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

aMusculoskeletal Research Unit, Central Queensland University, North Rockhampton, Qld., 4701 AustraliabSchool 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 epidemiolo-

gical 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).

1466-853X/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.ptsp.2005.02.003

* Corresponding author. Tel.: C61 07 49 309704; fax: C61 07 49

309871.

E-mail address: r.clark@cqu.edu.au (R. Clark).

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 compari-

son 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

Physical Therapy in Sport 6 (2005) 67–73

www.elsevier.com/locate/yptsp

R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–7368

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 ham-

string/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

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.

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.

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.

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,

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).

Table 1

Four week training protocol

Week Sessions

per week

Sets–Reps Technical notes

1 1 2/5 The subject is encouraged to resist

falling as long as possible

2 2 2/6 Subject tries to reduce lowering speed

3 3 3/6 Subjects can resist falling even longer,

and for an increased number of

repetitions

4 3 3/8 Load on the subject increases by

allowing more speed in the start phase,

as well as another gradual increase in

repetitions

Adapted from Oslo Sports Trauma Research Center (2004)

R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–7370

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

Table 2

Isokinetic performance measures assessed pre and post a 4 week eccentric hamst

Isokinetic performance

measure

Pre Post

Dominant Non-dominant Dominant

Quadriceps

PT 204.34 204.93 180.84

(N.m.) G20.1 G23.8 G19.8

Pos PT 69.32 62.82 66.84

(8) G4.0 G6.3 G5.4

Hamstrings

PT 98.61 99.00 97.30

(N.m.) G13.3 G28.4 G13.9

Pos PT 36.76 28.21 30.77

(8) G10.8 G4.0 G8.2

L, effect for Limb (dominant and non-dominant); T, effect for test (pre- and post-i

PT, position of peak torque. *Indicates significant difference (p!0.05).

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).

4. Discussion

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.,

ring training intervention

P and F values

Non-dominant L T L!T

182.09 0.90 0.01* 0.95

G20.0 0.02 9.77 0.00

65.11 0.06 0.95 0.07

G7.6 4.85 0.00 4.34

103.64 0.49 0.68 0.36

G19.3 0.53 0.19 0.93

21.61 0.01* 0.01* 0.91

G9.0 11.77 10.3 0.01

ntervention); L!T, interaction between limb and test; PT, peak torque; Pos

150

175

200

225

250

Pre Post

Testing Day

PeakTorque(N

.m.)

*

Fig. 3. Quadriceps peak torque pre- and post-training intervention.

*Indicates significant difference between pre- and post-testing results

(pZ0.01).

20

25

30

35

40

45

Pre Post

Testing Day

PositionofPeakTorque(°)

*

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).

R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73 71

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

20

25

30

35

40

45

Non-dominant Dominant

Limb

PositionofPeakTorque(°)

*

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).

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.

48

50

52

54

56

58

60

62

Pre Post

Testing

JumpHeight(cm)

*

Fig. 6. Vertical jump height measured pre- and post-training intervention.

*Indicates significant difference between pre- and post-testing results

(pZ0.04).

R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–7372

Despite the beneficial adaptations in terms of the length-

tension 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 sub-

elite athletes performing in sports requiring jumping

movements.

R. Clark et al. / Physical Therapy in Sport 6 (2005) 67–73 73

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