CHAPTER 6. RISING TO STAND FROM A CHAIR

Transcription

1 CHAPTER 6. RISING TO STAND FROM A CHAIR Contents Introduction Methods Results Duration of rising to stand from a chair Base of support during rising Ground Reaction Forces Stability and symmetry of ground reaction forces Kinematics of the right ankle, knee and hip joints Kinetics of the right ankle, knee and hip joints Kinematics of the trunk and upper body segments Discussion Effect of pregnancy on the kinematics and kinetics of rising to stand Coronal and transverse plane kinematics and kinetics Symmetry of ground reaction forces Postural stability Upper body motion Stability of variables associated with retesting Conclusions 100

2 Introduction Rising to stand from a chair is an important everyday activity. The action requires that the body mass move forward and then up, while simultaneously maintaining balance and transferring from support provided by the chair and the feet to the feet only. It is a mechanically demanding task (Riley et al 1991) which may be affected by restrictions in trunk motion (Shepherd and Gentile 1994). As pregnancy progresses, the maximum forward flexion of the trunk is reduced (Gilleard et al 1999) and body mass is increased by adipose tissue and the gravid uterus (Jensen et al 1996). Therefore rising to stand from a chair may be expected to become more difficult to perform as pregnancy progresses and may result in altered kinematics and kinetics and decreased stability. Some aspects of rising to stand from a chair during pregnancy have been investigated including knee and hip joint kinetics (Ellis et al 1985, Jensen et al 1996a), time to rise and hip joint kinematics (Hirao and Kajiyama 1994). While our understanding of the effects of pregnancy on rising to stand from a chair has increased, further information is required about possible adaptations related to increased body mass and trunk dimensions as pregnancy progresses and in the early postbirth period. Investigation of adaptations related to pregnancy requires longitudinal testing involving several retests. Therefore knowledge of the natural variability between tests is also needed. Although many researchers have investigated the mechanics of rising to stand from a chair, few papers have reported the consistency of performance of individual variables. The aim of this study was to investigate the three-dimensional kinematics and kinetics of the lower limbs and upper body segment kinematics during rising to stand from a chair as pregnancy progressed and in the early postbirth period. Comparisons were also made with the typical range and natural variability from test to test established using nulliparous subjects. 101

3 Many studies,investigating rising to stand from a chair, have restricted the use of the upper limbs and used a predetermined foot position (Crosbie et al 1997, Jevsevar et al 1993, Kralj et al 1990, Krebs et al 1992, Pai and Rogers 1991b, Riley et al 1991, Rodosky et al 1989, Schenkman et al 1990). Therefore in order to assist interpretation of the motion in the maternal population a constrained rise to stand was investigated where the upper limb motion was restricted and the initial ankle angle was predetermined. The use of the upper limbs (Carr and Gentile 1994), and initial foot position (Khemlani et al 1999), however have been found to significantly affect both kinetic and kinematic variables and movement strategies. Also these factors are not typically restricted in the everyday activity of rising to stand from a chair. Carr (1992) also suggested that the arms should be free to move when investigating individuals who may have difficulty in generating sufficient muscle force to complete the motion. This may apply to subjects in late pregnancy because the body mass has increased. Therefore in order to ensure the practical relevance of the study a free rise to stand from a chair was also investigated where the subjects chose the initial foot position and use of the upper limbs was unrestricted. 102

4 Methods Detailed methods for anthropometric measures, equipment and procedures used for kinematic and kinetic data collection are presented in Chapter 3. Detailed subject descriptions are listed in Appendix 1. In summary, nine maternal subjects and twelve nulliparous control subjects were included in the study. Retroreflective markers were used to define bilateral lower limb and upper limb segments and the head, thoracic and pelvic segments. Three non colinear makers were placed on each lower limb, trunk and head segment to allow three dimension analysis and two markers were used to define the upper arm for sagittal plane kinematics. Additional markers were placed on the right and left ASIS, and medial and lateral knee and ankle joints in order to define the ankle, knee and hip joint centres. A quiet sitting reference trial was recorded to establish the spatial relationship between the segment markers and the joint centres. These additional markers were removed during rising to stand from a chair so that the movement was not hindered. The subjects were seated on a height adjustable stool, with each foot placed on a force plate and their ischial tuberosities were positioned over a seat switch. The subjects rose to stand watching a standing eye level target at their preferred speed. Two conditions of rising to stand, constrained and free, were used. For constrained rising the subjects held their arms crossed and against the chest and initially placed the feet such that the shanks were angled anteriorly at 80 to the horizontal. The crossed arms were held against the chest as the subject rose to stand. For free rising, initial foot position was chosen by the subjects and arms started resting by the side. Subjects were free to move the arms as they rose, however, foot position was maintained once movement commenced. Three trials of each rising to stand condition were performed. 103

