Effects of alternating heat and cold stimulation using a wearable thermo-device on subjective and objective shoulder stiffness

Background Technological innovations have allowed the use of miniature apparatus that can easily control and program heat and cold stimulations using Peltier elements. The wearable thermo-device has a potential to be applied to conventional contrast bath therapy. This study aimed to examine the effects of alternating heat and cold stimulation (HC) using a wearable thermo-device on subjective and objective improvement of shoulder stiffness. Methods Twenty healthy young male individuals (20.3 ± 0.6 years) participated in this study. The interventions were randomly conducted under four conditions, including HC, heat stimulation, cold stimulation, and no stimulation on their bilateral trapezius muscle, after a 30-min typing task. Each intervention was administered at least 1 week apart. The analyzed limb was the dominant arm. Muscle hardness was assessed using a portable muscle hardness meter, as well as the skin temperature over the stimulated area. After each condition, the participants were asked for feedback regarding subjective improvement in refreshed feelings, muscle stiffness, and muscle fatigue using an 11-point numerical rating scale. Results With regard to muscle hardness, only the HC condition significantly decreased from 1.43 N to 1.37 N (d = 0.44, p < 0.05). Additionally, reduced muscle hardness in HC condition was associated with the degree of skin cooling during the intervention (cold max: r = 0.634, p < 0.01; cold change: r = −0.548, p < 0.05). Subjective improvement in refreshed feelings, muscle stiffness, and muscle fatigue was determined in the HC and heat stimulation conditions compared with the no stimulation condition (p < 0.01 and p < 0.05, respectively). Moreover, the HC condition showed significantly greater improvements in muscle stiffness and fatigue compared to the cold stimulation condition (p < 0.05). Conclusions The current study demonstrated that HC promoted not only better subjective symptoms, such as muscle stiffness and fatigue, but also lesser muscle hardness. Furthermore, an association was observed between the degree of skin temperature cooling and reduced muscle hardness during HC. Further investigations on the ratio and intensity of cooling should be conducted in the future to establish the optimal HC protocol for muscle stiffness or fatigue. Trial registration UMIN000040620. Registered 1 June 2020

Effect of Heat Stimulation on Circulating Irisin in Humans

High temperatures lead to oxidative stress. The aim of the study was to determine whether heat stimulation-induced hyperthermia can increase the level of circulating irisin. Twenty-one healthy female subjects (age, 26.3 ± 2.71 years; height, 162.1 ± 3.15 cm; weight, 54.2 ± 3.86 kg; and body surface area, 1.57 ± 0.11 m2) not taking contraceptives participated in this study. All experiments were performed individually for each participant when they were in the early proliferative menstrual phase. In an automated climate chamber (25 ± 0.5°C), the heat load was applied via half-body immersion into a hot water bath (42 ± 0.5°C). Five-minutes break was provided every after 5 min of immersion and the total passive heating time was 30 min. Tympanic temperature (Tty) and skin temperature (Ts) were measured. Mean body temperature (mTb) was calculated. Blood samples were collected before and immediately after immersion. Levels of irisin, cortisol, creatine kinase (CK), and lactate dehydrogenase (LDH) were analyzed. Tty, mTb and serum irisin levels increased after hot water immersion. The blood levels of cortisol, CK, and LDH were also elevated after hot water immersion. Heat stimulation might increase the levels of circulating irisin in humans in response to oxidative stress.

An intensity matched comparison of laser- and contact heat evoked potentials

Previous studies comparing laser (LEPs) and contact heat evoked potentials (CHEPs) consistently reported higher amplitudes following laser compared to contact heat stimulation. However, none of the studies matched the perceived pain intensity, questioning if the observed difference in amplitude is due to biophysical differences between the two methods or a mismatch in stimulation intensity. The aims of the current study were twofold: (1) to directly compare the brain potentials induced by intensity matched laser and contact heat stimulation and (2) investigate how capsaicin-induced secondary hyperalgesia modulates LEPs and CHEPs. Twenty-one healthy subjects were recruited and measured at four experimental sessions: (1) CHEPs + sham, (2) LEPs + sham, (3) CHEPs + capsaicin, and (4) LEPs + capsaicin. Baseline (sham) LEPs latency was significantly shorter and amplitude significantly larger compared to CHEPs, even when matched for perceived pain. Neither CHEPs nor LEPs was sensitive enough to detect secondary hyperalgesia. These differences provide evidence that a faster heating rate results in an earlier and more synchronized LEPs than CHEPs. To our knowledge, this was the first study to match perceived intensity of contact heat and laser stimulations, revealing distinct advantages associated with the acquisition of LEPs.

