Various essays dealing with information ranging from the brazenly false to the half truth to facts distorted for conversion into commercial enterprises have appeared under the subject heading “Misinformation Engineering” (at www.sportivnypress.com). In many cases the authors or subjects of these essays sport a list of initials after their names as if to proclaim they occupy the high ground of the highly educated; their knowledge is certified; unassailable. Therefore, it is rather easy to demonstrate the initials one touts are inversely proportional to knowledge and/or competence in the claimed endeavor.
Figure 1. It is generally outside the purview of the many who prescribe such injury prevention exercises as the one depicted on the left in figure 1; to establish a plausible cause and effect relationship between these types low coordination resistance exercises and susceptibility to injury. The professional football player on the right; holding his left hamstring; injured on the football field; is the self same athlete doing the so – called “nordic curls” in the picture on the left; an exercise touted to prevent such calamities.
Since an essay on the subject of hamstring injury (“Hamstring Injury in Sport”, Charniga, A.) will appear at www.sportivnypress.com the emphasis of this essay are various exercises touted to prevent hamstring injury; especially presented and promoted in online format. Generally, they are touted to prevent hamstring injury. There are way too many of these YouTube videos to cover in a meaningful way so the emphasis will focus on some of these videos as well as research which proclaim the injury prophylaxis of the “nordic curl”. Why this exercise is so designated is unclear. Even if some Nordic person thought of this protocol; the idea is neither new nor unique.
First, a little history is in order. Another popular exercise touted for strengthening hamstrings and even guteus maximus; which has been around for a long time; is the so – called ‘glut ham raise’. Machines, benches and such, of varying design to allow one to exercise in this manner, have cropped up in the fitness equipment market. The origin of this exercise concept is the USSR. This exercise, also called back hyper-extension was popularized by Olympic and world champion Vassily Alexseyev. Alexseyev liked using this exercise to strengthen his back so much he often included it in both his workouts when he was training twice a day.
This exercise along with sit – ups over a vaulting horse with discs behind the head and an allowable large arching of the back were valuable assistance exercises during the latter days of the press era. Both of these exercises developed the back; even the sit ups; because the erector muscles were activated as the athlete arched into the low position of the sit up. Alexseyev performed the back exercise exercise with barbell behind the neck, only until the back aligned with the legs – i.e., without flexing the legs.
Figure 2. Two versions of the same exercise. On the left (Kono photo) the ankles are supported by padded supports affixed to wall bars; allowing little flexing of the knees. Another version of the same exercise depicted on the right shows the athlete’s ankles are fixed to straps attached to a board covering the wall bars. This version with straps facilitated more flexing of the knees with foot pressure against the flat surface of the board. Hence, what was a back exercise could be touted to include more muscles such as knee flexors and gluteus.
Some Soviet weightlifting gyms just fastened straps to a wall for the feet; see depiction on right in figure 2. The knees could be flexed considerably more with pressure from the feet against the wall with this manner of fixing the feet. This version was brought to the attention of western coaches in a series of articles authored by yours truly; after two visits to the USSR, one in 1979; the other in 1983; and, actual experimentation.
Subsequent to the articles a commercial version of a ‘glut ham’ bench appeared on the scene in the USA; mid 1980s. The effect of this innovation is obvious to this day; as this type of device is in wide use in gyms; from university, college, high school, professional teams to commercial fitness clubs. The idea that the knee flexing action peculiar to this exercise would benefit athletes other than just weightlifters; has its roots in textbooks. Principles of anatomy and kinesiology are the sources which have been employed to ascertain which muscles are involved; then of course, the benefit from such exercise is projected to the field of play: court or field.
However, logical this may seem; this is not a good way to train the muscles of the so – called posterior chain for the dynamics of running, sprinting, cutting and otherwise complex dynamic maneuvers on the court or field. Apparently, this exercise has fallen out of favor in popularity somewhat; to be displaced by the so – called ‘nordic curl’; this, even though the mechanics of the two exercises are practically indistinguishable.
However, a number of inadequacies have been ignored in the rush to adopt the latest fad with these exercises variants for hamstrings; along with others:
/ strength training is angle specific; muscles stressed through a certain joint range of motion are affected by the training mostly within those joint ranges of the movement; a significant “spill over’ of strength does not transfer throughout the motion of the joints involved;
/ the strength developed from exercising muscles can vary with the disposition of the body, i. e., training quadriceps or hamstrings while seated, for instance, will not fully transfer to these muscles in other postures such as standing;
/ the greater the specificity the strength training to the actual dynamics of the sport such as sprinting for instance; the higher the training effect; training leg muscles with machines, lying or seated on benches and so forth, are sorely lacking in specificity;
/ the training effect of exercising muscles in the dynamic regime (concentric contraction) or eccentric or isometric will be higher for the specific regime of work: isometric strength will improve most from isometric training; eccentric strength from eccentric training, and so forth;
/ the prevailing belief rests on the assumption strength, whether eccentric, concentric or isometric is the main factor in injuries like hamstring pulls; if the muscles were only stronger, especially eccentrically; susceptibility to injury would lessen; so the thinking goes;
/ a technological/mathematical evaluation to solve your problem; which happens to be for sale (sans experience) is the answer.
