Elsevier

Clinical Neurophysiology

Volume 120, Issue 1, January 2009, Pages 210-217
Clinical Neurophysiology

Heteronymous reflex responses in a hand muscle when maintaining constant finger force or position at different contraction intensities

https://doi.org/10.1016/j.clinph.2008.10.013Get rights and content

Abstract

Objective

This study compared heteronymous reflex responses evoked in the first dorsal interosseous muscle by electrical and mechanical stimuli during force and position tasks performed at different target torques.

Methods

Twenty-two healthy human participants contracted the first dorsal interosseus muscle either to produce a constant force against a rigid restraint (force task) or to maintain a constant position of the index finger (position task) against a constant load of 20, 40, and 60% of maximum.

Results

The amplitude of the short-latency reflex evoked by electrical stimulation of the median nerve was significantly greater when maintaining finger position, whereas no difference was present for the long-latency responses. In contrast, the reflex responses (short- and long-latency) did not differ between tasks when elicited by tendon-taps.

Conclusions

Task difference in reflex responsiveness depended more on the type of stimulus applied than the reflex pathway and was consistent across three voluntary contraction forces.

Significance

The results suggest that afferent input from homonymous and heteronymous pathways is modulated similarly at the spinal level during such tasks, and implies the significance of presynaptic inhibition during motor performance.

Introduction

When an individual performs a submaximal isometric contraction with the first dorsal interosseus (FDI) either to produce a constant force against a rigid restraint (force task) or to maintain the position of the index finger against a constant load (position task), the amplitude of the stretch reflex (Doemges and Rack, 1992a, Maluf et al., 2007) and the tendon-tap reflex (T-reflex) (Maluf et al., 2007, Jordan et al., 2007) are similar during both tasks. In contrast, when a reflex was elicited in the FDI by electrical stimulation of the median nerve (heteronymous H-reflex), the amplitude of the reflex response was larger during the position task than during the force task (Maluf et al., 2007, Jordan et al., 2007). Similar results have been observed with single motor units recorded in FDI in response to the T-reflex and median nerve H-reflex (Jordan et al., 2007).

These divergent results for electrically and mechanically induced reflexes might be attributable either to the reflex pathway involved (i.e., homonymous for the stretch and T-reflexes and heteronymous for the median nerve stimulation) or to the type of stimulus applied (mechanical and electrical stimulus). Previous work, however, suggests similar modulation of the afferent input onto the motor neuron pool from the homonymous and heteronymous pathways (Meunier and Pierrot-Deseilligny, 1989). Moreover, the electrically induced reflex response is more sensitive to presynaptic inhibition compared with stretch and tendon-tap reflexes (Morita et al., 1998). If the different adjustments in the T- and H-reflexes during the force and position tasks are attributable to presynaptic inhibition, the greater amplitude of the heteronymous H-reflex during the position task should be present during contractions performed at different contraction intensities as presynaptic inhibition does not change with contraction force (Meunier and Pierrot-Deseilligny, 1989). Similarly, the absence of a difference in the T-reflex across tasks should not change with contraction force. If confirmed, these results suggest that changes in the efficacy of presynaptic inhibition, as observed in elderly adults (Butchart et al., 1993, Earles et al., 2001, Tsuruike et al., 2003), stroke patients (Aymard et al., 2000), individuals with spasticity (Morita et al., 2001), and in healthy subjects after a few weeks of limb immobilization (Lundbye-Jensen and Nielsen, 2008) and the consumption of ethanol (von Dincklage et al., 2007), could compromise motor performance.

The aim of the study was to compare heteronymous reflex responses evoked in the FDI by electrical and mechanical stimuli when the force and position tasks were performed at three target forces. These results indicate a similar modulation of homonymous and heteronymous afferent input onto the motor neuron pool of the agonist muscle, but a different adjustment of presynaptic inhibition during the force and position tasks. In addition, our results underscore that the use of the H-reflex method appears as a better tool to investigate fine differences in the afferent synaptic input onto the motor neuron pool between tasks compared with the mechanically evoked reflex.

Section snippets

Materials and methods

After informed consent was obtained, experiments were conducted on 22 subjects (9 women) aged between 18 and 37 yr (25.0 ± 5.7 yr; mean ± SD). None of the participants reported any signs of neurological disorder or cardiovascular disease. Subjects were all right-handed and were asked to refrain from exercising the arm muscles for 24 h before testing. The Human Subjects Committee at the University of Colorado in Boulder approved the experimental procedures.

