Can the hamstring strength assessment be improved?

Innovative Hamtech technology


The question is legitimate in view of recent publications. I would like to draw your attention to the fact of not generalizing too quickly the conclusions of studies relating to the measurement of eccentric force of the knee flexor and the risk of hamstring injury! Indeed, one should not make a study say more than what it is supposed to be able to say. I will try to explain myself in this article.

Point number 1: Do not make a shortcut too quickly when an article concludes that their results do not support the use of force of the eccentric knee flexor in managing the risk of hamstring injury.

Point number 2: Ask yourself the right questions: what summer was the protocol and which variable was used? Then ask yourself what are the limits, to better understand their conclusion and not to generalize.

Point number 3: Can the limits be lifted and if so could this change the conclusion?

We will take an example to better understand where I am coming from:

Let’s look together at a recent article in the Scandinavian journal Medecin & Science in Sports: 2019 Association between eccentric knee flexor strength and hamstring injury risk in 185 elite Gaelic football players I would like to point out that I do not question the above study, on the contrary their results are to be taken into account, but wish by an example to show that we should not conclude more than what is mentionned.

In this study, they conclude that there is no correlation between the eccentric force of the knee flexors and or the inter-leg imbalance with the history of injury or new hamstring injury.

Point numero 1

In this study, they conclude that there is no correlation between the eccentric force of the knee flexors and or the inter-leg imbalance with the history of injury or new hamstring injury.

point numero 2

These results were obtained with an eccentric force measurement protocol during a Nordic bilateral hamstring exercise to body weight. The variable used is the absolute peak of force. An important point to note is that the force results come from a single measurement at an instant t (upstream of 12 weeks of observation).

limit 1: unit of measure


The first of the limits that I will discuss and use the variable eccentric force in absolute. Indeed, this is a real problem when we make intra-group comparisons, here is an example illustrating this limit:

player A Fmax = 350N, (weight 85kg) or 4.11 N / kg
player B Fmax = 350N, (weight 75kg) or 4.66 N / kg

>> in F_absolute we conclude that player A = B
>> in F_relative we conclude that B> A with 12% difference! …

eccentric force measurement with a classic NHE ergometer?

Another limit: the use of a non-standardized force measurement which we can subdivided into 3 different limits (Non control): body weight, muscle length, speed of movement which we will see below more in detail:

Limit 2: Body weight


NHE bodyweight exercise may not be enough for some athletes and those who find themselves therefore undervalued.

limit 3: muscle length

part 1: knee angle

Not knowing the knee angle at the peak of force measured poses a problem of inter and intra subject comparison, knowing the impact of the force-length relationship on the expression of the force measured.

part 2: hip angle

Not knowing the hip angle at the peak force measured poses a problem of inter and intra subject comparison, knowing the impact of the force-length relationship on the expression of the evaluated force.

limit 4: movement speed

angular velocity

The non-control of the speed of movement poses a problem knowing that it influences the force returned.

After having seen the limits of a non-normalized measurement, we will discuss the limits of the bilateral condition, a mono-articular condition and finally the limits of the single measurement at an instant t:

limit 5: condition leg


The fifth limit that we can make is the evaluation in bilateral condition. Indeed, we can say in the light of our first pilot results that the bilateral condition is much less discriminating against the real deficit of force and can even miss it. We regularly observe this during our measurements and consider the unilateral measure as the most appropriate to discriminate a deficit. Here is an example recorded during one of our study where one of the subjects (player A) presented a discomfort (tip to the hamstrings) before taking the tests, I will let you see the forces in bilateral and unilateral conditions:

limit 6: Movement


The sixth limit that I will mention is that of the mono-articular condition used for risk discrimination purposes. I will explain myself on this subject, the fact of not measuring the force of the flexor of the knee in the zone of muscle length said to be at risk poses a problem. In fact, during the Nordic exercise, it is requested not to bend the hips and to stay the bust straight throughout the exercise. This corresponds to a so-called mono-articular movement which is not a natural movement, in any case which is not that of the late swing phase during the sprint. Knowing that the latter is identified as the moment when the eccentric contractions in the hamstrings reach their maximum and pose a problem in the occurrence of injuries, we can imagine that it is wiser to measure the eccentric forces in such a position. , which several studies also relay. A unilateral and bi-articular movement will therefore be preferable if we want more specificity and more discriminating power.

limit 7: test frequency

single measurement

Seventh limit to finish, I will discuss the limits of a single measurement not monitored over time. This poses a problem, in fact, because the notion of fatigue, which is an important risk factor for injury, cannot be taken into account. In order to show the limits of the single measurement, here is an example that we can commonly encounter: a player who presents during the test high values ​​of force who does not alert but who will accumulate fatigue at a time, who will cause an abnormal drop in force and give the appearance of an injury. If we consider the result of the single test we will conclude that the force is not a good indicator of the risk of injury !!! So beware of the hazardous shortcut, as you will have understood the conclusion would have been its opposite if the strength were monitored regularly. The measured fall in force would have allowed us to conclude that force is a good indicator of the risk of injury. Regarding the relation between the single test and the history now it is different. Unlike the study cited above, our work shows a good relationship between strength and previous injuries. This using our protocol and not that of the study. Note: we consider that the test at time t can also be an indicator of the risk of injury to some extent, since a player who does not have a minimum strength should be considered at risk. For example on the leftmost red dot shown in the graph below presented 2 hamstring injuries during the 3-4 months post test.

rapport de test
radar hamstring

Note: the test used above is an isometric test and not eccentric, in order to make the passage of the test as transparent as possible in the pre-season. This is part of the prevention strategy proposed by Human Kinematic.

point numero 3

« can the limits be lifted » yes « and if so, could that change the conclusion? » Yes

LimitErgometer Hamtech
1. Unit of measure: AbsoluteNot limited
2. Body weight: Intensity?Not limited
3.1. Length muscle: knee angleNot limited
3.2. Length muscle: hip angleNot limited
4. Movement speed: angular velocityNot limited
5. Condition leg: bilateralNot limited
6. Movement: mono-articularNot limited
7. Test frequency: single measurementNot limited

I hope that you now understand better the importance of the protocol used and how to go beyond certain limits mentioned here thanks to our innovative technology Hamtech.

Human Kinematic work in this direction is my all energy in research into injury prevention for performance. This article is an example of what Hamtech technology, which has many other innovations (not discussed here) can bring to the field. See you soon on twitter to be informed of the latest news.

This article is a real reflection on the measurement of force and offers a new methodological framework to scientists, technical and medical staff to optimize their work. The article was written in the form of a blog but could take scientific form soon because of its interest for the medico-sports world.

Author: Jean-Patrick GIACOMO

Msc, Human Kinematic

Fichier:Twitter Bird.svg — Wikipédia
@humankinematic and @jp_giacomo