Effect of Thermal Stimulation on Gene Expression Related to Skeletal Muscle-derived Cell Density

Aims: Our previous study demonstrated favorable changes in plasma protein levels such as adiponectin by fomentation in healthy people. We also reported that the thermal stimulation caused changes of mRNA levels to prevent atherosclerosis in human skeletal muscle-derived cell (SMDC). However, cell number decreased to 74.6% by heat stimulation. In order to clarify this mechanism, we investigated whether the heat stimulation affects the levels of mRNA related to cell density or number of SMDC. Study Design: Experimental study comparing transcriptome between cells cultured at higher temperature and control cells. Place and Duration of Study: From September 2015 to March 2017, Division of Physiology and Metabolism, University of Hyogo. Methodology: SMDC was cultured at 42°C and 37°C and its gene expression was analyzed by using microarray technique. Results: Thermal stimulation of SMDC significantly altered the expression of 10 genes related to apoptosis, 1 gene related to cell division and 1 gene related to cell adhesion. mRNA expression of apoptosis promoting gene, such as THAP2 (THAP domain containing, apoptosis associated protein 2), PDCD6 (programmed cell death 6), BCL2L13 (BCL2-like 13), LOC728613 (programmed cell death 6 pseudogene), CASP4 (caspase 4), and FAS (Fas cell surface death, receptor) was up-regulated. On the other hand, PAWR (PRKC, apoptosis, WT1, regulator) was downregulated, and mRNA expression of anti-apoptotic genes, such as NOL3 (nucleolar protein 3), CIAPIN1 (cytokine-induced apoptosis inhibitor 1) and NAIF1 (nuclear apoptosis inducing factor1), was up-regulated, Gene Ontology analysis showed alterations in the expression of genes that promote apoptosis and cell growth inhibition. Pathway analysis demonstrated the pathways that promote apoptosis, stimulate cell growth and negatively or positively regulate cell adhesion. Conclusion: The present study suggested that thermal stimulation of SMDC might predominantly promote apoptosis from consistent changes in related gene expression by any analysis.

Observation of others’ painful heat stimulation involves responses in the spinal cord

Observing others’ aversive experiences is central to know what is dangerous for ourselves. Hence, observation often elicits behavioral and physiological responses comparable to first-hand aversive experiences and engages overlapping brain activation. While brain activation to first-hand aversive experiences relies on connections to the spinal cord, it is unresolved whether merely observing aversive stimulation also involves responses in the spinal cord. Here, we show that observation of others receiving painful heat stimulation involves neural responses in the spinal cord, located in the same cervical segment as first-hand heat pain. However, while first-hand painful experiences are coded within dorsolateral regions of the spinal cord, observation of others’ painful heat stimulation involves medial regions. Dorsolateral areas that process first-hand pain exhibit negative responses when observing pain in others. Our results suggest a distinct processing between self and others’ pain in the spinal cord when integrating social information.

Influence of the Particle Size of Sandy Sediments on Heat and Mass Transfer Characteristics during Methane Hydrate Dissociation by Thermal Stimulation

Natural gas hydrate could be regarded as an alternative energy source in the future. Therefore, the investigation of the gas production from hydrate reservoirs is attracting extensive attention. In this work, a novel set-up was built to investigate sand production and sediment deformation during hydrate dissociation by heat stimulation. The influence of the particle sizes on the hydrate dissociation and sediment deformation was first investigated experimentally. The experimental results indicated that the rate of hydrate decomposition by heat stimulation was in proportion to the particle size of the sediment. The heat transfer rate and the energy efficiency decreased with the decrease of the particle size of the sediment. This was because higher permeability might lead to a larger sweep area of the fluid flow, which was beneficial for the supply of heat for hydrate dissociation. The sand production was found during hydrate dissociation by heat stimulation. The particle migration was due to the hydrodynamics of the water injection. The sand sediment expanded under the drive force from water injection and hydrate dissociation. Additionally, the smaller permeability led to the larger pressure difference leading to the larger sediment deformation. Because the sediment became loose after hydrate dissociation, small particle migration due to the hydrodynamics of the water injection could happen during the experiments. However, the sand production in the sediment with the larger particle size was more difficult, because the larger particles were harder to move due to the hydrodynamics, and the larger particles were harder to move across the holes on the production well with a diameter of 1 mm. Therefore, the sediment deformation during hydrate dissociation by heat stimulation should not be ignored.