Download Laboratory Exercise 6 - The University of British Columbia

THE UNIVERSITY OF BRITISH COLUMBIA
HUMAN KINETICS 563
Laboratory Exercise 6
Title: Lombard’s Paradox: co-contraction of knee extensors and flexors during walking
Objective: Today’s project deals with a specific example of muscle activation, namely cocontraction. While we might conclude that simultaneous action of an agonist and an antagonist
will result in no motion or ineffective motion there are many examples where this occurs without
reducing the quality of the movement. The object is to look at the case of simultaneous activation
of knee flexors and extensors during walking and examine and explain how this can occur.
Protocol :
For this lab you will need to record the movements of the lower leg in two dimensions and the
electrical activity associated with the knee flexors and extensors. Each student will walk on the
treadmill at two speeds, 1.0 m/s and 2.0 m/s. During this time, EMG recordings will be made
from 4 muscles; vastus lateralis, rectus femoris, biceps femoris, and semintendinosus. In addition
simultaneous video recordings of the lower limb will be made using the Peak Motus system.
Three markers will be used: one on the greater trochanter, one on the lateral aspect of the knee
joint line, and one on the ankles lateral malleolus.
Analysis: For this lab, you are to compute a group mean rather than looking at single-subject
data. This will encourage you to look at variability in your data. First, define an index of cocontraction and justify its use in further research. For the analysis, you will digitise the video data
to determine events like heel strike, toe off, stance phase, and swing phase. Further, as you are
looking at one and two-joint muscles knowing the ankle, knee, and hip angles will be useful. You
will also have to determine a method for linear interpolation of your data so that you can
standardize the analysis to a single stride.
For the EMG data, to facilitate across-student comparisons, a maximal contraction for extension
and for flexion will be performed. The amplitude normalized data will also be time-normalized
to match the kinematic data.
Equipment needed:
1. Wear clothes that will permit affixing electrodes over the muscle of the thigh and shank
and to place reflective markers over the hip, knee, and ankle.
2. Quinton treadmill
3. Therapeutics Unlimited EMG system
4. 4 pairs of electrodes
5. Peak Motus System
Questions: Consider the following.
1. What is Lombard’s Paradox?
2. How did you amplitude and time normalize your data? How effective was the method
used for amplitude normalization?
3. Describe the salient features of the EMG activation for each muscle during walking.
THE UNIVERSITY OF BRITISH COLUMBIA
HUMAN KINETICS 563
4. What are the major differences between the two speeds in terms of EMG activation
for each muscle?
5. How different were the time and amplitude normalized data for each subject.
6. To what extent was there co-contraction – identify which muscles.
7. Was the degree of co-contraction affected by walking speed?
8. How useful was your index? What were its strength and weaknesses?
9. Why is co-contraction a useful characteristic of two-joint muscles?
Reading:
1. Robertson, G., Caldwell, G., Hamill, J., Kamen, G., Whittlesey, S. Research Methods in
Biomechanics, Chapter 1, 3, 5, 8
2. Falconer, K. and Winter, D.A. (1985) Quantitative assessment of co-contraction at the
ankle joint in walking. Electromyography and Clinical Neurophysiology 25, 135-149.
3. Gregor, R., Cavanagh, P. and Lafortune, M. (1985). Knee flexor moments during
propulsion in cycling – a creative solution to Lombard’s paradox. Journal of
Biomechanics 18(5), 307-316.
4. Lombard, W.P., & Abbott, F.M. (1907). The mechanical effects produced by the
contraction of individual muscles of the thigh of the frog. American Journal of
Physiology, 20, 1-60.
5. Rasch, P.J., & Burke, R.K. (1978). Kinesiology and applied anatomy. (6th ed.).
Philadelphia: Lea & Febiger.
6. Therapeutics Unlimited Manual. A PDF file (you already have a copy).
7. Peak 2D manual. A PDF file (You already have a copy).
8. Winter, D.A. (1990) Biomechanics and Motor Control of Human Movement. Chapter 2.