Fatigue-Related Change in Surface Electromyographic Activities of the Perilaryngeal Muscles.

PURPOSE: This study set out to quantify the fatigue-related changes in surface electromyographic (sEMG) activities of the perilaryngeal muscles following a vocal loading task. METHOD: Thirty-six young healthy participants (M age = 22.4 years) with normal voice performed karaoke singing for at least 100 min. Before the singing task, all participants underwent the sEMG measure and completed a Perceived Vocal Fatigue Score (P-VFS) questionnaire. After the singing task, all participants were immediately measured with the P-VFS again. Half of the participants were then measured for their sEMG immediately after their karaoke singing task, and the other half were given 20 min of rest before undertaking the sEMG measure. The P-VFS and the median frequency (MDF) of the sEMG signals collected from the suprahyoid, infrahyoid, and sternocleidomastoid muscles before and after the singing task were compared using a linear mixed-effects model. RESULTS: All participants reported a perceived vocal fatigue after singing, with a significantly increased P-VFS. Compared with the presinging baseline, the MDF of the sEMG signals in perilaryngeal muscles was significantly lower immediately after the singing task. Such a significant difference was also found after 20 min following the singing task. CONCLUSIONS: The MDF analysis of the sEMG signals could identify and quantify the performance vocal fatigue contributed by perilaryngeal muscles following a vocal loading task. The findings also showed that such fatigue in perilaryngeal muscles, as far as sEMG activities are concerned, can last for at least 20 min.

Perinatal intermittent hypoxia alters γ-aminobutyric acid: a receptor levels in rat cerebellum.

Perinatal hypoxia commonly causes brain injury in infants, but the time course and mechanisms underlying the preferential male injury are unclear. Intermittent hypoxia disturbs cerebellar γ-aminobutyric (GABA)-A receptor profiles during the perinatal period, possibly responding to transient excitatory processes associated with GABA(A) receptors. We examined whether hypoxic insults were particularly damaging to the male rodent cerebellum during a specific developmental time window. We evaluated cerebellar injury and GABA(A) receptor profiles following 5-h intermittent hypoxia (IH: 20.8% and 10.3% ambient oxygen, switched every 240s) or room-air control in groups of male and female rat pups on postnatal d 1-2, wk 1, or wk 3. The cerebella were harvested and compared between groups. The mRNA levels of GABA(A) receptors α6, normalized to a house-keeping gene GAPDH, and assessed using real-time reverse-transcriptase PCR assays were up-regulated by IH at wk 1, more extensively in male rats, with sex influencing the regulatory time-course. In contrast, GABA(A) α6 receptor protein expression levels, assessed using Western blot assays, reached a nadir at wk 1 in both male and female rats, possibly indicating involvement of a post-transcriptional mechanism. The extent of cerebellar damage and level of apoptosis, assessed by DNA fragmentation, were greatest in the wk 3 IH-exposed group. The findings suggest partial protection for female rats against early hypoxic insult in the cerebellum, and that down-regulation of GABA(A) receptors, rather than direct neural injury assessed by DNA fragmentation may modify cerebellar function, with potential later motor and other deficits.