A new testing and training device for hamstring muscle function

Abstract

Modern team sport context is associated with both hightraining and games demands, and consequently high in-jury rates. Thus, reducing injuries is key for performance,health and economical reasons. For example, the training,research and medical communities are dedicated to better un-derstand and thus prevent or at least reduce the number ofhamstring injuries. This technical report presents a novelfield device designed to improve hamstring muscle function viamovement patterns closer to those observed when hamstringinjuries typically occur.

Full text

A new testing and training device for hamstring muscle function
A new testing and training device for hamstring
muscle function
Jean-Patrick Giacomo 1, Johan Lahti 2, Andras Hegyi 3, Pauline Gerus 2, Jean-Benoit Morin 2
1Centre d’´
Evaluation et d’Analyse de la Performance Sportive, Carros, France,2Universit´e Cˆote d’Azur, LAMHESS, Nice, France, and 3Neuromuscular Research Center, Faculty
of Sport and Health Sciences, University of Jyvaskyla, Jyvaskyla, Finland
Technical note |Testing |Hamstrings |Injuries
Headline
Modern team sport context is associated with both high
training and games demands, and consequently high in-
jury rates. Thus, reducing injuries is key for performance,
health and economical reasons. For example, the training,
research and medical communities are dedicated to better un-
derstand and thus prevent or at least reduce the number of
hamstring injuries. This technical report presents a novel
field device designed to improve hamstring muscle function via
movement patterns closer to those observed when hamstring
injuries typically occur.
Aim. Hamstring injury is a major, unresolved, health issue in
sports (1), with two main injury mechanisms: sprint-related
and overstretching-related strains (2-4). This raises the ques-
tion of e↵ective prevention and rehabilitation protocols (5,6),
during which hamstring strength output, especially during
lengthening actions, is a central component (9,10). The aim
of this technical report is to introduce a novel device for po-
tentially further optimizing hamstrings strength training and
testing.
Description of the device
The ”Hamtech” (Fig. 1) is a passive device based on an
exoskeleton-like light frame, and instrumented with a S-type
force sensor (1000 N capacity in traction) for each foot and
a potentiometer (P4500, Novotechnik U.S., Inc) for the knee
joint. The data is recorded by an acquisition card (National
instrument, Austin, TX, USA) at 1000 Hz through a custom
program (Labview v 8.5, National instrument, Austin, TX,
USA).
The overall motion with the Hamtech is similar to the
Nordic hamstring exercise (NHE)(7,8). When performing
NHE, relatively weaker players are unable to control the move-
ment until full knee extension, which clearly limits the maxi-
mal active lengthening of the muscles. This premature ending
of the action during the NHE was an important limitation
to address since long muscle lengths represent a target zone
Fig. 1. Description of the Hamtech device main exercise modalities: Nordic
Hamstring Exercise with extended hip (NHE0), Nordic Hamstring Exercise with 90
hip flexion (NHE90), Nordic Hamstring Exercise with sprint late swing phase kine-
matics (NHE Late Swing). Note that isometric testing can be performed at any of
the possible hip-knee angles within that range of motion. See video in Supplementary
material.
for injury prevention purpose (9–11). This well-known limi-
tation of the NHE is resolved when using the Hamtech since
the frame and assistance/resistance systems allow a progres-
sive work targeting a significant range of the hamstrings force-
length spectrum (Fig. 1). The specific settings of the Hamtech
thus allow to individually set exercise intensity by setting both
the knee extension and the hip flexion angles (which are both
known to directly influence the mechanical constraint put on
the hamstrings over a typical knee flexion-extension exercise
(11). Finally, as shown in Fig. 1, this device allows enough
assistance to the motion that each movement modality can be
performed in unilaterally, which may add further value from
an adaptation standpoint (12).
Exercises and testing modalities
Nordic Hamstring Exercise with hip at 0 (NHE0). The frame
of the device brings a support to the trunk, which helps to
maintain the hip angle at 0 throughout the knee range of mo-
tion. This improvement compared to the standard NHE will
thus provide the opportunities that (i) the hip extension is con-
trolled, and (ii) the muscular work is maintained throughout
the full knee range of motion including long muscle lengths.
