The effects of eccentric.pdf
Content
Physical Therapy in Sport 6 (2005) 67–73
www.elsevier.com/locate/yptsp
Original research
The effects of eccentric hamstring strength training on dynamic jumping
performance and isokinetic strength parameters: a pilot study on the
implications for the prevention of hamstring injuries
Ross Clarka,*, Adam Bryanta, John-Paul Culganb, Ben Hartleyb
b
a
Musculoskeletal Research Unit, Central Queensland University, North Rockhampton, Qld., 4701 Australia
School of Health and Human Performance, Central Queensland University, North Rockhampton, Qld., 4701 Australia
Received 25 August 2004; revised 3 February 2005; accepted 17 February 2005
Abstract
Objectives: Although previous research shows that the hamstring length–tension relationship during eccentric contractions plays a role in
hamstring injury, training methods to promote beneficial adaptations are still unclear. The purpose of this pilot study was to determine
whether an eccentric hamstring specific training programme results in favourable adaptations.
Design: Eccentric training consisting of the Nordic hamstring exercise performed twice a week for four weeks. Pre- and post-training
concentric/concentric isokinetic testing of peak torque (PT) and position of peak torque (POS) was performed for both the quadriceps and
hamstrings of both legs at 608 sK1. Vertical jump height was also assessed.
Participants: Nine athletic, male subjects with no previous strength training experience.
Results: There was a significant increase in vertical jump height (preZ51.0G4.8 cm, postZ54.4G6.3 cm, pZ0.04), a significant reduction
in quadriceps PT (preZ204.6G21.9 N.m., postZ181.5G19.9 N.m., pZ0.01), a significant decrease in hamstring POS from full knee
extension (preZ32.5G7.48, postZ26.2G8.68, pZ0.01) and a significant hamstring POS difference between limbs (dominantZ33.8G9.58,
non-dominantZ24.9G6.58, pZ0.01).
Conclusion: Nordic hamstring exercise training may produce favourable neuromuscular adaptations for the possible prevention of hamstring
injuries while enhancing performance in athletic, untrained males.
q 2005 Elsevier Ltd. All rights reserved.
Keywords: Eccentric training; Hamstring injury; Prevention
1. Introduction
One of the most common injuries in nearly all forms of
team and individual sports involving the lower body is the
hamstring strain (Bennell & Cossley, 1996; Moseley, 1996;
Orchard, James, Alcott, Carter, & Farhart, 2002; Orchard,
Wood, Seward, & Broad, 1998). Analysis of epidemiological injury studies assessing these sports consistently ranks
hamstring strain injuries as one of the most prevalent factors
resulting in missed playing time by athletes (Orchard et al.,
1998; Seward, Orchard, Hazard, & Collinson, 1993).
* Corresponding author. Tel.: C61 07 49 309704; fax: C61 07 49
309871.
E-mail address: [email protected] (R. Clark).
1466-853X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ptsp.2005.02.003
The widespread occurrence of this form of injury
necessitates the examination of optimal methods of both
prevention and rehabilitation. Previous studies have cited
numerous potential risk factors associated with hamstring
strains, such as muscle weakness and lack of flexibility
(Burkett, 1970), insufficient hamstring strength in comparison with the quadriceps (Coombs and Garbutt, 2002;
Orchard, Marsden, Lord, & Garlick, 1997), fatigue and
inadequate warm-up (Worrell, 1994) and poor lumbar
posture and core stability (Hennessy & Watson, 1993).
Although the risk factors for hamstring injury are numerous,
epidemiological evidence suggests that the actual occurrence
of hamstring muscle strains often takes place during eccentric
contraction of the hamstring muscles (Garrett, 1990; Kujala,
Orava, & Jarvinen, 1997; Stanton & Purdham, 1989).
More specifically, it has been previously suggested that it
is the portion of eccentric hamstring contraction occurring
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R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
during the descending limb of the muscle’s length–tension
relationship that results in hamstring injuries (Brockett,
Morgan, & Proske, 2004). This is postulated to be due to
non-uniform lengthening of sarcomeres due to sarcomere
length instability, resulting in microscopic damage to the
muscles of the hamstring (Gordon, Huxley, & Julian, 1966;
Morgan, 1990). If a sport requires multiple eccentric
contractions, these microscopic areas of damage may result
in a “weak link” of the musculature, from which a major soft
tissue tear may arise (Brockett et al., 2004).
This leads to another potential risk factor cited in
previous research, the position of knee extension at which
peak hamstring torque is produced (Armstrong, Warren, &
Warren, 1991; Brockett et al., 2004). In regards to the
length–tension relationship, it is suggested that the greater
the knee extension angle at which peak torque is produced
the lower risk of hamstring injury (Brockett et al., 2004).
Therefore, training to increase the knee extension angle at
which peak hamstring torque is produced would result in
reduced eccentric hamstring loading occurring during this
descending limb of the length–tension relation. A previous
single session eccentric training study found that just one
training session resulted in beneficial adaptations to the
length–tension relationship of the hamstrings (Brockett,
Morgan, & Proske, 2001). However, whether a multiple
session, longitudinal training programme specifically
designed to increase eccentric hamstring strength also
affects the knee extension angle at which peak hamstring
torque is produced is unknown.
One method of hamstring training known to increase
eccentric strength is the Nordic hamstring exercise
(Mjølnes, Arnason, Østhagen, Raastad, & Bahr, 2004).
This method of training was shown to increase eccentric
hamstring strength more effectively than traditional
hamstring curls. However, the effects of this method of
training on hamstring position of peak torque and dynamic
performance is unknown.
This pilot study attempts to determine whether the
Nordic hamstring exercise results in favourable adaptations
in relation to the length–tension relationship and hamstring
strength levels. Analysis of vertical jump height will also be
used to determine whether the training intervention has an
impact on lower body power output.
2. Methodology
2.1. Overview
The testing protocol consisted of pre- and post-training
intervention isokinetic dynamometer testing of the
quadriceps and hamstrings at a velocity of 608 sK1. Peak
torque, position of peak torque and vertical jump were
assessed to determine lower body strength, effects on the
length–tension relationship and dynamic power output.
