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Original research
Trunk muscle activation, fatigue and low back pain in tennis players José Pedro Correia ∗ , Raul Oliveira, João Rocha Vaz, Luís Silva, Pedro Pezarat-Correia Laboratory of Motor Behavior, CIPER, Faculdade de Motricidade Humana, Universidade de Lisboa, Portugal
a r t i c l e
i n f o
Article history: Received 2 September 2014 Received in revised form 23 March 2015 Accepted 8 April 2015 Available online xxx Keywords: Abdominal Activation Electromyography Endurance Lumbar
a b s t r a c t Objectives: To analyze differences in trunk endurance time, fatigue and activation in tennis players with and without low back pain. Design: Observational study, cross-sectional design. Methods: Thirty-five tennis players completed an isometric trunk endurance protocol comprising four tasks (flexor, extensor and side bridge tests). LBP history was obtained through the Nordic Musculoskeletal Questionnaire. Endurance time was recorded for each test. Surface electromyographic activity was recorded bilaterally from rectus abdominis, external obliques, iliocostalis lumborum and longissimus thoracis. Average electromyographic amplitude and median frequency slopes during the tests were calculated and used as indicators of change in muscle activation and fatigue. Results: Asymptomatic players had greater flexor (p = 0.004) and right side bridge (p = 0.043) endurance times. These players produced a greater increase in avrEMG during the right side bridge test for the left ES-I (p = 0.046) and right EO (p = 0.008). Players with LBP in the last 7 days showed reduced activation of the left (p = 0.014) and right (p = 0.013) ES-I and left longissimus thoracis (ES-L, p = 0.047) in the extensor test. In the left side bridge test there was a lower avrEMG slope of the left EO (p = 0.024) and left RA MF slope (p = 0.011). In the right side bridge test a lower left ES-I avrEMG slope was found (p = 0.048). Conclusions: Symptomatic players show lower activation of extensor muscles, less co-contraction patterns and less abdominal endurance. Tennis coaches and clinicians should consider these factors in their approach to players with LBP. © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction The trunk plays an important role on the kinetic chain of tennis strokes, being part of the force generating and transmission sequence.1 Trunk activation during the tennis serve can be elevated and asymmetric in various muscles.2,3 The serve presents significant trunk musculoskeletal demands, most notably during the wind-up phase, where players perform a trunk hyperextension, lateral flexion and rotation movement.4 Although this allows for greater storage of elastic energy for the acceleration phase, it places great stress on the posterior spinal structures, and is thought to be the main causative factor for spondylolysis in tennis players.5 Eccentric activity of the rectus abdominis (RA) is important to support the trunk and avoid excessive spinal stress. Afterwards, in the acceleration phase, a counter rotation occurs, eliciting forceful concentric activity of the trunk flexors and rotators. Finally, during the follow-through phase, eccentric control of the erector spinae (ES) is necessary to assure a correct deceleration of the serve motion.2,3
∗ Corresponding author. E-mail address: [email protected] (J.P. Correia).
The serve also involves high trunk motion speeds and imposes spinal loads of up to nearly 3000 N.6 Studies on lumbar kinematics during the tennis serve have also shown higher lateral flexion moments in players with LBP, which may be a potential injury mechanism.7,8 The repetitive nature of tennis, involving a majority of serve and forehand strokes, leads to asymmetrical musculoskeletal adaptations (e.g. in the shoulder and hip) that are commonly associated with injury.9 Evidence of trunk adaptations in tennis players has arisen in imaging studies of RA muscle volume10 and spinal osteoarticular changes (pars lesions, disk pathology and facet arthropathy).11 To the best of the authors’ knowledge, studies of trunk activation and low back pain (LBP) in tennis players have only comprised the extensor muscles. Tennis players with LBP history showed decreased ES activation during trunk extension.12,13 Despite these findings, there is a lack of research on trunk fatigue and activation in tennis players. Studies on sedentary and athletic populations have illustrated that there are different trunk endurance patterns between various muscle groups.14,15 However, very little is known about trunk endurance patterns between muscles in tennis players. Given the previously stated role of different trunk muscle groups on spinal loads during tennis strokes, it is likely their
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Please cite this article in press as: Correia JP, et al. Trunk muscle activation, fatigue and low back pain in tennis players. J Sci Med Sport (2015), http://dx.doi.org/10.1016/j.jsams.2015.04.002
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activity and fatigability will also be associated with LBP symptoms. Decreased trunk activation and co-contraction patterns have been found in LBP patients.16 Trunk co-contraction patterns have also been shown to increase spinal stability and decrease spinal load.17 Muscle fatigue is associated with decreased tennis performance and impaired injury protection mechanisms.18 The onset of fatigue also promotes a loss in neuromuscular control, decreasing spinal stability.19 Thus, the objectives of this study were to (1) analyze differences in trunk endurance time between tennis players with and without LBP; (2) analyze differences in EMG slopes (amplitude and median frequency) during fatiguing trunk isometric tasks between tennis players with and without LBP; and (3) verify the existence of a relation between endurance time and EMG slopes. We hypothesize that (1) players with LBP history show endurance time differences in various trunk muscle groups; (2) players with LBP history present differences in the fatigability and activation pattern of various trunk muscles; and (3) there is a correlation between endurance time and EMG parameters. 2. Methods Thirty-seven tennis players volunteered for the study. Thirtyfive (28 male, 7 female, 18.54 ± 3.00 years old) met the study’s criteria and were included in the final sample. There were 2 asymptomatic female players and 5 in all of the LBP subgroups. Inclusion criteria were (1) minimum 3 years of tennis practice, (2) minimum 6 h/week of tennis practice in the last year and (3) currently competing at a national level or higher. Exclusion criteria were (1) history of surgery to the trunk/spine, (2) history of serious trunk musculoskeletal pathology (trunk surgery, tumor, infection, structural scoliosis, spinal fracture), (3) practice of another sport for 3 or more times/week (excluding physical training) and (4) being unable to assume testing positions. Players were recruited without regard to their current LBP status.
One player was excluded due to previous trunk surgery and another was unable to assume testing positions due to an ankle sprain. All players were able to complete the protocol regardless of current LBP. Thirty-four of the 35 players were right-handed and 16 were minors. Full sample description is detailed in Table 1. All tests were performed by the same researcher at tennis clubs nationwide. All players (or their legal tutors) gave written consent for participation in the study. The study was approved by the Research Ethics Committee of the Faculty of Human Kinetics, University of Lisbon (approval number 5/2012). All procedures were taken in accordance with the Declaration of Helsinki. Players completed a trunk endurance protocol as described in McGill et al.,14 comprising four isometric tests (trunk flexor, extensor, and left/right side bridge tests, Fig. 1). This protocol has been considered a safe, reliable and cost-effective way of evaluating trunk endurance14,20 and was applied in order to evaluate the fatigue-related behavior of trunk muscles relevant to tennis practice. Players were encouraged to hold the positions for as long as they could and were given the opportunity to experience positions for a few seconds before measurement. Test order was randomized and 5 min of rest were given between tests. Tests began as soon as players assumed position. The termination criteria of the original protocol were used.14 Standard corrections were provided if players started deviating from the test position. The beginning and end of the recording were done via a keyboard trigger. All players reported fatigue as the reason for termination. LBP history was obtained through an adapted Portuguese version of the Nordic Musculoskeletal Questionnaire21 (NMQ) containing three yes/no questions on the lumbar region: (1) existence of symptoms over the last 12 months (LBP condition), (2) over the last 7 days (LBP-7d condition) and (3) being unable to train or play over the last 12 months because of LBP (LBP-TR condition). The last 2 questions were only answered by the players who answered question 1 affirmatively.
