Schuylkill County: Muscles are comprised of two different basic muscle types: fast twitch and slow twitch. Fast twitch muscle fibers have low endurance whereas slow twitch muscle fibers have high endurance. As an example, sprinters have a high percentage of fast twitch muscle fibers in their legs and long-distance runners have a higher percentage of slow twitch muscle fibers. Everyone has their own genetic mixture of these two types of muscle fibers in their muscles. Additionally, postural muscles, the muscles that hold us upright against gravity, have a high percentage of slow twitch fibers. Dynamic muscles, the muscles that enable us move have a higher percentage of fast twitch muscle fibers. That is why when you workout using your dynamic muscles you fatigue more easily than just standing using primarily your slow twitch muscles.
A recent study has shown a difference in muscle fatigue in fibromyalgia patients. In the study two groups of patients were utilized, one with fibromyalgia and the other normal controls. In the first test the subjects upper arm muscle was stimulated using electrical current to contract the muscle while measuring muscle activity with a surface EMG. In the second test, the subjects were asked to flex their upper arm muscle and hold it for 3 seconds. Muscle activity was also recorded with a surface EMG.
The researchers found that there was no difference in strength between normal subjects and fibromyalgia subjects. There was also no difference in muscle fatigability when the muscle was stimulated/contracted by the electrical impulse. However, there was a difference in fatigability of the muscle between the two groups when the subjects voluntarily contracted (under control of their brain) their muscle. Fibromyalgia patients had a higher rate of muscle fatigue and it occurred much earlier.
Fibromyalgia sufferers activate a higher percentage of fast twitch muscle fibers (the ones that fatigue easily) compared to normal subjects. The control of this activation is under the Central Nervous System (the brain and spinal cord). Therefore, the researchers concluded that the altered activation is a Central Nervous System motor (muscle) control-processing problem.
Although it is well established that fibromyalgia is a central pain-processing problem, this is the first time research demonstrated a central muscle control difference between normal subjects and fibromyalgia sufferers. The fatigue problem is not in the muscles, but is in how the brain and spinal cord recruit the muscle fibers and control the muscles.
Along with treating the central pain processing problem with transcranial electrical stimulation to increase the alpha waves it also explains why light exercise has been shown to be beneficial. Additional studies have shown improvement in muscle fatigue symptoms with whole body vibration (WBV). WBV exercise targets the fast twitch muscle fibers and therefore increases the number of fast twitch muscle fibers and fatigability is lessened.
An research paper can be found here: