The Open Sports Sciences Journal




ISSN: 1875-399X ― Volume 12, 2019
RESEARCH ARTICLE

Biomechanical Analysis of the Knee Joint Load During a Unilateral Sit-to-Stand Movement



Hannah Steingrebe2, *, Thorsten Stein2, Klaus Bös1, Marian Hoffmann2
1 Karlsruhe Institute of Technology, Institute of Sports and Sports Science, Karlsruhe, Germany
2 Karlsruhe Institute of Technology, Institute of Sports and Sports Science, BioMotion Center, Karlsruhe, Germany

Abstract

Background and Objectives:

Sit-to-Stand (STS) movements are fundamental activities of daily living. As STS movements can be physically demanding especially for the elderly, bi- and unilateral STS movements are frequently used in motor tests to measure lower limb strength. In contrast to bilateral STS movements, the knee joint loads occurring during unilateral STS movements as well as the influences of chair height or lower limb dominance are still unknown.

Methods:

In a randomized study approach knee joint loads during unilateral STS movements from three different chair heights have been analyzed using biomechanical motion analysis in a population of 19 healthy middle-aged adults. Additionally, the influence of lower limb dominance and the level of perceived exertion have been investigated.

Results:

Lower limb dominance had no effect on knee joint load. In contrast, chair height significantly affected the peak shear forces in anterior (high: 3.94 ± 0.63 N/kg; low: 4.09 ± 0.61 N/kg) and lateral (high: 1.52 ± 0.79 N/kg; low: 1.78 ± 0.88 N/kg) direction as well as the peak knee adduction moment (high: 0.56 ± 0.29 Nm/kg; low: 0.65 ± 0.32 Nm/kg). Additionally, chair height but not limb dominance significantly affected the level of perceived exertion (high: 11.1 ± 2.8; low: 12.5 ± 3.5).

Conclusion:

The detected knee joint loads occurring during a unilateral STS movements are similar to those of other activities of daily living like e.g. stair ascent and thus, unilateral STS movements are applicable for usage in motor tests for middle-aged subjects. While lower limb dominance has no impact on the knee joint load, lower chair heights increase the load on the knee joint. Therefore, chair height should be considered when using unilateral STS movements in motor tests.

Keywords: Ergonomics, Chair height, Sports for the elderly, Fitness tests, Rising, STS, One-legged, Motor tests.


Article Information


Identifiers and Pagination:

Year: 2018
Volume: 11
First Page: 78
Last Page: 87
Publisher Id: TOSSJ-11-78
DOI: 10.2174/1875399X01811010078

Article History:

Received Date: 23/4/2018
Revision Received Date: 27/9/2018
Acceptance Date: 12/11/2018
Electronic publication date: 31/12/2018
Collection year: 2018

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© 2018 Steingrebe et al

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


* Address correspondence to this author at the Karlsruhe Institute of Technology, Institute of Sports and Sports Science, Engler-Bunte-Ring 15, 76131 Karlsruhe, Germany; Tel: +49 721 608-41735; Fax: +49 721 608 – 44841; E-mail: hannah.steingrebe@kit.edu




1. INTRODUCTION

An important aspect of sports science is the analysis of human physical performance. Various methods are used for this purpose, including instrumented and motor performance tests, which measure the differences between various personal traits (e.g. motor ability or motor skill). Compared to instrumented test procedures as used in the fields of sports physiology and biomechanics, motor tests are less precise [1Tittlbach S, Knyrim H, Baumeister J, Bös K. Motorische Tests [Motor tests]. In: Banzer W, Pfeifer K, Vogt L, Eds. Funktionsdiagnostik des Bewegungssystems in der Sportmedizin [Functional diagnostics of the locomotor system in sports medicine] 2004; 71-86.[http://dx.doi.org/10.1007/978-3-642-18626-4_4] ], but more feasible and require less specific diag-nostic knowledge. Nonetheless, motor performance tests are scientific methods that must meet the test-theoretical quality criteria and be sufficiently sensitive to be able to test the underlying theoretical model [2Bös K. Allgemeine Aspekte der Diagnostik [General aspects of diagnostics]. In: Hottenrott K, Seidel I, Eds. Handbuch Trainingswissenschaft – Trainingslehre [Handbook of coaching science – exercise theory]. Schorndorf: Hofmann 2017; 120-3.].

