*2.2. Study Selection*

One author (MTC) conducted the identification of the studies, and added it to Rayyan QCRI, a web application for systematic reviews [27]. In this environment, the duplicates were removed by MTC. Before initiating the screening process, MTC and FSS performed an exhaustive training to include articles until they reached a concordance of the 92%; then, these two authors reviewed the list of titles for applying the inclusion criteria. So, the authors compared the results and discussed the discrepancies until they reach a consensus. If there was no consensus about a title, a third researcher resolved the disagreement (MPS). Such a process was repeated, reviewing abstracts and full texts, again applying the inclusion criteria. The identification of articles in the list of references and consultation with specialists supplemented the search strategy, added to the Rayyan application.

#### *2.3. Data Extraction and Methodological Quality Assessment (Risk of Bias)*

There was the extraction of the following data: Identification (author, year, and country of publication); objective, design, sample characteristics; STS outcome (process or product-oriented); results/conclusion strictly related to the STS task (Table 1). The number of trials, instruction for performance pace, participant's caring, and motivational strategies from the protocols' studies were also extracted (Table 2).

The quality of each article (risk of bias) was examined by 15 questions adapted from Law [28], and the scoring was as follows: 0 = does not meet criteria; 1 = satisfies the criteria; ? = not clearly described; NA = not applicable. In the classification, a study with score ≤ 7 = high risk of bias/low quality; studies that reached 8 to 11 points = moderate risk of bias/medium quality; scores ≥ 12 = low risk of bias/high quality (Supplementary material Table S1). Two researchers conducted these data extraction (MTC and FSS), and when there was no consensus, another researcher (ABD) resolved the disagreement.

The data were summarized in tables, and a narrative synthesis was done. Lastly, a full protocol was developed from the critical knowledge generated here. Some authors in this review worked in the clinical setting, and others are specialists in movement analysis, both in children and in the elderly. Then, the theoretical background and practical experience contributed to the presentation of this final protocol (Appendix A, Box A1).

#### **3. Results**

In this review, from of 13,155 studies found, 37 articles wereincluded (Figure 2) [8,11,12,14–17,20–24,29–35]. The studies investigated subjects ranging in age from 1 to 94 years; the largest proportion of studies investigated up to 100 subjects [11,14,17,31,36–40], and one of them [41] examined a very large sample with 2368 subjects; more than a third of them used both process and product-oriented measurements (Table 1); only one study combined these two approaches creating a full score (MOD score) [40].

**Figure 2.** Flowchart describing the process to include studies in the systematic review according to the PRISMA-P protocol. The figure was originally created by the authors.


**Table 1.**

Methodological

characteristics,

 main results, and conclusions

 from studies on STS task (ordered by

developmental

 phase and year of publication).

 The table




*IJERPH* **2020**, *17*, 5794











#### *IJERPH* **2020**, *17*, 5794



Just four studies reported the verbal instructions on starting position, which included legs extended and arms extended to the side of the trunk [14,31,36,40] five studies reported the final position as stable standing upright with both feet on the ground [23,24,31,38,40]. Nesbitt et al. [8] used final position goal combined with touching a designated point on the wall; Alexander et al. [4] asked the subjects to press a switch placed on a tripod when assuming the standing position, marking the end of the task. Other protocols' characteristics were summarized in Table 2.

None of the studies that investigated the STS task were classified as high risk of bias. However, the item most frequently absent in assessing the risk of bias was "Was the justification for the sample size?", with only 18.9% of studies presenting such a justification (for detailed information, see Supplementary Material Table S1).


**Table 2.** Absolute and relative frequencies of the protocols' characteristics of studies reviewed about the Supine-to-Stand (STS) task (*n* = 37).

\* Not all studies have described these procedures. The table was originally created by the authors.

#### *The STS Task Performance and Body Weight Status, Musculoskeletal Fitness and Physical Activity*

By investigating young children, Ng et al. [31] and Nesbit et al. [12] did not find an association between STS time and BMI; by investigating older children, Duncan et al. [11] found a moderate inverse correlation (r = −0.508). Naugle et al. [37] investigated older adults and found that each unit of BMI was associated with an increase in the severity of compensatory strategies to rise; also investigating older people, Manckoundia et al. [38] found that being overweight was associated with fails to perform STS (not able to rise); Henwood and Taaffe [47] investigated the effect of a fitness program in seniors and found a positive effect on STS time. Belt et al. [42] investigated people from ages 7 to 36 years with Prader-Willi syndrome and typical controls, and regardless of diagnosis, they found a very poor correlation between STS task process measurement and BMI, but there were not confirmed relationships between BMI and any of the three body region scores. However, some cautions are need because BMI at different ages is related to various components of body composition.

Four studies investigated the relationship between STS task performance and musculoskeletal fitness, which showed a direct relationship [23,32,33,39]. One investigated children by testing grip and trunk muscle strength [32]; lower limb power of the older people were investigated [23,33,37,39], as well as flexibility [23] and upper limb strength [39]. One study [20] investigated a musculoskeletal training intervention on STS time performance in seniors that showed a positive effect.