These testing sessions were separated by a supervised
4 week training intervention consisting of the Nordic
hamstring exercise.
2.2. Subjects
Nine amateur Australian Rules football players
(heightZ181.13G6.76 cm, body massZ79.38G10.33 kg)
participated in this experiment. The subjects involved in this
study participated in sport but had little strength training
experience. Potential subjects who had participated in
regular resistance training programmes were excluded.
This participation consisted of two Australian Rules football
training sessions and one amateur Australian Rules football
game per week. All subjects had no prior history of
musculoskeletal injuries and in particular hamstring injuries
that may have affected the results of the study. Ethical
approval was granted by Central Queensland University. All
subjects had to complete an Informed Consent form and
pass a Pre-Activity Readiness Questionnaire before
commencement of the study. Availability of potential
subjects for every supervised training and testing session
limited the subject numbers to nine.
2.3. Isokinetic dynamometry
Isokinetic measurement of concentric/concentric hamstring/quadriceps torque was measured using a Biodex
System 3 isokinetic dynamometer (Biodex Medical Systems,
Shirley, New York, USA) sampling at 300 Hz per second.
This system has been previously shown to produce valid and
reliable measurements of torque and position (Drouin,
Valovich-McLeod, Shultz, Gansneder, & Perrin, 2004).
Angular velocity was set at 608 sK1 with five repetitions
performed for each leg. These sets were performed with a
2 min rest between sets. This velocity and method of testing
were chosen because they closely resemble the testing
protocol performed in a previous epidemiological study
which reported the importance of position of peak torque as
a risk factor in hamstring injuries (Brockett et al., 2004).
Testing was preceded by a three minute standardised
warm-up on a stationary cycle ergometer at 50 W. The
dominant and non-dominant limbs were tested with the order
chosen by random assignment. Subjects were seated on the
Biodex with their hip joint at approximately 908 flexion,
their upper bodies secured with dual crossover straps and
their waist secured by a waist strap. The range of motion of
the knee was set at 908 of full extension, with the upper leg
secured using the thigh strap to limit excess movement of
the knee and limb. Full knee extension was standardised
between the testing sessions by equalizing knee joint angles
with a hand held goniometer. This ensured an accurate
assessment of knee joint angle at which peak torque was
produced between the testing sessions.
Analysis of isokinetic data was performed using
custom written analysis software for Labview (National
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
69
Instruments, Austin, TX, USA). The position of peak torque
data was measured in degrees from the start of the
concentric contraction. Therefore, for the quadriceps
the result was in degrees from 908 knee flexion and for the
hamstrings the result was in degrees from full knee
extension. This means that a lower value in degrees for
the hamstrings results in a greater angle of knee extension
whereas a lower value in degrees for the quadriceps results
in a lower angle of knee extension.
2.4. Dynamic lower body performance
Pre and post testing of vertical jump was performed to
assess whether a training programme emphasising the
hamstring muscle group would affect lower body dynamic
power output. Vertical jump was assessed using a Vertec
(Swift Performance Equipment, Lismore, NSW, Australia)
on the same surface for both pre and post testing. This
testing was performed after a three minute, standardised
stationary cycle warm-up replicating the one performed
prior to the isokinetic testing. Subjects were instructed to
wear the same shoes for both testing sessions to reduce the
influence of shoe properties on vertical jump performance
(Stefanyshyn & Nigg, 2000). Three trials were allowed for
the vertical jump, with the mean of the three tests for each
session determining the subjects vertical jump height.
Subjects were instructed to perform the vertical jump
from a stationary position with feet shoulder width apart and
no fidgeting for five seconds prior to the countermovement
jump. Prior to the jump the subjects were instructed to raise
their right hand into the air as high as possible and push the
tabs on the vertec so that a baseline level could be attained.
When the athlete jumped they were required to lightly tap
the highest tab on the vertec so that an accurate measure of
vertical jump height could be attained. The vertical jump
result was recorded from subtraction of the baseline figure
from the highest tab touched while in flight.
Fig. 1. Starting position for the Nordic Hamstring Stretch exercise. The
athlete lowers their torso towards the ground using the hamstring muscles
as the primary brake against the force of gravity.
they performed a push-up jump followed by concentric
contraction of the hamstrings to raise themselves back up
to the starting position. The exercise protocol is shown in
Figs. 1 and 2, which display the starting position and the
upper body ground contact respectively. The four week
training protocol was carried out according to the guidelines
outlined in Table 1. All training sessions were supervised by
the researchers and took place after the subjects Australian
rules football-training sessions.
2.6. Statistical analyses
Repeated measures ANOVA was used to compare the
peak and the position of peak torque produced by
the quadriceps and hamstrings of the dominant and
non-dominant limbs prior to, and following eccentric
hamstring strength training. Therefore, each ANOVA
design included two within factors (test limb; dominant
and non-dominant and test occasion; pre and post).
2.5. Training intervention
The Nordic hamstring exercise was chosen for this study
because of the ease of application and minimal time
requirements necessary. This exercise consists of the athlete
starting in a kneeling position, with their torso from the
knees upwards held rigid and straight. A training partner
applied pressure to the athletes’ heels to ensure the feet stay
in contact with the ground throughout the movement,
isolating the muscles of the hamstrings. The athlete begins
the exercise by slowly lowering their body forwards against
the force of gravity towards the ground, using the
hamstrings to control descent into the prone position. This
eccentric contraction of the hamstrings was held for as long
as possible by the subjects during lowering of the body to
ensure that the hamstrings were contracting at as long a
length as possible. Once the athlete could no longer control
descent using the eccentric contraction of the hamstrings,
Fig. 2. Upper body ground contact during the Nordic Hamstring Stretch
exercise. The athlete performs a dynamic push-up jump and attempts to use
this momentum along with concentric contraction of the hamstrings to
return to the starting position.
