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Gender differences in post-exercise sagittal knee translation: A comparison between elite volleyball players and swimmers
The Knee 13 (2006) 132 – 136 www.elsevier.com/locate/knee
Gender differences in post-exercise sagittal knee translation: A comparison between elite volleyball players and swimmers Joanna Kvist *, Desiree´ Cunningham, Hanna Tigerstrand-Wejlemark Division of Physiotherapy, Department of Health and Society, Faculty of Health Sciences, Linko¨ping University, SE-581 83 Linko¨ping, Sweden Received 19 October 2005; received in revised form 6 December 2005; accepted 9 December 2005
Abstract Background: There is an increased risk for anterior cruciate ligament injury during the last part of a match or training session and one reason for that could be a post-exercise increase in tibial translation. Purpose: To investigate if sagittal tibial translation is affected after a workout session in volleyball or swimming in elite athletes. In addition, gender differences in sagittal tibial translation after the workout session were investigated. Method: Thirty-one elite volleyball players (16 male) and 33 elite swimmers (15 male) participated in this study. Measurements of total tibial translation were taken before and after a workout session in either volleyball or swimming with the use of a KT-1000 arthrometer. Results: Total tibial translation increased by 1.1 mm (SD 1.9) in the group consisting of both male and female volleyball players ( p = 0.003) and remained unchanged in the swimmers. Male athletes increased their tibial translation with 1.8 mm (SD 1.8) and 0.6 mm (SD 1.1) in the two sports, respectively, while the tibial translation did not increase in the female athletes. Conclusion: Impact sports such as volleyball training leads to a post-exercise increase in tibial translation in male athletes. The increase in tibial translation in swimmers, that is a non-impact sport, was small and may not be clinically significant for the functional stability of the joint. It has been shown that female athletes have an increased risk for injury. Our results show no support for an increase in tibial translation being an important factor for this increased risk, and suggest that the difference between males and females in this regard should be sought elsewhere. D 2006 Elsevier B.V. All rights reserved. Keywords: Tibial translation; KT-1000; Laxity; Exercise
1. Introduction Injuries of the anterior cruciate ligament are common during sports activity. The injury rate is higher among women and many injuries occur during non-contact situations [1,2]. Muscle fatigue that results in impaired muscle reaction time [3] and decreased muscle coordination with a possible deterioration of the functional joint stability can be a risk factor. In addition, muscle fatigue results in a greater engagement of other structures, for example the ligaments, to absorb the movement energy. Repeated load may decrease the stiffness of the ligaments, indicating weakened structural properties of the ligament [4] and a * Corresponding author. Tel.: +46 13 224121; fax: +46 13 221706. E-mail address: [email protected] (J. Kvist). 0968-0160/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2005.12.003
larger strain for similar load. In the anterior cruciate ligament, this could be seen as an increased sagittal tibial translation when tested at the same load during an instrumented Lachman test [5]. There are contradictory results about the effects of a training session on the sagittal translation in the knee joint. Some authors have described an increased translation after exercise, [3,6 –11], while others have not found such a difference [8,12,13]. The different results may be due to the different training sessions that have been examined, both regarding the type of the exercises performed, but also the duration of the training session [8]. In addition, the test persons gender or experience on the specific training may influence the results. A better understanding of how exercises affect tibial translation is of importance in order to understand injury
J. Kvist et al. / The Knee 13 (2006) 132 – 136
mechanics and to enhance both injury prevention and rehabilitation after injury. The aim of the present study was to investigate if sagittal tibial translation is affected after a workout session in volleyball or swimming in elite athletes. In addition gender differences in sagittal tibial translation after the workout session were investigated. The hypothesis was that though volleyball includes weight bearing and closed kinetic chain movements that are supposed to result in low ACL-strain [14] and sagittal tibial translation [15,16] the great impact and forces during the landing phase in the jump, that expose the knee to anterior directed forces [17], increased ACL-strain [18] and cartilage compression, should result in increased tibial translation. On the other hand, swimming that is a non-impact sport that includes non-weight bearing exercises and movements with small co-contraction of the muscles (open kinetic chain exercises) may not result in similar increase in tibial translation. In addition, possible gender differences could indicate reasons for the greater injury risk in female athletes.
