IJSPT ORIGINAL RESEARCH ABSTRACT. CORRESPONDING AUTHOR Daniel Ramskov Klostermarken 3, 2th Aalborg, DN

Transcription

1 IJSPT ORIGINAL RESEARCH NORMATIVE VALUES OF ECCENTRIC HIP ABDUCTION STRENGTH IN NOVICE RUNNERS: AN EQUATION ADJUSTING FOR AGE AND GENDER Ramskov, D. 1,3 Pedersen, M.B. 3 Kastrup, K. 3 Lønbro, S. 1 Jacobsen, J.S. 2 Thorborg, K. 4 Nielsen, R.O. 1,3 Rasmussen S. 3 ABSTRACT Purpose: Low eccentric strength of the hip abductors, might increase the risk of patellofemoral pain syndrome and iliotibial band syndrome in runners. No normative values for maximal eccentric hip abduction strength have been established. Therefore the purpose of this study was to establish normative values of maximal eccentric hip abduction strength in novice runners. Methods: Novice healthy runners (n = 831) were recruited through advertisements at a hospital and a university. Maximal eccentric hip abduction strength was measured with a hand held dynamometer. The demographic variables associated with maximal eccentric hip abduction strength from a univariate analysis were included in a multivariate linear regression model. Based on the results from the regression model, a regression equation for normative hip abduction strength is presented. Results: A significant difference in maximal eccentric hip abduction strength was found between males and females: 1.62 ± 0.38 Nm/kg (SD) for males versus 1.41 ± 0.33 Nm/kg (SD) for females (p < 0.001). Age was associated with maximal eccentric hip abduction strength: per one year increase in age a ± Nm/kg (SD) decrease in strength was found, p < Normative values were identified using a regression equation adjusting for age and gender. Based on this, the equation to calculate normative values for relative eccentric hip abduction strength became: ( (age * ) + (gender (1 = male / 0 = female) * 0.215) ± 1 or 2 * 0.354) Nm/kg. Conclusion: Normative values for maximal eccentric hip abduction strength in novice runners can be calculated by taking into account the differences in strength across genders and the decline in strength that occurs with increasing age. Age and gender were associated with maximal eccentric hip abduction strength in novice runners, and these variables should be taken into account when evaluating eccentric hip abduction strength in this group of athletes. Level of Evidence: 2A Key words: Eccentric hip abduction strength, novice runners 1 Department of Public Health, Section for Sport Science, Faculty of Health Sciences, Aarhus University, DK Department of Physiotherapy and Occupational Therapy, Aarhus University Hospital, DK Orthopaedic Surgery Research Unit. Science and Innovation Center, Aalborg University Hospital, DK Arthroscopic Centre Amager, Copenhagen University Hospital, Hvidovre, DK-2300 Review board: Ethics committee, central Denmark region (M and 30/1012). and the Danish Data Protection Agency. CORRESPONDING AUTHOR Daniel Ramskov Klostermarken 3, 2th Aalborg, DN daniel.joergensen@folkesundhed.au.dk The International Journal of Sports Physical Therapy Volume 9, Number 1 February 2014 Page 68

