Thermal sensitivity to warmth during rest and exercise: a sex comparison

Purpose

The study aimed to compare thermal sensation in response to a fixed warm stimulus across 31 body locations in resting and active males and females.

Methods

Twelve males (20.6 ± 1.0 years, 78.1 ± 15.6 kg, 180 ± 8.9 cm, 34.4 ± 5.2 ml kg^?1 min^?1) and 12 females (20.6 ± 1.4 years, 62.9 ± 5.5 kg, 167 ± 5.7 cm, 36.5 ± 6.6 ml kg^?1 min^?1) rested in a thermoneutral (22.2 ± 2.2 °C, 35.1 ± 5.8 % RH) room whilst a thermal probe (25 cm²), set at 40 °C was applied in a balanced order to 31 locations across the body. Participants reported their thermal sensation 10 s after initial application. Following this, participants began cycling at 50 % \(\dot{V}{\text{O}}_{{ 2 {\text{max}}}}\) for 20 min, which was then lowered to 30 % \(\dot{V}{\text{O}}_{{ 2 {\text{max}}}}\) and the sensitivity test repeated.

Results

Females had significantly warmer magnitude sensations than males at all locations (4.7 ± 1.8 vs 3.6 ± 2.2, p < 0.05, respectively). Regional differences in thermal sensation were evident but were more prominent for females. Thermal sensation was greatest at the head then the torso and declined towards the extremities. In comparison to rest, exercise caused a significant reduction in thermal sensation for males (?thermal sensation; 0.86 ± 0.3, p < 0.05), but only at select locations in females (0.31 ± 0.56, p > 0.05).

Conclusion

The data provide evidence that the thermal sensation response to warmth varies between genders and between body regions and reduces during exercise. These findings have important implications for clothing design and thermophysiological modelling.     

The effect of ethnicity on the vascular responses to cold exposure of the extremities

Purpose

Cold injuries are more prevalent in individuals of African descent (AFD). Therefore, we investigated the effect of extremity cooling on skin blood flow (SkBF) and temperature (T _sk) between ethnic groups.

Methods

Thirty males [10 Caucasian (CAU), 10 Asian (ASN), 10 AFD] undertook three tests in 30 °C air whilst digit T _sk and SkBF were measured: (i) vasomotor threshold (VT) test—arm immersed in 35 °C water progressively cooled to 10 °C and rewarmed to 35 °C to identify vasoconstriction and vasodilatation; (ii) cold-induced vasodilatation (CIVD) test—hand immersed in 8 °C water for 30 min followed by spontaneous warming; (iii) cold sensitivity (CS) test—foot immersed in 15 °C water for 2 min followed by spontaneous warming. Cold sensory thresholds of the forearm and finger were also assessed.

Results

In the VT test, vasoconstriction and vasodilatation occurred at a warmer finger T _sk in AFD during cooling [21.2 (4.4) vs. 17.0 (3.1) °C, P = 0.034] and warming [22.0 (7.9) vs. 12.1 (4.1) °C, P = 0.002] compared with CAU. In the CIVD test, average SkBF during immersion was greater in CAU [42 (24) %] than ASN [25 (8) %, P = 0.036] and AFD [24 (13) %, P = 0.023]. Following immersion, SkBF was higher and rewarming faster in CAU [3.2 (0.4) °C min^?1] compared with AFD [2.5 (0.7) °C min^?1, P = 0.037], but neither group differed from ASN [3.0 (0.6) °C min^?1]. Responses to the CS test and cold sensory thresholds were similar between groups.

Conclusion

AFD experienced a more intense protracted finger vasoconstriction than CAU during hand immersion, whilst ASN experienced an intermediate response. This greater sensitivity to cold may explain why AFD are more susceptible to cold injuries.     

Differences in conductive foot cooling: a comparison between males and females

Purpose

This study investigated possible sex-related and intra-menstrual differences in local vascular and skin temperature responses when conductive cooling was applied to the soles of the feet.

Method

Twelve females and twelve males exposed the soles of their feet to a cooling plate (which cooled from 35 to 15 °C) on two occasions 12–15 days apart. For females, sessions took place during their inactive and active contraceptive pill phases. Tip of Great toe temperature and Great toe skin blood flow were recorded throughout.