2. Materials and methods Sixty-four volleyball players and swimmers from five different Swedish athletic clubs, competing in the highest divisions, participated in the study. The inclusion criteria were: athletes between 16 and 30 years of age, no history of knee injury or surgery, at least three years of active participation in their sport. The athletes should not have had hip, knee or foot problems within the last three months. The male athletes consisted of 16 volleyball players and 15 swimmers and the female athletes consisted of 15 and 18, respectively. Demographics are shown in Table 1. The study had been approved by the local ethics committee and informed consent was obtained from all subjects. All subjects were tested for sagittal knee translation before and after a regular workout session in either volleyball or swimming. The exercise bout consisted of one and a half to two hours and only exercise pertaining to the specific sport was carried out between the two measurements. The subjects were instructed to abstain from exercise 5 h prior to initial testing. The tests were carried out on the dominant leg of the subject, by definition the leg the subject would land on after jumping. Measurements of sagittal knee translation were made with the KT-1000 knee arthrometer (Medmetric Corp., San Diego, CA) and conducted in accordance with the guidelines of the KT-1000 manufacturers. During the test, the subjects were in supine position Table 1 Demographics of male and female athletes Volleyball
Swimming
Male
Male
Female
Female
N 16 15 15 18 Age (years) 23 (4) 21 (3) 18 (3) 17 (1) Weight (kg) 83 (10) 65 (11) 79 (12) 61 (8) Length (cm) 190 (5) 170 (6) 186 (9) 170 (6) Dominant leg (right/left) 2/14 11/4 12/3 13/5 Training dose (hours per week) 11 (2) 5 (1) 18 (3) 17 (4) Training frequency (days per week) 4 (1) 3 (1) 7 (1) 6 (0)
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Table 2 Mean (SD), difference and 95% confidence intervals of tibial translation in male and female athletes before and after the workout session Translation Translation Difference 95% CI of before after difference Volleyball Male (n = 16) 8.4 (2.8) Female 11.5 (2.2) (n = 15) All (n = 31) 9.9 (2.9) Swimming Male (n = 15) 9.1 (2.5) Female 11.7 (2.0) (n = 18) All (n = 33) 10.5 (2.6)
p-value
10.3 (2.6) 11.8 (2.4)
1.8 (1.8) 0.3 (1.8)
0.87 – 2.75 0.0009 0.67 – 1.34 0.4896
11.0 (2.6)
1.1 (1.9)
0.40 – 1.80 0.0033
9.7 (2.1) 11.9 (2.6)
0.6 (1.1) 0.2 (1.5)
0.00 – 1.27 0.0496 0.58 – 0.91 0.6423
10.9 (2.6)
0.4 (1.4)
0.10 – 0.86 0.1159
on firm ground. The thighs were relaxed on a thigh support and the knee joint was flexed in 30-. The lower extremity had to be relaxed during the test, therefore a strap was tightened around the thighs and the feet were placed on a footrest. The KT-1000 is proven to be valid [19] and has shown good repeatability [19 – 21]. All athletes were tested by the same examiner before and after exercise. To reduce bias, the subjects were told not to repeat the value from the previous test when tested after exercise. The examiner did not see the subjects or the group values until all measurements were conducted. 2.1. Statistical analysis All data were calculated in Statistical Package of Social Sciences (SPSS). Paired t-test was used to compare differences before and after training within each group. Unpaired t-test was used to compare values before and after training, between the groups. P-value 0.05 was used for each test.