Motor tests are often used in the field of elite sports for e.g. talent selection [3Roth A, Moll C, Seidel I, Bös K. Nachwuchsleistungssport an den NRW-Sportschulen –Talentsichtung unter Berücksichtigung sportartübergreifender, sportartspezifischer und sportpsychologischer Testverfahren [Youths elite sports at NRW sports schools – talent diagnostics in consideration of within sports, across sports and sport psychological test methods]. Leipziger Sportwissenschaftliche Beiträge 2017; 58(1): 132-57.] and performance diagnostics [4Pearson DT, Naughton GA, Torode M. Predictability of physiological testing and the role of maturation in talent identification for adolescent team sports. J Sci Med Sport 2006; 9(4): 277-87.[http://dx.doi.org/10.1016/j.jsams.2006.05.020] [PMID: 16844415] ]. They are also increasingly applied in the field of health-related sports as well as sports for the elderly [5Bös K, Ed. Sportmotorische Tests, Motorische Funktionstests, Fragebögen zur körperlich-sportlichen Aktivität und sportpsychologische Diagnoseverfahren [Handbook of motor tests: sports motor tests, functional motor tests, questionnaires for physical activity and sport psychological diagnostic methods]. 3rd ed Göttingen: Hogrefe; 2017.]. These tests determine performance in basic abilities such as strength and endurance, which can have a beneficial impact on health if manifested to a certain degree [6Tittlbach S, Woll A, Bös K. Motorische Entwicklung im frühen und mittleren Erwachsenenalter [Motor development in early and mid adulthood]. In: Baur J, Klenk C, Alfermann D, Eds. Handbuch motorische Entwicklung [Handbook of motor development]. 2nd rev. ed. Schorndorf: Hofmann 2009; 319-32., 7Shephard RJ. Physical Activity, Fitness, and Health: The Current Consensus. Quest 1995; 47(3): 288-303.[http://dx.doi.org/10.1080/00336297.1995.10484158] ]. Motor tests in the field of health-related sports or sports for the elderly are often derived from Activities of Daily Living (ADLs) [8 Simons H. Brauchen wir “alltagsferne“ Tests [Do we need tests which are “diverging from daily life”]. 252 Sportunterricht 1978; 27(8): 285-9.], which aim to detect a person’s capability to meet the practical demands of everyday life. One example of these ADL-derived test tasks is the group of Sit-to-Stand (STS) movements, which have a high relevance in various activities of everyday life [9Etnyre B, Thomas DQ. Event standardization of sit-to-stand movements. Phys Ther 2007; 87(12): 1651-66.[http://dx.doi.org/10.2522/ptj.20060378] [PMID: 17940102] , 10WHO. International classification of functioning, disability and health 2001.] since they are performed on average 60 times a day [11Dall PM, Kerr A. Frequency of the sit to stand task: An observational study of free-living adults. Appl Ergon 2010; 41(1): 58-61.[http://dx.doi.org/10.1016/j.apergo.2009.04.005] [PMID: 19450792] ].

As well as being an important part of everyday life, the STS movement is a challenging movement for elderly individuals [12Hortobágyi T, Mizelle C, Beam S, DeVita P. Old adults perform activities of daily living near their maximal capabilities. J Gerontol A Biol Sci Med Sci 2003; 58(5): M453-60.[http://dx.doi.org/10.1093/gerona/58.5.M453] [PMID: 12730256] ] due to decreased strength of the knee extensor muscles [13Hughes MA, Myers BS, Schenkman ML. The role of strength in rising from a chair in the functionally impaired elderly. J Biomech 1996; 29(12): 1509-13.[http://dx.doi.org/10.1016/S0021-9290(96)80001-7] [PMID: 8945648] ]. Therefore, the STS movement is frequently incorporated in motor tests with varying degrees of difficulty to determine the strength of the lower limbs. Examples of motor tests including STS movements with bilateral execution are the 5-Repetition STS test [14Bohannon RW. Sit-to-stand test for measuring performance of lower extremity muscles. Percept Mot Skills 1995; 80(1): 163-6.[http://dx.doi.org/10.2466/pms.1995.80.1.163] [PMID: 7624188] ], the Timed Up & Go test [15Podsiadlo D, Richardson S. The timed “Up & Go”: A test of basic functional mobility for frail elderly persons. J Am Geriatr Soc 1991; 39(2): 142-8.[http://dx.doi.org/10.1111/j.1532-5415.1991.tb01616.x] [PMID: 1991946] ] as well as the 30-second chair test [16Jones CJ, Rikli RE, Beam WCA. A 30-s chair-stand test as a measure of lower body strength in community-residing older adults. Res Q Exerc Sport 1999; 70(2): 113-9.[http://dx.doi.org/10.1080/02701367.1999.10608028] [PMID: 10380242] ]. A motor test including unilateral STS movements is the European Fitness Badge [17Bös K, Brehm W, Klemm K, Schreck M, Pauly P. European Fitness Badge. Handbook for Instructors. Erasmus Plus Research Report. Project 557244-EEP-1-2014-1-DE-SPO-ECP. Frankfurt: DTB 2017.]. For widespread applicability of the STS movement as a diagnostic tool in the field of health- or age-related sports, the scalability of task difficulty is of particular importance. With advancing age, motor performance develops multidirectional, leading to an increased inter-individual variability in the diverse dimensions of motor performance [18Spirduso WW, MacRae PG. Motor performance and aging.Handbook of the psychology of aging 1990; 183-200.[http://dx.doi.org/10.1016/B978-0-12-101280-9.50017-6] ]. This trend can already be observed in middle adulthood (35-65 years) [6Tittlbach S, Woll A, Bös K. Motorische Entwicklung im frühen und mittleren Erwachsenenalter [Motor development in early and mid adulthood]. In: Baur J, Klenk C, Alfermann D, Eds. Handbuch motorische Entwicklung [Handbook of motor development]. 2nd rev. ed. Schorndorf: Hofmann 2009; 319-32.] and continues throughout late adulthood (> 65 years) [19Eichberg S, Mechling H. Motorische Entwicklung im höheren Erwachsenenalter [Motor development in late adulthood]. In: Baur J, Klenk C, Alfermann D, Eds. Handbuch motorische Entwicklung [Handbook of motor development]. 2nd rev. ed. Schorndorf: Hofmann 2009; 333-48.].