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R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
Table 1
Four week training protocol
Week
Sessions
per week
Sets–Reps
Technical notes
1
1
2/5
2
3
2
3
2/6
3/6
4
3
3/8
The subject is encouraged to resist
falling as long as possible
Subject tries to reduce lowering speed
Subjects can resist falling even longer,
and for an increased number of
repetitions
Load on the subject increases by
allowing more speed in the start phase,
as well as another gradual increase in
repetitions
angle towards full extension (08 knee flexion) recorded for
the dominant limb compared to the non-dominant limb
when the data were pooled across test occasions (see Fig. 4).
In addition, statistical analysis of the position of hamstring
peak torque data indicated a significant main effect of test
occasion with a 19.4% increase in knee flexion angle
towards full extension (08 knee flexion) in the post-training
testing session compare to pre-training session when the
data were pooled across test limbs (see Fig. 5). Finally, a
significant increase of 6.6% was found for vertical jump
height between the pre and post-training sessions
(see Fig. 6).
Adapted from Oslo Sports Trauma Research Center (2004)
4. Discussion
The main purpose of this design was to determine whether
there were any significant differences in the dependant
variables as a consequence of test limb or test occasion. In
the event of a significant main effect or interaction following
ANOVA contrasts, post hoc comparisons of the means were
conducted using the least significant difference (LSD) test to
delineate differences amongst test limbs or test occasion.
Paired samples t-test were used to compare vertical jump
performance pre and post training. The level of significance
was set at p!0.05 for all tests. All analyses were performed
using SPSS version 12.
3. Results
The pre- and post-training intervention results for the
isokinetic testing including peak torque and position of peak
torque for the quadriceps and hamstrings of both limbs are
presented in Table 2. Statistical analysis revealed a
significant main effect of test occasion for quadriceps
peak torque with an 11.3% reduction in peak torque from
the pre to post tests when the data were pooled across test
limbs (see Fig. 3). Statistical analyses also revealed a
significant main effect of test limb for the position of
hamstring peak torque with a 36.4% increase in knee flexion
The purpose of this pilot study was to assess the effect of
a predominantly eccentric hamstring training programme on
isokinetic variables associated with hamstring injuries and
lower body dynamic power. The pre-intervention results for
position of peak hamstring torque for the untrained subjects
participating in this experiment were similar to those found
in uninjured elite athletes in a previous study (Brockett
et al., 2004). The subjects in the present study recorded
slightly higher pre-training knee extension angles for
production of peak torque in comparison to the elite athletes
in the previous study for both right (14.9%) and left (5.9%)
hamstrings. However, the post-intervention results for the
subjects in the present study were both lower than the results
for the previously mentioned elite athletes, by 4.9 and 38%
for the right and left leg respectively. This suggests that the
hamstring training protocol the elite athletes in the previous
study are participating in has not had a great effect on
position of peak hamstring torque. In contrast, the subjects
in the present study showed a 19.4% change in position of
peak torque for the hamstring muscles after just a 4 week
training intervention. This rapid alteration of the length–
tension relationship is similar to the significant shift in
position of peak hamstring torque reported in a previous
single session eccentric training study (Brockett et al.,
Table 2
Isokinetic performance measures assessed pre and post a 4 week eccentric hamstring training intervention
Isokinetic performance
measure
Quadriceps
PT
(N.m.)
Pos PT
(8)
Hamstrings
PT
(N.m.)
Pos PT
(8)
Pre
Post
P and F values
Dominant
Non-dominant
Dominant
Non-dominant
L
T
L!T
204.34
G20.1
69.32
G4.0
204.93
G23.8
62.82
G6.3
180.84
G19.8
66.84
G5.4
182.09
G20.0
65.11
G7.6
0.90
0.02
0.06
4.85
0.01*
9.77
0.95
0.00
0.95
0.00
0.07
4.34
98.61
G13.3
36.76
G10.8
99.00
G28.4
28.21
G4.0
97.30
G13.9
30.77
G8.2
103.64
G19.3
21.61
G9.0
0.49
0.53
0.01*
11.77
0.68
0.19
0.01*
10.3
0.36
0.93
0.91
0.01
L, effect for Limb (dominant and non-dominant); T, effect for test (pre- and post-intervention); L!T, interaction between limb and test; PT, peak torque; Pos
PT, position of peak torque. *Indicates significant difference (p!0.05).
*
250
Peak Torque (N.m.)
Position of Peak Torque (°)
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
225
200
175
150
Pre
71
45
*
40
35
30
25
20
Pre
Post
Testing Day
Fig. 3. Quadriceps peak torque pre- and post-training intervention.
*Indicates significant difference between pre- and post-testing results
(pZ0.01).
imbalance suggests that there may be a need for unilateral
eccentric hamstring training in untrained athletes to reduce
the difference between the legs before bilateral eccentric
specific training commences.
The results of the present study suggest that the training
intervention created a greater magnitude of difference
between test limbs. It appears that the limb with the initially
higher knee extension angle benefits most from this method
of training, which is logical due to the nature of the training
protocol. As the athlete lowers themselves towards the
ground using eccentric contraction of the hamstrings, the
limb with the higher knee extension angle of peak hamstring
torque may be required to take over control of the movement
towards the end of the repetition. This places a greater
magnitude of stress on the limb with the greater knee
extension angle of peak torque, because it may be required to
dominate control of the descending torso. This greater degree
of overload on the already dominant hamstring may result in
enhanced neuromuscular adaptation in this limb to the
training protocol, further increasing the magnitude of
imbalance between the limbs. This potential drawback to
bilateral eccentric hamstring training warrants further
examination.
*
62
45
*
60
40
35
30
25
20
Fig. 5. Hamstring joint angle position of peak torque from full knee
extension pre- and post-training intervention. *Indicates significant
difference between pre- and post-testing results (pZ0.01).
