**Risk Factors**

**Chapter 1**

**Provisional chapter**

**Muscle Pain and Muscle Spindles**

**Muscle Pain and Muscle Spindles**

DOI: 10.5772/intechopen.72223

Muscle pain is a common symptom associated with, for example, myofascial syndrome, fibromyalgia and polymyalgia rheumatica. Many diseases of the muscle tissue are, however, completely or nearly painless such as polymyositis and inclusion body myositis. Thus, a mere inflammation cannot be the cause of muscle pain. In needle electromyography (EMG), the insertion of a needle electrode causes pain but further advancement is usually painless. However, there are small spots of muscle tissue where sudden pain is elicited with the needle. In EMG, these 'active spots' are observed to produce spontaneous activity in the form of end plate noise and spikes (EPSs). End plate noise is elicited at the neuromuscular junction of α, β or γ motor neuron. EPSs are action potentials of γ or β motor units. Muscle spindles are the main nociceptors in muscle tissue, both in healthy muscle and in diseases with muscle pain by inflammation of the muscle spindles. Multiple possible mechanisms of muscle pain exist. Polymyalgia rheumatica may have interstitial pain and possibly pain associated with muscle spindle capsules. Delayed onset muscle soreness may reflect both interstitial muscle pain caused by minor injuries

**Keywords:** muscle pain, myalgia, myofascial syndrome, fibromyalgia, polymyalgia rheumatica, muscle spindle, nociception, fibrillation, fusimotor, electromyography, end plate activity, intrafusal, C-fibres, soreness, DOMS, trigger point, taut band, muscle

Additional information is available at the end of the chapter

and pain generated in mildly inflamed muscle spindles.

Additional information is available at the end of the chapter

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

The generation of muscle pain is enigmatic. There may exist several mechanisms for pain production. Many diseases of the muscle tissue are completely or nearly painless, even if there are inflammatory histopathological findings. Thus, inflammation *per se* may not be reflected as muscle pain, although generally inflammation is considered to be associated with pain. In needle EMG, pain caused by the EMG needle seems to be localised in small spots. The EMG

http://dx.doi.org/10.5772/intechopen.72223

Juhani V. Partanen

**Abstract**

afferents

**1. Introduction**

Juhani V. Partanen
