Is sit-to-stand test sensitive enough to measure the functional status in patients with chronic cardio/respiratory disease?

Functional status is defined as a “multidimensional concept characterising one’s ability to provide for the necessities of life; that is, those activities people do in the normal course of their lives to meet basic needs, fulfil usual roles, and maintain health and well-being” (Kocks et al., 2011, p.270). Functional status can be affected by factors such as biological or physiological impairment, symptoms and mood (Wilson & Cleary, 1995); therefore, it is often considered as the first sign of illness or exacerbation of a chronic condition. Deterioration in functional status can have an impact on individual’s independence in performing Activity of Daily living (ADL) (Saltzman, 1999). For that reason, measurements of functional status are used to: indicate presence and severity of a disease, monitor disease progression, measures the need for care and maintain the cost effective clinical operation (Saltzman, 1999). This chapter will highlight the importance of transferring from a sitting to a standing position in daily activity, then will review the history of the Sit-to-Stand test, how it started and how it changed over the time, later on will briefly inspect the cardiorespiratory patients where the gap in literature appears, and finally, will evaluate the standards of sit-to-stand test.

Progressive deterioration of physiological function and loss of leg muscles strength can lead to lose dependency in life style e.g. transferring, ambulating, or bathing (Webster et al., 1997). Such functional limitation impairs the ability to perform specific tasks such as rising from a seated position (Burdett et al., 1985). Standing from a sitting position is a demanding activity particularly for elderly and individuals with age-related conditions affecting the lower extremities such as stroke (Cameron et al., 2003), Parkinson’s disease (Inkster et al., 2003) and hip fracture (Zimmerman et al., 2006). Rising from sitting to standing is one of the essential tasks of normal daily activity (Schenkman et al., 1996); however, the ability to transfer from sitting to standing and back to sitting without assistance is important to ensure an independent life style (Rodosky et al., 1989; Burdett et al., 1985; Mazzà et al., 2004; Corrigan & Bohannon, 2001). The inability to perform this task, as a result of weakness, pain or incapability of the lower extremities, is recognized by the World Health Organization WHO as a disabling condition (World Health Organization & Assembly, 1980; Burdett et al., 1985).

Csuka and McCarty (1985), described a test to measure lower limbs muscles strength. In this test, an individual is seated on a standard height chair (44.5 cm) and is required to stand then sit again ten times, whereby the time taken to complete the ten stands is measured, and the test was called “the Timed-Stand test” (Csuka & McCarty, 1985). Since this, others have used the same test as an outcome measure, but did not follow the same protocol or test name. Guralnik et al. (1994) modified the test to a five repetition “Chair Stand test”, to assess 5000 community residents as a part of a physical assessment tests and found that 22% of individuals over the age of 71 years are unable to complete five chair stands (Guralnik et al., 1994). Afterwards, the Five-Repetition Sit-to-stand Test (FRSTST) has been used widely in assessing functional strength and physical performance in older adults (Seeman et al., 1994; Guralnik et al., 1995; Mazzà et al., 2004; Schaubert & Bohannon, 2005; Bohannon et al., 2007; Bohannon et al., 2010). It has also been used to evaluate the functional deterioration of elderly women aged 61-87 (Netz et al., 2004), physical activity in asthma patients (Mancuso et al., 2007), and performance in hemiparetic subjects (Ng, 2010).

The FRSTST has been validated in several studies. Criterion validity was supported by moderate correlation with knee extension force -0.563 (p<0.001) in older adults (Bohannon, 2006), and a significant correlation with muscle strength index -0.58 (p<0.001) in hemiperetic subjects, it also has a moderate correlation with distance walked in 6 minute walk test -0.60 (p<0.001)  (Ng, 2010). This test is not only discriminating between individuals with or without balance or vestibular disorder in adults younger than 60 years (15.3 seconds vs 8.2 seconds, respectively) (Whitney et al., 2005), it also has a significant predictor of recurrence of falls in adults over the age of 65 (Buatois et al., 2008). Those patients, who took longer than 15 seconds to complete the Sit-to-Stands (STS), were at risk of fall recurrence and reflected balance and lower limb muscles disorder (Whitney et al., 2005; Schenkman et al., 1996). The FRSTST has also been tested for reliability, Bohannon (2011) reviewed ten studies and used the Interclass Correlation Coefficient (ICC) to determine the reliability of the FRSTST and concluded that the mean coefficient of test retest reliability was 0.81 (Bohannon, 2011).

The FRSTST has a base of evidence to support validity and reliability; it gives a precise interval measure, which is the number of seconds taken to stand five times, in addition to more detailed information about level of assistance given during the test (Bohannon, 2012). Nevertheless, when an individual is unable to perform the assigned number of repetitions, i.e. five repetitions, the outcome data then transforms to a nominal scale “able vs. unable” (Bohannon, 2012). Having the data in its nominal form gives less detail about the outcome, and in addition suffers from a floor effect; i.e. individuals who attempt to perform four stands are equalised with those who perform one attempt or none, and considered as “unable”.

