Additional material for the book: Atlas of Muscle Innervation Zones:

1. Additional material for the book: Atlas of Muscle Innervation Zones: Understanding Surface Electromyography and Its Applications M. Barbero, R. Merletti, A. Rainoldi ISBN 978-88-470-2462-5 Material provided by: Laboratory for Engineering of the Neuromuscular System (LISiN), Politecnico di Torino, www.lisin.polito.it This material is made available under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License Description of the additional material: A set of Power Point animations showing the concepts of generation, propagation and extinction of motor unit action potentials, the identification of innervation zones, the concept of spatial filtering, EMG signals at different time scales, and the effect of pinnation angle Eleven movies showing time-evolving instantaneous or averaged EMG intensity maps of trapezius, gastrocnemius and tibialis anterior muscles during isometric contractions Use space bar and arrows to control slide show See also “Multimedia and educational tools” at www.lisin.polito.it

2. Generation and propagation of motor unit action potentials Slides 1-3 Animation n. 1 shows a motor neuron (a) innervating a motor unit (b) consisting of three fibers. When the motor neuron discharges, its action potential reaches the three neuromuscular junctions (NMJ) and triggers the muscle fiber action potentials that propagate to the right and to the left, towards the fiber terminations, where they extinguish. One single-fiber action potential (transmembrane voltage) is depicted in (c). Each depolarized zone behaves as an electric field source in the surrounding conducting volume. Animation n. 2 shows the same motor unit depicted in animation n.1. The motor unit is under the skin and the surface potential profile is generated in space by the depolarized regions which move to the right and to the left. The skin potential profile moving to the right passes under the electrodes A and B, causing the generation of a potential evolving in time at the amplifier output. The lower the conduction velocity of the motor unit, the wider is the potential at the amplifier output, and the narrower its amplitude or power spectra. Animation n. 3 shows a sequence of potential distributions on the skin above a muscle, 0.6 ms apart from each other, detected while a motor unit action potential propagates under a 2-D electrode array placed on one side of the IZ. LISiN, Torino, Italy www.lisin.polito.it

3. The Motor Unit (MU) (electrical activity) Inputs from other neurons motoneuron 60 m/s a) c) Axon 0 Schwan cells and Ranvier nodes Action potential (90-100 mVpp) Vm (mV) - 70 Muscle fibers 1 ms o 4 mm NMJ b) 4 m/s = 4 mm/ms 4 m/s = 4 mm/ms One muscle: 10-1000 MU One MU: 50-1000 fibers of the same type (I o II) Slide 1 LISiN, Torino

4. V(t) t Potential distribution on the skin x CV CV A B Innervation zone ( 3 NMJs ) Subcutaneous tissue Skin Depolarized Zone Muscle-tendon junctions V(x) x 0 mV CV - 70 mV Action potentials travelling towards the tendons Slide 2 LISiN, Torino

5. Animation n.3 – LISiN, Torino, IT 2D and 3D maps of a single MUAP in time each frame corresponds to one sample (sampling interval = 0.6 ms)

6. Generation and propagation of motor unit action potentials Slides 4-6 Animation n.4 shows the discharge of a motor neuron and the generation of depolarized regions along the fibers controlled by the corresponding motor unit. These regions propagate towards the tendons and generate a sequence of time shifted differential EMG potentials between adjacent pairs of electrode arranged in a linear array. From these potentials it is possible to estimate the conduction velocity of the fibers of the motor unit. Animation n.5 is like animation n.4 but two motor units (and therefore two motor unit action potentials) discharge at different times t1 and t2. Slide n.6 shows a real multichannel recording from a biceps brachii muscle, showing more than 20 firings of different motor units during 0.25 s. LISiN, Torino, Italy www.lisin.polito.it

7. 60 mm 15 ms Propagation of a single motor unit action potential (MUAP) under a linear electrode array aligned with the fiber direction Animation n.4 - LISiN, Torino, IT time e= 10 mm Conduction velocity = CV = 60mm/15 ms = 4 mm/ms = 4 m/s

8. Propagation of the motor unit action potentials (MUAP) of two motor units under a linear electrode array aligned with the fiber direction. MU 1 discharges at time t1 and MU 2 discharges at time t2 IZ1 time IZ 2 MU 1 MU 2 t2 t1 e= 10 mm Animation n.5 – LISiN, Torino, IT

9. Isometric contraction of biceps brachii at 70% MVC Multichannel recording Electrode array 1 7 1 mV 15 Differential EMG signals recorded using a linear array of 16 electrodes. The innervation zone and tendineous terminations can be clearly seen 10 mm 50 ms Depolarization area Slide n. 6 - LISiN, Torino, IT

