Ageing reduces light touch and vibrotactile sensitivity on the anterior lower leg and foot dorsum

Accepted Manuscript Ageing reduces light touch and vibrotactile sensitivity on the anterior lower leg and foot dorsum

R.L. Mildren, M.C. Yip, C.R. Lowery, C. Harpur, S.H.M. Brown, L.R. Bent PII: DOI: Reference:

S0531-5565(17)30449-7 doi: 10.1016/j.exger.2017.09.007 EXG 10150

To appear in:

Experimental Gerontology

Received date: Revised date: Accepted date:

5 June 2017 24 July 2017 11 September 2017

Please cite this article as: R.L. Mildren, M.C. Yip, C.R. Lowery, C. Harpur, S.H.M. Brown, L.R. Bent , Ageing reduces light touch and vibrotactile sensitivity on the anterior lower leg and foot dorsum, Experimental Gerontology (2017), doi: 10.1016/j.exger.2017.09.007

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ACCEPTED MANUSCRIPT Ageing reduces light touch and vibrotactile sensitivity on the anterior lower leg and foot dorsum R.L. Mildrena, M.C. Yipa, C.R. Loweryb, C. Harpura, S.H.M. Browna, L.R. Benta. a

Human Health and Nutritional Sciences, University of Guelph, ON, Canadas Centre for Neuroscience Studies, Queen's University, Kingston, ON, Canada

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Department of Kinesiology, University of British Columbia, BC, Canada

Corresponding author:

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Leah R. Bent

Human Health and Nutritional Sciences

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University of Guelph

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Professor

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E-mail: [email protected]

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50 Stone Rd East, Guelph, ON, Canada

Abbreviations:

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MPT: monofilament perceptual threshold VPT: vibrotactile perceptual threshold TUG: timed-up-and-go FRT: functional reach test FA: fast adapting SA: slowly adapting

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ACCEPTED MANUSCRIPT Abstract Cutaneous mechanoreceptors in the anterior lower leg and foot dorsum provide important information about contact with objects and movement at the knee and ankle. This cutaneous feedback contributes to static and dynamic balance control. We conducted

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experiment 1 to determine the effects of aging on anterior lower leg cutaneous feedback.

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We measured light touch (monofilament) perceptual thresholds (MPT) at seven skin sites

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across the anterior lower leg and foot dorsum in 12 young (5 male, aged 21-28) and 13 older adults (8 male, aged 73-92). Results showed that older adults had ~5.5 × higher

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MPTs across these skin sites. We conducted experiment 2 to probe how different

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cutaneous mechanoreceptor subtypes are affected by ageing through measures of vibrotactile perceptual threshold (VPT) at 3, 15, and 40Hz at six skin sites across the

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anterior lower leg and foot dorsum in 10 young (5 male, aged 21-26) and 10 older adults

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(3 male, aged 75-85). In this group, we also assessed functional balance using the timedup-and-go (TUG) and functional reach test (FRT). Older adults demonstrated

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significantly higher VPTs overall, and this effect was largest at 40Hz – a frequency

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primarily transmitted by fast adapting cutaneous afferents. Furthermore, higher thresholds at each frequency tended to correlate with poorer performance on the TUG

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within the older adult group (3Hz: r=.550; 15Hz: r=.689; 40Hz: r=.663). These results suggest ageing influences cutaneous feedback from regions of the lower leg that provide important information about movement and contact. Key words: age; cutaneous mechanoreceptor; balance; gait; skin sensitivity; proprioception

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ACCEPTED MANUSCRIPT 1. Introduction Age related changes in skin sensitivity are commonly assessed at the glabrous skin of the foot sole (Inglis et al., 2002; Wells et al., 2003; Perry, 2006; Machado et al., 2016; Peters et al., 2016). Foot sole cutaneous mechanoreceptors play an important role

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in signaling pressure distribution under the feet, ground contact, and slips. Reduced foot

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sole sensitivity is associated with poorer postural control and increased fall risk in older

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adults (Lord et al., 1994). While the changes in foot sole skin sensitivity with ageing have received considerable attention, less is known about more proximal, non-glabrous skin

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regions such as the foot dorsum and anterior lower leg. In addition to sensing contact

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with objects, these skin regions have been shown to play a prominent role in position and movement awareness (proprioception) and the control of posture and gait (Zehr and

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Stein, 1999; Aimonetti et al., 2007, 2012; Lowrey et al., 2010; Howe et al., 2015).

