ISCEV guidelines for clinical multifocal electroretinography -LRB- 2007 edition -RRB- The clinical multifocal electroretinogram -LRB- mfERG -RRB- is an electrophysiological test of local retinal function . With this technique , many local ERG responses , typically 61 or 103 , are recorded from the cone-driven retina under light-adapted conditions . This document specifies guidelines for performance of the test . It also provides detailed guidance on technical and practical issues , as well as on reporting test results . The main objective of the guidelines is to promote consistent quality of mfERG testing and reporting within and among centers . These 2007 guidelines , from the International Society for Clinical Electrophysiology of Vision -LRB- ISCEV : http://www.iscev.org -RRB- , replace the ISCEV guidelines for the mfERG published in 2003 . Introduction The electroretinogram -LRB- ERG -RRB- is a mass potential , the result of the summed electrical activity of the cells of the retina . Full-field electroretinography is a well-established clinical technique for evaluating global retinal function -LSB- 1 -RSB- . The multifocal ERG -LRB- mfERG -RRB- technique was developed to provide a topographic measure of retinal electrophysiological activity . With this technique , many local ERG responses , typically 61 or 103 , are recorded from the cone-driven retina under light-adapted conditions . In 2003 , the International Society for Clinical Electrophysiology of Vision -LRB- ISCEV -RRB- published guidelines for recording the mfERG -LSB- 2 -RSB- . These were guidelines , not standards , to allow for further research before standards were set . Although the mfERG now has been used for more than 10 years to aid in the diagnosis of diseases of the retina , ISCEV decided that it is still premature to set specific standards . However , to take into consideration recent developments in technology and practice , this document provides revised guidelines for recording clinical mfERGs . These guidelines will be reviewed periodically , consistent with ISCEV 's practice . Description of multifocal electroretinography The mfERG technique is a method of recording local electrophysiologic responses from different regions of the retina . Electrical responses from the eye are recorded with a corneal electrode as in conventional , full-field ERG recording . However , the nature of the stimulus and the form of the analysis differ . These differences allow a topographic map of local ERG activity to be measured . For the basic mfERG described here , the retina is stimulated with an array of hexagonal elements , each of which has a 50 % chance of being illuminated every time the frame changes -LRB- Fig. 1 -RRB- . Although the pattern appears to flicker randomly , each element follows the same pseudo-random sequence of illumination with the starting point displaced in time relative to other elements . By correlating the continuous ERG signal with the sequence of on - and off-phases of each element , the local ERG signal is calculated . Although we will refer to these local ERG signals as mfERG responses , it is important to keep in mind that they are not direct electrical potentials from local regions of retina , but rather they are a mathematical extraction of the signal . Further , because the stimulation rate is rapid , the waveform of the local mfERG response can be influenced both by preceding -LRB- ` adaptation effects ' -RRB- and subsequent stimuli -LRB- ` induced effects ' -RRB- , as well as by the responses to light scattered on other retinal areas . Fig. 1 -LRB- a -RRB- Representative hexagonal mfERG stimulus array with 61 elements scaled with eccentricity . Roughly half of the elements are illuminated at any one time . -LRB- b -RRB- Same as in panel A for an array with 103 elements The typical waveform of the basic mfERG response -LRB- also called the first-order response or first-order kernel -RRB- is a biphasic wave with an initial negative deflection followed by a positive peak -LRB- Fig. 2 -RRB- . There is usually a second negative deflection after the positive peak . These three peaks are called N1 , P1 and N2 , respectively . There is evidence that N1 includes contributions from the same cells that contribute to the a-wave of the full-field cone ERG , and that P1 includes contributions from the cells contributing to the cone b-wave and oscillatory potentials . Although there is some homology between the mfERG waveform and the conventional ERG , the stimulation rates are higher for the mfERG and , as noted above , the mfERG responses are mathematical extractions . Thus , the mfERG responses are not technically `` little ERG responses '' . Therefore , the designations ` a-wave ' and ` b-wave ' , used for the full-field ERG , are not appropriate to describe features of the mfERG waveform . Fig. 2Diagram of an mfERG response to show the designation of the major features of the waveform Basic technology Electrodes Recording electrodes Poor or unstable electrode contact is a major cause of poor quality records . It is important to follow the recommendations concerning fiber , foil , loop and contact lens electrodes in the full-field ERG Standard -LSB- 1 -RSB- and Pattern ERG -LRB- PERG -RRB- Standard -LSB- 3 -RSB- . In particular , electrodes that contact the cornea , or nearby bulbar conjunctiva , are required . In addition , good retinal image quality and proper refraction is desirable . Reference and ground electrodes Proper application of suitably conductive electrodes is essential for reliable mfERG recordings . Follow the recommendations made in other ISCEV Standards -LSB- 1 , 3 -RSB- . Electrode characteristics , stability and cleaning Follow the recommendations in the ISCEV full-field ERG and/or PERG Standards -LSB- 1 , 3 -RSB- . Stimulation Stimulus source Until recently , the mfERG stimuli were most commonly displayed on a cathode ray tube -LRB- CRT -RRB- , i.e. a monitor . CRT monitors are being rapidly replaced with other devices such as liquid crystal display -LRB- LCD -RRB- projectors , arrays of light emitting diodes -LRB- LEDs -RRB- and organic LEDs -LRB- OLEDs -RRB- . These alternative modes of stimulation can affect the amplitude and waveform of the mfERG making it essential to specify the type of display when reporting results .1 Frame frequency A CRT frame frequency of 75 Hz has been used widely . -LRB- LCD displays use 60 Hz . -RRB- Use of different frequencies can substantially alter the amplitude and waveform of the mfERG response . Whatever frame frequency is used , normative values for normal healthy subjects need to be determined separately for that frequency . Further , it is essential to specify the frame frequency when reporting results . Luminance and contrast In general , the luminance of the stimulus elements for CRT displays should be 100 -- 200 cd/m2 in the lighted state and low enough in the dark state to achieve a contrast of ≥ 90 % . This means that the mean screen luminance during testing will be 50 -- 100 cd/m2 . Although higher luminance levels can be used , the ability to detect local defects may be decreased due to the effects of stray light . In addition , the luminance requirements may differ if a non-CRT display is used . In any case , the surround region of the display -LRB- the area beyond the stimulus hexagons -RRB- should have a luminance equal to the mean luminance of the stimulus array . Calibration As with other electrophysiologic signals , luminance and contrast affect the recorded signal and it is important to calibrate the stimulus following ISCEV guidelines -LSB- 4 -RSB- . The luminance of the dark and the light stimulus elements should be measured with an appropriate calibrator or spot meter . Many monitor screens are not of uniform brightness over the entire screen . While some variation is to be expected , a variation of greater than 15 % is considered unacceptable . Some commercial systems are equipped to calibrate the display . If this ability is not present , we urge manufacturers to provide instructions for calibration of their devices . Stimulus parameters Stimulus pattern : The typical mfERG display is a hexagonal stimulus pattern scaled in size to produce mfERG responses of approximately equal amplitude across the retina . Thus , the central hexagons are smaller than the more peripheral ones . Different patterns may be useful in special cases -LRB- e.g. equal size hexagons for patients with eccentric fixation -RRB- . These guidelines cover only the typical stimulus pattern , scaled to produce approximately equal size responses for healthy control subjects . Flicker sequence : Most commercial mfERG instruments use an m-sequence to control the temporal sequence -LRB- between light and dark -RRB- of the stimulus elements . An m-sequence , in which the elements can change with every frame , is recommended for routine testing . Different sequences , or the inclusion of global light or dark frames , have been suggested for specialized applications , but they are not a part of these guidelines , and should not be done in exclusion of a `` standard '' mfERG for routine clinical purposes . Stimulus size and number of elements : The overall stimulus pattern should subtend a visual angle of 20 -- 30 ° on either side of the fixation point . The stimulus region can be divided into different numbers of hexagons . The most frequently used patterns have 61 or 103 hexagons , with 241 hexagons occasionally used . The choice depends on balancing the need for good spatial resolution and a high signal-to-noise ratio , while minimizing the recording time . -LRB- See discussion below under clinical protocol -RRB- . Fixation targets : Stable fixation is essential for obtaining reliable mfERG recordings . Central fixation dots , crosses and circles are available with most commercial systems . The fixation targets should cover as little of the central stimulus element as possible to avoid diminishing the response . However , the examiner should always verify that the patient can see the fixation target . When the fixation targets are enlarged for low-vision patients , care should be taken not to obscure regions of interest . For example , a larger central cross will lead to a smaller central response simply due to occlusion of more of the stimulus . Recording , analyzing and presenting results Amplifiers and filters The gain of the amplifier should produce recognizable signals without saturation . Appropriate band-pass filtering removes extraneous electrical noise , without distorting waveforms of interest . For a `` standard '' mfERG , the high pass cutoff can range between 3 and 10 Hz and the low pass cutoff between 100 and 300 Hz . Filter settings , even within the ranges suggested , will influence the response waveform . Thus , the filter settings should be the same for all subjects tested by a given laboratory , as well as for the norms to which they are compared . Line-frequency or notch filters should be avoided . Signal analysis Artifact rejection : Because blinks and other movements can distort the recorded waveforms , commercial software usually includes ` artifact rejection ' algorithms to eliminate some of these distortions . When applying an artifact rejection procedure after the recording , care should be exercised to assure that clinically important aspects of the waveform are not being modified . In any case , artifact rejection procedures should be specified when reporting mfERG results . Spatial averaging : In order to reduce noise and smooth the waveforms , some commercial programs allow the averaging of the response from each stimulus element with a percentage of the signal from the neighboring elements . Spatial averaging can help visualize the mfERG signal in noisy records . However , spatial averaging may obscure small , local changes or the borders of regions of dysfunction . Thus , it should be used with care and specified when reporting results . Further , the default conditions of commercial software should be examined , as spatial averaging may be a default condition . Displaying results Trace arrays : All commercial programs can produce an array of the mfERG traces -LRB- Fig. 3a , b -RRB- . This display of the results is useful for visualizing areas of abnormality and for comparing the mfERG results to visual fields from perimetry . The trace array is the basic mfERG display and should always be included in the report of clinical results . Commercial software typically allows for these responses to be displayed with either a visual field view or retinal view as the frame of reference . The frame of reference should be indicated . Note that in Fig. 3 , each of the 61 -LRB- panel a -RRB- or 103 -LRB- panel b -RRB- responses are shown in approximately correct topographic representation . Adding contours to show the loci of different eccentricities , as in Fig. 4 , can help in determining whether the regions of low amplitude correspond to regions of the visual field that show a loss of sensitivity . Fig. 3Sample mfERG trace arrays -LRB- field view -RRB- with 61 elements -LRB- panel a -RRB- and 103 elements -LRB- panel b -RRB- . -LRB- c , d -RRB- The 3-D response density plots -LRB- field view -RRB- associated with panels a and bFig . 4The mfERG trace array -LRB- left panel , field view -RRB- and the probability plot from standard automated perimetry -LRB- right panel -RRB- for a patient with retinitis pigmentosa . The contours for a radius of 5 and 15 ° are shown . The light gray , dark gray , and black squares indicate statistically significant field loss at the 5 , 1 and 0.5 percent levels , respectively Group averages : Commercial programs allow for the averaging of groups of responses from the trace arrays . This can be helpful for comparing quadrants , hemiretinal areas , normal and abnormal regions of two eyes , or successive rings from center to periphery . The latter is particularly useful for patients who have diseases that produce approximately radially symmetric dysfunction . In addition , responses from stimulus elements associated with a local area of interest can be averaged for comparison with a similar area in an unaffected eye or to data from control subjects . Figure 5 shows the result of grouping the responses in Fig. 3b by rings . The most commonly used display is response density -LRB- Fig. 5a -RRB- , in which the responses from the elements in each ring are summed and then divided by the area of these elements . Figure 5b and c are alternative representations of the data in which summed responses from each ring are shown -LRB- panel c -RRB- or are normalized so that they have the same amplitude -LRB- panel b -RRB- . Fig. 5The mfERG responses in Fig. 3b were grouped by concentric rings and summed to yield the ` Summed ' responses in panel c . These summed responses are divided by the area of the elements of the ring for the ` Response Density ' responses -LRB- panel a -RRB- and normalized so each has the same amplitude for the ` Normalized ' responses -LRB- panel b -RRB- Topographic -LRB- 3-D -RRB- response density plots : The 3-D plot -LRB- Fig. 3c , d -RRB- shows the overall signal strength per unit area of retina . This display can sometimes be useful for illustrating certain types of pathology . In addition , the quality of fixation can be assessed by observing the location and depth of the blind spot . However , there are major dangers in using the 3-D plot in assessing retinal damage . First , information about the waveforms is lost . Thus large , but abnormal , or delayed responses can produce normal 3-D plots . Second , a central peak in the 3-D plot can be seen in some records without any retinal signal -LRB- see , Appendix : Artifact recognition examples for electrical noise and weak signals -RRB- . Finally , the appearance of the 3-D plot from a given recording is dependent on how the local amplitude is measured . Whenever 3-D plots are presented , the method used to measure local amplitude should be identified , and the corresponding mfERG trace array also should be presented . Signal extraction : Kernels -- This document is aimed at the general mfERG user and only describes the