Fall in skin temperature during exercise

During light work using the arm in a warm environment, skin temperatures of the arms and chest fell and remained at lower levels during work. The fall in skin temperature during work was not observed in a cool environment. The fall in skin temperature was nearly proportional to work intensity and was observed in both static and dynamic work. Leg work of moderate intensity produced an initial decline and a subsequent rise in skin temperatures of the hands, thighs and legs. A significant fall in skin temperature was observed not only in the foot but also in inactive regions such as the epigastrium. The mean skin temperature remained practically unchanged during work. The fall in skin temperature during work was not due to increased evaporative cooling, but was the result of segmental vasoconstriction probably caused as a reflex in the spinal cord by non-thermal afferents from exercising muscles or moving tissues. The effect of thermoregulatory vasodilation was reduced by the reflex vasoconstriction caused by non-thermal factors. The rise in internal temperature during work could be explained by decreased heat loss due to persistently lower skin temperature.     

A comparison of the effects of mixed static and dynamic work with mainly dynamic work in hot conditions

Summary Current physiological criteria for limiting work in hot conditions are frequently based on responses to mainly dynamic work (eg treadmill walking). Their applicability to industrial situations containing mixed static and dynamic work is questioned, since the physiological responses to static work are different from those of dynamic work. Each of eight subjects attempted a one hour uphill treadmill walk (mainly dynamic work), and an uphill treadmill walk whilst intermittently carrying a 20 kg weight in the arms (mixed static and dynamic work). The external work rates in the two conditions were equal, effected by lowering the treadmill gradient in the loaded condition. Experiments were conducted in a hot climate (33‡ C dry bulb, 25‡ C wet bulb). Oxygen consumption, minute ventilation, sweat rate and rated perceived exertion were all significantly higher (p<0.001) for the mixed static and dynamic work than for the dynamic work. This was also the case for heart rate and forearm skin temperature (p<0.01), and for auditory canal temperature (p<0.05). There was no significant difference between the two types of work for mean skin temperature, calf skin temperature and chest skin temperature. These results show that for the same external work, physiological strain and perceived exertion are greater for mixed static and dynamic work (carrying a load in the arms) than for mainly dynamic work (walking on a treadmill). They suggest that it is not appropriate to make direct comparisons of laboratory studies based on dynamic work, with practical situations containing mixed static and dynamic work in the heat.     

Thermoregulation during Static Work with the Legs

Sustained static work with the legs, i.e., holding a weight of about 10% of maximal isometric strength for 25 min was compared to dynamic exercise on a bicycle ergometer causing the same rate of heat production. In the static work the subjective feeling of exertion was very high and the effort maximal. The pronounced increase in heart rate and blood pressure and a typical flush of the face and chest (flush areas) indicated a high sympathetic tonus. Plasma catecholamine levels were 1.3 times higher (significant at the P ≤ 0.05 level) after static work than after dynamic work. Although the sustained static work was nearly maximal, the rate of increase in sweating and the change in core temperature during work were not different from the responses to dynamic work.     

Thermoregulation during static work with the legs.

Sustained static work with the legs, i.e., holding a weight of about 10% of maximal isometric strength for 25 min was compared to dynamic exercise on a bicycle ergometer causing the same rate of heat production. In the static work the subjective feeling of exertion was very high and the effort maximal. The pronounced increase in heart rate and blood pressure and a typical flush of the face and chest (flush areas) indicated a high sympathetic tonus. Plasma catecholamine levels were 1.3 times higher (significant at the Pless than or equal to 0.05 level) after static work than after dynamic work. Although the sustained static work was nearly maximal, the rate of increase in sweating and the change in core temperature during work were not different from the responses to dynamic work.     