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Specifically, cutaneous afferents innervating skin on the foot dorsum and shin have been found to respond to the skin deformation produced by ankle movement (Aimonetti et al.,

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2007, 2012). Furthermore, a transient reduction in skin sensitivity on the foot dorsum and

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anterior lower leg in healthy young adults has been shown to impair passive joint position sense (Lowrey at al., 2010) and alter lower limb kinematics during gait (Howe et al.,

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2015). Cutaneous feedback may contribute to motor control reflexively to initiate stumbling corrective responses (Zehr and Stein, 1999) and modulate both lower and upper limb muscle activity (Fallon et al., 2005; Bent and Lowrey, 2013). Reductions in cutaneous afferent feedback from anterior leg regions with ageing may be one factor (along with changes in muscle strength and other sensorimotor systems) that interferes with balance control.

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ACCEPTED MANUSCRIPT Altogether, there is strong evidence to support that cutaneous feedback from nonglabrous skin regions across the lower leg has a critical function in balance and movement control. It is unknown how skin sensitivity across these regions is affected by healthy ageing; therefore, the purpose of the current study was to document the effects of

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ageing on skin sensitivity across the foot dorsum and anterior lower leg. A second aim

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was to determine if there is an association between sensitivity of different cutaneous

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afferent channels and functional balance measures in older adults. Two experiments were conducted to measure light touch (experiment 1) and vibrotactile (experiment 2)

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thresholds in young and older adults. Light touch thresholds were measured using

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monofilaments, a commonly used clinical tool. However, since monofilament perceptual threshold (MPT) is likely set by the firing of fast adapting (FA) cutaneous afferents

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(Strzalkowski et al., 2015), vibrotactile thresholds were also measured to assess

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sensitivity to stimuli that generate different cutaneous afferent population responses. Slowly adapting (SA) cutaneous afferents are maximally sensitive to low vibration

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frequencies (e.g., 3Hz) while FA afferents respond preferentially to higher frequencies

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(e.g., 40Hz) (Talbot et al., 1968; Johansson et al., 1982; Ribot-Ciscar et al., 1989; Toma and Nakajima, 1995). Previous research on the foot sole has demonstrated larger

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reductions in sensitivity to higher vibration frequencies that activate FA cutaneous afferents (Inglis et al., 2002; Wells et al., 2003; Perry, 2006). It was hypothesized that both monofilament and vibrotactile perceptual thresholds (particularly to high vibration frequencies) would be elevated in older adults compared to younger adults, and higher vibrotactile thresholds would be associated with poorer performance on functional balance tests within the older adult group.

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ACCEPTED MANUSCRIPT 2. Methods 2.1. Participants Twenty-two healthy young adults (aged 21-28) and 23 community-dwelling older adults (aged 75-92) participated in this study. One older adult participated in both

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experiments 1 and 2 on separate occasions; the remaining participants were involved in

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only one experiment. All participants were free of neurological and musculoskeletal

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disorders. Procedures were approved by the University of Guelph Research Ethics board, which abides by the declaration of Helsinki.

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2.2. Experiment 1: Light touch (monofilament) perceptual thresholds

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Twelve young adults (5 male, aged 21-28) and 13 older adults (8 male, aged 7392) participated in experiment 1. Participants sat with their right leg extended at the knee

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and right foot secured using a VersaForm pillow. While participants had their eyes

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closed, perceptual thresholds to light touch were assessed using Semmes-Weinstein monofilaments (SenseLab aesthesiometer, Somedic, Sweden). A modified 4-2-1 search

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method was used (Dyck et al., 1993) and participants were instructed to answer with a

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yes/no response when they were at least 90% confident that they perceived the stimulus. Participants were also informed there would be catch trials with no stimulus applied.

