Effects of a six week lower limb stretching programme on range of motion, peak passive torque and stiffness in people with and without osteoarthritis of the knee.
Abstract: The purpose of this study was to compare the effects of a six week stretching programme on knee extension range of motion (ROM), passive resistive torque and stiffness in older adults with and without osteoarthritis (OA) of the knee. A randomized controlled trial design was utilised. Twenty two females and seventeen males aged between 60 and 78 years (mean 68.7, SD: 4.8) participated. Twenty participants of the 39 participants had OA of the knee joint. Participants were randomly assigned to stretch and control groups. The intervention used was three 60 second stretches to all major muscles in the lower limb, five days per week for six weeks. Using a Kincom dynamometer, knee extension ROM, peak passive torque and stiffness in the final 10% of knee extension ROM were measured.

A significant (p<0.05) increase in knee extension ROM, peak passive torque and stiffness was observed in the stretch group following the six week intervention period. No changes were observed in the control group. There was no significant difference in these variables across OA and non OA groups. For knee extension ROM, the mean (95% CI) change was 7.7 degrees (2.6 to 12.7) in the stretching group and 1.8 degrees (-5.8 to 2.1) degrees in the control group. For peak passive torque, the mean change (95% CI) was 7.1 Nm (2.9 to 11.3) in the stretching group and 1.0 Nm (-6.0 to 4.1) for the control group. For stiffness in the final 10% of knee extension range of motion, the mean change (95% CI) was 0.22 Nm/deg (0.06 to 0.35) in the stretching group and 0.06 Nm/deg (-0.2 to -0.1) in the control group. These results indicate that older adults with and without arthritis of the knee are able to demonstrate sustained improvements in joint range of motion with stretching interventions. This is important as the study demonstrated that simple stretching exercises are effective as part of the long term management of knee osteoarthritis and as way of improving range of motion in older adult populations.

Key Words: Range of Motion; Knee Extension; Flexibility; Older adult; Arthritis
Article Type: Clinical report
Subject: Osteoarthritis (Care and treatment)
Osteoarthritis (Physiological aspects)
Stretching exercises (Usage)
Stretching exercises (Physiological aspects)
Knee joint (Physiological aspects)
Knee (Physiological aspects)
Joints (Range of motion)
Joints (Physiological aspects)
Authors: Reid, Duncan A.
McNair, Peter J.
Pub Date: 03/01/2011
Publication: Name: New Zealand Journal of Physiotherapy Publisher: New Zealand Society of Physiotherapists Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2011 New Zealand Society of Physiotherapists ISSN: 0303-7193
Issue: Date: March, 2011 Source Volume: 39 Source Issue: 1
Accession Number: 263880334
Full Text: INTRODUCTION

Connective tissue is known to lose extensibility as part of the ageing process (Maharam, Bauman, Kalman, Skolnik, & Perle, 1999; Mazzeo et al., 1998). This change is thought to be related to adaptations in the collagen architecture of tissues. For instance, ageing causes an increase in the crystallinity of the collagen fibres and increases their diameter, leading to less extensibility of muscles, ligaments and tendons (Maharam et al., 1999; Mazzeo et al., 1998). As a result of such changes, reductions in joint range of motion have been demonstrated in elderly participants and particularly those with a history of falling (Gajdosik, vander Linden, & Williams, 1999b; Kerrigan, Lee, Collins, Riley, & Lipsitz, 2001; Kerrigan, Xenopoulos, Sullivan, Lelas, & O'Reilly, 2003; Menz, Morris, & Lord, 2005). Another factor that adds to a reduction in joint range of motion commonly seen in older adults is degenerative joint disease. Osteoarthritis (OA) of the knee, is a common condition affecting a large proportion of the community (Thomson et al., 2005). It is a condition characterized by joint pain and swelling causing loss of strength, range of motion and function (Dieppe, 1999; Fitzgerald, Childs, Ridge, & Irrgang, 2002; Messier, Loeser, Hoover, Semble, & Wise, 1992). In people with knee OA, the joint loses flexion and extension range of motion. As knee extension range of motion is a common movement loss with OA, the hamstring muscles in particular may be affected by being maintained in a shortened position over time, specifically the extensibility and stiffness of the tissue may alter over time. Gajdosik, VanderLinden and Williams (1999a) have demonstrated that range of motion of the ankle joint and elasticity of the calf muscles reduces with age when compared to younger participants, and that these characteristics are most evident closer to the terminal range of the joint motion. The combination of the ageing process and the arthritic process affecting the knee joint in participants with OA may have an even greater impact. These changes have not been explored in the OA population.

