During prolonged experiments the influence of knee angular velocity, and stimulation parameters (interpulse interval (IPI), duty cycle (DC), number of pulses per cycle (NP)) on fatigue-induced torque\ud
decline of paralyzed human quadriceps was studied. Identification of torque-angle and -angular velocity was also performed. The overall loss of maximum torque (MT) and torque-time integral ('lTI) per cycle during sustained intermittent stimulation during isokinetic movement had a typical exponential decay reaching asymptotic values. Larger knee velocities resulted in a significantly faster and relative larger decay of MT and TTI. The rate and relative magnitude of fatigue during concentric contractions are in direct relation\ud
to NP. The results may be valuable in the design of optimal control systems for FES which pursue minimization of muscle fatigue

Boom, H.B.K.

Fidder, Marc

Franken, H.M.

Franken, Henry M.

Veltink, Petrus H.

English

Fidder, M.

University of Twente Research Information

Fatigue of Intermittently Stimulated Quadriceps during Imposed Cyclical Lower Leg Movements

In this study the torque output of intermittently stimulated paralyzed human knee extensor muscles during imposed isokinetic cyclical lower leg movements was investigated in four paraplegic subjects. During prolonged (10 min) experiments the influence of knee angular velocity and stimulation parameters on fatigue-induced torque decline was studied. Pulse width and amplitude were set to obtain maximal recruitment. The cycle time was maintained constant at 2 s, comparable to a walking cycle. The maximum torque and averaged torque per cycle were estimated to determine the muscle's performance during sustained intermittent stimulation. The overall loss in time of these parameters had a typical exponential decay reaching asymptotic values. Additionally, larger knee velocities resulted in a significantly faster and relatively larger decay of maximum and averaged torque. Also, the rate and relative decrement of torque output during concentric contractions increased with increasing number of pulses in a cycle. Identification trials, determining the (isometric) torque-angle and (isokinetic) torque-angular velocity relation, were performed. The relations appeared to change due to fatigue. The results might be valuable in the design of optimal control systems for functional electrical stimulation which pursue minimization of muscle fatigue. They may contribute to the derivation of a cost criterion, describing muscle fatigue as a function of both joint movement and stimulation parameters

Fatigue of intermittently stimulated human quadriceps during imposed cyclical lower leg movements

During prolonged experiments the influence of knee angular velocity, and stimulation parameters (interpulse interval (IPI), duty cycle (DC), number of pulses per cycle (NP)) on fatigue-induced torque decline of paralyzed human quadriceps was studied. Identification of torque-angle and -angular velocity was also performed. The overall loss of maximum torque (MT) and torque-time integral ('lTI) per cycle during sustained intermittent stimulation during isokinetic movement had a typical exponential decay reaching asymptotic values. Larger knee velocities resulted in a significantly faster and relative larger decay of MT and TTI. The rate and relative magnitude of fatigue during concentric contractions are in direct relation to NP. The results may be valuable in the design of optimal control systems for FES which pursue minimization of muscle fatigue

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Fatigue of intermittently stimulated quadriceps during imposed cyclical lower leg movements