In the context of a motor test, STS movements generally have three degrees of freedom that can be manipulated to account for the heterogeneous developmental processes, and subsequently to avoid ceiling effects: (I) chair height, (II) unilateral or bilateral execution and (III) number of repetitions in a given time period. However, it was previously shown that bilateral STS movements from decreasing chair heights can cause high loads, especially in the knee and hip joints [20Arborelius UP, Wretenberg P, Lindberg F. The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising. Ergonomics 1992; 35(11): 1377-91.[http://dx.doi.org/10.1080/00140139208967399] [PMID: 1425567] , 21Rodosky MW, Andriacchi TP, Andersson GBJ. The influence of chair height on lower limb mechanics during rising. J Orthop Res 1989; 7(2): 266-71.[http://dx.doi.org/10.1002/jor.1100070215] [PMID: 2918425] ], which probably also applies to unilateral or repeated executions of an STS movement. Additionally, it should be considered that the musculoskeletal system of middle-aged and old adults often show impairments such as osteoarthritis, with the highest prevalence at the knee joint [22Litwic A, Edwards MH, Dennison EM, Cooper C. Epidemiology and burden of osteoarthritis. Br Med Bull 2013; 105: 185-99.[http://dx.doi.org/10.1093/bmb/lds038] [PMID: 23337796] , 23Zhang Y, Jordan JM. Epidemiology of osteoarthritis. Clin Geriatr Med 2010; 26(3): 355-69.[http://dx.doi.org/10.1016/j.cger.2010.03.001] [PMID: 20699159] ]. Against this background, it is crucial to consider the load applied to the lower extremities – especially the knee joint – of middle-aged or elderly subjects while performing STS movements within a motor test.

Knee joint load during bilateral STS movements has been extensively studied in the literature [24Crosbie J, Herbert RD, Bridson JT. Intersegmental dynamics of standing from sitting. Clin Biomech (Bristol, Avon) 1997; 12(4): 227-35.[http://dx.doi.org/10.1016/S0268-0033(97)00003-X] [PMID: 11415727] -26Sibella F, Galli M, Romei M, Montesano A, Crivellini M. Biomechanical analysis of sit-to-stand movement in normal and obese subjects. Clin Biomech (Bristol, Avon) 2003; 18(8): 745-50.[http://dx.doi.org/10.1016/S0268-0033(03)00144-X] [PMID: 12957561] ]. It is well documented that chair height decisively influences the difficulty of the movement task and lower chair heights lead to significantly increased moments at the knee joint, resulting in an increased knee joint load [13Hughes MA, Myers BS, Schenkman ML. The role of strength in rising from a chair in the functionally impaired elderly. J Biomech 1996; 29(12): 1509-13.[http://dx.doi.org/10.1016/S0021-9290(96)80001-7] [PMID: 8945648] , 20Arborelius UP, Wretenberg P, Lindberg F. The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising. Ergonomics 1992; 35(11): 1377-91.[http://dx.doi.org/10.1080/00140139208967399] [PMID: 1425567] , 21Rodosky MW, Andriacchi TP, Andersson GBJ. The influence of chair height on lower limb mechanics during rising. J Orthop Res 1989; 7(2): 266-71.[http://dx.doi.org/10.1002/jor.1100070215] [PMID: 2918425] , 27Su FC, Lai KA, Hong WH. Rising from chair after total knee arthroplasty. Clin Biomech (Bristol, Avon) 1998; 13(3): 176-81.[http://dx.doi.org/10.1016/S0268-0033(97)00039-9] [PMID: 11415785] ]. However, no studies have investigated knee joint load during unilateral STS movement of subjects in middle-to-late adulthood. It was shown by Yamako et al. [28Yamako G, Deng G, Totoribe K, Chosa E. A novel protocol to test age-related decreases in sit-to-stand movement abilities in healthy subjects. J Orthop Sci 2016; 21(4): 517-23.[http://dx.doi.org/10.1016/j.jos.2016.04.006] [PMID: 27188931] ] that 89.5% of men and 71.0% of women aged 60-70 are able to perform a unilateral STS movement. Given the increased inter-individual variability in motor abilities of subjects in mid and late adulthood, the level of difficulty and the resulting joint loads must be considered when using STS movements as a motor test.

