The contribution of blood flow to the skin temperature responses during a cold sensitivity test

Purpose

The presumption in a cold sensitivity test (CST) used for cold injuries is that the skin temperature (T _sk) observed reflects the return of blood flow to the extremity following a local cold challenge. We questioned this assumption.

Methods

Six non-cold injured participants undertook two CSTs in 30 °C air. The control (CON) CST involved 12 min gentle exercise prior to immersing the foot into 15 °C water for 2 min followed by 15 min of spontaneous rewarming. The occlusion (OCC) CST was the same except that blood flow to the foot was occluded during the rewarming period. These results were compared to CSTs from six individuals with non-freezing cold injury and moderate–severe cold sensitivity (CS) and a non-perfused human digit model (NPDM).

Results

Before immersion, great toe skin blood flow (SkBF) was similar in CON and OCC conditions [255 (107) laser Doppler units (LDU)] and was higher than CS [59 (52) LDU]. During rewarming, SkBF in CON returned to 104 % of the pre-immersion value and was higher than both OCC and CS. Great toe T _sk before immersion was lower in CS [28.5 (2.1) °C] compared to CON [34.7 (0.4) °C], OCC [34.6 (0.9) °C] and NPDM [35.0 (0.4) °C]. During rewarming skin/surface temperature in OCC, CS and NPDM were similar and all lower than CON.

Conclusions

SkBF does contribute to the skin rewarming profile during a CST as a faster rate of rewarming was observed in CON compared to either OCC or NPDM. The lower T _sk in CS may be due to a reduced basal SkBF.     

Treatment of exertional heat stress developed during low or moderate physical work

Purpose

We examined whether treatment for exertional heat stress via ice water immersion (IWI) or natural recovery is affected by the intensity of physical work performed and, thus, the time taken to reach hyperthermia.

Methods

Nine adults (18–45 years; 17.9 ± 2.8 percent body fat; 57.0 ± 2.0 mL kg^?1 min^?1 peak oxygen uptake) completed four conditions incorporating either walking or jogging at 40 °C (20 % relative humidity) while wearing a non-permeable rain poncho. Upon reaching 39.5 °C rectal temperature (T _re), participants recovered either via IWI in 2 °C water or via natural recovery (seated in a ~29 °C environment) until T _re returned to 38 °C.

Results

Cooling rates were greater in the IWI [T _re: 0.24 °C min^?1; esophageal temperature (T _es): 0.24 °C min^?1] than the natural recovery (T _re and T _es: 0.03 °C min^?1) conditions (p < 0.001) with no differences between the two moderate and the two low intensity conditions (p > 0.05). Cooling rates for T _re and T _es were greater in the 39.0–38.5 °C (T _re: 0.19 °C min^?1; T _es: 0.31 °C min^?1) compared with the 39.5–39.0 °C (T _re: 0.11 °C min^?1; T _es: 0.13 °C min^?1) period across conditions (p < 0.05). Similar reductions in heart rate and mean arterial pressure were observed during recovery across conditions (p > 0.05), albeit occurred faster during IWI. Percent change in plasma volume at the end of natural recovery and IWI was 5.96 and 9.58 %, respectively (p < 0.001).

Conclusion

The intensity of physical work performed and, thus, the time taken to reach hyperthermia does not affect the effectiveness of either IWI treatment or natural recovery. Therefore, while the path to hyperthermia may be different for each patient, the path to recovery must always be immediate IWI treatment.     

Do greater rates of body heat storage precede the accelerated reduction of self-paced exercise intensity in the heat?

Aim

To reevaluate the previous hypothesis that greater reductions in self-paced exercise intensity in the heat are mediated by early differences in the rate of body heat storage (S).

Methods

Eight trained volunteers cycled in 19 °C/1.8 kPa (COOL), 25 °C/1.2 kPa (NORM), and 34 °C/1.6 kPa (HOT), while maintaining an RPE of 16. Potential differences in S following the onset of exercise were assessed by comparing rates of esophageal temperature change (ΔT _es/Δt); and estimated S values using a traditional two-compartment thermometric model (S _therm) of changes in rectal (T _re) and skin (T _sk) temperature, and partitional calorimetry (S _cal).