Newcomer et al. (1993) modified the original version of the test to a timed test by quantifying number of STS completed in 10 seconds (Newcomer et al., 1993). The 10 seconds protocol has valid correlation between repetitions and knee extension force 0.41-0.65 (p<0.001) (Bohannon, 1995; Bohannon, 1998), maximum walking speed 0.41 and 0.73 (p<0.001) (Bohannon, 1998) as well as stair climbing performance 0.56 and 0.57 (P<0.001) (Bohannon, 1995). It also has a test-retest reliability ICC of 0.84 (Bohannon, 1995). Later, Rikli and Jones (1999) used the similar evaluation approach with 30 seconds, demonstrating the validity by the correlating the number of repetitions of STS with leg strength, and test retest reliability of ICC 0.84 for men and 0.92 for women (Rikli & Jones, 1999; Jones et al., 1999). This protocol made it possible for all individuals to have an individual score, including zero in extreme cases. Then Ozalevi et al. (2007) used the 60 Seconds STS test was validated against 6-minute walk test (6MWT) for patients Chronic Obstructive Pulmonary Disease COPD. They found that there is a correlation between the number of STS with distance walked in 6MWT the 0.75 (p≤0.001) in patients and 0.54 (p≤0.05) in healthy individuals and suggested that the STS test results are as accurate as the 6MWT (Ozalevli et al., 2007). Additionally, they assumed that STS test is “less hemodynamically stressful” (Ozalevli et al., 2007, p. 292) as it does not cause an increase in Heart Rate (HR) or a decrease in Oxygen saturation (SpO2), this might be due to the absence of upper limb movement in STS test compared to the 6MWT (Ozalevli et al., 2007).

Cardiorespiratory conditions can restrict the ability to breath properly and affects the oxygen delivery to the body. Limitation of cardiorespiratory function affects the strength, vitality and sense of wellbeing, which leads to reduction in physical activity and fitness (Canadian Physiotherapy Association 2009). Functional status in patients with cardio-respiratory diseases is an indicator of the impact of the disease on the patients ability and capacity of daily activities (Coyne & Allen, 1998). Measures of function are used frequently for patients with cardiac or respiratory conditions to assess their disease or treatment progression (Guyatt et al., 1985). The STS was one of the recommended by the American Association of Cardiovascular and Pulmonary Rehabilitation (AACVPR) (Puthoff, 2011). Even though there is a very limited number of studies had used this test on respiratory patients (Ozalevli et al., 2007; Canuto et al., 2010); there is a lack it literature of STS test with cardiac patients.

The STS test has never been standardised, and there are not a guidelines available to follow to performing the test. Different chair heights have been used since the test started to evolve: 40 cm (Newcomer et al., 1993), 44.5 cm (Csuka & McCarty, 1985), and 46 cm (Bohannon et al., 1994; Bohannon et al., 1995). Chair height in relation to leg length (Knee to Floor) has a major effect of the ability to rise from a chair (Schenkman et al., 1996). Previous studies of biomechanics showed that mechanical parameters changes with chair height change. Rodosky et al. (1989) reported that knee extension moment was decreased by 50% when elevating the chair from 65% of leg length to 115% of leg length in healthy subject, it is also reported that motion and moments of all joints increases when chair is lower (Rodosky et al., 1989). Mazza et al. (2004) assumed that compensatory strategies are used to compromise functional status, otherwise the subject will not be able to stand from a lower chair (Mazzà et al., 2004). Using a fixed height chair has been proven in many papers to influence performance. Roy et al. (2006) analysed the affect of chair height in the STS task. They revealed that a higher chair will affect the duration of chair rise, with higher chairs standing duration is shorter whilst sitting takes longer, this is because of the eccentric contraction while going down to avoid hitting the chair (Roy et al., 2006). In other words, lower chair causes more effort and consumes more time than higher chair; for that reason, a standard height chair might not be reliable to give accurate results for all individuals who might have different heights, thus different leg length.

Changes in functional status might indicate biological or physiological impairment (Wilson & Cleary, 1995). In cases with cardiac or respiratory diseases, severe symptoms means limited physical activity and worse health and life quality (Holland et al., 2010; Engström et al., 1996); therefore, assessment plays a role in early detection of these changes. The STS test is considered to be easier to perform and interpret compared to the 6MWT which is the most common test used in cardio-pulmonary rehabilitation clinics (ATS, 2002). In some cases where patient is receiving assessment and therapy in the Intensive Care Unit (ICU), the patients is likely to be connected to monitoring devices and Intra-venous (IV) tubes as well as the limited space, it could not be easy to perform a 6MWT. And since the STS is validated against the 6MWT and proven to be accurate, it might be an accurate alternative. The aim of this paper is to review the available evidence to examine whether the STS test is a sensitive enough tool to measure functional status in patients with cardiac or respiratory diseases.

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