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Threshold was defined as the lowest monofilament force (mN) correctly perceived in at least 75% of trials. We assessed sensitivity at multiple locations on the anterior leg in an attempt to cover regions known to signal ankle movement and contacts (Aimonetti et al., 2007). Thresholds were measured at seven skin sites: the Distal foot, Low ankle, Lateral malleolus, Medial malleolus, Middle ankle, Middle shin, and Lateral knee. The Lateral

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ACCEPTED MANUSCRIPT and Medial malleolus sites were located just proximal to each malleolus, and the Middle ankle was located half way between those two points. The Middle shin site was located half way between the knee and middle ankle, and the Lateral knee site was located just distal to the fibular head. Each skin site was tested twice in randomized order and data

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from each site were averaged across the two tests.

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2.3. Experiment 2: Vibrotactile perceptual thresholds and balance tests

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Ten young adults (5 male, aged 21-26) and ten older adults (3 male, aged 75-85) participated in experiment 2. Participants sat with their eyes closed to eliminate visual

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cues and wore noise-cancelling headphones to minimize auditory cues from the motor.

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The position of the right foot was secured using a VersaForm pillow and a 6mm diameter probe was applied perpendicular to the test skin site (Fig. 1). Pre-load force (measured

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using a force transducer: Brüel and Kjær, type 8230, Denmark) was maintained at 1N.

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Vibration was applied using a linear motor (Brüel and Kjær Mini-Shaker, type 4810, Denmark) and perceptual thresholds were measured at six skin sites on the anterior lower

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leg and foot (Hallux, Centre dorsum, Lateral malleolus, Middle ankle, Medial malleolus,

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and Middle shin). The Hallux site was located half way between the proximal nail bed and metatarsalphalangeal joint and the Centre dorsum was located half way between the

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base of the ankle and metatarsalphalangeal joint. Probe acceleration data were measured using an accelerometer (type 4507B, Brüel and Kjær, Denmark), amplified (× 1000), and sampled at 5kHz. Three vibration frequencies (3, 15, and 40Hz) were selected to assess thresholds to stimuli that generate different cutaneous afferent population responses (Johansson et al. 1982). At low stimulus amplitudes, SA type I afferents are maximally responsive to

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ACCEPTED MANUSCRIPT stimulus frequencies ~15Hz, while SA type II afferents are more likely to transmit lower stimulus frequencies (~3Hz). FA type I afferents are maximally sensitive ~40 Hz and FA type II afferents are maximally sensitive to very high frequencies (>60 Hz); however, due to their high sensitivity FA type II afferents are likely activated by lower frequencies as

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well (particularly 40 Hz). Thresholds were measured at each skin site using a custom

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binary search method (Perry, 2006; Mildren et., al. 2016). Briefly, participants were

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instructed to press a hand-held trigger when they could detect vibration. Each trial began with a supra-threshold stimulus iteration (a 2s vibration pulse followed by a 3-5s pause)

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followed by a sub-threshold iteration. Each subsequent iteration was delivered at an

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amplitude half way between the preceding detected and undetected stimuli. Eleven stimulus iterations were delivered in each trial, and three trials were performed at each

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frequency and skin location. Vibrotactile perceptual threshold (the smallest perceived

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peak-to-peak probe amplitude) was averaged across the three trials at each frequency and skin site. Participants were excluded for positive responses to over 25% of catch trials;

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data from one older adult subject was excluded based on this criterion.

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Two basic tests were conducted to assess balance and functional mobility: the timed up and go (TUG) test and the functional reach test (FRT). For the TUG test,

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participants were instructed to perform a sit-to-stand with their arms crossed, quickly walk 3m forward, turn 180°, and walk back to their chair and perform a stand-to-sit with their arms crossed (Podsiadlo and Richardson, 1991). Participants performed three TUG trials; completion time (s) was recorded and averaged across the three trials. For the FRT, participants stood barefoot with one shoulder against the wall and one arm raised perpendicular to the floor. Participants were instructed to perform a maximal voluntary