Jump Height (cm)
Position of Peak Torque (°)
2001). The findings of this study showed that the position of
peak hamstring torque shifted to a more extended knee
position after the training intervention, which may allow for
reduced eccentric muscle damage of the hamstrings
occurring during eccentric contractions. This may be due
to a reduced length of the descending limb of the
length tension relationship, possibly resulting in diminished
non-uniform lengthening of the sarcomeres of the hamstring
muscles. A reduced descending limb of the length-tension
relationship has been previously suggested to lower the risk
of hamstring injury (Brockett et al., 2004). These results
suggest that a training protocol designed to produce a more
favourable hamstring length–tension relationship in terms
of hamstring injury prevention can be beneficial after only a
minimal amount of training sessions.
It is also worth noting that the position of peak hamstring
torque in both the present and the previously mentioned
study (Brockett et al., 2004) varied between the dominant
and non-dominant limb. However, in the uninjured elite
athletes (Brockett et al., 2004) there was only a 7%
difference between limbs, whereas in the present study there
was a 30.3% pre- and 42.4% post-intervention difference in
the position of peak hamstring torque. This between limb
Non-dominant
Post
Testing Day
Dominant
Limb
Fig. 4. Hamstring joint angle position of peak torque from full knee
extension between the dominant and non-dominant limbs. *Indicates
significant difference between dominant and non-dominant limb results
(pZ0.01).
58
56
54
52
50
48
Pre
Post
Testing
Fig. 6. Vertical jump height measured pre- and post-training intervention.
*Indicates significant difference between pre- and post-testing results
(pZ0.04).
72
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
Despite the beneficial adaptations in terms of the lengthtension relationship, there was no increase in hamstring
concentric peak torque as a result of the training
intervention. This replicates the findings of Mjølnes et al.
(2004) who found a limited effect of this method of training
on concentric hamstring strength.
Another interesting finding of this study was the
significant 11.3% reduction in peak torque produced by
the quadriceps after the training intervention. This may
be due to a number of factors, such as changes in the
viscoelastic properties of the muscular unit in response to
the training stimulus and/or increased antagonistic
activation of the hamstrings during the concentric
quadriceps phase of the testing protocol (Solomonow,
Baratta, & D’Ambrosia, 1989). A change in the stiffness
properties of the hamstrings and/or increased antagonistic
activation may adversely affect the force output of the
quadriceps by applying internal opposition to the
quadriceps contraction in addition to the external
opposition supplied by the isokinetic dynamometer
(Solomonow et al., 1989).
Although a dramatic reduction in quadriceps peak
torque and only minor changes in hamstring peak torque
were observed in the open kinetic chain testing, a
significant 6.6% increase in vertical jump height was
reported. This revealed that the Nordic hamstring exercise
not only appears to have a beneficial effect on the length
tension relationship of the hamstrings, but results in
enhanced explosive power performance in untrained
athletes. Although there was a reduction in open-kinetic
chain quadriceps peak torque in the post-training results,
this may not carry over into closed kinetic chain jumping
movements. Furthermore, the minor changes in hamstring
peak torque may not be the reason for the improvement in
vertical jump. The change in hamstring position of peak
torque towards a more extended knee angle is likely to
have contributed to the increase in vertical jump height.
This may be due to increased joint stability of the knee
during the final takeoff phase of the jumping movement,
allowing for more efficient transfer of force through the
joint (Baratta, Solomonow, Zhou, Letson, Chuinard, &
D’Ambrosia, 1988).
Previous studies have shown that the hamstrings play a key
role in preserving joint stiffness and stability during the
deceleration phase which occurs towards the terminal stage of
the knee extension movement (Baratta et al., 1988; Hagood,
Solomonow, Baratta, Zhou, & D’Ambrosia, 1990). Therefore
it would be expected that to optimise force transfer through the
knee joint during dynamic movements it would be necessary
to maintain or increase hamstring coactivation during the
terminal phase of the movement. However, Baratta et al.
(1988) found that in untrained athletes who participated in
sports requiring repetitive jumping movements, this activation
of the antagonist hamstring muscles during the final phase of
the knee extension was markedly reduced. This suggests that
in non-weight trained athletes the hamstring muscles reduce
their level of activation during the final phase of knee
extension to potentially decrease opposition to the quadriceps,
resulting in increased force output of the quadriceps at the
expense of the joint stability supplied by the hamstrings.
Not only would this reduction in joint stability reduce the
efficiency of the movement, but it may increase the risk of knee
joint injury (Baratta et al., 1988). In contrast, the athletes
involved in the Baratta et al. (1988) study who were
undertaking hamstring specific weight training produced
similar activation patterns of the hamstrings to control subjects
who were sedentary. These weight trained athletes recorded
similar or increased activation of the hamstrings in comparison
with the sedentary subjects, suggesting that performing
hamstring specific weight training maintained or increased
their knee joint stability. While the previous study did not look
at dynamic performance characteristics of the subjects, the
results of the present study suggests that hamstring specific
training can result in beneficial adaptations to hamstring
activation in terms of joint stability during the final phase of
knee extension as well as increase dynamic performance.
4.1. Limitations
Despite the limited number of subjects participating in
this study, a number of significant findings were observed.
However, further studies incorporating greater subject
numbers, the inclusion of a control group and multiple
trials for assessment of reliability would help to determine
the role of lower body eccentric training on performance
and injury risk factors. The results of this study suggest that
eccentric hamstring training may result in adaptations that
reduce the risk of hamstring strain injury, however further
studies are required before these benefits can be deemed
conclusive.
5. Practical applications and clinical relevance
The findings of this study suggest that the Nordic
hamstring exercise results in favourable adaptations to the
length–tension relationship in the hamstring muscle group.
Although the Nordic hamstring exercise was found to be
beneficial in terms of the hamstrings position of peak torque,
it had little effect on overall peak torque values. Possibly a
combination of Nordic hamstring exercise training and
traditional hamstring weight lifting movements may provide
beneficial strength and length-tension adaptations to prevent
soft tissue hamstring injuries. Overall the results of this
study suggest that the Nordic Hamstring exercise, because
of its ease of implementation, may be an effective method of
both enhancing performance and reducing injury in subelite athletes performing in sports requiring jumping
movements.