10. Generation and propagation of motor unit action potentials Slides 7 - 9 Slide n.7 shows a multichannel recording from a biceps brachii that presents two well identifiable innervazion zones. The motor units innervated in IZ 1 are marked in orange, while those innervated in IZ 2 are marked in green. The muscle tendon regions are outlined with red squares. Slide n.8 shows the discharge of three motor units in the biceps brachii. Two of them are innervated in the same location. The third one is innervated in a different location. They discharge at times t1, t2 and t3, respectively. Signals are propagating in opposite directions at different times under electrode pairs 5 to 8. The electrode array, in this case, is too short to show the muscle-tendon junctions. Slide n.9shows a progressive increase of voluntary contraction level and the recruitment of motor units with progressively larger MUAPs and progressively increasing firing frequency. Individual MUAPs can be identified and classified even at high levels of voluntary contraction (80% MVC). Conduction velocity of individual MUAPs and their statistical distributions can be estimated up to mid contraction levels. Surface EMG signals can be decomposed into their constituent MUAP potential trains. LISiN, Torino, Italy www.lisin.polito.it

11. I.Z. 1 I.Z. 2 Tendon junctions Identification of innervation zones, tendon junctions and fiber length 25 ms Biceps brachii: 50% MVC Slide n.7 - LISiN, Torino, IT from: Merletti, Farina, Granata, 1999

12. t1 t2 t3 MU1 MU3 MU2 11 10 9 e 8 7 6 5 4 3 2 1 e = 5 mm 0 10 20 30 40 time (ms) Discharge of three motor units in the biceps brachii. Two of them are innervated in the same location. They discharge at times t1, t2 and t3 Slide n.8 - LISiN, Torino, IT

13. HEALTHY BICEPS BRACHII SD DETECTION 0 % 100 % Force MVC MVC 0 1 25 % MVC 2 50 % MVC 3 75 % MVC time (s) 4 90 % MVC 5 e =10mm 250 ms Slide n.9 - LISiN, Torino, IT

14. Spatial filtering by a single electrode pair Slides 10 - 12 A sinusoidal waveform, representing one harmonic of the EMG signal, propagates under a cardboard carrying two slots that simulates two electrodes.The height of the mark appearing through each slot corresponds to the monopolar signal level. The difference between two mark levels corresponds to the differential EMG signal. The distance in space between two corresponding points of the sinusoid is called wavelength (λ, measured in meters) and the corresponding time interval is the period (T, measured in seconds). Period and wavelength are related by T=λ/v, where v is the propagation velocity. Animation n. 10 shows that if the distance d between the two slots (electrodes) is equal to λ, the output of the differential amplifier is zero. Animation n. 11 shows that if the distance d between the two slots (electrodes) is different from λ, the output of the differential amplifier is different from zero. In particular, if d = λ/2, the output is maximum. Animation n. 12 shows that if the distance d between the two slots (electrodes) is much smaller than λ, the output of the differential amplifier is small (with respect to the previous case) and proportional to the spatial derivative of the propagating signal. The differential detection system behaves differently with respect to different spatial frequencies and different inter-electrode distances, and therefore acts as a spatial filter. LISiN, Torino, Italy www.lisin.polito.it

15. Vo + _ t d = λ Animation n. 10 - LISiN, Torino, IT

16. Vo + _ t T = λ / v d ≠λ Animation n. 11- LISiN, Torino, IT

17. f ’(x) Vo + _ t d << λ Animation n. 12 - LISiN, Torino, IT

18. Array of EMG signals at different time scales Slides 13 - 16 Slide n.13 shows seven differential channels of surface EMG detected along the fiber direction during an isometric contraction, with force first increasing and then decreasing over a 40s interval (red plot and scale). Slide n.14 shows a time interval of about 3 s “zoomed in” from the previous slide. MUAPs discharges and the recruitment of individual motor units begin to appear. Slide n.15 shows a time interval of about 200 ms “zoomed in” from the previous slide. At this time resolution, discharges of individual motor units can be clearly seen. The muscle innervation zone is at the top of the slide and the bottom channels (6 and 7) correspond to the tendon area. Slide n.16 shows a time interval of about 25 ms “zoomed in” from the previous slide. The discharge of a single motor unit is clearly seen. The propagation velocity of this motor unit action potential (MUAP) can be estimated. Hundreds of MUAPs like this one form the signal shown in slide n.13. LISiN, Torino, Italy www.lisin.polito.it