Results

Females’ feet cooled to a greater extent than males’ (P = 0.001). Sensitivity of toe skin blood flow to changes in skin temperature (1 or 2 °C) was not different between males and females. Dimensions of males’ feet were larger than females’ (P < 0.05) and correlations between foot dimensions and toe skin cooling were found (r = 0.728, P < 0.001). Analysis of the residual variance showed that foot volume, contact area and skin blood flow correlated with the rate of toe skin cooling (r = 0.812, r ² = 0.659, P < 0.001). No intra-menstrual differences were found.

Conclusion

The feet of females cooled at a faster rate than those of males in response to the same conductive cooling stimulus to the soles of the feet. However, similar reductions in skin blood flow were found for the same change in toe skin temperature. Therefore, sex related differences may be due to the differing dimensions of the feet, but further research including males and females matched for foot dimensions are required to confirm this mechanism.     

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.     

Acute hyperglycaemia does not alter nitric oxide-mediated microvascular function in the skin of adolescents with type 1 diabetes

Purpose

We assessed the impact of an acute bout of hyperglycaemia on nitric oxide (NO)-mediated microvascular function in the skin of adolescents with type 1 diabetes (T1DM).

Methods

Twelve subjects (12–18 years) with T1DM were randomised into a control (n = 6) or hyperglycaemia (n = 6) group. Hyperinsulinaemic clamps were used to manipulate blood glucose level (BGL). Following a baseline period, where all subjects were euglycaemic (20 min), the experimental phase began. During the experimental phase, BGL was elevated to 16.7 ± 0.9 mmol L^?1 in the hyperglyceamic group, while it was maintained at euglycaemia (5.5 ± 0.1 mmol L^?1) in the control group. Simultaneously, cutaneous microvascular function (% max cutaneous vascular conductance, CVC%) was assessed using laser Doppler fluxometry following stimulation of skin blood flow using localised heating (42 °C). To determine the NO contribution to skin blood flow, two microdialysis sites were assessed, one perfused with Ringers and the other with the NO blocker, NG-monomethyl-l-arginine (l-NMMA).

Results

In the hyperglycaemic group, acute increase in BGL was not associated with changes in skin blood flow (CVC% 82.4 ± 8.7 % at 5.5 ± 0.1 mmol L^?1 vs 79.5 ± 9.1 % at 16.7 ± 0.9 mmol L^?1, unpaired t tests, P = 0.588) or the contribution of NO to vasodilation.

Conclusions

These results suggest that, in our group of adolescents with type 1 diabetes, acute hyperglycaemia did not affect skin microvascular NO-mediated function.     

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.     

Central and peripheral anti-inflammatory effects of maprotiline on carrageenan-induced paw edema in rats

Objective

To explore the site of action of maprotiline, as an atypical antidepressant, on carrageenan-induced paw edema.

Subjects

Male Wistar rats were used.

Methods

Firstly, the anti-inflammatory effect of systemic maprotiline (12.5, 25 and 50 mg kg^?1) was assessed using a paw edema model. Secondly, different doses of maprotiline were administrated intracerebroventricularly, intrathecally and locally before carrageenan challenge. Finally, we tried to reverse the anti-inflammatory effect of maprotiline by propranolol (10 mg kg^?1), prazosin (4 mg kg^?1), yohimbine (10 mg kg^?1), naloxone (4 mg kg^?1) and mifepristone (5 mg kg^?1).

Results

Systemic, intracerebroventricular and subplantar application of maprotiline significantly inhibited peripheral edema, but intrathecal maprotiline did not alter the degree of paw swelling. The applied antagonists failed to change the anti-inflammatory activity of maprotiline.

Conclusion

These results demonstrate that maprotiline has a potent anti-inflammatory effect and this effect is linked to the peripheral and supraspinal actions of the drug.     

Thermal perceptions and skin temperatures during continuous and intermittent ventilation of the torso throughout and after exercise in the heat

Objective

This study tested the hypothesis that intermittent cooling in air-perfused vests (APV) will not only maintain thermal balance but, due to cyclical activations of cutaneous thermoreceptors, also enhance thermal perceptions.