Results

After 15 min of exercise, workload decreased more in HOT vs. COOL (P = 0.03), resulting in a shorter time (HOT: 40.7 ± 14.9 min; COOL: 53.5 ± 18.7 min; P = 0.04) to 70 % of initial workload. However, there were no preceding differences in ΔT _es/Δt between conditions (P = 0.18). S _therm values were different between HOT and COOL during the first 5 min of exercise (P < 0.05), primarily due to negative S _therm values (?32 ± 15 kJ min^?1) in COOL, which according to partitional calorimetric measurements, required improbably high (~56 kJ min^?1) rates of evaporation when no sweating on the back and thigh was observed until after 7.6 ± 1.5 min and 4.8 ± 1.7 min of exercise, respectively. S _cal values in the first 5 min of exercise confirmed S was actually positive in COOL (+21 ± 8 kJ min^?1) and not negative. Different S _therm values following the onset of exercise at different environmental temperatures are simply due to transient differences in the rate of change in T _sk.

Conclusion

Reductions in self-paced exercise intensity in the heat are not mediated by early differences in S following the onset of exercise.     

One night of sleep deprivation decreases treadmill endurance performance

The aim was to test the hypothesis that one night of sleep deprivation will impair pre-loaded 30 min endurance performance and alter the cardio-respiratory, thermoregulatory and perceptual responses to exercise. Eleven males completed two randomised trials separated by 7 days: once after normal sleep (496 (18) min: CON) and once following 30 h without sleep (SDEP). After 30 h participants performed a 30 min pre-load at 60% $ \dot{V}{\text{O}}_{2\max } $ followed by a 30 min self-paced treadmill distance test. Speed, RPE, core temperature (T _re), mean skin temperature (T _sk), heart rate (HR) and respiratory parameters ( $ \dot{V}{\text{O}}_{2} $ , $ \dot{V}{\text{CO}}_{2} $ , $ \dot{V}{\text{E}} $ , RER pre-load only) were measured. Less distance (P = 0.016, d = 0.23) was covered in the distance test after SDEP (6037 (759) 95%CI 5527 to 6547 m) compared with CON (6224 (818) 95%CI 5674 to 6773 m). SDEP did not significantly alter T _re at rest or thermoregulatory responses during the pre-load including heat storage (0.8°C) and T _sk. With the exception of raised $ \dot{V}{\text{O}}_{2} $ at 30 min on the pre-load, cardio-respiratory parameters, RPE and speed were not different between trials during the pre-load or distance test (distance test mean HR, CON 174 (12), SDEP 170 (13) beats min^?1: mean RPE, CON 14.8 (2.7), SDEP 14.9 (2.6)). In conclusion, one night of sleep deprivation decreased endurance performance with limited effect on pacing, cardio-respiratory or thermoregulatory function. Despite running less distance after sleep deprivation compared with control, participants’ perception of effort was similar indicating that altered perception of effort may account for decreased endurance performance after a night without sleep.     

Increased air velocity during exercise in the heat leads to equal reductions in hydration shifts and interleukin-6 with age

Purpose

The effectiveness of increased air velocity in reducing hydration shifts and physiological strain during work in the heat was examined in young and older males.

Methods

Ten young (mean ± SE, 24 ± 1 years) and 10 older (59 ± 1 years) males, matched for height, mass, and body surface area, cycled 4 × 15-min at moderate-to-heavy heat production (400 W), with 15-min rest separations between exercise bouts (final recovery 30 min), while wearing work clothing in humid heat (35 °C, 60 % relative humidity) under low (~0.5 m s^?1) and high (~3.0 m s^?1) air velocity. Rectal temperature (T _re) and heart rate were measured continuously, whereas hydration indices and interleukin (IL)-6 were measured at rest (PRE) and following the final recovery (POST).

