analysis. Sports Med. 2017 May;47(5):907-916. doi: 10.1007/s40279-016-0638-2. PMID: 27752982.
Impellizzeri FM, McCall A, van Smeden M. Why methods matter in a meta-analysis: a reappraisal showed inconclusive injury preventive effect of Nordic hamstring exercise. J Clin Epidemiol. 2021 Dec;140:111-124. doi: 10.1016/j.jclinepi.2021.09.007. Epub 2021 Sep 11. PMID: 34520846.