Recruitment stability in masseter motor units during isometric voluntary contractions
Corresponding Author
Sheila D. Scutter BAppl Sc (Hons), MEd Studies
Department of Physiology, University of Adelaide, Adelaide, S.A., Australia
School of Physiotherapy, University of South Australia, North Terrace, Adelaide, S.A. 5000, AustraliaSearch for more papers by this authorKemal S. Türker BDS, PhD
Department of Physiology, University of Adelaide, Adelaide, S.A., Australia
Search for more papers by this authorCorresponding Author
Sheila D. Scutter BAppl Sc (Hons), MEd Studies
Department of Physiology, University of Adelaide, Adelaide, S.A., Australia
School of Physiotherapy, University of South Australia, North Terrace, Adelaide, S.A. 5000, AustraliaSearch for more papers by this authorKemal S. Türker BDS, PhD
Department of Physiology, University of Adelaide, Adelaide, S.A., Australia
Search for more papers by this authorAbstract
Recruitment of single motor units (SMUs) of the masseter muscle was studied using macro representation (MacroRep) as the indicator of motor unit size. When subjects followed a slow isometric force ramp, units were usually recruited in order of MacroRep size. However, pooling the data from repeated ramps in the same subject resulted in a weak relationship between MacroRep size and force recruitment threshold, probably due to marked variations in the relative contributions of the jaw muscles, and varying levels of cocontraction, in the development of total bite force in each ramp. The force recruitment thresholds of individual SMUs showed marked variability, but recruitment threshold stability was improved when expressed as a percentage of maximum surface electromyographic (SEMG) activity in the ipsilateral masseter. Therefore the SEMG recruitment threshold was concluded to be a more stable and accurate indicator of the SMU's position in the recruitment hierarchy in a given muscle. It was concluded that SMUs in masseter are recruited according to the size principle, and that when investigating recruitment in jaw muscles, SEMG recruitment threshold should be used in preference to force recruitment threshold. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:1290–1298, 1998.
References
- 1 Broman H, De Luca CJ, Mambrito B: Motor unit recruitment and firing rates interaction in the control of human muscles. Brain Res 1985; 337: 311–319.
- 2 Calancie B, Bawa P: Limitations of the spike-triggered averaging technique. Muscle Nerve 1986; 9: 78–83.
- 3 Calancie B, Bawa P: Motor unit recruitment in humans, in MD Binder, LM Mendell, (eds): The Segmental Motor System. New York, Oxford University Press, 1990, pp 75–95.
- 4 Clark W, Luschei ES, Hoffman DS: Recruitment order, contractile characteristics, and firing patterns of motor units in the temporalis muscle of monkeys. Exp Neurol 1978; 61: 31–52.
- 5 De Luca CJ: Control properties of motor units. J Exp Biol 1985; 115: 125–136.
- 6 Dengler R, Konstanzer A, Hesse S, Schubert M, Wolf W: Collateral nerve sprouting and twitch forces of single motor units in conditions with partial denervation in man. Neurosci Lett 1989; 97: 118–122.
- 7 Dengler R, Konstanzer A, Küther G, Hesse S, Wolf W, Struppler A: Amyotrophic lateral sclerosis: macro-EMG and twitch forces of single motor units. Muscle Nerve 1990; 13: 545–550.
- 8 Desmedt JE, Godaux E: Recruitment patterns of single motor units in the human masseter muscle during brisk jaw clenching. Arch Oral Biol 1979; 24: 171–178.
- 9
Erim Z,
De Luca CJ,
Mineo K,
Aoki T:
Rank-ordered regulation of motor units.
Muscle Nerve
1996;
19:
563–573.
10.1002/(SICI)1097-4598(199605)19:5<563::AID-MUS3>3.0.CO;2-9 CAS PubMed Web of Science® Google Scholar
- 10 Goldberg LJ, Derfler B: Relationship among recruitment order, spike amplitude, and twitch tension of single motor units in human masseter muscle. J Neurophysiol 1977; 40: 879–890.
- 11 Hagberg C, Agerberg G, Hagberg M: Regression analysis of electromyographic activity of masticatory muscles versus bite force. Scand J Dent Res 1985; 93: 396–402.
- 12 Hannam AG, McMillan AS: Internal organisation in the human jaw muscles. Crit Rev Oral Biol Med 1994; 5: 55–89.
- 13 Heckman CJ, Binder MD: Neural mechanisms underlying the orderly recruitment of motoneurons, in MD Binder, LM Mendell (eds): The Segmental Motor System. New York, Oxford University Press, 1990, pp 182–204.