Results

Young and older males experienced similar thermal and cardiovascular strain within the low (T _re end-exercise: young = 38.28 ± 0.11, older = 38.31 ± 0.08 °C) and high (T _re end-exercise: young = 37.94 ± 0.08, older = 37.87 ± 0.08 °C) air velocity conditions, with a reduced increase in both groups in high compared to low. Percent changes in plasma volume were similarly greater during the low (young = ?10.9 ± 1.2, older = ?10.8 ± 0.9 %) compared to high (young = ?5.7 ± 0.6, older = ?6.9 ± 0.7 %) condition for both groups. Despite elevated IL-6 at PRE in the older males, the IL-6 absolute change was similar between young (low = +4.10 ± 0.95, high = +0.99 ± 0.32 pg mL^?1) and older (low = +3.58 ± 0.83, high = +1.24 ± 0.28 pg mL^?1) males yet greater during the low compared to high condition.

Conclusions

Increased air velocity was effective in reducing the increase in hydration shifts and physiological strain (i.e. IL-6, thermal and cardiovascular strain) equally in young and older males.     

Three nights of sleep deprivation does not alter thermal strain during exercise in the heat

Purpose

Individuals exposed to total sleep deprivation may experience an increased risk of impaired thermoregulation and physiological strain during prolonged physical activity in the heat. However, little is known of the impact of more relevant partial sleep deprivation (PSD). This randomized counterbalanced study investigated the effect of PSD on thermal strain during an exercise-heat stress.

Methods

Ten healthy individuals performed two stress tests (45 min running, 70 % ${\dot{V}\text{O}}_{2\hbox{max} }$ V · O 2 max 33 °C, 40 % RH). Each trial followed three nights of controlled sleep: normal [479 (SD 2) min sleep night^?1; Norm] and PSD [116 (SD 4) min sleep night^?1]. Energy balance and hydration state were controlled throughout the trials. Rectal temperatures (T _re), mean skin temperature ( $\bar{T}_{\text{sk}}$ T ¯ sk ), heart rate (HR), RPE, and thermal sensations (TS) were measured at regular intervals during each heat stress trial.

Results

There was a significant main effect of time (P < 0.05) for all of these variables. However, no differences (P > 0.05) were observed between PSD and Norm, respectively, for T _re [39.0 (0.5) vs. 39.1 (0.5)  °C], $\bar{T}_{\text{sk}}$ T ¯ sk , [36.1 (0.6) vs. 36.0 (0.7)  °C] and HR [181 (13) vs. 182 (13) beats min^?1)] at the end of exercise-heat stress. There were no differences (P > 0.05) in $\bar{T}_{\text{sk}}$ T ¯ sk , PSI, RPE, TS and whole-body sweat rate between PSD versus Norm.

Conclusion

Since greater physiological strain during exercise-heat stress did not follow three nights of PSD, it appears that sleep loss may have minimal impact upon thermal strain during exercise in the heat, at least as evaluated within this experiment.     

General and local cold responses in humans after 2 weeks at high altitude

To investigate the effects of a short-term high altitude residence (2 weeks between 4150 m and 6885 m in the Andes) on the general and local cold responses after descent, 11 subjects were submitted both to a whole body standard cold air test (SCAT, dry bulb temperature = 1°C, 2 h, nude, at rest) and to a local cold water test of the right upper limb (CWT, 5°C, 5 min) both before and after the expedition. Compared to before the expedition, a lower systolic blood pressure was observed after the high altitude residence [130.00 (SEM 3.35) mm Hg vs 140.40 (SEM 4.74) mm Hg at the end of CWT, P?P? _sk) but metabolic heat production was slightly but significantly diminished [110 (SEM 4) W?·?m^?2 vs 125 (SEM 3) W?·?m^?2, P??1 vs 9.30 (SEM 2.30) kJ?·?kg^?1 , P?P? _sk observed at (d) was higher [25.70 (SEM 0.80)°C vs 23.57 (SEM 0.78)°C, P?相似文献   

NLRP3 gene is associated with ulcerative colitis (UC), but not Crohn’s disease (CD), in Chinese Han population

Objective

This study aimed to investigate whether NLRP3 is associated with IBD in Chinese Han population.

Methods

Three SNPs were genotyped using polymerase chain reaction with sequence-specific primers in 288 patients [232 Crohn’s disease (CD) patients, 56 ulcerative colitis (UC) patients] and 274 controls.

