JCLB-03946; No of Pages 9 Clinical Biomechanics xxx (2015) xxx–xxx

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Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis Georgios Bouchouras a,⁎, Glykeria Patsika b, Vassilia Hatzitaki a, Eleftherios Kellis d a b c

Motor Control and Learning Laboratory, Faculty of Physical Education and Sport Sciences, Aristotle University of Thessaloniki, Greece Laboratory of Neuromechanics, Faculty of Physical Education and Sport Sciences, Aristotle University of Thessaloniki, Greece Laboratory of Neuromechanics, Department of Physical Education and Sports Science of Serres, Aristotle University of Thessaloniki, Greece

a r t i c l e

i n f o

Article history: Received 7 December 2014 Accepted 24 March 2015 Keywords: Electromyography Hamstrings Quadriceps Ground reaction forces Arthritis Sit to stand

a b s t r a c t Backround: The purpose of this study was to compare joint kinematics, knee and trunk muscle activation and coactivation patterns during a sit-to-stand movement in women with knee osteoarthritis and age-matched controls. Methods: Eleven women with knee osteoarthritis (mean and standard deviation, age: 66.90, 4.51 years, height: 1.63, 0.02 m, mass: 77.63, 5.4 kg) and eleven healthy women (mean and standard deviation, age: 61.90, 3.12 years, height: 1.63 m, 0.03, mass: 78.30, 4.91 kg) performed a Sit to Stand movement at a self-selected slow, normal and fast speed. Three-dimensional joint kinematics of the lower limb, vertical ground reaction forces and electromyographic activity of the biceps femoris vastus lateralis and erectus spinae were recorded bilaterally. Findings: A two-way ANOVA showed that the osteoarhtitis group performed the sit to stand task using a smaller knee and hip range of motion compared with the control group while no differences in temporal kinematics and ground reaction force-related parameters were observed. In addition, women with osteoarhtritis displayed significantly lower vastus lateralis coupled with a higher biceps feomoris electromyographic activity and higher agonist–antagonist co-contraction and co-activation than asymptomatic women. The activation of erectus spinae was not different between groups. Interpretation: Results indicate that patients with moderate knee osteoarthritis rise from the chair using greater knee muscle co-contraction, earlier and greater activation of the hamstrings which results in reduced hip and knee range of motion. This may be a way to overcome the pain and potential muscle atrophy of knee extensor muscles without compromising overall task duration. © 2015 Elsevier Ltd. All rights reserved.

1. Introduction A growing number of studies have reported altered neuromuscular activation and movement patterns during functional activities in individuals with knee osteoarthritis (OA) (Bennell et al., 2008; Bennell et al., 2013; Childs et al., 2004; Hortobagyi et al., 2005; Hubley-Kozey et al., 2009; Lewek et al., 2004; Patsika et al., 2011; Slemenda et al., 1997). These alterations are linked with typical OA symptoms such as quadriceps muscle weakness (Bennell et al., 2008; Bennell et al., 2013) and pain (Slemenda et al., 1997) and may signify impairments in performance of daily activities with negative implications for quality of life in these individuals. Research studies have shown that individuals with knee OA display different movement strategies when performing a STS task than asymptomatic individuals (Pai et al., 1994; Segal et al., 2013; Turcot et al., 2012a). Particularly, OA patients perform the STS task at a slower ⁎ Corresponding author at: Laboratory of Motor Control and Learning, Aristotle University of Thessaloniki, Faculty of Physical Education and Sport Sciences at Thermi, 57001 Thessaloniki, Greece. E-mail address: [email protected] (G. Bouchouras).

