Journal of Bodywork & Movement Therapies (2012) 16, 488e492 Available online at www.sciencedirect.com journal homepage: www.elsevier.com/jbmt MUSCLE PHYSIOLOGY The effect of fatigue and velocity on the relative timing of hamstring activation in relation to quadriceps Maryam Abbaszadeh-Amirdehi, MSc, PT a, Khosro Khademi-Kalantari, PhD, PT b,*, Saeed Talebian, PhD, PT a, Asghar Rezasoltani, PhD, PT c, Mohammad Reza Hadian, PhD, PT d a Department of Physiotherapy, Faculty of Rehabilitation, Tehran University of Medical Sciences, Tehran, Iran Department of Physiotherapy, Physiotherapy Research Center, Faculty of Rehabilitation, Shahid Beheshti University of Medical Sciences, Damavand Ave. Opposite to Bo-Ali Hospital, 1616931111 Tehran, Iran c Department of Physiotherapy, Shahid Beheshti University of Medical Sciences, Faculty of Rehabilitation, Tehran, Iran d Department of Physiotherapy, Faculty of Rehabilitation, Brain and Spinal Injury Research Center, Tehran University of Medical Sciences, Tehran, Iran b Received 30 April 2012; received in revised form 16 June 2012; accepted 1 July 2012 KEYWORDS Fatigue; Velocity; Timing; Hamstring; Quadriceps; Activation Summary Inter-muscular coordination has an important role in proper function and prevention of injuries in the knee joint. The purpose of this study was to characterize the effect of velocity and fatigue on the relative activation onset of hamstring to quadriceps muscles during knee extension. Thirty one healthy and non-athletic volunteers (24 women, 7 men) were recruited for the study. The onset time of vastus medialis, vastus lateralis, rectus femoris, medial and lateral hamstring were measured during maximum voluntary extension of the knee joint at velocities of 45 /s, 150 /s & 300 /s before and after fatigue and the mean delay onset of all pairs of H-Q were measured. A two-way repeated measures ANOVA test was used to compare across the mean delayed onset of hamstring related to quadriceps muscles at various velocities. Hamstring muscle showed a delayed activation related to quadriceps and increasing the velocity of shortening has a prominent effect on the inter-muscular coordination with early activation of hamstring related to quadriceps muscles (F Z 6.7, p < 0.002 for Biceps-rectus femoris, F Z 6.31, p < 0.003 for semitendinosus-rectus femoris, F Z 6.26, p < 0.003 for biceps-vastus lateralis, F Z 5.98, p < 0.004 for semitendinosus-vastus lateralis, F Z 3.19, p < 0.04 for biceps-vastus medialis and F Z 3.2, p < 0.04 for semitendinosus-vastus medialis). * Corresponding author. Tel.: þ98 21 77561411; fax: þ98 21 77561406. E-mail address: [email protected] (K. Khademi-Kalantari). 1360-8592/$ - see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jbmt.2012.07.002 Fatigue and velocity effect on muscle activation timing 489 This could predispose these muscles to over strain and possible injuries. The main effect of fatigue condition and its interaction with velocity however, showed statistically nonsignificant result. ª 2012 Elsevier Ltd. All rights reserved. Introduction Methods Inter-muscular coordination has a major role in function and prevention of injuries in the knee joint (Billaut et al., 2005). It has been recently shown that the three most common sites of injury for senior or junior runners are the knee, foot and leg. Knee injuries should be a public health concern because it increases the likelihood of discontinuing regular physical activity and developing osteoarthritis (Lohmander et al., 2004). Among knee injuries, ACL injuries and hamstring muscle injuries are the most common ones. Hamstring injuries are the most prevalent muscle injury in sports involving rapid acceleration and maximum speed running. There have been several factors hypothesized to contribute to the risk of hamstring injury including inadequate warm-up, fatigue, previous injury, knee muscle weakness or strength imbalance, increasing age, poor movement discrimination, poor flexibility, increased lumbar lordosis and poor running technique (Hoskins and Pollard, 2005; Foreman et al., 2006). Hamstring injury is mainly attributed to eccentric mechanisms which are occurred during the late swing and early stance phase of running. During these periods the hamstring muscles act as a decelerator to control hip and knee motion in the late swing phase or to provide hip extensor torque in the early stance phase. During sprinting, these events occur over a very short period of time, and if the inter-muscular coordination is poor, muscle strain injury may occur. Inter-muscular coordination may also have a significant role in controlling the amount of loading of the knee ligaments especially anterior cruciate ligament. Quadriceps muscles produce extensor torque in the knee as well as vigorous anterior shear force to tibia. The most resultant anterior shear force applied to the tibia due to contraction of quadriceps muscles is occurred in terminal extension of the knee joint. This shear force is tolerated by anterior cruciate