Table 1 Sample description.
Age (years)
Height (m)
Weight (kg)
BMI (kg/m2 )
Years of practice
Practice hours/week
Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR
N
Minimum
Maximum
Mean ± SD
35 15 20 8 7 35 15 20 8 7 35 15 20 8 7 35 15 20 8 7 35 15 20 8 7 35 15 20 8 7
16 16 16 16 16 1.56 1.68 1.56 1.56 1.63 50.90 55.3 50.9 50.9 55.0 18.69 18.69 19.04 20.70 19.04 3 3 3 3 10 6 6 6 7 10
28 20 28 28 26 1.97 1.97 1.88 1.88 1.84 93.00 93.00 85.0 85.0 84.3 26.31 25.20 26.31 24.44 24.90 24 14 24 24 18 40 40 29.5 28.5 29.5
18.54 17.53 19.3 20.5 19.57 1.76 1.77 1.75 1.70 1.77 68.80 67.77 68.56 65.51 67.63 22.04 21.57 22.40 22.47 21.50 9.7 9.16 10.1 10.37 11.57 17.06 19.5 15.23 14.81 16.79
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
3.00 1.25 3.68 4.28 3.82 0.09 0.08 0.09 0.11 0.07 9.85 9.25 10.44 12.59 9.39 1.85 1.71 1.91 1.57 1.78 4.12 3.13 4.76 6.26 2.94 8.95 10.79 7.02 7.97 7.95
SD: standard deviation; BMI: body mass index; LBP: players with LBP in the last 12 months; LBP-7d: players with LBP in the last 7 days; LBP-TR: players prevented from training or playing due to LBP in the last 12 months.
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Fig. 1. Testing positions of the endurance protocol. A – Flexor test. B – Extensor test. C – Left side bridge. D – Right side bridge.
Endurance time was recorded for each test. EMG data was recorded from four muscles bilaterally (RA, external oblique (EO) and two portions of ES: longissimus thoracis (ES-L) and iliocostalis lumborum (ES-I)). Use of surface EMG to assess these muscles has been previously tested.22 In order to decrease impedance of the skin–electrode interface, skin was shaved and cleaned with alcohol prior to electrode placement. AMBU® BlueSensor N (AMBU, Ballerup, Denmark) bipolar electrodes (Ag–AgCl pre-gelled, disk shaped with 10 mm diameter) were aligned with muscle fiber orientation with a center-to-center distance of 20 mm. Sensor placement was taken from the SENIAM project23 for the ES and from Ng et al.22 for the RA and EO. Active electrodes (PLUX, Lisbon, Portugal) were connected to a bioPLUX research 2010 system (PLUX, Lisbon, Portugal) with a common mode rejection ratio of 110 dB, input impedance >100 M and a gain of 1000. Data were recorded with a sampling frequency of 1000 Hz. For left-handed players EMG data were reversed (left muscles processed as right and vice versa) so that the right side data corresponded to the dominant side in all players. EMG raw data were processed using MATLAB (The Mathworks Inc., Natick, Massachusetts, USA). EMG signals were digitally filtered (10–490 Hz). For amplitude processing, EMG data were full-wave rectified and smoothed using a 4th order 12 Hz Butterworth filter. Normalization was performed to the mean amplitude value of the data interval between the third and sixth seconds of task execution. The first 3 s were ignored in order to ensure better signal stability24 and consequently a more reliable basis for normalization. To account for different endurance times between players, test duration was normalized to 100%, as done in a previous study.25 Average EMG (avrEMG) values were obtained by the following equation: 1 |xi | N N
avrEMG =
(1)
i=1
where N is the number of samples considered and xi are the signal samples.
Median frequency (MF) values were obtained from the digitally filtered (10–490 Hz) data by the following equation:
f
med
Sm (f )df =
0
∞
f med Sm (f )df
(2)
where Sm (f) is the frequency spectrum of the signal, fmed is the MF of the signal and f is the frequency in Hz. MF was determined using a Fast Fourier Transform algorithm with 1000 ms windows. Signals that were damaged were discarded and not considered for analysis. The mean value of both EMG parameters (avrEMG and MF) was calculated across a 2000 ms window for every tenth percentile. Together with the initial value calculation previously described, this produced 11 avrEMG and MF values. Wider window lengths have previously been recommended in analysis of fatiguing contractions.26 AvrEMG and MF slopes were then calculated through the linear regression least square slope of the 11 values. The use of both amplitude and frequency slopes has been previously performed in another study.25 AvrEMG and MF were used, respectively, as measures of muscle activation and fatigue. Statistical analysis was performed using IBM© SPSS® Statistics for Windows 20.0 (IBM© Corp. Armonk, NY). Data normality was assessed using the Shapiro–Wilk test. To assess between-subjects differences in endurance time, avrEMG slope and MF slope, independent samples t-tests or Mann–Whitney tests were performed depending on normality. Pearson or Spearman correlation tests were performed between endurance time and EMG slopes. The Pearson coefficient was used in the whole sample analysis, while the Spearman coefficient was used in the sub-group analyses due to the reduced number of subjects. Significance was set at p < 0.05. 3. Results No significant differences were found in anthropometric measures between the sub-groups (Table 1); Twenty players (57.1%) reported having LBP in the last 12 months. Of these 20, 8 (22.8%)
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Fig. 2. Between-subjects differences in endurance time and EMG slopes. A – Endurance time differences in players with and without LBP. B – Significant avrEMG slope differences in players with and without LBP. C – Significant avrEMG slope differences in players with and without LBP in the last 7 days. D – Significant MF slope differences between players with and without LBP in the last 7 days. Error bars represent 1 standard deviation. SB: side bridge; ES-I: iliocostalis lumborum; ES-L: longuissimus thoracis; RA: rectus abdominis; EO: external oblique. a Significant difference at a 0.01 level. b Significant difference at a 0.05 level.
reported having LBP in the last 7 days and 7 (20%) reported not being able to train or play in the last 12 months. For endurance time results, players without LBP showed increased values for all tests when compared with symptomatic players. However, these differences were significant only for the flexor (t(16.529) = 3.389; p = 0.004) and right side bridge (t(33) = 2.104; p = 0.043) tests (Fig. 2A) were 121 and 22 s respectively, which correspond to relative differences of 84.6% and 27.7%. There were no significant endurance time differences in the LBP-7d and LBP-TR conditions. For the EMG analysis, there were significant differences between LBP and asymptomatic players in the right side bridge test for the avrEMG slope of the left ES-L (U = 90.00; p = 0.046) and right EO (U = 46.00; p = 0.008, Fig. 2B). Significant differences in EMG variables between players with and without LBP in the last 7 days were found in the extensor, left and right side bridge tests. Extensor test differences in the LBP-7d condition were found in the avrEMG slopes of the left (t(18) = 2.735; p = 0.014) and right (t(18) = 2.742; p = 0.013) ES-I and left ES-L (U = 22.00; p = 0.047). Additionally, a significant difference in the MF slope of the right EO was found (t(17) = 2.186; p = 0.043). In the left side bridge test there was a significant difference in the LBP-7d condition for the avrEMG slope of the left EO (t(17.979) = 2.471; p = 0.024) and for the MF slope of the left RA (t(18) = 2.820; p = 0.011). In the right side bridge test a difference in the left ES-I avrEMG slope was found in the LBP-7d condition (t(18) = 2.125; p = 0.048). These results are depicted in Fig. 2C and D. There were no significant differences in the LBP-TR condition. The full results of between-subjects testing for EMG slopes can be seen in the Supplementary material. Significant correlations between endurance time and EMG slopes were found in all tests.