Method

Ten physically active males completed four conditions where they exercised (walking: 5 km h^?1, 2 % gradient) in a hot environment (~34.0 °C, 50 % RH) for 72 min, followed by a 33-min period of rest. They wore an APV throughout. The four conditions differed in respect to the profile of ambient air that was perfused through the APV: continuous perfusion (CP); intermittent perfusion of 6 min ON/OFF periods (IP_onoff); a steady increase and decrease in flow rate in equal increments (IP_ramp); and an initial step-increase in the flow rate followed by an incremental decrease to zero flow rate (IP_triang). Whole body and torso thermal comfort (TC, TTC), whole body and torso temperature sensation (TS, TTS), whole body and torso skin temperature ( $\bar{T}_{\text{sk}}$ , $\bar{T}_{\text{sktorso}}$ ), local relative humidity ( $\overline{RH}_{\text{torso}}$ ) and rectal temperature (T _re) were measured.

Results

There were no significant differences in T _re, absolute whole body and local $\bar{T}_{\text{sk}}$ , TC, TTC and TS between the cooling profiles. However, TTS was cooler in CP and IP_ramp than IP_onoff and IP_triang. Even though intermittent cooling did not significantly enhance thermal perceptions in CP, a trend existed for TC (P = 0.063) to become less favourable over time.

Conclusion

To reduce the power consumption and extend the battery life of an APV, it is recommended that an intermittent cooling profile should be adopted.     

Hands and feet: physiological insulators,radiators and evaporators

The purpose of this review is to describe the unique anatomical and physiological features of the hands and feet that support heat conservation and dissipation, and in so doing, highlight the importance of these appendages in human thermoregulation. For instance, the surface area to mass ratio of each hand is 4–5 times greater than that of the body, whilst for each foot, it is ~3 times larger. This characteristic is supported by vascular responses that permit a theoretical maximal mass flow of thermal energy of 6.0 W (136 W m²) to each hand for a 1 °C thermal gradient. For each foot, this is 8.5 W (119 W m²). In an air temperature of 27 °C, the hands and feet of resting individuals can each dissipate 150–220 W m² (male–female) of heat through radiation and convection. During hypothermia, the extremities are physiologically isolated, restricting heat flow to <0.1 W. When the core temperature increases ~0.5 °C above thermoneutral (rest), each hand and foot can sweat at 22–33 mL h^?1, with complete evaporation dissipating 15–22 W (respectively). During heated exercise, sweat flows increase (one hand: 99 mL h^?1; one foot: 68 mL h^?1), with evaporative heat losses of 67–46 W (respectively). It is concluded that these attributes allow the hands and feet to behave as excellent radiators, insulators and evaporators.     

Enhancing performance during inclined loaded walking with a powered ankle–foot exoskeleton

Purpose

A simple ankle–foot exoskeleton that assists plantarflexion during push-off can reduce the metabolic power during walking. This suggests that walking performance during a maximal incremental exercise could be improved with an exoskeleton if the exoskeleton is still efficient during maximal exercise intensities. Therefore, we quantified the walking performance during a maximal incremental exercise test with a powered and unpowered exoskeleton: uphill walking with progressively higher weights.

Methods

Nine female subjects performed two incremental exercise tests with an exoskeleton: 1 day with (powered condition) and another day without (unpowered condition) plantarflexion assistance. Subjects walked on an inclined treadmill (15 %) at 5 km h^?1 and 5 % of body weight was added every 3 min until exhaustion.

Results

At volitional termination no significant differences were found between the powered and unpowered condition for blood lactate concentration (respectively, 7.93 ± 2.49; 8.14 ± 2.24 mmol L^?1), heart rate (respectively, 190.00 ± 6.50; 191.78 ± 6.50 bpm), Borg score (respectively, 18.57 ± 0.79; 18.93 ± 0.73) and \(\dot{V}{\rm O}_{2}\) peak (respectively, 40.55 ± 2.78; 40.55 ± 3.05 ml min^?1 kg^?1). Thus, subjects were able to reach the same (near) maximal effort in both conditions. However, subjects continued the exercise test longer in the powered condition and carried 7.07 ± 3.34 kg more weight because of the assistance of the exoskeleton.

