accuracy of gastrocnemius.. slide

Accuracy of gastrocnemius muscles forces in walking and running goats predicted by one-element and two-element Hill-type models

Author: Lee, S. S Published: Sep. 2013

Presenter: Christopher D. Whitney

Introduction

● Hill-type muscle models are commonly used to predict muscle forces ● However, they are not very accurate during relevant movements (i.e. walking,

running, etc.) ● This study evaluates a novel two element Hill-type model

○ Inspired by the different muscle fiber types (e.g ‘fast’ and ‘slow’)

Methods

● Data collection ○ Goats were trained to walk, trot and gallop on a motorized treadmill○ Lateral and medial gastrocnemius were instrumented w/

■ Implanted EMG electrodes to measure activation■ Sonomicrometry crystals to measure fascicle length (resolution 0.3 μm) ■ “E”-shaped tendon buckles to measure tendon forces

○ Recorded in-vivo during 15-20 strides during different conditions (e.g walking, trotting, galloping) at 5000 Hz

○ Force–length and force-velocity relationships were calculated in-situ

Methods (Cont.)

● Data processing ○ Motor recruitment signals for slow and fast fiber types were identified through a wavelet

optimization [2]

○ Transfer function were derived for the whole muscle as well as the slower and faster motor units (see below)

○ Constants were identified for the different motor units and were determined from in-situ data pooled from the six goats.

Constants

Muscle Model

Active-FL Passive FL Pennation AngleScaling Factor Total Force

Are you ready for the schematic?

Results

Results

● In-vivo forces yielded r2 values (0.26-0.51)● In-situ forces yielded r2 values (0.8–0.95) ● Two-element model more accurately than the one-element model under in situ

and in vivo conditions

Limitations

Limitations● Assumption that activation, force–length, and force–velocity properties are

independent ● Failure to account for history-dependent effects● Time resolution errors in the Gauss filter applied during the wavelet analysis● Exclusion of tendon in the model

Questions?Thoughts?

References 1. Lee, S.S., Arnold, A.S., Miara, M. de B., Biewener, A.A. and Wakeling, J.M. 2013. Accuracy

of gastrocnemius muscles forces in walking and running goats predicted by one-element and two-element Hill-type models. Journal of biomechanics. 46, 13 (Sep. 2013), 2288–95.

2. Lee, S.S., Miara, M. de B., Arnold, A.S., Biewener, A.A. and Wakeling, J.M. 2011. EMG analysis tuned for determining the timing and level of activation in different motor units. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology. 21, 4 (Aug. 2011), 557–65.