Relationship Between Active Hamstring Stretch Reflex Latency and Functional Knee Stability*

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1 Relationship Between Active Hamstring Stretch Reflex Latency and Functional Knee Stability* Nicholas Clark, BEd, BSc, MSc, MCSP, MMACP, CSCS 1,2 1 Integrated Physiotherapy & Conditioning Ltd. London. UK. 2 Institute of Human Performance. University College London. London. UK. *Winner of the Manipulation Association of Chartered Physiotherapists (MACP) 2005 Research Presentation Award. mail@integratedphysio.freeserve.co.uk 2 nd International Conference on Movement Dysfunction. Pain and Performance: Evidence and Effect September Edinburgh International Conference Centre. Edinburgh. Scotland. UK. Acknowledgements There are several people to whom the author would like to extend his thanks. This study would not have been possible without their support. First, to Professor Roger Woledge and Mr Tony Christopher of the University College London Institute of Human Performance (UK) for their patience, guidance, and technical support. Second, to Professors Scott Lephart and Joseph Myers of the Neuromuscular Research Laboratory at the University of Pittsburgh (US) for giving the author access to unpublished research and providing words of encouragement. Third, to the subjects who generously gave their time to participate in this study. Finally, thank you to the MACP for financial support to present this research.

2 Introduction Functional knee stability (FKS) is the condition where the tibiofemoral joint (TFJ) does not give symptoms of apprehension, giving way, or pain during physical activity, 1 and is thought to be dependent on proprioceptively-mediated muscle activity (i.e. neuromuscular control). 1,2 With regard to anterior cruciate ligament (ACL) injury, the hamstring muscles are of particular therapeutic interest due to their ability to limit excessive anterior tibial displacement 3 (ATD) and tibial transverse plane rotation. 4,5 Such kinematics are thought to contribute to persistent knee pain, 6 giving way, 7 patient disability, 6,7 and the onset and progression of TFJ arthrosis following ACL injury. 8 Consequently, hamstring reflex latency (HRL) has been extensively studied in ACL-deficient 9,10 (ACL-D) and ACLreconstruction 11 (ACL-R) subjects. Although significant increases in HRL have been identified in ACL-injured subjects versus uninjured controls, 9-11 to date, no published work has reported the relationship between HRL as a component of feed-back (F-B) muscle activity and objective measures of FKS (e.g. hop tests 12,13 ). Since it is currently

3 unknown which physical variable or combination of physical variables predicts FKS, 12,14 determining whether F-B hamstring muscle activity predicts FKS may identify a potential treatment priority in ACL-injured patients. However, because it is first necessary to identify normal or control relationships in the uninjured before making clinical judgements on the injured, 9,14 the purpose of this study was to determine the relationship between active hamstring stretch reflex latency (AHSRL) and FKS defined by a multiplanar hopping task 14 in apparently healthy subjects.

4 Methods Subjects: Twelve uninjured male athletes (mean ± SD; age 27.1 ± 5.2 years; height ± 5.7cm; mass 86.9 ± 13.7kg) who competed ( 3 sessions week 1 ) in agility-biased sports (Football n=5; Rugby Union n=4; Basketball n=1; Squash n=1; Judo n=1). Procedures: Data collection included height, mass, hamstring isometric maximum voluntary effort (IMVE), AHSRL using surface electromyography (semg), and the Adapted Crossover Hop for Distance 14 (ACHD) (Fig. 1). The IMVE, AHSRL, and ACHD data were collected from subjects self-reported dominant limb, defined as the preferred stance-limb when kicking a football. 14,15 All subjects were left-limb-dominant. Hamstring IMVE: Hamstring IMVE s were sampled to standardise the external load with which the knee was perturbed (see following) and normalise semg readings. Data were sampled using a strain-gauge attached to a CYBEX II+ isokinetic dynamometer lever-arm (Fig. 2) set to isometric mode. Subjects lay prone in 40 knee flexion, performed a warm-up effort at 75% of their perceived IMVE, followed by three recorded IMVE s.