3. Results The volleyball players were 5 years older compared to the swimmers (22 T 4 years compared to 18 T 2 years). The groups were similar with respect to weight and length. The training dose and frequency were smaller in the volleyball group compared to the swimmers group (Table 1). Total tibial translation increased by 1.1 (SD 1.9) mm in the group consisting of both male and female volleyball players (11% increase, p = 0.003). Male athletes increased their tibial translation with 1.8 (SD 1.8) mm (21% increase, p = 0.0009) whereas the total tibial translation was unchanged in the female volleyball players ( p > 0.05) (Table 2, Fig. 1). The total tibial translation was unchanged in the entire swimmers group, consisted of both male and female athletes ( p > 0.05). The male swimmers had a small increase in their translation, by 0.6 (SD 1.1) (7% increase, p = 0.0496), while the translation was unchanged in the female group ( p > 0.05) (Table 2, Fig. 1). Before the exercise, the male volleyball players had 3.4 mm smaller translation compared to the female volleyball players (8.4 (SD 2.8) mm versus 11.5 (SD 2.2) mm, p = 0.0019) and the male swimmers had 3.4 mm smaller translation compared to the female swimmers (9.1 (SD 2.5) mm versus 11.7 (SD 2.0) mm, p = 0.0021). After the exercise, the tibial translation in male volleyball players
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J. Kvist et al. / The Knee 13 (2006) 132 – 136 16 Female 14
All
Female All
Male Male
Translation (mm)
12 10 8 6 4 2 0
Before
After
Volleyball Swimming Fig. 1. Tibial translation (SD) in all athletes, male and female, before and after a training session in volleyball or swimming.
did not differ from the female volleyball players (10.3 (SD 2.6) mm versus 11.8 (SD 2.4), p = 0.0870). The male swimmers had still smaller tibial translation after the exercise compared to the female swimmers (9.7 (SD 2.1) mm versus 11.9 (SD 2.6) mm, p = 0.0142) (Table 2, Fig. 1).
4. Discussion The results of the present study show that volleyball training leads to a post exercise increase in tibial translation in male athletes. Such an increase was not found in the female athletes in contrast to previous studies [6,8,11]. The increase in tibial translation in the male volleyball players (1.8 mm) was only slightly higher than the intra-rater reliability limits for the KT-1000 (approx. 1.5 mm) [21], although that increase was 21% of the individual tibial translation and it should be clinically significant for the functional stability of the knee joint. In contrast, the increase in tibial translation in the male swimmers was only 7% of the individual tibial translation and may not be clinically significant for the functional stability of the joint. The two sports, volleyball and swimming that were examined in the present study were chosen as two extremes in the way they load the knee joint. Volleyball includes a lot of jumping and landing with great impact forces. On the other hand, swimming is non-weight bearing and only muscle action loads the joint. Rehabilitation exercises and training subject the knee joint to different loads and different strain on the ACL [14]. As a result, different amount of sagittal tibial translation have been recorded [15,16]. Though no ACL-injuries occur during swimming, an understanding of how the knee joint is affected by different loads is of importance in order to understand the complexity of the ACL-injury and its rehabilitation.
Knee kinematics differ between gender during landing [17,22,23] and cutting [24]. Exercise may also affect anterior shear load and tibial translation in a different manner depending on the tibial position at the moment the joint is subjected for the load. In the females who had a greater tibial translation before exercise compared to the male athletes, the tibia should be in a more anterior position during weight bearing [15,25]. In that position, the quadriceps angle decreases resulting in a decreased possibility of the quadriceps muscle to pull tibia anteriorly. On the other hand, female exhibit greater anterior shear force on tibia during landing compared to male [17]. More research is needed in order to fully understand how exercise affect tibial translation and possible gender differences. Our results insinuate that exercise affects male ligaments in a higher degree compared to the females’ ligaments. Wojtys et al. found that men have an increased ability to increase