Assessment of Knee Flexor and Extensor Muscle ... - Fitness for Life

Clinical Evaluation & Testing

Assessment of Knee Flexor and Extensor Muscle Balance Philip Graham-Smith, PhD, CSCS; Paul A. Jones, PhD, MSc, CSCS; Paul Comfort, MSc. CSCS*D • University of Salford; Allan G. Munro, BSc • University of Bradford

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eciprocal knee joint muscle strength balance has traditionally been assessed by the isokinetic concentric flexor (hamstrings) to concentric extensor (quadriceps) peak torque ratio. Several studies have found low concentric hamstring to quadriceps (H/Q) ratio to be associated with hamstring strains among athletes.1-3 However, Bennell et al.4 found that a low concentric H/Q ratio did not predict the occurrence of hamstring injuries during one season of Australian rules footKey Points ball. A limitation of the concentric H/Q ratio The angle of crossover is an alternative is its lack of specificity method for assessment of muscle balance. to the mechanism of hamstring strain injury. The angle of crossover and angle-specific As the quadriceps contorque ratios at 30°, 40°, and 50° of knee tract concentrically, the flexion are reliable measures of muscle hamstrings passively balance. lengthen just before contracting eccentrically to decelerate the lower limb and stabilize the knee joint.5 Thus, lack of consistency between testing and functional contraction modes could explain the lack of association between the concentric H/Q ratio and hamstring injuries.4 To overcome this limitation a “dynamic control ratio” (eccentric hamstrings to concentric quadriceps) has been proposed.6 However, neither the concentric H/Q ratio

nor dynamic control ratio predicted hamstring injury among Australian rules football players.4 A criticism of the dynamic control ratio is that it only represents the relationship between peak torque values, which can occur at different angular positions within the range of motion. This limitation has been acknowledged by calculation of the dynamic control ratio at angles of 30°, 40° and 50° of knee flexion.6 However, due to intersubject variability in torque-angle plots, such an approach is difficult to interpret, as a decision has to be made regarding which ratio is more meaningful. We propose a “dynamic control profile” that represents the net joint torque (eccentric flexor to concentric extensor) over the entire range of motion, and identifies the range of motion whereby the concentric quadriceps torque is greater than eccentric hamstrings torque. The dynamic control profile represents the net joint torque at corresponding 0.5° joint angles throughout the full range of motion (Figure 1). The point at which the net joint torque crosses zero on the x-axis is defined as the angle of crossover. The closer the angle of crossover is to 90° of flexion, the greater will be the range of motion over which the hamstrings can compensate for torque generated by the quadriceps and possibly a reduced risk of injury. Pilot data © 2013 Human Kinetics - IJATT 18(5), pp. 1-5

international journal of Athletic Therapy & training

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collected in our lab have demonstrated that the angle of crossover can identify female athletes who recently sustained a hamstring strain. Thus, the purpose of this study was to examine the reliability of various muscle balance ratios and to compare the dynamic control profile to other measures of muscle balance.

Procedures and Findings Twenty-three male athletes (age 23 ± 6 years; height 179 ± 6 cm and mass 89.3 ± 12.8 kg) from the sports

of soccer and rugby participated in the study. Isokinetic testing was performed on two occasions that were separated by seven days. The muscle strength of right extremity hamstrings and quadriceps was assessed at 60°·s-1 in both concentric and eccentric modes using a Kin Com isokinetic dynamometer. Data collection and analysis procedures are presented in Table 1. A common mechanism of hamstring strain is high-velocity eccentric loading during running.1,7,8 Hamstring strain injury usually occurs late in the swing phase, or early in the stance phase, of the gait

Figure 1 The dynamic control profile represents the net joint torque (eccentric hamstring in relation to concentric quadriceps) throughout the full range of motion (0° [full knee extension] to 90° of flexion). The point at which the net joint torque corresponds to zero is defined as the angle of crossover.

Table 1. The Isokinetic Dynamometer Data Collection and Analysis Procedure Utilized in the Study 1. The subjects were seated with the hip joint at 90° (supine position = 0°; Figure 2). 2. The axis of rotation of the dynamometer shaft was aligned with the best approximation of the knee axis of rotation (midway between the lateral condyles of the femur and tibia). 3. The cuff of the dynamometer lever arm was attached to the ankle, just proximal to the malleoli and the moment arm recorded for gravity correction purposes. 4. Extraneous movement was prevented by straps (positioned at the hip, shoulders, and tested thigh) and by subjects holding onto handles located underneath the seat. Range of motion was set to as close to 90° as possible (0 = full knee extension). 5. Eight submaximal concentric knee extension and flexion movements were performed as a warm-up. 6. The ‘overlay’ method was selected to generate individual angle-torque graphs per repetition. 7. Concentric and eccentric strength of the quadriceps were measured before the hamstrings. 8. The repetition exhibiting peak torque from four maximal efforts in each mode (10 s recovery between efforts) was saved for further analysis.

