Reliability of a Clinical Test for Measuring Eccentric Knee Flexor Strength Using a Handheld Dynamometer

in Journal of Sport Rehabilitation

Context: Eccentric knee flexor strength assessments have a key role in both prevention and rehabilitation of hamstring strain injuries. Objective: To verify the reliability of a clinical test for measuring eccentric knee flexor strength during the Nordic hamstring exercise using a commercially available handheld dynamometer. Design: Reliability study. Setting: Physical Therapy Laboratory, Federal University of Health Sciences of Porto Alegre (Brazil). Participants: Fifty male amateur athletes (soccer or rugby players; 24 [3] y). Main Outcome Measures: Eccentric knee flexor strength. Results: When compared with a load cell–based device, the clinical test using a handheld dynamometer provided smaller force values (P < .05) with large effect sizes (.92–1.21), moderate intraclass correlation (.60–.62), typical error of 30 to 31 N, and coefficient of variation of 10% to 11%. Regarding the test–retest reproducibility (2 sessions separated by 1 week), the clinical test provided similar force values (P > .05) with only small effect sizes (.20–.27), moderate to good correlation (.67–.76), typical error of 23 to 24 N, and coefficient of variation of 9% to 10%. Conclusion: The clinical test with handheld dynamometer proposed by this study can be considered an affordable and relatively reliable tool for eccentric knee flexor strength assessment in the clinical setting, but results should not be directly compared with those provided by load cell–based devices.

Hamstring strain injury (HSI) is one of the most common injuries in team sports.1 Cohort studies have supported that athletes with low eccentric knee flexor strength are more prone to sustain an HSI.26 In addition, although restoring strength is a widely used criterion for discharge from rehabilitation,7 it is not uncommon for players to return to play with residual strength deficits following an HSI.8 Therefore, eccentric knee flexor strength assessments have a key role in both prevention and rehabilitation of HSI.

Isokinetic dynamometry is the gold standard method to assess eccentric knee flexor strength.9 However, the cost (around US$ 25,000), size, nonportability, and time-consuming protocols make this option not feasible for large-scale use in the clinical setting. Opar et al10 validated a portable prototype designed to perform a reliable and fast measure of the eccentric knee flexor strength during execution of the Nordic Hamstring Exercise (NHE). This prototype became commercially available equipment (NordBord Hamstring Testing System; VALD Performance, Brisbane, Australia), but the cost (around US$ 5000/y) continues to be a barrier for many clinicians.

Handheld dynamometers (HHDs) have a relatively low cost (around US$ 1000) and may be an option for measuring eccentric knee flexor strength in the clinical setting. Whiteley et al11 found a moderate correlation of an HHD eccentric test with isokinetic dynamometry in professional soccer players. However, this test may be impracticable for examiners who are not strong enough to move the leg in the opposite direction to the knee flexor’s maximal active contraction of a big/strong athlete. Therefore, this study aimed to verify the reliability of a clinical test for measuring eccentric knee flexor strength during the NHE using a commercially available HHD.

Methods

Participants

Fifty male amateur athletes participated in this study (24 [3] y; 174 [15] cm; 78 [12] kg). They were 18- to 35-year-old soccer or rugby players, engaged in sports practice at least once a week, with experience in amateur leagues, strength training, and NHE. Volunteers with a muscle injury in the posterior thigh in the 12 months prior to the tests or any current musculoskeletal injury that could impair the NHE execution were considered ineligible.

Study Design

In the first phase of the study, results provided by the HHD assessment (ie, the “clinical test”) were compared with the standard testing in a load cell–based device (see descriptions next). Assessments were performed independently by 2 examiners in a single session. Examiners were blinded as a third researcher was responsible for checking and recording the force values. An online random allocation software (random.org) determined the participants’ testing sequence.

The second phase of the study assessed the test–retest reproducibility (ie, intrarater reliability) of the clinical test. Twenty-five volunteers returned to the laboratory 1 week later to repeat the clinical test with the same examiner.

