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Biomechanics of Human Movement: Mechanisms and Methods 17th International Symposium Neuromuscular Research Center (NMRC) University of Jyvskyl Is there inhibition during eccentric muscle contractions? Functional implications and

  1. Biomechanics of Human Movement: Mechanisms and Methods 17th International Symposium  Neuromuscular Research Center (NMRC)  University of Jyväskylä Is there inhibition during eccentric muscle contractions? Functional implications and effects of resistance training Per Aagaard Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark Types of muscle contraction Eccentric Eccentric muscle contraction muscle generating contractile force while lengthening Concentric Concentric muscle contraction muscle generating contractile force while shortening Isometric muscle contraction Isometric muscle generating contractile force while maintaining constant length Neural control of eccentric contractions Why is ECC strength important? In some sports very high eccentric muscle strength is a prerequisite for superior athletic performance... 1

  2. Neural control of eccentric contractions Why is neural modulation important? Human skeletal muscles may contract eccentrically to slowly decelerate movement: 'dampening' function low muscle stiffness However, skeletal muscles can also contract eccentrically very rapidly to decelerate-accelerate movement (SSC) : 'rebound' function high muscle stiffness Neural control of eccentric contractions Why is neural modulation important? Cat soleus, ventral nerve root stimulation in situ Joyce, Rack, Westbury, J Physiol 204, 1969 Neural control of eccentric contractions Why is neural modulation important? Cat soleus, ventral nerve root stimulation in situ Joyce, Rack, Westbury, J Physiol 204, 1969 2

  3. Neural control of eccentric contractions Why is neural modulation important? Neural input from the CNS to myofibers determines the stiffness behavior of the muscle: ► high-stiffness 'rebound' profile or ► compliant 'dampening' profile 3

  4. Neural control of eccentric contractions Expression of maximal ECC muscle strength in vivo Moment of Force (Nm)  350 300 250 200 150 100 50 0 80 K 70 n 60 e e 50 j o 40 i n 30 t C 240 O N a 20 C n -30 30 g 10 Angular velocity ( o s-1 ) C C E l e -240 ( o ) Contractile characteristics of skeletal muscle during maximal ECC and CON contraction 180 Katz B, J. Physiol. 96, 1939 180 Edman KAP, J. Physiol. 404, 1988 Muscle Force (isometric = 100%) Muscle Force (isometric = 100%) 160 160 140 Human quadriceps muscle, 140 electrical muscle stimulation 120 120 superimposed onto maximal voluntary contraction 100 100 (Westing et al 1990) 80 80 60 60 40 isometric 40 20 20 eccentric concentric eccentric concentric 0 0 -40 -20 0 20 40 60 80 100 Contraction Speed percent of V max Contraction Speed From Aagaard & Thorstensson. Neuromuscular aspects of exercise: Adaptive responses evoked by strength training, Textbook of Sports Medicine (Eds. Kjær et al) 2003 Increased electrically superimposed muscle torques only observed in untrained individuals, not in strength trained athletes... SEDENTARY subjects STRENGTH TRAINED subjects Knee Extensor torque Knee Extensor torque eccentric concentric eccentric concentric Knee Angular Velocity ( o /s) Knee Angular Velocity ( o /s) Amiridis, Martin, Van Hoecke et al, Eur J Appl Physiol 1996 4

  5. Expression of maximal ECCentric and CONcentric muscle strength in vivo Maximal ECC and CONC quadriceps contraction strength (elite alpine skier) based on peak Moment highly strength trained athlete 500 (Nm) (alpine skiier) based on peak Moment 400 sedentary subject of similar Moment of Force age and body mass max ECC strength 300 200 100 eccentric concentric 0 -240 -30 0 30 240 ( o/sec) Angular velocity Aagaard, unpubl. data Team Danmark Testcenter Neural control of eccentric contractions Surface EMG recording Neuromuscular activity during ECC contractions Segmented EMG patterns (burst behavior) typically is observed during slow submaximal ECC muscle contraction 800 400 uVolt 0 Vast Lat -400 -800 600 300 uVolt 0 Vast Med -300 -600 90 degrees 60 knee angle concentric 30 eccentric phase phase 0 0 500 1000 1500 2000 2500 3000 3500 4000 Time (miliseconds) 5

  6. Neuromuscular activity during ECC contractions Segmented EMG patterns (burst behavior) typically is observed during slow submaximal ECC muscle contraction How is it possible to evaluate neuromuscular activity during maximal ECC muscle contractions? Isokinetic dynamometry and muscle electromyography (EMG) recording position 100 Nm Moment 4000 uVolt EMG VL -4000 3000 uVolt EMG VM -3000 2500 uVolt EMG RF -2500 0 1000 2000 3000 4000 5000 Time (msec) Reduced neuromuscular activity (  EMG amplitude) during maximal ECC versus CON quadriceps contraction 4000 uVolt EMG VL -4000 3000 uVolt EMG VM -3000 2500 uVolt EMG RF -2500 0 1000 2000 3000 4000 5000 Time (msec) Westing et al 1991 6