5 For each movement trial, start of movement, seat-off and end of movement was determined in relation to specific events and checked by visual inspection of the data. Start of movement was defined as the time at which the horizontal velocity of the marker on the right greater tubercle was greater than or equal to 10 mms -1 (Khemlani et al 1999) and the right greater tubercle marker had not begun to move in a vertical direction. Seat off was determined as the time when the horizontal component of the ground reaction force under the right foot attained its largest value in the anterior direction (Kralj et al 1990). Where a clearly defined anterior ground reaction force peak was not seen for the right foot, the left foot data in combination with the seat switch data were used to determine seat off. Movement end was determined as when knee extension was maximal (Kralj et al 1990), and the vertical displacement of the right greater tubercle marker was maximal (Crosbie et al 1997). These events enabled the action of rising to stand to be divided into two phases: a pre extension phase (movement onset to seat-off) and an extension phase (seat-off to end). To enable comparison of timing of kinematic and kinetic variables each trial was time normalised with seat-off 0% and movement end 100%. Prior to seat-off is indicated by negative percentages of movement time (Doorenbosch et al 1994, Gross et al 1998). The base of support width during rising may have been increased as pregnancy progressed as seen in Chapter 5. Also, as rising to stand from a chair involves forward movement, it was possible that the size of the base of support was increased in the antero-posterior direction for increased stability by placing on foot forward and the other back. The mediolateral width and the antero-posterior depth were therefore calculated for each trial. The base of support width during rising was operationally defined as the mean difference between the y axis location of the Right lateral ankle marker and Left lateral ankle marker in the laboratory coordinate system. The base of support antero-posterior depth during 104

6 rising was defined as the mean difference between the x axis location of Right ankle marker and the Left ankle marker in the laboratory coordinate system. The feet were positioned such that one foot rested on each force plate and the chair was located immediately posterior to the force plates. Ground reaction forces were therefore measured under each foot. Although the subjects selected foot width, foot position was possibly constrained from 'natural' by placement on each force plate. It was possible that as pregnancy progressed the task became more difficult to perform and the medio-lateral and antero-posterior stability may have decreased as the subjects rose to stand. An unstable posture may include rapidly alternating movements of the body's centre of gravity which cause increased ground reaction force variability (Goldie et al 1989). The standard deviation of the horizontal ground reaction forces therefore may be used as an indicator of stability (Goldie et al 1989). The mean standard deviation of the GRFy and GRFx for each trial of rising to stand trial (stability index) was therefore calculated and the variation in the stability index was investigated as pregnancy progressed. Rising to stand from a chair occurs primarily in the sagittal plane, however, asymmetries occur between the left and right side (Hesse et al 1996). It was also possible that as pregnancy progressed the increased trunk mass and dimensions may result in increased motion asymmetry which may be reflected in the GRF. A symmetry index was calculated for maximum and minimum vertical GRF, peak anterior, posterior, medial and lateral GRF. In accordance with Durward and Rowe (1991) the calculations were Symmetry Index = R/(R+L) where R = right side value and L = left side value. A value of 0.5 indicates symmetry. 105

7 Data analysis was performed as described in Chapter 3. In summary, the consistency of performance of control data for each variable over the three test sessions was established using intra class correlations, ICC (2,1) (Domholdt 1993). The natural variability for each variable was investigated using the standard error of measurement between Control Session 1 and 3. Repeated measures ANOVA (Winer et al 1991) with planned orthogonal contrasts were used to investigate the existence of linear and quadratic trends which would show any systematic change within the control group over the three test sessions for each variable. Variables where there was a significant trend and the difference between the means was less than the natural variability were noted in the data tables. Due to technical difficulties, the left foot force plate data were not available for control subjects at Session 3. Therefore left lower limb kinetic data consistency and variability was assessed between Session 1 and Session 2 only and no trend analyses were performed on these data. Pregnancy is characterised by continuous changes over time, which may be expected to show systematic trends as the pregnancy progresses. A repeated measures ANOVA was used to investigate the existence of linear and quadratic trends which would show any systematic change within the maternal group over the four test sessions during pregnancy for each variable. For each variable, where an effect of pregnancy had occurred, the four test sessions were each compared graphically to the control group mean plus and minus twice the standard error and a two tailed student t-test assuming unequal variance was used to confirm any differences seen. The magnitude of the change by the maternal subjects was also compared with the natural variability associated with retesting and for changes less than the natural variability a note was made against the significant trend in the data tables. Two tailed student t-tests assuming unequal variance (Domholdt 1993) were used to compare the maternal postbirth (Session 5) variable results with the control Session

8 Results Duration of rising to stand from a chair The control subjects' descriptive data and the natural variability in movement duration associated with retesting for constrained and free rising are listed in Appendix 6, Table A6i. The consistency of performance as indicated by the ICC (2,1) was generally good for the duration of the extension phase and total movement duration although only fair for the duration of the pre-extension phase. The natural variability as indicated by the SEM was higher for the pre-extension phase than the extension phase and total movement duration. For the control group there were generally no significant trends over the three sessions for the pre-extension and extension phase duration or total movement duration (Appendix 6, Table A6i). The mean total movement duration over the three sessions was 1.8 s ± 0.26 and 1.9 s ± 0.31 for the free and constrained motion respectively. The pre-extension phase time as a percentage of total movement duration showed a significant trend (F linear = 5.16, p = 0.04) from 38.7 % ± 6.1 at Session 1 to 41.4 % ± 4.4 at Session 3. The difference between test session means, however, was less than the natural variability of ± 2.6 %. Maternal group The maternal subjects' descriptive data for the duration of the movement phases are listed in Appendix 6, Table A6ii. During constrained rising there were no significant trends seen in the duration for either the pre-extension or extension phase, or the whole movement duration as pregnancy progressed. During free rising the pre-extension phase showed a significant decreasing trend (41.2 % ± 3.9 at Session 1 to 38.3 % ± 4.0 at Session 4; F linear = 7.26, p = 0.03) while the extension phase duration showed a close to significant increasing trend (59.6%±3.8 at Session 1 to 61.9% ± 3.8 at Session 4; F linear =4.79, p=0.06). As shown in Figure 6.1, the duration of the free rise pre-extension phase was not 107