Effects of training on maximal working capacity and haemodynamic response during arm and leg-exercise in a group of paddlers

Maximal oxygen uptake and circulatory adaptation to work with legs and arms were studied in a group of 5 paddlers members of the Belgian national squad and a control-group of 9 trained subjects. The results showed that the specific armtraining of paddlers induced changes in the arm-to-leg ratio of physiological parameters at submaximal and maximal work. In the group of paddlers maximal oxygen intake and workload during arm-exercise averaged respectively 88.6% and 80.3% of the scores obtained with leg-exercise. In the control group the arm to leg ratio varied between 81.2% and 65.2%. At a submaximal load of 100 W the difference in heartfrequency was 21 beats/min in the canoë group and 35 beats/min in the control group. Oxygen consumption and ventilation during work with the arms was lower in the group of paddlers. The data of our study suggest that the specific training of paddlers do result in a effect on the haemodynamic adaptations to arm work     

Neural coupling between the arms and legs during rhythmic locomotor-like cycling movement

Neuronal coupling between the arms and legs allowing coordinated rhythmic movement during locomotion is poorly understood. We used the modulation of cutaneous reflexes to probe this neuronal coupling between the arms and legs using a cycling paradigm. Participants performed rhythmic cycling with arms, legs, or arms and legs together. We hypothesized that any contributions from the arms would be functionally linked to locomotion and would thus be phase-dependent. Reflexes were evoked by electrical stimulation of the superficial peroneal nerve at the ankle, and electromyography (EMG) was recorded from muscles in the arms and legs. The main finding was that the relative contribution from the arms and legs was linked to the functional state of the legs. For example, in tibialis anterior, the largest contribution from arm movement [57% variance accounted for (VAF), P < 0.05] was during the leg power phase, whereas the largest from leg movement (71% VAF, P < 0.05) was during leg cycling recovery. Thus the contribution from the arms was functionally gated throughout the locomotor cycle in a manner that appears to support the action of the legs. Additionally, the effect of arm cycling on reflexes in leg muscles when the legs were not moving was relatively minor; full expression of the effect of rhythmic arm movement was only observed when both the arms and legs were moving. Our findings provide experimental support for the interaction of rhythmic arm and leg movement during human locomotion.     

Blood flow changes in the duck during thermal panting

Carotid and sciatic blood flow have been measured in resting and panting Pekin ducks using electromagnetic flowmeters. Panting induced by high ambient temperature caused the carotid blood flow to increase from 9.6 to 26.0 ml min^-1, while the sciatic flow declined slightly from 41.6 to 38.1 ml min^-1. During panting breathing rate increased 10–20 times, but there were no significant changes in heart rate and mean arterial blood pressure. The carotid peripheral resistance was therefore greatly reduced, whereas sciatic resistance remained unchanged or increased slightly. The vascular beds perfused by the sciatic (legs) and carotid (upper respiratory tract) arteries are both important for heat dissipation. This study shows that when heat dissipation from the naked legs becomes inefficient due to high ambient temperature, blood flow in the sciatic tended to decline while conversely panting was associated with a large increase in carotid flow.     

Effect of rhythmic arm movement on reflexes in the legs: modulation of soleus H-reflexes and somatosensory conditioning

During locomotor tasks such as walking, running, and swimming, the arms move rhythmically with the legs. It has been suggested that connections between the cervical and lumbosacral spinal cord may mediate some of this interlimb coordination. However, it is unclear how these interlimb pathways modulate reflex excitability during movement. We hypothesized that rhythmic arm movement would alter the gain of reflex pathways in the stationary leg. Soleus H-reflexes recorded during arm cycling were compared with those recorded at similar positions with the arms stationary. Nerve stimulation was delivered with the right arm at approximately 70 degrees shoulder flexion or 10 degrees shoulder extension. H-reflexes were evoked alone (unconditioned) or with sural or common peroneal nerve (CP) conditioning to decrease or increase soleus IA presynaptic inhibition, respectively. Both conditioning stimuli were also delivered with no H-reflex stimulation. H-reflex amplitudes were compared at similar M-wave amplitudes and activation levels of the soleus. Arm cycling significantly reduced (P < 0.05) unconditioned soleus H-reflexes at shoulder flexion by 21.7% and at shoulder extension by 8.8% compared with static controls. The results demonstrate a task-dependent modulation of soleus H-reflexes between arm cycling and stationary trials. Sural nerve stimulation facilitated H-reflexes at shoulder extension but not at shoulder flexion during static and cycling trials. CP nerve stimulation significantly reduced H-reflex amplitude in all conditions. Reflexes in soleus when sural and CP nerve stimulation were delivered alone, were not different between cycling and static trials; thus the task-dependent change in H reflex amplitude was not due to changes in motoneuron excitability. Therefore modulation occurred at a pre-motoneuronal level, probably by presynaptic inhibition of the IA afferent volley. Results indicate that neural networks coupling the cervical and lumbosacral spinal cord in humans are activated during rhythmic arm movement. It is proposed that activation of these networks may assist in reflex linkages between the arms and legs during locomotor tasks.     

