Normative Biomechanics of Sit-To-Stand Position


Rising and standing is a crucial event in our lives. Through this event, an individual can be able to walk, run, and perform other daily activities. Compared to other fields in biomechanics, few studies have been focused on understanding the sit-to-stand movements. As such, in the last 50 years there was inadequate technology to necessitate these studies (Glassow 8). However, since the 1950s interests into the sit-to-stand movements have increased resulting in several researches. In the essay, understanding of sit–to-stand position has been analyzed. The purpose of this task is to understand the phases of sit-to-stand movement to aid in the analysis of postural movements. In the essay, several phases of sit-to-stand movements have been highlighted. These phases are categorized depending on the researchers. As such, in the essay the phases have been represented based on famous researchers’ findings. Therefore, the phases have been categorized into two and four categories concerning their respective researchers. Equally, through this analysis clinicians can gain an understanding of the distinctive phases, which may help them in identifying a strategy to be applied by their patients. During our studies, we noted several improvements in the research of sit-to-stand movements. Unlike in the early 1960s, currently there are several researches underway in this field (Tully & Mohammad 78). This implies that in the future more information will be known about this type of body movement. Through this, the clinicians will adopt better treatment strategies. Finally, feasible sit-to-stand trajectories are highlighted. In the section, we note that this type of body movement is a challenging manoeuvre. As such, the success of the movement relies on the proper joint movements and appropriate coordination of the required joint movements. Through this, we note that when the practical capability of the muscles in the lower extremity reduces, the CNS adjusts the multi-joint coordination strategy to execute the sit-to-stand manoeuvre.


Sitting or standing is a crucial functional movement that is carried out by all persons on a daily basis (Denny 12). The sit-to-stand position necessitates stability, muscle strength, and harmonized contraction of the required muscles. In general, the sit-to-stand movement is a requirement for several daily activities such as upright bipedal walking, getting in and out of the bed, and climbing stairs. Currently, several researches have been carried out on the sit-to-stand movement. However, it should be noted that limited studies have been carried out on different chair heights. For instance, it has been documented that the utilization of lower seat height augments hip extensor in non-obese individuals. On the other hand, no researches have been documented on the impacts of lower seat height on Total Hip Arthoplasty individuals (Knudson & Rafael 25). This paper seeks to highlight the current scientific understanding of normative biomechanical control of an aspect of sit to stand position.

So far, numerous researches on biomechanics have been carried out. Frank Pierce Jones carried out the first research on sit-to-stand movement in the early 1960s (Lanyon & Rubin 17). Notably, the success of earlier researches on sit-to-stand movements was inhabited by the lack of sufficient technology. In was not until the early 1990s that several researchers were initiated to understand the underlying biomechanical principles in sit-to-stand movement (Lanyon & Rubin 17). Like other body movements, this kind of movement results from accurate coordination of several muscles. Astonishingly, little information is known about how the nervous system harmonizes to control such a complex system. Equally, it has become a daunting task to understand the role played by individual muscles in relation to these body movements. Nevertheless, the coordination of body movement can be comprehended from three basic mechanical constraints worked out by the nervous system. These mechanical problems are maintaining the body’s centre of mass amid the feet and the chair contact, offering antigravity support, and coming up with forces that enable movement (Pheasant & Haslegrave 34). In general, the basic principles of sit-to-stand movements can be understood from these challenges. When an individual begins to stand up, the upper body parts are inclined forward. Because of this, the body mass is shifted towards the feet to allow balance after lift-off. Through these, the first constraint is solved. On the other hand, before leaving the seat the hip and the knee extensor muscles are set in motion to offer antigravity support. Through this, the second constraint is solved. Lastly, subsequent to leaving the seat the legs and the trunk joints are made straight to attain an upright posture. Through this, the third constraint is solved. Despite the fact that the above constraints may seem mechanically inappropriate, these restraints must be upheld for sit-to-stand movement to occur.

Phases of sit-to-stand and how are they defined

To look into the strategies of sit-to-stand manoeuvre, an individual has to represent the progress in terms of phase diagrams (Sahay 76). Through this representation, kinematic constraints will come into play. Because of this, the dimensions of the phase space will be reduced enabling experts to affect the theorems of topological dynamics. In the past, several researches have been undertaken to categorize the phases of sit-to-stand movement. Based on these researches, sit-to-stand movement has been categorized into distinctive phases depending on the researchers. In spite of the way the researchers categorize these phases, an appreciation of the biomechanics involved in this type of body movement is crucial in understanding the potential challenges that are experienced by physiotherapist when treating their patients. For instance, Shepherd and Gentile categorized sit-to-stand movements into two categories (Sahay 77). These categories are pre-extension and extension phases. According to the two researchers, pre-extension phase can be illustrated as the onset of movement to the position that the thighs are off the surface. On the other hand, the extension is characterized when the thighs-off the surface. Unlike the Shepherd and Gentile, Shenkman and his fellow researchers categorized the sit-to-stand movement into flexion momentum, momentum transfer, extension, and stabilization phases. The four phases were noted from the sitting position all the way to the standing position.

