Shoulder Joint Position Sense Improves with External Load David N. Suprak, PhD Louis R. Osternig,...
-
Upload
colin-robertson -
Category
Documents
-
view
223 -
download
0
Transcript of Shoulder Joint Position Sense Improves with External Load David N. Suprak, PhD Louis R. Osternig,...
Shoulder Joint Position Sense Improves with External Load
David N. Suprak, PhDLouis R. Osternig, PhD
Paul van Donkelaar, PhDAndrew R. Karduna, PhD
Introduction
• Joint stability– Functional activity– Contributing factors
• Proprioception– Feedback from limbs to CNS (Sherrington, 1906)
• Joint position sense (JPS) and kinesthesia (Dover et al,
2003)
– Muscle stiffness, coordination– Importance for shoulder function
Mechanoreceptors
• Capsuloligamentous• Pacinian
• Ruffini
• Golgi tendon organ-like
• End range (Salo and Tatton, 1993; Vangsness, 1995; Steinbeck, 2003)
• Musculotendinous• Muscle spindles
• Golgi tendon organs
• Throughout ROM (Rymer and D'Almeida, 1980)• Spindle sensitivity modulation (Burke, 1978; Durbaba, 2001; Jami, 1980)
Introduction
Muscle Spindle
• Alpha-gamma linkage (Edin and Vallbo, 1990)
• Increased stimulation and sensitivity w/ muscle contraction (Burke, 1978; Durbaba, 2001;
Jami, 1980)
Introduction
JPS and Muscle Activation
• Active JPS more accurate than passive (Aydin et al, 2001; Edmonds et al, 2003;
Potzl et al, 2004)
• Knee JPS with weight-bearing (Bullock-Saxton, 2001)
Introduction
Effect of Elevation Angle
• Decreased error approaching 90 deg (Suprak et al, 2006)– Torque
• Muscle spindle sensitivity
• Did not assess effect of muscle activation directly
Introduction
Purpose
• Effect of altering external load at constant position on repositioning error
• Hypothesis– Linear decrease in error with increased load
Introduction
Subjects
• 24 healthy subjects– (10 M, 14 F)– Inclusion
• No hx of shoulder injury requiring surgery or rehabilitation
– Exclusion• Limited elevation ROM
• Diagnosed neuromuscular disorders
Methods
Experimental Set-up
Load
Head-mounted display
Thoracic receiver
Humeral cuff and receiver
Methods
Load Calculation
• Baseline shoulder torque– Arm length– Body mass– Segment mass, COM estimates (Dempster, 1955)
• 10%, 20%, 30%, and 40% above baseline torque
• 5 Loading conditions
Methods
Methods
θθ
Absolute Error Calculation
Target Positions
20/30
35/50
50/7020/70
5 trials:
2 trials at 35/50
1 trial at distracters
Methods
Statistical Analysis
• Planned linear contrast
• One-way repeated measures ANOVA– IV: External resistance (5 levels)– DV: Vector error
• Analysis repeated for plane and elevation error
• α < 0.05
Methods
Vector Error by Resistance
4
5
6
7
8
9
NR 10% 20% 30% 40%
Resistance (% above baseline torque)
Vec
tor
Err
or (
Deg
)
0
Results
Plane Error by ResistanceResults
Elevation Error by ResistanceResults
4
5
6
7
8
9
NR 10% 20% 30% 40%
Resistance (% above baseline torque)
Vec
tor
Err
or (
Deg
)
0
Discussion
• Non-linear pattern– Internal representation
– Sampling variability
Discussion
• JPS increases with external load– Muscle activation – receptor sensitivity
(Durbaba, 2001)
• Only in direction of load
• Role of musculotendinous receptors
• Injury prevention under high forces
Thank you