The study was approved by the ethics in research committee of the Federal University of Health Sciences of Porto Alegre (Brazil), and all volunteers provided written informed consent before participation.

Procedures

The proper NHE execution was explained by the researcher and demonstrated through a video. Volunteers performed a general warm-up protocol (5-min cycle ergometer exercise) and up to 3 submaximal NHE executions for specific warming-up and familiarization. In both testing methods, NHE was performed following recommendations previously described8 and with similar verbal encouragement.

Load Cell–Based Device

We used a custom-made device to measure eccentric knee flexor strength during the NHE.8 In summary, 2 independent load cells (sForce 250; Miotec, Porto Alegre, Brazil) fixed in a platform were attached to the volunteer’s ankles (right superior to the lateral malleolus) by velcro strips and collected force signals simultaneously. Force signals were collected using a 4-channel A/D converter (Miotool 400; Miotec, Porto Alegre, Brazil) with a 2000 Hz sampling rate. The volunteer performed 3 NHE executions with a 30-second rest between attempts. The highest peak force among the 3 recorded attempts was considered for analysis in each load cell (right leg and left leg). In a pilot study, this method presented a good to excellent test–retest reliability (ICC scores = .88–.95).

Clinical Test

All assessments were carried out by a male undergraduate student, 23 years old, 1.79 m height, 75 kg of body mass, with no experience with HHD handling. This examiner was instructed by the researcher on how to use the HHD and how to apply the clinical test. He had ∼3 hours of training with the assessment procedure. During testing, volunteers assumed a kneeling position with the feet hanging over the edge of a physiotherapy treatment table (Figure 1). Each hand of the examiner was positioned on the corresponding leg side, immediately superior to the volunteer’s lateral malleolus. The examiner used an HHD (MicroFet 2; Hoggan Scientific, Salt Lake City, UT) at his hand positioned on the assessed leg, and the other hand was kept in direct contact with the nonassessed leg (Figure 1). The HHD collected data with a sample rate of 100 Hz and a precision scale of 0.44 N. During the NHE execution, the examiner had to keep the HHD stationary, applying only the force necessary to prevent upward movement of the ankles. The examiner assessed the right and left legs’ force alternately, according to previous randomization. Three attempts for each leg were performed with a 30-second rest between them.

Figure 1
Figure 1

The execution of the NHE clinical test. The examiner used the handheld dynamometer in his left hand to assess the volunteer’s left leg and changed it to his right hand to assess the volunteer’s right leg. NHE indicates Nordic hamstring exercise.

Citation: Journal of Sport Rehabilitation 2021; 10.1123/jsr.2020-0014

Statistical Analysis

Shapiro–Wilk test confirmed the normality of data distribution. Paired sample t tests were used to compare measures provided by the device and the clinical test and to compare the 2 sessions with the clinical test. Cohen d effect sizes of such differences were classified as trivial (<.20), small (.20–.49), moderate (.50–.79), and large (>.80).

Intraclass correlation coefficient (ICC), typical error (TE), and percentual coefficient of variation (CV) were calculated to access intertest correlation (device vs clinical test) and test–retest reliability of the clinical test. The ICC values were classified as: poor (<.50), moderate (.50–.74), good (.75–.90), and excellent (>.90). A measure was considered reliable when CV was 10% or less. The minimum detectable change (MDC) of the clinical test was calculated. The between-measures agreement was tested using the Bland–Altman 95% agreement limits method.

Results

When compared with the device, the clinical test provided smaller force values (P < .05) with large effect sizes, moderate ICC, typical error of 30 to 31 N, and CV of 10% to 11% (Table 1). The Bland–Altman plots for comparing individual measures highlight the systematic variation trend in favor of the device (Figure 2A and 2B).

