1.1

Introduction

Postural instability is frequent in the elderly and its consequences constitute a major public health issue. The detection, analysis and understanding of alterations in balance and gait are part of routine clinical practice. Many different fall-risk screening tests have been introduced; one of the most common is the Functional Reach Test (FRT) .

The FRT evaluates the forward stability of a standing subject who voluntarily extends one arm as far forward as possible in the horizontal plane, while keeping both heels in contact with the ground. The score is obtained by measuring the distance between fingertip’s starting and end position.

The FRT’s good reliability and low inter-examiner variability have been demonstrated in a range of studies . The FRT score correlates with the anteroposterior excursion of the centre of pressure (CoP) . Furthermore, the FRT also shows good reproducibility over time and is sensitive to change . Lastly, the FRT score is known to decrease with age, and an abnormally low score is a good predictor of the risk of falls .

Performance of the FRT involves flexion of the leg, hip and trunk joints. Hence, several different strategies can be used to achieve the same FRT score. For example, it is known that older people tend to flex more at the hips and younger people are more likely to flex their ankles .

A few studies have looked at whether flexion strategies have an impact on the FRT score. Takasaki et al. performed a video analysis of FRT performance in a large sample of subjects and proposed an empirical classification of strategies. Wernick-Robinson et al. used a movement analysis system and force platforms to explore FRT strategies in healthy subjects and in individuals with impaired vestibular function.

Our starting hypothesis was that different movement patterns can be used to perform the FRT; these may have an impact on test performance and may be age-dependant. We used a quantitative movement analysis device to investigate this hypothesis.

1.2

Methods

The study was performed in compliance with the tenets of the Declaration of Helsinki.

1.2.3

Procedure

After the investigator had explained and demonstrated the FRT, the subject first performed the conventional, clinical FRT while standing alongside a wall. The examiner noted the score (in millimetres).

The FRT was then performed in the motion analysis laboratory. The subject was equipped with 18 markers ( Fig. 1 ) located on the first sacral process (FSP), the anterior superior iliac spines (ASISs), the greater trochanters, the lateral femoral condyles, the lateral malleoli, the tip of the metatarsophalangeal joint of the second toe on each foot, the heels, the acromia, the C7 process, the right epicondyle and the tip of the metacarpophalangeal joint of the right index finger.

The marker positions.

The subject then stepped onto the force platform and stood in an upright but relaxed position.

The recording started with the subject in the standing position and with the right index finger pointing forward for 10 s. Upon hearing an auditory cue, the subject initiated the test at the speed of his/her choice. The subject leant forward as far as possible without moving his/her feet. The recording was stopped when the subject took his/her heel(s) off the ground or when his/her index finger reached the maximum distance.

Five consecutive trials were recorded. The test instructions were repeated before each trial.

1.3

Results

1.3.3

Parameters recorded during movement

The FRT score was lower during the movement analysis than during the clinical examination. The clinical and movement analysis FRT scores were correlated (Pearson’s correlation coefficient = 0.6). The over-75 group again displayed a lower mean score than the under-50 group ( P = 0.028). Although there was no intergroup difference in the movement duration, the movement velocity was significantly greater in the under-50 group ( P = 0.039). The over-75 group displayed a greater CoP TDD ( P < 0.05) but a lower CoP APD ( P < 0.01). The pelvis moved forward in some subjects, backwards in others or even forwards and then backwards ( Figs. 2–4 ). Backward pelvic displacement was more ample in the over-75 group ( P < 0.05).

Trajectory in the sagittal plane of the pelvis, the centre of pressure (CoP) and the finger during FRT. All markers move forward.

Trajectory in the sagittal plane of the pelvis, the centre of pressure (CoP) and the finger during FRT. The pelvis moves backward, the finger moves forward, and centre of pressure oscillates around the initial position.

Trajectory in the sagittal plane of the pelvis, the centre of pressure (CoP) and the finger during FRT. The pelvis moves forwards and then backwards, whereas the finger and the CoP move forward.

Relative to the under-50s, the over-75 subjects displayed less trunk rotation during the FRT ( P = 0.024). We did not observe any significant intergroup differences in trunk flexion, knee motion or ankle motion. The amplitude of right hip flexion was greater in the over-75 group ( P < 0.05), whereas the intergroup difference in left hip flexion did not achieve statistical significance ( P = 0.051).

At the end of the test, there were no significant differences between the two groups in terms of the hip, knee and ankle positions.

1.3.3.1

Cluster analysis

Two subjects (one in the under-50 group and one in the over-75 group) were excluded from the analysis because more than two-thirds of their parameters were outliers ( Fig. 5 , Table 2 ).

Dendrogram representing the minimum variance hierarchical classification of the Functional Reach Test (FRT) patterns of healthy young and elderly participant (Ward method; Euclidian distances). The figure is read from the left where the individual mean pattern are listed, in four families, to right where all the FRT trials are grouped into a single family. On the left, participants: S(x) + age group (old[V]/young[J]); two subjects were excluded (one young and one old) considering more than 2/3 of extreme data (cf. methods).

