The loads on the non-paretic leg were greater than loads on paretic legs in all postural configurations (P < 0.001), which led a rather consistent leg load sharing
strategy for the two leg placements (Figure 3-4). The load on the anterior leg (the non-paretic side) in PLP was greater (P < 0.001) than that on the posterior one. In NPLP, the load on the posterior leg (the non-paretic side) was greater (P < 0.001) than that on the anterior one. In addition, the load on the non-paretic side in PLP was smaller (P <
0.05) than that in NPLP, but the load on the paretic side in PLP was greater (P < 0.05) than that in NPLP. Whether non-paretic or paretic, the leg placed posterior is in a more favored position for accepting biomechanical load than the same leg otherwise placed during StandTS movements.
Figure 3-4 Illustrations of leg load strategies of two leg placements corresponding to (a) SA arm placement and (b) GA arm placement. * represents that there is a
significant difference between two bars.
Discussion
No significant differences regarding the parameters utilized in this study were
found between the two arm placements adopted. Leg load discrepancy was not reduced by adopting the arm grasped placement which however has been a common practice to facilitate symmetrical functional movements [23]. This result might be due to the criteria used in this research of subject selection, which required the participants to be in high functional levels. More sophisticated assessment of postural control,
such as COP-BCOM relationship [27] and angular momentum modulation [28], might be required to detect the influence of arm placement on StandTS.
In this study, the descending periods of participants did not demonstrate any significant difference among different postural configurations. From previous
research, the length of time required to finish SitTS, which reflects the gross muscle strength to accelerate the body rising up, has been related to task performance [2,7,13,14,20]. Some authors have pointed out that a shorter ascending period would correlate to better performance of SitTS [2,20]. Since the primary concern during StandTS is how well the patient modulates the body downwards velocity, rather than how fast the patient drops, the length of descending period may not be an appropriate indicator for evaluating performance of StandTS. Because not only muscle strength
but also muscle coordination is involved in the deceleration process, descending faster may actually reflect poor control during sitting down rather than good performance.
Our results imply that the duration of the descending period (in the patients with relatively good functioning level recruited in this research) was not able to differentiate performance quality.
The pathological joint movements of stroke subjects play an important role during StandTS in order to differentiate the performance of postural configurations. The
types of leg muscle contraction for SitTS and StandTS are quite different since rising up requires concentric contractions of hip extensors, knee extensors and ankle plantar flexors for acceleration whereas eccentric contraction is demanded for deceleration
while sitting down [15,29]. However, eccentric contractions of paretic muscles, in which the selective control of joints is limited in stroke patients, may account for the difficulty to modulate StandTS movement [30]. The StandTS with PLP leg
placements would be more difficult than that with NPLP leg placements because PLP
leg placement requires the paretic muscles to be primary power to perform the eccentric contractions for the deceleration during sitting down. Clinicians should let stroke patients be aware that adopting the PLP leg placement to sit down without the supervision of medical professionals may put them in a dangerous circumstance
particularly for those in low functional levels.
In addition to abnormal muscle synergy, disuse muscle atrophy is also an important issue in stroke rehabilitation. Research has shown that improvement of paretic muscle strength prevents overuse of the non-paretic side [16,25] and decreases disability [19,22,26]. In accordance with previous studies [5,6,15,16], placing the paretic leg posterior in this research not only increases activity of the paretic leg, which is suitable for strength-training, but also improves the asymmetrical load condition of StandTS due to the decrease of leg load discrepancy. However, these improvements cannot transfer to better postural control for stroke patients because the sitting impact is increased with the PLP leg placement. Hence, more symmetrical load condition accomplished by more exertions of paretic muscles cannot explicitly relate to better StandTS performance although it is beneficial in strength-training rehabilitation.
The asymmetrical load condition of NPLP is not a source of postural instability but rather a result of safe postural configurations during StandTS since the sitting impact
can be reduced with NPLP placement as shown in Table 3-1. Due to the fundamental characteristic of stroke patients regarding their preferred use of the non-paretic side, the dominant role of the non-paretic leg on bearing loads consistently ensures safety
despite the alteration of postural configurations. The leg load sharing strategy of StandTS with the NPLP leg placement achieves an effort-efficient status because the posterior leg bears more load than the anterior leg (Figure 3-4) due to the preferred use of the non-paretic leg and the favored position for accepting biomechanical load.