Results

In IBD group, the results showed no significant association. When subdivided to CD and UC, it showed in CD subgroup, there was no significant association. However, in UC subgroup, rs10754558 (P _allele = 0.015272, P _genotype = 0.029776, OR [95 % CI] = 0.604190[0.401200–0.909886]) and rs10925019 (P _allele = 0.013042, P _genotype = 0.037045, OR [95 % CI] = 2.022613[1.149854–3.557812]) have significant associations with UC. The G and T alleles were risk factors of the susceptibility of UC, the GG and TT genotypes may increase risk of this disease. Rs4925648 has no association with UC. The haplotypes analysis results showed as follow: for rs4925648–rs10925019, CC and TT are risk factors for UC (for CC, χ ² = 3.605, P = 0.057613, OR [95 % CI] = 1.645 [0.980–2.761], for TT, χ ² = 5.522, P = 0.018804, OR [95 % CI] = 0.426[0.205–0.884]), and for rs10754558–rs10925019, CT and GC haplotypes are risk factors for UC (for CT, χ ² = 3.545, P = 0.059739, OR [95 % CI] = 0.571[0.317–1.029], for GC, χ ² = 9.359, P = 0.002228, OR [95 % CI] = 1.904 [1.255–2.887]).

Conclusions

We first demonstrated that rs10754558 and rs10925019 are significantly associated with the susceptibility of UC, but not CD in Chinese Han population, suggesting that NLRP3 may play an important role in the pathogenesis of UC.     

Ramp-incremented and RPE-clamped test protocols elicit similar VO2max values in trained cyclists

Purpose

The present study compared the efficacy of ramp incremented and ratings of perceived exertion (RPE)-clamped test protocols for eliciting maximal oxygen uptake (VO_2max).

Methods

Sixteen trained cyclists (age 34 ± 7 years) performed a ramp-incremented protocol and an RPE-clamped protocol 1 week apart in a randomized, counterbalanced order. The RPE-clamped protocol consisted of five, 2-min stages where subjects self-selected work rate and pedal cadence to maintain the prescribed RPE. After completing both test protocols subjects were asked which they preferred.

Results

The mean ± SD test time of 568 ± 72 s in the ramp protocol was not significantly different to the 600 ± 0 s in the RPE-clamped protocol (mean difference = 32 s; p = 0.09), or was the VO_2max of 3.86 ± 0.73 L min^?1 in the ramp protocol significantly different to the 3.87 ± 0.72 L min^?1 in the RPE-clamped protocol (mean difference = 0.002 L min^?1; p = 0.97). Furthermore, no significant differences were observed for peak power output (p = 0.21), maximal minute ventilation (p = 0.97), maximal respiratory exchange ratio (p = 0.09), maximal heart rate (p = 0.51), and post-test blood lactate concentration (p = 0.58). The VO_2max attained in the preferred protocol was significantly higher than the non-preferred protocol (mean difference = 0.14 L min^?1; p = 0.03).

Conclusion

The RPE-clamped test protocol was as effective as the ramp-incremented protocol for eliciting VO_2max and could be considered as a valid alternative protocol, particularly where a fixed test duration is desirable.     

Inflammatory responses of older Firefighters to intermittent exercise in the heat

Purpose

Repeated strenuous work in the heat may predispose firefighters to augmented immune responses and inflammation. This study examined the immune responses in 12 older Firefighters (FF) and 12 older Non-Firefighters (Non-FF), and a group of 6 young FF and 6 young Non-FF, following intermittent exercise in the heat.

Methods

The participants, matched for age, body surface area, body composition, and VO_2peak, cycled 4 × 15 min at moderate-to-high heat production (400 W), each followed by 15-min rest, in dry [10–20 % relative humidity (RH)] and humid (60 % RH) heat (35 °C). Rectal temperature (T_re) and heart rate (HR) were measured continuously, and blood samples at baseline (PRE) and following 60-min recovery (POST) were analyzed for Interleukin (IL)-6, Tumor Necrosis Factor (TNF-α), C-reactive protein (CRP), platelet count (PLT), and mean platelet volume (MPV).