(from Charniga, 2019) “For example, another ‘tech answer’ to the proliferation of lower extremity injuries in the NFL”:
(https://www.cnbc.com/2020/02/29/tech-company-sparta-science-combats-nfl-injuries-with-ai.html) purports to “identify foot and knee issues”, “to identify soft tissue problems usually blamed for hamstring injuries in sports”; with computer analysis of vertical jumps and so forth. Teams can pay tens of thousands of dollars for this information.
The NFL alone began the 2018 season on 9-2-2018 with a reported 74 hamstring injuries. In 2019 the NFL had a reported 43 hamstring injuries by August 2, 2019; 41 on October 12, 2019 and 36 on January 2, 2020. At any given time throughout the 2018 & 2019 seasons there are at least 25 hamstring injuries. Go figure!” (Charniga, A.).
The point of citing the references to NFL as just one example; despite (or because of) special gym exercises and/or tech solutions; hamstring injuries from running and sprinting are still very much commonplace.
The hamstrings (and others) function as antagonist muscles at the moment most agree injury occurs which is in the late swing phase of running and sprinting. That is to say, according to Kuznyetsov (1975) these muscles are subjected to a “passive” phase followed by an active phase which is “braking” the leg up until ground contact:
“It was established that the antagonists are passive only in the first half of a movement when significant inertia is developed in ballistic movements. Then the movement proceeds under the influence of inertia against a background of the rising tension of the antagonists which are “braking” the movement. In this instance the antagonists are working in a strictly sequential manner.” V. Kuznyetsov, 1975
The hamstring and other knee flexors rapidly switch function as agonists to antagonists and vice versa, during sprinting. They are ‘braking” the thigh – shin – foot leg spring in the late swing phase. It is at this moment most say injury occurs as the leg is straightening just before ground contact. The hamstrings and other knee flexors according to Kuznyetsov, are “passive in the first half of the movement”, i.e., relaxed stretching. Most of the hamstring literature; where one finds exercise prescription like ‘nordic curls’ leg curls on bench, ham glut raises or eccentric forms of these movements feature prolonged tension; either a concentric to eccentric or eccentric; inconsistent with what actually occurs in the late swing phase of running and sprinting.
Figure 2. Hamstring stretch exercise typical of the functional training methods.
Possible Effectiveness of Exercise Variants
It is very likely the continued search for a magic bullet, i.e., hamstring injury prophylactic exercise(s) and protocols; has been driven by myth; a quadriceps to hamstring strength ratio. The long held belief has been the optimum ratio hamstring to quadriceps strength should be 60%.
This is a fallacy of logic for several reasons.
First, the ubiquitous testing and/or measuring hamstring to quadriceps ratio seated; for the reasons already spelled about above; is a non – predictive as to how an athlete’s muscles will function when running, sprinting or various rapid evasive or pursuit manoeuvres in an upright posture. All of the muscles of the lower extremities are active in those endeavors; not just muscles at the knee.
Second, measuring an athlete’s muscles with a isokinetic leg extension/curl, i.e., simple, controlled flexion and extension; as this is most often done has no bearing on the self same muscles ability to function as a spring like mechanism; which they must in running, sprinting and the like.
Third, muscles measured are isolated with two (knee and ankle) of the three ‘choke points’ fixed; which is not at all characteristic of dynamic sports.
Fourth, the measurements do not specify other muscles are being measured in tandem; just an assumption hamstrings to quadriceps ratios are being determined. In point of fact, even a simple glance at the people doing ‘nordic’ curls in figures 1&3; it is obvious other muscles are involved – especially gastrocnemius.
Fifth, even if other bi – articular muscles such as gracilis, gastrocnemius, sartoris are discounted; the seated leg curl doesn’t involve all the muscles in the group. (see Tesch 1993). According to Tesch (1993) the biceps femoris is not “involved in seated leg curl. Yet this muscle is most frequently cited as the site of hamstring pulls:
“gracilis, sartoris, semitendinosis show marked involvement in this exercise. Surprisingly, the biceps femoris is not”. Tesch, P., 1993
Consequently, the academic crowd; whom employ ultra – expensive isokinetic machines to determine hamstring to quad ratios don’t even know which muscles they are measuring.
Sixth, in addition to the points made above of the deficits of lab type testing; several authors have shown the tibialis anterior; the attachments of which do not even cross the knee; but, by means of inertia coupling (Zajac, 2002) can be knee flexors are the single most active of a sprinter’s muscles.