Nordic Hamstring Exercise with hip at 90 (NHE90). This
modality (13) has the main advantage of specifically loading
Fig. 2. Schematic analysis of hip and knee angles during a real football game
overstretch injury (game video footage analysed with Dartfish software) compared
to the NHE90 data (hip angle set constant at 90 ) and knee angle measured by elec-
tronic potentiometer. For the lesion area, the hip-knee angles with the Hamtech
closely match the estimated angles in the game situation.
Fig. 3. Schematic illustration of the sprint swing phase hip and knee angles in the
sagittal plane (computed from 240 frames per second videos at 5 and 25 m in profes-
sional academy football players), in comparison to the hip and knee angles measured
with the Hamtech device in the NHE Late Swing mode. Zero degree correspond
to no hip or knee flexion, and late swing phase is defined as the time between the
contralateral foot take-o↵and the ipsilateral foot landing.
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A new testing and training device for hamstring muscle function
the hamstrings at long muscle length thanks to the constant
90 hip flexion induced by the frame of the device and the
trunk support. This possibility is particularly interesting for
prevention-rehabilitation work (9,10). A common mechanism
of hamstring injury is by an overstretching motion with a
flexed hip and a maximally extended knee, which places the
hamstring group at particular risk due to substantial length-
ening (11). The schematic analysis below (Fig. 2) shows how
the hip-knee angles during the NHE90 exercise match the over-
stretch injury conditions (lesion grey area).
Finally, some of our data under review show higher maximal
torque produced during NHE90 than in NHE0. This is in ac-
cordance with the results of Guex et al. (11) who discussed the
clear influence of hip flexion angle on the hamstring maximal
torque capability.
Nordic hamstring exercise with sprint late swing phase hip-
knee kinematics (NHE Late Swing). This third modality is
based on the idea that a specific training of the hamstring
should include training that targets maximal torque output in
the hip-knee angle combinations (and thus associated muscle
lengths) that are close to the late swing phase of the sprint mo-
tion, which is thought to be where most sprint related injuries
happen (4,14–17). The Hamtech frame allows simulation of
the late swing hip and knee angular kinematics (Fig. 1 and
3) at two di↵erent phases of the sprint acceleration: early ac-
celeration (5-m zone) and late acceleration (top speed, 25-m
zone). As seen in the video (Supplementary material), and in
the schematic analysis shown in Fig. 3, the coordinated hip
and knee extensions throughout the late swing phase angular
sector covered using the Hamtech closely match the late swing
phase of sprinting, be it at 5 or 25m.
Furthermore, these two sub-settings of the NHE Late Swing
mode also allow a stimuli correspondence towards the specific
length-tension conditions of the sprint from the early phase (5
m) to the top speed phase (25 m). The latter mode is designed
to reproduce the hip-knee angles of top speed running, since
at that distance (i) most team sport players reach at least 95%
of their individual top running speed, and (ii) hamstring EMG
activity showed a relatively stable maximal level (18).
Measurements
In the various types of exercises shown in Fig. 1, the Hamtech
allows measurements to be performed in concentric, isometric
and eccentric modes. The ”eccentric action” is seen here as
the active lengthening of the hamstring muscle-tendon units
during knee extension. The torque output is computed from
force measurements and the femoral epicondyle to ankle sup-
port distance (standardized at 5 cm above the lateral malleo-
lus, the force sensors being aligned with the ankle support).
Isometric: maximal torque output and rate of torque devel-
opment.Assessing maximal voluntary isometric contraction
(MVIC) torque is a classic of exercise and sport science, due
to the safe, easy-to-standardize and high reliability. The
Hamtech device allows this in bilateral and unilateral test-
ing modes, with a large panel of hip-knee angle combinations
(from 0 hip-90 knee to 90 hip-0 knee, as set with the device
frame), and thus a large number of muscle length possibilities.
Fig. 4 shows a typical unilateral test where the MVIC torque
is identified at a stable plateau of a 1-s contraction. The rate
of torque development might also be measured as shown in
Fig. 4, which is typically used to estimate the explosiveness of
the hamstrings (19). This may be of particular interest when
assessing fatigue and/or in a rehabilitation context (20,21).
Fig. 4. Illustration of a typical isometric test (raw force data converted into
torque data via the measurement of the knee flexion lever arm) and the associated
variables of maximal torque and rate of torque development. The maximal torque is
computed via a 200 ms moving average.