One way of improving range of motion in both the short and long term is to undertake stretching exercises. While periodic or long term stretching programmes have been investigated in older populations (Feland, Myrer, Schulthies, Fellingham, & Meason, 2001; Gajdosik, Vander Linden, McNair, Williams, & Riggin, 2005; Girouard & Hurley, 1995; Kerrigan et al., 2003; Raab, Agre, McAdam, & Smith, 1988), the majority of these studies have used range of motion as the primary variable of interest following stretching, and few have measured changes in range of motion together with changes in peak passive torque and stiffness. Such measures provide greater insight into the structural changes that may be taking place in muscle tissue as a consequence of a stretching intervention. One study by Gajdosik et al (2005) investigated the effects of an eight week periodic stretching programme on the calf muscles of 19 elderly females (mean age 74.2 years). The results of the study demonstrated that peak passive torque and maximal passive doriflexion angles significantly increased. Only one study to date has investigated the immediate affects of a hamstring stretching intervention in older adults with and without OA of the knee (Reid & McNair, 2010). This study found short term improvements in knee extension ROM in both those with and without knee OA. The effect of longer term stretching interventions in those with pathological conditions such as OA has not received the same attention as the non pathological older populations. Therefore, the purpose of this study was to investigate the effects of a six week stretching programme on range of motion, passive resistive torque and stiffness in the hamstring muscles in participants with OA of the knee and compare these findings with participants of a similar age without knee OA. The hypothesis to be tested was that the stretching intervention will improve knee extension ROM, peak torque and stiffness in those with and without knee OA. The null hypothesis was that there would be no difference between the groups for any of the measured variables.

METHODS

Participants

Ethical approval from the Auckland University of Technology (AUT) Ethics Committee was granted for all procedures and the participants signed an informed consent document. Based on Gajdosik et al (2005), a 5[degrees] change in knee extension range of motion was considered clinically significant, therefore for 80% power, [alpha] = 0.05, a sample size of 10 in each group was required to detect a difference of 5.5[degrees].

In response to a local newspaper advertisement, 100 participants from the local community applied to participate in the study. With respect to these selection criteria, participants with osteoarthritis (OA) of the knee joint had to meet the American College of Rheumatology criteria (Altman, 1991) and/ or have X-ray findings that were at least grade 2 on the Kellgren Lawrence criteria (1963). Where participants had X-rays, these and the radiological reports were viewed to ensure this criterion was met. These participants had to be free of any other lower limb pathology and were not eligible for the study if they were currently participating in physical therapy treatments for the OA knee condition or had any other condition that would affect their ability to exercise. With respect to the control group, the participants were required to have no lower limb orthopaedic conditions or injuries, neurological conditions or significant cardiovascular conditions, which would prevent them from undertaking the testing. All participants who met the inclusion criteria signed written consent forms before participating in the study. To gain an appreciation of their functional capacity and level of disability, the OA knee participants completed the visual analogue version of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) (Bellamy, Buchanan, Goldsmith, Campbell, & Stitt, 1988), and the activities of daily living section of the Lower Limb Task Questionnaire (LLTQ) (McNair et al., 2007) (See Table 1).

Forty three participants met the inclusion criteria. All participants were randomly allocated to one of four groups via a sealed envelope. The process of randomisation was undertaken by two allied staff within the University who were unaware of the study and not aware of the group allocation indicated in a sealed envelope. The four groups were: a stretching group of participants with knee OA (N=14), a group of participants with knee OA who were controls (N=10), a group of non knee OA participants who stretched (N=8) and a group of non knee OA participants who acted as controls (N=11). A number of levels of blinding were included in the study. The principal investigator (DR) was blinded to the allocation of the participants to the four groups and took no part in the assessment of the participants or the delivery of the interventions. The two research assistants, who undertook the Kincom[R] assessments, the WOMAC, and LLTQ assessments, were blinded to the group allocation. The two research assistants, who supervised the stretching intervention, were also blinded to the assessment results.

Independent t tests indicated that there was no significant difference between the group for age, height, body mass index, WOMAC and LLTQ scores (p>0.05) at baseline. Data collection was performed at the Health and Rehabilitation Research Institute at AUT University.