Additionally, several studies found an uneven load distribution between the lower limbs during the bilateral STS movement [29Hesse S, Schauer M, Jahnke MT. Standing-up in healthy subjects: Symmetry of weight distribution and lateral displacement of the centre of mass as related to limb dominance. Gait Posture 1996; 4(4): 287-92.[http://dx.doi.org/10.1016/0966-6362(95)01051-3] -31Slajpah S, Kamnik R, Burger H, Bajd T, Munih M. Asymmetry in sit-to-stand movement in patients following transtibial amputation and healthy individuals. Int J Rehabil Res 2013; 36(3): 275-83.[http://dx.doi.org/10.1097/MRR.0b013e3283606235] [PMID: 23528389] ] as well as asymmetries in the knee extension muscles of the dominant and non-dominant limb [32Keller K, Engelhardt M. Strength and muscle mass loss with aging process. Age and strength loss. Muscles Ligaments Tendons J 2014; 3(4): 346-50.[PMID: 24596700] , 33Perry MC, Carville SF, Smith ICH, Rutherford OM, Newham DJ. Strength, power output and symmetry of leg muscles: Effect of age and history of falling. Eur J Appl Physiol 2007; 100(5): 553-61.[http://dx.doi.org/10.1007/s00421-006-0247-0] [PMID: 16847676] ]. Therefore, lower limb dominance should be considered when conducting biomechanical analyses of unilateral STS movements.

The present study aims to fulfill the research gap by analysing knee joint loads in a unilateral STS movement in a population of healthy, middle-aged adults under consideration of different chair heights and lower limb dominance.

2. MATERIAL & METHODS

2.1. Participants

A total of 19 subjects participated in this study (age: 52.2 ± 5.1 years; height: 173 ± 10 cm; weight: 71.8 ± 12.1 kg; BMI: 24.0 ± 2.9; 12 females). The age group was selected based on studies showing a decrease in strength abilities after the age of 40 [32Keller K, Engelhardt M. Strength and muscle mass loss with aging process. Age and strength loss. Muscles Ligaments Tendons J 2014; 3(4): 346-50.[PMID: 24596700] ] and though to maintain the feasibility of the movement task for the subject population [28Yamako G, Deng G, Totoribe K, Chosa E. A novel protocol to test age-related decreases in sit-to-stand movement abilities in healthy subjects. J Orthop Sci 2016; 21(4): 517-23.[http://dx.doi.org/10.1016/j.jos.2016.04.006] [PMID: 27188931] ]. Subjects were excluded from participation if they suffered from any self-reported pain, limited mobility in the lower extremities or any kind of balance disorder. The study was approved by the Institutional Review Board. All participants were informed about the protocol and gave their written informed consent before participating in the study.

2.2. Study Design

The research questions were addressed using a cross-sectional study design with subjects performing unilateral STS movements from three different chair heights as well as their dominant and non-dominant limb. Based on an extensive internet research on commercially available chair heights of different manufacturers, the low chair height was determined at 42 cm and the high chair height at 47 cm. However, if the chair height of 42 cm resulted in a knee flexion angle below 90°, both chair heights were increased by 5 cm resulting in a low chair height of 47 cm and a high chair height of 52 cm. An individual chair height resulting in a knee angle of 90° was added for enhanced inter-subject comparability. The mean chair height in this condition was 44.4 ± 3.5 cm.

2.3. Study Procedure

Following an independent warm-up, subjects were given standardized instructions regarding the execution of the task and were permitted to perform a practice trial. The subjects then performed a unilateral STS task under six different conditions (Fig. 1) in a randomized order. For each condition, three consecutive trials were recorded with a resting period of one minute between each trial and three minutes between each condition, resulting in a total of 18 trials per subject. Following each trial, the subjects were asked to rate their level of perceived exertion on the Borg scale [34Borg GA. Perceived exertion: A note on “history” and methods. Med Sci Sports 1973; 5(2): 90-3.[PMID: 4721012] ] ranging from 6 (no exertion) to 20 (maximal exertion). Unsuccessful trials were classified as maximal exertion.

Fig. (1)
Six testing conditions (left side) and experimental setup (right side).


The seating position was standardized by only allowing chair contact with the buttock (crotch at the anterior chair edge). The feet were positioned so that the shank was perpendicular to the ground. Both the seating and foot positions were marked to allow consistent positioning throughout all trials and conditions. The hands rested on the trunk during the entire trial to prevent active use of the upper limbs (Fig. 1). Subjects were equipped with standardized footwear (Puma Vellum).

2.4. Data Acquisition and Processing

3D biomechanical motion analysis was conducted to quantify knee joint loads during the STS movement. A 12-camera motion capture system (Vicon Motion Systems Ltd., Oxford, UK) with a recording frequency of 200 Hz and a force plate (AMTI, Watertown, Massachusetts, USA) with a recording frequency of 1000 Hz were used for data acquisition. Data from all valid trials were processed using Vicon Nexus software (v 1.8.5) and marker trajectories were filtered using a 4th order Butterworth filter with a cut-off frequency of 10 Hz. The Centre of Mass (COM), knee moments and forces were calculated using the Vicon Plug-in Gait model [35Vicon-Motion-Systems Ltd. Plug-In Gait 2010.]. Peak external knee moments and shear forces were normalized to body weight and served as dependent variables for the quantification of knee joint load.

Trials were considered invalid and excluded from analysis if no stable upright standing position (knee flexion angle < 25°) was achieved prior to foot strike of the contralateral limb, or if the arms were removed from the trunk. After exclusion of invalid trials, one trial of each condition was selected for analysis for each subject (2nd trial for 2 or 3 valid trials, 1st trial for one valid trial).