speed (Patsika et al., 2011), a lower knee range of motion, extension (Pai et al., 1994) and flexion torque (Turcot et al., 2012b), a higher hip extension torque (Pai et al., 1994) and a more posterior position of the center of pressure (Patsika et al., 2011) than asymptomatic controls. Furthermore, there is evidence that OA affects the activity of major trunk extensors muscles. Turcot et al. (2012a, 2012b) reported that patients with knee OA showed a higher maximal trunk flexion and a higher lateral trunk lean on the contralateral side when compared with the control group, making the trunk a major contributor to STS task. All these factors imply that pathological or pain-related constraints set by knee OA on the musculoskeletal system, may lead to altered intersegmental coordination solutions to accomplish the same overall task goal. Yet, the redundancy of the degrees of freedom available in the human motor system allows for the development of new movement affordances ensuring effective interaction with the physical environment for the successful accomplishment of the tasks of daily living. Altered neuromuscular patterns are mostly translated into different muscle co-contraction patterns while individuals perform a given movement (Mills et al., 2013). Co-contraction is defined as the simultaneous activity of agonist and antagonist muscles surrounding a joint (Kellis, 1998). Higher co-contraction may be linked with higher joint

http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025 0268-0033/© 2015 Elsevier Ltd. All rights reserved.

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

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G. Bouchouras et al. / Clinical Biomechanics xxx (2015) xxx–xxx

stiffness (Baratta et al., 1988; De Luca and Mambrito, 1987; Solomonow et al., 1987) and altered control of force transfer from the hip to the knee via the work of the bi-articular components of the hamstrings and quadriceps (Roebroeck et al., 1994). Evidence indicates elevated quadriceps and hamstrings co-contraction in OA patients during isolated strength exercises (Kellis et al., 2013), stance phase of walking (Childs et al., 2004; Hortobagyi et al., 2005) or stand-to-sit (STS) movement (Patsika et al., 2011). Particularly, research studies have found that individuals with knee OA display a high vastus lateralis (VL) to biceps femoris (BF) activation ratio (lateral muscle co-contraction) (Childs et al., 2004; Hubley-Kozey et al., 2009; Lewek et al., 2004). In a systematic review (Mills et al., 2013), co-contraction was considered as “a prevalent muscle adaptation” when the knee is fully loaded, in order to protect the medial knee joint from excessive loading. In a previous study, Patsika et al. (2011) found similar activity of the vastii muscles but a higher antagonist BF activation during the STS task in women with knee OA compared with controls. However, the co-contraction patterns during the STS movement have not been thoroughly investigated. Altered muscle activation patterns when performing a movement are not only associated with the concurrent changes in amplitude but also on the timing of muscle activity. Studies have shown that individuals with knee OA demonstrated 1.5 times longer vastus lateralis (VL), medial hamstrings, tibialis anterior, medial gastrocnemius and rectus femoris activation during level and inclined walking (Patsika et al., 2011; Rutherford et al., 2011) or toe out walking (Rutherford et al., 2011) than that observed in asymptomatic individuals. To our knowledge, relative duration of muscle activation or more specifically temporal co-activation of agonist–antagonist muscle pairs at the knee when performing a STS task by people with OA has not been previously examined. Examination of the relative onset of activation of several muscles that are activated during a task may provide additional information on co-ordination patterns that accompany the altered movement strategies adopted by people with knee OA. Performance of the STS task may also depend on the speed of execution of this task (Janssen et al., 2002; Pai et al., 1994). An increase of speed leads to a greater hip flexion torque and a lower knee extension and ankle dorsiflexion moments during STS (Pai et al., 1994). Vander Linden et al. (1994) reported that when individuals were asked to stand as fast as possible, muscle onsets and movement phases were shortened. Elderly individuals generally show a slower speed of the STS task than younger ones (Mourey et al., 2000), but they show less hip flexion when performing the STS movement faster (Papa and Cappozzo, 1999). Since older individuals with knee OA perform STS even slower than asymptomatic ones (Patsika et al., 2011), then examining the effects of speed on muscle activation and joint kinematics during the STS task is worthwhile. The purpose of this study was to determine whether women with knee osteoarthritis (OA) and asymptomatic controls (CON) show different movement, trunk and knee muscle activation and co-contraction patterns when rising from a chair at different self-selected speeds. Movement kinematics and muscle activation were examined using both amplitude and time domain measures. 2. Method 2.1. Participants Eleven women with knee OA (mean and standard deviation, age: 66.90, 4.51 yr, height: 1.63, 0.02 m, mass: 77.63, 5.4 kg) and eleven controls (mean and standard deviation, age: 61.90, 3.12 yr, height: 1.63, 0.03, mass: 78.30, 4.91 kg) volunteered to participate in this study. A power analysis performed prior to experimentation indicated that a minimum number of ten participants per group was sufficient to ensure statistical power considering an effect size of 0.75, a minimum power of 0.80, and a p value of 0.05. Women with knee OA displayed grade II or III unilateral OA at the medial tibiofemoral compartment of