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
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Worrell, T. W. (1994). Factors associated with hamstring injuries: an
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www.elsevier.com/locate/yptsp
Original research
The effects of eccentric hamstring strength training on dynamic jumping
performance and isokinetic strength parameters: a pilot study on the
implications for the prevention of hamstring injuries
Ross Clarka,*, Adam Bryanta, John-Paul Culganb, Ben Hartleyb
b
a
Musculoskeletal Research Unit, Central Queensland University, North Rockhampton, Qld., 4701 Australia
School of Health and Human Performance, Central Queensland University, North Rockhampton, Qld., 4701 Australia
Received 25 August 2004; revised 3 February 2005; accepted 17 February 2005
Abstract
Objectives: Although previous research shows that the hamstring length–tension relationship during eccentric contractions plays a role in
hamstring injury, training methods to promote beneficial adaptations are still unclear. The purpose of this pilot study was to determine
whether an eccentric hamstring specific training programme results in favourable adaptations.
Design: Eccentric training consisting of the Nordic hamstring exercise performed twice a week for four weeks. Pre- and post-training
concentric/concentric isokinetic testing of peak torque (PT) and position of peak torque (POS) was performed for both the quadriceps and
hamstrings of both legs at 608 sK1. Vertical jump height was also assessed.
Participants: Nine athletic, male subjects with no previous strength training experience.
Results: There was a significant increase in vertical jump height (preZ51.0G4.8 cm, postZ54.4G6.3 cm, pZ0.04), a significant reduction
in quadriceps PT (preZ204.6G21.9 N.m., postZ181.5G19.9 N.m., pZ0.01), a significant decrease in hamstring POS from full knee
extension (preZ32.5G7.48, postZ26.2G8.68, pZ0.01) and a significant hamstring POS difference between limbs (dominantZ33.8G9.58,
non-dominantZ24.9G6.58, pZ0.01).
Conclusion: Nordic hamstring exercise training may produce favourable neuromuscular adaptations for the possible prevention of hamstring
injuries while enhancing performance in athletic, untrained males.
q 2005 Elsevier Ltd. All rights reserved.
Keywords: Eccentric training; Hamstring injury; Prevention
1. Introduction
One of the most common injuries in nearly all forms of
team and individual sports involving the lower body is the
hamstring strain (Bennell & Cossley, 1996; Moseley, 1996;
Orchard, James, Alcott, Carter, & Farhart, 2002; Orchard,
Wood, Seward, & Broad, 1998). Analysis of epidemiological injury studies assessing these sports consistently ranks
hamstring strain injuries as one of the most prevalent factors
resulting in missed playing time by athletes (Orchard et al.,
1998; Seward, Orchard, Hazard, & Collinson, 1993).
* Corresponding author. Tel.: C61 07 49 309704; fax: C61 07 49
309871.
E-mail address: [email protected] (R. Clark).
1466-853X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ptsp.2005.02.003
The widespread occurrence of this form of injury
necessitates the examination of optimal methods of both
prevention and rehabilitation. Previous studies have cited
numerous potential risk factors associated with hamstring
strains, such as muscle weakness and lack of flexibility
(Burkett, 1970), insufficient hamstring strength in comparison with the quadriceps (Coombs and Garbutt, 2002;
Orchard, Marsden, Lord, & Garlick, 1997), fatigue and
inadequate warm-up (Worrell, 1994) and poor lumbar
posture and core stability (Hennessy & Watson, 1993).
Although the risk factors for hamstring injury are numerous,
epidemiological evidence suggests that the actual occurrence
of hamstring muscle strains often takes place during eccentric
contraction of the hamstring muscles (Garrett, 1990; Kujala,
Orava, & Jarvinen, 1997; Stanton & Purdham, 1989).
More specifically, it has been previously suggested that it
is the portion of eccentric hamstring contraction occurring
68
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
during the descending limb of the muscle’s length–tension
relationship that results in hamstring injuries (Brockett,
Morgan, & Proske, 2004). This is postulated to be due to
non-uniform lengthening of sarcomeres due to sarcomere
length instability, resulting in microscopic damage to the
muscles of the hamstring (Gordon, Huxley, & Julian, 1966;
Morgan, 1990). If a sport requires multiple eccentric
contractions, these microscopic areas of damage may result
in a “weak link” of the musculature, from which a major soft
tissue tear may arise (Brockett et al., 2004).
This leads to another potential risk factor cited in
previous research, the position of knee extension at which
peak hamstring torque is produced (Armstrong, Warren, &
Warren, 1991; Brockett et al., 2004). In regards to the
length–tension relationship, it is suggested that the greater
the knee extension angle at which peak torque is produced
the lower risk of hamstring injury (Brockett et al., 2004).
Therefore, training to increase the knee extension angle at
which peak hamstring torque is produced would result in
reduced eccentric hamstring loading occurring during this
descending limb of the length–tension relation. A previous
single session eccentric training study found that just one
training session resulted in beneficial adaptations to the
length–tension relationship of the hamstrings (Brockett,
Morgan, & Proske, 2001). However, whether a multiple
session, longitudinal training programme specifically
designed to increase eccentric hamstring strength also
affects the knee extension angle at which peak hamstring
torque is produced is unknown.
One method of hamstring training known to increase
eccentric strength is the Nordic hamstring exercise
(Mjølnes, Arnason, Østhagen, Raastad, & Bahr, 2004).
This method of training was shown to increase eccentric
hamstring strength more effectively than traditional
hamstring curls. However, the effects of this method of
training on hamstring position of peak torque and dynamic
performance is unknown.
This pilot study attempts to determine whether the
Nordic hamstring exercise results in favourable adaptations
in relation to the length–tension relationship and hamstring
strength levels. Analysis of vertical jump height will also be
used to determine whether the training intervention has an
impact on lower body power output.
2. Methodology
2.1. Overview
The testing protocol consisted of pre- and post-training
intervention isokinetic dynamometer testing of the
quadriceps and hamstrings at a velocity of 608 sK1. Peak
torque, position of peak torque and vertical jump were
assessed to determine lower body strength, effects on the
length–tension relationship and dynamic power output.