Fig. 5. Typical angle-torque profile for a football player, during a 1RM test in
NHE0 exercise (light grey), in the NHE Late Swing mode (dark grey) and in the
NHE90 mode (black). After calibration, start and end position angles correspond the
actual anatomical knee angle (calibrated, as on an isokinetic machine) and not to the
Hamtech frame angles.
Finally, this assessment of both maximal isometric and explo-
sive isometric torque output is possible at hip-knee angles close
to those typically seen during the sprint motion (see previous
section).
Eccentric: p eak torque output. Although hamstring muscles
lengthening during sprinting is debated (22,23), the concomi-
tant hip flexion and knee extension during the sprint swing
phase place the hamstring muscle-tendon units in both length-
ening and very high force demand conditions. To our knowl-
edge, Hamtech is the only field device that allows measur-
ing eccentric knee flexion torque concomitantly with hip and
knee angles in individually maximal conditions (1RM). This
is specifically possible thanks to (i) adjustable levels of assis-
tance or resistance (ii) trunk support and (iii) support and
guidance added to the knee angle and torque measurements
throughout the angular sector covered (Fig. 5). These features
remove some limitations of existing systems (e.g. 24,25), with
which force assessment does not match some of the previously
described specificity criteria. This setting also allows conform-
ing to studies showing recommending that e↵ective hamstring
torque assessment should be accompanied by angle-torque as-
sessment (26). Some studies suggest that the key metrics in
the eccentric modality should be peak torque (especially ex-
pressed relatively to the athlete’s body mass (27,28)) and total
angular work (i.e. the area under the torque-angular displace-
ment curve (25,29)) (Fig. 5).
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A new testing and training device for hamstring muscle function
Practical Applications
The Hamtech possibly allows an accurate, progressive and
individualized training and injury prevention-rehabilitation
work. For example, in pre-season, the e↵ects of inter-season
break on hamstring function could be assessed in isometric
mode (MVIC and rate of torque development) (30) before
progressively orienting the work and monitoring towards
eccentric actions.
The modularity of the Hamtech (Fig.1) allows a progressive
and controlled increase in the mechanical load at the tar-
geted muscle lengths, which seem to be major components
of hamstring rehabilitation.
Rate of torque development might also be of value in the
return-to-sport decision (e.g. after hamstring or anterior
cruciate ligament injuries) to both ensure an e↵ective re-
habilitation and a possibly lower risk of re-injury (31).
All the aforementioned exercises and modalities can be per-
formed (i) on the training version of the device, that is
not equipped with sensors and (ii) in fatigue conditions in-
duced by sport-specific training or exercise repetitions on
the Hamtech.
Limitations
As for any ergometer, the Hamtech has a limited biome-
chanical specificity compared to the actual sprint move-
ment. However, as discussed before, its sprint-specificity
is possibly further optimized compared to existing devices
due to hip-knee angle kinematics, the late swing modality,
and the assistance-resistance setting that allows individu-
alized maximal intensity in both bilateral and unilateral
conditions.
The Hamtech is not intended to replace actual sprint train-
ing and the incomparable stimulation it represents in terms
of performance and hamstring injury prevention and re-
habilitation (32,33). Thus, it should be considered as a
tool for specific, complementary (or preparatory) muscular
stimulation and/or assessment.
Finally, this article aims only at presenting the Hamtech
device, and some ongoing works will discuss the reliability
and reproducibility of the measurements (13).
Conflict of interest
The first author, Jean-Patrick Giacomo is the inventor and
patent owner (patent under review) of the Hamtech device.
Contact: twitter: @jp giacomo. More information on the
Hamtech and Hamtech Lab . None of the other authors has a
potential conflict of interest to declare.
Supplementary Material
This video shows the typical exercise modalities of the device
presented.
Twitter: Follow JP Giacomo: @jp giacomo, J Lahti:
@lahti johan, A Hegyi: @And Hegyi, P Gerus: @Pauli-
neGerus, JB Morin: @jb morin
References
1. Ekstrand J, Wald´en M, H¨agglund M. Hamstring injuries
have increased by 4% annually in men’s professional football,
since 2001: a 13-year longitudinal analysis of the UEFA Elite
Club injury study. Br J Sports Med. 2016;50(12):731–7.
