Sit to Stand (STS) movement is believed to be one of the most demanding activities. The given activity can be described as the process of standing up from a chair or any other object to an upright posture. It is a movement with great clinical interest that helps in defining an individual’s motor and functional level. This movement requires an individual to move from a sitting position that is a more stable 3 point base to a standing position that is a less stable 2 point base (Tully et al., 2005).
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Thus, it requires more muscle strength. In addition, it involves peak joint moments and yields greater hip joint contact pressure, which sets the difference between a sit-to-stand process and any other activity involving movement. Stroke is the leading cause of disability in the world. Because of the changes that a human body undergoes because of impairments and the subsequent treatment, the organism becomes highly susceptible to any outside factors, especially mechanical ones.
In addition, inside and outside factors that cause mechanical effects are likely to have rather a tangible effect on a human body. That being said, it can be supposed that movement changes as a kind of an inside mechanical factor may both be the cause and the effect of the impairment.
Impairment is due to the kinetic and kinematic changes that cause one to be incapacitated in the performance of STS movement whereas functional limitation influences the ability to remain independent and relates to the quality of life. This paper will discuss both kinetic and kinematic changes of sit to stand position following stroke. Therefore, to complete the research, it will be required to identify compensatory patterns and clinical implications to quantify the functional limitations by the effect of foot positioning and height of the seat.
The change of posture in STS has three aspects. They are flexion, an extension of a trunk, and extension of the legs which is essential for normal movement. STS kinetic and kinematic parameters are relevant in the assessment of functional recovery and the effects of the intervention. Some of how stroke affects an individual’s STS movement include causing a slowdown in bodily functions, the center of pressure (COP) displacement, asymmetry of the kinematics of the person’s joints, asymmetry of joint moments, disproportionate support of body weight & force over the heels and the need of support of the person (Janssen et al., 2002).
Patients suffering from chronic stroke have serious issues arising from an inability to balance their weight during the performance of STS movement and is mostly due to asymmetry of kinetics and kinematics (Hesse et al, 1994a). Having the capacity to control one’s weight when one is standing requires the proper functioning of the central nervous system. Some stroke patients are completely unable to perform the movement whereas others require some assistance or are completely slow in their performance.
The types of performance that require assistance may include the strength of the muscle and the balance of a person. Getting up from a sitting position to a standing position leads to instability in hemiplegia due to the displacement of the center of gravity (COG) within the base of support (Eng and Chu, 2002). It is required to control the equilibrium deviations due to the unequal distribution of body weight. Also, the ability of a person to execute STS depends on various factors which include the height of the chair, with or without armrest, the tilting position of the chair, speed of the movement, and the position where one has placed their feet.
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In addition, the age and the strength of the lower limb of an individual also determine the ability of a person to perform the STS movement. Asymmetrical bodyweight distribution is related to impaired balance, increased expenditure of energy and may be associated with a high risk of falls and fractures. Balance and stability in the performance of this movement are important in guaranteeing the safety of an individual. Thus the main aims of rehabilitation are ensuring that patients can have a symmetrical weight-bearing and to improve their speed with balance and stability on their performance of STS movement.
The study of Galli et al., (2008) reported both kinetic and kinematic parameters in 13 normal and 7 right hemiplegia subjects which is suitable for clinical application. The study selected 8 camera optoelectronic systems for evaluation of kinematics and used two force platforms for kinetic evaluation, a pair of pressure-sensitive switches on the seat placed in contact recording, and a synchronized video system.
Temporal, kinematic, and kinetic parameters were recorded. The chair used in the study have no armrest and the subjects were asked to cross the arms in front of the chest to prevent upper limb movement and to evaluate forward trunk movement. The data were collected in 2 to 5 trials with a break. Based on the study the subject prepared to seat off is the preparation phase, the seat off happens and vertical acceleration is converted to deceleration in ascending phase.
The final phase is stabilization the subject begins the phase reaching quite standing. Since Lee et al (1997) defines STS movement as a movement that alters one position from the position of sitting to a standing, which involves the movement of the center of mass without loss of balance, in the sitting position, the center of mass (COM) is more stable where it acquires the highest position in the ascending phase. Therefore, this movement leads to instability in hemiplegia due to the presence of kinematic and kinetic asymmetry between the left and right side: “Common approaches to evaluating asymmetrical movement in hemiplegia include measures of kinematics and kinetics” (Taguch, Igarashi & Mori, 1994, 263).