Knee extension range of motion

A passive knee extension test using the Kincom dynamometer (Kinetic Communicator, II 500H, Chattex Corp., Chattanooga, TN, USA) was utilised to measure knee extension ROM, passive resistive torque and stiffness. These methods were similar to that used by other investigators (Magnusson et al., 1995; Magnusson, Simonsen, Aagaard, Sorenson, & Kjaer, 1996; Reid & McNair, 2004, 2010). Participants were seated in the Kincom[R] and in accordance with the manufacturer's instructions, their limb weight was collected with the participant's knee in 60 degrees flexion, and subsequent torque measures were corrected. A firm lumbar roll was placed in the low lumbar spine (L2-L4 level) to maintain the lumbar lordosis and reduce the likelihood of the pelvis rotating posteriorly during the stretch procedure. The thigh to be tested was placed on a specially constructed pad that created an angle of 25 degrees to the horizontal. The height of the pad was such that during the stretch procedure the lower leg was unable to reach full knee joint extension. The thigh was secured with a Velcro strap onto the pad. The participant was also secured with a Velcro strap across the chest and a seat belt over the anterior aspect of the pelvis. The knee joint was positioned with the approximate axis of rotation in line with the axle of the lever arm of the Kincom[R]. Once participants were ready, the limb to be tested was moved to the starting position at 80 degrees of knee flexion. A blind-fold was placed over the participants' eyes and they were asked to relax the muscles about the knee joint throughout the motion and to concentrate on the sensation of the stretch. In participants with knee OA the affected leg was tested. In those participants without knee OA, the right leg was tested. Surface electromyographic (EMG) activity from the rectus femoris and the lateral hamstring muscles was monitored to ensure that participants complied with this request. EMG preparation involved shaving and cleaning the skin and electrode placement was in accordance with SENIAM (surface EMG for a non-invasive assessment of muscles) guidelines (Hermens, Freriks, Disselhorst-Klug, & Rau, 2000). The root mean square (RMS) of muscle activity during the joint motion was normalised to that recorded during a maximum voluntary isometric contraction performed in 60[degrees] knee flexion at the completion of the protocol (McNair and Stanley, 2001). If a participant's EMG data were greater than one percent of a maximum voluntary contraction, then that participant's data were discarded. The Kincom[R] dynamometer extended the knee passively at 10 degrees per second. The EMG data were recorded simultaneously with signals from the Kincom[R]'s load cell and potentiometer at a sampling frequency of 500 Hz, and relayed to a computerised data acquisition system for subsequent processing. Participants used an emergency stop switch to halt knee extension at the point when they perceived the maximum tolerable stretch on the hamstring muscles. This terminal position was designated as the point of maximal passive knee extension. Following familiarization with the procedure two trials were undertaken at baseline, two further trials were undertaken following the stretching intervention. The mean of the two trials was used for data analyses. The reliability of these procedures has been previously determined in other studies using a similar methodology (Intraclass Coefficient: 0.97, with a lower confidence interval of .93) (Reid & McNair, 2004).

Data Reduction

The following dependent variables were of interest: peak torque, maximal knee extension range of motion, range of motion at 50% of baseline peak torque, and stiffness in the final 10% of the knee extension ROM. Peak torque and range of motion were analysed in the following ways (See Figure 1). At point A, the peak torque and maximal knee extension ROM pre intervention were compared with the same torque value at point B post intervention. At Point C, 50% of the baseline peak torque level and knee extension ROM measurements pre intervention were compared with point D post intervention. At Point E, the post intervention peak torque and maximum range of motion post intervention were compared to point A pre intervention. Stiffness was calculated in the final 10% of the knee extension range of motion at baseline and compared to post intervention measures. The measurement of the final 10% was calculated directly from the graph data. Knee extension range of motion was designated as 0 degrees at the start position (80 degrees knee flexion while seated in the Kincom[R]).