9 significantly different to the control mean at any test session. The whole movement duration showed a significant increasing trend (1.76 s ± 0.21 at Session 1 to 1.93 s ± 0.17 at Session 2; F quadratic = 18.76, p = 0.003). The time for whole movement duration remained similar at Session 2, 3 and 4. Therefore as the change was not consistent across pregnancy the trend was not thought to be a true indication of change related to pregnancy. Percentage of movement duration (%) Maternal session Maternals Control group mean ± 2 SE Figure 6.1. Free rise pre-extension phase duration as a proportion of total movement time for Maternal Session 1 to 4 and postbirth mean (2 SE) and the control group mean ± 2 SE. Postbirth Postbirth (Session 5) maternal and control Session 3 data are listed in Appendix 6, Table A6iii. There were no significant differences between the groups for the pre-extension or extension phase, or for the whole movement duration for either condition. Base of support during rising The base of support may be affected by the placement of the feet relative to each other and the dimensions may be altered to increase stability and ease of rising. The control subjects' descriptive data and the natural variability associated with retesting, for the medio-lateral 108

10 width and antero-posterior depth of the base of support are listed in Appendix 6, Table A6iv. The medio-lateral base of support width showed significant increasing linear (constrained; F linear = 10.58, p = 0.008: free; F linear = 16.12, p = 0.002) and quadratic (constrained; F quadratic = 16.26, p = 0.002) trends. There were no significant trends for antero-posterior base of support depth. The consistency of performance of both the base of support width and depth was generally poor and the natural variability was relatively large. Maternal group The maternal subjects' descriptive data for the base of support are listed in Appendix 6, Table A6v. The medio-lateral width showed a significant increasing trend (constrained; F linear = 11.39, p = 0.01: free; F linear = 8.92, p = 0.02) as pregnancy progressed. The mediolateral base of support width was significantly larger than the control mean at Sessions 3 and 4 for free (Figure 6.2) and Session 4 for constrained (Figure 6.3) rising. Medio-lateral width (cm) * p=.001 * p= Maternal session Maternals Control group mean ± 2 SE Figure 6.2. Constrained rise base of support medio-lateral width for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2SE. 109

11 Medio-lateral width (cm) * p= Maternal session Maternals Control group mean ± 2 SE Figure 6.3. Free rise base of support medio-lateral width for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2SE. The base of support antero-posterior depth showed a significant trend (F linear = 5.46, p = 0.05) from 0.5 cm ± 0.9 at Session 1 to - 0.5cm ± 0.7 at Session 4 suggesting an increased preference for left foot forward as pregnancy progressed. The magnitude of the maternal subjects antero-posterior depth, however was less than 1cm and the natural variability for repeated testing ranged from ± 0.9 cm for constrained rise to stand, to ± 2.1 cm for free rising. Therefore although the linear trend was significant, the magnitude of the change was not thought have a practical relevance. Postbirth Postbirth (Session 5) maternal and control Session 3 base of support width and depth data during constrained and free rising to stand are listed in Appendix 6, Table A6vi. There was no significant difference between the groups for the neither width nor depth of the base of support for either chair rise conditions. 110

12 Ground reaction forces Ground reaction forces (GRF) were defined as those forces applied by the person to the forceplate with respect to the three axes of the force plate coordinate system. The vertical GRF showed a decrease (minimum vertical GRF) during the pre-extension phase then increased (maximum vertical GRF) during the extension phase (Figure 6.4). Vertical GRF (N) Figure 6.4. Typical pattern for vertical GRF Control subject 1, Trial 3, Session 2, Free Condition. Negative % of movement indicates prior to seat-off % of Movement Antero-posterior GRF first showed a small posterior peak (peak posterior GRF) during the pre-extension phase then a larger anterior peak (peak anterior GRF) (Figure 6.5) Antero-posterior GRF (N) Right Left % of Movement Figure 6.5. Typical pattern for right and left side antero-posterior GRF. Control subject 1, Trial 3, Session 2, Free Condition. 0% denotes seat-off. Positive values indicate anteriorly directed force on the forceplate. 111

13 Medio-lateral GRF showed a medially directed force at seat-off (peak medial GRF) followed by steadily increasing lateral directed force (peak lateral GRF) during rising to stand (Figure 6.6). Medio-lateral GRF (N) Right Left % of Movement Figure 6.6. Typical patterns for right and left side mediolateral GRF. Control subject 1, Trial 3, Session 2, Free Condition. 0% denotes seat-off. Positive values indicate medially directed force on the forceplate. Control group The control subjects' GRF data are listed in Appendix 6, Tables A6vii and A6viii in absolute (N) and relative (%BW) units. Due to technical difficulties there was no left Session 3 forceplate data. For the control group there were generally no significant trends over the three sessions in the maximum and minimum vertical GRF and the peak anterior and posterior GRFs greater than the natural variability. Some significant quadratic trends were found where the difference between the means was greater than natural variability for the peak vertical, anterior and posterior GRFs, however, they were associated with poor consistency of performance as indicated by the ICC (2,1) results. The consistency of performance was better and natural variability was less for the maximum in comparison to 112