basic response , the first-order kernel . Higher order kernels , particularly the second-order kernel , occasionally are reported , and used in special applications . Clinical protocol Patient preparation Pupils The pupils should be fully dilated and pupil size noted . Patient positioning Subjects should sit comfortably in front of the screen . Relaxation of facial and neck muscles will reduce artifacts from muscles ; a headrest may be helpful . The appropriate viewing distance will vary with screen size , in order to control the area -LRB- visual angle -RRB- of retina being stimulated . Fixation monitoring Good fixation , both central and steady , is essential . Thus , fixation should be monitored , preferably by the use of monitoring instrumentation available on some units . When this option is not available , careful direct observation may be employed . Refraction Although there is some evidence that the mfERG is unaffected by moderate blurring of the retinal image in healthy individuals , we recommend refraction for optimal acuity . On some commercial machines , a manual adjustment of the viewing optics is possible . Alternatively , lenses can be placed in a holder positioned in front of the eye . In the latter case , the viewing distance must be adjusted to compensate for the relative magnification of the stimulus . Also care must be taken to avoid blocking the view of the stimulus screen by the rim of the lens or the lens holder and thus creating an apparent scotoma . Monocular versus binocular recording Recording is typically done with monocular stimulation . Those who record binocularly should be aware that signals can be altered by misalignment of the eyes . Adaptation Pre-adaptation -LRB- before test -RRB- : Subjects should be exposed to ordinary room lighting for at least 15 min prior to testing . Longer adaptation times may be needed after exposure to bright sun or bright lights such as those used for fundus photography or retinoscopy . Room illumination : Moderate or dim room lights should be on and ideally should produce illumination close to that of the stimulus screen . Stimulus and recording parameters Stimulus Size The stimulus should subtend 20 -- 30 ° of visual angle on either side of the fixation point . Number of elements A display containing 61 or 103 elements should be used . Duration of recording A total recording time of at least 4 min for 61 element arrays , or 8 min for 103 element arrays , is recommended , although these times might be adjusted by experienced laboratories according to clinical needs . The overall recording time is divided into shorter segments -LRB- e.g. 15 -- 30 s -RRB- so that subjects can rest between runs if necessary and also so that a poor record -LRB- from noise , movement or other artifacts -RRB- can be discarded and repeated without losing prior data . Trade-offs Various manipulations will affect the signal-to-noise ratio -LRB- SNR -RRB- of the responses . In particular , decreasing the size -LRB- increasing the number for a fixed stimulus field size -RRB- of the stimulus elements and decreasing the duration of the recording will decrease the SNR of the responses . While decreasing the number -LRB- increasing the size -RRB- of elements will increase the SNR , it will decrease the spatial resolution of the test . In general , conditions with larger -LRB- i.e. 61 -RRB- elements and a shorter recording time -LRB- e.g. 4 min -RRB- are easier for the patient and suitable for a general screening of macular function . On the other hand , conditions with 103 elements and a longer recording time -LRB- e.g. 8 min -RRB- are useful for assessing foveal function and mapping the outline of retinal defects . Very small elements -LRB- such as a 241 hexagon array -RRB- may sometimes be helpful for diseases with very small or irregular effects . Repeat recording is recommended to confirm small or subtle abnormalities . Further , the choice of electrode type will also influence the SNR of the responses . For example , bipolar corneal contact electrodes yield recordings with the highest SNR . Thus , longer recording times , repeat measurements and/or fewer stimulus elements are necessary to obtain comparable SNRs when a foil or fiber electrode is used . Data reporting Mode of display Trace arrays : It is essential to show the trace array when reporting mfERG results -LRB- see Fig. 3a , b -RRB- . These arrays not only show topographic variations , but also demonstrate the quality of the records , which is important in judging the validity of any suspected variations from normal . Trace lengths of 100 ms or more should be used for these displays . -LRB- It is hard to detect interference from line frequency and/or kernel overlap in shorter trace lengths . -RRB- . Group averages : Arranging responses by groups can be a useful way to summarize the data . Concentric rings of traces , from the center outward , are most commonly used . Regions with fundus pathology can be averaged together if desired . Most laboratories report response density -LRB- Fig. 5a -RRB- . Three-dimensional plots : These should be used with caution and only when accompanied by trace arrays -LRB- see above -RRB- . The 3-D plots -LRB- Fig. 3c , d -RRB- , without accompanying trace arrays , can be misleading -LRB- see Appendix -RRB- . Note that if fixation is steady and central , a clear depression due to the blindspot should be present and located in the appropriate place . Measurements calibration marks : Calibration marks must accompany all traces or graphs . This will enable comparisons among patients or within a patient on sequential visits . Measuring mfERG amplitude and timing : The N1 response amplitude is measured from the starting baseline to the base of the N1 trough ; the P1 response amplitude is measured from the N1 trough to the P1 peak -LRB- see Fig. 2 -RRB- . The peak times -LRB- implicit times -RRB- of N1 and P1 are measured from the stimulus onset . Measurements of group averages should routinely include the N1 and P1 amplitudes and peak times . Commercial software provides measures of the overall amplitude and timing of the mfERG traces . There are various procedures for measuring amplitude -LRB- e.g. trough-to-peak amplitude -RRB- , latency -LRB- e.g. response shifting , response stretching , time to peak -RRB- , or overall response waveform -LRB- e.g. scalar product , root-mean-square -LRB- RMS -RRB- -RRB- . A description of these techniques is beyond the scope of these guidelines . However , it should be noted that when a template is needed -LRB- e.g. for scalar product measures -RRB- , the template should be formed from age-similar control data obtained from that laboratory . Color scales : The use of color scales is optional ; care should be taken when reproducing color images on a gray scale as the luminance sequences may not be in the proper order . Normal values Each laboratory must develop its own normative data . Variations in recording equipment and parameters make the use of data from other sources inappropriate . Because electrophysiologic data are not necessarily described by a normal distribution , laboratories should report the median value rather than the mean , and determine boundaries of normality . The mfERG , like the full-field ERG , is somewhat smaller in amplitude in older individuals and in those with highly myopic eyes . Although these effects are generally not large , they can be important in the evaluation of some patients . In any case , age-adjusted normative data is recommended . Reporting of artifacts and their resolution Reports should indicate any problems with the recording such as movement , head tilt , poor refraction capability , poor fixation , etc. that might affect reliability and interpretation . Also , indicate explicitly any artifact reduction procedures or post-processing maneuvers used to prepare the data . This should include the type and number of artifact rejection steps , the spatial averaging with neighbors -LRB- noting the extent and number of iterations -RRB- , and any other averaging or filtering procedures .