Temporal and kinematic changes
In the findings of Galli et al., (2008) the time taken by stroke patients (3.89 seconds) to stand up was 60% longer than normal subjects (2.42 seconds) due to compensatory pattern addressing muscle weakness of the lower limb:
STS requires some skills, such as coordination between the trunk and lower limbs movements, correction of muscles strength, control of equilibrium, and stability and it is often considered into clinical evaluation scales of different pathologies. In literature, although some studies are focused on STS, the essential functions of standing up are not well standardized and uniformly defined: for this reason, its application in clinical centers is difficult. (Galli et al., 2008, 80)
Thus, the execution of STS mainly done by the unaffected limb required a longer period for standing up and need to stabilize during limb extension: “It requires significant torque and range of motion at the knee joint and to a lesser extent the ankle joint” (Galli et al., 2008, 80). In particular, ascending phase took double the duration (2.16 seconds) to maintain balance in the stabilization phase, as Tully, Footahabadi & Galea (2005) also state.
In cases where the patients were unable to stand from a sitting position, the Peak angular velocity was also relatively low at the knee and the hip((Osman, 2011)?). Especially to improve the stability at seat off and during standing up, affected individuals showed an excessive trunk forward flexion movement. During the preparation phase, there was an excessive inclination and rotation in the forward and transverse plane and the trunk was shifted more towards the affected side.
As a result, the shoulder on the affected side had a high range of motion in all planes (shoulder tilt, obliquity, rotation was 42.1 (27.28), 7.34 (4.08), and 7.45 (5.41) degrees respectively) and was more forward than the normal side during the ascending phase (Tully et al., 2005). This finding of initial trunk flexed position and increased duration in limb extension was supported by Schenkman et al., (1990) who specified the elements of a momentum transfer strategy in which the momentum generated by the upper body is later on used in kinematic changes. Unlike Tully, however, Schenkman et al. did not relate their paper to impairments, providing a full overview of the kinematic changes around the hip. Moreover, as the results of shoulder tilt, ankle movements indicated an excessive dorsiflexion movement.
This movement can be used as a strategy to align the forward displacement of the center of gravity with the supporting area of the foot and improved the stability, as Schenkman et al (1990) claim. In patients following chronic stroke, poor coordination in the creation of momentum is also a factor that may lead to failure in the execution of STS movement. This is particularly useful in cases a training strategy that targets the temporal characteristics may be beneficial. All this was indicated represents the asymmetrical distribution of kinematics between hemiplegic and normal limb.
Although there was no change in peak support moment (Schenkman et al., 1990, 58), increased duration of the maximum support moment was observed during the initial more flexed trunk position. Using the trunk’s maximum flexion strategy (flexing the trunk towards the knee before standing from the chair), the knee joint moment is decreased by 27% compared to normal subjects. The kinetic parameters represented a strong asymmetry between the peak vertical ground reaction force (normal side 6.67 N/kg and 4.73 N/kg hemiplegic sides) and Anteroposterior ground reaction force ( a normal side -0.77 N/kg and -0.31 N/kg hemiplegic side).
It was also confirmed by a maximum joint moment of the knee (normal side 0.87 N m/kg and hemiplegic side 0.39 N m/kg) and maximum joint moment of the ankle (normal side 0.52 N m/kg and hemiplegic side 0.35 N m/kg). This highlighted more force distribution on the normal side and fewer joint moments on the hemiplegic side. In comparison with normal subjects, hemiplegic subjects demonstrated lateral force asymmetry. The maximum forces beneath the hemiplegic side heel were 37% body weight and the mean hell value was 21%. The maximum forces beneath the normal side heel, i.e., the non-flat, were 63% body weight, and the mean heal value was 42%.
The new issue, new paragraph? The maximum ankle power of the unaffected and affected side of 0.09 w/kg and 0.08 w/kg respectively represented low capacity of bilateral propulsion. Cheng et al., (2004) classified the phases based on the changes in vertical ground reaction force in stroke patients by the force plates. Phase one is the initial phase which starts when the vertical reaction force is decreased at the beginning of trunk flexion.
Serving as the execution phase, which starts once the vertical force reaches its maximum and ends when peak vertical momentum has been reached, phase two is also crucial for the process. Phase three is the standing phase begins at the moment of peak vertical momentum and ends with the stabilization of vertical force with body weight and achieves stable standing. As a result of this compensatory mechanism, stroke patients decrease the speed of ascent during the STS task.