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9. The resistance provided by the weight of the lower leg was recorded at full knee extension for gravity correction purposes. 10. Data was exported in ASCII format into Microsoft Excel® for further examination. 11. Using a tolerance of ± 1°·s-1, phases of acceleration and deceleration were deleted from the analysis. 12. The data were gravity-corrected by adding (for the quadriceps) or subtracting (for the hamstrings) the gravity correction factor [weight of leg] × [moment arm] × [cos (angle of flexion)]. 13. The gravity-corrected peak torque value from concentric hamstrings and concentric quadriceps was used to determine the concentric hamstring / quadriceps ratio, whereas for the dynamic control ratio peak torque recorded from the eccentric hamstrings was divided by the concentric quadriceps. 14. To obtain the dynamic control profile and derive the angle of crossover, the torque-angle plots for eccentric hamstrings and concentric quadriceps (Figure 3) were exported and gravity-corrected (see step 12) in Microsoft Excel®. For each data point (angle), the torque value for concentric quadriceps was subtracted from the eccentric hamstrings and represented on a graph (Figure 1).Consequently, the point where the net joint torque crosses zero on the x-axis is the angle of crossover. 15. To determine angle-specific ratios, the gravity-corrected torque values at each angle for eccentric or concentric hamstrings were divided by concentric quadriceps, and the values obtained at 30°, 40°, and 50° were reported.

H/Q ratio and the dynamic control ratio.6 Concentric H/Q and dynamic control ratios were calculated from knee flexor and extensor torque (Nm) measurements at angles of 30°, 40°, and 50°,6 and the angle of crossover was identified (Figure 1). Intraclass correlation coefficient (ICC) values were calculated for each variable.11 ICC values ≥ 0.80 represent highly consistent measurements.11,12 Standard error of measurement (SEM = SDPOOLED √ 1 - ICC) and the coefficient of variation (CV = SD / mean × 100) were also calculated for each variable. The calculated ICCs indicated acceptable test-retest repeatability for all variables (Table 2).

Discussion

Figure 2 Positioned on the Kin Com isokinetic dynamometer.

cycle.9,10 During late swing phase, the hamstrings eccentrically decelerate the lower leg in preparation for ground contact.9,10 Thus, muscle strength assessments were performed to evaluate the ability to decelerate the lower leg, and thereby prevent injury to the hamstrings during such actions. Measures of reciprocal knee joint muscle balance included the concentric


The results suggest that the angle of crossover, dynamic control ratio, and angle-specific ratios at 30°, 40°, and 50° are reliable measures of muscle balance. Our ICC values were similar to those reported for a previous isokinetic reliability study,13 which were 0.93 for concentric quadriceps knee extension; 0.93 for eccentric quadriceps knee flexion; 0.93 for concentric hamstrings knee flexion; and 0.94 for eccentric hamstrings knee extension at the same 60°·s-1 test velocity. The ICC values calculated for concentric H/Q ratio and dynamic control ratio were much greater than the values of 0.43 for concentric H/Q ratio and 0.73 for dynamic control ratio previously reported.13 The 0.03 SEM for concentric H/Q ratio and 0.04 SEM for dynamic control ratio were much lower than the


Figure 3 Torque versus knee flexion angle graphs for eccentric hamstrings and concentric quadriceps at 60°·s-1. To create the dynamic control profile, the concentric quadriceps torque is subtracted from the eccentric hamstrings torque throughout the full range of motion.

Table 2. Reliability Values for Various Isokinetic Knee Flexor And Extensor Performance Assessment Methods Variable Concentric quadricep Eccentric quadricep Concentric hamstring Eccentric hamstring Concentric hamstring / concentric quadricep ratio (peak torque, regardless of knee angle for each) Dynamic control ratio—eccentric hamstring / concentric quadricep (peak torque, regardless of knee angle for each) Angle of crossover Eccentric hamstring / concentric quadricep @ 50° Eccentric hamstring / concentric quadricep @ 40° Eccentric hamstring / concentric quadricep @ 30° Concentric hamstring / concentric quadricep @ 50° Concentric hamstring / concentric quadricep @ 40° Concentric hamstring / concentric quadricep @ 30° aRatio

ICC

SEMa

CV (%)

0.928 0.937 0.955 0.952

11.02 Nm 14.22 Nm 5.10 Nm 7.18 Nm

4.61 5.83 4.43 4.90

0.875

0.03

6.08

0.850 0.934 0.935 0.923 0.939 0.844 0.843 0.855

0.04 1.94 0.04 0.06 0.08 0.04 0.06 0.08

6.32 5.88 6.41 7.14 7.23 6.99 7.86 8.10

unless stated.