sagittal plane knee stiffness by voluntary knee muscle co-contraction, compared to women. These results suggest that men have an increased ability to protect the knee joint by muscle co-contraction [26]. When the muscles get fatigued, the stabilization ability of the muscles may deteriorate, leading to increased load on the ligaments and subsequent weakened structural properties. That can be a reason for the post exercise increased tibial translation. On the other hand, female may not relay on the same extension on their muscles to stabilize the knee joint and that can be a reason for the absence of a post exercise tibial translation increase. Another reason for the absence of the post exercise increase in tibial translation in the female athletes may be that the female athletes had a greater tibial translation before the training session compared to the male athletes, which is in accordance to previous results [20,27 – 29]. Results from
J. Kvist et al. / The Knee 13 (2006) 132 – 136
a non athlete population are contradictory ([27] and unpublished results). It is not clear if increased knee joint laxity or general increased joint laxity is associated with an increased risk for injury [30 – 33]. On the other hand, general increased laxity that some individuals have despite previous workout activities is not the same as the specific post exercise increase in laxity. For example, the mechanoreceptors in a joint should regulate the response from mechanical deformation and variations in ligament tensions in accordance to the possible joint play in the specific joint. In a lax joint, movement may be larger before the mechanoreceptors respond and in a tight joint the response may come earlier. When the joint play increases as in post exercise increased laxity, this feedback system may be disturbed, leading to a decreased ability of the fatigued muscles to coordinate a functional stability in the joint. In other words, a post exercise increase in tibial translation may be more harmful compared to a general increased joint laxity. Previous results have shown increased tibial translation after a training session in women basketball players [6,8,11]. Kirkley et al. found significant difference in translation after 15 min running on a treadmill. However, only 15% of the test persons were female and they were not elite athletes. Grana and Muse tested a normal population with no elite athletes. They found significant increase in tibial translation after 20 min bicycling, with no gender differences [9]. On the other hand, Belanger et al. did not find a post exercise increase in tibial translation in female athletes after 20 min cycling on a stationary bicycle [13]. The results of the present study indicate that exercise affects tibial translation in a different manner depending on gender. Although training resulted in a post-exercise increase in tibial translation in the male athletes, such an increase was not found in the female athletes. It has been shown that female athletes have an increased risk for injury. Our results show no support for a post exercise increase in tibial translation being an important factor for this increased risk, and suggest that the difference between males and females in this regard should be sought elsewhere.
Acknowledgments The authors thank physical therapists Patrik Genberg, Susanna Qvist and Lance Smith for assistance in collecting the data. This work was supported by the Faculty of Health Sciences Linko¨ping University.
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[2] Myklebust G, Maehlum S, Engebretsen L, Strand T, Solheim E. Registration of cruciate ligament injuries in Norwegian top level team handball. A prospective study covering two seasons. Scand J Med Sci Sports 1997;7(5):289 – 92. [3] Wojtys EM, Wylie BB, Huston LJ. The effects of muscle fatigue on neuromuscular function and anterior tibial translation in healthy knees. Am J Sports Med 1996;24(5):615 – 21. [4] Weisman G, Pope MH, Johnson RJ. Cyclic loading in knee ligament injuries. Am J Sports Med 1980;8(1):24 – 30. [5] Beynnon BD, Johnson RJ, Toyama H, Renstrom PA, Arms SW, Fischer RA. The relationship between anterior – posterior knee laxity and the structural properties of the patellar tendon graft. A study in canines. Am J Sports Med 1994;22(6):812 – 20. [6] Sumen Y, Ochi M, Adachi N, Urabe Y, Ikuta Y. Anterior laxity and MR signals of the knee after exercise. A comparison of 9 normal knees