Conclusion

Our results show that plantarflexion assistance during push-off can increase walking performance during a maximal exercise test as subjects were able to carry more weight. This emphasizes the importance of acting on the ankle joint in assistive devices and the potential of simple ankle–foot exoskeletons for reducing metabolic power and increasing weight carrying capability, even during maximal intensities.     

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.     

Urinary trypsin inhibitor suppresses excessive generation of superoxide anion radical, systemic inflammation, oxidative stress, and endothelial injury in endotoxemic rats

Objective and design

The protective effects of ulinastatin, a human urinary trypsin inhibitor (UTI), against superoxide radical (O ₂ ^?· ) generation, systemic inflammation, lipid peroxidation, and endothelial injury were investigated in endotoxemic rats.

Materials and treatment

Twenty-one Wistar rats were allocated to a control group, a UTI group, and a sham group. A bolus of lipopolysaccharide (LPS; 3 μg/g) was administered intravenously to the control group, a bolus of LPS and UTI (5 U/g) to the UTI group, and a bolus of saline to the sham group.

Methods

The O ₂ ^?· generated was measured as the current in the right atrium using an electrochemical O ₂ ^?· sensor. Plasma nitrite, high mobility group box 1 (HMGB1), tumor necrosis factor (TNF)-α, inteleukin (IL)-6, malondialdehyde, and soluble intercellular adhesion molecule-1 (sICAM-1) were measured 360 min after LPS administration.

Results

The O ₂ ^?· current increased in the control group and was significantly attenuated in the UTI group after 55 min (P < 0.05 at 55–60 min, P < 0.01 at 65–360 min). Plasma nitrite, HMGB1, TNF-α, IL-6, malondialdehyde, and sICAM-1 were attenuated in the UTI group.

Conclusions

UTI suppressed excessive O ₂ ^?· generation, systemic inflammation, lipid peroxidation, and endothelial injury in endotoxemic rats.     

Self-selected speeds and metabolic cost of longboard skateboarding

Purpose

The purpose of this study was to determine self-selected speeds, metabolic rate, and gross metabolic cost during longboard skateboarding.

Methods

We measured overground speed and metabolic rate while 15 experienced longboarders traveled at their self-selected slow, typical and fast speeds.

Results

Mean longboarding speeds were 3.7, 4.5 and 5.1 m s^?1, during slow, typical and fast trials, respectively. Mean rates of oxygen consumption were 24.1, 29.1 and 37.2 ml kg^?1 min^?1 and mean rates of energy expenditure were 33.5, 41.8 and 52.7 kJ min^?1 at the slow, typical and fast speeds, respectively. At typical speeds, average intensity was ~8.5 METs. There was a significant positive relationship between oxygen consumption and energy expenditure versus speed (R ² = 0.69 (P < 0.001), and R ² = 0.78 (P < 0.001), respectively). The gross metabolic cost was ~2.2 J kg^?1 m^?1 at the typical speed, greater than that reported for cycling and ~50 % smaller than that of walking.

Conclusion

These results suggest that longboarding is a novel form of physical activity that elicits vigorous intensity, yet is economical compared to walking.     

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.     

Short-term high-intensity interval and continuous moderate-intensity training improve maximal aerobic power and diastolic filling during exercise

Purpose

This study examined the effects of short-term high-intensity interval training (HIT) and continuous moderate-intensity training (CMT) on cardiac function in young, healthy men.

Methods

Sixteen previously untrained men (mean age of 25.1 ± 4.1 years) were randomly assigned to HIT and CMT (n = 8 each) and assessed before and after six sessions over a 12-day training period. HIT consisted of 8–12 intervals of cycling for 60 s at 95–100 % of pre-training maximal aerobic power ( $\dot{V}$ O_2max), interspersed by 75 s of cycling at 10 % $\dot{V}$ O_2max. CMT involved 90–120 min of cycling at 65 % pre-training $\dot{V}$ O_2max. Left ventricular (LV) function was determined at rest and during submaximal exercise (heart rate ~105 bpm) using two-dimensional and Doppler echocardiography.