Table 2

Parameter significantly different in the two groups found by cluster analysis.

	ANOVA univariate with 2 classes	Classe 1 Mean ± SD	Classe 2 Mean ± SD	Post-hoc HSD Tuckey
Age	0.007	36.8 ± 19.3	67.3 ± 21.0	0.007
FRT (mm)	0.004	356.3 ± 65.4	259.8 ± 83.2	0.004
Movement latency (s)	0.036	0.3 ± 0.1	0.2 ± 0.1	0.037
Pelvis range of motion	0.002	−8.0 ± 29.6	−76.0 ± 29.5	0.002
Sagittal displacement of CoP during FRT	0.005	89.8 ± 24.4	43.1 ± 31.8	0.005
Length CoP during FRT	0.023	353.6 ± 61.5	432.0 ± 191.0	0.023
Index CoP during FRT	0.000	4.5 ± 2.1	62.6 ± 123.1	0.000
Left ankle range of motion	0.008	7.0 ± 1.9	11.3 ± 5.3	0.008
Right ankle range of motion	0.042	6.0 ± 2.3	11.0 ± 5.8	0.042
Left knee range of motion	0.007	4.8 ± 2.6	16.4 ± 20.4	0.007
Right knee range of motion	0.078	6.3 ± 2.4	18.3 ± 21.6
Left hip range of motion	0.022	37.0 ± 10.0	56.6 ± 14.2	0.022
Right hip range of motion	0.022	34.9 ± 11.4	56.4 ± 15.9	0.022
Trunk initial angle	0.000	85.9 ± 3.5	79.6 ± 5.6	0.000
Trunk final angle	0.019	35.5 ± 13.5	22.1 ± 11.4	0.019
Trunk rotation	0.034	−15.5 ± 7.2	−5.9 ± 9.3	0.034

 

The ascendant hierarchical clustering analysis revealed two distinct clusters ( n = 7 and 20, respectively), with a Euclidean distance of 15.84. Calculation of the R ratio confirmed the existence of two distinct clusters.

The two groups differed significantly in terms of age, FRT score, pelvis translation, anteroposterior CoP displacement, total COP displacement, the CoP index, the ankle range of motion, the hip range of motion, trunk flexion and shoulder rotation.

The first, larger cluster ( n = 20 subjects, of whom 16 [80%] were under 50) stood straighter, had a higher FRT score and a longer CoP displacement ( Fig. 2 ), flexed their leg and hip joints less and performed a larger shoulder rotation during the test (relative to the second, smaller cluster).

The smaller cluster ( n = 7 subjects, of whom 6 were over 75) was associated with a lower FRT score and smaller CoP displacements ( Fig. 3 ). More ample trunk flexion was compensated by rearward translation of the pelvis and flexion of the ankle, knee and hip joints.

1.4

Discussion

We observed significant differences between under-50 adults and non-faller, over-75 adults in terms of the FRT score and the strategy adopted during the test. Our results are consistent with the literature data on the FRT score and the magnitude of the CoP excursion in the static position .

The clinical FRT score was always higher than that obtained in the motion analysis laboratory. During the clinical test, the proximity of the wall may have made the subjects less apprehensive of losing their balance. The marks on the wall may also have guided the subjects and increased their level of motivation.

The speed of test performance decreased with age, as evidenced by the shorter reach achieved over a similar duration. Kozak et al. also reported that older women performed the FRT more slowly than young women.

Reduced trunk rotation may explain (at least in part) the lower FRT score in older subjects. This finding was also reported by Cavanaugh et al. . However, the FRT primarily assesses the subject’s ability to displace his/her centre of gravity forwards. Aufauvre et al. have shown that the FRT score was well correlated with the greatest anterior CoP excursion. We found significant intergroup differences in the magnitudes of the CoP TDD and APD during the test, as also reported by Cavanaugh et al. . We did not find any difference between the two groups in terms of trunk flexion; this contrasts with the report by Kosak et al. , who observed an age-related decrease in trunk flexion during the FRT. In the present study, the older subject avoided a forward displacement of the CoP by moving the pelvis backwards, rather than by avoiding trunk flexion.

Greater hip and knee flexion in the over-75 group:

• •
  

  lowered the centre of gravity (making the subject feel safer) and;

  
  
• •
  

  reduced the activity of the calf muscles and the degree of hamstring stretch (which decreases with age).

Horak and Nashner described both a hip strategy and an ankle strategy for maintaining balance during anteroposterior balance perturbations . Takasaki et al. and Wernick-Robinson et al. defined an FRT hip strategy that involved at least 20° of hip flexion and just 5° of ankle flexion on both body sides. In our study, fifteen subjects (6 of the over-75s and 9 of the under-50s) adopted a hip strategy that matched these criteria.

An ankle strategy involves significant ankle plantar flexion and little hip flexion; this approach was not observed in the present study and was rarely observed in the studies by Takasaki et al. and Wernick-Robinson et al. . In our study, two subjects (one in each group) performed FRT with ankle plantar flexion but this was combined with ample knee flexion (i.e. similar to a squat). Indeed, a “squat” strategy was also observed in a few cases in the studies by Takasaki et al. and Wernick-Robinson et al.