INTERVENTIONS

Participants in the stretching group were instructed to stretch all the major muscle groups in the lower limb: hip flexors, quadriceps, hamstrings, and upper and lower calf muscles. The stretches were used to provide a balanced stretching programme as per other studies investigating OA of the knee joint (Borjesson, Robertson, Weidenhielm, Mattson, & Olsson, 1996; Deyle et al., 2005; Deyle et al., 2000; Fransen, Crosbie, & Edmonds, 2001; Law, 2001; Peloquin, Bravo, Gauthier, & Billiard, 1999; Rogind et al., 1998). The stretches were taken to the point where the participant perceived a stretching sensation in the target muscle group. The stretch was held for 60 seconds and repeated three times on each muscle group and on each leg. The stretches were performed once a day for a minimum of five days of the week for a period of six weeks. The participants in the stretch groups were supplied with written information with relevant pictures to ensure compliance. On two days of the week, participants attended a supervised stretching session at the University. Preceding their stretching sessions, participants undertook a warm-up routine consisting of light aerobic activity such as walking on a treadmill or cycling on a stationary bicycle for three minutes. A research assistant modified the stretches as required, to ensure that all participants understood how to do the stretches and ensure compliance with the stretching programme. The remaining three stretching sessions were undertaken independently at the participants' homes. The participants kept a diary of the number and frequency of these stretching sessions and an attendance record was kept for the sessions at the AUT University gymnasium. Following the completion of the stretching intervention, participants in the stretching groups discontinued the stretching programme and were advised to return to their normal daily activities. Participants in the control groups did not stretch and were instructed to maintain normal activities of daily living throughout the intervention period. It is important to note that while a balanced lower limb stretching programme was instigated, the methodology used above only allowed for testing of the hamstring muscle group on the Kincom.[R]

[FIGURE 1 OMITTED]

Statistical Analysis

Descriptive statistics were analysed to determine the appropriateness of utilising parametric analyses. A three factor (time x group x condition) ANOVA was utilised. The three factors were time (pre and post intervention), which was the repeated measure, and group (experimental and control) and condition (OA and non OA). Pair-wise comparisons using the Bonferonni test were undertaken to examine specific differences across group and time. The statistical analysis was undertaken using Statistical Package for Social Sciences Version 14.0 (Chicago, Illinois). The alpha level was 0.05.

RESULTS

Participants

While forty three participants were eligible for the study, following the baseline measurements of age, height, mass, WOMAC and LLTQ data, one participant indicated that he was suffering an acute episode of low back pain. Therefore this participant was not eligible to continue through to the physical data collection and subsequently withdrew from the study. Three participants had high BMI's (range 32-34) and it was difficult to secure their legs to the Kincom[R]. As a consequence of this issue, their terminal range of motion may not have been limited by the hamstring muscles and they were able to move through an unusually large range of motion compared the other participants. Following analysis of the baseline range of motion, peak torque and stiffness data, these participants in the OA control group had values that were deemed as outliers (Grubbs test) so their data were removed from further analysis. Therefore data from thirty nine participants were analysed (see Table 1 demographic data). There were twenty two females and seventeen males aged between 60 and 78 years (mean 68.7, SD: 4.8). There were twenty participants with OA of the knee joint and nineteen participants without OA of the knee joint. All participants in the control groups and the intervention groups completed the programme. An analysis of the participants' diaries indicated moderate compliance with attendance at the supervised stretching classes (58%) and high levels of compliance with the home stretching programme (98%) over the course of the intervention.

Changes in range of motion, torque and stiffness

Across all dependent variables there was no significant interaction with condition (OA and non OA) (p>0.05). Therefore the condition data were combined to form a stretch and control group that were compared over time.

Knee extension range of motion

The torque angle curve for a typical participant pre and post intervention is displayed in Figure 2. It illustrates the key findings and shows that the participant moved further into the range following the stretching intervention, the curve moved upward to the left and the steepness of the curve also increased in the final 10% of knee extension ROM.

With respect to peak knee extension range of motion, there was a significant main effect for time (p<0.05). There was also a significant interaction for group and time (p<0.05). Figure 3 displays the mean peak knee extension range of movement for the stretch group and the control group pre intervention and post intervention. The zero start position for the test movement was 80 degrees of knee flexion. Participants in the stretch group increased by 11% having a mean of 69.5 (SD: 15.4) degrees knee extension pre intervention that increased significantly to 77.2 (SD: 13.7) degrees post intervention (p<0.05). The mean difference was 7.7 degrees (95% CI 2.6 to 12.7). Participants in the control group were a mean 71.1 (SD: 10.3) degrees pre intervention and 69.3 (SD: 11.1) degrees post intervention. The mean difference was 1.8 degrees (95% CI -5.8 to 2.1).