5 Surface EMG: Data were collected using active double-differential surface electrodes (Fig. 2) which minimise the need for skin preparation 16 and muscle cross-talk. 17 Skin was prepared with pre-injection sterile wipes to remove dirt, natural oil, and dead cells. 16 Semitendinosus and biceps femoris were identified using standard manual muscle tests 18 (MMT). Electrodes were aligned parallel to the muscle fibres in the mid-line of the muscle belly 17 mid-way between the motor point and the musculotendinous junction 17 (Fig. 2), where motor points were approximated according to Robinson. 19 Electrodes were securely fixed with athletic tape, and a sub-maximal MMT performed with visual inspection of the computer display to confirm secure electrode placement 9 and EMG signal integrity. 20 Electrical signals were double-differential amplified and filtered using custom-made equipment (Department of Medical Physics & Bioengineering. University College London. London. UK.) interfaced with a Dell personal computer, where raw EMG data was saved using Testpoint software at 600Hz for 3,600 samples, giving a sample window of six seconds.

6 AHSRL: Subjects AHSRL s were sampled using a custom-made knee extension perturbation pendulum (Fig. 3 & 4) which was modified from a model originally designed by Lephart et al at the University of Pittsburgh to study the rotator cuff. Subjects lay in the same position as that for the hamstring IMVE (see previous), and maintained 20% IMVE against a strain-gauge attached to the dynamometer lever-arm (Fig. 2). The perturbation pendulum was loaded to 30% hamstring IMVE and manually released from perpendicular to the floor (Fig. 3) to strike the distal shank and induce a knee extension perturbation (Fig. 4). Three trials were administered to collect semg data. ACHD: The ACHD (Fig. 1) is a reliable and construct-valid definition and measure of FKS. 12,14 Test administration has previously been described in detail. 14 Six sub-maximal practice trials were performed to saturate any acute learning effect, 24 followed by three maximal-effort measured trials, 14 with a 60 second between-trial recovery period. 14

7 Perturbation Pendulum Strain-Gauge Surface Electrodes Figure 1. Adapted Crossover Hop for Distance (ACHD). 14 Figure 2. Subject Relaxed Positioning Prior to Hamstring Isometric Maximum Voluntary Effort (IMVE).

Perturbation Pendulum Starting Position Perturbation Pendulum Finishing Position Subject pushes up against lever-arm @

Knee Extension Perturbation Pendulum Starting Position Perpendicular to Floor *IMVE = isometric maximum voluntary

8 Perturbation Pendulum Starting Position Perturbation Pendulum Finishing Position Subject pushes up against 20% hamstring IMVE* Ankle-Strap-Stop Chair-Stop Figure 3. Knee Extension Perturbation Pendulum Starting Position Perpendicular to Floor *IMVE = isometric maximum voluntary effort Figure 4. Knee Extension Perturbation Pendulum Finishing Position* *Note pendulum stopped by chair-stop and shank stopped by ankle-strap-stop to prevent knee hyperextension injury

9 Data Reduction Raw electromyograms (EMG) were full-wave rectified 17 and analysed off-line in a custom-written Mathcad computer programme. Since the strain-gauge force signal was synchronized with the EMG, the exact instant of perturbation was identified as a sudden decrease in the force trace this represented the shank losing contact with the lever-arm as it was struck by the pendulum. A 400ms linear envelope was created by extending analyses 200ms either side of the instant of perturbation. The onset of post-perturbation hamstring reflex activity was defined as the first EMG peak five standard deviations above that of the mean pre-perturbation baseline noise. 11,20 Active hamstring stretch reflex latency (AHSRL) was then defined as the timeframe between the instant of perturbation and the onset of reflex muscle activity (Fig. 5). The mean of three clean trials was used for data analysis. For the ACHD, the mean of three measured trials was used for data analysis.