Two studies examined the association between STS task performance with physical activity [14,39]. Green and Williams [14] investigated 72 middle-age adults and noted that the most active adults used

more advanced STS task patterns than those who were rarely active, but they did not perform an inferential test. Klima et al. [39] investigated older adults and found an inverse correlation between STS task time and physical activity level (rho = −0.29).

#### **4. Discussion**

In this present review, the methods used in the STS assessment were summarized and critically examined. Furthermore, this review verified the association of STS task performance with select health variables. The results showed that the STS task performance was investigated throughout the life cycle, in various countries, and several studies used large samples [3,12,15–17,31,36–38]. In general, these results suggest the STS task can be considered a functional health assessment, from youth to old age.

However, the measurement type can be a critical issue. For example, by using a dichotomous variable (to be able or not gets up from the floor), Bergland et al. [15–17] investigated seniors (over 75 years) and concluded that the STS task is a valid marker of health and function problems, as well as a significant predictor of falls-related severe injuries in this life phase. One's ability to stand up is a validated measure; however [15], it does not reveal the phenomenon of functional MC throughout life, since it seems to have been very suitable for use in the sample of older subjects, but it must have a ceiling effect at younger ones.

Both process and product-oriented measurements were used in a similar proportion in the literature. Process-oriented measurement identifies the difficulties in the task but demands much time to code and seems to be more valuable to propose intervention, mainly in older adults. Alternatively, product-oriented measurement, as movement time, maybe more related to functional outcomes. Facing a challenge, such as standing up as fast as possible, and relating this outcome to functional capabilities, like muscular strength and endurance, speaks to the ability to solve a functional motor task in various ways and at various speeds. This task speaks to the importance of being able to vary the execution of STS based on specific task demands. Thus, STS time is a resourceful way to operationalize functional MC, mainly with large samples or studies with many variables, as it requires limited technological resources and provides better discrimination and sensitivity in measurement than process-oriented assessments.

#### *4.1. Risk of Bias and Procedure Protocols*

Since all studies showed a moderate or low risk of bias, the internal validity was considered satisfactory. The more comprehensive analysis of the STS protocols showed a wide variety of procedures, which can be a severe problem if one proposes to have one protocol to be used for all the developmental levels. The instruction on the mechanics of the movement can facilitate performance [34,35] so for an understanding of how people typically get off the ground, controlling the instructions is critical to STS assessment. All studies instructed subjects individually, and most of them relied on verbal information rather than demonstration; some researchers even explicitly prevented any visual demonstration or explanation of the STS mechanics [11]. In summary, it was clear that researchers avoided any modeling or verbal instruction bias to examine the movement patterns typically used by participants.

Also, the time constraint instruction needs to be highlighted, since maximum speed instruction can affect the automaticity of the movements (i.e., minimizing the conscious analysis of the motor action) [53]. An external focus of attention (i.e., time restriction) organizes the motor system according to individual constraints and choice, rather than when the focus of attention is internal (i.e., on a movement pattern), which can interfere with the automatic process control as explained by the "constrained-action hypothesis" [35,53]. Depending on the measurement intents, a researcher can choose whether to impose a time constraint. For instance, to examine a general STS movement process that individuals would use in everyday life, a time constraint would not be necessary. Alternatively, to examine functional capacity as it relates to a "best" or "maximal" performance, a time constraint may be the most appropriate option. The time factor may be a more salient choice to predict health outcomes as the ability to produce power has strong implications for all-cause mortality and functional independence

in older adults [54], as well as fitness, physical activity, and weight status in youth and young adults [5,55,56].

The final position of the task is another critical element related to the instructions. Two studies combined the goal of postural alignment with an external target [4,12]. This seems to be an efficient methodological strategy, since the performer has a simple and easy-to-execute external goal (touching the point in front of him/her), and in turn, the evaluators' job is facilitated to stop the chronometer or video frame. However, understanding whether providing a final position with an additional reaching task might alter how an individual stand needs to be addressed.

Regarding feedback and rewards, three studies detailed the procedures given to motivate children by using verbal reinforcement during or after the task execution, using praise or words highlighting their efforts [3,12,24]. Motivational feedback was used only with early childhood children, since the motivational climate can dramatically affect preschoolers' performance [55]. Encouraging may be highly beneficial if the time task constraint is "maximum" (i.e., shortest time) [40].

The number of repetitions varied widely among the studies. This lack of uniformity weakens the findings as a high number of repetitions without adequate rest can cause fatigue, adversely affecting motor performance. It seems to be the case with older or frail individuals that demonstrate limited physical function and fitness. Conversely, only one trial may not represent typical behavior. When addressing the movement process, two to five trials would be necessary to gain insight into an individual's most probable movement process.