Flexion momentum

The flexion-momentum phase involves the generation of the upper body momentum while the subject remains seated. This phase commences during the beginning of the movement progress and stops prior to the lifting of the buttocks from a seat. During this phase, the whole body remains stable because the vertical projection of the centre of mass of the body remains over the supports, which are the buttocks and the feet while an individual is seated. The most significant body movement here is the trunk and pelvis rotation forward into flexion. During one of the researches, in seven out of the nine individuals employed in the research their trunks flexed on their pelvises on an average of 16 degrees attaining maximum flexion (Mcnaughton 48). On the other hand, the two subjects did not indicate any trunk motion in relation to their pelvises. Since there is a connection between angular momentum and angular velocity, maximum angular velocity can aid in the determination of maximum angular. Similarly, from the above relationship aspects of the propulsion phases can be recognized during the movement. During this phase, aspects such as maximum trunk-flexion angular speed, hip-flexion angular speed, and head-extension angular speed can be achieved.

Momentum transfer

The momentum transfer phase is the second phase where the projection of the centre of mass of the body moves from the initial base of support to the new base of support, which is now the feet planted on the floor (Ethier & Craig 12). The phase begins when the buttocks are lifted off from the chair and is completed on attainment of the maximal forward-flexed position. The body becomes less stable as the centre of mass is of the body is moved upward thus the area of support is greatly reduced. During this phase, maximum ankle dorsi-flexion, trunk flexion, hip flexion, and head extension are reached (Pheasant & Haslegrave 37). Equally, the dissimilarities between right and left sides for maximum hip flexion, maximum ankle dorsiflexion, or total knee expansion were not exhibited. Notably, the dissimilarities between the hip, knee, and ankle’s right and left sides were insignificant during the phase. The difference between the first phase and the second phase is that during the second phase the projection of the centre of mass, COM, changes from the original base of support to the new base of support. Equally, dissimilarity between the two phases is that during the second phase the subject’s body to rely on dynamic stability (Schofield 35).

Extension phase

The extension phase is the third and is where the body is translated vertically while still in a stable position. This phase is commenced once maximum ankle dorsiflexion is attained and ended the moment the hips stop to expand. These extensions include leg and trunk extensions. In addition, maximum hip, trunk and knee extension velocities and maximum head–flexion angular velocities are reached. The first three positions are all important in translating the various body parts through space.

Stabilization phase

This stage commences once the hip extension is attained and terminates just after the end of all motions accredited with stabilizations are ended. The final phase that the body goes through while performing sit to stand movement is the stabilization phase. It results in standing upright. This is where the translation of the body through space is terminated so that the body returns to its normal posture or gait. In general, the movement prior to thighs off represents approximately 35% of the rising to stand cycle. The remaining 65% comprises phases associated with extension and body stabilization.

Clinical application of phases of rising

Physiotherapists understanding about the phases of sit-to-stand movement can help them in the analysis of the postural movements (Ekholm & Schuldt 56). Similarly, this understanding can aid clinicians in distinguishing postural movements from normal postural sways. By focusing their attention in kinematics employed at each phase, clinicians can come up with clear hypotheses concerning the strategies to be adopted by a given patient (Pons 10). Through this, a clinician can commence interpreting the reasons for his or her choice of strategies. Particularly, a clinician can approximate the time the patient can take under momentum transfer phase. All these approximations will be based on how much the trunk is placed in relation to the position of the feet before the lift-off.

Notably, the utilization of momentum-transfer plan may necessitate several requirements (Cuisinier & Olivier 45). As such, the patients should have sufficient strength and be able to generate appropriate upper-body velocity and energy before lift-off from the seating position. Equally, the patient should be able to employ eccentric contractions to have power over the trunk and hip musculature. Through this, the patient will be able to lower the body’s forward progression in the event of lift-off. Or else, the patient might fall forward during the second phase. In addition, clinicians should ensure that the lower extremity joint integrity is sufficient for an extension component of rising.

Feasible sit-to-stand trajectories

Sit- to-stand movement or position is a challenging manoeuvre (Wagner 17). As such, its success relies on proper joint movements and appropriate coordination of involved joint movements. When the practical capability of the muscles in the lower extremity reduces, the CNS adjusts the multi-joint coordination strategy to execute the sit-to-stand manoeuvre (Bowser 56). These modifications have been evidenced from the elderly individuals who flex the trunk more before standing compared to the youths. These initiatives are carried out to reduce the burden on the knee joint muscles. Notably, this gradual adaptation is not usual. However, when an individual looses important muscle capacity and the capability to stand unaided the event is inevitable. Such occurrences occur due to illnesses that affect the lower extremity muscles (Knudson & Rafael 89). Such ailments may include paralysis, surgery, or atrophy. To enable these patients to stand on their own, it is required that a physiotherapist determines whether the patient can manage to stand with the reduced muscle’s capacity and what patient trajectory model should be employed for multi-joint coordination (Pheasant & Haslegrave 65).


In conclusion, we should appreciate the researches that have been done so far in this field. Through the current researches, the understanding of sit-to-stand movement has been enhanced. Equally, the results of these biomechanical researches can be considered in quantifying functional limitation and identifying compensatory patterns. In addition, the key findings from other related researches can be useful. These researches include studies between moments in knee joints and hip joints in relation to movement time, the height of the seats, the effects of the upper limbs, and the differences in weight bearing parameters. These findings can be recommended during exercises, rehabilitations, and other subjects that experience neurological or musculoskeletal disorders such as stroke.

Finally, the sit-to-stand task is summarized into flexion momentum, momentum transfer, extension, and stabilization phases. The four phases were noted from the sitting position all the way to the standing position. Not considering the way the researchers categorize these phases, an appreciation of the biomechanics involved in this type of body movement is crucial in understanding the potential challenges that are experienced by hemiplegic patients. Currently, the sit- to-stand movement has been analyzed kinetically and data obtained has been used to structure experimental studies of recovery or loss of function in people with functional disability.

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