2. Askling CM, Tengvar M, Thorstensson A. Acute hamstring
injuries in Swedish elite football: a prospective randomised
controlled clinical trial comparing two rehabilitation proto-
cols. Br J Sports Med. 2013;47(15):953–9.
3. Ekstrand J, Healy JC, Wald´en M, Lee JC, English B,
H¨agglund M. Hamstring muscle injuries in professional foot-
ball: the correlation of MRI findings with return to play. Br
J Sports Med. 2012;46(2):112–7.
4. Woods C, Hawkins RD, Maltby S, Hulse M, Thomas
A, Hodson A, et al. The Football Association Medical
Research Programme: an audit of injuries in professional
football–analysis of hamstring injuries. Br J Sports Med.
2004;38(1):36–41.
5. Mendiguchia J, Martinez-Ruiz E, Edouard P, Morin J-
B, Martinez-Martinez F, Idoate F, et al. A Multifactorial,
Criteria-based Progressive Algorithm for Hamstring Injury
Treatment. Med Sci Sport Exerc. 2017;49(7):1482–92.
6. Mendiguchia J, Alentorn-Geli E, Brughelli M. Hamstring
strain injuries: are we heading in the right direction? Br J
Sports Med. 2012;46(2):81–5.
7. Petersen J, Thorborg K, Nielsen MB, Budtz-Jørgensen E,
H¨olmich P. Preventive E↵ect of Eccentric Training on Acute
Hamstring Injuries in Men’s Soccer. Am J Sports Med. Avail-
able from: http://www.ncbi.nlm.nih.gov/pubmed/21825112
8. van der Horst N, Smits D-W, Petersen J, Goedhart EA,
Backx FJG. The Preventive E↵ect of the Nordic Hamstring
Exercise on Hamstring Injuries in Amateur Soccer Players.
Am J Sports Med. 2015;43(6):1316–23.
9. Tyler TF, Schmitt BM, Nicholas SJ, McHugh MP. Rehabil-
itation After Hamstring-Strain Injury Emphasizing Eccentric
Strengthening at Long Muscle Lengths: Results of Long-Term
Follow-Up. J Sport Rehabil. 2017;26(2):131–40.
10. Schmitt B, Tim T, McHugh M. Hamstring injury reha-
bilitation and prevention of reinjury using lengthened state
eccentric training: a new concept. Int J Sports Phys Ther.
2012;7(3):333–41.
11. Guex K, Gojanovic B, Millet GP. Influence of Hip-Flexion
Angle on Hamstrings Isokinetic Activity in Sprinters. J Athl
Train. 2012;47(4):390–5.
12. ˇ
Skarabot J, Cronin N, Strojnik V, Avela J. Bilateral
deficit in maximal force production. Eur J Appl Physiol.
2016;116(11–12):2057–84.
13. Lahti J, Giacomo J-P, Gerus P, Noul´e T, Hegyi A, Morin
J-B. Nordic hamstring exercise torque and sprint acceleration
mechanical profile and performance in team sport athletes; are
they related? In: World Congress of Biomechanics. Dublin;
2018.
14. Chumanov ES, Heiderscheit BC, Thelen DG. Ham-
string Musculotendon Dynamics during Stance and Swing
Phases of High-Speed Running. Med Sci Sport Exerc.
2011;43(3):525–32.
15. Heiderscheit BC, Hoerth DM, Chumanov ES, Swanson
SC, Thelen BJ, Thelen DG. Identifying the time of occurrence
of a hamstring strain injury during treadmill running: A case
study. Clin Biomech. 2005;20(10):1072–8.
16. Thelen DG, Chumanov ES, Best TM, Swanson SC, Hei-
derscheit BC. Simulation of biceps femoris musculotendon me-
chanics during the swing phase of sprinting. Med Sci Sports
Exerc. 2005;37(11):1931–8.
17. Schache AG, Dorn TW, Blanch PD, Brown NAT, Pandy
MG. Mechanics of the Human Hamstring Muscles during
Sprinting. Med Sci Sport Exerc. 2012;44(4):647–58.