and 6 anterior cruciate ligament reconstructed knees. Acta Orthop Scand 1999;70(3):256 – 60. [7] Kirkley A, Mohtadi N, Ogilvie R. The effect of exercise on anterior – posterior translation of the normal knee and knees with deficient or reconstructed anterior cruciate ligaments. Am J Sports Med 2001;29(3):311 – 4. [8] Steiner ME, Grana WA, Chillag K, Schelberg-Karnes E. The effect of exercise on anterior – posterior knee laxity. Am J Sports Med 1986; 14(1):24 – 9. [9] Grana WA, Muse G. The effect of exercise on laxity in the anterior cruciate ligament deficient knee. Am J Sports Med 1988; 16(6):586 – 8. [10] Nawata K, Teshima R, Morio Y, Hagino H, Enokida M, Yamamoto K. Anterior – posterior knee laxity increased by exercise. Quantitative evaluation of physiologic changes. Acta Orthop Scand 1999;70(3): 261 – 4. [11] Sakai H, Tanaka S, Kurosawa H, Masujima A. The effect of exercise on anterior knee laxity in female basketball players. Int J Sports Med 1992;13(7):552 – 4. ¨ berg B, Kvist J. Passive and dynamic translation in the [12] Tagesson S, O knee is not influenced by knee exercises in healthy individuals. Scand J Med Sci Sports 2005;15(3):139 – 47. [13] Belanger MJ, Moore DC, Crisco JJ III, Fadale PD, Hulstyn MJ, Ehrlich MG. Knee laxity does not vary with the menstrual cycle, before or after exercise. Am J Sports Med 2004;32(5):1150 – 7. [14] Beynnon BD, Johnson RJ, Fleming BC. The science of anterior cruciate ligament rehabilitation. Clin Orthop Relat Res 2002;402: 9 – 20. [15] Kvist J. Sagittal tibial translation during exercises in the anterior cruciate ligament deficient knee. Scand J Med Sci Sports 2005; 15(3):148 – 58. [16] Kvist J, Gillquist J. Sagittal plane knee translation and electromyographic activity during closed and open kinetic chain exercises in anterior cruciate ligament-deficient patients and control subjects. Am J Sports Med 2001;29(1):72 – 82. [17] Chappell JD, Yu B, Kirkendall DT, Garrett WE. A comparison of knee kinetics between male and female recreational athletes in stop-jump tasks. Am J Sports Med 2002;30(2):261 – 7. [18] Cerulli G, Benoit DL, Lamontagne M, Caraffa A, Liti A. In vivo anterior cruciate ligament strain behaviour during a rapid deceleration movement: case report. Knee Surg Sports Traumatol Arthrosc 2003; 11(5):307 – 11. [19] Highgenboten CL, Jackson AW, Jansson KA, Meske NB. KT-1000 arthrometer: conscious and unconscious test results using 15, 20, and 30 pounds of force. Am J Sports Med 1992;20(4):450 – 4. [20] Uh BS, Beynnon BD, Churchill DL, Haugh LD, Risberg MA, Fleming BC. A new device to measure knee laxity during weightbearing and non-weightbearing conditions. J Orthop Res 2001;19(6): 1185 – 91. [21] Wroble RR, Van Ginkel LA, Grood ES, Noyes FR, Shaffer BL. Repeatability of the KT-1000 arthrometer in a normal population. Am J Sports Med 1990;18(4):396 – 9.
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Gender differences in post-exercise sagittal knee translation: A comparison between elite volleyball players and swimmers Joanna Kvist *, Desiree´ Cunningham, Hanna Tigerstrand-Wejlemark Division of Physiotherapy, Department of Health and Society, Faculty of Health Sciences, Linko¨ping University, SE-581 83 Linko¨ping, Sweden Received 19 October 2005; received in revised form 6 December 2005; accepted 9 December 2005
Abstract Background: There is an increased risk for anterior cruciate ligament injury during the last part of a match or training session and one reason for that could be a post-exercise increase in tibial translation. Purpose: To investigate if sagittal tibial translation is affected after a workout session in volleyball or swimming in elite athletes. In addition, gender differences in sagittal tibial translation after the workout session were investigated. Method: Thirty-one elite volleyball players (16 male) and 33 elite swimmers (15 male) participated in this study. Measurements of total tibial translation were taken before and after a workout session in either volleyball or swimming with the use of a KT-1000 arthrometer. Results: Total tibial translation increased by 1.1 mm (SD 1.9) in the group consisting of both male and female volleyball players ( p = 0.003) and remained unchanged in the swimmers. Male athletes increased their tibial translation with 1.8 mm (SD 1.8) and 0.6 mm (SD 1.1) in the two sports, respectively, while the tibial translation did not increase in the female athletes. Conclusion: Impact sports such as volleyball training leads to a post-exercise increase in tibial translation in male athletes. The increase in tibial translation in swimmers, that is a non-impact sport, was small and may not be clinically significant for the functional stability of the joint. It has been shown that female athletes have an increased risk for injury. Our results show no support for an increase in tibial translation being an important factor for this increased risk, and suggest that the difference between males and females in this regard should be sought elsewhere. D 2006 Elsevier B.V. All rights reserved. Keywords: Tibial translation; KT-1000; Laxity; Exercise