The flexor test produced significant correlations for LBP and LBP7d players. The extensor test endurance time produced significant correlations for the whole sample, LBP players and LBP-7d players. Left side bridge endurance time showed significant correlations for the whole sample, LBP-7d players and LBP-TR players. Right side bridge endurance time showed significant correlations for the whole sample and LBP-TR players. Significant correlation coefficients and their level of significance are depicted in Fig. 3. 4. Discussion Endurance time results showed that although asymptomatic players had higher values in all tests, only those of the flexor and right side bridge tests achieved significance when compared to players with LBP. In the LBP-7d and TR conditions, no significant differences were recorded. The lack of extensor endurance has previously been found in LBP patients both in sedentary and athletic populations.27,28 Other research illustrated no such differences;20 our results support these findings and are comparable with those found in the general population.29 Flexor endurance results of LBP subjects showed similar values to those of the healthy general population.14 Mean flexor endurance is comparable to values found in golfers15 and lower than those found in an athletic population.20 Asymptomatic players produced a higher right side bridge endurance time. These results are similar to those found in an athletic population.20 Side bridge endurance times for asymptomatic players are also comparable to normative values.14 The higher flexor and right side bridge endurance times of asymptomatic players are in accordance with previous evidence of lower abdominal endurance in LBP patients.27 EMG results showed higher activation of the left ES-L and right EO in the right side bridge test in asymptomatic players.
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Fig. 3. Significant correlations between endurance time and EMG slopes. LBP: players with low back pain in the last 12 months; LBP-7d: players with low back pain in the last 7 days; LPB-TR: players unable to train or play because of low back pain in the last 12 months; SB: side bridge; ES-I: iliocostalis lumborum; ES-L: longuissimus thoracis; RA: rectus abdominis; EO: external oblique. n(whole sample) = 35; n(LBP) = 20; n(LBP-7d) = 8; n(LBP-TR) = 7. a Significant correlation at a 0.05 level. b Significant correlation at a 0.01 level.
Co-contraction of different muscle groups during a task is associated with increased spinal stability; LBP patients have been shown to possess poorer trunk co-contraction patterns.16,17 Players without LBP in the last 7 days also showed increased extensor activation (i.e. left ES-I) during the right side bridge. The results from our study are in line with others17,30 that suggest dynamic stability of the spine plays a role in LBP prevention. Greater spinal stability during side bridges may also indicate asymptomatic players are more capable of avoiding excessive lateral spinal loads, which have been found to be increased in LBP players.7,8 The increase in left ES-I avrEMG slope found in asymptomatic players can be related to the extensor muscles’ high level of activation during the follow-through phase of the serve.2,3 Players with LBP in the last 7 days showed reduced ES activation during the extensor test when compared with those without symptoms in this period. This is in accordance with previous studies of isometric extensor activity in tennis players.12,13 These players also showed less fatigability (as evaluated by the MFslope) of the left RA in the left side bridge. A greater muscle volume of the left (nondominant) RA has been found in tennis players,10 which may help explain our result. Only asymptomatic players had significant endurance time differences, indicating that the presence or absence of symptoms was a more decisive factor in test performance than their specific features (whether they occurred in the last 7 days and whether they caused the player to stop tennis practice). Asymptomatic players showed a greater right side bridge endurance time coupled with multiple trunk muscle activation during this test. Since there were no differences in fatigability as assessed by the MF slope, the increased stability may allow players to maintain position for a longer time as there is less movement to compensate. The lower ES-I and ES-L avrEMG slope found in players with LBP in the last 7 days during the extensor test, where these muscles play an agonist role, can be due to the fact that they increased activation in other synergistic muscles to maintain the position in order to avoid a pain-generating contraction of the ES muscles. This is supported by the absence of differences in endurance time and MF slope in these players. As previously stated, ES activity is important in the deceleration phase of the serve to reduce spinal load. This may explain why the reduced activation was found in players with LBP in the last 7 days.
Globally, EMG results of asymptomatic players show a greater distinction in terms of activation pattern than in fatigability. Endurance time-EMG slopes correlation results show most of the associations were made in situations in which the muscle was not an agonist for the test, pointing to the relevance of cocontraction mechanisms in maintaining spinal stability for a longer time in our sample of tennis players. All significant correlations between endurance time and EMG slopes found in LBP and LBP-7d players were negative and all but one pertained to extensor muscles. Thus, a greater avrEMG or MF slope was associated with less endurance time in flexor and extensor tests. This indicates, once again, symptomatic players inhibited extensor muscle activity in order to avoid a painful contraction that would prevent them from achieving a greater endurance time. Results from the current study provide original evidence that coupled agonist–antagonist activation was a feature found in asymptomatic players and that the endurance time of abdominal muscles, rather than that of the extensors, was a distinctive factor between players with and without history of LBP. The current study has some limitations. Its retrospective nature may induce a recall bias; moreover, it has a relatively small sample size. Given its cross-sectional design, no assumptions should be made as to whether the EMG changes found were the cause or effect of LBP history. Future studies should be of a prospective nature and measure fatigue as a result of tennis practice (e.g. performing EMG analysis during endurance testing before and after a series of tennis strokes) while also adding measurements like trunk kinematics and lumbar curvature.
5. Conclusion This study determined the differences in trunk fatigue and activation profile in tennis players with and without LBP history. Tennis players with LBP in the last year show reduced endurance time for the abdominal muscles. The extensor muscles’ activation pattern was more distinct between players than their fatigability. Tennis coaches and clinicians should pay attention to their athletes’ abdominal endurance and test the ability to activate different trunk muscles in lumbar stability exercises. Data from this study could provide an initial physiologic evidence basis for a tennis-specific approach to LBP.
