Examination of the Relationship between Straight Leg Raising Repetition Count and both Knee Extension Strength and Walking Independence in Patients with Collagen Disease

ABSTRACT

Objective: The aim of the current study was to examine the relationship between the straight leg raising (SLR) repetition count and both the knee extension strength (KES) and walking independence. Methods: We enrolled 106 inpatients aged ≥20 years with collagen disease in a cross-sectional study. We measured the SLR repetition count, KES, and walking independence of each participant. The correlations between the SLR repetition count and KES/walking independence were then examined. Furthermore, patients were divided into three groups depending on their SLR repetition count (low, medium, or high), and the differences among the groups were analyzed. Results: A moderately significant correlation was found between the SLR repetition count and KES (right: r=0.46, P<0.01; left: r=0.55, P<0.01). Moreover, there was a strong correlation between the maximum SLR repetition count and walking independence (r=0.74, P<0.01). Differences in KES and walking independence were observed among the SLR repetition groups (P<0.01). KES and walking independence in the group with a low repetition count were 0.08±0.04 kgf/kg and 1 (1–4) point, whereas the values in the group with a medium repetition count were 0.25±0.08 kgf/kg and 5 (1–7) points and those in the group with a high repetition count were 0.40±0.13 kgf/kg and 7 (4–7) points. Conclusion: The SLR repetition count is related to KES and walking independence. SLR repetition counts can be used in the clinical setting for the assessment of lower limb strength and walking independence.

INTRODUCTION

There are several methods for assessing lower limb function in the context of rehabilitation, including tests for measuring lower limb muscle strength. These methods include manual muscle testing (MMT)¹⁾ using hand-held dynamometers (HHDs)²⁾ and isokinetic dynamometers³⁾; balance tests, such as the functional reach test (FRT)⁴⁾ and the Berg balance scale (BBS)⁵⁾; and complex performance tests, such as the timed up and go (TUG) test⁶⁾ and the 30-s chair stand (CS-30) test.⁷⁾ These tests measure walking independence with good validity and reliability.^8,9,10) However, such tests require a measuring instrument and a suitable place to perform the measurements, and they can be time-consuming. Hospitalized patients in acute care hospitals are often bed-bound because of problems related to treatment and/or their general condition. In particular, those with collagen disease are often confined to bed to undergo corticosteroid treatment, making it difficult to perform muscle strength tests that require a designated place and time. Therefore, we believe that a simple test that can be performed at the bedside is desirable for patients with collagen disease.

Straight leg raising (SLR) is widely used by physiotherapists in clinical situations. Although hip flexion and knee extension in the sitting position are single-muscle evaluations for the iliopsoas and quadriceps, SLR requires hip flexor, knee extensor, and abdominal muscle activities.^11,12) Moreover, even in patients who cannot achieve a sitting position or for whom the required rest level demands the lying position, SLR can be easily performed with the patient on a bed, irrespective of their mobility. Furthermore, the test results can be easily quantified as the SLR repetition count. Therefore, we used the SLR repetition count to evaluate lower limb function. We hypothesized that the SLR repetition count is related to the muscular strength of the lower limbs and to walking independence.

The purpose of the current study was to examine the relationships between the SLR repetition count and knee extension strength (KES) and between the SLR repetition count and walking independence in patients with collagen disease. The overall aim was to find a simple method for evaluating lower limb function that can be used at the bedside in the acute phase without requiring specific measuring instruments or a specific measurement time or place.

MATERIALS AND METHODS

The current study was cross-sectional by design and was performed according to the principles of the Declaration of Helsinki. We enrolled 117 collagen disease patients age more than 20 years who were able to undergo assessment. The patients were hospitalized at Hyogo College of Medicine Hospital between April 2012 and March 2017 and had requested help with rehabilitation to maintain and improve their physical function. The exclusion criteria were as follows: patients who had undergone orthopedic surgery during this hospitalization, patients with severe joint deformity, patients with apparent central nervous symptoms, patients with cognitive impairment, patients who could not walk as a result of poor respiratory or circulatory function, patients who could not walk because of pain, and patients with severe sensory disorders. After excluding patients who met the exclusion criteria and patients with insufficient data for analysis, 106 patients were finally analyzed. The study was approved by the Hyogo College of Medicine Ethics Review Committee (Approval No. 2715). Informed consent was obtained from the 106 patients on the basis that they could opt-out at a later stage if they so wished.