- 14 Henneman E, Somjen G, Carpenter D: Functional significance of cell size in spinal motoneurons. J Neurophysiol 1965; 28: 560–589.
- 15
Jabre JF,
Spellman NT:
The demonstration of the size principle in humans using macro electromyography and precision decomposition.
Muscle Nerve
1996;
19:
338–341.
10.1002/(SICI)1097-4598(199603)19:3<338::AID-MUS9>3.0.CO;2-E CAS PubMed Web of Science® Google Scholar
- 16 Kernell D, Sjoholm H: Recruitment and firing rate modulation of motor unit tension in a small muscle of the cat's foot. Brain Res 1975; 98: 57–72.
- 17 Kukulka CG, Clamann HP: Comparison of the recruitment and discharge properties of motor units in human brachial biceps and adductor pollicis during isometric contractions. Brain Res 1981; 219: 45–55.
- 18 Lindauer SJ, Gay T, Rendell J: Electromyographic-force characteristics in the assessment of oral function. J Dent Res 1991; 70: 1417–1421.
- 19 Lund JP, Smith AM, Sessle BJ, Murakami T: Activity of trigeminal alpha and gamma motoneurons and muscle afferents during performance of a biting task. J Neurophysiol 1979; 42: 710–725.
- 20 Mao J, Osborn JW: Direction of bite force determines the pattern of activity in jaw-closing muscles. J Dent Res 1994; 73: 1112–1120.
- 21 Masakado Y, Akaboshi K, Nagata M, Kimura A, Chino N: Motor unit firing behaviour in slow and fast contractions of the first dorsal interosseous muscle of healthy men. Electroencephalogr Clin Neurophysiol 1995; 97: 290–295.
- 22 Masakado Y, Noda Y, Nagata M, Kimura A, Chino N, Akaboshi K: Macro-EMG and motor unit recruitment threshold—differences between the young and the aged. Neurosci Lett 1994; 179: 1–4.
- 23 McMillan AS, Sasaki K, Hannam AG: The estimation of motor unit twitch tensions in the human masseter muscle by spike triggered averaging. Muscle Nerve 1990; 13: 697–703.
- 24 Miles TS, Nordstrom MA, Türker KS: Length-related changes in activation threshold and wave form of motor units in human masseter muscle. J Physiol (Lond) 1986; 370: 457–465.
- 25 Romaiguere P, Vedel J-P, Pagni S: Fluctuations in motor unit recruitment threshold during slow isometric contractions of wrist extensor muscles in man. Neurosci Lett 1989; 103: 50–55.
- 26 Schmeid A, Morin D, Vedel J-P, Pagni S: The size principle and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurons during wrist extension. Exp Brain Res 1997; 113: 214–229.
- 27 Senn W, Wyler K, Clamann HP, Kleinle J, Luscher HR, Muller L: Size principle and information theory. Biol Cybern 1997; 76: 11–22.
- 28 Stålberg EV: Macro EMG, a new recording technique. J Neurol Neurosurg Psychiatry 1980; 43: 475–482.
- 29 Stålberg EV: Macro EMG. Muscle Nerve 1983; 6: 619–630.
- 30 Stålberg EV: Single fibre EMG, macro EMG and scanning EMG, new ways of looking at the motor unit. CRC Crit Rev Clin Neurobiol 1986; 2: 125–167.
- 31 Türker KS, Miles TS, Le HT: The lip-clip: a simple, lowimpedance ground electrode for use in human electrophysiology. Brain Res Bull 1988; 21: 139–141.
- 32 Türker KS, Yang J, Brodin P: Conditions for excitatory or inhibitory masseteric reflexes elicited by tooth pressure in man. Arch Oral Biol 1997; 42: 121–128.
- 33 van Eijden TMGJ, Brugman P, Weijs WA, Oosting J: Coactivation of jaw muscles: recruitment order and level as a function of bite force direction and magnitude. J Biomech 1990; 23: 475–485.
- 34 Vogt T, Nix WA, Pfeifer B: Relationship between electrical and mechanical properties of motor units. J Neurol Neurosurg Psychiatry 1990; 53: 331–334.
- 35 Yemm R: The orderly recruitment of motor units of the masseter and temporal muscles during voluntary isometric contraction in man. J Physiol (Lond) 1977; 265: 163–174.
- 36 Yoneda T, Oishi K, Fujikura S, Ishida A: Recruitment threshold force and its changing type of motor units during voluntary contraction at various speeds in man. Brain Res 1986; 372: 89–94.
- 37 Zijdewind I, Kernell D: Index finger position and force of the human first dorsal interosseous and its ulnar nerve antagonist. J Appl Physiol 1994; 77: 987–997.
Citing Literature