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ACCEPTED MANUSCRIPT forward flexion with their feet in place (Duncan et al., 1990). The initial and final reach distances (cm) were recorded. Three trials were performed with each arm and data were averaged across trials and arms. 2.4. Data analyses and statistics

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Peak-to-peak probe amplitude (μm) was calculated using a custom MATLAB

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program (MathWorks, USA). Functional reach distance was calculated as the final minus

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the initial reach distances and normalized to participant height. Data were checked for normality, homogeneity of variance (Levene’s test, for between-subject effects), and

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sphericity (Mauchly’s test, for within-subject effects). Monofilament perceptual threshold

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(MPT) and vibrotactile perceptual threshold (VPT) data were log transformed to correct for violations of normality and homogeneity. When necessary, a Greenhouse-Geisser

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correction was applied with violations of sphericity.

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To determine differences in MPT between younger and older adults across skin sites, a two-way mixed analysis of variance (ANOVA) with the factors age and skin site

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was conducted, with age as a between-subject factor. To determine differences in VPT

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between younger and older adults across frequencies and skin sites, a three-way mixed ANOVA with the factors age, skin site, and vibration frequency was conducted.

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Significant ANOVA effects were followed up with independent samples t-tests comparing younger and older adults at each skin site. To determine the relationship between skin sensitivity and functional measures within the older and younger adult groups, Pearson’s product moment correlation coefficients were calculated between VPT at each frequency (averaged across skin sites) and functional reach length and TUG time.

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ACCEPTED MANUSCRIPT 3. Results 3.1. Experiment 1 There was a significant main effect of age on MPT (F(1,23)=55.384, p<0.001); indicating that overall thresholds were higher in older adults (i.e., lower sensitivity)

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compared to younger adults by ~5.5× (Fig. 2). On average, older adult thresholds across

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the seven skin regions were 5.05 mN, compared to thresholds of 0.92 mN in younger

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adults. There was no significant difference in MPT across the seven skin sites (F(4.17,95.97)=1.464, p=0.217). There was a trend toward an age × site interaction

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(F(6,138)=1.951, p=0.077). When the LK skin location (most proximal location that

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exhibited the largest amount of variability between older adults), was removed from the analysis, the age × site interaction was significant (F(5,120)=2.709, p=0.023); larger

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differences in sensitivity between older and younger adults was observed at the Middle

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ankle and Low ankle and smaller differences at the Medial malleolus and Lateral malleolus. Independent samples t-tests showed significant differences in MPT between

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younger and older adults at each of the seven skin sites [p-values <0.001 for Distal foot

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(0.71 vs. 4.96 mN), Low ankle (0.50 vs. 5.55 mN), Medial malleolus (0.95 vs. 3.98 mN), Middle ankle (0.64 vs. 5.89 mN), and Middle shin (1.42 vs 5.67 mN); p=0.008 for

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Lateral malleolus (1.30 vs. 4.14 mN), and p=0.012 for Lateral knee (0.92 vs. 5.15 mN)]. 3.2. Experiment 2

There was a significant main effect of age on VPT (F(1,17)=10.888, p=0.004), indicating that overall older adults had higher thresholds compared to younger adults. There was a significant frequency × age interaction effect (F(2,34)=9.737, p<0.001), where larger differences in VPT between older and younger adults were observed at the 40Hz

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ACCEPTED MANUSCRIPT frequency relative to the lower frequencies (3 and 15Hz) (Fig. 3). There was no significant site × age interaction effect (p>0.05), suggesting that there is a similar level of decline in vibrotactile sensitivity with ageing across all skin areas tested. There was also no significant site × age × frequency interaction (p>0.05).

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Independent samples t-tests comparing older to younger adults showed that at

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3Hz, older adults had significantly higher thresholds at the Centre dorsum (1029 vs. 466

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μm; p=0.003), Lateral malleolus (1032 vs. 463 μm; p=0.012), and Middle shin (1068 vs. 438 μm; p=0.007). At 15Hz, older adults had higher thresholds at the Centre dorsum (272

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vs. 113 μm; p<0.001), Middle ankle (575 vs. 309 μm; p=0.049), and Middle shin (553 vs.