The following information was collected from patients’ medical records: sex, age, height, body weight, body mass index (BMI), collagen disease diagnosis, comorbidities, past history, duration of hospitalization, dose of corticosteroids, and blood chemical analysis data. The following items were examined: C-reactive protein, total protein, albumin, red blood cells, hemoglobin, and creatinine. In addition, the SLR repetition count, the KES, and walking independence were assessed.

SLR Repetition Count

The SLR¹³⁾ repetition count was measured with the patient supine with their arms folded over the trunk. The participants raised their lower limb with the knee extended and the ankle dorsiflexed; the contralateral lower limb was extended on the bed. The movement counted as one repetition once leg elevation was achieved with a hip joint flexure angle of ≥30°. The activity was performed at a rate of one repetition per 2 s (the leg was raised for 1 s and placed down for 1 s). The count was continued until participants were no longer able to lift their legs or until they were no longer able to reach a hip joint angle of 30°. SLR with obvious hip external/internal rotation or obvious knee flex by knee extension lag was not counted. Measurement was performed with a maximum number of repetitions set at 30. Measurements were performed for each leg, and the largest value was used in the analysis.

Knee Extension Strength

HHDs¹⁴⁾ (μ-tas MT1; ANIMA Co., Tokyo, Japan) were used to measure knee extension strength (KES) as an index of lower-limb muscle strength. Measurements were made with the patient in the sitting position with the upper limbs folded in front of the chest. When the knees were flexed at approximately 90°, the sensor pad was placed on the distal part of the lower leg and the length of the fixing belt was adjusted. Isometric knee extension with maximal effort was performed for 5 s. Measurement was performed twice on each leg. The value used in the analysis was the higher of the two measurements divided by the body weight (i.e., the muscle-strength-to-body-weight ratio: kgf/kg).

Walking Independence

Walking independence was evaluated using the functional independence measure (FIM).¹⁵⁾ Walking ability was given a score out of 7 (1=total assistance from a helper, 2=maximal assistance from a helper, 3=moderate assistance from a helper, 4=minimal assistance from a helper, 5=supervision or setup from a helper, 6=modified independence with no helper, 7=complete independence with no helper). The use of a walker was not permitted. However, we permitted the use of aids such as canes, which are used in everyday life, to eliminate any bias resulting from allowing the use of an assistive device.

Statistical Analyses

Normality in all data was confirmed using the Shapiro-Wilk test. Correlations between the SLR repetition count and KES and between the SLR repetition count and walking independence were examined. Items that were normally distributed on an interval or proportional scale were analyzed using Pearson’s correlation coefficient, and non-normally distributed variables were analyzed using Spearman’s rank correlation coefficient. To avoid spurious correlations, partial correlation coefficients were calculated using the following control variables: sex, age, BMI, diagnosis, comorbidities, past history, duration of hospitalization, dose of corticosteroids, and blood chemical analysis data. Furthermore, the patients were stratified by the SLR repetition count: 0–9 (low group), 10–29 (medium group), and ≥30 (high group). Differences among the groups were then analysed. One-way analysis of variance was performed on items that were recognized as normally distributed on an interval or proportional scale. The Kruskal-Wallis test was used when items were non-normally distributed on an ordinal scale. Statistical analysis was performed with SPSS 17.0 J (SPSS Japan, Inc., Tokyo, Japan). Statistical significance was set at P<0.05.

RESULTS

Table 1 shows the patient characteristics, diagnoses, and measured values. The correlation coefficients between the SLR repetition count and KES/walking FIM are shown in table 2. A moderate significant correlation was found between the SLR repetition count and KES (right: Rs=0.46, P<0.01; left: Rs=0.55, P<0.01). In addition, there was a strong correlation between the maximum SLR repetition count and walking independence (Rs=0.74, P<0.01). Furthermore, differences were observed in the maximum KES and walking FIM between the three SLR repetition count groups (Table 3) (P<0.01).

Table 1. Patient characteristics, diagnoses, and measurements (n=106)

