+ Site Statistics
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn

+ Translate
+ Recently Requested

Discharge of human muscle spindle afferents innervating ankle dorsiflexors during target isometric contractions

Discharge of human muscle spindle afferents innervating ankle dorsiflexors during target isometric contractions

Journal Of Physiology (cambridge). 504(1): 221-232

1. There are discrepancies in the literature about the reproducibility of forces at which human muscle spindle afferents accelerate their discharge during isometric voluntary contractions. The aim of this study was to determine for single muscle spindle afferents both the reproducibility of the 'acceleration threshold' and the factors contributing to variability of ,acceleration threshold'. 2. Microneurographic recordings were made from muscle spindle afferents innervating tibialis anterior while subjects performed isometric ankle dorsiflexions. Subjects matched the force of their contractions with a visually displayed 'ramp-and-hold' template. Template parameters were determined by the force of maximal isometric ankle dorsiflexion (MVC), and expressed as per cent MVC. The required 'ramp' rate and 'hold' force was adjusted between trials (range, 0.5-5% MVC s' and 0.5-20% MVC, respectively). The duration of the hold phase was 4 s and, following each contraction, stretch was applied transversely to the tendon to minimize the influence of any 'after-effects' on spindle afferent responses in subsequent contractions. 3. For each contraction, the force at which the rate of muscle spindle discharge increased was defined as the 'acceleration threshold'. Of twenty-six muscle spindle afferents innervating tibialis anterior, all but two increased their discharge in the test contractions. In 90% of contractions, acceleration thresholds were less than 3.2% MVC (range, 0.01-11.9% MVC). 4. Individual muscle spindle afferents increased their discharge at similar but not identical forces in repeated contractions. There was a positive correlation between the rate of contraction and the acceleration threshold (P lt 0.001), but the strength of the target contraction had no effect on the threshold, and there was no trend for thresholds to change over time. 5. The results suggest, first, that most muscle spindle endings in the human pretibial muscles receive a significant increase in fusimotor drive during relatively weak isometric efforts and secondly, that when fusimotor after-effects are controlled, much of the residual variability in 'acceleration threshold' for any one spindle in repeated contractions is due to extrafusal factors, particularly variability in contraction rate.

(PDF emailed within 0-6 h: $19.90)

Accession: 008482632

Download citation: RISBibTeXText

PMID: 9350632

DOI: 10.1111/j.1469-7793.1997.221bf.x

Related references

Discharge patterns in human muscle spindle afferents during isometric voluntary contractions. Acta Physiologica Scandinavica 80(4): 552-566, 1970

The discharge rate of human motoneurons innervating ankle dorsiflexors in the absence of muscle afferent feedback. Journal of Physiology (Cambridge) 438: 219P, 1991

Human muscle spindle discharge during isometric voluntary contractions. Amplitude relations between spindle frequency and torque. Acta Physiologica Scandinavica 90(2): 319-336, 1974

Neuromuscular fatigue induced by alternating isometric contractions of the ankle plantar and dorsiflexors. Journal of Electromyography and Kinesiology 21(3): 471-477, 2011

Can pennation angles be predicted from EMGs for the primary ankle plantar and dorsiflexors during isometric contractions?. Journal of Biomechanics 41(11): 2492-2497, 2008

Aging does not affect voluntary activation of the ankle dorsiflexors during isometric, concentric, and eccentric contractions. Journal of Applied Physiology 99(1): 31-38, 2005

Increased resting discharge of human spindle afferents following voluntary contractions. Journal of Physiology 488: 833-840, 1995

Discharge rates and discharge variability of muscle spindle afferents in human chronic spinal cord injury. Clinical Neurophysiology 124(1): 114-119, 2013

Response patterns of human muscle spindle endings to isometric voluntary contractions. Acta Physiologica Scandinavica 80(4): 43a-43a, 1970

Classification of muscle spindle afferents innervating the masseter muscle in rats. Archives of Oral Biology 51(9): 740-747, 2006

Changes in muscle fascicles of tibialis anterior during anisometric contractions are not associated with motor-output variability of the ankle dorsiflexors in young and old adults. European Journal of Applied Physiology 110(6): 1175-1186, 2011

Physiologic and morphologic properties of motoneurons and spindle afferents innervating the temporal muscle in the cat. Journal of Comparative Neurology 406(1): 29-50, March 29, 1999

Sex-Related Differences in the Accuracy of Estimating Target Force Using Percentages of Maximal Voluntary Isometric Contractions vs. Ratings of Perceived Exertion During Isometric Muscle Actions. Journal of Strength and Conditioning Research 32(11): 3294-3300, 2017

Differential changes in muscle oxygenation between voluntary and stimulated isometric fatigue of human dorsiflexors. Journal of Applied Physiology 100(3): 890-895, 2005

The dependence of the discharge frequency of muscle spindle afferents in the cat on the direction of the change in muscle loading. Neirofiziologiia 22(6): 840-843, 1990