In the present study, hip and ankle movements do not appear to be the best parameters for define movement strategies during the FRT. Knee flexion occurred more frequently than in the literature studies, and influenced hip and ankle position. The marked knee flexion during the FRT in the present study may be explained by our instrumental procedure, which does not provide horizontal landmarks that might facilitate performance of the test. In Takasaki et al.’s experiments, subjects leant forward while holding a horizontal, sliding bar with the right hand. This paradigm is similar to Duncan et al.’s description of the test, and maintenance of contact with the bar limits knee flexion.

In the present study, posterior translation of the pelvis was the kinematic parameter that best distinguished between the two main FRT strategies. Takasaki et al. also found that older adults moved their pelvis backward during the FRT, in order to limit anterior displacement of the CoP.

Force platform data are often used to assess balance in older subjects performing dynamic tasks . These data (especially CoP sagittal displacement and the CoP index) were very discriminant in the present study. This is not surprising, since people with poor balance or fear of falling tend to avoid displacements of the CoP. We conclude that the choice of strategy depends on the subject’s ability (or will) to move his/her CoP.

1.5

Conclusion

As reported in the literature, we found that the FRT score decreased with age.

The present study provides a better understanding of factors associated with a low FRT score. Performance in the FRT is linked to the ability to move the CoP forwards. In the FRT, elderly people avoid displacing their CoP by flexing the trunk and moving the pelvis backwards.

Cluster analysis enabled us to identify two movement strategies during the FRT. Although age was indeed one of the discriminant parameters in the cluster analysis, both “movement strategy groups” included subjects from the two age groups studied here.

It would be interesting to use the same methodology to study the FRT strategy used by older adults with frequent falls or with fear of falling.

Disclosure of interest

The authors declare that they have no conflicts of interest concerning this article.

2.1

Introduction

L’instabilité posturale est un phénomène fréquent chez la personne âgée et ses conséquences constituent un problème majeur de santé publique. La détection, l’analyse et la compréhension des perturbations de l’équilibre et de la marche font partie de la pratique quotidienne. De très nombreuses méthodes d’évaluation du risque de chute ont été proposées, l’une des plus communes est le Functional Reach Test (FRT).

La FRT évalue la stabilité vers l’avant d’une personne debout qui étend volontairement son bras en avant que possible dans un plan horizontal, pendant qu’elle garde les deux talons au contact avec le sol. Le score est obtenu en mesurant la distance entre la position du bout des doigts au départ et à l’arrivée.

Il a été démontré dans plusieurs études que le FRT est fiable et a une variabilité inter-examinateur faible. Le score du FRT est corrélé avec le déplacement antéro-postérieur du centre de pression (CdP) . De plus, le FRT a également une bonne reproductibilité dans le temps et est sensible au changement . Enfin on sait que le score du FRT diminue avec l’âge mais qu’un score anormalement bas et un bon prédicateur du risque de chute .

La réalisation du FRT fait participer les articulations de la cheville, du genou, de la hanche et du tronc; plusieurs stratégies de mise en jeu de ces articulations pourraient donc théoriquement arriver au même score de FRT. Par exemple, on sait que les sujets âgés ont tendance à plus fléchir leurs hanches et les sujets jeunes à plus réaliser une dorsiflexion de cheville pour se pencher en avant .

Peu d’études ont essayé de déterminer si la stratégie de réalisation influençait sur le score du FRT. Takasaki et al. ont réalisé une analyse vidéo du FRT sur un large échantillon d’individu et ont proposé une classification empirique des stratégies. Wernick-Robinson et al. ont utilisé un système d’analyse du mouvement et une plateforme de force pour déterminer les stratégies de réalisation du FRT chez des sujets sains et chez des sujets avec des fonctions vestibulaires altérées.

Notre hypothèse de départ est que différents schémas peuvent être utilisés pour réaliser le FRT, que ceux-ci peuvent avoir un impact sur le résultat du test et peuvent être liés à l’âge. Nous avons utilisé un système d’analyse du mouvement pour explorer cette hypothèse.

2.2

Méthode

L’étude a été conduite en conformité avec les principes de la déclaration d’Helsinki.

2.2.3

Procédure

Après que l’investigateur ait expliqué le FRT et réalisé une démonstration, le sujet réalisait d’abord le FRT conventionnel, clinique, en se tenant debout le long d’un mur. L’investigateur notait le score en millimètre. Le FRT était ensuite effectué dans le laboratoire d’analyse du mouvement. Le sujet était équipé de 18 marqueurs ( Fig. 1 ) placés sur le premier processus sacré, les épines iliaques antéro-supérieures, le grand trochanter, le condyle fémoral latéral, l’articulation métatarsophalangienne du 2 ^e rayon de chaque pied, les talons, les acromions, le processus épineux de C7, l’épicondyle droit, l’articulation métacarpophalangienne de l’index droit.

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