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189 μm; p<0.001). Finally, at 40Hz older adults had higher thresholds at the Centre dorsum (171 vs. 31 μm; p<0.001), Lateral malleolus (169 vs. 101 μm; p=0.030), Middle

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ankle (397 vs. 87 μm; p<0.001), and Middle shin (373 vs. 60 μm; p<0.001) (Fig. 4).

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Mean (± SE) time to complete the TUG was 5.30 ± 0.24 s for the younger adult group and 8.79 ± 0.51 s for the older adult group. Mean reach distance for the FRT was

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33.7 ± 2.67 cm for the younger adult group and 22.60 ± 1.98 cm for the older adult

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group. In the older adult group, thresholds to 15Hz vibration were found to be positively correlated with TUG time (r=.689, p=0.040), and there was a trend toward a significant

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positive correlation between 40Hz thresholds and TUG time (r=0.663, p=0.067) and a non-significant positive correlation between 3Hz thresholds and TUG time (r=0.550, p=0.125) (Table 1). These correlations indicate that higher thresholds (i.e., lower sensitivities) were associated with longer completion time in the TUG test. There were no significant correlations between VPT at 3, 15, and 40Hz and FRT (p-values >0.05) in the

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ACCEPTED MANUSCRIPT older adult group. There were also no significant correlations between the functional tests and threshold measures within the younger adult group (Table 2).

4. Discussion

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In healthy young adults, mechanoreceptors in the anterior lower leg and foot

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dorsum have previously been shown to respond to skin stretch and compression during

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ankle movement (Aimonetti et al., 2007, 2012) and contribute to proprioception at the ankle (Lowrey et al., 2010) and the control of posture and gait (Zehr and Stein, 1999;

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Howe et al., 2015). Our results demonstrate that older adults have dramatically higher

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light touch and vibrotactile thresholds (i.e., lower sensitivity) across the anterior lower leg and foot dorsum. Furthermore, there was an association between VPT and

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performance on a functional balance task (the timed up and go) within the older adult

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group.

4.1. Light touch (monofilament) perceptual thresholds

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MPTs were significantly higher in older adults across all skin regions tested (Fig.

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2). On average, older adult MPTs were ~5.5 times higher than younger adults. This finding suggests lower sensitivity to stimuli that target FA cutaneous afferents

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(Strzalkowski et al., 2015). FA afferents can signal contact and release as well as skin deformation. Specifically, FA type I afferents have small receptive field sizes and are activated by joint movements that induce skin stretch or compression when their receptive field is situated close to that joint (Edin and Abbs, 1991; Edin, 2001). The high MPTs around the anterior ankle (particularly the Middle and Low ankle) as well as the Lateral knee indicate compromised signaling from regions where FAI afferents code

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ACCEPTED MANUSCRIPT ankle and knee movement. Meanwhile, FA type II afferents have larger receptive field sizes and can respond to stimuli applied more remotely, and they predominantly code skin stretch over compression (Aimonetti et al., 2007, 2012). The loss of FAII feedback from regions near and remote to a joint can therefore have implications for

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proprioception; this includes the Middle shin and Distal foot. FA type I and II afferent

4.2. Vibrotactile perceptual thresholds

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thus providing the earliest sensory feedback of a trip.

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feedback from the anterior lower leg is also important for sensing contact with an object,

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Vibrotactile perceptual thresholds were higher in older adults across the three

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frequencies applied (3, 15, and 40Hz), which suggests that ageing increases thresholds to tactile stimuli that activate over a range of afferent classes. The largest threshold

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difference was seen at the highest frequency (40Hz; Fig. 3) – a frequency that

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predominantly activates FA afferents (Johansson et al., 1982). This finding is in alignment with the dramatic reductions in MPT (which is primarily mediated by FA

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afferents – see section 4.1) observed in experiment 1. Similarly, previous work has found

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that foot sole thresholds to high vibration frequencies (>25Hz) are the most affected by ageing (Inglis et al., 2002; Wells et al., 2003; Perry, 2006). Histological examinations

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provide evidence that the mechanoreceptive end organs of FA afferents are noticeably impaired with ageing; notably, examinations have shown a decline in the number of Pacinian corpuscles (the end organ of FAII afferents) and a decline in the number as well as structural changes in Meissner’s corpuscles (the end organ of FAI afferents) (Cauna and Mannan, 1958; Iwasaki et al., 2003; Bolton et al., 1966; Paré et al., 2007).