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Practical implications • The endurance of abdominal muscles should be monitored in tennis players in regard to their LBP history. • Coaches and clinicians dealing with symptomatic players should focus in their ability to activate multiple trunk muscles in different positions. • The approach to LBP in tennis players should take into account performance evaluation of all trunk muscle groups. Acknowledgments The authors would like to thank the collaboration of all tennis players who took part in the study, as well as their coaches. The contribution of Dr. Duane Button during the final review of the text also deserves our highest appreciation. No source of funding was used for this study and the authors declare they have no conflicts of interest. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jsams.2015.04.002 References 1. Van der Hoeven H, Kibler WB. Shoulder injuries in tennis players. Br J Sports Med 2006; 40(5):435–440. http://dx.doi.org/10.1136/bjsm.2005.023218 [discussion 440]. 2. Chow JW, Shim J, Lim Y. Lower trunk muscle activity during the tennis serve. J Sci Med Sport 2003; 6(4):512–518. 3. Chow JW, Park S-A, Tillman MD. Lower trunk kinematics and muscle activity during different types of tennis serves. Sport Med Arthrosc Rehabil Ther Technol 2009; 1(1):24. http://dx.doi.org/10.1186/1758-2555-1-24. 4. Roetert E, Ellenbecker T, Reid M. Biomechanics of the tennis serve: implications for strength training. Strength Cond J 2009; 31(4):35–40. 5. Ellenbecker TS, Pluim B, Vivier S et al. Common injuries in tennis players: exercises to address muscular imbalances and reduce injury risk. Strength Cond J 2009; 31(4):50–58. 6. Abrams GD, Harris AH, Andriacchi TP et al. Biomechanical analysis of three tennis serve types using a markerless system. Br J Sports Med 2012:1–5. http://dx.doi.org/10.1136/bjsports-2012-091371. 7. Campbell A, Straker L, O’Sullivan P et al. Lumbar loading in the elite adolescent tennis serve: link to low back pain. Med Sci Sports Exerc 2013; 45(8):1562–1568. http://dx.doi.org/10.1249/MSS.0b013e31828bea5e. 8. Campbell A, O’Sullivan P, Straker L et al. Back pain in tennis players: a link with lumbar serve kinematics and range of motion. Med Sci Sports Exerc 2014; 46(2):351–357. http://dx.doi.org/10.1249/MSS.0b013e3182a45cca. 9. Chandler TJ, Ellenbecker TS, Roetert EP. Sport-specific muscle strength imbalances in tennis. Strength Cond J 1998; 20(2):7–10. 10. Sanchis-Moysi J, Idoate F, Dorado C et al. Large asymmetric hypertrophy of rectus abdominis muscle in professional tennis players. PLoS ONE 2010; 5(12):e15858. http://dx.doi.org/10.1371/journal.pone.0015858. 11. Alyas F, Turner M, Connell D. MRI findings in the lumbar spines of asymptomatic, adolescent, elite tennis players. Br J Sports Med 2007; 41(11):836–841. http://dx.doi.org/10.1136/bjsm.2007.037747 [discussion 841].
12. Renkawitz T, Boluki D, Grifka J. The association of low back pain, neuromuscular imbalance, and trunk extension strength in athletes. Spine J 2006; 6(6):673–683. http://dx.doi.org/10.1016/j.spinee.2006.03.012. 13. Renkawitz T, Linhardt O, Grifka J. Electric efficiency of the erector spinae in tennis players. J Sports Med Phys Fitness 2008; 48:409–416. 14. McGill SM, Childs A, Liebenson C. Endurance times for low back stabilization exercises: clinical targets for testing and training from a normal database. Arch Phys Med Rehabil 1999; 80(8):941–944. 15. Evans K, Refshauge KM, Adams R et al. Predictors of low back pain in young elite golfers: a preliminary study. Phys Ther Sport 2005; 6(3):122–130. http://dx.doi.org/10.1016/j.ptsp.2005.05.003. 16. Graham RB, Oikawa LY, Ross GB. Comparing the local dynamic stability of trunk movements between varsity athletes with and without non-specific low back pain. J Biomech 2014; 47(6):1459–1464. http://dx.doi.org/10.1016/j.jbiomech.2014.01.033. 17. McGill SM, Grenier S, Kavcic N et al. Coordination of muscle activity to assure stability of the lumbar spine. J Electromyogr Kinesiol 2003; 13:353–359. http://dx.doi.org/10.1016/S1050-6411(03)00043-9. 18. Hornery DJ, Farrow D, Mujika I et al. Fatigue in tennis. Sport Med 2007; 37(3):199–212. 19. Donatelli R, Dimond D, Holland M. Sport-specific biomechanics of spinal injuries in the athlete (throwing athletes, rotational sports, and contact-collision sports). Clin Sports Med 2012; 31(3):381–396. http://dx.doi.org/10.1016/j.csm.2012.03.003. 20. Evans K, Refshauge KM, Adams R. Trunk muscle endurance tests: reliability, and gender differences in athletes. J Sci Med Sport 2007; 10(6):447–455. http://dx.doi.org/10.1016/j.jsams.2006.09.003. 21. Mesquita CC, Ribeiro JC, Moreira P. Portuguese version of the standardized Nordic musculoskeletal questionnaire: cross cultural and reliability. J Public Health (Bangk) 2010; 18:461–466. http://dx.doi.org/10.1007/s10389010-0331-0. 22. Ng JK, Richardson CA, Parnianpour M et al. EMG activity of trunk muscles and torque output during isometric axial rotation exertion: a comparison between back pain patients and matched controls. J Orthop Res 2002; 20: 112–121. 23. Hermens HJ, Freriks B, Merletti R et al. European recommendations for surface electromyography. Results of the SENIAM project, 1999. 24. Oddsson LIE, De Luca CJ. Activation imbalances in lumbar spine muscles in the presence of chronic low back pain. J Appl Physiol 2003; 94(4):1410–1420. http://dx.doi.org/10.1152/japplphysiol.01183.2001. 25. Pereira GR, de Oliveira LF, Nadal J. Isometric fatigue patterns in time and time-frequency domains of triceps surae muscle in different knee positions. J Electromyogr Kinesiol 2011; 21(4):572–578. http://dx.doi.org/10.1016/j.jelekin.2011.03.010. 26. Hollman JH, Hohl JM, Kraft JL et al. Does the fast Fourier transformation window length affect the slope of an electromyogram’s median frequency plot during a fatiguing isometric contraction? Gait Posture 2013; 38(1):161–164. http://dx.doi.org/10.1016/j.gaitpost.2012.10.028. 27. Arab AM, Salavati M, Ebrahimi I et al. Sensitivity, specificity and predictive value of the clinical trunk muscle endurance tests in low back pain. Clin Rehabil 2007; 21(7):640–647. http://dx.doi.org/10.1177/0269215507076353. 28. Demoulin C, Vanderthommen M, Duysens C et al. Spinal muscle evaluation using the Sorensen test: a critical appraisal of the literature. Joint Bone Spine 2006; 73(1):43–50. http://dx.doi.org/10.1016/j.jbspin.2004.08.002. 29. Coleman JL, Straker LM, Campbell A et al. Biering–Sorensen test performance of Japanese young males: comparison with other ethnicities and relationship to electromyography, near-infrared spectroscopy and exertion ratings. Ergonomics 2011; 54(7):636–655. http://dx.doi.org/10.1080/00140139.2011. 586062. 30. Van Dieën JH, Selen LPJ, Cholewicki J. Trunk muscle activation in low-back pain patients, an analysis of the literature. J Electromyogr Kinesiol 2003; 13(4):333–351. http://dx.doi.org/10.1016/S1050-6411(03)00041-5.