1. Introduction Injuries of the anterior cruciate ligament are common during sports activity. The injury rate is higher among women and many injuries occur during non-contact situations [1,2]. Muscle fatigue that results in impaired muscle reaction time [3] and decreased muscle coordination with a possible deterioration of the functional joint stability can be a risk factor. In addition, muscle fatigue results in a greater engagement of other structures, for example the ligaments, to absorb the movement energy. Repeated load may decrease the stiffness of the ligaments, indicating weakened structural properties of the ligament [4] and a * Corresponding author. Tel.: +46 13 224121; fax: +46 13 221706. E-mail address: [email protected] (J. Kvist). 0968-0160/$ - see front matter D 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2005.12.003
larger strain for similar load. In the anterior cruciate ligament, this could be seen as an increased sagittal tibial translation when tested at the same load during an instrumented Lachman test [5]. There are contradictory results about the effects of a training session on the sagittal translation in the knee joint. Some authors have described an increased translation after exercise, [3,6 –11], while others have not found such a difference [8,12,13]. The different results may be due to the different training sessions that have been examined, both regarding the type of the exercises performed, but also the duration of the training session [8]. In addition, the test persons gender or experience on the specific training may influence the results. A better understanding of how exercises affect tibial translation is of importance in order to understand injury
J. Kvist et al. / The Knee 13 (2006) 132 – 136
mechanics and to enhance both injury prevention and rehabilitation after injury. The aim of the present study was to investigate if sagittal tibial translation is affected after a workout session in volleyball or swimming in elite athletes. In addition gender differences in sagittal tibial translation after the workout session were investigated. The hypothesis was that though volleyball includes weight bearing and closed kinetic chain movements that are supposed to result in low ACL-strain [14] and sagittal tibial translation [15,16] the great impact and forces during the landing phase in the jump, that expose the knee to anterior directed forces [17], increased ACL-strain [18] and cartilage compression, should result in increased tibial translation. On the other hand, swimming that is a non-impact sport that includes non-weight bearing exercises and movements with small co-contraction of the muscles (open kinetic chain exercises) may not result in similar increase in tibial translation. In addition, possible gender differences could indicate reasons for the greater injury risk in female athletes.
2. Materials and methods Sixty-four volleyball players and swimmers from five different Swedish athletic clubs, competing in the highest divisions, participated in the study. The inclusion criteria were: athletes between 16 and 30 years of age, no history of knee injury or surgery, at least three years of active participation in their sport. The athletes should not have had hip, knee or foot problems within the last three months. The male athletes consisted of 16 volleyball players and 15 swimmers and the female athletes consisted of 15 and 18, respectively. Demographics are shown in Table 1. The study had been approved by the local ethics committee and informed consent was obtained from all subjects. All subjects were tested for sagittal knee translation before and after a regular workout session in either volleyball or swimming. The exercise bout consisted of one and a half to two hours and only exercise pertaining to the specific sport was carried out between the two measurements. The subjects were instructed to abstain from exercise 5 h prior to initial testing. The tests were carried out on the dominant leg of the subject, by definition the leg the subject would land on after jumping. Measurements of sagittal knee translation were made with the KT-1000 knee arthrometer (Medmetric Corp., San Diego, CA) and conducted in accordance with the guidelines of the KT-1000 manufacturers. During the test, the subjects were in supine position Table 1 Demographics of male and female athletes Volleyball