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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O

clinical guidelines
multifocal electroretinogram


Identification

of

elderly

fallers

by

muscle

strength

measures

For

efficient

prevention

of

falls

among

older

adults

individuals

at

a

high

risk

of

falling

need

to

be

identified

In

this

study

we

searched

for

muscle

strength

measures

that

best

identified

those

individuals

who

would

fall

after

a

gait

perturbation

and

those

who

recovered

their

balance

Seventeen

healthy

older

adults

performed

a

range

of

muscle

strength

tests

We

measured

maximum

and

rate

of

development

of

ankle

plantar

flexion

moment

knee

extension

moment

and

whole

leg

push-off

force

as

well

as

maximum

jump

height

and

hand

grip

strength

Subsequently

their

capacity

to

regain

balance

after

tripping

over

an

obstacle

was

determined

experimentally

Seven

of

the

participants

were

classified

as

fallers

based

on

the

tripping

outcome

Maximum

isometric

push-off

force

in

a

leg

press

apparatus

was

the

best

measure

to

identify

the

fallers

as

cross-validation

of

a

discriminant

model

with

this

variable

resulted

in

the

best

classification

-LRB-

sensitivity

and

specificity

-RRB-

Jump

height

and

hand

grip

strength

were

strongly

correlated

to

leg

press

force

-LRB-

r

and

respectively

-RRB-

and

can

also

be

used

to

identify

fallers

although

with

slightly

lower

specificity

These

results

indicate

that

whole

leg

extension

strength

is

associated

with

the

ability

to

prevent

a

fall

after

a

gait

perturbation

and

might

be

used

to

identify

the

elderly

at

risk

of

falling

Introduction

One-third

of

those

over

years

of

age

fall

at

least

once

per

year

About

of

them

will

suffer

recurrent

falls

-LRB-

Masud

and

Morris

-RRB-

Even

in

the

large

group

of

relatively

fit

and

healthy

elderls

falls

are

common

-LRB-

Stel

et

al.

-RRB-

Consequences

of

falls

are

known

to

contribute

substantially

to

the

prevalence

of

health

problems

-LRB-

Lord

and

Dayhew

-RRB-

health

care

costs

-LRB-

Stevens

et

al.

-RRB-

and

to

lost

quality

of

life

-LRB-

Cumming

et

al.

-RRB-

Prevention

of

falls

is

therefore

imperative

and

should

address

the

people

at

risk

and

the

physiological

causes

of

falling

-LRB-

Lord

et

al.

-RRB-

Numerous

epidemiological

studies

have

shown

that

falls

are

associated

with

many

risk

factors

-LRB-

for

overviews

see

e.g.

Lord

et

al.

-RRB-

Reduced

muscle

strength

especially

of

the

lower

limbs

has

been

indicated

as

one

of

the

most

important

risk

factors

for

falls

-LRB-

Lord

et

al.

de

Rekeneire

et

al.

Moreland

et

al.

Rao

Rubenstein

Skelton

et

al.

-RRB-

Experimental

studies

can

provide

causal

verification

and

insight

into

the

contribution

of

muscle

strength

to

fall

incidence

in

standardized

situations

For

example

tripping

over

an

obstacle

which

accounts

for

up

to

of

falls

-LRB-

Berg

et

al.

Roudsari

et

al.

-RRB-

can

be

induced

and

measured

in

older

adults

in

experimental

settings

-LRB-

Pavol

et

al.

Pijnappels

et

al.

Schillings

et

al.

-RRB-

Previous

findings

provided

insight

into

the

-LRB-

neuro

-RRB-

physical

requirements

of

preventing

a

fall

after

tripping

over

an

obstacle

-LRB-

for

overviews

see

van

Dieën

et

al.

Pijnappels

et

al.

-RRB-

It

was

shown

that

older

adults

were

less

able

to

successfully

recover

balance

than

younger

adults

due

to

lower

maximum

ankle

moments

and

lower

rates

of

moment

generation

around

all

leg

joints

during

the

push-off

phase

of

balance

recovery

-LRB-

Pijnappels

et

al.

-RRB-

These

results

suggest

that

leg

strength

may

be

the

limiting

factor

in

preventing

a

fall

Pavol

et

al.

-LRB-

-RRB-

have

investigated

the

relation

between

muscle

strength

and

the

outcome

of

an

induced

trip

In

a

group

of

older

adults

they

compared

isolated

ankle

knee

and

hip

flexion

and

extension

strength

between

those

who

recovered

from

a

trip

and

those

who

fell

Although

some

strong

adults

fell

presumably

due

to

their

high

walking

velocity

they

also

found

that

muscle

strength

was

lower

in

several

other

fallers

If

low

muscle

strength

indeed

is

a

physiological

cause

of

falls

this

raises

the

question

whether

people

with

a

high

risk

of

falling

can

be

identified

by

means

of

relatively

simple

maximum

muscle

strength

measures

The

aim

of

this

study

was

to

find

the

best

predictor

of

falls

after

a

gait

perturbation

in

a

standardized

situation

from

a

range

of

muscle

strength

measures

in

older

adults

There

are

numerous

maximum

strength

capacity

measures

that

have

been

assessed

in

aged

populations

for

example

to

evaluate

training

interventions

-LRB-

Ferri

et

al.