Movement initialization was determined as the first instance of the COM crossing the anterior chair edge. Movement termination was defined as no further extension of the knee joint. Seat-off was defined when contact with the chair ended and was detected by means of the vertical ground reaction force corresponding to 100% of the subject’s body weight [9Etnyre B, Thomas DQ. Event standardization of sit-to-stand movements. Phys Ther 2007; 87(12): 1651-66.[http://dx.doi.org/10.2522/ptj.20060378] [PMID: 17940102] ]. This detection method demonstrated reasonable accuracy during a validation trial using two force plates: a discrepancy of 0.017 (± 0.011) seconds was found compared to actual seat-off.

2.5. Statistical Analysis

All statistical tests were performed using IBM SPSS Statistics (v 24.0). Data were analysed for normal distribution using a Shapiro-Wilks normality test and for sphericity using Mauchly’s test. If sphericity was violated, a Greenhouse-Geisser correction was used. Four repeated-measures two-way ANOVAs were conducted to assess the effects of chair height and lower limb dominance on each of the dependent variables. In addition, effect sizes (ƞ2p) were calculated for main and interaction effects. Significant results of the ANOVAs were analysed in post hoc analyses with Bonferroni adjustment for multiple comparisons. Data of perceived exertion were analysed for differences due to chair height and lower limb dominance using a Friedman test and a Wilcoxon signed-rank test, respectively. Values of p < 0.05 were considered statistically significant.

3. RESULTS

Of the 19 subjects, 17 were able to successfully conduct the unilateral STS movement under all imposed conditions. Only two subjects were unable to perform the unilateral STS movement in the low and 90° conditions.

An overview of the peak knee shear forces and moments (means ± SD) during the unilateral STS movement under various conditions is given in Table 1.

Table 1
Overview of peak knee shear forces and moments in the sagittal and frontal plane (Mean ± SD for each of the six testing conditions as well as MW ± SD for each chair height averaged across both lower limbs). * represents a significant difference in post-hoc comparison to high chair height.


3.1. Knee Joint Load in the Sagittal Plane

There was no significant main effect of chair height (p = 0.48; = 0.05) or limb dominance (p = 0.84; < 0.01) on the peak external flexion moment. Likewise, there was no significant interaction effect of chair height and limb dominance (p = 0.41; = 0.06; Fig. 2).

Chair height had a significant main effect on anterior knee shear force (p = 0.01; = 0.27). However, there was no significant main effect of limb dominance (p = 0.43; = 0.05) nor a significant interaction effect of chair height and limb dominance (p = 0.18; = 0.12). Post-hoc analysis showed that low chair heights caused significantly higher anterior shear forces (p = 0.02).

Fig. (2)
Time-normalized knee moments (Mean ± SD) in the sagittal plane for each of the six testing conditions.


3.2. Knee Joint Load in the Frontal Plane

In terms of peak adduction moment, there was a significant effect of chair height (p = 0.02; = 0.33) but not limb dominance (p = 0.44; = 0.04). The interaction effect of chair height and limb dominance was not significant (p = 0.34; = 0.07). Post-hoc analysis showed significantly lower peak adduction moments in the high chair height condition compared to the low chair height condition (p < 0.01, Fig. 3).

The peak lateral shear force at the knee was significantly affected by chair height (p < 0.01; = 0.43) and the interaction of chair height and limb dominance (p = 0.04; = 0.2), but not limb dominance itself (p = 0.32; = 0.07). Post-hoc analysis showed significantly lower peak shear forces for high chair height than for low height (p < 0.01) and for high chair height than for the 90° condition (p = 0.02).

Fig. (3)
Time-normalized knee moments (Mean ± SD) in the frontal plane for each of the six testing conditions.


3.3. Level of Perceived Exertion

Individual exertion ratings ranged from 7.1 (extremely light) to 18.1 (very/extremely hard). The mean level of perceived exertion was 11.1 (± 2.8) for the high chair height, 12.5 (± 3.5) for the low chair height and 13.5 (± 3.1) in the 90° chair height condition. For the dominant and non-dominant lower limb, the mean ratings were 12.3 (± 3.3) and 12.3 (± 3.2) respectively, a non-significant difference (p = 0.19). The Friedman test revealed that chair height had a significant main effect on the level of perceived exertion (p < 0.01). Subsequent pairwise comparison showed that rising from the high chair height was perceived as less effort than rising from the low height (p = 0.03) and the 90° condition (p < 0.01).

4. DISCUSSION

To the best of our knowledge, this is the first study to investigate knee joint load during a unilateral STS task. The present study revealed the following main findings: (I) chair height had a significant impact on the peak adduction moment as well as on the anterior and lateral peak shear forces acting at the knee joint during the unilateral STS movement: Forces and moments were significantly lower at higher chair heights. (II) Lower limb dominance had no effect on knee joint load, determined via peak knee moments and forces. (III) Chair height but not limb dominance significantly affected the level of perceived exertion during the execution of unilateral STS movements.

