A Related Study On Muscle Fatigue Induced By Cancer And Chronic Joint Diseases

Objective: To investigate whether the muscle fatigue induced by motor fatigue task differed in the origin and pattern between healthy subjects and patients with cancer-related fatigue(CRF) or temporomandibular disorders(TMD).Methods: Part I: Ten patients with CRF who were off chemo and radiation therapies and 14 age-matched healthy controls were enrolled. Participants completed a Brief Fatigue Inventory(BFI) and performed a fatigue task consisting of intermittent elbow-flexion contractions at submaximal(40% maximal voluntary contraction) intensity till self-perceived exhaustion. Twitch force was measured by eliciting an electrical stimulation to the biceps brachii muscle. The relative degree of peripheral(muscle) vs. central contribution to fatigue induced by the intermittent motor task(IMT) was assessed using twitch force ratio(TFratio) defined as post IMT twitch force to pre IMT twitch force. The total number of trials(intermittent contractions) and total duration of all trials performed by each subject were also quantified. Median frequency(MF) of Biceps brachii(BB) and Brachioradialis(BR) at the beginning,middle and ending of IMT were calculated. Part II: Fifteen patients with TMD and 13 age- and gender-matched healthy controls performed a fatigue task consisting of sustained unilateral clenching contractions at submaximal(30% MVC) intensity till bite force decrease below 27% MVC more than 3 seconds. Pre- and post SMT MVC was measured. Surface EMG signals were recorded from the superficial masseter and anterior temporalis muscles bilaterally, MF at the beginning, middle, ending of SMT were caculated. The duration of SMT was also quantified. Results: Part I: BFI scores were higher(P<0.001) in CRF than controls, indicating greater feeling of fatigue in CRF patients than controls. A significantly smaller number of trials and shorter total duration of the trials(P<0.05) were observed in CRF than control participants. The TFratio in CRF was higher(P<0.05) compared with that of controls, suggesting CRF patients experienced a significantly lower degree of muscle(peripheral) fatigue at the time of perceived exhaustion.MF of BB at the ending of IMT decreased significantly in CRF but no decrease in BR. MF of BB at the ending of IMT decreased but no significant difference in controls,and significant decrease in BR. Part II: Maximal bite force in TMD patients was smaller than controls(p<0.01) at pre-SMT. No significant difference was found in post- to pre- Maximal bite force between groups. The duration of SMT in TMD patients was somewhat shorter than controls(p=0.07). During the three stages of SMT(the beginning, middle,ending), the decreasing tendency of MF and the increasing tendency of normalized RMS of the jaw elevator muscles in TMD patients is similar with the controls. Conclusion: Part I: Our results indicate that motor fatigue in CRF is more of central than peripheral origin during IMT. Significant central fatigue in CRF patients limits their ability to prolong motor performance. Part II: TMD patients have a significantly reduced performance of the jaw elevator muscles, and more fatiguable than healthy subjects, but the pattern of fatigue is similar between TMD patietns and controls.