Table 1

Force Values Provided by the Load Cell–Based Device and the Clinical Test Using a Handheld Dynamometer

Device and clinical test comparison (n = 50)Clinical test intrarater reliability (n = 25)
Left legRight legLeft legRight leg
DeviceClinical testDeviceClinical testDay 1Day 2Day 1Day 2
Force, N315 (300–331)271 (260–281)318 (302–334)257 (245–269)271 (256–287)282 (265–298)259 (238–279)269 (249–288)
P value<.001<.001.120.223
ES0.94 (0.52–1.35)1.21 (0.77–1.63)−0.27 (−0.82–0.29)−0.20 (−0.76–0.36)
ICC0.60 (0.38–0.75)0.62 (0.41–0.76)0.67 (0.38–0.84)0.76 (0.53–0.89)
TE, N30.45 (25.44–37.95)31.41 (26.24–39.15)23.47 (18.33–32.65)24.28 (18.96–33.77)
CV, %10.06 (8.34–12.69)10.71 (8.87–13.52)9.10 (7.04–12.88)10.03 (7.75–14.22)

Abbreviations: CI, confidence interval; CV, coefficient of variation; ES, effect size; ICC, intraclass correlation coefficient; TE, typical error. Note: Values in parentheses are 95% CI.

Figure 2
Figure 2

The Bland–Altman plots. Gray dashed lines represent the 95% CI for the difference and the solid black lines represent mean of 2 measures. Each black dot represents an individual participant. Difference between the NHE device and the NHE clinical test against the mean of the tests for the eccentric knee flexor strength for (A) left and (B) right legs. Intrarater between-session differences against the mean of both sessions for the eccentric knee flexor strength for (C) left and (D) right legs. NHE indicates Nordic hamstring exercise.

Citation: Journal of Sport Rehabilitation 2021; 10.1123/jsr.2020-0014

Regarding the test–retest performance, the clinical test provided similar force values (P > .05) with only small effect sizes, moderate to good ICC, typical error of 23 to 24 N, and CV of 9% to 10% (Table 1). The clinical test presented MDC values of 65 and 67 N for left and right legs, respectively. The Bland–Altman plots highlight no systematic variability for intersession measurements performed by the same examiner (Figure 2C and 2D).

Discussion

The eccentric knee flexor strength measured with the HHD (ie, clinical test) was lower than with the load cell–based device. The apparent greater stabilization provided by the velcro strips compared with the examiner’s hands may have influenced the confidence of volunteers in exerting their maximum strength. Moreover, lower values of the clinical test may have resulted from the skill of the examiner who needed to counteract the athlete’s strength while keeping the ankles firmly positioned without forcing them against the table and avoid HHD movements in any direction. Using a fixed base (eg, straps) to stabilize the HHD could generate a more stable condition for performing the test and enhance the force values. However, it would affect the practicality of the clinical test.

We observed a moderate to good test–retest reliability with the clinical test (ICC scores of .67–.76), which was lower than that found with the isokinetic dynamometer (.83–.95)12,13 or the Nordbord (.85–.89),10 possibly because HHD assessments are more examiner dependent. Reliable assessments with HHD require that the volunteer’s strength does not exceed the ability of the examiner to counteract it.14 Therefore, using HHD directly by the evaluator without the aid of straps or other external stabilization devices may be a limitation in stronger populations by reducing the measurement reliability, especially in testing lower limbs.15,16

The ∼10% CV of our clinical test is at the limit for a measure to be considered reliable,17 and this variation is a little higher compared with the Nordbord (6.5%–8.4%).10 Moreover, the MDC of 65 to 67 N is similar to the Nordbord (61–69 N)10 and represents the minimum difference that can be interpreted as a real change of strength capacity with the clinical test. For instance, the clinical test could not be sufficiently accurate to identify the strength deficit of ∼35 N in the previously injured leg of professional soccer players with a history of HSI in the prior season.8 Conversely, eccentric knee flexor strength increased by ∼100 N in response to training programs in amateur athletes18 would be properly detected by this test. Clinicians should be aware of the MDC when interpreting the results of a clinical trial with HHD or any other strength test.

It is important to note that the test–retest reliability reported here is specific to the examiner who participated in this trial. The literature has shown that the examiner’s strength capacity interferes with measurement reliability and that his/her clinical experience in HHD assessment procedures may affect the reproducibility of those more challenging tests.19,20 Thus, it is reasonable to assume the clinical test reliability may be even greater with more experienced examiners. We recommend that clinicians should practice the clinical test extensively (at least until reaching a CV lower than 10%) before applying it to patients.

Conclusion

The clinical test with HHD proposed by this study can be considered an affordable and relatively reliable tool for eccentric knee flexor strength assessment in the clinical setting, but results should not be directly compared with those provided by load cell–based devices.

Acknowledgments

The authors declare no conflict of interest. This specific research received no funding. B.M.B. thanks CNPq-Brazil for the research productivity fellowship.

References

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    Opar DA, Williams MD, Shield AJ. Hamstring strain injuries: factors that lead to injury and re-injury. Sports Med. 2012;42(3):209226. PubMed ID: 22239734

    • Crossref
    • PubMed
    • Search Google Scholar
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  • 2.

    Croisier JL, Ganteaume S, Binet J, Genty M, Ferret JM. Strength imbalances and prevention of hamstring injury in professional soccer players: a prospective study. Am J Sports Med. 2008;36(8):14691475. PubMed ID: 18448578 doi:

    • Crossref
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  • 3.

    Fousekis K, Tsepis E, Poulmedis P, Athanasopoulos S, Vagenas G. Intrinsic risk factors of non-contact quadriceps and hamstring strains in soccer: a prospective study of 100 professional players. Br J Sports Med. 2011;45(9):709714. PubMed ID: 21119022 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Lee J, Mok K, Chan H, Patrick S, Chan K. Eccentric hamstring strength deficit and poor hamstring-to-quadriceps ratio are risk factors for hamstring strain injury in football: a prospective study of 146 professional players. J Sci Med Sport. 2017;21(8):789793. PubMed ID: 29233665 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    Timmins RG, Bourne MN, Shield AJ, Williams MD, Lorenzen C, Opar DA. Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study. Br J Sports Med. 2016;50(24):15241535. PubMed ID: 26675089 doi:

    • Crossref
    • PubMed
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  • 6.

    Bourne MN, Opar DA, Williams MD, Shield AJ. Eccentric knee flexor strength and risk of hamstring injuries in rugby union. Am J Sports Med. 2015;43(11):26632670. PubMed ID: 26337245 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Medeiros DM, Aimi M, Vaz MA, Baroni BM. Effects of low-level laser therapy on hamstring strain injury rehabilitation: a randomized controlled trial. Phys Ther Sport. 2020;42:124130. PubMed ID: 31991284 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Ribeiro-Alvares JB, Oliveira GDS, De Lima-E-Silva FX, Baroni BM. Eccentric knee flexor strength of professional football players with and without hamstring injury in the prior season. Eur J Sport Sci. 2021;21(1):131139. PubMed ID: 32180535 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Baroni BM, Ruas CV, Ribeiro-Alvares JB, Pinto RS. Hamstring-to-quadriceps torque ratios of professional male soccer players: a systematic review. J Strength Cond Res. 2020;34(1):281293. PubMed ID: 29794893

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10.

    Opar DA, Piatkowski T, Williams MD, Shield AJ. A novel device using the Nordic hamstring exercise to assess eccentric knee flexor strength: a reliability and retrospective injury study. J Orthop Sports Phys Ther. 2013;43(9):636640. PubMed ID: 23886674 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11.

    Whiteley R, Jacobsen P, Prior S, Skazalski C, Otten R, Johnson A. Correlation of isokinetic and novel hand-held dynamometry measures of knee flexion and extension strength testing. J Sci Med Sport. 2012;15(5):444450. PubMed ID: 22424705 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    Impellizzeri FM, Bizzini M, Rampinini E, Cereda F, Maffiuletti NA. Reliability of isokinetic strength imbalance ratios measured using the Cybex NORM dynamometer. Clin Physiol Funct Imaging. 2008;28(2):113119. PubMed ID: 18070123 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13.

    Li RC, Wu Y, Maffulli N, Chan KM, Chan JL. Eccentric and concentric isokinetic knee flexion and extension: a reliability study using the Cybex 6000 dynamometer. Br J Sports Med. 1996;30(2):156160. PubMed ID: 8799603 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14.