18. Morin J-B, Gimenez P, Edouard P, Arnal P, Jim´enez-
Reyes P, Samozino P, et al. Sprint Acceleration Mechanics:
The Major Role of Hamstrings in Horizontal Force Produc-
tion. Front Physiol. 2015;6:404.
sportperfsci.com 3 SPSR - 2018 |Dec |40 |v1

A new testing and training device for hamstring muscle function
19. Maffiuletti NA, Aagaard P, Blazevich AJ, Folland J,
Tillin N, Duchateau J. Rate of force development: physiolog-
ical and methodological considerations. Eur J Appl Physiol.
2016;116(6):1091–116.
20. Marshall PWM, Lovell R, Jeppesen GK, Andersen K,
Siegler JC. Hamstring Muscle Fatigue and Central Motor Out-
put during a Simulated Soccer Match. Hug F, editor. PLoS
One. 2014;9(7):e102753.
21. Buckthorpe M, Pain MTG, Folland JP. Central fa-
tigue contributes to the greater reductions in explosive than
maximal strength with high-intensity fatigue. Exp Physiol.
2014;99(7):964–73.
22. Van Hooren B, Bosch F. Preventing hamstring injuries -
Part 2: There is possibly an isometric action of the hamstrings
in high-speed running and it does matter. Sport Perform Sci
Reports. 2018;Apr. 25.
23. Shield A, Murphy S. Preventing hamstring injuries - Part
1: Is there really an eccentric action of the hamstrings in high
speed running and does it matter? Sport Perform Sci Reports.
2018;Apr. 25.
24. Opar DA, Piatkowski T, Williams MD, Shield AJ. A novel
device using the Nordic hamstring exercise to assess eccen-
tric knee flexor strength: a reliability and retrospective injury
study. J Orthop Sports Phys Ther. 2013;43(9):636–40.
25. Hickey JT, Hickey PF, Maniar N, Timmins RG, Williams
MD, Pitcher CA, et al. A Novel Apparatus to Measure Knee
Flexor Strength During Various Hamstring Exercises: A Reli-
ability and Retrospective Injury Study. J Orthop Sport Phys
Ther. 2018;48(2):72–80.
26. Brockett CL, Morgan DL, Proske U. Predicting ham-
string strain injury in elite athletes. Med Sci Sports Exerc.
2004;36(3):379–87.
27. Buchheit M, Cholley Y, Nagel M, Poulos N. The Ef-
fect of Body Mass on Eccentric Knee-Flexor Strength As-
sessed With an Instrumented Nordic Hamstring Device (Nord-
bord) in Football Players. Int J Sports Physiol Perform.
2016;11(6):721–6.
28. Roe M, Malone S, Delahunt E, Collins K, Gissane C,
Persson UM, et al. Eccentric knee flexor strength profiles
of 341 elite male academy and senior Gaelic football players:
Do body mass and previous hamstring injury impact perfor-
mance? Phys Ther Sport. 2018;31:68–74.
29. Opar DA, Williams MD, Timmins RG, Dear NM, Shield
AJ. Rate of Torque and Electromyographic Development Dur-
ing Anticipated Eccentric Contraction Is Lower in Previously
Strained Hamstrings. Am J Sports Med. 2013;41(1):116–25.
30. Presland JD, Timmins RG, Bourne MN, Williams MD,
Opar DA. The e↵ect of Nordic hamstring exercise training
volume on biceps femoris long head architectural adaptation.
Scand J Med Sci Sports. 2018;28(7):1775–83.
31. Angelozzi M, Madama M, Corsica C, Calvisi V, Prop-
erzi G, McCaw ST, et al. Rate of Force Development as an
Adjunctive Outcome Measure for Return-to-Sport Decisions
After Anterior Cruciate Ligament Reconstruction. J Orthop
Sport Phys Ther. 2012;42(9):772–80.
32. Malone S, Roe M, Doran DA, Gabbett TJ, Collins K.
High chronic training loads and exposure to bouts of maximal
velocity running reduce injury risk in elite Gaelic football. J
Sci Med Sport. 2017;20(3):250–4.
33. Stares J, Dawson B, Peeling P, Drew M, Heasman J, Ro-
galski B, et al. How much is enough in rehabilitation? High
running workloads following lower limb muscle injury delay
return to play but protect against subsequent injury. J Sci
Med Sport. 2018;21(10):1019–24.
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