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

With respect to the knee extension angle at 50% of the maximum torque level, there was a significant main effect for time (p<0.05). There was no interaction effect between groups across time (p >0.05). The mean knee extension range of movement recorded at 50% of the peak torque level for the stretch group pre intervention was 55.9 (SD: 15.0) degrees and this decreased to 50.8 (SD 12.3) degrees post intervention. The mean difference was 5.1 degrees (95% CI 0.4 to 9.7). In the control group knee extension range of movement recorded at 50% of the peak torque level pre intervention was 60.2 (SD: 11.4) degrees and this decreased to 55.8 (SD 10.6) degrees post intervention. The mean difference was 4.3 degrees (95% CI -0.2 to 8.9).

In regard to the knee extension range of movement recorded at maximum peak torque level pre intervention (points A-B in Figure 1), there was a significant main effect for time (p<0.05). There was no interaction effect for group and time (p>0.05). The stretch group had 69.5 (SD: 15.4) degrees knee extension range of motion pre intervention and this decreased to 63.7 (SD 12.9) degrees at the same torque level post intervention. The mean difference was 5.8 degrees (95% CI 2.4 to 9.1). The mean maximal knee extension range of movement recorded at maximum peak torque level for the control group pre intervention was 71.0 (SD: 10.3) degrees and this decreased to 69.3 (SD 11.1) degrees at the same torque level post intervention. The mean difference was 2.1 degrees (95% CI -2.2 to 5.7).

Peak passive torque measurements

With respect to peak passive torque, there was a significant main effect for time (p<0.05) and a significant interaction (p<0.05) for time and group (see Figure 4). Participants in the stretch groups generated a mean peak torque of 14.5 (SD: 8.4) Nm pre intervention and this increased significantly to 21.6 (SD: 12.2) Nm post intervention (p<0.05). The mean difference was 7.1 Nm (95% CI 2.9 to 11.3). This corresponds to a 49.5% increase in peak torque. The participants in the control group generated a mean peak torque of 17.2 (SD: 6.3) Nm pre intervention, a mean of 16.2 (SD: 7.9) Nm following post intervention. The mean difference was 1.0 Nm (95% CI -6.0 to 4.1).

[FIGURE 4 OMITTED]

Stiffness

With respect to stiffness in the final 10 % of knee extension ROM, there was a significant main effect for time (p<0.05) and a significant interaction for time and group (p<0.05) (see Figure 5). In the stretch groups mean stiffness increased 35.5% from 0.63 (SD: 0.3) Nm/deg pre intervention to 0.84 (SD: 0.3) Nm/deg post intervention (p<0.05). The mean difference was 0.22 Nm/deg (95% CI 0.06 to 0.35). The control groups mean stiffness was 0.72 (SD: 0.2) Nm/deg pre intervention, and 0.66 (SD: 0.3) Nm/deg post intervention. The mean difference was 0.06 Nm/deg (95% CI -0.2 to 0.1).

DISCUSSION

The purpose of this study was to examine the effects of a six week periodic lower limb stretching intervention in elderly participants with OA of the knee and compare these with a group of participants of a similar age without OA of the knee. Only one other study has examined the variables of torque and stiffness in association with range of motion in individuals with OA of the knee joint but this was a following short term intervention (Reid and McNair, 2010). The main findings of the study have demonstrated that elderly participants with and without OA of the knee joint did not respond differently across any of the measured variables. However, post intervention, those participants allocated to the stretching groups were significantly different from the control groups with respect to the primary variables of knee extension range of motion, peak passive torque and stiffness. With respect to knee extension ROM, the stretch and control groups had a similar range at baseline, but the stretching groups improved significantly more following the six week stretching intervention. For a total stretching duration (TSD) of 5400 seconds a 7.7 degree increase in range of motion was achieved. Raab et al (1988) reported an 11.4 degree increase in hip flexion with a TSD of 1500 seconds and Giroud and Hurley (1995) found a 10 degree increase in hip flexion with a TSD of 1800 seconds. Feland et al (2001) had participants stretch for a total of 7200 seconds and observed an increase in hip flexion of 14.4 degrees. These results indicate that the total stretching volume may not be indicative of potential gains in range of motion and that further work is required that focuses upon different prescriptions (sets and repetitions) as they may play a more influential role in the magnitude of adaptations.