right knee joint, as evidenced by radiographic assessment using Kellgren and Lawrence criteria (Kellgren and Lawrence, 1957). All women completed the Western Ontario and McMaster University Index (WOMAC) as an indicator of self-reported pain, stiffness and function (Bellamy et al., 1988). Healthy women had no musculoskeletal or neuromuscular pain or any injury of the knee and hip joint. All participants were regularly active, but they didnot participate in systematic training programs. They werefully informed on the purpose of the study and signed a written consent form, in order to participate in this study. The study was approved by University Ethnics Committee.

2.2. Instrumentation Two adjusted force plates (Balance Plate 6501, Bertec Corp., Columbus, USA) with a sampling frequency of 100 Hz, were used to record the vertical ground reaction forces during performance of the STS task. A 10 camera Vicon system (Bonita 3, Nexus Vicon, Oxford, UK, sampling, 100 Hz) was used to record joint kinematics for the lower body. In addition an 8-channel wireless EMG system (Telemyo DTS, Noraxon USA Inc), sampling at 1000 Hz, was used to record the bilateral EMG activity of selected knee muscles. The ground reaction forces, EMG signals and markers 3D position coordinates were synchronously sampled using the Vicon system that was connected to an A/D card (MX Giganet Oxford, UK). All signals were stored and further processed using the NEXUS (version 1.8.3) software and custom analysis software, programmed in Matlab (Version 7.7, MathWorksInc, USA).

2.3. Procedure and task EMG activity of selected knee muscles was collected using bipolar active surface electrodes (Ag/AgCl electrodes, EL504, BIOPAC Systems). The skin was shaved with alcohol wipes to remove any dead cells. The electrodes were placed according to S.E.N.I.A.M. recommendations (Hermens et al., 2000). Particularly, two electrodes were placed over the long head of the Biceps Femoris (BF), half way on the line between the ischial tuberosity and the head of the fibula, over the distal position of the vastus lateralis (VL) muscle, 10 cm above and medially from the superior border of patella of both legs. Further, an additional pair of electrodes was placed on the right Erectus Spinae muscle, approximately 3 cm laterally from the L1 spinal process. The EMG signals were amplified (gain 1000, input impedance 10 MΩ, CMRR 130 dB) and filtered using a band-pass filter (20 Hz–450 Hz) before stored for further digital processing. Also, for the purpose of the present experiment, 16 passive reflective markers were attached to specific anthropometric landmarks dictated by the analysis software (NEXUS 1.8.3.), for the calculation of the segment and joint angles from the markers 3D position coordinates using the Plug-in-Gait model. A static trial was captured in order to calculate the anatomical angles from the marker coordinates using Vicon's Plug In Gait model. The measurement volume was approximately 3.5 × 3.5 × 3 m and the mean image error for all cameras was 0.10 mm (st. deviation = 0.01). The experimental task required rising from a chair, at three different self selected speeds. The chair had no arms and its height was adjusted to the participant's height so as to ensure a right knee angle at the sitting position. The feet were placed parallel to each other, one over each force platform while the arms were stabilized on the waist. From this position, participants were asked to rise from the chair without using their arms. After three practice trials, the participants performed three trials at their self selected normal speed (Gross et al., 1998). They were then asked to perform additional three trials “faster” and then “slower” than their normal speed. Appropriate rest interval was provided between trials. The sequence of trials was randomized across participants.