    Thorborg K, Bandholm T, Hölmich P. Hip- and knee-strength assessments using a hand-held dynamometer with external belt-fixation are inter-tester reliable. Knee Surg Sports Traumatol Arthrosc. 2013;21(3):550555. PubMed ID: 22773065 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15.

    Agre J, Magness J, Hull S, et al. . Strength testing with a portable dynamometer: reliability for upper and lower extremities. Arch Phys Med Rehabil. 1987;68(7):454458. PubMed ID: 3606371

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16.

    Fulcher ML, Hanna CM, Raina Elley C. Reliability of handheld dynamometry in assessment of hip strength in adult male football players. J Sci Med Sport. 2010;13(1):8084. PubMed ID: 19376747 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17.

    Cormack S, Newton R, McGuigan M, Doyle T. Reliability of measures obtained during single and repeated countermovement jumps. Int J Sports Physiol Perform. 2008;3(2):131144. PubMed ID: 19208922

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18.

    Bourne MN, Duhig SJ, Timmins RG, Williams MD, Opar DA, Al Najjar A, Kerr GK, Shield AJ. Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention. Br J Sports Med. 2017;51(5):469477. PubMed ID: 27660368 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19.

    Wikholm JB, Bohannon RW. Hand-held dynamometer measurements: tester strength makes a difference. J Orthop Sports Phys Ther. 1991;13(4):191198. PubMed ID: 18796845 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20.

    Kelln BM, McKeon PO, Gontkof LM, Hertel J. Hand-held dynamometry: reliability of lower extremity muscle testing in healthy, physically active, young adults. J Sport Rehabil. 2008;17(2):160170. PubMed ID: 18515915 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

Oliveira, Ribeiro-Alvares, Lima-e-Silva, and Baroni are with the Universidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre, Brazil. Rodrigues is with the Centro Universitário da Serra Gaúcha, Caxias do Sul, Brazil. Vaz is with the Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.

Baroni (bmbaroni@yahoo.com.br) is corresponding author.
  • View in gallery

    The execution of the NHE clinical test. The examiner used the handheld dynamometer in his left hand to assess the volunteer’s left leg and changed it to his right hand to assess the volunteer’s right leg. NHE indicates Nordic hamstring exercise.

  • View in gallery

    The Bland–Altman plots. Gray dashed lines represent the 95% CI for the difference and the solid black lines represent mean of 2 measures. Each black dot represents an individual participant. Difference between the NHE device and the NHE clinical test against the mean of the tests for the eccentric knee flexor strength for (A) left and (B) right legs. Intrarater between-session differences against the mean of both sessions for the eccentric knee flexor strength for (C) left and (D) right legs. NHE indicates Nordic hamstring exercise.

  • 1.

    Opar DA, Williams MD, Shield AJ. Hamstring strain injuries: factors that lead to injury and re-injury. Sports Med. 2012;42(3):209226. PubMed ID: 22239734

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2.

    Croisier JL, Ganteaume S, Binet J, Genty M, Ferret JM. Strength imbalances and prevention of hamstring injury in professional soccer players: a prospective study. Am J Sports Med. 2008;36(8):14691475. PubMed ID: 18448578 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3.

    Fousekis K, Tsepis E, Poulmedis P, Athanasopoulos S, Vagenas G. Intrinsic risk factors of non-contact quadriceps and hamstring strains in soccer: a prospective study of 100 professional players. Br J Sports Med. 2011;45(9):709714. PubMed ID: 21119022 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4.

    Lee J, Mok K, Chan H, Patrick S, Chan K. Eccentric hamstring strength deficit and poor hamstring-to-quadriceps ratio are risk factors for hamstring strain injury in football: a prospective study of 146 professional players. J Sci Med Sport. 2017;21(8):789793. PubMed ID: 29233665 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5.