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Original research
Trunk muscle activation, fatigue and low back pain in tennis players José Pedro Correia ∗ , Raul Oliveira, João Rocha Vaz, Luís Silva, Pedro Pezarat-Correia Laboratory of Motor Behavior, CIPER, Faculdade de Motricidade Humana, Universidade de Lisboa, Portugal
a r t i c l e
i n f o
Article history: Received 2 September 2014 Received in revised form 23 March 2015 Accepted 8 April 2015 Available online xxx Keywords: Abdominal Activation Electromyography Endurance Lumbar
a b s t r a c t Objectives: To analyze differences in trunk endurance time, fatigue and activation in tennis players with and without low back pain. Design: Observational study, cross-sectional design. Methods: Thirty-five tennis players completed an isometric trunk endurance protocol comprising four tasks (flexor, extensor and side bridge tests). LBP history was obtained through the Nordic Musculoskeletal Questionnaire. Endurance time was recorded for each test. Surface electromyographic activity was recorded bilaterally from rectus abdominis, external obliques, iliocostalis lumborum and longissimus thoracis. Average electromyographic amplitude and median frequency slopes during the tests were calculated and used as indicators of change in muscle activation and fatigue. Results: Asymptomatic players had greater flexor (p = 0.004) and right side bridge (p = 0.043) endurance times. These players produced a greater increase in avrEMG during the right side bridge test for the left ES-I (p = 0.046) and right EO (p = 0.008). Players with LBP in the last 7 days showed reduced activation of the left (p = 0.014) and right (p = 0.013) ES-I and left longissimus thoracis (ES-L, p = 0.047) in the extensor test. In the left side bridge test there was a lower avrEMG slope of the left EO (p = 0.024) and left RA MF slope (p = 0.011). In the right side bridge test a lower left ES-I avrEMG slope was found (p = 0.048). Conclusions: Symptomatic players show lower activation of extensor muscles, less co-contraction patterns and less abdominal endurance. Tennis coaches and clinicians should consider these factors in their approach to players with LBP. © 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.
1. Introduction The trunk plays an important role on the kinetic chain of tennis strokes, being part of the force generating and transmission sequence.1 Trunk activation during the tennis serve can be elevated and asymmetric in various muscles.2,3 The serve presents significant trunk musculoskeletal demands, most notably during the wind-up phase, where players perform a trunk hyperextension, lateral flexion and rotation movement.4 Although this allows for greater storage of elastic energy for the acceleration phase, it places great stress on the posterior spinal structures, and is thought to be the main causative factor for spondylolysis in tennis players.5 Eccentric activity of the rectus abdominis (RA) is important to support the trunk and avoid excessive spinal stress. Afterwards, in the acceleration phase, a counter rotation occurs, eliciting forceful concentric activity of the trunk flexors and rotators. Finally, during the follow-through phase, eccentric control of the erector spinae (ES) is necessary to assure a correct deceleration of the serve motion.2,3
∗ Corresponding author. E-mail address: [email protected] (J.P. Correia).
The serve also involves high trunk motion speeds and imposes spinal loads of up to nearly 3000 N.6 Studies on lumbar kinematics during the tennis serve have also shown higher lateral flexion moments in players with LBP, which may be a potential injury mechanism.7,8 The repetitive nature of tennis, involving a majority of serve and forehand strokes, leads to asymmetrical musculoskeletal adaptations (e.g. in the shoulder and hip) that are commonly associated with injury.9 Evidence of trunk adaptations in tennis players has arisen in imaging studies of RA muscle volume10 and spinal osteoarticular changes (pars lesions, disk pathology and facet arthropathy).11 To the best of the authors’ knowledge, studies of trunk activation and low back pain (LBP) in tennis players have only comprised the extensor muscles. Tennis players with LBP history showed decreased ES activation during trunk extension.12,13 Despite these findings, there is a lack of research on trunk fatigue and activation in tennis players. Studies on sedentary and athletic populations have illustrated that there are different trunk endurance patterns between various muscle groups.14,15 However, very little is known about trunk endurance patterns between muscles in tennis players. Given the previously stated role of different trunk muscle groups on spinal loads during tennis strokes, it is likely their
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activity and fatigability will also be associated with LBP symptoms. Decreased trunk activation and co-contraction patterns have been found in LBP patients.16 Trunk co-contraction patterns have also been shown to increase spinal stability and decrease spinal load.17 Muscle fatigue is associated with decreased tennis performance and impaired injury protection mechanisms.18 The onset of fatigue also promotes a loss in neuromuscular control, decreasing spinal stability.19 Thus, the objectives of this study were to (1) analyze differences in trunk endurance time between tennis players with and without LBP; (2) analyze differences in EMG slopes (amplitude and median frequency) during fatiguing trunk isometric tasks between tennis players with and without LBP; and (3) verify the existence of a relation between endurance time and EMG slopes. We hypothesize that (1) players with LBP history show endurance time differences in various trunk muscle groups; (2) players with LBP history present differences in the fatigability and activation pattern of various trunk muscles; and (3) there is a correlation between endurance time and EMG parameters. 2. Methods Thirty-seven tennis players volunteered for the study. Thirtyfive (28 male, 7 female, 18.54 ± 3.00 years old) met the study’s criteria and were included in the final sample. There were 2 asymptomatic female players and 5 in all of the LBP subgroups. Inclusion criteria were (1) minimum 3 years of tennis practice, (2) minimum 6 h/week of tennis practice in the last year and (3) currently competing at a national level or higher. Exclusion criteria were (1) history of surgery to the trunk/spine, (2) history of serious trunk musculoskeletal pathology (trunk surgery, tumor, infection, structural scoliosis, spinal fracture), (3) practice of another sport for 3 or more times/week (excluding physical training) and (4) being unable to assume testing positions. Players were recruited without regard to their current LBP status.
One player was excluded due to previous trunk surgery and another was unable to assume testing positions due to an ankle sprain. All players were able to complete the protocol regardless of current LBP. Thirty-four of the 35 players were right-handed and 16 were minors. Full sample description is detailed in Table 1. All tests were performed by the same researcher at tennis clubs nationwide. All players (or their legal tutors) gave written consent for participation in the study. The study was approved by the Research Ethics Committee of the Faculty of Human Kinetics, University of Lisbon (approval number 5/2012). All procedures were taken in accordance with the Declaration of Helsinki. Players completed a trunk endurance protocol as described in McGill et al.,14 comprising four isometric tests (trunk flexor, extensor, and left/right side bridge tests, Fig. 1). This protocol has been considered a safe, reliable and cost-effective way of evaluating trunk endurance14,20 and was applied in order to evaluate the fatigue-related behavior of trunk muscles relevant to tennis practice. Players were encouraged to hold the positions for as long as they could and were given the opportunity to experience positions for a few seconds before measurement. Test order was randomized and 5 min of rest were given between tests. Tests began as soon as players assumed position. The termination criteria of the original protocol were used.14 Standard corrections were provided if players started deviating from the test position. The beginning and end of the recording were done via a keyboard trigger. All players reported fatigue as the reason for termination. LBP history was obtained through an adapted Portuguese version of the Nordic Musculoskeletal Questionnaire21 (NMQ) containing three yes/no questions on the lumbar region: (1) existence of symptoms over the last 12 months (LBP condition), (2) over the last 7 days (LBP-7d condition) and (3) being unable to train or play over the last 12 months because of LBP (LBP-TR condition). The last 2 questions were only answered by the players who answered question 1 affirmatively.