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

G. Bouchouras et al. / Clinical Biomechanics xxx (2015) xxx–xxx

2.4. Data analysis Data processing of the collected signals was held in two phases in order to extract the dependent variables. The first phase involved the processing of the kinematic data using Nexus software (version 1.8.3) based on the kinematic equations provided by the Vicon Plug-in-Gait model. The second stage involved the processing of the kinematic, force and EMG signals with custom algorithms developed in MATLAB (Mathworks Inc, version 7.7.0471) in order to derive the outcome variables of the study. Kinematic analysis involved the calculation of the whole trial and sub-phase duration (s) as well as the peak to peak amplitude of the ankle, knee and hip joint angular displacement (deg). Trial onset was defined as the point in time where the hip angle exceeded by 5 standard deviations the initial hip angle of the sitting position for more than 10 consecutive frames. Similarly, trial offset was defined as the point in time where the hip angle dropped by 5 standard deviations below the maximum hip extension angle of the final position. The trial was divided into three phases (Caruthers et al., 2013) based on selected joint kinematic events (Fig. 1). Specifically, the following phases were identified; a) leaning phase; defined from the start of the trial to the maximum hip flexion, b) momentum phase; defined from maximum hip flexion to

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maximum ankle flexion and c) extension phase; defined from maximum ankle flexion to the end of the trial. Vertical ground reaction force (VGRF) signals were low pass filtered using a Butterworth digital filter (dual pass, 4th order, cut-off: 6 Hz) prior to the calculation of the peak VGRF amplitude that was normalized to body weight. EMG signals were full wave rectified and low-pass filtered (4th order, dual pass Butterworth digital filter, cut-off: 6 Hz) in order to obtain the linear envelope of the signal. Then, the EMG integral (IEMG) was calculated for the burst duration of each muscle (VL, BF, ES, Fig. 2). EMG burst onset and offset times were identified using a combination of algorithm detection (based on the criterion of 5 standard deviations above the baseline) and manual digitization after visual inspection of the signal. The IEMG of each burst during the STS task was normalized to the IEMG amplitude of the same muscle calculated over 2 s of normal quiet standing. The following EMG indexes were calculated: a) the knee co-activation index defined by taking the difference in burst onset time in seconds between the agonist (VL) and antagonist (BF) muscle also known as agonist–antagonist onset latency. Co−activation ¼ VL burst onset−BF burst onset

Fig. 1. Representative right ankle (top), knee (middle) and hip (bottom) range of motion of one OA and one CON group participant. Vertical lines indicate trial separation.

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

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Fig. 2. Representative IEMG agonist (VL—blue) and antagonist (BF—red) curves of right knee muscles for one OA and CON group participant. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

b) the knee co-contraction index was defined by taking the ratio of the agonist (VL) over the antagonist (BF) IEMG value according to the following formula: Co−contraction index ¼

normalized VL IEMG normalized B F IEMG

2.5. Statistical analysis At first, independent samples t-tests was used to compare WOMAC scores among groups. Then, a two-way analysis of variance (2 × 3 repeated measures ANOVA) was used to examine the differences between groups (OA, CON) and speeds (slow, normal, fast) on each dependent variable. Significant group by speed interaction effects were further analyzed using Tukey's post hoc tests to determine which pair means were significantly different. The level of significance was set at p b 0.05. All tests were made using IBM SPSS 21.

significantly the other two phase durations. No statistically significant interaction effects between the group and the speed condition were noted for any of the duration variables. Group results for the joints range of motion (peak to peak amplitude) are shown in Table 3. Ankle range of motion did not differ significantly between the two groups (p N 0.05). The OA group, however, showed smaller knee and hip range of motion compared to the CON group at all three speeds. Specifically, group effects were statistically significant for the right (F1,18 = 7.01, p = 0.016) and left (F1,18 = 6.06, p = 0.025) knee, and for the right (F1,18 = 4.62, p = 0.045) and left (F1,18 = 5.77, p = 0.027) hip range of motion. Speed of execution also affected the joint range of motion. Specifically, the right knee range of motion was larger in the slow speed compared to the other two speeds (F 2,17 = 0.87, p = 0.43). Similarly, the right hip range of motion was significantly larger in the slow, when compared to the fast task condition (F2,17 = 5.80, p = 0.012). No statistically significant group by speed interaction effects were noted for any of the joint angular ranges of motion examined.