Effects of kinematic and kinetic changes of STS in gait
To evaluate the effects of kinematic and kinetic changes in the STS Gail, it is important to keep in mind that there is a significant relationship between the functional movement of STS and gait speed (Berger et al, 1988). The duration of STS movement in stroke patients is a main predictive for gait speed and symmetry. According to Ahmed and Ahmed (2008), ST’s dysfunction experienced due to the kinetics and kinematic changes in stoke patient’s joints located on the lower limbs has a direct influence mainly during the walking process. Therefore, during the first phase of the Sit to stand cycle, the mean value of maximum ankle angle for hemiplegia was greater than the normal individuals.
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These patients registered a decrease in the dorsiflexion of the ankle when they start walking. This happened because of the paretic weakness of plantar flexors. The reduction in ankle dorsiflexion caused the knee joint to have more flexion. Simultaneously, flexion of the hip and knee joints was reduced in these cases. A similar mobility style was registered on the other side where the lower limbs were not affected. However, this similarity was not due to paretic muscle weakness.
It was because of the heightened mechanisms in co-contraction. As a result, asymmetry in the kinetic and kinematics in ST’s movement influences over increased stride time and decreased walking speed with decreased single limb support and increased double limb support. Chou et al., (2003) findings suggested that the chronic stroke patient who could stand up from a sitting position for less than 4.5 seconds and had a vertical ground reaction force asymmetry of less than 30% could have a better gait performance. This includes increased velocity, stride time, and single support. This highlighted completing the STS movement in a safe and controlled manner which is a basic requirement for normal daily living.
The integration of gait analysis from STS is significant clinically during the execution of movement and to identify and monitor Neuro-motor treatment. In addition, gait speed also influences the fall risk of a person. A slow rate of STS is an important tool in the foretelling of further disability in a patient. The transfer of more weight on the unaffected side causes the patients to limp and resulted in stiffed hip and knee gait.
This highlights the weakness of the affected side compensation mechanism by unaffected limb due to the asymmetrical distribution of the anteroposterior force, vertical force, and lateral distribution of the force. Considering the differences in weight-bearing parameters and characteristics of stroke affiliated patients and normal people, stroke patients portrayed asymmetrical weight-bearing may lead to disequilibrium during sit-to-stand actions. Instructions and training to perform better through practicing on standing symmetrically portrayed improvements on the symmetry of weight-bearing and to prevent poor balance ability (Janssen et al., 2002).
Effects of foot position and height of the chair in rehabilitation
Understanding the biomechanical abnormalities in the STS task can provide a rationale for the therapist to target their treatment to the appropriate areas. Therefore, Various methods of measuring the effects of the determinants have also elicited different reactions to increase symmetrical weight-bearing in rehabilitation. Some scholars have ventured into the biomechanical factors that affect the ability of patients with chronic stroke when they are rising from a sitting position to a standing position. The foot position, the height of the chair, and the tilting of the chair have all elicited different reactions from various clinicians.
Height of the seat
Various clinicians use chairs with different heights. For instance, chairs with 40 and 43 cm are commonly used for assessments (Whitney et al., 2005, 1034). For the successful execution of STS for elderly people appears to be 120% of their lower leg length ( Janssen et al., 2002). When sitting on low chairs, patients with chronic stroke experience an increase in their trunk flexion angular velocity and hip flexion angular velocity which can make STS activity unsuccessful. During rehabilitation, the alterations in the height of the chair affect the biomechanical demands of an individual. Alteration in the height of a chair affects the maximum moment that is required at the hip and knee to enable one to rise from a sitting position (Janssen et al., 2002).
The joint moment depends on horizontal forces and the center of pressure. The maximum value of vertical ground reaction force will be decreased with an increase in height of the chair (Whitney et al., 2005). Also, it reduces the total displacement of the Center of mass and pressure and it showed a trend towards a shorter duration in STS movement. These include the fact that one is expected to move the center of mass of the body over a large distance in low chairs. It was also found that when rising from a high chair than with a low chair knee joint forces and muscle tension were reduced between 8% to 56%, irrespective of arm activity (Ellis et al., 1984).
Overall, less demanding tasks by the elevated height of the chair promote the asymmetrical distribution of body weight. Consequently, the use of armrests affects the distribution of forces, reduction in trunk forward flexion, and reduction in hip and knee joint moment. Eriksrud et al., (2003) reported that the maximum vertical force of 15% body weight was lowered by each hand during STS movement.