Table 1 Sample description.
Age (years)
Height (m)
Weight (kg)
BMI (kg/m2 )
Years of practice
Practice hours/week
Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR Whole sample Asymptomatic LBP LBP-7d LBP-TR
N
Minimum
Maximum
Mean ± SD
35 15 20 8 7 35 15 20 8 7 35 15 20 8 7 35 15 20 8 7 35 15 20 8 7 35 15 20 8 7
16 16 16 16 16 1.56 1.68 1.56 1.56 1.63 50.90 55.3 50.9 50.9 55.0 18.69 18.69 19.04 20.70 19.04 3 3 3 3 10 6 6 6 7 10
28 20 28 28 26 1.97 1.97 1.88 1.88 1.84 93.00 93.00 85.0 85.0 84.3 26.31 25.20 26.31 24.44 24.90 24 14 24 24 18 40 40 29.5 28.5 29.5
18.54 17.53 19.3 20.5 19.57 1.76 1.77 1.75 1.70 1.77 68.80 67.77 68.56 65.51 67.63 22.04 21.57 22.40 22.47 21.50 9.7 9.16 10.1 10.37 11.57 17.06 19.5 15.23 14.81 16.79
± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
3.00 1.25 3.68 4.28 3.82 0.09 0.08 0.09 0.11 0.07 9.85 9.25 10.44 12.59 9.39 1.85 1.71 1.91 1.57 1.78 4.12 3.13 4.76 6.26 2.94 8.95 10.79 7.02 7.97 7.95
SD: standard deviation; BMI: body mass index; LBP: players with LBP in the last 12 months; LBP-7d: players with LBP in the last 7 days; LBP-TR: players prevented from training or playing due to LBP in the last 12 months.
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Fig. 1. Testing positions of the endurance protocol. A – Flexor test. B – Extensor test. C – Left side bridge. D – Right side bridge.
Endurance time was recorded for each test. EMG data was recorded from four muscles bilaterally (RA, external oblique (EO) and two portions of ES: longissimus thoracis (ES-L) and iliocostalis lumborum (ES-I)). Use of surface EMG to assess these muscles has been previously tested.22 In order to decrease impedance of the skin–electrode interface, skin was shaved and cleaned with alcohol prior to electrode placement. AMBU® BlueSensor N (AMBU, Ballerup, Denmark) bipolar electrodes (Ag–AgCl pre-gelled, disk shaped with 10 mm diameter) were aligned with muscle fiber orientation with a center-to-center distance of 20 mm. Sensor placement was taken from the SENIAM project23 for the ES and from Ng et al.22 for the RA and EO. Active electrodes (PLUX, Lisbon, Portugal) were connected to a bioPLUX research 2010 system (PLUX, Lisbon, Portugal) with a common mode rejection ratio of 110 dB, input impedance >100 M and a gain of 1000. Data were recorded with a sampling frequency of 1000 Hz. For left-handed players EMG data were reversed (left muscles processed as right and vice versa) so that the right side data corresponded to the dominant side in all players. EMG raw data were processed using MATLAB (The Mathworks Inc., Natick, Massachusetts, USA). EMG signals were digitally filtered (10–490 Hz). For amplitude processing, EMG data were full-wave rectified and smoothed using a 4th order 12 Hz Butterworth filter. Normalization was performed to the mean amplitude value of the data interval between the third and sixth seconds of task execution. The first 3 s were ignored in order to ensure better signal stability24 and consequently a more reliable basis for normalization. To account for different endurance times between players, test duration was normalized to 100%, as done in a previous study.25 Average EMG (avrEMG) values were obtained by the following equation: 1 |xi | N N
avrEMG =
(1)
i=1
where N is the number of samples considered and xi are the signal samples.
Median frequency (MF) values were obtained from the digitally filtered (10–490 Hz) data by the following equation:
f
med
Sm (f )df =
0
∞
f med Sm (f )df
(2)
where Sm (f) is the frequency spectrum of the signal, fmed is the MF of the signal and f is the frequency in Hz. MF was determined using a Fast Fourier Transform algorithm with 1000 ms windows. Signals that were damaged were discarded and not considered for analysis. The mean value of both EMG parameters (avrEMG and MF) was calculated across a 2000 ms window for every tenth percentile. Together with the initial value calculation previously described, this produced 11 avrEMG and MF values. Wider window lengths have previously been recommended in analysis of fatiguing contractions.26 AvrEMG and MF slopes were then calculated through the linear regression least square slope of the 11 values. The use of both amplitude and frequency slopes has been previously performed in another study.25 AvrEMG and MF were used, respectively, as measures of muscle activation and fatigue. Statistical analysis was performed using IBM© SPSS® Statistics for Windows 20.0 (IBM© Corp. Armonk, NY). Data normality was assessed using the Shapiro–Wilk test. To assess between-subjects differences in endurance time, avrEMG slope and MF slope, independent samples t-tests or Mann–Whitney tests were performed depending on normality. Pearson or Spearman correlation tests were performed between endurance time and EMG slopes. The Pearson coefficient was used in the whole sample analysis, while the Spearman coefficient was used in the sub-group analyses due to the reduced number of subjects. Significance was set at p < 0.05. 3. Results No significant differences were found in anthropometric measures between the sub-groups (Table 1); Twenty players (57.1%) reported having LBP in the last 12 months. Of these 20, 8 (22.8%)
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Fig. 2. Between-subjects differences in endurance time and EMG slopes. A – Endurance time differences in players with and without LBP. B – Significant avrEMG slope differences in players with and without LBP. C – Significant avrEMG slope differences in players with and without LBP in the last 7 days. D – Significant MF slope differences between players with and without LBP in the last 7 days. Error bars represent 1 standard deviation. SB: side bridge; ES-I: iliocostalis lumborum; ES-L: longuissimus thoracis; RA: rectus abdominis; EO: external oblique. a Significant difference at a 0.01 level. b Significant difference at a 0.05 level.
reported having LBP in the last 7 days and 7 (20%) reported not being able to train or play in the last 12 months. For endurance time results, players without LBP showed increased values for all tests when compared with symptomatic players. However, these differences were significant only for the flexor (t(16.529) = 3.389; p = 0.004) and right side bridge (t(33) = 2.104; p = 0.043) tests (Fig. 2A) were 121 and 22 s respectively, which correspond to relative differences of 84.6% and 27.7%. There were no significant endurance time differences in the LBP-7d and LBP-TR conditions. For the EMG analysis, there were significant differences between LBP and asymptomatic players in the right side bridge test for the avrEMG slope of the left ES-L (U = 90.00; p = 0.046) and right EO (U = 46.00; p = 0.008, Fig. 2B). Significant differences in EMG variables between players with and without LBP in the last 7 days were found in the extensor, left and right side bridge tests. Extensor test differences in the LBP-7d condition were found in the avrEMG slopes of the left (t(18) = 2.735; p = 0.014) and right (t(18) = 2.742; p = 0.013) ES-I and left ES-L (U = 22.00; p = 0.047). Additionally, a significant difference in the MF slope of the right EO was found (t(17) = 2.186; p = 0.043). In the left side bridge test there was a significant difference in the LBP-7d condition for the avrEMG slope of the left EO (t(17.979) = 2.471; p = 0.024) and for the MF slope of the left RA (t(18) = 2.820; p = 0.011). In the right side bridge test a difference in the left ES-I avrEMG slope was found in the LBP-7d condition (t(18) = 2.125; p = 0.048). These results are depicted in Fig. 2C and D. There were no significant differences in the LBP-TR condition. The full results of between-subjects testing for EMG slopes can be seen in the Supplementary material. Significant correlations between endurance time and EMG slopes were found in all tests.