3. Results 3.2. Electromyographic (EMG) activity Average WOMAC scores are shown in Table 1, for both groups. The OA group demonstrated higher symptoms of pain (t20 = 7.286, p b 0.05), stiffness (t20 = 8.948, p b 0.05) and reduced physical function (t20 = 10.237, p b 0.05). 3.1. Kinematics STS duration was not significantly different between groups (Table 2). Similarly, duration of the leaning, momentum and extension phases did not differ between the OA and CON group participants. In contrast, there was a significant main effect of speed on STS duration (F2,17 = 47.02, p = 0.000) and momentum phase duration (F2,16 = 4.70, p = 0.025). As expected, trial duration was significantly longer in the slow compared to the other two speed conditions (p b 0.05). Also, the duration of the momentum phase was significantly longer in the fast than the slow speed conditions (p b 0.05). Speed, did not affect

Table 1 Outcomes measures of the Western Ontario and McMaster University Index with the pain, stiffness and function subscales between women with knee osteoarthritis (OA) and controls (means and standards deviations). WOMAC scores

Pain Stiffness Function

OA

CΟΝ

3.60 (1.01)⁎ 3.27 (1.00)⁎ 22.54 (4.74)⁎

0.81 (0.75) 0.27 (0.46) 3.63 (3.88)

⁎ Significantly different between groups, p b 0.05.

IEMG activity at the knee joint was significantly different between the two groups for both knee muscles examined (Fig. 3). Specifically, the OA patients had significantly lower right (F1,19 = 5.890, p = 0.025) and left VL (F1, 19 = 8.062, p = 0.010) IEMG amplitude and higher right (F1,19 = 6.463, p = 0.020) and left BF (F1, 19 = 4.425, p = 0.049) IEMG amplitude compared to the CON group participants. Also, the speed of task execution significantly influenced the amplitude of EMG activity at the joint. Specifically, both VL and BF IEMG amplitude was higher at the slow relative to the other two speed conditions (right VL: F2, 19 = 15.56, p = 0.00, left VL: F2, 19 = 20.82, p = 0.00, right BF: F2, 19 = 47.38, p = 0.00, left BF: F2, 19 = 24.19, p = 0.00). Analysis also revealed a significant group by speed interaction effect for right and left VL (F2, 19 = 5.814, p = 0.006) and for right BF (F2, 19 = 3.848, p = 0.030) IEMG amplitude. Post-hoc analysis indicated that BF IEMG was significantly higher (p b 0.05) in the OA compared to the CON group participants only during the normal speed condition. By contrast, BF IEMG activity was not different between groups in the other two speed conditions. ES IEMG was not found to be statistically different between groups (F1, 19 = 0.216, p = 0.647) or speeds examined (F2, 19 = 2.87, p = 0.07). The co-activation index was significantly different between the two groups (F1,19 = 7.11, p = 0.015) for the right leg. Specifically, the OA patients activated the antagonist (BF) earlier than the agonist (VL) muscle when rising from the chair, resulting in negative co-activation index values at all three speeds in that leg (Fig. 4). The co-activation index was negative for the CON group participants as well, but only during the slow task execution. There was a statistically significant speed effect on latency values for the right (F2,19 = 6.31, p = 0.015)

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

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Table 2 Group means and standard deviations for whole trial duration (sec) and duration of various phases of the STS task (% of trial duration) between women with knee osteoarthritis (OA) and control (CON) group participants. Movement speed Normal