ICC = intraclass correlation coefficient; SEM = standard error of measurement; CV = coefficient of variation.

corresponding values reported elsewhere (0.07 and 0.08, respectively).13 Previous research pertaining to the value of the concentric H/Q ratio1-4 and the dynamic control ratio4 for prediction of hamstring strain occurrence has not

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yielded conclusive results. A limitation of both ratios is the comparison of peak torque output produced at different points in the range of motion for the two muscle groups. The angle of crossover might better identify at risk individuals. Theoretically, the greater the angle


of crossover, the greater the range of motion within which the hamstrings can eccentrically counteract the concentric action of the quadriceps. This finding suggests that the angle of crossover may be a useful indicator of progress toward restoration of normal hamstring function after injury, which is known to reduce risk for a subsequent injury of the hamstrings.14 However, as with any retrospective analysis of injury, it cannot be clearly established whether the angle of crossover deficit is the cause or the effect of the injury. Future research should evaluate the value of the angle of crossover for prospective prediction of hamstring strain occurrence.

Conclusion The study results demonstrate that balance between the hamstrings and quadriceps muscle groups may be more reliably assessed by an angle-specific torque ratio than either the peak torque ratio or the dynamic control ratio. However, the dynamic control ratio, which is a representation of joint torque generated throughout the range of motion by the two muscle groups, does appear to be a reliable measure of muscle balance. Alternatively, assessing the dynamic control ratio at specific joint angles is another reliable measure of muscle balance. These measures may provide more insight when screening athletes for hamstring injury risk, providing a fruitful avenue for future research. 

Acknowledgements The authors would like to thank Samantha Hargreaves for assistance with the manuscript.

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3. Yamamoto, T. Relationship between hamstring strains and leg muscle strength. J Sports Med Phys Fit. 1993;33:194-199. 4. Bennell, K, Wajswelner, H, Lew, P, Schall-Riaucour, A, Leslie, S, Plant, D, Cirone, J. Isokinetic strength testing does not predict hamstring injury in Australian rules footballers. Br J Sports Med. 1998;32:309-314. 5. Smith, AM. The coactivation of antagonist muscles. Can J Phyisol Pharma. 1981;59:733-747. 6. Aagard, P, Simonsen, EB, Magnusson, SP, Larsson, B, Dyhre-Poulsen, P. A new concept for isokinetic hamstring: quadriceps muscle strength ratio. Am J Sports Med. 1998;26:231-237. 7. Kujala, UM, Orava, S, and Jarvinen, M. Hamstring injuries: current trends in treatment and prevention. Sports Med. 1997;23:397-404. 8. Brockett, CL, Morgan, DL, and Proske, U. Predicting hamstring strain injury in elite athletes. Med Sci Sports Exerc. 2004;36:379-387. 9. Heiderscheit, BC, Hoerth, DM, Swanson, SC, Thelen, BJ, and Thelen, DG. Identifying the time of occurrence of a hamstring strain injury during treadmill running: A case study. Clin Biomechanics. 2005;20:1072-1079. 10. Thelen, D, Chumanov, D, and Hoerth, M. Hamstring muscle kinematics during treadmill sprinting. Med Sci Sports Exerc. 2005;38:108-114. 11. Vincent, WJ. Statistics in kinesiology. Champaign, IL: Human Kinetics, 1995:178-191. 12. Cortina, J.M. What is co-efficient alpha? An examination of theory and application. Journal of Applied Psychology, 1993;78:98-104. 13. Sole, G, Hamren, J, Milosavljevic, S, Nicholson, H, and Sullivan, J. Test-retest reliability of isokinetic knee extension and flexion. Arch Phys Med Rehabil. 2007;88:626-631. 14. Woods, C, Hawkins, RD, Maltby, S, Thomas, A and Hodson, A. The Football Association Medical Research Programme: an audit of injuries in professional football - analysis of hamstring injuries. Br J Sports Med. 2004;38:36-41. 15. Baltzopoulos V. Isokinetic Dynamometry. In: Biomechanical evaluation of movement in sport and exercise. The British Association of Sport and Exercise Sciences Guidelines: Payton, C, Bartlett, R, eds. London: Routledge; 2008;103-128.

Philip Graham-Smith is a Senior Lecturer in Sports Biomechanics at the University of Salford. He has worked with UK Athletics for over 20 years and was former consultant Head of Biomechanics at the English Institute of Sport. Paul A. Jones is a Lecturer in Sports Biomechanics at the University of Salford. Paul Comfort is the programme leader for MSc Strength and Conditioning at the University of Salford and head of sports science for Salford City Reds Rugby League. Allan G. Munro is a Lecturer in Sports Rehabilitation at the University of Bradford. Joseph M. Hart, PhD, ATC, University of Virginia, is the report editor for this article.