14 the minimum vertical GRFs. The consistency of performance of the peak anterior and posterior GRFs was fair to poor and the natural variability was a relatively large proportion of the mean. The consistency of the data with retesting did not change whether the data were treated in absolute or relative units. For the control group peak medial and lateral GRFs, there were generally no significant linear trends over the three sessions where the difference between the means was greater than the natural variability between testing sessions (Appendix 6, Table A6vii and A6viii). The consistency of the peak medial and lateral GRFs was fair to good for both constrained and free conditions, however the natural variability from test to test was a relatively large proportion of the mean values. The consistency of performance and the natural variability were similar for medial and lateral GRF data in both absolute and relative units. In general the lateral GRF, was larger than the medial GRF for both sides (Appendix 6, Table A6vii and A6viii). Maternal group The maternal subjects' descriptive GRF data are listed in Appendix 6, Table A6ix. Significant trends were seen as pregnancy progressed for the magnitude of the maximum vertical GRF, peak lateral, posterior and anterior GRF. There were no significant trends for minimum vertical GRF and the medial GRF. The left and right maximum vertical and peak lateral GRF showed a significant increasing trend in both constrained and free rise to stand (Table 6.1). The peak anterior GRFs generally increased, with significant increasing trends in anterior GRFs for the right side during constrained rising and the left sides during free rising (Table 6.1) 113

15 Table 6.1. Maternal maximum vertical, peak lateral and anterior GRF mean (SD) at Session 1 and Session 4 and associated linear trends and natural variability. GRF Side Session 1 (N) Session 4 (N) F linear p SEM (N) Max. vertical Constrained Left (76.5) (107.5) * ±19.7 Right (50.7) (60.8) * ±22.4 Free Left (74.7) (121.6) * ±29.7 Right (43.9) (53.5) * ±24.2 Peak lateral Constrained Left 21.2 (14.6) 37.6 (11.4) * ±5.6 Right 29.1 (8.0) 39.5 (10.8) * ±4.2 Free Left 20.2 (13.7) 39.1 (17.5) * ±1.8 Right 28.5 (9.0) 42.2 (14.2) * ±4.8 Peak anterior Constrained Left 26.6 (10.7) 36.6 (17.7) ±2.5 Right 32.3 (10.7) 43.0 (17.7) * ±4.7 Free Left 24.6 (10.9) 36.7 (15.9) * ±4.2 Right 35.9 (14.5) 41.0 (18.7) ±3.8 * significant linear trend Although the maximum vertical GRF, peak lateral and anterior GRF showed significant trends and the increases from Session 1 to Session 4 were greater than the natural variability (Table 6.1), the magnitude of the maternal subjects' GRF was not significantly greater than the control group mean at any session. Examples of the lack of difference between the maternal group and the control group are shown for a constrained rise to stand for maximum vertical GRF (Figure 6.7), for peak lateral GRF (Figure 6.8) and for peak anterior GRF (Figure 6.9). 114

16 Maximum vertical GRF (N) Maternal session Maternals Control group mean ± 2 SE Figure 6.7. Constrained rise right maximum vertical GRF (N) for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. 50 Peak lateral GRF (N) Maternal session Maternals Control group mean ± 2 SE Figure 6.8. Constrained rise right peak lateral GRF (N) for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. 115

17 60 Peak anterior GRF (N) Maternal session Maternals Control group mean ± 2 SE Figure 6.9. Constrained rise right peak anterior GRF (N) for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. Left peak posterior GRF showed a significant decreasing trend (F linear = 6.82, p = 0.03) as pregnancy progressed during free rising. The maternal subject peak posterior GRF was significantly smaller than the control mean at Session 4 (Figure 6.10). Peak posterior GRF (N) Maternal session * p=.009 Maternals Control group mean ± 2 SE Figure Free rise left peak posterior GRF (N) for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. 116

18 The maternal subjects' descriptive data for the vertical, antero-posterior and medio-lateral relative GRF (relgrf) are listed in Appendix 6, Table A6x. There were generally no significant trends for the maximum or minimum vertical relgrf as pregnancy progressed for either constrained or free conditions. For a free rise to stand, right maximum vertical relgrf showed a significant decreasing trend (F linear = 6.37, p = 0.04) from 61.8 % ± 6.8 at Session 1 to 58.2% ± 8.7 at Session 4. The difference between the means, however, was very small and less than the natural variability (± 4.0 %). Constrained rising right anterior relgrf showed a significant increasing trend (F linear = 7.37, p = 0.03) from 5.3 %BW ± 1.4 at Session 1 to 5.7 %BW ± 1.9 at Session 4. No significant trends were seen for the left peak anterior relgrf, or peak left and right posterior relgrf for constrained rising. Free rising left antero-posterior relgrf showed a significant increasing trend (F quadratic = 5.65, p = 0.04) in the anterior direction from 3.8 %BW ± 1.5 at Session 1, to 5.0 %BW ± 2.3 at Session 4. A significant decreasing trend (F linear = 10.71, p = 0.01) was seen in the posterior direction from 2.2 %BW ± 1.9 at Session 1 to 0.8 %BW ± 0.8 at Session 4. These trends in antero-posterior relgrf were not seen on the right side. The peak medial relgrf generally did not show any significant trends as pregnancy progressed. For left peak medial relgrf during a constrained rise, however, there was a significant decreasing trend (F linear = 5.75, p = 0.04). The differences between the means were very small, reducing from 1.5 %BW ± 1.2 at Session 1 to 0.1 %BW ± 1.5 at Session 4 and were within the variability associated with retesting (± 1.2). Free rising right lateral relgrf to stand showed a significant increasing trend (F linear = 6.40, p = 0.04) from 4.4 %BW ± 0.9 at Session 1 to 5.6 %BW ± 1.7 at Session 4. The difference between the means of Session 1 and Session 4 were greater than the retesting natural 117