Effects of skin temperature on cold defense after cutaneous denervation of the trunk

In intact goats the core temperature threshold below which heat production increases with falling core temperature, is inversely related to the temperature of the water bath in which they stand and is therefore assumed to be indicative of the central integration of signals from skin and core temperature receptors. The present study shows that a difference in core temperature thresholds for bath temperatures of 35°C and 40°C persisted after denervation of about two-thirds of the skin of the trunk and limbs. Also, for a given combination of skin and core temperatures, heat production was as great or greater after cutaneous denervation as before. It is concluded that, following denervation of the trunk and upper limbs, intact temperature receptors in the non-denervated skin of the legs and tail, and/or also in tissues between the skin and core, provide important and significant inputs to the temperature regulating system. But these inputs cannot explain fully the thermoregulatory responses observed unless it is assumed that the thermosensitivity of these tissues increased.     

A bicycle ergometer for investigating the effect of eccentric exercise with arms and legs

Summary An induction clutch is combined with aKrogh's bicycle ergometer. In this way it is possible to transmit known work loads from an electromotor to theKrogh ergometer. The work load can be calibrated by the magnetic brake of theKrogh ergometer and when the direction of revolution is reversed it is possible for the subject to brake the ergometer by either the arms or the legs. It is concluded that the device may be useful in investigating the eccentric dynamic work with arms and legs.     

Studies on the Mechanism of Shock: The Effect of Cocaine and Theophylline on the Temperature Response to Injury in the Cold-Acclimated Rat

The effects of cocaine and theophylline on the changes in core temperature, O₂ consumption and the rate of heat loss from the tail were studied in 20° and 3° acclimated rats during and after a 4-hr. period of bilateral hindlimb ischaemia at an environmental temperature of 20°.Cocaine (7 mg. base per kg. body wt. intravenously) had no effect on injured 20° acclimated rats but increased the core temperature in both injured and uninjured 3° acclimated ones. The changes in O₂ consumption were unaffected and heat loss from the tail decreased. Cocaine acted mainly by increasing peripheral vasoconstriction and so decreasing heat loss.Theophylline (90 mg. per kg. body wt. intraperitoneally), given 1 hr. before removal of the tourniquets, depressed the core temperature in 20° acclimated rats but increased it in 3° acclimated ones. Theophylline increased heat production in 3° acclimated rats, raising O₂ consumption and causing a maximal increase in heat loss from the tail. Whereas this increased heat loss could prevent a rise in the temperature of the uninjured it was insufficient to do so in the injured.Since previous work has shown that limb ischaemia causes a similar increase in adrenaline and noradrenaline secretion in 20° and 3° acclimated rats these results support the view that the difference between the responses to trauma in these 2 types of rat is due to the greater sensitivity of cold-acclimated rats to catecholamines.     