Sex, n (%)
Male	25 (23.6)
Female	81 (76.4)
Age, years, median (range)	70 (37–85)
Height, cm, mean±SD	156.6±8.0
Weight, kg, median (range)	50.0 (28.0–98.0)
Body mass index, kg/m2, median (range)	19.9 (11.6–41.3)
Diagnosis, n (%)
Dermatomyositis	20 (18.9)
Rheumatoid arthritis	16 (15.1)
Polymyositis	15 (14.2)
ANCA-associated vasculitis	14 (13.2)
Systemic lupus erythematosus	13 (12.3)
Systemic sclerosis	10 (9.4)
Polymyalgia rheumatica	3 (2.8)
Sjögren’s syndrome	3 (2.8)
Behcet’s disease	3 (2.8)
Mixed connective tissue disease	2 (1.9)
Ankylosing spondylitis	2 (1.9)
Cryoglobulinemia	2 (1.9)
Polyarteritis nodosa	1 (0.9)
Temporal arthritis	1 (0.9)
Adult-onset Still’s disease	1 (0.9)
Comorbidities, n (%)
Lung disease	42 (39.6)
Diabetes mellitus	33 (31.1)
Hypertension	27 (25.5)
Heart disease	7 (6.6)
Renal failure	3 (2.8)
Past history, n (%)
Orthopedics such as knee osteoarthritis and spinal stenosis etc.	22 (20.8)
Stroke	4 (3.8)
Duration of hospitalization, days, median (range)	23 (1–238)
Dose of corticosteroid, mg/day, median (range)	15 (0–60)
Blood chemical analysis, mean±SD
C-reactive protein, mg/dL	1.1±2.4
Total protein, g/dL	6.0±0.9
Albumin, g/dL	3.1±0.6
Red blood cells, g/dL	379.9±63.0
Hemoglobin, g/dL	11.3±1.9
Creatinine, mg/dL	0.7±0.9
KES, kgf/kg, mean±SD
Right	0.30±0.15
Left	0.30±0.15
SLR repetition count, times, median (range)
Right	30 (0–30)
Left	30 (0–30)
FIM-Walking, n (%)
1 point	10 (9.4)
2 points	4 (3.8)
3 points	3 (2.8)
4 points	13 (12.3)
5 points	8 (7.5)
6 points	8 (7.5)
7 points	60 (56.6)

SD, standard deviation; ANCA, anti-neutrophil cytoplasmic antibody; KES, knee extention strength; SLR, straight leg raising; FIM, Functional Independence Measure.

Table 2. Correlation coefficient for SLR repetition count versus KES and walking FIM

	KES-Right		KES-Left		KES-Maximum		FIM-Walking
	CC	PCC	CC	PCC	CC	PCC	CC	PCC
SLR repetition count-Right	0.69**	0.46**
SLR repetition count-Left			0.73**	0.55**
SLR repetition count-Maximum					0.71**	0.52**	0.76**	0.74**

CC, correlation coefficient; PCC, partial correlation coefficient.

**P<0.01.

Table 3.  Comparison of KES and walking FIM between groups stratified by SLR repetition count

	Low group	Medium group	High group	P value
KES-Maximum, kgf/kg, mean±SD	0.08±0.04	0.25±0.08	0.40±0.13	<0.01
FIM-Walking, points, median (range)	1 (1–4)	5 (1–7)	7 (4–7)	<0.01

Low group: SLR repetition count 0–9 times, medium group: 10–29 times, high group: ≥30 times.

DISCUSSION

In this study, we identified significant correlations between the SLR repetition count and KES and between the SLR repetition count and walking independence. Moreover, differences in the maximum KES and walking FIM were observed between the three SLR repetition count groups.

SLR requires the activity of the knee extensor muscles¹⁶⁾; therefore, it is intuitive to assume that the SLR repetition count and KES are correlated. However, because the partial correlation coefficient was lower than the correlation coefficient, this relationship may be biased by age and other individual-related factors. The SLR repetition count and walking independence were found to be strongly correlated, and the partial correlation coefficient was very similar to the correlation coefficient. Therefore, the relationship between the SLR repetition count and walking independence does not appear to be biased by patient age or other individual-related factors. Statistically significant differences were observed among the three groups stratified according to the SLR repetition count. In particular, the KES and walking independence (FIM) in the high group were 0.40±0.13 kgf/kg and 7 (4–7) points. Therefore, it appears that an SLR repetition count ≥30 and KES of approximately 0.4 kgf/kg will increase the likelihood of unsupported walking. Because KES affects walking ability,¹⁷⁾ the higher the KES, the better the walking ability.¹⁸⁾ SLR requires hip flexor, knee extensor, and abdominal muscle activities,^11,12) and reflects lower limb function, thereby explaining its high correlation with walking ability.