Reeves

et

al.

Verschueren

et

al.

-RRB-

or

to

compare

fallers

with

non-fallers

-LRB-

Gehlsen

and

Whaley

Pavol

et

al.

-RRB-

We

focused

on

the

most

common

measures

by

use

of

a

dynamometer

isometric

ankle

and

knee

extension

moment

and

rate

of

moment

generation

In

addition

to

isolated

joint

moments

total

lower

limb

push-off

force

can

be

measured

by

a

leg

press

dynamometer

-LRB-

Gehlsen

and

Whaley

-RRB-

Performance

on

a

maximum

vertical

jump

could

be

a

more

functional

test

used

to

assess

maximum

lower

limb

strength

-LRB-

Izquierdo

et

al.

Runge

et

al.

-RRB-

Finally

hand

grip

strength

is

thought

to

reflect

general

body

strength

and

has

been

used

as

predictor

of

falls

in

epidemiological

studies

-LRB-

Pluijm

et

al.

-RRB-

Elderly

volunteers

performed

these

maximum

strength

capacity

tests

and

we

measured

their

ability

to

prevent

a

fall

after

being

tripped

We

hypothesized

that

maximum

muscle

strength

measures

can

be

used

to

differentiate

fallers

from

non-fallers

If

so

this

would

not

only

allow

identification

of

potential

fallers

but

also

indicate

specific

limiting

factors

to

target

with

exercise-based

interventions

Methods

Seventeen

healthy

older

adults

participated

-LSB-

women

age

-LRB-

SD

-RRB-

years

mass

-LRB-

SD

-RRB-

kg

height

-LRB-

SD

-RRB-

m

-RSB-

All

participants

were

fit

and

had

no

orthopedic

neuromuscular

cardiac

or

visual

problems

The

Ethics

Committees

the

VU

Medical

Center

and

of

the

Manchester

Metropolitan

University

approved

the

procedure

and

all

subjects

gave

their

written

informed

consent

before

participation

Capacity

measures

Participants

performed

a

series

of

static

and

dynamic

maximum

force

generating

capacity

tests

First

isometric

ankle

plantar

flexion

moment

and

knee

extension

moment

-LRB-

maximum

as

well

as

rate

of

moment

development

-RRB-

were

assessed

using

a

dynamometer

In

view

of

constraints

on

equipment

and

subject

availability

nine

of

the

participants

were

tested

using

an

isokinetic

dynamometer

-LRB-

Cybex

Norm

New

York

USA

-RRB-

-LRB-

Reeves

et

al.

-RRB-

and

eight

using

a

custom-built

dynamometer

-LRB-

de

Ruiter

et

al.

-RRB-

-LRB-

Fig.

b

-RRB-

Isometric

knee

extension

moment

was

measured

in

both

settings

with

a

knee

joint

angle

of

-LRB-

full

extension

-RRB-

and

a

hip

angle

of

-LRB-

supine

position

-RRB-

Isometric

plantar

flexion

moment

was

measured

using

the

Cybex

with

the

knee

in

full

extension

and

the

ankle

at

-LRB-

anatomical

position

-RRB-

In

the

custom

ankle

dynamometer

the

knee

joint

was

fixed

at

and

to

obtain

a

similar

gastrocnemius

muscle

length

compared

to

that

during

the

tests

using

the

Cybex

the

ankle

angle

was

set

at

dorsiflexion

-LRB-

see

equation

in

Reeves

et

al.

p.

-RRB-

Plantar

flexion

moment

of

the

right

leg

-LRB-

push-off

leg

in

the

tripping

experiments

-RRB-

and

knee

extension

of

the

left

leg

-LRB-

landing

leg

for

tripping

-RRB-

were

measured

Measurements

resulted

in

comparable

values

between

settings

and

were

repeated

times

with

min

rest

between

contractions

Subjects

first

performed

a

maximum

isometric

contraction

by

increasing

their

effort

in

a

linear

ramp

fashion

so

that

maximum

moment

was

reached

within

s

and

then

maintained

for

s.

From

these

measurements

the

maximum

moments

-LRB-

anklemax

and

kneemax

-RRB-

were

calculated

relative

to

body

mass

Next

subjects

were

instructed

to

increase

their

moment

from

to

at

least

of

their

maximum

as

quickly

as

possible

without

counter

movement

Moment

onset

-LRB-

N

m

above

baseline

-RRB-

was

determined

and

rate

of

moment

development

-LRB-

anklertd

and

kneertd

-RRB-

was

calculated

over

the

first

ms

after

moment

onset

and

expressed

relative

to

body

mass

Fig.

of

the

experimental

settings

for

a

right

plantar

flexion

moment

measurements

b

left

knee

extension

moment

measurements

c

leg

press

push-off

force

measurements

d

jumping

measurements

and

e

tripping

experiments

Maximum

leg

press

push-off

force

of

each

lower

limb

was

measured

for

all

subjects

using

the

same

leg

press

fitness

instrument

-LRB-

MR

Systems

Haarlem

the

Netherlands

-RRB-

-LRB-

Fig.

-RRB-

Subjects

performed

a

one-legged

-LRB-

horizontal

-RRB-

push-off

starting

with

the

ankle

joint

angle

at

and

the

knee

joint

angle

at

This

position

was

comparable

to

the

configuration

of

the

support

limb

during

tripping

-LRB-

Pijnappels

et

al.

c

-RRB-

The

fore-foot

was

positioned

on

a

cm

force

transducer

-LRB-

AMTI

Watertown

USA

-RRB-

that

was

mounted

in

the

push-off

platform

Subjects

first

performed

a

maximum

isometric

contraction

with

the

sled

fixed

and

subsequently

a

maximum

dynamic

contraction

with

the

weight

stack

set

equal

to

body

mass

so

the

only

external

resistance

was

the

mass

and

inertia

of

the

body

and

sled

Both

conditions

were

repeated

times

for

both

legs

with

a

min

rest

between

contractions

The

maximum

horizontal

leg

press

push-off

force

-LRB-

legpressmax

-RRB-

was

calculated

from

the

isometric

contractions

and

the

rate

of

force

development

-LRB-

legpressrfd

-RRB-

was

calculated

from

the

dynamic

contractions

over

ms

after

onset

of

force

generation

averaged

over

both

legs

and

expressed

relative

to

body

mass

For

the

jumping

measurement

subjects

performed

a

maximum

two-legged

counter

movement

jump

-LRB-

Fig.