Potential versus actual prophylaxis benefit of various exercises rest with the various points made above about the specificity of the exercise performed in the gym to the actual dynamics on the field. Some research cited (You Tube videos and the like) does not compare effectiveness between Nordics and standard leg curls on a bench or commercial machine. Especially: the relative contribution of the muscles involved in flexing and acting as antagonists in ‘braking”: See Tesch, 1993
In most, if not all prophylactic exercises prescribed, one or more of the three (3) ‘choke points’: hip, knee and ankle joints are fixed in the exercises; which is not at all specific to running; as all three are moving.
One extraordinary salient factor in the entirety of the hamstring injury conundrum is the near universally perceived need for special strengthening exercises for the hamstrings; because, it is implied they are somehow ‘weakened’ from running and need of special strength training to ‘catch up’ to the quadriceps; this despite the fact runners, sprinters, jumpers and so forth use all the muscles of the lower extremities to run fast, jump for height and distance, execute evasive cutting maneauvres, and so forth.
Furthermore, various papers with EMG diagrams of major muscle activity in sprinting and running show Tibialis Anterior is the most active; even though the attachments this muscle do not cross the knee. Typically, hamstring injury etiology papers make no mention a possible role this muscle among other lower extremity muscles may have in predisposing one to hamstring pull.
Some common exercises touted for prophylaxis of hamstring pulls:
/ leg curls seated on a bench or lying face down: simple contraction of knee flexors against two fixed joints: hip and knee. Activation of hamstring group is uneven: biceps femoris not even activated in the seated on a bench version; biceps femoris, semitendinosis, sartoris and gracilis only moderate use in lying face down version; involvement of gastrocnemius not even recorded. (Tesch, 1993). Training occurs in different postures than running or sprinting: seated and lying face down lack specificity.
/ standing leg flexion with pulleys: correct posture; relative inclusion of muscles in knee flexor group uncertain; involvement is primarily simple muscle contraction which is only partially consistent with running and sprinting;
/ deadlift with slight knee bend: prolonged tension over varying range of motion without fully straightening the knees; likewise lacking a specificity as tension is continuous;
/ nordic curls are the current fad gym exercise touted to prevent hamstring injuries by strengthening these muscles.
Numerous videos promoting this fad exercise lack evidence demonstrating this movement is actually a hamstring injury prophylactic. Since this is the current fad and many features ‘nordic curls’ share in common with the other knee flexion exercises; it either disproves the effectiveness of the ‘nordic curl’; which is very likely; or, it proves it is just as ineffective as they are; also very likely.
Consider just one such video which has had more than 500,000 views:
https://www.youtube.com/watch?v=6NCN6kOagfY 566,000 views
Figure 3. Video author demonstrating ‘nordic curl’ with obvious heavy involvement of gastrocnemius muscles.
The first, and perhaps the most glaring insufficiency of this exercise as it is demonstrated in the video link above: is the slow grinding nature of the knee flexion; including and especially the slow eccentric portions. The slow contraction and especially slow eccentric segments are inconsistent with the dynamic functioning of these muscles in running; especially sprinting.
The second insufficiency: knee and ankle joints are fixed. These ‘choke’ points are not fixed in running and sprinting.
The third insufficiency: the contraction of the gastrocnemius and other ankle muscles in this exercise; obvious from the video and the photo in figure 2; are shortening to flex the knee; which from the standpoints of personal experience and reasonable logic; can result in negative consequences; since the muscles should be trained to lengthen, stretching along with hamstring and other bi-articular muscles. Furthermore, the muscles involved in the lengthening segment should not apply slow heavy resistance as the leg spring straightens prior to ground contact.
The fourth insufficiency: the muscles which cross two ‘choke points’: knee and ankle are training to shorten not to lengthen inconsistent with the actual dynamics of running and sprinting.
Various exercise suggestions can be found in the following essay: “Hamstring Injury in Sport”, www.sportivnypress.com
/ Charniga, A., “Hamstring injury in sport”, www.sportivnypress.com
/ Charniga, A., “Muscles of the shank, movement of the shin & susceptibility to lower extremity injury”, www.sportivnypress
/ Charniga, A., “Nine Straps” 2020 www.sportiCharniga, A., “Muscles of the shank, movement of the shin & susceptibility to lower extremity injury”. 2020 www.sportivnypessvnypess
/ Zvijac, J., Toriscelli, T., Merrick, W., Papp, D., Kiebzak, G., “Isokinetic Concentric Quadriceps and Hamstring Normative Data for Elite Collegiate American Football Players Participating in the NFL Combine”, National Strength and conditioning Association journal, :28:04: April 2014:875 – 883
/ Kuznyetsov, V.V., Special Strength Training For Athletes, Soviet Russia, 1975; Translated by Andrew Charniga
/ Tesch, P., Muscle meets magnet 1993
/ Zajac, F.E., “Understanding muscle coordination of the human leg with dynamic simulations”, J. Biomechanics; 35:1011-1018:2002