In contrast to the NPLP leg placement, adopting the PLP leg placement to sit down for hemiplegics is unlikely to achieve an effort-efficient status, i.e.the posterior (paretic) leg bears more loads than the anterior (non-paretic) leg. In other words, the non-paretic leg is placed anterior in an awkward position with the PLP leg placement for sitting and thus is unable to adequately compensate paretic muscles on modulating body descending velocity, which consequently induces the greater sitting impact as we found in this research. Our result echoes previously published findings [21]
concluding that the postural instability is caused by the inability of the non-paretic leg to compensate the postural impairment of the paretic leg, rather than by asymmetrical load condition. Despite the load asymmetry, we found that the NPLP leg placement reduces sitting impact in addition to the effort-efficient movements when patients perform StandTS.
This study has demonstrated the sensitivity of the sitting impact on the changes of leg load sharing strategy due to postural configurations. Hence, sitting impact can be a
performance indicator of StandTS since it not only reflects the sitting down efforts of
both legs on decelerating but also represent the smoothness of the weight-transfer process from legs to a stool. When smooth weight-transfer can be achieved, the risk of falls may be reduced. Further research is needed to correlate other characteristics of StandTS to sitting impact in order to uncover the relationship between postural control and the sitting impact in more detail. Possible predictors of sitting impact might be the impacting velocity of BCOM, muscle strength of lower extremities, COP-BCOM relationship, and angular momentum modulation. The ultimate goal of our study group is to develop reliable predictors on falls, which would contribute to fall prevention for stroke patients. A longitudinal project has been launched for this purpose.
The main limitation of this study was that only a chronic population with a high functional level was examined and hence, the relevance of our findings to an acute stroke population or to less able chronic patients has not clarified by our current work.
In conclusion, this study confirmed that, in stroke patients with good functional levels, leg placement significantly influences leg load sharing strategies and sitting impact
forces whereas arm placements do not. The preferred role of the non-paretic leg in load-bearing and the favored biomechanical load position of the posterior leg
accounts for the leg load sharing strategies with the two leg placements investigated.
Consequently, the inability of the anterior non-paretic leg to compensate the poor controlled paretic leg induces greater sitting impact compared with the non-paretic leg posterior placement. For training purposes, placing the non-paretic leg anterior would increase exertions of the paretic leg.
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Postural Configuration on Phase Duration and Vertical Force Asymmetry during Sit-to-Stand Tasks in Patients with Stroke
Introduction
Cerebrovascular accidents, a leading cause of death in many countries with a high morbidity rate, have become a significant public health problem. Complications often occurring as a direct result of injury to the brain following stroke include an inability to move freely or to sustain balance. As a result, stroke patients have a high risk of falling: with 14 to 39% of patients falling in the first month following stroke, and 75%
in the first six months [1,2]. The injury rate in such falls has been reported between 13 and 29% [3–8]. Previous stroke has been demonstrated as a risk factor (adjusted OR, 2.9; 95% CI, 1.3–6.3) for fall-induced hip fractures among elderly persons dwelling in communities [9]. Poor force exertion in the lower extremities and impaired
coordination of body segments during the SitTS tasks are correlated with fall risk [2,10].
Past studies have demonstrated longer task duration, larger displacements of the COM, and asymmetrical weight bearing during SitTS is commonly observed in
patients following stroke [11–14]. By comparing fall and non-fall stroke patients, it was found that asymmetrical distribution of body weight and greater postural sway were predictors of falls [14]. The asymmetry of body-weight distribution can be estimated from the vertical ground-reaction forces on feet, and used to quantitatively assess SitTS movement.
In previous studies, the hand placement position of crossed-arms-on-chest has been adopted in experimental settings simulating the SitTS task [15]. However, clinically, crossed-arms-on-chest deprives the patient of the ability to adjust postural sway and may result in atypical patterns of movement.
The aims of this study were to evaluate the effect of different postural
configurations of the hands and feet on weight bearing in stroke patients during SitTS tasks. The hands-clasped position is frequently used in clinical practice for SitTS task training of stroke patients as it is believed to provide better control of upper limbs and trunk. In addition, activity with hands-clasped position is believed to inhibit the flexor synergy of upper limbs and facilitate body and joint proprioception in the stroke patients. Positioning the affected foot backward is also used to facilitate weight bearing of the weakened leg. We hypothesized the hands-clasped position with the
affected foot backward will decrease time expenditure and asymmetry of vertical ground-reaction forces (GRF) in stroke patients during the SitTS task.
Methods
4.2.1 Participants
Subjects were recruited from the rehabilitation program at a tertiary medical center.
A total of 21 stroke patients (17 males, 4 females) were enrolled in this study. The mean age was 58.8 years (SD = 12.4), and the time post-onset ranged from 1.7 to 44 months. The mean Functional Independence Measure (FIM) was 108.6 (SD = 17.3).