2 INTRODUCTION Injuries related to running are common. Novice runners have an increased risk per 1000 hours of running when compared with their recreational peers. 1,2 The hip abductors work eccentrically during the stance phase of walking and running to control multi-planar movements such as hip adduction, rotation, and knee abduction. 7,9 Low eccentric strength of the hip abductors may result in lack of control of movements in the frontal plane, and the hip can be forced into adduction and the knee into internal rotation which may increase the risk of injury. 6 9 Hip abductor muscle weakness is related to pathological conditions of the lower limb, and has been documented in patellofemoral pain and iliotibial band syndromes. 6,10 13 No normative values for maximal eccentric hip abduction strength in novice runners have, however, been established. Therefore, low eccentric hip abductor strength at the individual level in novice runners remains unidentified. Maximal muscle strength is usually related to gender and age. This relationship may also have an influence on hip strength Normative values for maximal isometric hip abduction strength have been reported by Meldrum et al 14 and Andrews et al, 15 and the strength values were significantly associated with age, gender, and activity level. Normative values for maximal concentric hip abduction strength measured using an isokinetic dynamometer have also been reported in a study by Harbo et al 16 with values being significantly related to age and gender. The purpose of the present study was to establish normative values for maximal eccentric hip abduction strength in novice runners. These values could be used in the evaluation of maximal eccentric hip abduction strength, in order to identify individuals with low maximal eccentric hip abduction strength. It was hypothesized that females and subjects who were non-active prior to inclusion in the study would demonstrate lower maximal strength compared with males and active individuals. Furthermore, it was hypothesized that maximal muscle strength would decline with increasing age. METHOD Design Data were retrieved from July to August 2011 in the DANO-RUN study investigating the aetiology behind running-related injuries in novice runners. 17 The DANO-RUN study was presented to the Local Ethics Committee of Central Denmark Region (M and 30/1012). The committee waived the request of ethics approval, since this study according to Danish law does not require approval owing to the observational design. Recruitment was made through advertisements at Aarhus University Hospital and Aarhus University. All participants provided written consent prior to inclusion, and approval was obtained from the Danish Data Protection Agency. Participants Initially, interested individuals completed an online questionnaire. All submitted questionnaires were evaluated to identify healthy eligible individuals from years. Individuals were excluded if they: 1) used insoles on a daily basis, 2) used knee or ankle braces, 3) had diabetes, 4) had had a fever within the last two weeks, 5) had been diagnosed with a heart problem, 6) had chest pain during strenuous activity, 7) had had a stroke, 8) experienced shortness of breath during strenuous activity, 9) had swollen ankles, 10) had experienced that the heart skipped a beat during activity or rest, 11) had a relative who had died from a stroke, 12) were pregnant, 13) had had an injury in the lower extremities in the past three months, 14) participated in physical activity exceeding 4 hours per week. Final inclusion depended on the individual s level of running. The current study used a novice runner definition stating that to be included the total volume of running within the past 12 months must not have exceeded 10 kilometres. 18,19 Body-weight, height, age, gender and activity level were collected at baseline. Two categories of activity level were identified: non-active (no previous physical activity) and active (1-4 hours per week). The categorization was based on the amount of weekly hours of either weight bearing physical activity (e.g. tennis, soccer, or gymnastics) or non-weight bearing physical activity (e.g. swimming, water gymnastics, or cycling). Participants were categorized as active if they participated in either weight bearing activities or non-weight bearing activities, with a maximum of 4 hours per week. 20 Outcome measures Maximal eccentric hip abduction strength was measured on both legs, without determining the dominant side, with a hand-held dynamometer (Comman- The International Journal of Sports Physical Therapy Volume 9, Number 1 February 2014 Page 69

3 derpowertrack II Muscle Dynamometer, JeTech Medical,Salt Lake City, USA) using a reliable technique. 21,22,23 The intra-tester and inter-tester reliability of this technique has previously been reported. 21,22 One male and two female testers experienced in performing break-tests using a hand-held dynamometer performed all strength measurements. The break-test was defined according to the method used by Tyler et al 24 and Thorborg et al 22 where a force was manually applied in order to break the isometric muscle contraction, with the participant still exerting force. The dynamometers were calibrated prior to each test. To ensure standardisation of all measurements, an anatomical landmark was identified and marked on both limbs five centimetres proximal to the proximal edge of the lateral malleolus. Limb length was measured from the anatomical landmark to the most prominent point on the anterior superior iliac spine in the supine position. 13,22 Randomised measurements of bilateral maximal eccentric muscle force were performed. Participants were placed on an examination table in a side-lying position and instructed to stabilise themselves by holding on to the examination table, using the hand of the side being tested, while the head rested on the other arm. 22 The hip and knee of the non-tested limb were placed in 90 flexion, while the limb being tested was fully extended. The participants were guided to place the pelvis in a 90 angle relative to the examination table. The examiner elevated the limb of the participants into the neutral hip position in the frontal plane. The participants were instructed to abduct the hip with maximal force against the examiners resistance, keeping the heel as the highest point. The standardised command used by the tester was Go ahead! Push! Push! Push! Push! Relax!. 22 Resistance against hip abduction was given at the anatomical landmark, while the participant exerted a 3-second Maximum Voluntary Isometric Contraction (MVIC) before the tester initiated testing of maximal eccentric force, by breaking the isometric contraction, moving the leg into adduction, while the participant continued to exert maximum force 22 Prior to testing one practice trial was performed including sub-maximal contraction without the dynamometer. Each test was repeated until the participants reached a force plateau of less than 5% between two consecutive measurements. 22 The mean of the two consecutive measurements with a force plateau within 5% was defined as the maximal eccentric hip abduction strength and used in the analysis. To avoid fatigue, participants rested for one minute between each measurement. A participant was excluded if the force plateau was not reached within 6 attempts, owing to a possible muscle fatigue and decline in force production. Data analysis Descriptive data were presented as counts and percentage for dichotomous data, and as mean, standard deviation and 95% confidence interval for continuous data. All continuous data were normally distributed. By pooling data from right and left limbs of the same participant, the assumption of independence is violated. 25 Therefore, data from either the right leg or the left leg of each participant was randomly included in the analysis. Maximal eccentric hip abduction strength was normalised to limb length and bodyweight by multiplying the strength values with the moment arm and dividing this by the body-weight (normalised strength = (absolute strength * moment arm) / body-weight). Normative values were defined using the cut-off points employed previously by Redmond et al. 26 and Moseley et al. 27, namely: Normal range: between ± 1 standard deviation (SD) of the mean (68% prediction interval) Low strength: Values from - 1 to - 2 SDs of the mean Very low strength: Values outside - 2 SDs of the mean. High strength: Values from + 1 to + 2 SDs of the mean Very high strength: Values outside + 2 SDs of the mean. Unpaired student s t-test was used to test for differences in maximal eccentric hip abduction strength among males and females as well as among inactive and active participants. A linear regression model was used to assess if maximal hip abduction strength declined with increasing age. Since the analyses of age and gender revealed a significant association with hip strength, these variables were included in a multivariate linear regression model. Based on the results from this model, an equation for maximal eccentric hip abduction strength was presented. The International Journal of Sports Physical Therapy Volume 9, Number 1 February 2014 Page 70