Results

Training resulted in increased calculated plasma volume (PV) in both groups, accompanied by improved $\dot{V}$ O_2max in HIT (HIT: from 39.5 ± 7.1 to 43.9 ± 5.5 mL kg^?1 min^?1; CMT: from 39.9 ± 5.9 to 41.7 ± 5.3 mL kg^?1 min^?1; P < 0.001). Resting LV function was not altered. However, increased exercise stroke volume (P = 0.02) and cardiac output (P = 0.02) were observed, secondary to increases in end-diastolic volume (P < 0.001). Numerous Doppler and speckle tracking indices of diastolic function were similarly enhanced during exercise in both training groups and were related to changes in PV.

Conclusion

Short-term HIT and CMT elicit rapid improvements in $\dot{V}$ O_2max and LV filling without global changes in cardiac performance at rest.     

Interdependence of torque,joint angle,angular velocity and muscle action during human multi-joint leg extension

Purpose

Force and torque production of human muscles depends upon their lengths and contraction velocity. However, these factors are widely assumed to be independent of each other and the few studies that dealt with interactions of torque, angle and angular velocity are based on isolated single-joint movements. Thus, the purpose of this study was to determine force/torque–angle and force/torque–angular velocity properties for multi-joint leg extensions.

Methods

Human leg extension was investigated (n = 18) on a motor-driven leg press dynamometer while measuring external reaction forces at the feet. Extensor torque in the knee joint was calculated using inverse dynamics. Isometric contractions were performed at eight joint angle configurations of the lower limb corresponding to increments of 10° at the knee from 30 to 100° of knee flexion. Concentric and eccentric contractions were performed over the same range of motion at mean angular velocities of the knee from 30 to 240° s^?1.

Results

For contractions of increasing velocity, optimum knee angle shifted from 52 ± 7 to 64 ± 4° knee flexion. Furthermore, the curvature of the concentric force/torque–angular velocity relations varied with joint angles and maximum angular velocities increased from 866 ± 79 to 1,238 ± 132° s^?1 for 90–50° knee flexion. Normalised eccentric forces/torques ranged from 0.85 ± 0.12 to 1.32 ± 0.16 of their isometric reference, only showing significant increases above isometric and an effect of angular velocity for joint angles greater than optimum knee angle.

Conclusions

The findings reveal that force/torque production during multi-joint leg extension depends on the combined effects of angle and angular velocity. This finding should be accounted for in modelling and optimisation of human movement.     

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.     

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.     

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.     

The effect of arm training on thermoregulatory responses and calf volume during upper body exercise

Purpose

The smaller muscle mass of the upper body compared to the lower body may elicit a smaller thermoregulatory stimulus during exercise and thus produce novel training-induced thermoregulatory adaptations. Therefore, the principal aim of the study was to examine the effect of arm training on thermoregulatory responses during submaximal exercise.

Methods

Thirteen healthy male participants (Mean ± SD age 27.8 ± 5.0 years, body mass 74.8 ± 9.5 kg) took part in 8 weeks of arm crank ergometry training. Thermoregulatory and calf blood flow responses were measured during 30 min of arm cranking at 60 % peak power (W _peak) pre-, and post-training and post-training at the same absolute intensity as pre-training. Core temperature and skin temperatures were measured, along with heat flow at the calf, thigh, upper arm and chest. Calf blood flow using venous occlusion plethysmography was performed pre- and post-exercise and calf volume was determined during exercise.

Results

The upper body training reduced aural temperature (0.1 ± 0.3 °C) and heat storage (0.3 ± 0.2 J g^?1) at a given power output as a result of increased whole body sweating and heat flow. Arm crank training produced a smaller change in calf volume post-training at the same absolute exercise intensity (?1.2 ± 0.8 % compared to ?2.2 ± 0.9 % pre-training; P < 0.05) suggesting reduced leg vasoconstriction.

Conclusion

Training improved the main markers of aerobic fitness. However, the results of this study suggest arm crank training additionally elicits physiological responses specific to the lower body which may aid thermoregulation.