Trial (s) Leaning phase (%) Momentum phase (%) Extension phase (%)

Fast

Slow

OA

CON

OA

CON

OA

CON

1.88 (0.30) 33.31 (5.39) 21.09 (9.22) 45.42 (9.30)

1.58 (0.29) 34.41 (8.81) 21.65 (8.41) 46.25 (11.14)

1.40 (0.36) 33.87 (3.91) 23.13 (12.54) 42.34 (12.67)

1.41 (0.37) 33.82 (10.08) 26.63 (14.40) 43.29 (12.26)

3.20 (1.02) 34.39 (5.05) 15.87 (12.98) 49.58 (14.99)

3.22 (0.66) 35.15 (10.48) 19.96 (10.59) 48.25 (8.99)

and left (F2,19 = 6.03, p = 0.05) leg. Post-hoc tukey tests indicated that latencies during the slow speed tasks (collapsed for groups) were lower than those recorded at normal and fast speed tasks (p b 0.05). No statistically significant interactions (group by speed) effects were found. The co-contraction index was significantly different between the two groups for the right (F1,19 = 18.988, p = 0.00) and left (F1,19 = 22.879, p = 0.00) leg. Specifically, the OA patients had significantly lower (closer to 1) co-contraction index compared to the CON group participants suggesting similar IEMG activity for the agonist and antagonist muscle at all (three) speed conditions (Fig. 5). On the other hand, this index was greater than 1 for the CON group, suggesting higher agonist (VL) compared to antagonist (BF) activity. Finally, no main effect of speed or group by speed interaction on the co-contraction index was noted. 3.3. Ground reaction forces The peak vertical ground reaction force, normalized to bodyweight, was not significantly different between groups or speeds of task execution (Table 4). 4. Discussion The main finding of this study is that women with knee OA rise from the chair with greater muscle co-contraction at the knee joint and reduced knee and hip range of motion when compared to asymptomatic age-matched controls. Despite these activation differences, women with knee OA perform the STS task at the same movement time as controls and with similar duration of the subphases of the task. In the present study, OA patients showed a higher co-activation index compared to control participants (Fig. 4). There is some evidence that individuals with OA demonstrate an earlier and longer muscle recruitment of BF and VL than asymptomatic individuals during walking (Childs et al., 2004; Rutherford et al., 2011), but such intra-muscular differences in muscle recruitment onset during performance of a functional dynamic task (i.e. chair rise) have not been previously documented. It appears that women with knee OA performed the STS task by recruiting the BF muscle earlier than the VL. This earlier activation of the antagonist relative to the agonist muscle resulted in a reduced

knee and hip range of motion. Based on this evidence it is speculated that women in knee OA used the greater agonist–antagonist coactivation as a strategy to control the hip and knee joint excursion. This speculation is supported by experimental evidence from upper limb reaching suggesting that individuals use the timing of the agonist–antagonist muscle activation as a strategy to systematically accommodate changes in distance or control the amplitude of movement (Buneo et al., 1994; Gottlieb et al., 1989; Lestienne, 1979). Therefore, it seems reasonable to suggest that women with knee OA recruited the BF earlier than the VL muscle in order to reduce the range of motion at the joint, protect the impaired joint and avoid the pain possibly associated with extreme joint locations or excursions (Kuhlow et al., 2010). The co-contraction index values were 3.5 to 5 times lower in the OA group compared with CONs indicating a higher BF activation compared to the VL (Fig. 5). This large difference in relative amplitude between this pair of antagonistic muscles is in agreement with previous findings (Childs et al., 2004; Hortobagyi et al., 2005; Kellis et al., 2013; Patsika et al., 2011). Muscle co-contraction increases joint stifness and it may protect the knee joint from injury under conditions of excessive loading (Janssen et al., 2002; Kellis et al., 2013; Mourey et al., 2000; Rutherford et al., 2011; Vander Linden et al., 1994). Increased joint stifness leads to a reduced range of motion (Bong and Di Cesare, 2004) which was observed in women with knee OA (Table 3). This is in line with previous findings which reported that individuals with OA recruit their lateral musculature during early and mid-stance of walking with greater amplitudes and for longer duration than medial musculature (Hubley-Kozey et al., 2009; Rutherford et al., 2011). Surprisingly, however, the modified knee muscle co-activation strategy did not alter the overall movement duration, a finding that is not in line with previous studies reporting a longer STS duration in patients with advanced OA compared to healthy controls (Boonstra et al., 2010; Christiansen and Stevens-Lapsley, 2010; Turcot et al., 2012b). This discrepancy may have several explanations. First, previous studies attributed the longer STS task duration to greater forward lean of the trunk in OA patients (Su et al., 1998). Although trunk kinematics were not measured in the present study, the absence of between group differences in ES activation suggests that the amount of forward lean was similar across the two groups. Therefore, a differential trunk