    Timmins RG, Bourne MN, Shield AJ, Williams MD, Lorenzen C, Opar DA. Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study. Br J Sports Med. 2016;50(24):15241535. PubMed ID: 26675089 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 6.

    Bourne MN, Opar DA, Williams MD, Shield AJ. Eccentric knee flexor strength and risk of hamstring injuries in rugby union. Am J Sports Med. 2015;43(11):26632670. PubMed ID: 26337245 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 7.

    Medeiros DM, Aimi M, Vaz MA, Baroni BM. Effects of low-level laser therapy on hamstring strain injury rehabilitation: a randomized controlled trial. Phys Ther Sport. 2020;42:124130. PubMed ID: 31991284 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 8.

    Ribeiro-Alvares JB, Oliveira GDS, De Lima-E-Silva FX, Baroni BM. Eccentric knee flexor strength of professional football players with and without hamstring injury in the prior season. Eur J Sport Sci. 2021;21(1):131139. PubMed ID: 32180535 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 9.

    Baroni BM, Ruas CV, Ribeiro-Alvares JB, Pinto RS. Hamstring-to-quadriceps torque ratios of professional male soccer players: a systematic review. J Strength Cond Res. 2020;34(1):281293. PubMed ID: 29794893

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 10.

    Opar DA, Piatkowski T, Williams MD, Shield AJ. A novel device using the Nordic hamstring exercise to assess eccentric knee flexor strength: a reliability and retrospective injury study. J Orthop Sports Phys Ther. 2013;43(9):636640. PubMed ID: 23886674 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 11.

    Whiteley R, Jacobsen P, Prior S, Skazalski C, Otten R, Johnson A. Correlation of isokinetic and novel hand-held dynamometry measures of knee flexion and extension strength testing. J Sci Med Sport. 2012;15(5):444450. PubMed ID: 22424705 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 12.

    Impellizzeri FM, Bizzini M, Rampinini E, Cereda F, Maffiuletti NA. Reliability of isokinetic strength imbalance ratios measured using the Cybex NORM dynamometer. Clin Physiol Funct Imaging. 2008;28(2):113119. PubMed ID: 18070123 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 13.

    Li RC, Wu Y, Maffulli N, Chan KM, Chan JL. Eccentric and concentric isokinetic knee flexion and extension: a reliability study using the Cybex 6000 dynamometer. Br J Sports Med. 1996;30(2):156160. PubMed ID: 8799603 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 14.

    Thorborg K, Bandholm T, Hölmich P. Hip- and knee-strength assessments using a hand-held dynamometer with external belt-fixation are inter-tester reliable. Knee Surg Sports Traumatol Arthrosc. 2013;21(3):550555. PubMed ID: 22773065 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 15.

    Agre J, Magness J, Hull S, et al. . Strength testing with a portable dynamometer: reliability for upper and lower extremities. Arch Phys Med Rehabil. 1987;68(7):454458. PubMed ID: 3606371

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 16.

    Fulcher ML, Hanna CM, Raina Elley C. Reliability of handheld dynamometry in assessment of hip strength in adult male football players. J Sci Med Sport. 2010;13(1):8084. PubMed ID: 19376747 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 17.

    Cormack S, Newton R, McGuigan M, Doyle T. Reliability of measures obtained during single and repeated countermovement jumps. Int J Sports Physiol Perform. 2008;3(2):131144. PubMed ID: 19208922

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 18.

    Bourne MN, Duhig SJ, Timmins RG, Williams MD, Opar DA, Al Najjar A, Kerr GK, Shield AJ. Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention. Br J Sports Med. 2017;51(5):469477. PubMed ID: 27660368 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 19.

    Wikholm JB, Bohannon RW. Hand-held dynamometer measurements: tester strength makes a difference. J Orthop Sports Phys Ther. 1991;13(4):191198. PubMed ID: 18796845 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 20.

    Kelln BM, McKeon PO, Gontkof LM, Hertel J. Hand-held dynamometry: reliability of lower extremity muscle testing in healthy, physically active, young adults. J Sport Rehabil. 2008;17(2):160170. PubMed ID: 18515915 doi:

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
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