10 Instant of perturbation Onset of reflex activity Microvolts (µv) Pre-Perturbation Baseline Activity Time.* Figure 5. Typical Rectified Semitendinosus EMG Trace Following Knee Extension Perturbation Trial * entire X axis is equal to 1000ms for illustrative purposes only

11 Data Analysis All data were analysed using Microsoft Excel (V5) with α set at Pearson-product moment correlations (r) were performed with mean semitendinosus and biceps femoris AHSRL s as the independent variables and ACHD mean hop distance as the dependent variable. Results A typical rectified EMG trace for semitendinosus is illustrated in Figure 5. Mean (± SD) semitendinosus and biceps femoris AHSRL were 36.7 (± 8.1) and 34.8 (± 12.5) milliseconds (P>0.05), respectively. The mean ACHD hop distance was (± 88.2) centimetres. Correlation analyses revealed weak and non-significant relationships (r= , P>0.05) between variables (Fig. 6 & 7).

12 Adapted Crossover Hop for Distance (cm) r=0.27, r 2 =0.07, P= Semitendinosus Active Stretch Reflex Latency (ms). Figure 6. Relationship Between Semitendinosus Mean Active Stretch Reflex Latency and the Adapted Crossover Hop for Distance

13 Adapted Crossover Hop for Distance (cm) r= 0.33, r 2 =0.11, P= Biceps Femoris Active Stretch Reflex Latency (ms). Figure 7. Relationship Between Biceps Femoris Mean Active Stretch Reflex Latency and the Adapted Crossover Hop for Distance

14 Discussion The mean AHSRL in this study are consistent with those obtained by others using accessory joint motion perturbations in uninjured subjects, 9 being classified as short-loop (i.e. <50ms) spinal reflexes. 25 The mean ACHD in this study is greater than in previous work (601.6±117.6cm). 14 Considering the correlation analyses, these data imply that AHSRL does not predict FKS in uninjured subjects. Since others 9 have demonstrated that ACL-injured subjects possess prolonged AHSRL (90.4±32.9ms, P<0.05), future research should employ the present study s design with ACL-injured subjects in order to determine whether relationships differ following ACL injury. Furthermore, the relationship between feed-forward (F-F) hamstring muscle activity and multiplanar hop tests should also be considered. Since this study s data implies that AHSRL does not predict FKS, future research should also study relationships between F-B and F-F muscle activity in lower limb proximal (e.g. gluteals) and distal (e.g. tibialis anterior) muscles and FKS.

15 References 1. Johansson et al., 1991, Clin Ortho Rel Res, 268, Swanik et al., 1997, J Sp Rehab, 6, Imran & O Connor, 1998, Clin Biomech, 13, Hirokawa et al., 1991, J Electromyo Kinesiol, 1, Shultz et al., 2000, J Electromyo Kinesiol, 10, Daniel et al., 1994, Am J Sp Med, 22, Houck & Yack, 2001, J Ortho Sp Phys Ther, 31, Mow et al., 2000, Effects of instability on articular cartilage, In- Knee ligament rehabilitation. 9. Beard et al., 1994, J Ortho Res, 12, Wojtys et al., 1994, Am J Sp Med, 22, Beard et al., 2000, Clin Ortho Rel Res, 372, Clark, 2001, Phys Ther Sport, 2, Fitzgerald et al., 2001, J Ortho Sp Phys Ther, 31, Clark et al., 2002, Phys Ther Sport, 3, Colby et al., 1999, J Ortho Sp Phys Ther, 29, Soderburg & Cook, 1984, Phys Ther, 64, De Luca, 1997, J App Biomech, 13, Kendall et al., 1993, Muscles Testing and function. 19. Robinson, 1991, Neuromuscular electrical stimulation for control of posture and movement, In- Clinical electrophysiology. 20. Di Fabio, 1987, Phys Ther, 67, Lephart, 2002, Personal communication, Neuromuscular Research Laboratory, University of Pittsburgh. 22. Myers, 2002, Personal communication, Neuromuscular Research Laboratory, University of Pittsburgh. 23. Myers et al, 2003, Clin Ortho Rel Res, 407, Bolgla et al., 1997, J Ortho Sp Phys Ther, 26, Matthews, 1991, Trends Neurosci, 14,

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