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