Thermoregulatory stress during rest and exercise in heat in patients with a spinal cord injury

Summary Twelve subjects with spinal cord injuries and four controls (all male) were exposed to heat while sitting at rest or working at each of three environmental temperatures, 30, 35 and 40°C, with a relative humidity of 50%. Exercise was accomplished at a load of 50 W on a friction-braked cycle ergometer which was armcranked or pedalled. Functional electrical stimulation of the legs was provided to the subjects with quadriplegia and paraplegia to allow them to pedal a cycle ergometer. The data showed that individuals with quadriplegia had the poorest tolerance for heat. As an example, in this group, accomplishing armcrank ergometry while working at an environmental temperature of 40°C resulted in an increase in aural temperature of 2°C in 30 min. The aural temperature of individuals with paraplegia working for the same length of time under the same conditions rose approximately 1°C. There was virtually no change in the aural temperature in the control subjects.     

Effects of local restriction of evaporation and moderate local ventilation on thermoregulatory responses in exercising humans

Ten healthy young men participated in two series of three trials: series 1 (C1) with, or without, local restriction of evaporation (either on the trunk or on the legs) and series 2 (C2) with, or without, local moderate nitrogen ventilation (40 l · min^?1) under an impermeable garment (trunk or leg ventilation). After 60-min rest in a thermoneutral environment, the subjects exercised in a warm environment [30°C, 47% relative humidity (rh) during Cl and 29% rh during C2] on a cycle ergometer for 60 min at 70 W during C1 or at 60 W during C2. During C1, local covering with plastic foil did not increase internal temperature, but increased the mean skin temperature with a higher effect in the case of leg restriction. The trunk skin temperature was affected by the leg covering while the leg skin temperature was not changed by the trunk covering. Only the local sweat rate of the trunk was increased by the two restriction conditions. During C2, internal temperature was decreased by local ventilation while mean skin temperature was reduced only by trunk ventilation. The local ventilation affected only trunk skin temperature with a greater decrease during trunk ventilation. Trunk ventilation did not influence the skin temperature of the legs while ventilation of the legs decreased trunk skin temperature. In addition, leg ventilation decreased the sweat rate of the legs. The impermeable suit worn during C2 led to a greater physiological strain compared to the plastic film worn during C1 even with local ventilation under the impermeable garment. As expected, limiting sweat evaporation led to an increase in physiological strain. Microclimate ventilation at a rate of 40 l · min^?1 was not sufficient to allow total heat dissipation but allowed 60-min exercise in a warm environment to be completed without excessive heat accumulation. It would appear that ventilation of the trunk locally was the best solution because of the smaller increase in skin temperature and higher sweating capacity of the trunk.     

Relationships between skin temperature and perfusion in the arm and leg

Relationships between skin temperature (Tsk) and perfusion have been studied to provide a basis for the use of Tsk in the non-invasive assessment of limb circulation in peripheral vascular disease. Raising the ambient temperature (Ta) from 20 to 30 degrees C increased the perfusion of the glabrous skin of the hands and feet without changing that of the skin of the forearm or calf. On a fractional basis the response in the hand and foot was the same. Tsk was higher in the arms than the legs and in the proximal than distal parts of the limbs. A fall in Tsk was often seen when Ta rose from 20 to 25 degrees C and was attributed to counter-current cooling. Subsequently Tsk rose even in regions where there was no increase in skin perfusion. Tsk can only be related to its perfusion in the fingers, palm and toes. Forearm Tsk was related to the perfusion of the digits. This relationship implies a link with the arterial inflow to the limb which determines the size of its thermal core. Heat conduction from the core seemed important for the skin of areas like the forearm and calf where the constant, low perfusion limited the amount of heat which could be transported to it directly by the blood. The importance of conduction was supported by studies, at Ta 20 degrees C, on subjects during calf muscle exercise and on patients with arterio-venous fistulae. Here an increase in the arterial inflow to the limb was associated with a rise in Tsk of the forearm/calf unrelated to the perfusion of its skin.     

Is brain prostaglandin synthesis involved in responses to cold?

