The physiological strain index does not reliably identify individuals at risk of reaching a thermal tolerance limit

Purpose The physiological strain index (PSI) was developed to assess individuals' heat strain, yet evidence supporting its use to identify individuals at potential risk of reaching a thermal tolerance limit (TTL) is limited. The aim of this study was to assess whether PSI can identify individuals at risk of reaching a TTL. Methods Fifteen females and 21 males undertook a total of 136 trials, each consisting of two 40-60 minute periods of treadmill walking separated by ~ 15 minutes rest, wearing permeable or impermeable clothing, in a range of climatic conditions. Heart rate (HR), skin temperature (T sk), rectal temperature (T re), temperature sensation (TS) and thermal comfort (TC) were measured throughout. Various forms of the PSI-index were assessed including the original PSI, PSI fixed , adaptive-PSI (aPSI) and a version comprised of a measure of heat storage (PSI HS). Final physiological and PSI values and their rate of change (ROC) over a trial and in the last 10 minutes of a trial were compared between trials completed (C, 101 trials) and those terminated prematurely (TTL, 35 trials). Results Final PSI original , PSI fixed , aPSI, PSI HS did not differ between TTL and C (p > 0.05). However, differences between TTL and C occurred in final T sk , T re-T sk , TS, TC and ROC in PSI fixed , T re , T sk and HR (p < 0.05). Conclusion These results suggest the PSI, in the various forms, does not reliably identify individuals at imminent risk of reaching their TTL and its validity as a physiological safety index is therefore questionable. However, a physiological-perceptual strain index may provide a more valid measure

Oral l-menthol reduces thermal sensation, increases work-rate and extends time to exhaustion, in the heat at a fixed rating of perceived exertion

PurposeThe study investigated the effect of a non-thermal cooling agent, l-menthol, on exercise at a fixed subjective rating of perceived exertion (RPE) in a hot environment.MethodEight male participants completed two trials at an exercise intensity between ‘hard’ and ‘very hard’, equating to 16 on the RPE scale at ~35 °C. Participants were instructed to continually adjust their power output to maintain an RPE of 16 throughout the exercise trial, stopping once power output had fallen by 30%. In a randomized crossover design, either l-menthol or placebo mouthwash was administered prior to exercise and at 10 min intervals. Power output, VO2, heart rate, core and skin temperature was monitored, alongside thermal sensation and thermal comfort. Isokinetic peak power sprints were conducted prior to and immediately after the fixed RPE trial.ResultsExercise time was greater (23:23 ± 3:36 vs. 21:44 ± 2:32 min; P = 0.049) and average power output increased (173 ± 24 vs. 167 ± 24 W; P = 0.044) in the l-menthol condition. Peak isokinetic sprint power declined from pre-post trial in the l-menthol l (9.0%; P = 0.015) but not in the placebo condition (3.4%; P = 0.275). Thermal sensation was lower in the l-menthol condition (P = 0.036), despite no changes in skin or core temperature (P > 0.05).Conclusion These results indicate that a non-thermal cooling mouth rinse lowered thermal sensation, resulting in an elevated work rate, which extended exercise time in the heat at a fixed RPE

Effects of umbilical cord tissue mesenchymal stem cells (UCX®) on rat sciatic nerve regeneration after neurotmesis injuries

Peripheral nerves have the intrinsic capacity of self-regeneration after traumatic injury but the extent of the regeneration is often very poor. Increasing evidence demonstrates that mesenchymal stem/stromal cells (MSCs) may play an important role in tissue regeneration through the secretion of soluble trophic factors that enhance and assist in repair by paracrine activation of surrounding cells. In the present study, the therapeutic value of a population of umbilical cord tissue-derived MSCs, obtained by a proprietary method (UCX®), was evaluated on end-to-end rat sciatic nerve repair. Furthermore, in order to promote both, end-to-end nerve fiber contacts and MSC cell-cell interaction, as well as reduce the flush away effect of the cells after administration, a commercially available haemostatic sealant, Floseal®, was used as vehicle. Both, functional and morphologic recoveries were evaluated along the healing period using extensor postural thrust (EPT), withdrawal reflex latency (WRL), ankle kinematics analysis, and either histological analysis or stereology, in the hyper-acute, acute and chronic phases of healing. The histological analysis of the hyper-acute and acute phase studies revealed that in the group treated with UCX ® alone the Wallerian degeneration was improved for the subsequent process of regeneration, the fiber organization was higher, and the extent of fibrosis was lower. The chronic phase experimental groups revealed that treatment with UCX® induced an increased number of regenerated fibers and thickening of the myelin sheet. Kinematics analysis showed that the ankle joint angle determined for untreated animals was significantly different from any of the treated groups at the instant of initial contact (IC). At opposite toe off (OT) and heel rise (HR), differences were found between untreated animals and the groups treated with either UCX® alone or UCX® administered with Floseal®. Overall, the UCX® application presented positive effects in functional and morphologic recovery, in both the acute and chronic phases of the regeneration process. Kinematics analysis has revealed positive synergistic effects brought by Floseal® as vehicle for MSCs

The effects of swilling an l(−)-menthol solution during exercise in the heat

We have previously demonstrated that provision of a cold fluid (4 degrees C) during exercise in the heat increases fluid intake and improves exercise capacity when compared to a control fluid (19 degrees C). The present study investigated whether these positive effects could simply be replicated with a cooling agent, menthol. Nine healthy, non-acclimatised males (25 +/- 7 years; .VO(2max): 54 +/- 5 ml kg(-1) min(-1)) cycled to exhaustion at 65% of their peak aerobic power output at 34 degrees C, swilling 25 ml of either an L: (-)-menthol (0.01%) or orange-flavoured placebo solution every 10 min, whilst water was available ad libitum; all fluids were kept at 19 degrees C. Eight out of nine subjects cycled for longer whilst swilling with menthol and this resulted in a 9 +/- 12% improvement in endurance capacity. Rectal temperatures rose by 1.7 degrees C during exercise with the same time course in both conditions, whilst skin temperature remained largely unchanged. Swilling with menthol resulted in hyperventilation by 8 +/- 10 L min(-1) and reduced central (cardiopulmonary) ratings of perceived exertion by 15 +/- 14%. No differences between trials were observed for heart rate, oxygen uptake or carbon dioxide production, blood concentrations of glucose or lactate, sweat rate or volume of water ingested. We conclude that a change in the sensation of oropharyngeal temperature during exercise in the heat significantly affects endurance capacity, ventilation and the (central) sense of effort