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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.