19 variability (± 0.8 %BW). Figure 6.11 shows, however, that the maternal right lateral relgrf was not significantly different from the control group at any test session. A similar increasing mean was seen for the left side from 3.1%BW ± 1.6 at Session to 5.2 %BW ± 2.4 at Session 4, however the trend was not significant (F linear = 4.82, p =0.059). No significant trends were seen for constrained rising peak lateral relgrf. Peak lateral GRF (%BW) Maternal session Maternals Control group mean ± 2 SE Figure Free rise right peak lateral GRF (%BW) for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. Postbirth Postbirth (Session 5) maternal and control Session 3 vertical maxima and minima, and peak anterior, posterior, medial and lateral GRF data are listed in Appendix 6, Table A6xi. There are no comparisons between groups for the left side, as control Session 3 data were not available due to technical difficulties. There was generally no significant difference between the groups for the right peak GRFs during either rise conditions. Postbirth right minimum vertical GRF, however, was significantly less (p=0.02) than the control group. When the GRF data were normalised to body weight, the postbirth maximum and 118

20 minimum vertical GRF for both conditions were also significantly less (p<0.05) than the control group. The postbirth vertical GRF values, however, were similar to the values during pregnancy with no significant difference over the five test sessions (Table 6.2). There was no significant difference between the postbirth group and the controls for anterior, posterior, medial and lateral GRF normalised to body weight. Table 6.2. Repeated measures ANOVA for Maternal data Session 1 to Session 5 for maximum and minimum vertical GRF. Condition Variable F p Constrained minimum vertical GRF (N) maximum vertical GRF (%BW) minimum vertical GRF (%BW) Free maximum vertical GRF (%BW) minimum vertical GRF (%BW) Constrained timing maximum vertical GRF (%) Timing of maximum and minimum vertical GRFs The control subjects' timing of the maximum and minimum vertical GRFs are listed in Appendix 6, Table A6xii. There were no significant trends over the three test sessions. The consistency of performance was generally fair to poor. The maternal subjects' showed during constrained rise to stand there was a significant trend for the timing of the right minimum vertical GRF (F linear = 5.34, p =0.049) (Appendix 6, Table A6xiii). The mean time occurred later and therefore closer to seat-off as pregnancy progressed with % ± 9.2 at Session 1 and % ± 7.7 at Session 4. A similar result was seen for the left side, however the trend was not significant (F linear = 4.06, p =0.08). No effect of pregnancy was seen for the timing of maximum vertical GRF. For free rise to stand, the timing of the minimum vertical GRF showed a significant trend (left F linear = 6.26, p =0.04; right F linear = 15.42, p =0.004), indicating that as pregnancy 119

21 progressed the minimum vertical GRF occurred later and closer to seat-off. The timing of right maximum vertical GRF showed a significant trend (F linear = 7.89, p =0.02) from 9.6 % ± 6.0 at Session 1 to 15.9 % ± 10.9 at Session 4, indicating that the peak tended to occur later. This later peak timing was not seen for the left side. Postbirth (Session 5) maternal and control Session 3 timing of maximum and minimum vertical GRF for constrained and free rising to stand are listed in Appendix 6, Table A6xiv. There was generally no significant difference between the groups for the timing of right vertical GRF peaks during both conditions. Although the timing of postbirth (Session 5) right maximum vertical GRF was significantly (p = 0.01) later than the control group there was no significant difference between maternal subjects' Session 1 to 5 (Table 6.2). Stability and symmetry of ground reaction forces It is possible that as pregnancy progresses, rising to stand may become more difficult to perform and the medio-lateral and antero-posterior stability may decrease. Therefore a stability index (the mean standard deviation of the GRFy and GRFx) for each trial was investigated as pregnancy progressed. The control subjects' descriptive data and the natural variability associated with retesting for the stability index of antero-posterior and medio-lateral GRFs are listed in Appendix 6, Table A6xv. There were no significant trends over the three sessions for the stability indices of either constrained or free rising. The consistency of performance ranged from poor to excellent and the natural variability associated with retesting was generally a high proportion of the mean (~15%). The maternal subjects' antero-posterior and mediolateral stability indices as pregnancy progressed are listed in Appendix 6, Table A6xvi. As there were no significant trends for 120

