Modulation of muscle spindles pathway with height of the standing - - PowerPoint PPT Presentation

Modulation of muscle spindles pathway with height of the standing surface in young and older adults

Johannsson J, Duchateau J, Baudry S Laboratory of Applied Biology and Neurophysiology Université libre de Bruxelles, Belgium

Postural control

Integration of vestibular, visual and proprioceptive information in the central nervous system (Fransson et al. 2004) Measure of Centre of Pressure (CoP) excursion: Point location of the vertical ground reaction force vector Spectral analysis of CoP provides indirect informations of the sensory inputs controlling upright standing:

• 0.2-0.5 Hz: Visual contribution

(Mauritz et al. 1977; Singh et al. 2012)

• 0.5-2 Hz: Vestibular contribution

(Mauritz and Dietz 1980; Mauritz and Römmelt 1979)

• 2-20 Hz: Proprioceptive contribution

(Dietz et al. 1979; Dietz et al. 1980)

Spinal Modulation during postural control

Baudry et al. 2015

Hoffman (H) reflex

Hoffman (H) reflex is modulated depending on upright standing conditions

H reflex when young adults stand at the edge of a platform at 1.6 m

(Sibley et al. 2007)

restricting stepping response

Ageing

Specific neural adjustments in balance control

(Baudry 2016)

fear of falling associated with stair negociation

(Tiedemann et al. 2007)

Investigate the modulation of the muscle spindles pathway at the top of a staircase in young and older adults

Methods

• 10 young adults [24.7 (1.3) yrs]

10 elderly adults [72.2 (7.9) yrs]

• Two experimental situations

Downstairs Upstairs

0.7m

Variables of interest

H reflex recruitment curve:

• 50% (H50) of the maximal amplitude of H reflex in soleus (expressed relative

to Mmax)

• Slope of the input-output relation of H reflex calculated at H50

Electromyographic activities (EMG)

• Soleus (SOL)
• Gastrocnemius medialis (GM)
• Tibialis anterior (TA)

CoP Parameters Frequency domain

• Power spectral density (PSD) of CoP: 0.2-0.5 Hz; 0.5-2 Hz; 2-20 Hz

Time domain

• Path length (mm)
• Sway area (mm²)
• Mean Velocity (mm/s)

H-reflex amplitude decreases upstairs

Situation main effect: p=0.06

Age main effect: p=0.06 Situation x Age: p>0.05 Age main effect: p=0.02 Situation x Age: p>0.05

5 10 15 20 25

Young Older

Down Up * H reflex amplitude (%M max)

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Down Up Slope of H reflex

0.00 0.01 0.02 0.03 0.04

Down Up

Young Older

EMG-SOL (mV)

0.000 0.005 0.010 0.015 0.020 0.025

Down Up * EMG-TA (mV)

No change in SOL and GM EMG but change in TA EMG

Tibialis anterior:

Age main effect: p> 0.05 Situation x Age: p>0.05

Soleus:

Age main effect: p> 0.05 Situation x Age: p>0.05

No relation with H reflex amplitude (r²=0.01, p>0.05)

25 50 75 100

Down Up *

Young Older

PSD 0.2-0.5 Hz

2 4 6 8 10 12 14 16 18 20

Down Up * PSD 2-20 Hz

Opposite shift in low- and high frequency band

Visual modulation: 0.2-0.5 Hz

Age main effect: p> 0.05 Situation x Age: p>0.05

Proprioceptive modulation: 2-20 Hz

Age main effect: p> 0.05 Situation x Age: p>0.05

Vestibular modulation: 0.5-2 Hz: No modulation

Greater CoP excursions upstairs

CoP Path length: Situation main effect: p= 0.005 Age main effect: p=0.04 Situation x Age: p>0.05 CoP mean velocity: Situation main effect: p= 0.002 Age main effect: p=0.02 Situation x Age: p>0.05

100 200 300 400 500

Down Up *

Young Older

CoP Sway area (mm2)

Increase in CoP excursions when standing upstairs In contrast with previous literature

(Adkin et al. 2000; Davis et al. 2009)

Increase TA EMG activity: change of posture (backward shift)

(Carpenter et al 1999)

Changes in CoP parameters depends on the height of the surface

(Davis et al. 2009)

Possibility to use stepping strategy

Increase in CoP excursions

Decrease in the proprioceptive contribution

Decrease in H-reflex amplitude and slope upstairs

(Sibley et al 2007)

• Increase in TA EMG but no relation between H reflex and TA EMG

Likely not reciprocal inhibition: inhibition of the antagonist by the activation of the agonist

(Johannsson et al. 2015)

• No changes in plantar flexors EMG and no relation between H reflex and

plantar flexors EMG Likely not due to a change in the excitability of the motor neurones pool

(Matthews 1986)

Role of presynaptic inhibition: inhibition of the Ia afferent input onto the motor neuron pool

(Rudomin and Schmidt 1999)

Situation-related modulation of H-reflex pathway

Reduce the risk of unexpected reflex activity that may impair balance control

(Diener et al. 1983)

Increase in PSD in 0.2-0.5 Hz frequency band Increased contribution of visual information Decrease in PSD in 2-20 Hz frequency band Decreased contribution of proprioceptive information

Reweighting of the sensory sources when standing upstairs: Shift to greater reliance on visual inputs to control upright standing at the top of the stairs

Decrease in the proprioceptive contribution

Younger = Older

Similar H reflex pathway modulation

• Greater from a seated to upright standing position

(Baudry et al. 2015)

• Lesser during contraction tasks

(Chen et al. 2015; Holmes et al. 2015)

Task-dependent modulation Healthy and active elderly adults :

• Berg scale > 45
• Short Physical Performance Battery (8-12)

Daily live situation Increase risk of fall in staircase when < 4 steps

(Jackson and Cohen, 1995)

Conclusion

Decrease in H-reflex amplitude with a reduced contribution of proprioceptive inputs and a greater dependance of visual inputs when standing upstairs in young and older adults

Reweighting of sensory inputs when standing at the top of a staircase Healthy older adults preserved their ability to adjust postural control to environmental demand

jjohanns@ulb.ac.be

Thank you for your attention!

jjohanns@ulb.ac.be