Compared with other examinations, MMT is a simple and widely used muscle strength evaluation tool that does not require instruments. However, the interpretation of the results is somewhat subjective. In particular, when muscle strength is 3–5 in terms of MMT, the results can be hard to accurately assess.¹⁹⁾ In contrast, SLR is easy to quantify as the number of repetitions and is considered to be more objective than MMT. HHDs are small, portable, and inexpensive compared to isokinetic dynamometers. HHDs are also reported to be reliable.²⁰⁾ However, the measurement instrument itself is necessary and it is required to perform measurements with the patient in the sitting position.²¹⁾ In contrast, the SLR repetition count does not require evaluation equipment and it is not necessary for patients to be in the sitting position.

The SLR repetition count can be measured with the patient in the supine position on a bed. The CS-30 test is often impractical because many elderly people cannot stand up repeatedly with their arms folded.²²⁾ In contrast, the SLR repetition count can be used for elderly people who cannot stand up from a chair because it can be easily performed on a bed, regardless of the mobility of the patient. The TUG test requires a space of at least 3 m and can sometimes be difficult to measure at the bedside. However, SLR can even be performed by people who are receiving continuous infusions because it does not require a specific location. Care must be taken, however, because SLR is not as reliable as other methods and does not comprehensively evaluate lower limb muscle strength and balance function like the TUG and CS-30 tests do.^23,24)

STUDY LIMITATIONS

There are several limitations to the current study. First, we employed a cross-sectional design and examined only the relevance of the SLR repetition count to walking independence. It will be necessary to verify the predictors of walking independence in a longitudinal study in the future. Second, because enrolment in the study was not targeted at inpatients with all types of collagen disease and because we only included patients who were referred for rehabilitation and were able to perform measurement procedures, some selection bias might have been introduced. Third, although the participants had various diagnoses, the specific characteristics of the diseases were not considered. However, when calculating partial correlation coefficients, the diagnosis was input as a control variable. Fourth, because it was difficult to identify the definite time of diagnosis from the medical records, it was not possible to clarify the history of the diagnosis in each case. Finally, the inter-rater reliability of the SLR repetition count has not been evaluated. Therefore, we should consider the inter-rater reliability in future studies.

CONCLUSIONS

The SLR repetition count is related to KES and walking independence. Measurement of the SLR repetition count is simple and does not require special equipment. This method can be used in the clinical setting for the assessment of lower limb strength and walking independence.

ACKNOWLEDGEMENTS

The authors would like to thank the study participants and the physiotherapists at the hospital’s Rehabilitation Department. The funding source had no role in the study design; in the collection, analysis, and interpretation of the data; in the writing of the report; or in the decision to submit the article for publication.

CONFLICTS OF INTEREST

The authors declare that there are no conflicts of interest.