22 the stability indices, pregnancy was not thought to have significantly affected the mediolateral and antero-posterior stability when rising from a chair. Rising to stand from a chair moves the body forward and up, however, the motion may not be symmetrical (Hesse et al 1996). It is also possible that as pregnancy progresses the increased mass and dimensions may result in increased asymmetry. Therefore the asymmetry of the GRF was investigated using an asymmetry index where the right side data was expressed as a proportion of the sum of the right and left side data (Durward and Rowe 1991). A value of 0.5 indicates symmetry. Control Session 3 left GRF data was not available due to technical difficulties. Therefore the consistency associated with retesting was assessed between control group Sessions 1 and 2. The control subjects' descriptive data and the natural variability associated with retesting for the symmetry of maximum and minimum vertical GRF, antero-posterior GRF and medio-lateral GRF during rising to stand are listed in Appendix 6, Table A6xvii. Symmetry was not the same for each GRF. For example; there was minimal asymmetry for maximum vertical GRF, left side asymmetry for minimum vertical GRF and right side asymmetry for peak anterior GRF. Although the symmetry index was usually analogous from test to test, the consistency of performance from Session 1 to Session 2 was generally poor to fair. The maternal subjects' symmetry for maximum and minimum vertical GRF, anteroposterior GRF and medio-lateral GRF as pregnancy progressed are listed in Appendix 6, Table A6xviii. As with the control group, the side and degree of asymmetry varied between GRF, however the asymmetry for each GRF generally remained similar as pregnancy progressed. There was, however, a significant trend for the peak anterior GRF to become more right sided asymmetrical as pregnancy progressed for constrained (F linear = 7.59, p = 0.02) and free (F linear = 8.92, p = 0.02) rises. 121

23 Kinematics of the right ankle, knee and hip joints As there were no significant trends in the stability index data for either rise condition as pregnancy progressed, the increased mass and dimensions of pregnancy were not thought to have significantly affected the stability of rising to stand from a chair. In addition the asymmetry between the right and left side GRFs generally remained similar as pregnancy progressed with the exception of peak anterior GRF. The pattern of right and left side involvement in the motion therefore showed little change. Therefore all lower limb kinematic and moment variables were statistically analysed for right side data only. The typical sagittal plane displacements of the lower limb joints are shown in Figure The ankle joint first dorsiflexed then plantarflexed as the knee and hip joint first flexed then extended. Displacement ( ) Ankle Knee Hip % Movement Figure Typical patterns for ankle, knee and hip joint sagittal plane displacement. Subject 6, Right side, Trial 1, Session 2, Constrained Condition. 0% denotes seat-off. 122

24 Control group The control subjects' descriptive data and the natural variability associated with retesting for the sagittal plane kinematics of the right lower limb joints are listed in Appendix 6, Table A6xix. There were no significant trends over the three sessions in the initial angle, angle at seat-off, peak angle, range of motion and the peak angular velocities for the either the right ankle, knee or hip joints where the difference between the means was greater than the natural variability associated with retesting. The consistency of performance of the initial angle and angle at seat off for both conditions was poor to fair. The consistency of the peak angle was fair to good while for the range of motion, consistency ranged from good to excellent. The consistency of peak angular velocities was generally good to excellent for the ankle, knee and hip joints during both conditions although the hip joint peak flexion velocity was only fair. The natural variability between control Session 1 and Session 3, was a small proportion of the mean for all right lower limb angular displacement variables (less than 10% of the mean). The natural variability of the peak angular velocities was relatively large (approximately 10% of the mean or more). Maternal group The maternal subjects' descriptive data for the sagittal plane kinematic variables of the lower limb joints are listed in Appendix 6, Table A6xx. There were generally no significant trends seen in initial angle, angle at seat-off, peak angle nor in the range of motion at the right ankle and hip joints. A significant trend (F quadratic = 7.09, p = 0.03) was seen for ankle joint range of motion during the constrained rise, however, the difference between the test session means was very small (2.3 ) and within the natural variability associated with retesting. No significant trends were seen for the angular displacement variables of the knee joint during the free chair rise. A significant trend, however, was seen for the maternal 123

25 group knee initial angle, angle at seat-off and peak knee flexion during constrained chair rise where the difference between the means for Session 1 and Session 4 were greater than the natural variability (Table 6.3). The maternal group right knee was significantly more flexed that the control group at Session 2, 3 and 4 for initial angle, angle at seat-off and peak knee flexion (Figures ). No significant trends, however, were seen for total knee joint range of motion during a constrained rise (Table 6.3). Table 6.3. Maternal subjects' F linear, Session 1 and Session 4 means (SD) and the natural variability associated with retesting for knee joint initial angle, angle at seat-off, peak knee flexion and range of motion in the sagittal plane during a constrained rise. Variable F linear p Session 1 ( ) Session 4 ( ) SEM ( ) Initial angle * (7.1) (13.6) ±1.9 Angle at seat-off * (6.0) (8.2) ±1.8 Peak flexion * (6.6) (8.8) ±2.0 Range of motion (6.0) 86.0 (9.9) ±2.6 * significant at Initial Angle ( ) * p=.023 * p=.012 Maternal session * p=.025 Maternals Control group mean ± 2 SE Figure Constrained rise knee joint initial angle for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. 124