  7. Reduced neuromuscular activity (  EMG amplitude) during maximal ECC versus CON quadriceps contraction Komi et al, Med Sci Sports Exerc 32, 2000 Neuromuscular activity m. quadriceps slow ECC contraction slow CONC contraction pre training pre training 10 o 10 o position 90 o 90 o 100 Nm Moment 4000 uVolt EMG VL -4000 Calculating mean Calculating mean filtered EMG amplitude (iEMG) filtered EMG amplitude (iEMG) 3000 uVolt EMG VM -3000 2500 uVolt EMG RF -2500 0 1000 2000 3000 4000 5000 0 1000 2000 3000 4000 5000 Time (msec) Time (msec) Aagaard et al, J Appl Physiol 2000 Suppressed quadriceps EMG activity during maximal ECC contraction * * 200 Average quadriceps EMG and strength 180 * Percent 160 quadriceps force moment 140 percent * * 200 120 100 180 * * Quadriceps 100 * EMG VL Percent force moment percent 160 * Percent 90 * (percent) * 80 140 70 120 60 100 100 EMG VM 90 * percent Percent 100 * 80 * * 70 90 * Percent mean EMG 60 * 80 * EMG RF Quadriceps 100 * percent (percent) Percent 90 70 80 60 70 fast ECC slow slow CONC fast 60 eccentric concentric -240 -30 30 240 eccentric concentric -240 -30 30 240 Knee angular velocity ( o s-1 ) ( o s-1 ) Knee angular velocity Aagaard et al, J Appl Physiol 2000 7

  8. Quadriceps muscle activity (EMG amplitude) varies with contraction mode (CON vs ECC) and knee joint angle Moment of vastus lateralis Force (Nm) EMG (  V) 350 700 300 600 250 500 200 400 150 300 100 200 50 100 0 0 80 80 Knee joint angle Knee joint angle 70 70 60 60 50 50 40 40 30 CONC 240 30 240 CONC 20 -30 30 20 ECC 10 Angular velocity ( o s-1 ) -30 30 10 Angular velocity ( o s-1 ) ECC -240 -240 ( o ( o ) ) (n=14) Aagaard et al, J Appl Physiol 2000 Quadriceps muscle activity (EMG) is reduced in the high-force region of the F-V relationship Moment of vastus lateralis Force (Nm) EMG (  V) 350 700 300 600 250 500 200 400 150 300 100 200 50 100 0 0 80 80 Knee joint angle ( o ) Knee joint angle ( o ) 70 70 60 60 50 50 40 40 30 C 240 O N 30 240 20 C N C O -30 30 20 C C -30 30 10 Angular velocity ( o s-1 ) E C Angular velocity ( o s-1 ) 10 C C E -240 -240 (n=14) Aagaard et al, J Appl Physiol 2000 In contrast, quadriceps muscle activity is not reduced in the low-force region of the F-V relationship Moment of vastus lateralis Force (Nm) EMG (  V) 350 700 300 600 250 500 200 400 150 300 100 200 50 100 0 0 80 80 K K 70 n 70 n 60 e e 60 e e 50 j j o 50 o 40 i i n 40 n 30 240 t t N C 30 O a 240 a 20 C N C n n C O -30 30 20 g Angular velocity ( o s-1 ) C C g -30 30 10 E l Angular velocity ( o s-1 ) C l e 10 C e -240 E ( o ) -240 ( o ) (n=14) Aagaard et al, J Appl Physiol 2000 8

  9. In contrast, quadriceps muscle activity is not reduced in the low-force region of the F-V relationship Moment of vastus lateralis Force (Nm) EMG (  V) 350 700 300 600 250 Indicating that neuromuscular activity during maximal ECC 500 200 400 150 muscle force production in vivo is mainly influenced 300 100 200 by negative force-feedback mechanism(s) 50 100 0 0 80 80 K K 70 n n 70 60 e e e 60 e 50 j 50 j o o 40 i i n n 40 30 t t C 240 O N a 30 240 a C C 20 n O N n -30 30 20 C C g g 10 Angular velocity ( o s-1 ) C -30 30 E l 10 Angular velocity ( o s-1 ) C l e e E C -240 -240 ( o ) ( o ) (n=14) Aagaard et al, J Appl Physiol 2000 Neural control of eccentric contractions Central activation - interpolated twitch analysis ECC CONC Reduced central activation during maximal eccentric muscle contraction in vivo? Isometric CONcentric ECCentric m. quadriceps femoris, maximal voluntary contraction efforts superimposed stimulation (triplet, 300 Hz) femoral nerve Beltman, De Haan et al, Regularly active subjects ~6 h per wk (28±8 yrs, n=10) J Appl Physiol 2004 9

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