REFERENCES

• 1.  Hislop 2013: Saunders.
• 2.  Deones VL, Wiley SC, Worrell T: Assessment of quadriceps muscle performance by a hand-held dynamometer and an isokinetic dynamometer. J Orthop Sports Phys Ther 1994;20:296–301. PMID:7849749, DOI:10.2519/jospt.1994.20.6.296
• 3.  Martin HJ, Yule V, Syddall HE, Dennison EM, Cooper C, Aihie Sayer A: Is hand-held dynamometry useful for the measurement of quadriceps strength in older people? A comparison with the gold standard Bodex dynamometry. Gerontology 2006;52:154–159. PMID:16645295, DOI:10.1159/000091824
• 4.  Duncan PW, Weiner DK, Chandler J, Studenski S: Functional reach: a new clinical measure of balance. J Gerontol 1990;45:M192–M197. PMID:2229941, DOI:10.1093/geronj/45.6.M192
• 5.  Berg KO, Wood-Dauphinee SL, Williams JI, Maki B: Measuring balance in the elderly: validation of an instrument. Can J Public Health 1992;83(Suppl 2):S7–S11.
• 6.  Podsiadlo D, Richardson S: The timed “Up & Go”: a test of basic functional mobility for frail elderly persons. J Am Geriatr Soc 1991;39:142–148. PMID:1991946, DOI:10.1111/j.1532-5415.1991.tb01616.x
• 7.  Jones CJ, Rikli RE, Beam WC: A 30-s chair-stand test as a measure of lower body strength in community-residing older adults. Res Q Exerc Sport 1999;70:113–119. PMID:10380242, DOI:10.1080/02701367.1999.10608028
• 8.  Nankaku M, Ito H, Furu M, Kuriyama S, Nakamura S, Ikeguchi R, Matsuda S: Preoperative factors related to the ambulatory status at 1 year after total knee arthroplasty. Disabil Rehabil 2017;1–4. PMID:28478687, DOI:10.1080/09638288.2017.1323025
• 9.  Nankaku M, Tsuboyama T, Akiyama H, Kakinoki R, Fujita Y, Nishimura J, Yoshioka Y, Kawai H, Matsuda S: Preoperative prediction of ambulatory status at 6 months after total hip arthroplasty. Phys Ther 2013;93:88–93. PMID:23001525, DOI:10.2522/ptj.20120016
• 10.  Hirano Y, Hayashi T, Nitta O, Takahashi H, Nishio D, Minakawa T, Kigawa H: Prediction of independent walking ability for severely hemiplegic stroke patients at discharge from a rehabilitation hospital. J Stroke Cerebrovasc Dis 2016;25:1878–1881. PMID:27156902, DOI:10.1016/j.jstrokecerebrovasdis.2015.12.020
• 11.  Soderberg GL, Cook TM: An electromyographic analysis of quadriceps femoris muscle setting and straight leg raising. Phys Ther 1983;63:1434–1438. PMID:6611665, DOI:10.1093/ptj/63.9.1434
• 12.  Mayhew TP, Norton BJ, Sahrmann SA: Electromyographic study of the relationship between hamstring and abdominal muscles during a unilateral straight leg raise. Phys Ther 1983;63:1769–1773. PMID:6227021, DOI:10.1093/ptj/63.11.1769
• 13.  Gajdosik RL, LeVeau BF, Bohannon RW: Effects of ankle dorsiflexion on active and passive unilateral straight leg raising. Phys Ther 1985;65:1478–1482. PMID:4048283, DOI:10.1093/ptj/65.10.1478
• 14.  Katoh M, Isozaki K: Reliability of isometric knee extension muscle strength measurements of healthy elderly subjects made with a hand-held dynamometer and a belt. J Phys Ther Sci 2014;26:1855–1859. PMID:25540481, DOI:10.1589/jpts.26.1855
• 15.  Keith RA, Granger CV, Hamilton BB, Sherwin FS: The functional independence measure: a new tool for rehabilitation. Adv Clin Rehabil 1987;1:6–18.
• 16.  Soderberg GL, Minor SD, Arnold K, Henry T, Chatterson JK, Poppe DR, Wall C: Electromyographic analysis of knee exercises in healthy subjects and in patients with knee pathologies. Phys Ther 1987;67:1691–1696. PMID:3454656, DOI:10.1093/ptj/67.11.1691
• 17.  Scott D, Stuart AL, Kay D, Ebeling PR, Nicholson G, Sanders KM: Investigating the predictive ability of gait speed and quadriceps strength for incident falls in community-dwelling older women at high risk of fracture. Arch Gerontol Geriatr 2014;58:308–313. PMID:24331098, DOI:10.1016/j.archger.2013.11.004
• 18.  Hayashida I, Tanimoto Y, Takahashi Y, Kusabiraki T, Tamaki J: Correlation between muscle strength and muscle mass, and their association with walking speed, in community-dwelling elderly Japanese individuals. PLoS One 2014;9:e111810. PMID:25365291, DOI:10.1371/journal.pone.0111810
• 19.  Ploeg RJ, Oosterhuis HJ, Reuvekamp J: Measuring muscle strength. J Neurol 1984;231:200–203. PMID:6512574, DOI:10.1007/BF00313939
• 20.  Bohannon RW: Measuring knee extensor muscle strength. Am J Phys Med Rehabil 2001;80:13–18. PMID:11138949, DOI:10.1097/00002060-200101000-00004
• 21.  Piao C, Yoshimoto N, Shitama H, Makino K, Wada F, Hachisuka K: Validity and reliability of the measurement of the quadriceps femoris muscle strength with a hand-held dynamometer on the affected side in hemiplegic patients. J UOEH 2004;26:1–11. PMID:15038067, DOI:10.7888/juoeh.26.1
• 22.  Murata S, Otao H, Murata J, Horie J, Onituka M, Yokoyama T, Hara H: Relationship between the 10-second chair stand test (Frail CS-10) and physical function among the frail elderly. Rigakuryoho Kagaku 2010;25:431–435. DOI:10.1589/rika.25.431
• 23.  Whitney SL, Wrisley DM, Marchetti GF, Gee MA, Redfern MS, Furman JM: Clinical measurement of sit-to-stand performance in people with balance disorders: validity of data for the Five-Times-Sit-to-Stand Test. Phys Ther 2005;85:1034–1045.
• 24.  Wall JC, Bell C, Campbell S, Davis J: The Timed Get-up-and-Go test revisited: measurement of the component tasks. J Rehabil Res Dev 2000;37:109–113.