Results

No differences were observed for T_re, HR, TNF-α, CRP, or PLT between the FF and Non-FF in either condition. The Non-FF had greater changes in IL-6 (Warm/Dry = +1.10 ± 0.18, Warm/Humid = +2.94 ± 0.74 pg mL^?1), compared to the FF (Warm/Dry = +0.67 ± 0.17, Warm/Humid = +0.70 ± 0.33 pg mL^?1), and MPV at PRE/POST compared to the FF. Between the young and older FF and Non-FF, no differences in T _re, HR, PLT, or MPV were observed, however, elevated CRP (Warm/Dry) in the older FF, and IL-6 (Warm/Dry) and TNF-α (both conditions) in the older Non-FF, were observed.

Conclusions

The elevated IL-6 in the Non-FF is potentially indicative of increased strain in the Non-FF and/or adaptive changes in the FF due to the occupational demands.     

Changes in heart rate variability during the induction and decay of heat acclimation

Purpose

We evaluated the changes in core temperature, heart rate, and heart rate variability (HRV) during the induction and decay of heat acclimation.

Methods

Ten males (23 ± 3 years; 79.5 ± 3.5 kg; 15.2 ± 4.5 percent body fat; 51.13 ± 4.61 mLO²?kg^?1?min^?1 peak oxygen uptake) underwent a 14-day heat acclimation protocol comprising of 90-min cycling at ~50 % peak oxygen uptake at 40 °C and ~20 % relative humidity. Core temperature, heart rate, and 102 HRV measures were recorded during a heat tolerance test conducted at baseline (day 0) and at the end of the induction (day 14) and decay (day 28) phases.

Results

Heat acclimation resulted in significantly reduced core temperature [rectal (χ ² = 1298.14, p < 0.001); esophageal (χ ² = 1069.88, p < 0.001)] and heart rate (χ ² = 1230.17, p < 0.001). Following the decay phase, 26, 40, and 60 % of the heat acclimation-induced reductions in rectal temperature, esophageal temperature, and heart rate, respectively, were lost. Heat acclimation was accompanied by profound and broad changes in HRV: at the end of the induction phase, 75 of the 102 variability measures computed were significantly different (p < 0.001), compared to only 47 of the 102 at the end of the decay phase.

Conclusions

Heat acclimation is accompanied by reduced core temperature, significant bradycardia, and marked alterations in HRV, which we interpret as being related to vagal dominance. The observed changes in core temperature persist for at least 2 weeks of non-exposure to heat, while the changes in heart rate and HRV decay faster and are only partly evident after 2 weeks of non-exposure to heat.     

Heart rate variability during exertional heat stress: effects of heat production and treatment

Purpose

We assessed the efficacy of different treatments (i.e., treatment with ice water immersion vs. natural recovery) and the effect of exercise intensities (i.e., low vs. high) for restoring heart rate variability (HRV) indices during recovery from exertional heat stress (EHS).

Methods

Nine healthy adults (26 ± 3 years, 174.2 ± 3.8 cm, 74.6 ± 4.3 kg, 17.9 ± 2.8 % body fat, 57 ± 2 mL·kg·^?1 min^?1 peak oxygen uptake) completed four EHS sessions incorporating either walking (4.0–4.5 km·h^?1, 2 % incline) or jogging (~7.0 km·h^?1, 2 % incline) on a treadmill in a hot-dry environment (40 °C, 20–30 % relative humidity) while wearing a non-permeable rain poncho for a slow or fast rate of rectal temperature (T _re) increase, respectively. Upon reaching a T _re of 39.5 °C, participants recovered until T _re returned to 38 °C either passively or with whole-body immersion in 2 °C water. A comprehensive panel of 93 HRV measures were computed from the time, frequency, time–frequency, scale-invariant, entropy and non-linear domains.

Results

Exertional heat stress significantly affected 60/93 HRV measures analysed. Analyses during recovery demonstrated that there were no significant differences between HRV measures that had been influenced by EHS at the end of passive recovery vs. whole-body cooling treatment (p > 0.05). Nevertheless, the cooling treatment required statistically significantly less time to reduce T _re (p < 0.001).

