PubMed · 14855865
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A E WHITE, J D AMOS. 1951. Electromyography.. https://pubmed.ncbi.nlm.nih.gov/14855865/
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The purpose of this study was to investigate knee muscle activity patterns in experienced Tai-Chi (TC) practitioners during normal walking and TC stepping. The electromyographic (EMG) activity of vastus lateralis (VL), vastus medialis (VM), bicep femoris (BF), and gastrocnemius (GS) muscles of 11 subjects (five females and six males) during the stance phase of normal walking was compared to stance phase of a TC step. Knee joint motion was also monitored by using an Optotrak motion analysis system. Raw EMG was processed by root-mean-square (RMS) technique using a time constant of 50 ms, and normalized to maximum of voluntary contraction for each muscle, referred to as normalized RMS (nRMS). Peak nRMS and co-contraction (quantified by co-contraction index) during stance phase of a gait cycle and a TC step were calculated. Paired t-tests were used to compare the difference for each muscle group peak and co-contraction pair between the tasks. The results showed that only peak values of nRMS in quadriceps and co-contraction were significantly greater in TC stepping compared to normal walking (Peak values of nRMS for VL were 26.93% for normal walking and 52.14% for TC step, p=0.001; VM are 29.12% for normal walking and 51.93% for TC stepping, p=0.028). Mean co-contraction index for VL-BF muscle pairs was 13.24+/-11.02% during TC stepping and 9.47+/-7.77% in stance phase of normal walking (p=0.023). There was no significant difference in peak values of nRMS in the other two muscles during TC stepping compared to normal walking. Preliminary EMG profiles in this study demonstrated that experienced TC practitioners used relatively higher levels of knee muscle activation patterns with greater co-contraction during TC exercise compared to normal walking.
AIM: The physiology of urinary continence during stress is complex and the role of passive and active mechanisms remains unclear. Coughing leads to a contraction of urethral rhabdomyosphincter and pelvic floor muscles leading to a positive urethro-vesical gradient and continence. Neuromuscular fatigue can involve all striated muscles, including rhabdomyosphincter, peri-urethral and pelvic floor muscles. This article reviews results of studies assessing perineal muscular fatigue in urinary incontinence. MATERIALS AND METHODS: A systematic review of the literature (Medline, Pascal and Embase) with use of the MESH keywords fatigue, stress, urinary incontinence, pelvic floor, urethra, urethral pressure, and muscle. RESULTS: Animal models have shown that the pelvic muscles (iliococcygeus and pubococcygeous) exhibit more neuromuscular fatigue than classical skeletal striated muscles (i.e. soleus muscle). Although the human external urethral sphincter is considered to be a highly fatigue-resistant muscle with its high proportion of slow muscle fibers, repeated coughing seems to lead to decreased urethral pressure in numerous women affected with stress urinary incontinence. In this case, "urethral fatigue" might be a possibility. CONCLUSIONS: Although few studies have focused on perineal muscular fatigue, such increased fatigue in pelvic floor muscles may play a role in the pathophysiologic features of stress urinary incontinence in women.