26 Angle at seat off ( ) * p=.024 * p=.006 * p=.012 Maternal session Maternals Control group mean ± 2 SE Figure Constrained rise knee joint angle at seat-off for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. Peak knee flexion ( ) * p=.013 * p=.001 * p=.007 Maternal session Maternals Control group mean ± 2 SE Figure Constrained rise peak knee joint angle for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. 125

27 The maternal group peak hip flexion velocity showed a significant decreasing trend (F linear =34.48, p= ) as pregnancy progressed during a constrained rise (Figure 6.16) (Appendix 6, Table A6xx). The peak hip flexion velocity was significantly slower than the control group at Session 3 and 4 (Figure 6.16). The maternal group showed no significant trends for peak right ankle dorsiflexion, ankle plantarflexion, knee extension and hip extension velocity (Appendix 6, Table A6xx). * p=.0009 Peak flexion velocity ( s -1 ) * p= Maternal session Maternals Control group mean ± 2 SE Figure Constrained rise peak hip flexion velocity for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control group mean ± 2 SE. During free rising a significant decreasing trend (F linear = 8.91, p = 0.02) was seen for peak ankle dorsiflexion velocity from 87.5 s -1 ± 18.7 at Session 1 to 65.6 s -1 ± 21.5 at Session 4. Significant linear and quadratic decreasing trends (F linear = 6.19, p = 0.04) and (F quadratic = 7.60, p = 0.02) were also seen for peak hip extension velocity from s -1 ± 20.1 at Session 1 to s -1 ± 19.7 at Session 4. There were no significant trends seen in peak extension velocity of the right knee joint as pregnancy progressed. 126

28 Postbirth Postbirth (Session 5) maternal and control Session 3 right lower limb joint sagittal plane kinematic data are listed in Appendix 6, Table A6xxi. There were significant differences between the groups for knee joint initial angle, angle at seat-off and peak flexion for both conditions (Appendix 6, Table A6xxi). The postbirth values, however, were similar to the values during early pregnancy as seen in Figures 6.13 to 6.15 and Appendix 6, Table A6xxi. There were no significant differences between the groups for the ankle and hip joint initial angle, angle at seat-off, peak flexion angle or range of motion nor knee joint range of motion. There were generally no significant differences between the postbirth (Session 5) maternal group and control group (Session 3) for the ankle, knee and hip joint peak angular velocities during both conditions. Postbirth peak hip joint flexion velocity was significantly less that the control group for a free rise, however the postbirth values were similar to the values during pregnancy with no significant difference over the five test sessions (F= 0.007, p = 0.9). Timing of peak flexion angle The control group showed no significant trends in the time of peak flexion angle for either the right ankle, knee or hip joints where the difference between the means was greater than the variability associated with retesting (Appendix 6, Table A6xxii). The consistency of performance was generally fair for the ankle, knee and hip joints during both conditions. The natural variability for retesting was relatively large (Appendix 6, Table A6xxii). The maternal subjects' descriptive data for the timing of peak ankle dorsiflexion, knee and hip flexion for constrained and free rising to stand from a chair are listed in Appendix 6, Table A6xxiii. During free rising there were no significant trends seen in timing of peak 127

29 ankle dorsiflexion, knee flexion and hip flexion as pregnancy progressed. The maternal group also showed no significant trends for timing of peak knee flexion and hip flexion during a constrained rise to stand. Timing of peak ankle dorsiflexion showed a significant trend (F linear = 18.14, p = 0.002) from an earlier time of 24.3 % ± 7.0 at Session 1 to 16.7 % ± 6.9 at Session 4. The maternal group timing of peak ankle dorsiflexion, however, was not significantly different to the control group mean at any test session (Figure 6.17). 30 Time (%) Maternal session Maternals Control group mean ± 2 SE Figure Constrained rise peak right ankle dorsiflexion timing for Maternal Session 1 to 4 and postbirth (Session 5) mean (2 SE) and the control mean ± 2 SE. Postbirth (Session 5) maternal and control Session 3 data for the time of peak angles for the ankle, knee and hip for constrained and free rising to stand are listed in Appendix 6, Table A6xxiv. There was no significant difference between the two groups for the timing of peak ankle dorsiflexion, knee flexion or hip flexion. 128

30 Coronal and transverse plane kinematics Although the motion of rising to stand from a chair occurs principally in the sagittal plane, coronal and transverse plane motions also occurred. Typical coronal plane motion of continuous ankle inversion, knee adduction and a neutral hip is shown in Figure Angular Displacement ( ) % Movement Ankle Knee Hip Figure Typical patterns for ankle, knee and hip joint coronal plane displacement. Positive displacement indicates ankle joint inversion, and knee and hip joint adduction. Maternal Subject 3, Trial 1, Session 1, Free Condition. 0% denotes seat-off. A typical transverse plane pattern of motion is shown in Figure The lower limb joints were in neutral posture until seat-off. The ankle then abducted while the knee and hip joint showed an inconsistent pattern of displacement. Angular Displacement ( ) % Movement Ankle Knee Hip Figure Typical patterns for ankle, knee and hip joint transverse plane displacement. Positive displacement indicates ankle joint abduction, and knee and hip joint external rotation. Maternal Subject 3, Trial 1, Session 1, Free Condition. 0% denotes seatoff. 129