These testing sessions were separated by a supervised
4 week training intervention consisting of the Nordic
hamstring exercise.
2.2. Subjects
Nine amateur Australian Rules football players
(heightZ181.13G6.76 cm, body massZ79.38G10.33 kg)
participated in this experiment. The subjects involved in this
study participated in sport but had little strength training
experience. Potential subjects who had participated in
regular resistance training programmes were excluded.
This participation consisted of two Australian Rules football
training sessions and one amateur Australian Rules football
game per week. All subjects had no prior history of
musculoskeletal injuries and in particular hamstring injuries
that may have affected the results of the study. Ethical
approval was granted by Central Queensland University. All
subjects had to complete an Informed Consent form and
pass a Pre-Activity Readiness Questionnaire before
commencement of the study. Availability of potential
subjects for every supervised training and testing session
limited the subject numbers to nine.
2.3. Isokinetic dynamometry
Isokinetic measurement of concentric/concentric hamstring/quadriceps torque was measured using a Biodex
System 3 isokinetic dynamometer (Biodex Medical Systems,
Shirley, New York, USA) sampling at 300 Hz per second.
This system has been previously shown to produce valid and
reliable measurements of torque and position (Drouin,
Valovich-McLeod, Shultz, Gansneder, & Perrin, 2004).
Angular velocity was set at 608 sK1 with five repetitions
performed for each leg. These sets were performed with a
2 min rest between sets. This velocity and method of testing
were chosen because they closely resemble the testing
protocol performed in a previous epidemiological study
which reported the importance of position of peak torque as
a risk factor in hamstring injuries (Brockett et al., 2004).
Testing was preceded by a three minute standardised
warm-up on a stationary cycle ergometer at 50 W. The
dominant and non-dominant limbs were tested with the order
chosen by random assignment. Subjects were seated on the
Biodex with their hip joint at approximately 908 flexion,
their upper bodies secured with dual crossover straps and
their waist secured by a waist strap. The range of motion of
the knee was set at 908 of full extension, with the upper leg
secured using the thigh strap to limit excess movement of
the knee and limb. Full knee extension was standardised
between the testing sessions by equalizing knee joint angles
with a hand held goniometer. This ensured an accurate
assessment of knee joint angle at which peak torque was
produced between the testing sessions.
Analysis of isokinetic data was performed using
custom written analysis software for Labview (National
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
69
Instruments, Austin, TX, USA). The position of peak torque
data was measured in degrees from the start of the
concentric contraction. Therefore, for the quadriceps
the result was in degrees from 908 knee flexion and for the
hamstrings the result was in degrees from full knee
extension. This means that a lower value in degrees for
the hamstrings results in a greater angle of knee extension
whereas a lower value in degrees for the quadriceps results
in a lower angle of knee extension.
2.4. Dynamic lower body performance
Pre and post testing of vertical jump was performed to
assess whether a training programme emphasising the
hamstring muscle group would affect lower body dynamic
power output. Vertical jump was assessed using a Vertec
(Swift Performance Equipment, Lismore, NSW, Australia)
on the same surface for both pre and post testing. This
testing was performed after a three minute, standardised
stationary cycle warm-up replicating the one performed
prior to the isokinetic testing. Subjects were instructed to
wear the same shoes for both testing sessions to reduce the
influence of shoe properties on vertical jump performance
(Stefanyshyn & Nigg, 2000). Three trials were allowed for
the vertical jump, with the mean of the three tests for each
session determining the subjects vertical jump height.
Subjects were instructed to perform the vertical jump
from a stationary position with feet shoulder width apart and
no fidgeting for five seconds prior to the countermovement
jump. Prior to the jump the subjects were instructed to raise
their right hand into the air as high as possible and push the
tabs on the vertec so that a baseline level could be attained.
When the athlete jumped they were required to lightly tap
the highest tab on the vertec so that an accurate measure of
vertical jump height could be attained. The vertical jump
result was recorded from subtraction of the baseline figure
from the highest tab touched while in flight.
Fig. 1. Starting position for the Nordic Hamstring Stretch exercise. The
athlete lowers their torso towards the ground using the hamstring muscles
as the primary brake against the force of gravity.
they performed a push-up jump followed by concentric
contraction of the hamstrings to raise themselves back up
to the starting position. The exercise protocol is shown in
Figs. 1 and 2, which display the starting position and the
upper body ground contact respectively. The four week
training protocol was carried out according to the guidelines
outlined in Table 1. All training sessions were supervised by
the researchers and took place after the subjects Australian
rules football-training sessions.
2.6. Statistical analyses
Repeated measures ANOVA was used to compare the
peak and the position of peak torque produced by
the quadriceps and hamstrings of the dominant and
non-dominant limbs prior to, and following eccentric
hamstring strength training. Therefore, each ANOVA
design included two within factors (test limb; dominant
and non-dominant and test occasion; pre and post).
2.5. Training intervention
The Nordic hamstring exercise was chosen for this study
because of the ease of application and minimal time
requirements necessary. This exercise consists of the athlete
starting in a kneeling position, with their torso from the
knees upwards held rigid and straight. A training partner
applied pressure to the athletes’ heels to ensure the feet stay
in contact with the ground throughout the movement,
isolating the muscles of the hamstrings. The athlete begins
the exercise by slowly lowering their body forwards against
the force of gravity towards the ground, using the
hamstrings to control descent into the prone position. This
eccentric contraction of the hamstrings was held for as long
as possible by the subjects during lowering of the body to
ensure that the hamstrings were contracting at as long a
length as possible. Once the athlete could no longer control
descent using the eccentric contraction of the hamstrings,
Fig. 2. Upper body ground contact during the Nordic Hamstring Stretch
exercise. The athlete performs a dynamic push-up jump and attempts to use
this momentum along with concentric contraction of the hamstrings to
return to the starting position.