The flexor test produced significant correlations for LBP and LBP7d players. The extensor test endurance time produced significant correlations for the whole sample, LBP players and LBP-7d players. Left side bridge endurance time showed significant correlations for the whole sample, LBP-7d players and LBP-TR players. Right side bridge endurance time showed significant correlations for the whole sample and LBP-TR players. Significant correlation coefficients and their level of significance are depicted in Fig. 3. 4. Discussion Endurance time results showed that although asymptomatic players had higher values in all tests, only those of the flexor and right side bridge tests achieved significance when compared to players with LBP. In the LBP-7d and TR conditions, no significant differences were recorded. The lack of extensor endurance has previously been found in LBP patients both in sedentary and athletic populations.27,28 Other research illustrated no such differences;20 our results support these findings and are comparable with those found in the general population.29 Flexor endurance results of LBP subjects showed similar values to those of the healthy general population.14 Mean flexor endurance is comparable to values found in golfers15 and lower than those found in an athletic population.20 Asymptomatic players produced a higher right side bridge endurance time. These results are similar to those found in an athletic population.20 Side bridge endurance times for asymptomatic players are also comparable to normative values.14 The higher flexor and right side bridge endurance times of asymptomatic players are in accordance with previous evidence of lower abdominal endurance in LBP patients.27 EMG results showed higher activation of the left ES-L and right EO in the right side bridge test in asymptomatic players.
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Fig. 3. Significant correlations between endurance time and EMG slopes. LBP: players with low back pain in the last 12 months; LBP-7d: players with low back pain in the last 7 days; LPB-TR: players unable to train or play because of low back pain in the last 12 months; SB: side bridge; ES-I: iliocostalis lumborum; ES-L: longuissimus thoracis; RA: rectus abdominis; EO: external oblique. n(whole sample) = 35; n(LBP) = 20; n(LBP-7d) = 8; n(LBP-TR) = 7. a Significant correlation at a 0.05 level. b Significant correlation at a 0.01 level.
Co-contraction of different muscle groups during a task is associated with increased spinal stability; LBP patients have been shown to possess poorer trunk co-contraction patterns.16,17 Players without LBP in the last 7 days also showed increased extensor activation (i.e. left ES-I) during the right side bridge. The results from our study are in line with others17,30 that suggest dynamic stability of the spine plays a role in LBP prevention. Greater spinal stability during side bridges may also indicate asymptomatic players are more capable of avoiding excessive lateral spinal loads, which have been found to be increased in LBP players.7,8 The increase in left ES-I avrEMG slope found in asymptomatic players can be related to the extensor muscles’ high level of activation during the follow-through phase of the serve.2,3 Players with LBP in the last 7 days showed reduced ES activation during the extensor test when compared with those without symptoms in this period. This is in accordance with previous studies of isometric extensor activity in tennis players.12,13 These players also showed less fatigability (as evaluated by the MFslope) of the left RA in the left side bridge. A greater muscle volume of the left (nondominant) RA has been found in tennis players,10 which may help explain our result. Only asymptomatic players had significant endurance time differences, indicating that the presence or absence of symptoms was a more decisive factor in test performance than their specific features (whether they occurred in the last 7 days and whether they caused the player to stop tennis practice). Asymptomatic players showed a greater right side bridge endurance time coupled with multiple trunk muscle activation during this test. Since there were no differences in fatigability as assessed by the MF slope, the increased stability may allow players to maintain position for a longer time as there is less movement to compensate. The lower ES-I and ES-L avrEMG slope found in players with LBP in the last 7 days during the extensor test, where these muscles play an agonist role, can be due to the fact that they increased activation in other synergistic muscles to maintain the position in order to avoid a pain-generating contraction of the ES muscles. This is supported by the absence of differences in endurance time and MF slope in these players. As previously stated, ES activity is important in the deceleration phase of the serve to reduce spinal load. This may explain why the reduced activation was found in players with LBP in the last 7 days.
Globally, EMG results of asymptomatic players show a greater distinction in terms of activation pattern than in fatigability. Endurance time-EMG slopes correlation results show most of the associations were made in situations in which the muscle was not an agonist for the test, pointing to the relevance of cocontraction mechanisms in maintaining spinal stability for a longer time in our sample of tennis players. All significant correlations between endurance time and EMG slopes found in LBP and LBP-7d players were negative and all but one pertained to extensor muscles. Thus, a greater avrEMG or MF slope was associated with less endurance time in flexor and extensor tests. This indicates, once again, symptomatic players inhibited extensor muscle activity in order to avoid a painful contraction that would prevent them from achieving a greater endurance time. Results from the current study provide original evidence that coupled agonist–antagonist activation was a feature found in asymptomatic players and that the endurance time of abdominal muscles, rather than that of the extensors, was a distinctive factor between players with and without history of LBP. The current study has some limitations. Its retrospective nature may induce a recall bias; moreover, it has a relatively small sample size. Given its cross-sectional design, no assumptions should be made as to whether the EMG changes found were the cause or effect of LBP history. Future studies should be of a prospective nature and measure fatigue as a result of tennis practice (e.g. performing EMG analysis during endurance testing before and after a series of tennis strokes) while also adding measurements like trunk kinematics and lumbar curvature.
5. Conclusion This study determined the differences in trunk fatigue and activation profile in tennis players with and without LBP history. Tennis players with LBP in the last year show reduced endurance time for the abdominal muscles. The extensor muscles’ activation pattern was more distinct between players than their fatigability. Tennis coaches and clinicians should pay attention to their athletes’ abdominal endurance and test the ability to activate different trunk muscles in lumbar stability exercises. Data from this study could provide an initial physiologic evidence basis for a tennis-specific approach to LBP.