Fatigue of Intermittently Stimulated Quadriceps during Imposed Cyclical Lower Leg Movements Henry M. Franken, Student Member, IEEE, Peter H. Veltink, Member, IEEE, Marc Fidder and Herman B.K. Boom, Member, IEEE. University of Twente, Department of Electrical Engineering, P.O. Box 217, 7500 AE, The Netherlands. ABSTRACT - During prolonged experiments the influence of knee angular velocity, and stimulation parameters (interpulse interval (IPI), duty cycle (DC), number of pulses per cycle (NP)) on fatigue-induced torque decline of paralyzed human quadriceps was studied. Identification of torque-angle and -angular velocity was also performed. The overall loss of maximum torque (MT) and torque-time integral ('lTI) per cycle during sustained intermittent stimulation during isokinetic movement had a typical exponential decay reaching asymptotic values. Larger knee velocities resulted in a significantly faster and relative larger decay of MT and TTI. The rate and relative magnitude of fatigue during concentric contractions are in direct relation to NP. The results may be valuable in the design of optimal control systems for FES which pursue minimization of muscle fatigue. I. INTRODUCTION A major issue in the control of functional electrical stimulation (FES) of paralysed muscles is the decay of muscle force as a result of fatigue under sustained (continuous and intermittent) stimulation [ 1-3, ( 2 :  in press)]. Stimulated paralyzed human quadriceps fatigue under isometric condition can be described by an exponential decay [2,3]. In this study the torque of intermittently stimulated paralysed human knee extensors during (isokinetic) cyclical lower leg movements has been investigated. 11. METHODS A. Subjects The subjects who participated in this study were complete T 5 T 6  level spinal cord injured patients. All had normal excitable quadriceps muscle and had been enrolled in the FES training program of the rehabili- tation center 't Roessingfi (Enschede, The Netherlands). B. Protocol A protocol of 7 fatigue trials (FT) was designed to compare overall loss of tetanic torque at the knee joint during sustained intermittent stimulation at different isokinetic velocities. The angle and velocity ranges were limited by the anatomical restrictions of the lower leg, the restrictions imposed by the dynamometer bench and the desire to maintain a constant cycle time ( 2  s.), comparable to a walking cycle. The experimental set-up is shown in fig. 1. The influence of IPI (20 and 40 ms), DC ([ontime/cycle time]: 16 and 32 %) and NP ([ontime/IPI]: 16 and 32), at isokinetic joint movement, was investigated. Pulsewidth (PW =300 ps) and stimulation amplitude (SA=100 mA) were set to obtain maximal rccruitment. Three muscle identification trials, determining the torque-angle (isometric measurement) and torque-angular velocity (isokineti- cally measured at 50 deg.) relations, were performed. Force, knee angular position, and velocity were sampled at 100 Hz. These signals and stimulus data were stored on disk for off-line analysis. C. Off-line data anaIysis From the active torque, the maximum torque (MT) and torque-time integral per swing (lTI) are calculated. "Fatigue parameters", describing the decay of the MT and TTI as a function of time (one sample per cycle), were derived by curve-fitting the following equation to the data: where is either MT or TIT, t is time, Emax is the maximum achieved in the considered trial, 7 is the time constant of decay in C due to fatigue, and ( 0  is the relative asymptotic value to which ((t) descends. The first part of the data (approximately 10 samples) which increases to Emax has been ignored. Equation (1) is fitted iteratively by minimizing the resulting RMS deviation from the experimental data (see also [2]). t I M i ?  I rnt F 3tor go9 Fig. 1. Schematic of experimental set-up. The angular position and velocity, measured at the motor ais ,  are defined positive in extension motion with zero as indicated. The patient is strapped at the hip and knee to measure knee torque (at the tibia) only and to ensure static position of the body. 0-7803-0785-2/92$03.00 OIEEE 1311 111. RESULTS A. Measured and estirnated signals Fig. 2 displays a typical registration of measured and estimated signals for one cycle. 100 -25 25 -2s I P -r b 0 Time [SI 2 0 Time [SI 2 Fig. 2. a: Total knee torque (TT [Ntnl), angular position (A [deg]) and velocity (V [de&'?]), und the applied stirnulutinn burst (S [r?A]), for one cycle witli concentric contraction. b: Total (TT [Nm]), passive (PT [Ntn]) and active knee torque (AT /Nni]). Esstimated parurmters TTI [Nrns] and M T  [Ntnl. 0 '  -40 Veloci ty [deg/s]  SO 2 I O 0  E Z - U (D 3 W t- 6 o - * -  I I Angle [deg] 80 -40 Velocity [de!3/sl 8 0  0 Fig. 4. Identification results of TN. (1): prior to FT I ;  (2): after FT 3, (3): after FT 7. (IPI = 20 ms) a: Torque-angle relation. b: Torque-angular velocity rehrion. IV. DISCUSSION The apparent dependence of the quadriceps fatigue curve on the isokinetic knee joint velocity has not been reported before. The de endence might be explained by lower metabolic efgciency (shortage in ATP or high IMP concentrations) of the total muscle or by complete exhaustion of fast twitch fibers, which are more susceptible to FES than slow twitch fibers. 0 i - i  -40 Velocity [degjs] 80 -+- ss l I  I 0 '  I 1 4 Velocity [degisj 80 Fig. 3. pararneters. (Subjects: SS, JM, MD,  TN)  a: TTllll;l.; b: Different velocities refer to scJpperute futiguc tricrls witli identical stimulation c: P l i  B. Fatigue purunzeters Concerning stimulation parameters, the  results Fig. 3 depicts the fatigue parameters estimated from indicate that, within the boundary conditions for a the decay in 'ITI. T T I n i a n  displays a I-iiil type given task, NP should be minimized to postpone dependence on velocity, indicating comparat)le muscle fatigue. This can be accomplished by minimization of condition for each trial. The graphs f o r  7 and  T T I c  UC, and/or l/IPI. The results may contribute to the IT1 derivation of an  optimization criterion, describing show that higher velocities result in a significantly muscle fatigue as a function of both joint movement larger and faster decay of 7 T I  (a<0.05). Variations in and stimulation parameters. stimulation parameters indicated that the rate and magnitude of fatigue for concentric contractions are in direct relation to NP. The fatigue parameters for MT are similar. IlI7,IXIlENCES C. Muscle dynamics. ly generated torque on the angle was found (fig. 4a). The measured torque-angular velocity relations i w 2 ,  supports the Hill equation. The relations alter due to fatigue. The decline in torque output due to fatigue is larger at higher velocities (see also fig. 3c). I Anclrev% 111. Il;irnctt RW. Pl i i l l ip r  qr a n d  K i r k w i o d  CA: Rule-harecl control  of :I hybrid IrliS o r t l imic  firr ; ~ ~ s i n t i n g  p;ir;iplegic Iocoiiiotio11. Auronrrdicn l i . l 7 5 ~ l W ,  1040, 2 I l o r i m  III3K.  Miildcr AJ n n d  Vel t i i ik  P l l :  Fatigue dur ing finite stale control  d ~ i i i i i g  ~ie~~roi i i~icc~i l i i r  sti i i i i l : i I ion D i ~ r c i r  I!) nroin Rrsmnlr. in press, 2 .  I cry M .  hli7riitii .T arid Susnk %: Rccriritiiient, iorce arid faiigire cliarilcteris- (IC'. of qi i i l t l r ice F tI1mcIeT c i f  ~wraplepics isc~riietricall activated hy 511 rliice 5t i iiiirl;, t ion, I 2: I 50- 156, I O'J11 A typical Gaussian-type dependence of the isometrical- iii nct inii;iT elect rim I .i. niorwd. Erg. 1317 

Fatigue of intermittently stimulated quadriceps during imposed cyclical lower leg movements

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