4.1. Unilateral STS Movement as a Motor Skill Test in Health-related Sports or Sports for the Elderly

Various test systems are currently used to diagnose motor ability levels in health-related sports as well as sports for the elderly [5Bös K, Ed. Sportmotorische Tests, Motorische Funktionstests, Fragebögen zur körperlich-sportlichen Aktivität und sportpsychologische Diagnoseverfahren [Handbook of motor tests: sports motor tests, functional motor tests, questionnaires for physical activity and sport psychological diagnostic methods]. 3rd ed Göttingen: Hogrefe; 2017.]. With regard to the increased inter-individual variability in motor abilities in middle [6Tittlbach S, Woll A, Bös K. Motorische Entwicklung im frühen und mittleren Erwachsenenalter [Motor development in early and mid adulthood]. In: Baur J, Klenk C, Alfermann D, Eds. Handbuch motorische Entwicklung [Handbook of motor development]. 2nd rev. ed. Schorndorf: Hofmann 2009; 319-32., 18Spirduso WW, MacRae PG. Motor performance and aging.Handbook of the psychology of aging 1990; 183-200.[http://dx.doi.org/10.1016/B978-0-12-101280-9.50017-6] ] and late [18Spirduso WW, MacRae PG. Motor performance and aging.Handbook of the psychology of aging 1990; 183-200.[http://dx.doi.org/10.1016/B978-0-12-101280-9.50017-6] , 19Eichberg S, Mechling H. Motorische Entwicklung im höheren Erwachsenenalter [Motor development in late adulthood]. In: Baur J, Klenk C, Alfermann D, Eds. Handbuch motorische Entwicklung [Handbook of motor development]. 2nd rev. ed. Schorndorf: Hofmann 2009; 333-48.] adulthood, the scalability of motor test difficulty is an important aspect when creating test variants appropriate for the intended subject population.

The results of this study show that the unilateral STS movement was subjectively perceived as moderately strenuous with mean ratings between 11 and 13 on the Borg scale. This indicates the feasibility of this movement task for the population under investigation. However, the inter-individual differences in motor performance become apparent in the wide range of individual exertion ratings. These findings stress the need for scalable motor tests and the requirement of motor tests with difficulty levels beyond those of bilateral STS tests.

In terms of the ecological validity of the unilateral STS motor test in comparison to ADLs, it is acknowledged that most everyday STS movements are executed bilaterally. However, there are several everyday situations, e.g. car egress, which are performed unilaterally by all subjects in early adulthood and even most of the subjects in late adulthood [36Chateauroux E, Wang X. Car egress analysis of younger and older drivers for motion simulation. Appl Ergon 2010; 42(1): 169-77.[http://dx.doi.org/10.1016/j.apergo.2010.07.001] [PMID: 20797693] ]. As motor tests require rigorous objectivity, ADL movements like car egress [36Chateauroux E, Wang X. Car egress analysis of younger and older drivers for motion simulation. Appl Ergon 2010; 42(1): 169-77.[http://dx.doi.org/10.1016/j.apergo.2010.07.001] [PMID: 20797693] ] with its many degrees of freedom are not as suitable as the unilateral STS movement, which can be controlled more easily.

4.2. Knee Joint Load During the Unilateral STS Movement

Peak moments and forces are frequently used to quantify knee joint load [37Hunt MA, Birmingham TB, Bryant D, et al. Lateral trunk lean explains variation in dynamic knee joint load in patients with medial compartment knee osteoarthritis. Osteoarthritis Cartilage 2008; 16(5): 591-9.[http://dx.doi.org/10.1016/j.joca.2007.10.017] [PMID: 18206395] , 38Messier SP, Gutekunst DJ, Davis C, DeVita P. Weight loss reduces knee-joint loads in overweight and obese older adults with knee osteoarthritis. Arthritis Rheum 2005; 52(7): 2026-32.[http://dx.doi.org/10.1002/art.21139] [PMID: 15986358] ]. During the unilateral STS movement, particularly high external flexion (1.44-1.52 Nm/kg) and adduction moments (0.52-0.67 Nm/kg) as well as anterior (3.90-4.19 N/kg) and lateral (1.43-1.94 N/kg) shear forces were observed.

Other studies analysing the dynamics of ADLs reported peak flexion moments of 0.7-1.5 Nm/kg during stair ascent, 0.5 Nm/kg during level walking [39Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Post 2002; 16(1): 31-7.[http://dx.doi.org/10.1016/S0966-6362(01)00201-6] [PMID: 12127184] ] and 0.4 Nm/kg during the bilateral STS movement with various knee angles [26Sibella F, Galli M, Romei M, Montesano A, Crivellini M. Biomechanical analysis of sit-to-stand movement in normal and obese subjects. Clin Biomech (Bristol, Avon) 2003; 18(8): 745-50.[http://dx.doi.org/10.1016/S0268-0033(03)00144-X] [PMID: 12957561] , 40Galli M, Cimolin V, Crivellini M, Campanini I. Quantitative analysis of sit to stand movement: Experimental set-up definition and application to healthy and hemiplegic adults. Gait Posture 2008; 28(1): 80-5.[http://dx.doi.org/10.1016/j.gaitpost.2007.10.003] [PMID: 18618956] ]. Thus, the peak flexion moments observed during the unilateral STS movement are comparable to those reported for stair ascent, which at times also requires unilateral lifting of the body weight. However, the peak knee flexion moments are three to four times higher than during level walking or the bilateral STS movement. The increased knee flexion moments in unilateral STS movements compared to level walking can rationally be attributed to the increased distance between the support area and the COM due to its more posterior position, causing a larger lever arm for the ground reaction force vector. Similarly, increased knee flexion moments in unilateral STS movements compared to bilateral STS movements are caused as the moment produced by the COM around the knee joint is not allocated to two but only one knee joint. The peak knee adduction moments during the unilateral STS movement are similar to those described for stair ascent [39Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Post 2002; 16(1): 31-7.[http://dx.doi.org/10.1016/S0966-6362(01)00201-6] [PMID: 12127184] ]. The peak knee anterior shear forces of 4.7 N/kg during stair ascent and 3.2 N/kg during level walking [39Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Post 2002; 16(1): 31-7.[http://dx.doi.org/10.1016/S0966-6362(01)00201-6] [PMID: 12127184] ] are slightly higher and lower, respectively, than those found in the present study. Finally, the peak lateral shear force is, in either case, higher than during stair ascent (1.3 N/kg) or level walking (1.5 N/kg) [39Costigan PA, Deluzio KJ, Wyss UP. Knee and hip kinetics during normal stair climbing. Gait Post 2002; 16(1): 31-7.[http://dx.doi.org/10.1016/S0966-6362(01)00201-6] [PMID: 12127184] ].