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ACCEPTED MANUSCRIPT The higher VPTs observed in older adults at low frequencies (3 and 15Hz) also suggests slowly adapting (SA) afferents are affected by ageing, although this change was less dramatic than the changes seen at the more strictly FA mediated frequency (40Hz). SA afferents provide relatively sustained and graded information about pressure and skin

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stretch. For example, recordings from cat SA afferents during gait demonstrate activity

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during the stance phase even when the receptive field does not make contact with the

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ground (Loeb et al., 1980). In addition, Sinkjær et al., (1994) showed that human sural nerve cutaneous afferents were activated by foot drop in a hemiplegic patient. With

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ageing, previous research has described evidence of Merkel disk degeneration (the end

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organ of SAI afferents) in the mystacial pad of the rat (Fundin et al., 1997) and a decreased number of Ruffini endings (the end organs of SAII afferents) in human

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ligaments (Morisawa, 1998). In addition, changes in the afferent nerves themselves such

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as loss of myelination (Verdú et al., 2000) as well as changes in mechanical properties of the skin (Rittlé and Fisher, 2015; Montagna and Carlisle, 1979; Strzalkowski et al., 2015)

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with aging also likely contribute to reduced cutaneous afferent feedback.

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4.3. Skin sensitivity and functional balance Strong positive correlations (r-values ~.6; Table 1) were found between VPT and

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TUG completion time in the older adults, indicating that lower vibrotactile sensitivity was associated with poorer performance on this functional balance assessment. However, these strong correlations failed to reach significance at all vibration frequencies likely due to the low sample size of older adults, and therefore should be interpreted with caution. Our findings agree with previous work that has shown a correlation between VPT at 128Hz and composite mobility scores in a sample of over 600 older adults (Buchman et

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ACCEPTED MANUSCRIPT al., 2009). Further analysis by Buchman et al., (2009) showed that the gait and balance components were primarily driving the relationship between skin sensitivity and composite mobility scores. Similarly, previous work has highlighted the importance of skin feedback from the anterior lower leg during gait in healthy young adults (Howe et

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al., 2015). The TUG involves gait as well as postural transitions that are challenging for

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balance control. Therefore, it is not surprising that reduced skin sensitivity on the anterior

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lower leg is associated with poorer TUG performance; the strength of this relationship

postural control during postural transitions.

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(r~.6) could highlight the importance of skin feedback from these regions in gait and

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There were no associations between VPTs and performance on the FRT. The FRT may be a good predictor of postural instability encountered during daily activities such as

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reaching to cupboards (Jenkins et al., 2010). The absence of an association between VPT

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and FRT performance may be due to a larger influence of other components on the FRT, including joint mobility and trunk and upper body strength and coordination. In addition,

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during the FRT the ankle muscles are primarily isometrically contracted; therefore, ankle

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control may be more reliant upon sensory feedback from receptors in muscle and tendon. The lack of relationship between VPT and FRT might also support the idea that skin

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feedback from the anterior lower leg has a greater involvement in the control of more automated movement sequences (such as gait) over slower deliberate movements (such as maximal forward reaches). Skin feedback from the foot has been shown to be capable of reflexive modulation of both lower limb (Van Wezel et al., 1997; Zehr and Stein, 1999; Fallon et al., 2005) and upper limb (Bent and Lowrey, 2013) muscle activity.