[FIGURE 5 OMITTED]

The increase in knee extension range of motion in the stretching group was also accompanied by an increase in peak torque (49%) and stiffness (35%) in the final 10% of the range of motion. The example of a torque angle curve provided in Figure 2 would indicate a possible shift of the torque angle curve to the left. However, based on the analysis outlined in Figure 1, both the stretch and control groups had a reduction in range of motion at the 50% of peak passive torque measurement point (C-D on Figure 1) and the peak torque at baseline measurement point (A-B on Figure 1). This implies that in the initial section of the torque angle curve there was little difference in the curve behaviour between the stretch and control groups.

The results were consistent with studies examining younger participants and using similar variables (Chan, Hong, & Robinson, 2001; Gajdosik, 1991; Magnusson, Simonsen, Aagaard et al., 1996; Reid & McNair, 2004). Reid and McNair examined the effects of a six week hamstring stretching programme in young participants (mean age 15.8 yrs). The results demonstrated a 10 degree increase in knee extension range of motion in the stretching group. An examination of the force angle curve also demonstrated that the increase in range of motion was accompanied by an increase in peak passive torque and stiffness in the final 10% of the range, but the curve did not move to the left. Movement of the torque angle curve to the left has been demonstrated by Gajdosik at al (2005). Their study involved an eight week stretching programme to the calf muscles of sedentary elderly women with reduced ankle dorsiflexion. The results indicated that there was an increase in maximal dorsiflexion ROM and an associated increase in maximal torque and a shift of the torque angle curve to the left. As the participants in this study were more sedentary than the current study, it is possible that the muscle characteristics of this group may differ from more active participants. This premise would require further investigation.

Increases in peak passive torque and stiffness may reflect architectural changes to the stretched muscles. Stretching exercises undertaken in a terminal range of joint motion place considerable force on the muscle tendon unit. Such load could increase not only sarcomeres in series but also in parallel and thus induce muscle hypertrophy. In support of this concept, increases in muscle stiffness and cross sectional area have been observed following strengthening exercises (Chleboun, Howell, Conaster, & Giesey, 1997; Gajdosik et al., 1999a; Klinge et al., 1997) but may not have been considered as an adaptation to a long term stretching intervention.

Another possible explanation of the increases in peak torque and stiffness associated with the increase in range of motion is the concept of stretch tolerance (Folpp, Deall, Harvey, & Gwinn, 2006; Halbertsma, Mulder, Goeken, & Eisma, 1999; Magnusson, Simonsen, Aagaard et al., 1996; Weppler & Magnusson, 2010). Stretch tolerance is a term that describes the psycho-physiological response to stretching, that is, as the joint being stretched approaches the terminal range of motion, an increasing amount of discomfort is felt in the muscle tissue resisting that motion. Gajdosik et al (2004) commented that this phenomena is a subjective limitation of joint range and may not reflect the true mechanical end point of joint range of motion. Authors such as Halbertsma et al (1999) and Magnusson et al (1996) have suggested the increases in ROM observed following a stretching intervention are possible because the participant has adapted to pain and therefore is more tolerant of the stretching induced discomfort in the new range. Weppler and Magnusson (2010) have also commented that alterations in sensory input are a more likely explanation because examination of torque angle curves in current research has not consistently seen movement to the left following long term stretching programmes. Hence these changes may be more reflective of increased stretch tolerance in the new range rather than tissue adaptation. It has been suggested that pain modulation via the nociceptive nerve endings in both muscles and joints may be responsible for this effect (Magnusson, Simonsen, Per Aagaard et al., 1996; Weppler & Magnusson, 2010).

A key finding of the study was that people with OA of the knee had similar increases in joint range of motion when compared to non OA participants. This is encouraging as it indicates that having an arthritic joint is not a barrier to improving range of motion with a long term stretching programme. Possible reasons for this lack of difference may be related to the level of impairment in the OA knee group. An evaluation of the WOMAC and the LLTQ scores (See Table 1) indicates that the participants with OA knee were only moderately affected by the disease. Thus at this stage of the disease process, the soft tissues that resist changes in range of motion still appear to be adaptable. The Osteoarthritis Research Society International (OARSI) consensus statement on the management of osteoarthritis (Zhang et al., 2008) states that a key aim of exercise programmes should be to reduce the amount of joint deterioration over time. The document recommends that one way of achieving this is for individuals to undertake regular strengthening and range of motion exercises. As osteoarthritis is a long term condition, exercises that are simple to do and effective in the long term should be encouraged. An examination of the participants' diaries indicated they were compliant with the stretching programme and had no difficulties undertaking the stretching programme, nor did they have any associated increase in pain levels while exercising.