In summary, it can be stated that the forces and moments acting at the knee joint during the unilateral STS movement are higher than those previously described for level walking but similar to those for stair ascent. However, it should be considered that joint angles during stair ascent are not directly comparable to those during the unilateral STS movement [40Galli M, Cimolin V, Crivellini M, Campanini I. Quantitative analysis of sit to stand movement: Experimental set-up definition and application to healthy and hemiplegic adults. Gait Posture 2008; 28(1): 80-5.[http://dx.doi.org/10.1016/j.gaitpost.2007.10.003] [PMID: 18618956] ] and an altered impact on the underlying biological structures is therefore presumed [41Nagura T, Dyrby CO, Alexander EJ, Andriacchi TP. Mechanical loads at the knee joint during deep flexion. J Orthop Res 2002; 20(4): 881-6.[http://dx.doi.org/10.1016/S0736-0266(01)00178-4] [PMID: 12168682] ].

4.3. Effect of Chair Height on Knee Joint Load During the Unilateral STS Movement

Chair height influenced peak adduction moment as well as peak anterior and lateral shear forces acting at the knee joint. High chair height resulted in significantly lower peak adduction moments than the low chair height. We suspect this to be due to an increased lateral evasive movement of the knee during the unilateral STS movement from the low chair height leading to a more medial course of the ground reaction force vector. These findings might be important when executing STS movements with subjects suffering from medial compartment knee osteoarthrosis, as increased knee adduction moments have been associated with increased medial compartment knee joint load [42Kutzner I, Trepczynski A, Heller MO, Bergmann G. Knee adduction moment and medial contact force-facts about their correlation during gait. PLoS One 2013; 8(12): e81036.[http://dx.doi.org/10.1371/journal.pone.0081036] [PMID: 24312522] ]. The increasing anterior shear forces observed with decreasing chair height might be explained by a greater contraction of the quadriceps muscle. This presumption is supported by findings of increasing vastus lateralis activity with decreasing chair height during the bilateral STS movement [20Arborelius UP, Wretenberg P, Lindberg F. The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising. Ergonomics 1992; 35(11): 1377-91.[http://dx.doi.org/10.1080/00140139208967399] [PMID: 1425567] ].

Altogether, these results are consistent with previous studies on the bilateral STS movement [20Arborelius UP, Wretenberg P, Lindberg F. The effects of armrests and high seat heights on lower-limb joint load and muscular activity during sitting and rising. Ergonomics 1992; 35(11): 1377-91.[http://dx.doi.org/10.1080/00140139208967399] [PMID: 1425567] , 21Rodosky MW, Andriacchi TP, Andersson GBJ. The influence of chair height on lower limb mechanics during rising. J Orthop Res 1989; 7(2): 266-71.[http://dx.doi.org/10.1002/jor.1100070215] [PMID: 2918425] , 27Su FC, Lai KA, Hong WH. Rising from chair after total knee arthroplasty. Clin Biomech (Bristol, Avon) 1998; 13(3): 176-81.[http://dx.doi.org/10.1016/S0268-0033(97)00039-9] [PMID: 11415785] ], which have reported increasing moments and task difficulty with reduced chair height.

4.4. Effect of Lower Limb Dominance on Knee Joint Load During the Unilateral STS Movement

Despite the asymmetries in knee extensor muscle strength reported in several studies of comparably-aged subject groups [32Keller K, Engelhardt M. Strength and muscle mass loss with aging process. Age and strength loss. Muscles Ligaments Tendons J 2014; 3(4): 346-50.[PMID: 24596700] , 33Perry MC, Carville SF, Smith ICH, Rutherford OM, Newham DJ. Strength, power output and symmetry of leg muscles: Effect of age and history of falling. Eur J Appl Physiol 2007; 100(5): 553-61.[http://dx.doi.org/10.1007/s00421-006-0247-0] [PMID: 16847676] ] no differences were found between the dominant and non-dominant limb in this study. Therefore, the results suggest that lower limb dominance has no impact on knee joint load during the unilateral STS movement within the selected experimental conditions and population.