Positions of the foot
Another important factor is the position of the feet which is found to cause changes in a joint moment and body movement. The study of Brunt et al., (2002) Foot positioning is used as one of the stabilization strategies used to improve asymmetrical weight-bearing patterns in hemiparesis. Roy et al., (2006) tested 12 chronic hemiparesis subjects at their natural speed level of sit to stand movement with different foot positions. In the cases when the patient was asked to stand up without any instruction and in symmetrical both the feet are placed with 15 degrees of ankle dorsiflexion with 90 degrees standardized knee angle, the given instances of sit to stand movement seem spontaneous.
An asymmetrical 1 and in asymmetrical 2 the affected foot is placed forward and backward respectively with 15 degrees of ankle dorsiflexion at a distance to 50% of the subject’s foot length. The mean asymmetry was compared and reported that the mean asymmetry mainly at the transition phase was nearly 10% in the affected foot placed backward as compared to 24% in the spontaneous foot position, 21% in the symmetry condition, and 28% in the unaffected foot backward position. In the other three movements except the affected limb placed posteriorly, there is no difference in peak vertical reaction forces of the two sides during STS which resulted in asymmetrical weight-bearing.
The results revealed that there is a need to control the position of the foot which had a strong correlation with asymmetry in knee strength and knee extensor moments. Based on Briere et al., (2013) findings in normal subjects suggested that the foot placed backward asymmetrically resulted in a displacement of the trunk towards the posterior foot with more weight-bearing and higher moment on this side. This can be used to modify asymmetry of trunk position, knee joint moment, and body weight distribution in hemiparetic patients. The clinical implication of this finding suggests that the training with the hemiparesis foot placed backward considerably reduced the asymmetry of vertical ground reaction force between the lower limbs, indicating more symmetrical weight-bearing under the thighs and feet during sit to stand.
The effect of foot positioning with the increased height of seat 130% of knee-height could be presented as a therapeutic route to increase the symmetrical STS task. It is important that asymmetry can also be observed in other positions, noty necessarily in feet motion. For example, the study of Hesse et al., (1994a) has reported that chronic stroke patients shifted their COG laterally by 78% before seat off and 50% after seat off. This showed that asymmetry of weight-bearing is mostly occurred before seat off.
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Training is a useful tool in helping patients with chronic stroke to execute STS movements with symmetrical weight bearing. Training that lasts for four weeks where these patients undergo rehabilitation can help them perform STS more easily than when they try to do it without any prior training. During these four weeks, patients are trained how to spread the weight equally on their two legs prevent the trunk from tilting laterally (Eng and Chu, 2002). The four weeks training is aimed at teaching the patients concerning the temporal and spatial aspects of STS movement. Such training is most effective when done on people with left hemiparetic stroke.
Patients who suffer from left hemiplegia have greater difficulty in achieving a stable position as they tended to have visual, spatial and perceptual problems. This was due to having more media lateral sway than anterior posterior direction and this leads to poor postural control and increased risk of fall in left hemiplegic patients. This indicates that stroke fellers from sit to stand position has taken a longer duration with an asymmetrical distribution of body weight and greater COP sway in the mediolateral direction.
So prevention strategies also important to be developed and included in the rehabilitation program. Consequently, patients with chronic stroke with right hemiparesis are in a better position to exercise postural control and balance than people with left hemiparesis due to the damage of the learning process (Adams, Gandevia, Skuse, 1990). However, in patients with right hemiparesis and left hemiparesis, a significant difficulty is experienced when rising up from a sitting to a standing position.
Kinetic and kinematic data are the most effective ways to model the path of the center of mass and for evaluation of muscle inactivity caused by a stroke in a patient. This helps in the identification of various abnormal movements exhibited by the joints found in the lower limbs. The reduction in the ability to coordinate one’s muscles as well as weakness and spasticity of various muscles were considered to differentiate stroke subjects from normal subjects.
Therefore the findings from the study of Galli et al., (2008) about the kinetic and kinematic asymmetry in relation to the findings of Roy et al., (2006) the effects of the foot positioning, height of the chair and the differences in weight bearing parameters can be used during rehabilitation. This helps them to overcome any mechanical challenges that they may encounter in this process. Inactivity makes one leads to decreased speed in performing the STS movement. The slowdown in the STS times that cause huge deficiencies in the major activities that a person does in their day to day lives. Therefore, recovery from the inability to perform successful sit to stand task with symmetrical weight distribution with increased speed should be the priority of physiotherapists.
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