The present study was performed to investigate the effects of long-term heat stress on mass, strength and gene expression profile of human skeletal muscles without exercise training. Eight healthy men were subjected to 10-week application of heat stress, which was performed for the quadriceps muscles for 8 h/day and 4 days/week by using a heat- and steam-generating sheet. Maximum isometric force during knee extension of the heated leg significantly increased after heat stress (~5.8%, P < 0.05). Mean cross-sectional areas (CSAs) of vastus lateralis (VL, ~2.7%) and rectus femoris (~6.1%) muscles, as well as fiber CSA (8.3%) in VL, in the heated leg were also significantly increased (P < 0.05). Statistical analysis of microarrays (SAM) revealed that 10 weeks of heat stress increased the transcript level of 925 genes and decreased that of 1,300 genes, and gene function clustering analysis (Database for Annotation, Visualization and Integrated Discovery: DAVID) showed that these regulated transcripts stemmed from diverse functional categories. Transcript level of ubiquinol-cytochrome c reductase binding protein (UQCRB) was significantly increased by 10 weeks of heat stress (~3.0 folds). UQCRB is classified as one of the oxidative phosphorylation-associated genes, suggesting that heat stress can stimulate ATP synthesis. These results suggested that long-term application of heat stress could be effective in increasing the muscle strength associated with hypertrophy without exercise training.
To promote the practical application of a Japanese traditional medical treatment, such as hot compresses, we developed a plaster-type warming device consisting of a heat- and steam-generating sheet (HSG sheet). First, we tested its effects when applied to the anterior abdominal wall or lumbar region of women complaining of a tendency towards constipation. Application of the sheet to either region produced a feeling of comfort in the abdomen, as assessed by a survey of the subjects. The significant increases in the total hemoglobin observed in these regions suggested an increase in peripheral blood flow, and significant increases in the HF component on ECG and in the amplitude of gastric motility suggested parasympathetic predominance. We concluded that application of the HSG sheet improves the peripheral hemodynamics and autonomic regulation, induces a feeling of comfort in the abdomen, and provides a beneficial environment for the improvement of gastrointestinal movements.
Appropriate warming of the periocular or posterior cervical skin has been reported to induce autonomic or mental relaxation in humans. To clarify the effects of cutaneous warming on human sleep, eight male subjects with mild sleep difficulties were asked to try three experimental conditions at home, each lasting for 5 days, in a cross-over manner: warming of the periocular skin with a warming device for 10 min before habitual bedtime, warming of the posterior cervical skin with a warming device for 30 min before habitual bedtime, and no treatment as a control. The warming device had a heat- and steam-generating sheet that allowed warming of the skin to 40 °C through a chemical reaction with iron. Electroencephalograms (EEGs) were recorded during nocturnal sleep using an ambulatory EEG device and subjected to spectral analysis. All the participants reported their sleep status using a visual analog scale. We found that warming of the periocular or posterior cervical skin significantly improved subjective sleep status relative to the control. The EEG delta power density in the first 90 min of the sleep episode was significantly increased under both warming of the periocular or posterior cervical skin relative to the control. These results suggest that warming of appropriate skin regions may have favorable effects on subjective and objective sleep quality.
Menthol is thought to stimulate lacrimation via activation of cold-sensitive primary afferent neurons in the cornea. We evaluated a warm compress containing menthol as a potential treatment for dry eye by examining its effects on the tear film in healthy subjects (n = 20) and dry eye patients (n = 35). Disposable eyelid-warming steamers that either did (MH) or did not (HO) contain menthol were applied to one eye of each subject either once only for 10 min or repeatedly over 2 weeks. Single application of MH significantly increased tear meniscus volume (P = 8.6 × 10−5, P = 1.3 × 10−5) and tear film breakup time (P = 0.006, P = 0.002) as well as improved meibum condition in healthy subjects and dry eye patients, respectively. Repeated application of MH significantly increased tear meniscus volume (P = 0.004, P = 1.7 × 10−4) and tear film breakup time (P = 0.037, P = 0.010) in healthy subjects and dry eye patients, respectively. Repeated application of MH thus induced persistent increases in tear fluid volume and tear film stability in dry eye patients, suggesting that repeated use of a warm compress containing menthol is a potential novel treatment for dry eye disease.
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