The clinical implications of a long term stretching intervention may be an improvement in step length during gait and agility. Gajdosik et al (2005) have demonstrated that elderly women with short calf muscles can improve agility in a walking task with an eight week stretching programme and Christiansen (2008) has shown improvements in stride length in elderly participants following an eight week stretching programme to the hip and ankle region. Such improvement may also be of benefit to those individuals with OA of the knee as they are known to have a reduced stride length as a consequence of the pain and discomfort in the knee joint (Al-Zahrani & Bakheit, 2002; Gok, Egin, & Yavuzer, 2002; Messier et al., 1992). Those elderly individuals at risk of falling can also benefit from utilising stretching exercises as part of a fall prevention programme (Lord, Ward, Williams, & Strudwick, 1995).

Limitations

One of the key limitations of this study is the sample size. The four individual groups ended up having quite small numbers and were somewhat uneven in their distribution despite attempts to achieve this through the randomisation process. This may have contributed to a potential type II error in the statistics and also insufficient power to detect a difference between the four groups. The small sample size may also have led to an inability to detect changes in functional measures such as the LLTQ and the WOMAC. The data will however be useful to help develop future studies with larger sample sizes.

Secondly there was no attempt to measure the passive stiffness of the knee joint per se. The hamstring muscles influence on total knee joint range of motion was the key focus of this study. Future studies could investigate the effects of this intervention on the passive range of knee joint motion either alone or combined with joint mobilisation.

CONCLUSION

This study has demonstrated that a group of elderly individuals with and without osteoarthritis of the knee joint can significantly improve knee extension range of motion using a stretching prescription over a six week time frame. The increase in the knee joint angle was accompanied by an increase in peak torque and stiffness towards the terminal range of knee extension range of motion. These changes may reflect adaptive changes in the muscle structure as well as improvements in stretch tolerance. Having an arthritic joint did not affect participants' ability to demonstrate improvements in range of motion in the knee joint. These findings indicate that there are benefits of periodic stretching in older adults and those living with osteoarthritis of the knee joint, and support the use of this intervention.

KEY POINTS

* OA is a common condition affecting the knee joint resulting in pain, loss of range of motion and function.

* Stretching exercises to the muscles around the knee may be of benefit to maintain or increase range of motion.

* A simple prescription of stretches 3 x 60 seconds, once per day, 5 days a week for six weeks to the hamstring muscles can achieve the goal of increasing knee joint range of motion in both those with OA of the knee and those without.

ADDRESS FOR CORRESPONDENCE

Duncan Reid, Health and Rehabilitation Research Institute, School of Rehabilitation and Occupation Studies, Auckland University of Technology, Private Bag 92006, Auckland, New Zealand. Phone 0064 (9) 917-9999 ext 7806, Fax 0064 (9) 917-9620, Email duncan.reid@aut.ac.nz

ACKNOWLEDGEMENTS

The New Zealand Society of Physiotherapists (NZSP) and the New Zealand Manipulative Physiotherapists Association (NZMPA) provided funding for this study.

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Duncan A Reid DHSc and Peter J McNair PhD

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Table 1: Participants' age, height, mass, body mass index, WOMAC and
LLTQ scores.

Group          Number   Age           Height          Mass
                        (yrs)         (cm)            (kgs)

OA stretch     13       69.0 (5.8)    166.9 (13.0)    81.9 (13.3)

OA control     7        67.4 (5.0)    168 (11.9)      82.3 (17.8)

Non OA         8        67.9 (4.0)    168.2 (9.2)     74.3 (19.3)
Stretch

Non OA         11       69.6 (4.3)    163.3 (5.7)     74.8 (9.9)
Control

Total          39       68.7 (4.8)    166.3 (10.2)    78.4 (14.6)

Group          BMI             WOMAC Total     LLTQ (40)
                               (2400)

OA stretch     29.4 (4.8)      686.6 (427)     30.9 (7.1)

OA control     28.7 (4.2)      819.6 (440)     28.4 (7.0)

Non OA         25.9 (4.9)      N/A             N/A
Stretch

Non OA         27.9 (3.5)      N/A             N/A
Control

Total          28.1 (4.4)      N/A             N/A

Key: WOMAC, Western Ontario and McMaster University Osteoarthritis
Index; LLTQ, Lower Limb Task Questionnaire; N/A, Not applicable.
Data are means and standard deviations.
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