4 Table 1. Demographic characteristics of gender, age, weight, BMI, and activity level among included participants presented in mean ± standard deviation. * = counts presented. A result was considered statistically significant if p Statistical analyses were performed using STATA/SE version 12.0 (Dallas, Texas, USA). RESULTS The total sample comprised 832 participants. One participant was excluded from the study because of a missing weight value. Demographic characteristics are presented in Table 1. A statistically significant difference between the maximal, eccentric abduction strength between males and females was found: 1.62 ± 0.38 Nm/kg (SD) for males versus 1.41 ± 0.33 Nm/kg (SD) for females, p < Maximal eccentric strength ranged from 0.68 to 2.95 Nm/kg in males and from 0.75 to 2.74 Nm/kg in females. A negative relation between age and maximal eccentric hip abduction strength was found: per one year increase in age a ± N*m/kg (SD) decrease in strength was found, p < There were no statistically significant differences in abduction strength between the non-active and active participants (1.53 ± 0.38 Nm/kg (SD) versus 1.50 ± 0.35 Nm/kg (SD), p = 0.26). The results from the multivariate analysis including age and gender are presented in Table 2 and scatter plots for the relationship between eccentric hip strength and age stratified by gender are presented in Figure 1. The regression equation to obtain normative values with respect to age and gender is: Maximal eccentric hip abduction strength = ( (age * ) + (gender * 0.215) ± 1 or 2 * 0.354) Nm/kg. If normative values for maximal eccentric hip abduction strength normalised for age and gender is to be obtained, age must be inserted in years and gender inserted as either 0 for female or 1 for male in the regression equation with the ± 1 Root MSE or ± 2 Root MSE added. If normative values between a very low strength and low strength or very high strength and high strength is to be calculated the ± 2 * Root MSE is used. The ± 1 * Root MSE is used to calculate normative values between normal strength and either low strength or high strength. DISCUSSION In the present study normative values for maximal eccentric hip abduction strength in 831 novice runners were established. A negative relationship between age and hip abduction strength was found. Furthermore, a significant difference in strength between genders was identified. These findings are supported by studies on isometric strengh 14,15 and the study by Harbo et al 16 on maximal concentric hip abduction strength. The activity level of the participants did not affect the maximum eccentric hip abduction strength. When establishing normative values for maximal eccentric hip abduction strength in novice runners the effect of age and gender should Table 2. Multivariate regression analysis on age and gender. CI = Confidence interval. N = Newton. Kg = kilogram The International Journal of Sports Physical Therapy Volume 9, Number 1 February 2014 Page 71