Conclusions

While EHS has a marked effect on autonomic nervous system modulation and whole-body immersion in 2 °C water results in faster cooling, there were no observed differences in restoration of autonomic heart rate modulation as measured by HRV indices with whole-body cold-water immersion compared to passive recovery in thermoneutral conditions.     

Neck cooling and cognitive performance following exercise-induced hyperthermia

Purpose

To assess the efficacy of neck cooling on cognitive performance following exertional hyperthermia.

Methods

Twelve healthy men completed two experimental trials [control (CON) and neck cooling collar (NCC)] in a counter-balanced design. They ran on a treadmill at 70 % VO_2peak under warm and humid conditions (dry bulb temperature: 30.2 ± 0.3 °C, relative humidity: 71 ± 2 %) for 75 min or until volitional exhaustion. Gastrointestinal, neck and skin temperatures, heart rate and subjective ratings were assessed. Serum brain-derived neurotrophic factor (BDNF) levels were measured before and after each run. Cognitive performance comprising symbol digit matching, search and memory, digit span, choice reaction time and psychomotor vigilance test (PVT) were assessed before and after exercise.

Results

Mean gastrointestinal temperature was similar after exercise between trials (CON: 39.5 ± 0.4 °C vs. NCC: 39.6 ± 0.3 °C; p = 0.15). Mean neck temperature was lowered in NCC compared to CON after the run (36.4 ± 1.6 °C vs. NCC: 26.0 ± 0.3 °C; p < 0.001). Exercise-induced hyperthermia improved mean reaction time in the symbol digit matching test (?134 ± 154 ms; p < 0.05) and the PVT (?18 ± 30 ms; p < 0.05). Maximum span was increased in the digit span test (1 ± 2; p < 0.05). Application of NCC reduced the number of search errors made in level 3 of the search and memory test (p < 0.05). Mean serum BDNF levels were increased following exercise-induced hyperthermia in both trials (p < 0.05).

Conclusion

Exercise-induced hyperthermia improves working memory and alertness. Neck cooling may only enhance performance in tasks of higher complexity.     

Assessing neonatal heat balance and physiological strain in newborn infants nursed under radiant warmers in intensive care with fentanyl sedation

Purpose

To assess heat balance status of newborn infants nursed under radiant warmers (RWs) during intensive care.

Methods

Heat balance, thermal status and primary indicators of physiological strain were concurrently measured in 14 newborns nursed under RWs for 105 min. Metabolic heat production (M), evaporative heat loss (E), convective (C) and conductive heat flow (K), rectal temperature (T _re) and mean skin temperatures (T _sk) were measured continuously. The rate of radiant heat required for heat balance (R _req) and the rate of radiant heat provided (R _prov) were derived. The rate of body heat storage (S) was calculated using a two-compartment model of ‘core’ (T _re) and ‘shell’ (T _sk) temperatures.

Results

Mean M, E, C and K were 10.5 ± 2.7 W, 5.8 ± 1.1 W, 6.2 ± 0.8 W and 0.1 ± 0.1 W, respectively. Mean R _prov (1.7 ± 2.6 W) and R _req (1.7 ± 2.7 W) were similar (p > 0.05). However, while the resultant mean change in body heat content after 105 min was negligible (–0.1 ± 3.7 kJ), acute time-dependent changes in S were evidenced by a mean positive heat storage component of +6.4 ± 2.6 kJ and a mean negative heat storage component of –6.5 ± 3.7 kJ. Accordingly, large fluctuations in both T _re and T _sk occurred that were actively induced by changes in RW output. Nonetheless, no active physiological responses (heart rate, breathing frequency and mean arterial pressure) to these bouts of heating and cooling were observed.

Conclusions

RWs maintain net heat balance over a prolonged period, but actively induce acute bouts of heat imbalance that cause rapid changes in T _re and T _sk. Transient bouts of heat storage do not exacerbate physiological strain, but could in the longer term.     