-RRB-

Position

data

of

markers

placed

bilaterally

on

the

trochanter

major

were

measured

by

Optotrak

cameras

-LRB-

Northern

Digital

Waterloo

Canada

-RRB-

From

the

best

of

two

attempts

maximum

jump

height

-LRB-

jumph

-RRB-

was

calculated

as

the

vertical

distance

between

the

highest

averaged

hip

position

during

jumping

and

averaged

hip

height

during

normal

standing

Hand

grip

strength

was

measured

using

a

digital

strain-gauge

dynamometer

-LRB-

Takei

TKK

Takei

Scientific

Instruments

Tokyo

Japan

-RRB-

Subjects

performed

two

maximum

force

trials

with

each

hand

The

maximum

values

of

the

right

and

left

hand

-LRB-

in

kg

-RRB-

were

added

together

-LRB-

handf

-RRB-

Tripping

measurements

and

falls

The

ability

to

prevent

a

fall

after

a

gait

perturbation

was

determined

by

tripping

measurements

-LRB-

Pijnappels

et

al.

-RRB-

Subjects

walked

at

a

self-selected

velocity

over

a

m

walkway

Fourteen

cm

high

obstacles

were

hidden

at

the

left

side

and

seven

obstacles

were

hidden

at

the

right

side

of

the

walkway

over

a

total

distance

of

m

-LRB-

Fig.

-RRB-

In

of

trials

one

of

the

obstacles

suddenly

appeared

-LRB-

based

on

online

kinematic

data

-RRB-

to

catch

the

subject

's

left

swing

leg

at

mid-swing

usually

causing

an

elevating

strategy

for

balance

recovery

This

strategy

involves

the

limb

contacting

the

obstacle

being

elevated

over

the

obstacle

-LRB-

Eng

et

al.

Schillings

et

al.

-RRB-

whilst

the

contralateral

support

limb

provides

push-off

Subjects

were

aware

that

they

could

be

tripped

on

either

leg

but

did

not

know

whether

and

where

an

obstacle

would

appear

in

the

ongoing

trial

They

wore

a

safety

harness

that

moved

along

a

track

above

the

walkway

Subjects

were

classified

as

fallers

based

on

visual

detection

of

full

body

support

by

the

harness

-LRB-

checked

by

video

-RRB-

in

more

than

of

the

tripping

trials

Statistical

analysis

Pearson

's

coefficients

of

correlation

between

the

capacity

measures

were

calculated

In

case

of

high

correlations

between

the

dependent

variables

as

we

found

the

power

of

a

multivariate

analysis

of

variance

-LRB-

MANOVA

-RRB-

decreases

when

the

expected

effect

sizes

are

reasonably

large

and

consistent

in

the

same

direction

-LRB-

Cole

et

al.

-RRB-

We

therefore

focused

on

separate

univariate

ANOVAs

to

determine

which

capacity

measures

differed

between

fallers

and

non-fallers

The

variables

that

appeared

to

be

determinants

of

falls

from

the

ANOVAs

were

used

in

discriminant

analyses

in

order

to

find

the

variable

-LRB-

s

-RRB-

best

discriminating

between

fallers

and

non-fallers

and

to

determine

sensitivity

and

specificity

In

addition

a

cross-validation

was

performed

to

assess

the

generalizability

of

the

predictive

models

each

case

was

classified

by

the

functions

derived

from

all

other

cases

-LRB-

leave-one-out-classification

-RRB-

SPSS

statistical

software

was

used

and

the

level

of

significance

was

set

at

p

Results

Tripping

measurements

and

falls

Seven

of

the

participants

-LRB-

all

women

-RRB-

were

fully

supported

by

the

safety

harness

in

more

than

half

of

the

tripping

trials

Six

of

them

fell

in

all

trials

the

other

fell

in

three

out

of

five

trials

Non-fallers

were

never

fully

supported

by

the

safety

harness

The

averaged

walking

velocity

was

-LRB-

SD

-RRB-

m/s

and

did

not

differ

between

fallers

and

non-fallers

-LRB-

p

-RRB-

Capacity

measurement

as

predictor

for

falls

legpressmax

jumph

and

handf

were

significantly

correlated

with

almost

all

other

capacity

measures

-LRB-

Table

-RRB-

Leg

press

push-off

force

was

not

significantly

different

between

the

left

and

right

leg

of

the

subjects

-LRB-

p

for

legpressmax

and

p

for

legpressrfd

-RRB-

there

was

no

significant

interaction

with

groups

-LRB-

p

for

legpressmax

and

p

for

legpressrfd

-RRB-

and

the

values

were

highly

correlated

between

legs

-LRB-

overall

r

p

for

legpressmax

and

r

p

for

legpressrfd

-RRB-

Table

coefficients

between

capacity

measuresanklertdkneemaxkneertdlegpressmaxlegpressrfdjumphhandfanklemax0

a

bSignificant

correlations

are

in

bold.ap

bp

All

but

one

of

the

univariate

ANOVAs

resulted

in

significant

differences

indicating

several

measures

to

be

different

between

fallers

and

non-fallers

-LRB-

Fig.

-RRB-

Ankle

and

knee

capacity

measures

-LRB-

both

maximum

and

rate

of

moment

development

-RRB-

maximum

leg

press

force

jump

height

and

grip

strength

were

significantly

lower

for

fallers

compared

to

non-fallers

Fig.

