'Sit-to-stand' exercise uses the repetitive motion of standing up and sitting down in a chair, a common activity of daily living. A new assessment using an incremental sit-to-stand exercise test employs an external sound to control the speed of standing-up and allows increases in work rate. The aims of the study were to examine the effect of different seat heights on peak oxygen uptake (peak V[O.sub.2]) during an incremental sit-to-stand exercise and to assess any difference between peak V[O.sub.2] values during incremental sit-to-stand exercise compared with a cycle ergometer test. Thirteen healthy young women (age: 23.1 [+ or -] 2.6 years, height: 1.61 [+ or -] 0.06 m, body mass: 51.9 [+ or -] 7.4 kg x [m.sup.-2]) participated in four incremental sit-to-stand tests with different seat heights and cycle tests in random order. The seat heights were adjusted to 100%, 80%, 120%, and 140% of knee height distance (100%, 80%, 120%, and 140% incremental sit-to-stand exercise, respectively). The peak V[O.sub.2] and completion time were measured during incremental sit-to-stand and cycle ergometer tests, and repeated-measures analysis of variance and Student's paired t-test with Holm's method were used to evaluate differences between these variables. The peak V[O.sub.2] values increased by about 10-12 mL x mm x [kg.sup.-1] as the seat height on the ISTS decreased over a 60% range of lower leg lengths. The peak V[O.sub.2] values on the 80%, 100%, 120%, and 140% incremental sit-to-stand tests were about 11%, 25%, 40%, and 50% lower than that on the cycle ergometer test, respectively. The peak V[O.sub.2] on the incremental sit-to-stand test increased as seat height decreased. These findings are useful to determine which seat height on the incremental sit-to-stand tests test is suitable for different populations.
Key words: Sit-to-stand test, oxygen cost, seat height.
Aerobic fitness measurements, such as peak V[O.sub.2] and anaerobic threshold (AT), may be important to understand the effects of the exercise interventions (Myers et al., 2002; Wasserman et al., 2012). Aerobic fitness can be assessed by cardiopulmonary exercise testing (CPX) using either gas exchange analysis or determination of blood lactate concentration. Common types of ergometry assessments include cycle (CE) or treadmill testing which are regarded as the "gold standard" in clinical practice (Wasserman et al., 2012). However, "gold standard" measures are not widely available for use in the clinical setting because they require specially trained staff together with expensive and specialized equipment (Goto et al., 2007). Furthermore, traditional modes of testing may not be suitable for elderly and/or frail patients who cannot cycle or walk safely (Siconolfi et al., 1982; Wasserman et al., 2012).
Conversely, field tests, which are simpler, inexpensive, and do not require complicated instrumentation are commonly used in clinical settings e.g. the incremental shuttle walking test (ISWT) (Singh et al., 1994). Furthermore, most studies observed strong correlations between distance walked and peak V[O.sub.2] (r [greater than or equal to] 0.70) during the ISWT, thus the ISWT can be considered a valid test to assess aerobic fitness in individuals with chronic respiratory and cardiac diseases (Parreira et al., 2014). However, Macsween et al. (2001) found no relationship between V[O.sub.2] max and number of shuttles completed during the ISWT in patients with cardiac disease or rheumatoid arthritis, due to limitations in musculoskeletal and locomotor ability in 50% of patients, which supports the earlier findings of Arnott (1997). Therefore, field tests such as the ISWT may not be suitable for patients with locomotor disability who cannot walk safely.
Sit-to-stand (STS) exercise uses the repetitive motion of standing up and sitting down on a chair, a common activity of daily living (Dall and Kerr, 2010). STS exercise can be performed by a large number of patients. In addition, it only requires a small space and a chair, and the exercise intensity can be easily adjusted by changing the patients' STS speed or seat height (Kamimura and Akiyama, 2011; Nakamura et al., 2014). An STS test has been used to measure lower body strength in older adults and stroke patients in previous studies (Bohannon, 2011; Jones et al., 1999). However, few studies have used an STS test to assess aerobic fitness. If a simple test using STS exercise to evaluate aerobic fitness were established, similar to the ISWT, then the aerobic fitness of a greater number of subjects could be evaluated in clinical practice.
In a previous study, we developed the incremental (I) STS exercise protocol for assessing aerobic fitness (Table 1) (Nakamura et al., 2014; 2015). The ISTS test uses an external sound to control the speed of standing-up and allows an increase in work rate. Another study showed a strong correlation between ATs during the ISTS test with arm support and CE test, and the ISTS with arm support is a potentially valid, reproducible, and safe test for evaluating the AT in healthy young adults (Nakamura et al., 2015). In these previous studies, the seat height setting on the ISTS was adjusted on the basis of the standing knee height (Nakamura et al., 2014; 2015). Chair seat height is one of the important factors of an STS task, because it affects joint moments during an STS task (Yoshioka et al., 2014). Yoshioka et al. (2014) reported that during STS movement, the peak hip and knee joint moments decrease inversely, relative to the seat height within the range of normal to high seat height. Furthermore, lowering the height of the seat makes the STS movement difficult for the elderly (Schurr et al., 2012; Weiner et al., 1993). For example, the minimum height for successful seat rising for community-dwelling elderly people (64-105 years of age) with chair rise difficulties appears to be less than 120% of the knee height, when standing up from the chair without arm support (Weiner et al., 1993). In other words, many elderly people may be able to stand up from a chair seat at 120% or more of the knee height without arm support.
A greater understanding of the impact of the seat height during STS exercise on aerobic fitness is critical to developing valid methods for the evaluation of aerobic fitness. However, the effect of seat height on oxygen uptake during the ISTS exercise remains unclear. Furthermore, leg strength is an important component of being able to do STS tasks. However, the relationships between leg strength and ISTS performance remain unclear.
Therefore, the aims of the present study were to 1) investigate the effect of seat height during the ISTS test on V[O.sub.2]; 2) examine any difference between peak V[O.sub.2] during the ISTS and CE tests; and 3) examine the relationship between leg strength and ISTS performance. We hypothesized that the highest V[O.sub.2] during the ISTS test would increase as the seat height decreased.
The present study had a within-subject design to examine any difference between the values of peak V[O.sub.2], peak heart rate (HR), and completion time during the ISTS tests using four different seat heights compared with a CE test.