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ACCEPTED MANUSCRIPT 4.4. Conclusions and significance Our light touch (monofilament) and vibrotactile perceptual threshold data demonstrate that older adults have dramatically reduced skin sensitivity across the foot dorsum and anterior lower leg. Cutaneous afferent feedback from these regions is

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important for proprioception (Lowrey et al., 2010; Aimonetti et al., 2007, 2012) and gait

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(Howe et al., 2015 Choi et al., 2016). Our results also showed an association between

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vibrotactile thresholds and performance on the TUG test; a task that involves postural transitions and gait. Through the assessment of perceptual thresholds to vibrotactile

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stimuli that target different afferent classes (based on frequency), our results provide

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evidence of a decline in sensitivity across all afferent channels with ageing; however, FA channels are likely influenced to the greatest extent.

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Foot sole skin feedback is commonly assessed and targeted with devices to

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augment feedback and improve postural stability (Perry et al., 2008; Priplata et al., 2006). The decline in skin sensitivity on the anterior lower leg and foot dorsum also likely

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contributes to the changes in balance control with ageing. Therefore, skin over this region

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foot sole.

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could be a target for improving mobility and stability in addition to efforts aimed at the

Acknowledgements: This work was supported by funding from the Natural Sciences and Engineering Research Council (NSERC) of Canada

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ACCEPTED MANUSCRIPT Wells, C., Ward, L.M., Chua, R., Inglis, J.T., 2003. Regional variation and changes with ageing in vibrotactile sensitivity in the human footsole. J. Gerontol. A. Biol. Sci. Med. Sci. 58:680–686. Zehr, E.P., Stein, R.B., 1999. What functions do reflexes serve during human

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locomotion? Prog .Neurobiol. 58:185–205.

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ACCEPTED MANUSCRIPT Figure captions: Fig. 1) Experimental setup for vibrotactile perceptual threshold testing. The foot and leg were secured using a VersaForm pillow and the probe (fixed to a linear motor) was

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positioned perpendicular to the skin with a pre-load force of 1N.

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Fig. 2) Mean (± SE) monofilament perceptual threshold comparisons between older and

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younger adults across skin sites on the lower leg. Older adults had significantly higher thresholds at all skin sites.

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DF=distal foot; LA=low ankle; LM=lateral malleolus; MM=medial malleolus;

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MA=middle ankle; MS=middle shin; LK=lateral knee.

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*p<0.05.

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Fig. 3) Mean (± SE) vibrotactile perceptual threshold changes with aging at 3, 15 and 40Hz frequencies. Thresholds were significantly higher in older adults; furthermore,

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thresholds to 40Hz vibration were the most affected by age.

Fig. 4) Mean (± SE) vibrotactile perceptual thresholds at 3Hz (A), 15Hz (B), and 40Hz

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(C) for younger and older adults across skin regions on the lower leg. H=hallux; CD=centre dorsum; LM=lateral malleolus; MM=medial malleolus; MA=middle ankle; MS=middle shin. *p<0.05.

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Fig. 1

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Fig. 2

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Fig. 3

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Fig. 4

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ACCEPTED MANUSCRIPT Table 1: Correlations between skin vibration perceptual threshold measures and functional assessment outcomes within the group of older adults. r

p

3Hz TUG

.550

0.125

15Hz TUG

.689*

0.040

40Hz TUG

.663†

0.067

3Hz FRT

-.045

0.908

15Hz FRT

-.073

40Hz FRT

-.257

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0.851 0.505

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†p<0.1, *p<0.05.

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Note. Threshold measures for each frequency were averaged across skin sites.

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ACCEPTED MANUSCRIPT Table 2: Correlations between skin vibration perceptual threshold measures and functional assessment outcomes within the group of younger adults. r

p

3Hz TUG

-.368

0.295

15Hz TUG

0.200

0.579

40Hz TUG

-.177

0.626

3Hz FRT

.322

0.365

15Hz FRT

-.229

40Hz FRT

.080

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0.827

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0.524

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Highlights

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We examined the effects of ageing on anterior leg and foot dorsum skin

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sensitivity Different cutaneous channels were targeted using specific vibration frequencies

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Ageing strongly increased thresholds to stimuli that targeted fast adapting

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receptors

Thresholds correlated with performance on an assessment of gait and transitions

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Impaired anterior lower leg skin sensitivity with ageing should be considered

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

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