31 Control group The control subjects' descriptive data and the natural variability associated with retesting for the ankle, knee and hip joint range of motion in the coronal and transverse planes are listed in Appendix 6, Table A6xxv. There were no significant trends over the three test sessions for the lower limb joints' range of motion in the coronal and transverse planes where the difference between the means was greater than the natural variability associated with retesting. The range of motion in the coronal plane was small for the lower limb joints. The consistency of performance ranged from poor to fair and the natural variability with retesting was generally a large proportion of the mean. The range of motion of the ankle and hip joints in the transverse plane was larger than in the coronal plane. The consistency of performance for the lower limb joints was higher in the transverse plane than that for the coronal plane, ranging from fair to excellent, and the natural variability from test to test was smaller. Maternal group The maternal subjects' descriptive data for the ankle, knee and hip joint range of motion in the coronal and transverse planes are listed in Appendix 6, Table A6xxvi. The lower limb joints' range of motion in the coronal and transverse plane was similar to the control group. As pregnancy progressed there were generally no significant trends for the lower limb joints' range of motion in the coronal and transverse planes. The knee joint range of motion in the transverse plane showed a significant decreasing trend (F quadratic = 17.47, p = 0.003), however the difference between the means was small and less than the natural variability associated with retesting. 130

32 Kinetics of the right ankle, knee and hip joints Right lower limb joint external applied moments were calculated after seat-off for the extension phase only. All reported moments are relative to the segment coordinate system and are applied to the distal segment. Ankle joint moment therefore refer to external moments applied to the foot, knee joint moment refer to external moments applied to the shank and hip joint moments refer to external moments applied to the thigh. Sagittal plane external applied moments A representative example of the lower joint moments in the sagittal plane is shown in Figure The knee and hip joint extension moment reached peak values near the time of seat off then decreased. The ankle joint showed a plantarflexion moment during the extension phase with a minimum near seat off (minimum flexion). 60 Extensor Mz (Nm) % Movement Ankle Knee Hip Figure Typical ankle, knee and hip joint sagittal plane moments during the extension phase. Control subject 4, Right side, Trial 1, Session 1, Free Condition. 131

33 The control subjects' descriptive data and consistency of performance for the right ankle, knee and hip peak moments in the sagittal plane (Mz) are listed in Appendix 6, Table A6xxvii expressed as Newton Metres (Nm) and in Table A6xxviii normalised to Body Weight multiplied by height (Nm.BW -1.H -1 ) (Hof 1996). There were no significant trends over the three sessions for the peak moments where the difference between the means was greater than the natural variability associated with retesting. The consistency of performance was generally fair although the consistency of the peak knee extension moment for both conditions tended to be higher than those of the ankle and hip joints. The natural variability associated with retesting for the minimum ankle joint flexion moment was greater than those of the peak knee and hip extension moments for both conditions. The maternal subjects' descriptive data for the right ankle, knee and hip peak moments in the sagittal plane (Mz) are listed in Appendix 6, Table A6xxix absolute (Nm) and in Table A6xxx as relative units (Nm.BW -1.H -1 ) (Hof 1996). As pregnancy progressed the absolute mean values for minimum ankle flexion, and peak knee and hip extension moments tended to increase although there were no significant trends. When the lower limb joint moments were normalised to body weight and height, the relative moments remained similar as pregnancy progressed. Timing of peak sagittal plane moments The control subjects' descriptive data and consistency of performance for the timing of the right ankle, knee and hip peak moments in the sagittal plane are listed in Appendix 6, Table A6xxxi. The minimum ankle flexion moment and peak knee and hip extension moment occurred shortly after seat off in the order of ankle, hip then knee and there were no significant trends. The consistency of performance of the timing of the peak ankle and knee moments was poor and the natural variability with retesting was relatively large for both 132

34 conditions. The consistency of peak hip extension moment timing, however, was fair to good with a smaller natural variability. The maternal subjects' descriptive data for the timing of the right ankle, knee and hip peak sagittal plane moments are listed in Appendix 6, Table A6xxxii. As pregnancy progressed there were no significant trends in the timing of peak right lower limb joint sagittal plane moments for either constrained or free rising to stand conditions. Postbirth sagittal plane lower limb joint moments Postbirth (Session 5) maternal and control Session 3 right lower limb joint peak moments are listed in Appendix 6, Table A6xxxiii. There were no significant differences between the two groups for minimum ankle flexion moment and peak knee extension moment expressed in absolute or relative units for either condition. There was no significant difference between the two groups for peak hip extension moment in absolute units. When normalised for body weight and height, however, the postbirth peak hip extension moment was significantly less than the control group for both constrained (p = 0.03) and free (p = 0.02) conditions. The relative postbirth peak hip extension moment, however, was not significantly different to the maternal results at any session (free; F = 3.88, p = 0.08: constrained; F = 0.47, p = 0.51). Therefore the differences can be attributed to disparity between the two groups rather than a continuing effect of pregnancy. Postbirth (Session 5) maternal and control Session 3 timing of right lower limb joint moments are listed in Appendix 6, Table A6xxxiv. There were no significant differences between the two groups for the timing of minimum ankle flexion and peak hip extension moment. The peak knee extension moment occurred significantly earlier (p=0.04) in the postbirth maternal group in comparison the control group for both conditions. The timing, however, was not significantly different to the maternal results at any session 133