4.5. Limitations

The present study is the first to investigate knee joint load during the unilateral STS movements frequently included in motor test profiles [17Bös K, Brehm W, Klemm K, Schreck M, Pauly P. European Fitness Badge. Handbook for Instructors. Erasmus Plus Research Report. Project 557244-EEP-1-2014-1-DE-SPO-ECP. Frankfurt: DTB 2017., 43Bös K, Wydra G, Karisch G. Gesundheitsförderung durch Bewegung, Spiel und Sport: Ziele und Methoden des Gesundheitssports in der Klinik [Health promotion by motion, play and sports: aims and methods of health related sports in the clinic]. Perimed-Fachbuch-Verlag-Ges 1992.]. However, it has to be considered that in the majority of biomechanical studies, with exception of those using instrumented joint replacements [44Kutzner I, Heinlein B, Graichen F, et al. Loading of the knee joint during activities of daily living measured in vivo in five subjects. J Biomech 2010; 43(11): 2164-73.[http://dx.doi.org/10.1016/j.jbiomech.2010.03.046] [PMID: 20537336] ], knee forces and moments are calculated using the inverse dynamics approach. Therefore, comparability of study results always depends on the applied signal processing routines (e.g. digital filtering) and the inverse dynamics model used. These issues most likely influence the calculated forces and moments. For this reason, the signal processing methods used in this study were geared towards the relevant literature [45Kristianslund E, Krosshaug T, van den Bogert AJ. Effect of low pass filtering on joint moments from inverse dynamics: Implications for injury prevention. J Biomech 2012; 45(4): 666-71.[http://dx.doi.org/10.1016/j.jbiomech.2011.12.011] [PMID: 22227316] ] and the authors used a biomechanical model widespread in the field of clinical biomechanics [46Schwartz MH, Rozumalski A, Trost JP. The effect of walking speed on the gait of typically developing children. J Biomech 2008; 41(8): 1639-50.[http://dx.doi.org/10.1016/j.jbiomech.2008.03.015] [PMID: 18466909] ]. However, there are several underlying simplifications to the Plug-in Gait model [35Vicon-Motion-Systems Ltd. Plug-In Gait 2010.] used in the present study, as there are to any biomechanical model of the human body. The issues emerging from these simplifications are discussed in a number of publications along with the benefit of a widespread distribution of this model in clinical biomechanics. There is, therefore, a certain comparability of published study results [46Schwartz MH, Rozumalski A, Trost JP. The effect of walking speed on the gait of typically developing children. J Biomech 2008; 41(8): 1639-50.[http://dx.doi.org/10.1016/j.jbiomech.2008.03.015] [PMID: 18466909] ]. Moreover, the present study focused on a population of healthy, middle-aged individuals with normal weight. The investigated population was generally able to perform a unilateral STS movement and the observed loads seemed acceptable from the authors’ point of view, especially as the unilateral STS movement is not intended to be performed in a high volume repetitive manner in the context of a motor test [17Bös K, Brehm W, Klemm K, Schreck M, Pauly P. European Fitness Badge. Handbook for Instructors. Erasmus Plus Research Report. Project 557244-EEP-1-2014-1-DE-SPO-ECP. Frankfurt: DTB 2017.]. In addition, the average level of perceived exertion did not exceed 13.5 in any of the investigated conditions, representing medium perceived exertion.

CONCLUSION

The present study revealed the following main findings: (I) Forces and moments acting at the knee joint during a unilateral STS movement are similar to those provoked by other ADLs. (II) Forces and moments acting at the knee joint as well as the subjectively perceived exertion increase with decreasing chair height. (II) Lower limb dominance has no effect on the knee joint load.

These results document the objective and subjective feasibility of the unilateral STS movement as well as the tenability of the arising loads for the musculoskeletal system and therefore its suitability as a motor test in the population under investigation. However, these results cannot be generalized to e.g. obese or older (> 65 years) populations. For these populations, further investigations are needed to quantify knee joint loads during the bi- and unilateral STS movement from various chair heights.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE

The study was approved by the Institutional Review Board.

HUMAN AND ANIMAL RIGHTS

No animals were used for this study. All humans research procedures performed in the current study were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

CONSENT FOR PUBLICATION

All participants were informed about the protocol and gave their written informed consent before participating in the study.

CONFLICT OF INTEREST

The authors declare no conflict of interest, financial or otherwise.

ACKNOWLEDGEMENTS

We acknowledge support from Deutsche Forschungsgemeinschaft and Open Access Publishing Fund of Karlsruhe Institute of Technology. Additionally, we sincerely thank K. Franke and K. Wöhlken for their support during the data acquisition process.

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(Chiba University, Japan)

"Open Access journals offer an innovative and efficient way of publication for academics and professionals in a wide range of disciplines. The papers published are of high quality after rigorous peer review and they are Indexed in: major international databases. I read Open Access journals to keep abreast of the recent development in my field of study."


Daniel Shek
(Chinese University of Hong Kong, Hong Kong)

"It is a modern trend for publishers to establish open access journals. Researchers, faculty members, and students will be greatly benefited by the new journals of Bentham Science Publishers Ltd. in this category."


Jih Ru Hwu
(National Central University, Taiwan)


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