group

differences

in

capacity

measures

between

fallers

and

non-fallers

Maximum

-LRB-

max

-RRB-

and

rate

of

moment

development

-LRB-

RTD

-RRB-

of

plantar

flexion

moment

-LRB-

anklemax

and

anklertd

-RRB-

and

knee

extension

moment

-LRB-

kneemax

and

kneertd

-RRB-

maximum

and

rate

of

force

development

-LRB-

RFD

-RRB-

of

leg

press

push-off

force

-LRB-

legpressmax

and

legpressrfd

-RRB-

jump

height

-LRB-

jumph

-RRB-

and

hand

grip

strength

-LRB-

handf

-RRB-

Significant

differences

between

groups

are

indicated

with

p-values

These

seven

variables

were

entered

in

a

stepwise

discriminant

analysis

which

resulted

in

a

significant

model

-LRB-

p

-RRB-

with

legpressmax

as

the

only

predictor

This

model

resulted

in

correctly

classified

cases

and

a

cross-validation

of

-LRB-

Table

-RRB-

For

comparison

discriminant

analyses

with

the

ankle

and

knee

capacity

tests

-LRB-

stepwise

-RRB-

and

with

jump

height

and

grip

strength

as

single

predictors

also

resulted

in

significant

predictive

models

with

slightly

lower

predictive

values

-LRB-

Table

-RRB-

Figure

presents

the

distribution

of

individual

jumph

and

handf

values

both

in

relation

to

legpressmax

Table

variables

resulting

from

stepwise

discriminant

analyses

and

cross-validation

on

capacity

measuresCapacity

measuresPredictive

variablepDiscriminant

analysis

-LRB-

sensitivity/specificity

-RRB-

Cross-validation

-LRB-

sensitivity/specificity

-RRB-

legpressmax

anklemax

anklemax

kneemax

kneertd

jumph

anklertd

kneemax

kneertdanklemax

predictive

modelFig

of

the

individual

values

of

maximum

leg

press

push-off

force

-LRB-

legpressmax

-RRB-

with

jump

height

-LRB-

jumph

-RRB-

and

hand

grip

strength

-LRB-

handf

-RRB-

for

fallers

and

non-fallers

Crosses

indicate

the

incorrect

classified

cases

-LRB-

x

for

legpressmax

for

jumph

and

handf

-RRB-

Discussion

It

is

important

to

identify

individuals

most

at

risk

of

falling

because

they

should

be

considered

with

priority

for

receiving

targeted

exercise

interventions

aimed

at

reducing

the

incidence

of

falls

This

study

investigated

the

possibility

to

identify

fallers

from

maximum

strength

measures

that

could

be

applied

in

clinical

settings

The

results

showed

that

participants

who

fell

after

a

gait

perturbation

could

indeed

be

identified

based

on

these

measures

Especially

a

classification

model

based

on

maximum

leg

press

push-off

force

yielded

high

sensitivity

and

specificity

in

cross-validation

The

subjects

in

this

study

were

relatively

fit

and

healthy

older

adults

Nevertheless

muscle

strength

varied

greatly

between

subjects

with

coefficients

of

variation

between

subjects

ranging

from

to

for

all

strength

measures

Pavol

et

al.

-LRB-

-RRB-

found

that

not

only

people

with

low

muscle

strength

but

also

the

stronger

people

had

a

higher

risk

of

falling

after

a

trip

This

was

explained

by

a

higher

walking

velocity

in

the

stronger

group

which

increases

the

demands

for

adequate

balance

recovery

These

subjects

mainly

used

a

lowering

strategy

which

implies

that

they

were

tripped

at

late

swing

-LRB-

Eng

et

al.

Pijnappels

et

al.

-RRB-

Since

the

trip

was

induced

manually

it

may

be

that

faster

walkers

were

more

likely

to

be

tripped

in

late

swing

It

is

therefore

unclear

whether

velocity

or

instant

of

trip

initiation

was

responsible

for

a

number

of

stronger

subjects

falling

In

our

study

however

walking

velocity

was

not

different

between

fallers

and

non-fallers

and

in

the

range

of

fast

walkers

of

the

study

of

Pavol

even

though

we

did

not

standardize

it

and

explicitly

instructed

subjects

to

walk

at

their

normal

and

comfortable

velocity

Furthermore

we

were

able

to

trip

all

subjects

at

exactly

mid-swing

-LRB-

when

the

toe

height

is

minimal

and

a

trip

is

most

likely

in

daily

life

-RRB-

This

implies

that

the

effect

of

the

trip

by

impact

with

the

obstacle

was

equal

over

subjects

and

could

not

affect

the

outcome

of

the

trip

Yet

this

also

may

suggest

that

instant

of

trip

initiation

and

in

a

more

heterogeneous

group

differences

in

preferred

walking

velocity

must

be

taken

into

account

when

attempting

to

identify

fallers

Although

we

were

able

to

trip

our

subjects

repeatedly

three

of

the

fallers

and

one

non-faller

did

not

complete

the

whole

protocol

up

to

five

tripping

trials

due

to

discomfort

Nevertheless

the

fallers

fell

in

all

trials

and

the

non-faller

did

not

fall

in

four

tripping

trials

Hence

the

number

of

tripping

trials

did

not

affect

the

classification

of

the

participants

Hip

extension

and

knee

flexion

strength

were

not

measured

but

might

also

contribute

to

fall

prediction

as

the

rate

of

development

of

hip

extension

and

knee

flexion

moments

during

push-off

after

tripping

were

found

to

be

lower

in

older

fallers

compared

to

young

adults

-LRB-

Pijnappels

et

al.

-RRB-

Since

especially

hip

extension

capacity

is

quite

difficult

to

determine

-LRB-

especially

in

a

clinical

setting

-RRB-

and

given

limitations

in

the

total

number

of

capacity

measurements

to

be

performed

in

a

single

session

these

variables

were

not

included

in

the

present

study

During

the

push-off

phase

of

a

tripping

reaction

the

knee

is

generating

an

internal

flexion

moment

while

extention

-LRB-

Pijnappels

et

al.

-RRB-

Preliminary

data

suggest

that

a

high

extension

moment

is

required

in

the

leg

making

ground

contact

at

landing

-LRB-

van

Dieën

et

al.

-RRB-

and

a

limited

capacity

to

generate

sufficiently

high

knee

extension

moments

might

thus

increase

the

fall

risk

In

this

study

fallers

could

not

position

their

recovery

foot

adequately

and

were

therefore

fully

supported

by

the

safety

harness

mostly

even

before

landing

This

underlines

that

most

of

the

balance

recovery

takes

place

during

push-off

by

the

support

limb

However

as

falls

can

also

occur

after

landing

-LRB-

Pavol

et

al.