Results

Nineteen of the 22 subjects who participated in the study were included in the statistical analysis of the reflex responses induced by the median nerve stimulation (11 men; 25.0 ± 5.7 years; 165.7 ± 12.7 cm; 65.8 ± 10.6 kg) and 18 were included in the analysis of the tendon-tap of APB (8 women; 25.2 ± 5.8 years; 167.9 ± 13.8 cm; 65.6 ± 10.9 kg). Data were excluded for the electrically induced reflex from three subjects. In two subjects, the difference in EMG activity between the force and position tasks

Discussion

The main finding of this study was the greater response for the heteronymous H-reflex during the position task compared with the force task performed at the three contraction forces. In contrast, there was no difference between tasks in the size of the heteronymous T-reflex at any contraction force. In combination with previous work, these results indicate that the task difference in reflex responsiveness depends more on the type of stimulus applied than the reflex pathway used, and are

Acknowledgments

The work was supported by an award (NS043275) from the National Institute of Neurological Disorders and Stroke to R.M. Enoka.

References (47)

  • F. von Dincklage et al.

    Ethanol reduces motoneuronal excitability and increases presynaptic inhibition of Ia afferents in the humans spinal cord

    Brain Res

    (2007)
  • E.P. Zehr et al.

    What functions do reflexes serve during human locomotion?

    Prog Neurobiol

    (1999)
  • J.M. Aimonetti et al.

    Mechanical cutaneous stimulation alters Ia presynaptic inhibition in human wrist extensor muscles: a single motor unit study

    J Physiol

    (2000)
  • K. Akazawa et al.

    Modulation of reflex EMG and stiffness in response to stretch of human finger muscle

    J Neurophysiol

    (1983)
  • C. Aymard et al.

    Presynaptic inhibition and homosynaptic depression: a comparison between lower and upper limbs in normal human subjects and patients with hemiplegia

    Brain

    (2000)
  • Barry BK, Narazaki K, Jordan K, Enoka RM. Muscles are activated differently with compliant loads. Motor Control at the...
  • Burke RE. Motor units: anatomy, physiology, and functional organization. In: Handbook of physiology. The Nervous...
  • D. Burke et al.

    The effect of voluntary contraction on the H reflex of various muscles

    Brain

    (1989)
  • D. Burke et al.

    Voluntary activation of spindle endings in human muscles temporarily paralysed by nerve pressure

    J Physiol

    (1979)
  • D. Burke et al.

    The afferent volleys responsible for spinal proprioceptive reflexes in man

    J Physiol (Lond)

    (1983)
  • P. Butchart et al.

    The effect of age and voluntary contraction on presynaptic inhibition of soleus muscle Ia afferent terminals in man

    Exp Physiol

    (1993)
  • C. Crone et al.

    Sensitivity of monosynaptic test reflexes to facilitation and inhibition as a function of the test reflex size: a study in man and the cat

    Exp Brain Res

    (1990)
  • S.J. De Serres et al.

    Wrist muscle activation patterns and stiffness associated with stable and unstable mechanical loads

    Exp Brain Res

    (1991)
  • Cited by (23)

    • Residual force enhancement due to active muscle lengthening allows similar reductions in neuromuscular activation during position- and force-control tasks

      2020, Journal of Sport and Health Science
      Citation Excerpt :

      To date, rTE has not been studied during a position task that requires the participant to hold an inertial load in the same anatomical position as a rigid load (i.e., position-matching task) but with unconstrained movement. Position-matching tasks are known to differ from torque-matching tasks in activation strategies of the motor neuron pool22–25 in that position-matching tasks are associated with decreased presynaptic inhibition23 and increased muscle spindle sensitivity compared with torque-matching tasks.24 During eccentric contractions, there is a distinction to be made between the 2 separate actions of displacing a load during a position-matching task and resisting a torque motor in a torque-matching task,26 which lead to different control strategies during dynamic contractions.27,28

    • Changes in constraint of proximal segments effects time to task failure and activity of proximal muscles in knee position-control tasks

      2013, Clinical Neurophysiology
      Citation Excerpt :

      However, the persistence of a 15% shorter TTF in the position-control task, despite equivalent constraint, indicates other factors also contribute. These mechanisms are likely to involve the differences in motor unit recruitment and muscle spindle sensitivity that have been described previously (Akazawa et al., 1983; Baudry and Enoka, 2009; Baudry et al., 2009a; Maluf et al., 2005; Mottram et al., 2005). Differences in EMG amplitude between force- and position-control tasks with equivalent constraint were less than those between position-control tasks with unmatched constraint.

    • Unraveling the neurophysiology of muscle fatigue

      2011, Journal of Electromyography and Kinesiology
      Citation Excerpt :

      Earlier work found that the distribution of activity among synergist muscles and the responsiveness of stretch-reflex pathways differ with load compliance (Akazawa et al., 1983; Buchanan and Lloyd, 1995; Colebatch and McCloskey, 1987; Doemges and Rack, 1992a,b; Perreault et al., 2008). When maintaining limb position while supporting an inertial load, for example, individuals tend to augment reflex responsiveness so that any deviation from the target position can be corrected as quickly as possible (Baudry et al., 2009a; Maluf et al., 2007; Perreault et al., 2008). Such a control strategy is not necessary when pushing against a rigid restraint, however, as the low compliance of the load will not permit any deviation in limb position, only variation in the force exerted by the limb.

    View all citing articles on Scopus
    View full text