70
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
Table 1
Four week training protocol
Week
Sessions
per week
Sets–Reps
Technical notes
1
1
2/5
2
3
2
3
2/6
3/6
4
3
3/8
The subject is encouraged to resist
falling as long as possible
Subject tries to reduce lowering speed
Subjects can resist falling even longer,
and for an increased number of
repetitions
Load on the subject increases by
allowing more speed in the start phase,
as well as another gradual increase in
repetitions
angle towards full extension (08 knee flexion) recorded for
the dominant limb compared to the non-dominant limb
when the data were pooled across test occasions (see Fig. 4).
In addition, statistical analysis of the position of hamstring
peak torque data indicated a significant main effect of test
occasion with a 19.4% increase in knee flexion angle
towards full extension (08 knee flexion) in the post-training
testing session compare to pre-training session when the
data were pooled across test limbs (see Fig. 5). Finally, a
significant increase of 6.6% was found for vertical jump
height between the pre and post-training sessions
(see Fig. 6).
Adapted from Oslo Sports Trauma Research Center (2004)
4. Discussion
The main purpose of this design was to determine whether
there were any significant differences in the dependant
variables as a consequence of test limb or test occasion. In
the event of a significant main effect or interaction following
ANOVA contrasts, post hoc comparisons of the means were
conducted using the least significant difference (LSD) test to
delineate differences amongst test limbs or test occasion.
Paired samples t-test were used to compare vertical jump
performance pre and post training. The level of significance
was set at p!0.05 for all tests. All analyses were performed
using SPSS version 12.
3. Results
The pre- and post-training intervention results for the
isokinetic testing including peak torque and position of peak
torque for the quadriceps and hamstrings of both limbs are
presented in Table 2. Statistical analysis revealed a
significant main effect of test occasion for quadriceps
peak torque with an 11.3% reduction in peak torque from
the pre to post tests when the data were pooled across test
limbs (see Fig. 3). Statistical analyses also revealed a
significant main effect of test limb for the position of
hamstring peak torque with a 36.4% increase in knee flexion
The purpose of this pilot study was to assess the effect of
a predominantly eccentric hamstring training programme on
isokinetic variables associated with hamstring injuries and
lower body dynamic power. The pre-intervention results for
position of peak hamstring torque for the untrained subjects
participating in this experiment were similar to those found
in uninjured elite athletes in a previous study (Brockett
et al., 2004). The subjects in the present study recorded
slightly higher pre-training knee extension angles for
production of peak torque in comparison to the elite athletes
in the previous study for both right (14.9%) and left (5.9%)
hamstrings. However, the post-intervention results for the
subjects in the present study were both lower than the results
for the previously mentioned elite athletes, by 4.9 and 38%
for the right and left leg respectively. This suggests that the
hamstring training protocol the elite athletes in the previous
study are participating in has not had a great effect on
position of peak hamstring torque. In contrast, the subjects
in the present study showed a 19.4% change in position of
peak torque for the hamstring muscles after just a 4 week
training intervention. This rapid alteration of the length–
tension relationship is similar to the significant shift in
position of peak hamstring torque reported in a previous
single session eccentric training study (Brockett et al.,
Table 2
Isokinetic performance measures assessed pre and post a 4 week eccentric hamstring training intervention
Isokinetic performance
measure
Quadriceps
PT
(N.m.)
Pos PT
(8)
Hamstrings
PT
(N.m.)
Pos PT
(8)
Pre
Post
P and F values
Dominant
Non-dominant
Dominant
Non-dominant
L
T
L!T
204.34
G20.1
69.32
G4.0
204.93
G23.8
62.82
G6.3
180.84
G19.8
66.84
G5.4
182.09
G20.0
65.11
G7.6
0.90
0.02
0.06
4.85
0.01*
9.77
0.95
0.00
0.95
0.00
0.07
4.34
98.61
G13.3
36.76
G10.8
99.00
G28.4
28.21
G4.0
97.30
G13.9
30.77
G8.2
103.64
G19.3
21.61
G9.0
0.49
0.53
0.01*
11.77
0.68
0.19
0.01*
10.3
0.36
0.93
0.91
0.01
L, effect for Limb (dominant and non-dominant); T, effect for test (pre- and post-intervention); L!T, interaction between limb and test; PT, peak torque; Pos
PT, position of peak torque. *Indicates significant difference (p!0.05).
*
250
Peak Torque (N.m.)
Position of Peak Torque (°)
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
225
200
175
150
Pre
71
45
*
40
35
30
25
20
Pre
Post
Testing Day
Fig. 3. Quadriceps peak torque pre- and post-training intervention.
*Indicates significant difference between pre- and post-testing results
(pZ0.01).
imbalance suggests that there may be a need for unilateral
eccentric hamstring training in untrained athletes to reduce
the difference between the legs before bilateral eccentric
specific training commences.
The results of the present study suggest that the training
intervention created a greater magnitude of difference
between test limbs. It appears that the limb with the initially
higher knee extension angle benefits most from this method
of training, which is logical due to the nature of the training
protocol. As the athlete lowers themselves towards the
ground using eccentric contraction of the hamstrings, the
limb with the higher knee extension angle of peak hamstring
torque may be required to take over control of the movement
towards the end of the repetition. This places a greater
magnitude of stress on the limb with the greater knee
extension angle of peak torque, because it may be required to
dominate control of the descending torso. This greater degree
of overload on the already dominant hamstring may result in
enhanced neuromuscular adaptation in this limb to the
training protocol, further increasing the magnitude of
imbalance between the limbs. This potential drawback to
bilateral eccentric hamstring training warrants further
examination.
*
62
45
*
60
40
35
30
25
20
Fig. 5. Hamstring joint angle position of peak torque from full knee
extension pre- and post-training intervention. *Indicates significant
difference between pre- and post-testing results (pZ0.01).