-RRB-

the

requirements

for

landing

need

further

investigation

Fallers

and

non-fallers

were

classified

in

this

study

based

on

their

ability

to

prevent

a

fall

after

an

experimentally

induced

gait

perturbation

In

daily

life

there

are

many

various

ways

in

which

people

fall

Furthermore

this

experimental

study

included

a

small

number

of

participants

which

might

have

influenced

the

predictive

values

A

prospective

study

with

a

larger

cohort

is

necessary

to

generalize

the

results

of

this

study

to

the

prediction

of

falls

in

daily

life

Overall

sufficient

leg

extension

strength

is

required

for

adequate

balance

recovery

after

tripping

This

might

explain

why

a

capacity

measure

that

involves

extension

of

all

lower

limb

joints

-LRB-

i.e.

leg

press

push-off

-RRB-

yielded

the

best

identification

of

fallers

This

one-legged

task

is

highly

similar

to

the

actual

movement

during

the

push-off

phase

of

tripping

-LRB-

Pijnappels

et

al.

c

-RRB-

Jumping

also

requires

rapid

moment

generation

and

was

therefore

expected

to

be

a

good

and

practical

measure

of

whole

lower

limb

strength

Studies

have

shown

that

maximum

jumping

forces

are

lower

in

the

elderly

-LRB-

Izquierdo

et

al.

Runge

et

al.

-RRB-

and

related

to

balance

performance

-LRB-

Izquierdo

et

al.

-RRB-

Jump

height

indeed

resulted

in

good

sensitivity

and

specificity

This

task

was

less

similar

to

the

actual

tripping

action

than

the

leg

press

and

does

not

solely

reflect

strength

as

it

also

requires

complex

coordination

of

many

joints

One

might

argue

that

the

older

fallers

who

were

all

women

may

have

been

more

afraid

to

jump

maximally

than

their

counterparts

However

jump

height

was

strongly

correlated

to

maximum

leg

press

push-off

force

which

was

measured

in

a

secure

and

comfortable

setting

Jumping

performance

therefore

more

likely

reflects

lower

limb

strength

than

an

effect

of

gender

or

fear

Fall

incidents

and

the

ensuing

injury

process

are

multi-factorial

Muscle

strength

is

only

one

of

many

factors

that

associate

with

falls

and

that

has

to

be

taken

into

account

when

identifying

one

's

fall

risk

Yet

this

particular

factor

has

been

indicated

as

one

of

the

main

causal

factors

for

falls

and

is

essential

in

risk

profiles

For

example

in

the

physiological

profile

approach

by

Lord

et

al.

-LRB-

-RRB-

muscle

force

is

tested

in

lower

extremity

muscle

groups

However

these

tests

are

not

based

on

empirically

demonstrated

causal

relations

Our

experimental

study

allowed

investigating

the

relation

between

strength

measures

and

gait

perturbations

in

a

standardized

situation

It

can

be

questioned

whether

the

findings

in

this

study

on

tripping

over

an

obstacle

in

mid-swing

can

be

transferred

to

other

fall

mechanisms

that

occur

in

daily

life

Yet

leg

extension

force

has

also

been

indicated

to

play

an

important

role

in

other

fall

mechanics

such

as

slipping

-LRB-

Chambers

and

Cham

Tang

and

Woollacott

-RRB-

The

results

of

this

study

may

therefore

contribute

to

improvement

of

risk

profiles

for

identification

of

high-risk

fallers

particularly

by

using

relatively

simple

but

specific

measures

of

maximum

strength

For

clinical

use

a

maximum

vertical

jump

test

might

be

more

practical

than

the

leg

press

test

as

it

requires

little

instrumentation

Rittweger

et

al.

-LRB-

-RRB-

demonstrated

that

such

a

test

is

feasible

also

for

subjects

over

the

age

of

and

that

reliability

is

high

Hand

grip

strength

is

a

common

clinically

used

strength

capacity

measure

It

has

been

shown

in

epidemiological

studies

to

be

related

to

leg

extension

strength

and

to

be

associated

to

recurrent

falling

in

daily

life

-LRB-

Stel

et

al.

-RRB-

Our

data

indeed

showed

that

grip

strength

is

significantly

correlated

with

lower

limb

capacities

and

that

it

can

be

used

to

identify

fallers

from

non-fallers

Although

hand

grip

strength

is

easy

to

measure

and

assumed

to

be

related

to

whole

body

strength

one

should

bear

in

mind

that

this

measure

may

be

less

accurate

as

a

predictor

for

falls

it

is

not

task

specific

for

balance

recovery

With

respect

to

fall

prevention

the

associations

found

in

this

study

suggest

that

maximum

whole

leg

extension

force

is

an

important

target

in

conducting

exercise-based

interventions

In

a

pilot

study

we

showed

that

lower

limb

resistance

training

has

the

potential

to

improve

balance

recovery

as

older

trainers

improved

more

in

moment

generation

upon

tripping

than

controls

-LRB-

Pijnappels

et

al.

-RRB-

It

can

be

questioned

whether

fall

prevention

training

should

focus

on

strength

training

alone

as

task-specific

training

of

motor

skills

has

been

shown

to

be

important

-LRB-

Bieryla

et

al.

Owings

et

al.

Troy

and

Grabiner

-RRB-

A

combination

of

both

strength

and

balance

training

is

most

likely

to

be

most

beneficial

for

reduction

of

fall

incidence

-LRB-

Gillespie

et

al.

-RRB-

Finally

it

should

be

noted

that

training

effects

are

only

valuable

if

task-specific

requirements

can

be

achieved

and

it

can

be

questioned

whether

this

is

the

case

in

older

and

more

frail

elderly

Therefore

resistance

training

may

be

particularly

useful

in

the

group

of

relatively

fit

and

healthy

elderly

-LRB-

Barry

and

Carson

Hunter

et

al.

Latham

et

al.

Macaluso

and

De

Vito

-RRB-

which

might

prevent

these

people

from

becoming

recurrent

fallers

Conclusion

Relatively

simple

and

accessible

measures

of

maximum

strength

did

identify

elderly

fallers

from

non-fallers

after

a

standardized

gait

perturbation

The

capacity

to

generate

maximum

extension

force

by

the

whole

leg

-LRB-

e.g.

in

a

leg

press

apparatus

or

during

jumping

-RRB-

resulted

in

the

best

classification

of

older

fallers

and

non-fallers

Follow

up

studies

on

larger

cohorts

with

a

wide

range

of

muscle

strength

and

walking

velocities

are

necessary

to

generalize

these

results

towards

a

valid

prediction

of

fall

risk

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