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Practical implications • The endurance of abdominal muscles should be monitored in tennis players in regard to their LBP history. • Coaches and clinicians dealing with symptomatic players should focus in their ability to activate multiple trunk muscles in different positions. • The approach to LBP in tennis players should take into account performance evaluation of all trunk muscle groups. Acknowledgments The authors would like to thank the collaboration of all tennis players who took part in the study, as well as their coaches. The contribution of Dr. Duane Button during the final review of the text also deserves our highest appreciation. No source of funding was used for this study and the authors declare they have no conflicts of interest. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jsams.2015.04.002 References 1. Van der Hoeven H, Kibler WB. Shoulder injuries in tennis players. Br J Sports Med 2006; 40(5):435–440. http://dx.doi.org/10.1136/bjsm.2005.023218 [discussion 440]. 2. Chow JW, Shim J, Lim Y. Lower trunk muscle activity during the tennis serve. J Sci Med Sport 2003; 6(4):512–518. 3. Chow JW, Park S-A, Tillman MD. Lower trunk kinematics and muscle activity during different types of tennis serves. Sport Med Arthrosc Rehabil Ther Technol 2009; 1(1):24. http://dx.doi.org/10.1186/1758-2555-1-24. 4. Roetert E, Ellenbecker T, Reid M. Biomechanics of the tennis serve: implications for strength training. Strength Cond J 2009; 31(4):35–40. 5. Ellenbecker TS, Pluim B, Vivier S et al. Common injuries in tennis players: exercises to address muscular imbalances and reduce injury risk. Strength Cond J 2009; 31(4):50–58. 6. Abrams GD, Harris AH, Andriacchi TP et al. Biomechanical analysis of three tennis serve types using a markerless system. Br J Sports Med 2012:1–5. http://dx.doi.org/10.1136/bjsports-2012-091371. 7. Campbell A, Straker L, O’Sullivan P et al. Lumbar loading in the elite adolescent tennis serve: link to low back pain. Med Sci Sports Exerc 2013; 45(8):1562–1568. http://dx.doi.org/10.1249/MSS.0b013e31828bea5e. 8. Campbell A, O’Sullivan P, Straker L et al. Back pain in tennis players: a link with lumbar serve kinematics and range of motion. Med Sci Sports Exerc 2014; 46(2):351–357. http://dx.doi.org/10.1249/MSS.0b013e3182a45cca. 9. Chandler TJ, Ellenbecker TS, Roetert EP. Sport-specific muscle strength imbalances in tennis. Strength Cond J 1998; 20(2):7–10. 10. Sanchis-Moysi J, Idoate F, Dorado C et al. Large asymmetric hypertrophy of rectus abdominis muscle in professional tennis players. PLoS ONE 2010; 5(12):e15858. http://dx.doi.org/10.1371/journal.pone.0015858. 11. Alyas F, Turner M, Connell D. MRI findings in the lumbar spines of asymptomatic, adolescent, elite tennis players. Br J Sports Med 2007; 41(11):836–841. http://dx.doi.org/10.1136/bjsm.2007.037747 [discussion 841].
12. Renkawitz T, Boluki D, Grifka J. The association of low back pain, neuromuscular imbalance, and trunk extension strength in athletes. Spine J 2006; 6(6):673–683. http://dx.doi.org/10.1016/j.spinee.2006.03.012. 13. Renkawitz T, Linhardt O, Grifka J. Electric efficiency of the erector spinae in tennis players. J Sports Med Phys Fitness 2008; 48:409–416. 14. McGill SM, Childs A, Liebenson C. Endurance times for low back stabilization exercises: clinical targets for testing and training from a normal database. Arch Phys Med Rehabil 1999; 80(8):941–944. 15. Evans K, Refshauge KM, Adams R et al. Predictors of low back pain in young elite golfers: a preliminary study. Phys Ther Sport 2005; 6(3):122–130. http://dx.doi.org/10.1016/j.ptsp.2005.05.003. 16. Graham RB, Oikawa LY, Ross GB. Comparing the local dynamic stability of trunk movements between varsity athletes with and without non-specific low back pain. J Biomech 2014; 47(6):1459–1464. http://dx.doi.org/10.1016/j.jbiomech.2014.01.033. 17. McGill SM, Grenier S, Kavcic N et al. Coordination of muscle activity to assure stability of the lumbar spine. J Electromyogr Kinesiol 2003; 13:353–359. http://dx.doi.org/10.1016/S1050-6411(03)00043-9. 18. Hornery DJ, Farrow D, Mujika I et al. Fatigue in tennis. Sport Med 2007; 37(3):199–212. 19. Donatelli R, Dimond D, Holland M. Sport-specific biomechanics of spinal injuries in the athlete (throwing athletes, rotational sports, and contact-collision sports). Clin Sports Med 2012; 31(3):381–396. http://dx.doi.org/10.1016/j.csm.2012.03.003. 20. Evans K, Refshauge KM, Adams R. Trunk muscle endurance tests: reliability, and gender differences in athletes. J Sci Med Sport 2007; 10(6):447–455. http://dx.doi.org/10.1016/j.jsams.2006.09.003. 21. Mesquita CC, Ribeiro JC, Moreira P. Portuguese version of the standardized Nordic musculoskeletal questionnaire: cross cultural and reliability. J Public Health (Bangk) 2010; 18:461–466. http://dx.doi.org/10.1007/s10389010-0331-0. 22. Ng JK, Richardson CA, Parnianpour M et al. EMG activity of trunk muscles and torque output during isometric axial rotation exertion: a comparison between back pain patients and matched controls. J Orthop Res 2002; 20: 112–121. 23. Hermens HJ, Freriks B, Merletti R et al. European recommendations for surface electromyography. Results of the SENIAM project, 1999. 24. Oddsson LIE, De Luca CJ. Activation imbalances in lumbar spine muscles in the presence of chronic low back pain. J Appl Physiol 2003; 94(4):1410–1420. http://dx.doi.org/10.1152/japplphysiol.01183.2001. 25. Pereira GR, de Oliveira LF, Nadal J. Isometric fatigue patterns in time and time-frequency domains of triceps surae muscle in different knee positions. J Electromyogr Kinesiol 2011; 21(4):572–578. http://dx.doi.org/10.1016/j.jelekin.2011.03.010. 26. Hollman JH, Hohl JM, Kraft JL et al. Does the fast Fourier transformation window length affect the slope of an electromyogram’s median frequency plot during a fatiguing isometric contraction? Gait Posture 2013; 38(1):161–164. http://dx.doi.org/10.1016/j.gaitpost.2012.10.028. 27. Arab AM, Salavati M, Ebrahimi I et al. Sensitivity, specificity and predictive value of the clinical trunk muscle endurance tests in low back pain. Clin Rehabil 2007; 21(7):640–647. http://dx.doi.org/10.1177/0269215507076353. 28. Demoulin C, Vanderthommen M, Duysens C et al. Spinal muscle evaluation using the Sorensen test: a critical appraisal of the literature. Joint Bone Spine 2006; 73(1):43–50. http://dx.doi.org/10.1016/j.jbspin.2004.08.002. 29. Coleman JL, Straker LM, Campbell A et al. Biering–Sorensen test performance of Japanese young males: comparison with other ethnicities and relationship to electromyography, near-infrared spectroscopy and exertion ratings. Ergonomics 2011; 54(7):636–655. http://dx.doi.org/10.1080/00140139.2011. 586062. 30. Van Dieën JH, Selen LPJ, Cholewicki J. Trunk muscle activation in low-back pain patients, an analysis of the literature. J Electromyogr Kinesiol 2003; 13(4):333–351. http://dx.doi.org/10.1016/S1050-6411(03)00041-5.
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