ligament. Hamstring muscles, with posterior attachment to tibia on the other hand, produce posterior shear force that would neutralize the amount of stress on the anterior cruciate ligament (Shelburne and Pandy, 1997; Lutz et al., 1993; Orchard and Seward, 2002). Numerous studies have evaluated the ratio of hamstring and quadriceps muscles activation during different activities (Croce and Miller, 2003; Reilly and Marfell-Jones, 2003; Jnhagen, 2005; Olyaei et al., 2006). Little is known about the temporal pattern of activation of quadriceps and hamstring muscles and the factors that may affect it. Coordinate activation of these antagonist group of muscles are crucial for the knee joint stability and also any impairment in this temporal coordination can predispose the ACL and also hamstring muscles to injury. Participants Thirty-one healthy and non athletic participants (24 female & 7 male, age: 23.5 2.5 years, height: 165 10 cm, weight: 60 9) were recruited for this study. Each participant provided informed written consent, and the experimental protocol was approved by local Research Ethics committee. Procedure An isokinetic dynamometer (Biodex Medical System, Inc. Shirley, New York) was used to apply different knee flexionextension velocities and to measure the knee extensor torque. Prior to the test, the cases with hamstring contracture were identified and excluded from the study. The participant lies in supine position, flexes both hips to 90 and actively extend each knee as much as possible. For normal flexibility in the hamstrings, knee extension should be within 20 of full extension. The leg with which the participant would kick a ball was selected as dominant side for the experiment. In this study, dominant leg of all participants was right leg. Surface EMG of rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF) and semitendinosus (ST) were recorded according to SENIAM guidelines (Hermens et al., 1999). To minimize the movement artifacts, the electrodes were taped to the skin with surgical tape. The ground electrodes were positioned on the wrist. The participant seated with the hip fixed at 90 flexion with strap. The axis of the dynamometer was aligned with the axis of the knee, and the tibial pad was placed proximal to the medial malleole. Various angular velocity sequences including 45 /s, 150 /s and 300 /s were applied randomly for each participant. Each participant performed three repetition of maximum knee flexion-extension from 0 to 90 at each velocity with 10 s rest interval between different velocities. The maximum torque and the onset time were calculated for each muscle and at all velocities. Sixty repetition of knee extension-flexion (concentriceconcentric) with max effort in angular velocities of 45 /s were done to fatigue the muscles which follows immediately with 5 maximum knee extension-flexion at 150 /s and 300 /s. The last three trials at each velocity were used for extracting the maximum torque and the onset time after fatigue. The onset time of activation was defined as the instant when the rectified SEMG passed above the 3SD of the background EMG and lasted for more than 10 ms. The mean delayed activation onset of hamstring in relation to quadriceps muscles (H-Q onset 490 M. Abbaszadeh-Amirdehi et al. delay) in the last 3 trials post fatigue was then calculated by extracting the onset time of hamstring from quadriceps muscles. Measurements & data analysis Data analysis was carried out using SPSS software, Version 16 and a priori significance level was set at 0.05. The average values of dependent variables for three velocities of each experimental condition were used for statistical analysis. A 2 3 (fatigue and non-fatigue conditions, three levels of velocities of movement) repeated measures analysis of variance (ANOVA) test was used to determine main effects and interactions of these factors for H-Q onset delay. For multiple comparisons, the Bonferroni adjustment method was used. Intra class correlation of the last 3 trials pre and post fatigue was also computed for the stability of the H-Q onset delay. Results The ICC coefficient of the H-Q onset delay in the last 3 trials pre and post fatigue showed values ranged from 0.82 to 0.93. Hamstring muscle activated with a delay related to quadriceps muscles during knee extension at all velocities. The changes in the H-Q onset delay at different velocities, before and after fatigue can be seen in Table 1. The main effect of velocity was statistically significant for all pairs of H-Q onset delay; meaning that with increasing the velocities the delay onset of hamstring muscles to quadriceps was decreased (Fig. 1). The main effect of fatigue and the interaction of fatigue and velocity on the other hand, were statistically nonsignificant. The F ratios and p values for all pairs of H-Q onset delay can be seen in Table 2. Multiple comparisons showed that the delayed activation onset of BF and ST in relation with VL showed significant decrease at velocity of 150 /s compared to 45 /s before fatigue and between 45 /se150 /s and 45 /se300 / s after fatigue (P < 0.01). Biceps femoris and ST also showed earlier activation in relation to RF with increasing velocity from 45 /s to 150 /s (p < 0.01) and also to 300 /s (p < 0.001). When the onset time of ST and BF was compared with VM, the changes in velocity showed statistically nonsignificant effect except for the velocity of 150 / s compared to 45 /s (p < 0.03). Discussion The main findings of this study showed that significant changes on the temporal coordination between hamstring and quadriceps muscles can be interrupted at high velocity and not by fatigue. Our results expressed that vastus lateralis and rectus femoris have an important role in the fast knee movements and activation time differences between these two muscles and hamstring muscles decreased with increased velocity. Namely, with decision making for knee extensors to contract at higher velocity, antagonist muscles (hamstrings) were contracted earlier. This also means that with increasing the rate of activation of Q muscles, utilization of semitendinosus and biceps femoris as a controller at the beginning of motion also increases. It has been reported that with the increased velocity the amount of stretch of hamstring does not change, however the amount of negative work increases significantly (Thelen et al., 2005). These can increase the risk of injuries at higher velocity movements. Obviously, premature activation of hamstring muscle at higher velocity can affect negative work calculated in this research which is similar to the results of Thelen et al. (2006). The acceptable correlation coefficient of the H-Q onset delay in the 3 trials used for extracting the data, pre and post fatigue, suggests the temporal stability of neuromuscular control on the knee musculature. This would also implies that averaging the delay time in the last 3 trials pre and post fatigue could represent a reliable values for each participant and at all conditions. There isn’t statistically significant difference of delayed activation onset of hamstring related to VM across the studied velocities. This may indicate that vastus medialis are not involved in the fast movements and motor programming of this muscle does not change along with changes in velocities. Co-contraction of this muscle with its antagonist muscle is defined with fixed schedule timing. Our results mainly showed insignificant changes in H-Q onset delay with increasing the velocity from 150 /s to 300 /s. This can be due to the low optimum maximum torque of knee musculature activation and the constant rate of motor programming in the CNS in our non athletic participants. It is plausible that elite athletes involving in high speed sports such as sprinters may show continuously earlier activation of hamstrings with increasing the velocity to higher values. The fatigued muscles showed statistically insignificant changes in the H-Q onset delay. It seems that corrupted Table 1 Mean SD of activation time of H-Q muscles at different velocities and conditions. The * represent the significant values compared to velocity of 45 at each condition. Non fatigue Fatigue Velocity (%s) ST-VM (msec) 45 150 300 45 150 300 68 48 50 76 50 53 77 40* 28 46 34* 99 BF-VM (msec) 53 38 45 60 33 48 81 35* 28 46 33* 58 ST-VL (msec) 87 58 64 77 62 52 66 29* 42 42 34* 90* BF-VL (msec) 74 48 58 61 46 52 49 29* 38 34 32* 90* ST-RF (msec) 89 60 55 76 65 48 65 41* 41* 51 40 99 BF-RF (msec) 75 50 50 60 49 43 47 36* 30* 41 38 52 Fatigue and velocity effect on muscle activation timing 491 Figure 1 The mean changes of delay onset time of H-Q muscles activation at three different velocities and two conditions. The lower values represent the shorter delay of hamstring muscle activation in relation to quadriceps muscles. temporal inter-muscular coordination is not the possible mechanism that fatigue can predispose the knee joint ligaments or hamstring muscles to injury. It is known that fatigue can be caused by many different mechanisms commonly classified as central and peripheral. Knowing Table 2 that the mechanisms that cause fatigue are specific to the task being performed, it is possible that different method to induce fatigue may result in different outcomes. The results of this study are similar to the results of studies done on woman athletes (Rozzi et al., 1999), but F ratios and P values of all pairs of H-Q onset delay. ST-VM Condition (fatigue, non fatigue) Velocity Condition * Velocity BF-VM ST-VL BF-VL ST-RF BF-RF F Sig. F Sig. F Sig. F Sig. F Sig. F Sig. 0.22 3.10 0.05 0.64 0.05 0.94 0.03 3.19 0.32 0.86 0.04 0.72 0.41 5.98 0.48 0.52 0.004 0.61 0.09 6.26 0.94 0.15 0.03 0.39 0.19 6.31 0.61 0.66 0.003 0.54 1.22 6.71 0.8 0.27 0.002 0.45 492 are opposed to the study of Billaut et al. (2005). Totally, the results of this study represent the more specific effect of high velocity and not fatigue on the activation onset of hamstring to quadriceps muscles. 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