Influence of blood donation on the incidence of plateau at \dot{V}{\text{O}} 2max

Purpose

The purpose of this study was to examine the effects of reductions in blood volume and associated oxygen-carrying capacity on the incidence of plateau at $\dot{V}{\text{O}}$ _2max.

Methods

Fifteen well-trained athletes (age 23.3 ± 4.5; mass 77.4 ± 13.1 kg, height 180.1 ± 6.0 cm) completed three incremental cycle tests to volitional exhaustion, of which the first was defined as familiarisation, with the remaining two trials forming the experimental conditions of pre- (UBL) and post-(BLE) blood donation (~450 cm³). The work rate for the incremental tests commenced at 100 W for 60 s followed by a ramp of 0.42 W s^?1, with cadence being held constant at 80 rpm. Throughout all trials, $\dot{V}{\text{O}}$ ₂ was determined on a breath-by-breath basis using a pre-calibrated metabolic cart. The criteria for plateau determination was a ? $\dot{V}{\text{O}}$ ₂ ≤ 50 ml min^?1 over the final two consecutive 30 s sampling periods.

Results

Despite a significant (P = 0.0028) 9.4 % reduction in haemoglobin concentration and 10.8 % (P = 0.016) reduction in erythrocyte count between UBL and BLE, there was no change in plateau incidence. However, significant differences were observed for both $\dot{V}{\text{O}}$ _2max (P = 0.0059) 51.3 ± 7.6 (UBL) 48.4 ± 7.9 ml kg^?1 min^?1 (BLE) and gas exchange threshold arrival time 383.4 ± 85.2 s (UBL) 349.2 ± 71.4 s (BLE) (P = 0.0028).

Conclusion

These data suggest that plateau at $\dot{V}{\text{O}}$ _2max is unaffected by O₂ availability lending support to the notion of the plateau being dependent on the anaerobic capacity and the classically orientated concept of $\dot{V}{\text{O}}$ _2max.     

Exercise volume and intensity: a dose–response relationship with health benefits

Introduction

The health benefits of exercise are well established. However, the relationship between exercise volume and intensity and health benefits remains unclear, particularly the benefits of low-volume and intensity exercise.

Purpose

The primary purpose of this investigation was, therefore, to examine the dose–response relationship between exercise volume and intensity with derived health benefits including volumes and intensity of activity well below international recommendations.

Methods

Generally healthy, active participants (n = 72; age = 44 ± 13 years) were assigned randomly to control (n = 10) or one of five 13-week exercise programs: (1) 10-min brisk walking 1×/week (n = 10), (2) 10-min brisk walking 3×/week (n = 10), (3) 30-min brisk walking 3×/week (n = 18), (4) 60-min brisk walking 3×/week (n = 10), and (5) 30-min running 3×/week (n = 14), in addition to their regular physical activity. Health measures evaluated pre- and post-training including blood pressure, body composition, fasting lipids and glucose, and maximal aerobic power (VO₂max).

Results

Health improvements were observed among programs at least 30 min in duration, including body composition and VO₂max: 30-min walking 28.8–34.5 mL kg^?1 min^?1, 60-min walking 25.1–28.9 mL kg^?1 min^?1, and 30-min running 32.4–36.4 mL kg^?1 min^?1. The greater intensity running program also demonstrated improvements in triglycerides.

Conclusion

In healthy active individuals, a physical activity program of at least 30 min in duration for three sessions/per week is associated with consistent improvements in health status.     

Shoulder bony landmarks location using the EOS® low-dose stereoradiography system: a reproducibility study

Purpose

To investigate the reproducibility of shoulder bony landmarks location using the EOS^® low-dose stereoradiography system, in order to validate this new tool for the study of gleno-humeral pseudo-kinematics.

Methods

An inter and intraobserver reproducibility study of shoulder bony landmarks location concerning 22 healthy volunteers. This study concerned the neutral position, arm at rest. Humerus and scapula were modeled with simple geometric shapes using specific software. Those shapes were positioned on A-P and lateral x-rays views. Images analysis of the 22 subjects was carried out three times (n _r = 3), by two observers (n _o = 2), for a total of n _tot = 132 analyses.