5 Figure 1. Scatter plots for the relationship between eccentric hip strength and age stratified by gender. Categorising individuals based on their eccentric hip abduction strength using an easy and inexpensive method of assessment is important for clinicians to evaluate changes in patients with hip-related musculoskeletal pain problems. 28 Several studies on subjects with musculoskeletal pain problems of the lower limb, also report muscle strength deficits of the hip abductors. 6,13,29 31 The values makes it possible for the clinicians to evaluate changes over time and evaluate the effect of the chosen intervention. 7 Figure 2. Measurement of eccentric abduction strength (with permission 22 ). be taken into account in order to make it possible to categorize the measured value of any individual as very low, low, normal, high, or very high. The findings of the present study may also be used in future prospective studies to investigate whether maximal eccentric hip abduction strength is associated with development of running-related injuries. In the design of prospective studies participants can be categorized into exposure groups according to the level of maximal eccentric hip abduction strength using the regression equation presented in the current study. This would be valuable when investigating whether the risk of sustaining an injury varies among individuals in the different categories of maximal eccentric hip abduction strength. However, values presented in this study should not be considered as normative values for athletes other than novice runners, as this group of athletes only participate in physical activity to a limited extent. The International Journal of Sports Physical Therapy Volume 9, Number 1 February 2014 Page 72

6 Average eccentric strength of novice runner appears to be lower than eccentric hip abduction strength in young football players. 22 The present study used a handheld dynamometer to assess maximal eccentric hip abduction strength. This method is easily applicable in general clinical practice. 23 Other studies have suggested use of an isokinetic dynamometer. 16,32 This methodology is, however, costly and time-consuming. Furthermore, eccentric hip abduction strength is possibly a better estimate of functional strength, then isometric strength. Because, in relation to everyday life eccentric hip abduction strength measurement relates to the biomechanical function of the hip abductors in walking and running. 3 The present study has some limitations that need to be considered when interpreting the results. Mainly, the handheld dynamometry has not been validated against a gold standard like an isokinetic dynamometer. Additionally, three different individuals performed all measurements of maximal eccentric hip abduction strength. Different testers may negatively affect the reliability of the measurements compared to measurements from studies involving only one tester. Thorborg et al. 32 argued that physical strength of an examiner will influence the reliability of measurements, and reported a systematic difference in muscle strength increasing linearly with the muscle strength of the examiner. The measurements in that study were performed on isometric contractions, and complete stability during the test at a high level of isometric muscle strength may require specific technical and physical demands of the examiner. The dynamic nature of eccentric testing may reduce the stability requirements, and despite the fact that the examiner should overcome the force generated by the participant, the physical demands of the tester may be reduced compared to the testing setup during isometric contractions. The strength of the hip abductors was measured in an open chain movement, which is opposed to the way these muscles work during running, where the hip abductors work eccentrically in a closed chain manner. This choice was made in order to evaluate an easy and inexpensive method available for most clinicians. Therefore, electromyography (EMG) was not an option in this study even though EMG during running may have given a better estimate of the eccentric muscle work in a closed chain movement. The authors though believe that the methods utilized in the current study offer a reliable and clinically useful estimate of a possible strength deficit in running among novice runners. The external validity of the present study should also be considered. Healthy adults were recruited for a different study on running-related injuries. 18 Thus, individuals with chronic diseases, pain or an activity level above four hours per week were excluded. Possibly, persons with different diseases or activity profiles may have different eccentric hip abduction strength as compared to the participants included in the present study. Therefore, the normative values reported in the present study should only be generalised to healthy, novice runners between 18 and 65 years. The non-siginificant relationship between activity level and maximum eccentric hip abduction strength can have several possible explanations. The muscle activity required in eccentric hip abduction movement is lateral acceleration, and maybe the participants reporting a high activity level, did not participate in activities that contained lateral accelerations. Another explanation could be low sensitivity of our activity level examination. Activity level was reported using a self-reported questionnaire and misinterpretation of questions or even recall bias is possible. The possible information bias introduced here is however suspected to be evenly distributed between individuals with different strength, and will not bias the estimates. CONCLUSION Normative values for maximal eccentric hip abduction strength in novice runners can be calculated by taking into account the differences in strength across genders and the decline in strength that occurs with increasing age. Age and gender were associated with maximal eccentric hip abduction strength in novice runners, and these variables should be taken into account when evaluating eccentric hip abduction strength in this group of athletes. REFERENCES 1. Taunton JE, Ryan MB, Clement DB, McKenzie DC, Lloyd-Smith DR, Zumbo BD. A retrospective case- The International Journal of Sports Physical Therapy Volume 9, Number 1 February 2014 Page 73

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