19. One array with 8 contacts. Right biceps brachii short head - 80% MVC - ramp 40s Torque %MVC 80 70 60 50 40 30 20 10 0 zoom 1 mV EMG ch. 1 2 3 4 5 6 7 0 5 10 15 20 25 30 35 40 Time (s) Slide n.13 - LISiN, Torino, IT

20. Torque %MVC 80 70 60 50 40 30 20 10 0 Right biceps brachii short head - 80% MVC - ramp 40s zoom 1 mV EMG ch. 1 2 3 4 5 6 7 4 4.5 5 5.5 6 6.5 Time (s) Slide n. 14 - LISiN, Torino, IT

21. Torque %MVC 80 70 60 50 40 30 20 10 0 Right biceps brachii, short head - 80% MVC - ramp 40s zoom EMG ch. 1 mV 1 2 3 4 5 6 7 5.58 5.6 5.62 5.64 5.66 5.68 5.7 5.72 5.74 5.76 5.78 Time (s) Slide n.15 - LISiN, Torino, IT

22. Torque %MVC 80 70 60 50 40 30 20 10 0 Right biceps brachii, short head - 80% MVC - ramp 40s 1 mV EMG ch. 1 2 3 4 5 6 7 5.690 5.695 5.700 5.705 Time (s) Slide n.16 - LISiN, Torino, IT

23. Effect of the innervation zone sliding under an electrode pair Slides 17 - 18 Two pairs of electrodes, collecting two single differential EMG signals SD1 and SD2 are positioned on the biceps brachii muscle. When the elbow is flexed, the muscle shortens under the two electrodes. In animation n.17, the innervation zone is distal with respect to SD2, and progressively slides under it, causing a decrement of the SD2 signal and its envelope. In animation n.18, the innervation zone is near SD2 and progressively slides under SD2 and SD1, causing first the SD2 signal to be smaller than SD1, and then a decrement of SD1 amplitude. These amplitude changes are due exclusively to geometrical changes and not to changes in the muscle activation level. LISiN, Torino, Italy www.lisin.polito.it

24. Effect of Innervation Zone (IZ) shift under the electrodes SD1 SD2 Animation n.17 - LISiN, Torino, IT EMG Prox. SD1 1 mV 25 mm 1 Elbow angle: 0o Elbow angle: 90o SD2 0.8 0.6 Norm. envelope 0.4 IZ 0.2 Dist. 0 2 4 6 8 10 12 14 16 Elbow flexion from 0° to 90°: biceps brachii muscle Electrodes: Ø = 15 mm, d = 25 mm IZ near electrode pair 2 Time (s)

25. Effect of Innervation Zone (IZ) shift under the electrodes Slide n.18 - LISiN, Torino, IT SD1 EMG Prox. SD1 1 mV SD2 25 mm 1.0 SD2 SD2 0.8 ZI 0.6 SD1 Norm. envelope 0.4 Dist. Elbow angle: 0o Elbow angle: 90o 0.2 0 2 4 6 8 10 12 14 16 Elbow flexion from 0° to 90°: biceps brachii muscle Electrodes: Ø = 15 mm, d = 25 mm IZ under electrode pair 2 Time (s)

26. Local representation of motor unit action potentials in pennate muscles Slide 19 - 20 Animation n.19 A shows a multichannel action potential generated by fibers parallel to the skin. Animation n.19 B shows the multichannel action potential generated by fibers inclined with respect to the skin. Slide n.20 A shows the distribution of the motor unit action potential on the skin above a motor unit with a large territory. Slide n.20 B shows the distribution of the motor unit action potential on the skin above a motor unit with a small territory. LISiN, Torino, Italy www.lisin.polito.it

27. Action potentials in pennate fibres as they appear locally on the skin Pennation angle = 20° + – A.U. + – A.U. 5 ms Animation n.19 - LISiN, Torino, IT Mesin, Merletti, Vieira (2011) J Biomech 44: 1096–103 A) B) Pennation angle = 0° + – Fat tissue + – Skin Conduction velocity: 4 m/s Skin thickness: 1 mm Fat thickness: 3 mm 16 electrodes with 5 mm IED

28. Testing for the localisation of motor units in the human MG muscle Slide n.20 - LISiN, Torino, IT Vieira, Loram, Muceli, Merletti, Farina (2011) J Physiol 589:431-43 Non-localised motor unit Localised motor unit B) A) End-plate Action potential Tibial nerve Muscle fibres Skin Action potential propagation Fat tissue Medial gastrocnemius (longitudinal section)