Results

We obtained a very good reproducibility for the humeral head center and the diaphysis axis with 95% confidence interval (IC95%) inferior to 1.09 mm and 0.41°, respectively. The uncertainty was higher for the lateral and medial epicondyles. Regarding the scapular bony landmarks, we observed a good reproducibility for the tip of the coracoid process, the inferior glenoid rim, and the axillar border with a 95% confidence interval lower than 2.13, 2.91 mm, and 3.67°, respectively. The uncertainty was higher for the most postero-lateral point of the acromion and the superior glenoid rim.

Conclusion

Our analysis of the x-rays obtained with the EOS^® low-dose stereoradiography system assessed the location reliability and reproducibility of specific scapular and humeral bony landmarks. This work opens the way to gleno-humeral pseudo-kinematics analysis using EOS^® imaging system.     

Vitamin D supplementation does not improve human skeletal muscle contractile properties in insufficient young males

Purpose

Vitamin D may be a regulator of skeletal muscle function, although human trials investigating this hypothesis are limited to predominantly elderly populations. We aimed to assess the effect of oral vitamin D₃ in healthy young males upon skeletal muscle function.

Methods

Participants (n = 29) received an oral dose of 10,000 IU day^?1 vitamin D₃ (VITD) or a visually identical placebo (PLB) for 3 months. Serum 25[OH]D and intact parathyroid hormone (iPTH) were measured at baseline and at week 4, 8 and 12. Muscle function was assessed in n = 22 participants by isokinetic dynamometry and percutaneous isometric electromyostimulation at baseline and at week 6 and 12.

Results

Baseline mean total serum 25[OH]D was 40 ± 17 and 41 ± 20 nmol L^?1 for PLB and VITD, respectively. VITD showed a significant improvement in total 25[OH]D at week 4 (150 ± 31 nmol L^?1) that remained elevated throughout the trial (P < 0.005). Contrastingly, PLB showed a significant decrease in 25[OH]D at week 12 (25 ± 15 nmol L^?1) compared with baseline. Despite marked increases in total serum 25[OH]D in VITD and a decrease in PLB, there were no significant changes in any of the muscle function outcome measures at week 6 or 12 for either group (P > 0.05).

Conclusions

Elevating total serum 25[OH]D to concentrations > 120 nmol L^?1 has no effect on skeletal muscle function. We postulate that skeletal muscle function is only perturbed in conditions of severe deficiency (<12.5 nmol L^?1).     

Reactive oxygen and nitrogen species in sepsis-induced hepatic microvascular dysfunction

Objective and design

Hepatic microvascular dysfunction is a critical event in the development of liver failure during sepsis. Activated blood cells and reactive oxygen and nitrogen species (RONS) have been implicated in the pathogenesis of sepsis.

Methods

Intravital-videomicroscopy was used to determine whether RONS contribute to the recruitment of leukocytes/platelets in the hepatic microvasculature during sepsis. Six hours following cecal-ligation and puncture (CLP), disturbances of the hepatic microvasculature were assessed in WT-mice (C57Bl/6 J; n = 8), in mice lacking gp91^phox(n = 5), overexpressing superoxide-dismutase (SOD, n = 8), in WT-mice treated with a NOS-inhibitor (l-NAME, n = 5), lacking nNOS, eNOS or iNOS (n = 5 each), treated with the NO-donor DetaNO (n = 5), in WT-mice treated with gadolinium-chloride (GdCl₂, n = 5) and compared to a group of WT-mice following a sham operation (n = 8). Six hours post-CLP, the adhesion of leukocytes and platelets in terminal hepatic venules (THV) and sinusoids was quantified.

Results

In WT-mice, CLP elicited increases in the number of adherent leukocytes and platelets. Similar responses to CLP were noted in mice overexpressing SOD or lacking either eNOS or gp91^phox. The blood-cell recruitment was significantly blunted in septic iNOS-knockout mice and this response was reversed by pre-treatment with DetaNO.

Conclusion

These findings suggest that iNOS-derived NO is a determinant of the pro-inflammatory phenotype assumed by the hepatic microvasculature during sepsis.