Modeling Variability of Force During Isometric Contractions of the Quadriceps Femoris

Abstract The authors modeled variability of force during continuous isometric contractions of the quadriceps femoris. Twenty adults (aged 25 ± 6 years old) performed isometric leg extensions Target forces were 11 percentages of maximum voluntary contraction (%MVC), ranging from 2 to 95%, and 5 absolute levels, from 25 to 225 N. The authors used standard deviation of absolute force, coefficient of variation, and signal-to-noise ratio as measures of variability. The results suggested a nonlinear relationship between variability and level of force, which could best be expressed as %MVC and not as absolute force. Variability for continuous isometric contractions was described best by a sigmoidal logistic function. The sigmoidal pattern of variability as a function of %MVC is consistent with physiological mechanisms.

[1]  G. Stelmach.  Information processing in motor control and learning , 1978 .

[2]  E. Henneman.  Relation between size of neurons and their susceptibility to discharge. , 1957, Science.

[3]  H. Zelaznik,et al.  Motor-output variability: a theory for the accuracy of rapid motor acts. , 1979, Psychological review.

[4]  R. Enoka.  Neural strategies in the control of muscle force , 1997, Muscle & nerve. Supplement.

[5]  A J Fuglevand,et al.  Motor unit activity during isometric and concentric-eccentric contractions of the human first dorsal interosseus muscle. , 1995, Journal of neurophysiology.

[6]  R M Enoka,et al.  Motor-unit synchronization is not responsible for larger motor-unit forces in old adults. , 2000, Journal of neurophysiology.

[7]  H. Clamann,et al.  Nonlinear force addition of newly recruited motor units in the cat hindlimb , 1988, Muscle & nerve.

[8]  P. Fitts.  The information capacity of the human motor system in controlling the amplitude of movement. , 1954, Journal of experimental psychology.

[9]  K M Newell,et al.  Variability and Noise in Continuous Force Production , 2000, Journal of motor behavior.

[10]  J. Cullen,et al.  Manual Asymmetries in Goal-Directed Movement: Examination of the Motor Output Hypothesis , 1998, Brain and Cognition.

[11]  J. Abbs,et al.  Orofacial fine motor control impairments in congenital spasticity , 1984, Neurology.

[12]  R. Donaghy.  The perception of small differences , 1980 .

[13]  C. Patten,et al.  Maximal motor unit discharge rates in the quadriceps muscles of older weight lifters. , 1999, Medicine and science in sports and exercise.

[14]  K. Newell,et al.  Noise, information transmission, and force variability. , 1999, Journal of experimental psychology. Human perception and performance.

[15]  D. McCabe.  Motor Behavior and Human Skill: A Multidisciplinary Approach , 1998 .

[16]  R. Enoka,et al.  Reduced control of motor output in a human hand muscle of elderly subjects during submaximal contractions. , 1993, Journal of neurophysiology.

[17]  R. Schmidt,et al.  The force/force-variability relationship under controlled temporal conditions. , 1988, Journal of motor behavior.

[18]  R. Enoka,et al.  Steadiness is reduced and motor unit discharge is more variable in old adults , 2000, Muscle & nerve.

[19]  R M Enoka,et al.  Training-related enhancement in the control of motor output in elderly humans. , 1994, Journal of applied physiology.

[20]  J. Lohr,et al.  Fine force instability: a quantitative measure of neuroleptic-induced dyskinesia in the hand. , 1990, The Journal of neuropsychiatry and clinical neurosciences.

[21]  Michael H. Kutner.  Applied Linear Statistical Models , 1974 .

[22]  R. Enoka,et al.  Coactivation of the antagonist muscle does not covary with steadiness in old adults. , 2000, Journal of applied physiology.

[23]  R. Enoka,et al.  Motor-unit synchronization increases EMG amplitude and decreases force steadiness of simulated contractions. , 2000, Journal of neurophysiology.

[24]  P. Rack,et al.  The effects of length and stimulus rate on tension in the isometric cat soleus muscle , 1969, The Journal of physiology.

[25]  David H. Perrin,et al.  The Reliability of Four Different Methods. of Calculating Quadriceps Peak Torque Angle-Specific Torques at 30°, 60°, and 75 ° , 1993 .

[26]  C. Romano,et al.  Selective recruitment of high‐threshold human motor units during voluntary isotonic lengthening of active muscles. , 1989, The Journal of physiology.

[27]  Lohr Jb,et al.  Fine force instability: a quantitative measure of neuroleptic-induced dyskinesia in the hand. , 1990 .

[28]  James H. Stapleton,et al.  Linear Statistical Models , 1995 .

[29]  K M Newell,et al.  Impulse variability in isometric tasks. , 1993, Journal of motor behavior.

[30]  G. Sutton,et al.  The variation of hand tremor with force in healthy subjects , 1967, The Journal of physiology.

[31]  V. Barnett,et al.  Applied Linear Statistical Models , 1975 .

[32]  R M Enoka,et al.  Older adults use a unique strategy to lift inertial loads with the elbow flexor muscles. , 2000, Journal of neurophysiology.

[33]  K. Newell,et al.  Force variability in isometric responses. , 1988, Journal of experimental psychology. Human perception and performance.

[34]  William J. Kraemer,et al.  Terminology and Measurement in Exercise Performance , 1987 .

[35]  R. Schmidt,et al.  The relationship between force and force variability in minimal and near-maximal static and dynamic contractions. , 1980, Journal of motor behavior.

[36]  L G Carlton,et al.  Old adults exhibit greater motor output variability than young adults only during rapid discrete isometric contractions. , 2001, The journals of gerontology. Series A, Biological sciences and medical sciences.

[37]  K. Newell,et al.  On the relationship between peak force and peak force variability in isometric tasks. , 1985, Journal of motor behavior.

[38]  H. Zelaznik,et al.  Sources of Inaccuracy in Rapid Movement , 1978 .

[39]  C. Rice,et al.  Age‐related changes in motor unit function , 1997, Muscle & nerve.

[40]  W. Löscher,et al.  Myo-electric signals from two extrinsic hand muscles and force tremor during isometric handgrip , 2004, European Journal of Applied Physiology and Occupational Physiology.

[41]  D. Winter,et al.  Models of recruitment and rate coding organization in motor-unit pools. , 1993, Journal of neurophysiology.

[42]  M Schieppati,et al.  Shift of activity from slow to fast muscle during voluntary lengthening contractions of the triceps surae muscles in humans. , 1988, The Journal of physiology.

[43]  H. Meltzer,et al.  Isometric force control in schizophrenic patients with tardive dyskinesia , 1991, Psychiatry Research.

[44]  K. Newell,et al.  Intermittency in the control of continuous force production. , 2000, Journal of neurophysiology.

[45]  Les G. Carlton,et al.  Force variability and movement accuracy in space-time , 1988 .

[46]  R. Burke.  Motor Units: Anatomy, Physiology, and Functional Organization , 1981 .

[47]  M. Solomonow,et al.  Motor unit recruitment strategy of knee antagonist muscles in a step-wise, increasing isometric contraction , 2004, European Journal of Applied Physiology and Occupational Physiology.

[48]  R. Enoka.  Eccentric contractions require unique activation strategies by the nervous system. , 1996, Journal of applied physiology.

[49]  K. Newell,et al.  Kinetic analysis of response variability , 1984 .