#### *4.2. STS Performance and Body Weight Status, Musculoskeletal Fitness, and Physical Activity*

Seven studies examined the body weight status and the STS task performance, and three of them demonstrating significant associations. It seems reasonable to expect that weight status, specifically with increased adipose tissue, is associated with STS performance. In overweight or obese individuals, the motor system has to overcome higher inertia to accelerate the body mass against the force of gravity to attain an upright position. Individuals can accomplish these using variable body actions that may not require high power outputs. Rather, maximizing postural alignments that minimize the demand for high muscle activity levels (i.e., manipulation of multiple degrees of freedom with minimum energy expenditure) would be a favorable strategy for individuals who demonstrate low muscular power/strength and endurance. However, while these strategies may be useful for minimizing energy expenditure, they may increase the time to stand. This potential trade-off may also speak to the variability in individuals' MC. If individuals demonstrate higher MC levels, they may be able to stand using different coordination patterns regardless of energy used (i.e., level of neuromuscular demand or segmental coordination patterns), as demonstrated in Didier's study [43]. However, individuals with low levels of overall MC may be more restricted in their movement patterns, due to a lack of muscular strength or coordinative capabilities across multiple joints. It is possible to think that the bodyweight status is a good candidate to be a moderator variable to the STS task performance, playing a role integrated with other fitness variables. More scientific pieces of evidence are necessary on this topic.

This review has confirmed there is a positive association between the STS task performance and musculoskeletal fitness for all ages, confirming previous literature results [5,6,55]. Therefore, it seems the STS is a good candidate to be a musculoskeletal health indicator in all cycle life.

The association between STS task performance and physical activity was examined in only two studies [14,39]. Even though the results had agreed with each other, and both studies have shown a low risk of bias, they have used different approaches, and one of them [14] did not report inferential associations. Thus, it seems too early to state that there is evidence of a direct association between physical activity and STS task performance. A previous study [56] has supported the notion of reciprocal action between the physical activity and MC, and perhaps it was the case of thinking more about how they enhance each other than just the simple relationship between them.

#### *4.3. Clinical Applications*

Hofmeyer et al. [20] carried out the only study that tested training for getting off the ground: Their results showed an improvement in the experimental group performance compared to the controls. This study reinforces that the STS task also has interventional value to health professionals. By taking all results of this review, one can generally state that STS is a potentially useful tool to examine functional MC and a general health status marker, as well as a useful approach to clinicians and researchers. It is notable in the present review that the STS task was investigated in the stages of childhood, adulthood, and old age. These results allow us to recognize that this is a task that is appropriate to play at all ages; in particular, a measure of the STS time has shown to have sufficient variability to distinguish individuals in all ages, without having a ceiling or floor effects.

The upright posture enables the subject to dominate his environment, and righting behaviors is an expression of physical independence [1]. Also, achieving such an upright posture in the shortest possible time, challenging individual constraints (e.g., unfavorable weight status), is a clear expression of human motor competence, i.e., the ability to solve motor problems in the face of challenging demands from the environment or of the subject itself. However, more evidence across the lifespan is needed to demonstrate these linkages.

Even the results of this review allow affirming that the STS task has a strong potential to uncover MC at any phase of life, the studies used diversified protocols and methodological strategies along with what prevented comparison and the generalization of findings. So, as a by-product of this review, a unique and universal protocol is proposed (Appendix A). We also understand that we are in agreement with contemporary literature on this subject. A very recent article [52] researched the same task with minor differences, showing its importance for older adults and investigating its clinimetric properties. We reinforce and extend the results of this study because we proposed that this task can be tested for all ages.

#### *4.4. Study Strengths and Limitations*

The strength of this study was that it examined all STS literature across the lifespan, and disentangled the various methods used to assess this task in several countries. It is plausible to present STS as a good candidate for a valid and non-culturally biased measure of functional MC across the lifespan. It is also advantageous to have a unique protocol that can be applied across all ages to facilitate tracking motor competence over time. The limitations of this study were that only studies in English were reviewed. Moreover, since the objective of this study was only to review methods, other studies should be carried out to establish typical values and significant cutoff points for the STS task performance.

#### **5. Conclusions**

This review showed that the STS task was tested at all ages, in various parts of the world, confirming it as a useful tool to track functional motor competence throughout life, in a universal way. In particular, measuring the time of the STS task is an ingenious way to operationalize functional motor competence mainly in large-scale studies. In addition, as it was found that the STS task has a strong relationship with musculoskeletal fitness over the years, it can help to monitor this health variable throughout life. It is not yet possible to recognize a factual relationship between the performance of the STS task and health variables, such as body weight status and physical activity.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1660-4601/17/16/5794/s1, Table S1 Risk of bias within articles included in the review regarding the performance of the supine-to-stand (STS) task.

**Author Contributions:** Conceptualization, M.T.C., F.S.d.S. and M.P.S.; methodology, M.T.C., F.S.d.S. and M.P.S.; formal analysis, M.T.C. and F.S.d.S.; investigation, M.T.C. and F.S.d.S.; resources, M.P.S., data curation, M.T.C.; writing—original draft preparation, M.T.C. and F.S.d.S.; writing—review and editing M.P.S., A.H.N.R., D.R.N., A.B.D.S., A.H.P.F. and D.F.S.; visualization, A.H.N.R., D.R.N., A.B.D.S., A.H.P.F. and D.F.S.; supervision, D.F.S.; project administration, M.T.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