Swimming
Male
Male
Female
Female
N 16 15 15 18 Age (years) 23 (4) 21 (3) 18 (3) 17 (1) Weight (kg) 83 (10) 65 (11) 79 (12) 61 (8) Length (cm) 190 (5) 170 (6) 186 (9) 170 (6) Dominant leg (right/left) 2/14 11/4 12/3 13/5 Training dose (hours per week) 11 (2) 5 (1) 18 (3) 17 (4) Training frequency (days per week) 4 (1) 3 (1) 7 (1) 6 (0)
133
Table 2 Mean (SD), difference and 95% confidence intervals of tibial translation in male and female athletes before and after the workout session Translation Translation Difference 95% CI of before after difference Volleyball Male (n = 16) 8.4 (2.8) Female 11.5 (2.2) (n = 15) All (n = 31) 9.9 (2.9) Swimming Male (n = 15) 9.1 (2.5) Female 11.7 (2.0) (n = 18) All (n = 33) 10.5 (2.6)
p-value
10.3 (2.6) 11.8 (2.4)
1.8 (1.8) 0.3 (1.8)
0.87 – 2.75 0.0009 0.67 – 1.34 0.4896
11.0 (2.6)
1.1 (1.9)
0.40 – 1.80 0.0033
9.7 (2.1) 11.9 (2.6)
0.6 (1.1) 0.2 (1.5)
0.00 – 1.27 0.0496 0.58 – 0.91 0.6423
10.9 (2.6)
0.4 (1.4)
0.10 – 0.86 0.1159
on firm ground. The thighs were relaxed on a thigh support and the knee joint was flexed in 30-. The lower extremity had to be relaxed during the test, therefore a strap was tightened around the thighs and the feet were placed on a footrest. The KT-1000 is proven to be valid [19] and has shown good repeatability [19 – 21]. All athletes were tested by the same examiner before and after exercise. To reduce bias, the subjects were told not to repeat the value from the previous test when tested after exercise. The examiner did not see the subjects or the group values until all measurements were conducted. 2.1. Statistical analysis All data were calculated in Statistical Package of Social Sciences (SPSS). Paired t-test was used to compare differences before and after training within each group. Unpaired t-test was used to compare values before and after training, between the groups. P-value 0.05 was used for each test.
3. Results The volleyball players were 5 years older compared to the swimmers (22 T 4 years compared to 18 T 2 years). The groups were similar with respect to weight and length. The training dose and frequency were smaller in the volleyball group compared to the swimmers group (Table 1). Total tibial translation increased by 1.1 (SD 1.9) mm in the group consisting of both male and female volleyball players (11% increase, p = 0.003). Male athletes increased their tibial translation with 1.8 (SD 1.8) mm (21% increase, p = 0.0009) whereas the total tibial translation was unchanged in the female volleyball players ( p > 0.05) (Table 2, Fig. 1). The total tibial translation was unchanged in the entire swimmers group, consisted of both male and female athletes ( p > 0.05). The male swimmers had a small increase in their translation, by 0.6 (SD 1.1) (7% increase, p = 0.0496), while the translation was unchanged in the female group ( p > 0.05) (Table 2, Fig. 1). Before the exercise, the male volleyball players had 3.4 mm smaller translation compared to the female volleyball players (8.4 (SD 2.8) mm versus 11.5 (SD 2.2) mm, p = 0.0019) and the male swimmers had 3.4 mm smaller translation compared to the female swimmers (9.1 (SD 2.5) mm versus 11.7 (SD 2.0) mm, p = 0.0021). After the exercise, the tibial translation in male volleyball players
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J. Kvist et al. / The Knee 13 (2006) 132 – 136 16 Female 14
All
Female All
Male Male
Translation (mm)
12 10 8 6 4 2 0
Before
After
Volleyball Swimming Fig. 1. Tibial translation (SD) in all athletes, male and female, before and after a training session in volleyball or swimming.
did not differ from the female volleyball players (10.3 (SD 2.6) mm versus 11.8 (SD 2.4), p = 0.0870). The male swimmers had still smaller tibial translation after the exercise compared to the female swimmers (9.7 (SD 2.1) mm versus 11.9 (SD 2.6) mm, p = 0.0142) (Table 2, Fig. 1).