Jump Height (cm)
Position of Peak Torque (°)
2001). The findings of this study showed that the position of
peak hamstring torque shifted to a more extended knee
position after the training intervention, which may allow for
reduced eccentric muscle damage of the hamstrings
occurring during eccentric contractions. This may be due
to a reduced length of the descending limb of the
length tension relationship, possibly resulting in diminished
non-uniform lengthening of the sarcomeres of the hamstring
muscles. A reduced descending limb of the length-tension
relationship has been previously suggested to lower the risk
of hamstring injury (Brockett et al., 2004). These results
suggest that a training protocol designed to produce a more
favourable hamstring length–tension relationship in terms
of hamstring injury prevention can be beneficial after only a
minimal amount of training sessions.
It is also worth noting that the position of peak hamstring
torque in both the present and the previously mentioned
study (Brockett et al., 2004) varied between the dominant
and non-dominant limb. However, in the uninjured elite
athletes (Brockett et al., 2004) there was only a 7%
difference between limbs, whereas in the present study there
was a 30.3% pre- and 42.4% post-intervention difference in
the position of peak hamstring torque. This between limb
Non-dominant
Post
Testing Day
Dominant
Limb
Fig. 4. Hamstring joint angle position of peak torque from full knee
extension between the dominant and non-dominant limbs. *Indicates
significant difference between dominant and non-dominant limb results
(pZ0.01).
58
56
54
52
50
48
Pre
Post
Testing
Fig. 6. Vertical jump height measured pre- and post-training intervention.
*Indicates significant difference between pre- and post-testing results
(pZ0.04).
72
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
Despite the beneficial adaptations in terms of the lengthtension relationship, there was no increase in hamstring
concentric peak torque as a result of the training
intervention. This replicates the findings of Mjølnes et al.
(2004) who found a limited effect of this method of training
on concentric hamstring strength.
Another interesting finding of this study was the
significant 11.3% reduction in peak torque produced by
the quadriceps after the training intervention. This may
be due to a number of factors, such as changes in the
viscoelastic properties of the muscular unit in response to
the training stimulus and/or increased antagonistic
activation of the hamstrings during the concentric
quadriceps phase of the testing protocol (Solomonow,
Baratta, & D’Ambrosia, 1989). A change in the stiffness
properties of the hamstrings and/or increased antagonistic
activation may adversely affect the force output of the
quadriceps by applying internal opposition to the
quadriceps contraction in addition to the external
opposition supplied by the isokinetic dynamometer
(Solomonow et al., 1989).
Although a dramatic reduction in quadriceps peak
torque and only minor changes in hamstring peak torque
were observed in the open kinetic chain testing, a
significant 6.6% increase in vertical jump height was
reported. This revealed that the Nordic hamstring exercise
not only appears to have a beneficial effect on the length
tension relationship of the hamstrings, but results in
enhanced explosive power performance in untrained
athletes. Although there was a reduction in open-kinetic
chain quadriceps peak torque in the post-training results,
this may not carry over into closed kinetic chain jumping
movements. Furthermore, the minor changes in hamstring
peak torque may not be the reason for the improvement in
vertical jump. The change in hamstring position of peak
torque towards a more extended knee angle is likely to
have contributed to the increase in vertical jump height.
This may be due to increased joint stability of the knee
during the final takeoff phase of the jumping movement,
allowing for more efficient transfer of force through the
joint (Baratta, Solomonow, Zhou, Letson, Chuinard, &
D’Ambrosia, 1988).
Previous studies have shown that the hamstrings play a key
role in preserving joint stiffness and stability during the
deceleration phase which occurs towards the terminal stage of
the knee extension movement (Baratta et al., 1988; Hagood,
Solomonow, Baratta, Zhou, & D’Ambrosia, 1990). Therefore
it would be expected that to optimise force transfer through the
knee joint during dynamic movements it would be necessary
to maintain or increase hamstring coactivation during the
terminal phase of the movement. However, Baratta et al.
(1988) found that in untrained athletes who participated in
sports requiring repetitive jumping movements, this activation
of the antagonist hamstring muscles during the final phase of
the knee extension was markedly reduced. This suggests that
in non-weight trained athletes the hamstring muscles reduce
their level of activation during the final phase of knee
extension to potentially decrease opposition to the quadriceps,
resulting in increased force output of the quadriceps at the
expense of the joint stability supplied by the hamstrings.
Not only would this reduction in joint stability reduce the
efficiency of the movement, but it may increase the risk of knee
joint injury (Baratta et al., 1988). In contrast, the athletes
involved in the Baratta et al. (1988) study who were
undertaking hamstring specific weight training produced
similar activation patterns of the hamstrings to control subjects
who were sedentary. These weight trained athletes recorded
similar or increased activation of the hamstrings in comparison
with the sedentary subjects, suggesting that performing
hamstring specific weight training maintained or increased
their knee joint stability. While the previous study did not look
at dynamic performance characteristics of the subjects, the
results of the present study suggests that hamstring specific
training can result in beneficial adaptations to hamstring
activation in terms of joint stability during the final phase of
knee extension as well as increase dynamic performance.
4.1. Limitations
Despite the limited number of subjects participating in
this study, a number of significant findings were observed.
However, further studies incorporating greater subject
numbers, the inclusion of a control group and multiple
trials for assessment of reliability would help to determine
the role of lower body eccentric training on performance
and injury risk factors. The results of this study suggest that
eccentric hamstring training may result in adaptations that
reduce the risk of hamstring strain injury, however further
studies are required before these benefits can be deemed
conclusive.
5. Practical applications and clinical relevance
The findings of this study suggest that the Nordic
hamstring exercise results in favourable adaptations to the
length–tension relationship in the hamstring muscle group.
Although the Nordic hamstring exercise was found to be
beneficial in terms of the hamstrings position of peak torque,
it had little effect on overall peak torque values. Possibly a
combination of Nordic hamstring exercise training and
traditional hamstring weight lifting movements may provide
beneficial strength and length-tension adaptations to prevent
soft tissue hamstring injuries. Overall the results of this
study suggest that the Nordic Hamstring exercise, because
of its ease of implementation, may be an effective method of
both enhancing performance and reducing injury in subelite athletes performing in sports requiring jumping
movements.
R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73
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