Table 3 Anterior–posterior joint range of motion (deg) for left (L) and right (R) leg between women with knee OA (OA) and control (CON) group participant. Means and standard deviations. Movement speed Normal

Rankle (deg) Lankle (deg) Rknee Lknee Rhip Lhip

Fast

Slow

OA

CON

OA

CON

OA

CON

19.28 (3.48) 20.05 (4.54) 79.29 (6.38)⁎ 74.63 (7.60)⁎ 90. 72 (8.62) 84.18 (10.62)

21.60 (4.77) 22. 45 (7.08) 86. 97 (8.08) 85.36 (10.10) 96.22 (8.82) 91.85 (6.75)

18.81 (3.42) 20.78 (12.51) 78.18 (5.39)⁎ 72.63 (8.82)⁎ 86.56 (9.53) 79.18 (11.33)⁎

20.86 (5.58) 19.89 (8.96) 86.75 (9.55) 84.36 (11.93) 94.99 (10.32) 89.31 (6.21)

18.00 (4.53) 18.78 (6.83) 80.80 (5.69)⁎ 79.56 (12.93) 88.49 (10.38)⁎ 86.36 (11.53)⁎

21.48, 7.89 24.79, 10.45 89.26, 7.90 88.23 (9.78) 99.45 (11.11) 96.26 (7.38)

⁎ Significantly different between groups, p b 0.05.

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

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G. Bouchouras et al. / Clinical Biomechanics xxx (2015) xxx–xxx 25

*† Amplitude VL Left (%)

20

*

*†

15

10

5

0 Normal

Fast

Slow

Fig. 3. IEMG amplitude of VL and BF for left (L) and right (R) leg and ES for with the knee osteoarthritis (OA) and control (CON) group, normalized(%) to baseline activity recorded during upright stance. Group means and st. deviations are shown. *Significantly different compared with osteoarthritis (OA) group b .05. †Significantly different compared with OA based on posthoc analysis p b .05.

contribution to overall movement duration by the two groups seems unlikely. Second, longer movement duration could be due to weight bearing asymmetries in patients with advanced knee OA (Boonstra et al., 2010; Christiansen and Stevens-Lapsley, 2010; Turcot et al., 2012b), which increases medio-lateral sway during chair rising. This loading occurs with the leaning of the trunk towards the unaffected leg, in order to unload the affected one. So, weight bearing asymmetry may alter the trunk kinematics and prolong task execution. The results of the present study did not reveal any weight bearing asymmetry for the women with knee OA, as shown by the vertical ground reaction forces, which were the same between groups and the two sides of the body. Based on this evidence, we suggest that the severity of the knee OA in the women participating in our study was not sufficient to induce weight bearing asymmetries and thus alter the duration of STS task

execution. Third, the similar task duration in combination with a reduced hip and knee range motion noted in the present study suggests that women with OA performed the task with lower joint velocities and ended it in a more flexed posture (with greater knee and hip flexion). Being able to rise from the chair at the same movement time as healthy individuals is critical, because the developing of intersegmental passive forces contribute significantly to the momentum required for overcoming the body's inertia against gravity. In this case, less muscular effort is required compared to a slower movement which seriously limits the exploitation of intersegment forces increasing thus the need for active (muscle) torque production (Eng et al., 1997; Patla and Prentice, 1995). Indeed, this was confirmed by our results showing increased BF activation in the normal speed condition where movement time was longer for the OA patients (1.88 s vs. 1.58 s,