4. Discussion The results of the present study show that volleyball training leads to a post exercise increase in tibial translation in male athletes. Such an increase was not found in the female athletes in contrast to previous studies [6,8,11]. The increase in tibial translation in the male volleyball players (1.8 mm) was only slightly higher than the intra-rater reliability limits for the KT-1000 (approx. 1.5 mm) [21], although that increase was 21% of the individual tibial translation and it should be clinically significant for the functional stability of the knee joint. In contrast, the increase in tibial translation in the male swimmers was only 7% of the individual tibial translation and may not be clinically significant for the functional stability of the joint. The two sports, volleyball and swimming that were examined in the present study were chosen as two extremes in the way they load the knee joint. Volleyball includes a lot of jumping and landing with great impact forces. On the other hand, swimming is non-weight bearing and only muscle action loads the joint. Rehabilitation exercises and training subject the knee joint to different loads and different strain on the ACL [14]. As a result, different amount of sagittal tibial translation have been recorded [15,16]. Though no ACL-injuries occur during swimming, an understanding of how the knee joint is affected by different loads is of importance in order to understand the complexity of the ACL-injury and its rehabilitation.
Knee kinematics differ between gender during landing [17,22,23] and cutting [24]. Exercise may also affect anterior shear load and tibial translation in a different manner depending on the tibial position at the moment the joint is subjected for the load. In the females who had a greater tibial translation before exercise compared to the male athletes, the tibia should be in a more anterior position during weight bearing [15,25]. In that position, the quadriceps angle decreases resulting in a decreased possibility of the quadriceps muscle to pull tibia anteriorly. On the other hand, female exhibit greater anterior shear force on tibia during landing compared to male [17]. More research is needed in order to fully understand how exercise affect tibial translation and possible gender differences. Our results insinuate that exercise affects male ligaments in a higher degree compared to the females’ ligaments. Wojtys et al. found that men have an increased ability to increase sagittal plane knee stiffness by voluntary knee muscle co-contraction, compared to women. These results suggest that men have an increased ability to protect the knee joint by muscle co-contraction [26]. When the muscles get fatigued, the stabilization ability of the muscles may deteriorate, leading to increased load on the ligaments and subsequent weakened structural properties. That can be a reason for the post exercise increased tibial translation. On the other hand, female may not relay on the same extension on their muscles to stabilize the knee joint and that can be a reason for the absence of a post exercise tibial translation increase. Another reason for the absence of the post exercise increase in tibial translation in the female athletes may be that the female athletes had a greater tibial translation before the training session compared to the male athletes, which is in accordance to previous results [20,27 – 29]. Results from
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a non athlete population are contradictory ([27] and unpublished results). It is not clear if increased knee joint laxity or general increased joint laxity is associated with an increased risk for injury [30 – 33]. On the other hand, general increased laxity that some individuals have despite previous workout activities is not the same as the specific post exercise increase in laxity. For example, the mechanoreceptors in a joint should regulate the response from mechanical deformation and variations in ligament tensions in accordance to the possible joint play in the specific joint. In a lax joint, movement may be larger before the mechanoreceptors respond and in a tight joint the response may come earlier. When the joint play increases as in post exercise increased laxity, this feedback system may be disturbed, leading to a decreased ability of the fatigued muscles to coordinate a functional stability in the joint. In other words, a post exercise increase in tibial translation may be more harmful compared to a general increased joint laxity. Previous results have shown increased tibial translation after a training session in women basketball players [6,8,11]. Kirkley et al. found significant difference in translation after 15 min running on a treadmill. However, only 15% of the test persons were female and they were not elite athletes. Grana and Muse tested a normal population with no elite athletes. They found significant increase in tibial translation after 20 min bicycling, with no gender differences [9]. On the other hand, Belanger et al. did not find a post exercise increase in tibial translation in female athletes after 20 min cycling on a stationary bicycle [13]. The results of the present study indicate that exercise affects tibial translation in a different manner depending on gender. Although training resulted in a post-exercise increase in tibial translation in the male athletes, such an increase was not found in the female athletes. It has been shown that female athletes have an increased risk for injury. Our results show no support for a post exercise increase in tibial translation being an important factor for this increased risk, and suggest that the difference between males and females in this regard should be sought elsewhere.
Acknowledgments The authors thank physical therapists Patrik Genberg, Susanna Qvist and Lance Smith for assistance in collecting the data. This work was supported by the Faculty of Health Sciences Linko¨ping University.
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