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

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Fig. 4. Co-activation index for the left (L) and right (R) leg of the knee osteoarthritis (OA) and control (CON) group. Group means and st, deviations are shown.

respectively, Table 1). In addition, ending the task at a more flexed posture protects against excessive loading of the impaired joints. Collectively, the results of the current study, indicate that patients with moderate knee OA develop compensatory mechanisms, which enable them to maintain the same global task dynamics as healthy individuals (i.e. similar movement duration), despite pathology induced changes in the local dynamics (increased muscle coactivation and reduced range of knee and hip motion). This idea is corroborated by previous studies showing that several possible intersegmental coordination solutions are available for accomplishing a certain task (Hatzitaki and Konstadakos, 2007; Hong and Newell, 2006) due to redundancy/ degeneracy of the degrees of freedom available in the human body (Bernstein, 1967; Edelman and Gally, 2001; White et al., 1998). The present study adds further insights to this principle by demonstrating that the recruitment of the local degrees of freedom, required to achieve a stable task solution (i.e. perform the STS task with a similar overall movement duration), does not only depend on task or environmental constraints, but is also a function of pathology or pain-related constraints induced by knee OA on the musculoskeletal system. Kinematic analysis with use of external passive markers, poses some limitations that may originate either from the relative motion between

the markers and the skin or by innapropriate marker placement. Nevertheless, motion analysis is a widely accepted and reliable method for the analysis of segment and joint kinematics (Chambers and Sutherland, 2002; Gage, 1993). The reliability of the methodology, increases, when the markers are placed by the same investigator, when the task does not involve movements at high speed and when there is no overlap or coverage of the reflective markers during task execution (Waite et al., 2005). In this research the above requirements were all met. 5. Conclusion This research was an attempt to explore the differences and compensatory mechanisms that patients with moderate OA develop when they rise from a chair. The results showed that patients with moderate OA rise from the chair using greater muscle co-contraction of the knee muscles and earlier and greater activation of the hamstrings which results in reduced hip and knee range of motion. Nevertheless, they are able to perform the movement at the same duration compared to healthy subjects. The combination of greater muscle co-contraction and co-activation (premature activation of the antagonist muscle), is leading to substantial deactivation of the knee extensor muscles,

Fig. 5. Co-contraction index for left (L) and right (R) leg between women with knee osteoarthritis (OA) and control (CON) group. *Significantly different compared with osteoarthritis (OA) group p b .05. †Significantly different compared with OA based on post-hoc analysis p b .05.

Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025

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G. Bouchouras et al. / Clinical Biomechanics xxx (2015) xxx–xxx

Table 4 Vertical ground reaction forces (VGRF) amplitude (% body weight) for left (L) and right (R) leg between women with knee osteoarthritis (OA) and control (CON) group. Means and standard deviations. Movement speed Normal

VGRF max R VGRF max L

Fast

Slow

OΑ

CON

OA

CON

OA

CON

55.31 (5.66) 54.70 (5.82)

47.43 (8.61) 52.49 (10.74)

55.79 (8.18) 55.70 (8.79)

55.16 (9.61) 56.35 (9.87)

50.87 (12.90) 49.42 (9.80)

53.54 (6.32) 52.41 (5.15)

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Please cite this article as: Bouchouras, G., et al., Kinematics and knee muscle activation during sit-to-stand movement in women with knee osteoarthritis, Clin. Biomech. (2015), http://dx.doi.org/10.1016/j.clinbiomech.2015.03.025