1. Experiments with rats have suggested that prostaglandin synthesis in the C.N.S. may mediate thermoregulatory reactions to cold. This possibility was investigated in cats using two types of experiment. 2. In one series of experiments, c.s.f. collected from the cisterna magna of conscious cats exposed to a cold and a hot environment was assayed for prostaglandin-like activity. During cold exposure there was a slight increase in activity which persisted after return to neutral ambient temperature. There was no correlation between prostaglandin-like activity and rectal temperature. During the heat exposure there was no demonstrable change in activity. 3. In the second series, conscious cats were exposed to cold conditions and given intravenous injections of salicylate, paracetamol, or indomethacin, all of which inhibit prostaglandin synthesis. Indomethacin salicylate nor paracetamol caused any significant change in rectal temperature. 4. The results do not support a role for C.N.S. prostaglandin synthesis in thermoregulatory reactions to cold in cats.     

Slow skeletal muscles of the mouse have greater initial efficiency than fast muscles but the same net efficiency

The aim of this study was to determine whether the net efficiency of mammalian muscles depends on muscle fibre type. Experiments were performed in vitro (35°C) using bundles of muscle fibres from the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles of the mouse. The contraction protocol consisted of 10 brief contractions, with a cyclic length change in each contraction cycle. Work output and heat production were measured and enthalpy output (work + heat) was used as the index of energy expenditure. Initial efficiency was defined as the ratio of work output to enthalpy output during the first 1 s of activity. Net efficiency was defined as the ratio of the total work produced in all the contractions to the total, suprabasal enthalpy produced in response to the contraction series, i.e. net efficiency incorporates both initial and recovery metabolism. Initial efficiency was greater in soleus (30 ± 1%; n = 6) than EDL (23 ± 1%; n = 6) but there was no difference in net efficiency between the two muscles (12.6 ± 0.7% for soleus and 11.7 ± 0.5% for EDL). Therefore, more recovery heat was produced per unit of initial energy expenditure in soleus than EDL. The calculated efficiency of oxidative phosphorylation was lower in soleus than EDL. The difference in recovery metabolism between soleus and EDL is unlikely to be due to effects of changes in intracellular pH on the enthalpy change associated with PCr hydrolysis. It is suggested that the functionally important specialization of slow-twitch muscle is its low rate of energy use rather than high efficiency.     

Heterogeneity of growth of bone in children at the spine, radius and total skeleton.

Bone mineral content (BMC), density (BMD), and size were measured in 202 subjects ranging from 3 to 25 years of age (106 males and 96 females), half of which were children and half young adults. BMC and BMD were measured using single photon absorptiometry at the proximal and distal radius and dual photon absorptiometry at the lumbar spine and the total body. In the pre-pubertal age group (3-9 yrs), no differences were found in BMC nor BMD between males and females at any site. Growth of bone during puberty was characterized by an increase in BMC, bone size and BMD. The percent increase in BMC was greater at the lumbar spine and the total body (+200 to +390 %) than at the radius (+90 to +270 %). The increase in BMC was higher than the increase in BMD (+50 to +90 %). Overall bone growth in the total body was not reflected by changes in BMC of the appendicular skeleton. The increase in BMD was heterogeneous and was higher in the legs than in the arms. In males, the increase in BMC and size during growth was greater than in females resulting in a higher peak bone mass and size in males. The increase in BMD was similar between males and females at the distal radius, the lumbar spine and the total body, but higher at the proximal radius, the arms and the legs in males.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interlimb coupling from the arms to legs is differentially specified for populations of motor units comprising the compound H-reflex during “reduced” human locomotion

Recent experiments have identified neuromechanical interactions between the arms and legs during human locomotor movement. Previous work reported that during the rhythmic movement of all four limbs, the influence of the arms on reflex expression in the legs was superimposed on the dominant effect of the legs. This evidence was based upon studies using cutaneous and H-reflex modulation as indices of neuronal activity related to locomotion. The earlier H-reflex study was restricted to one phase of movement and to only a fixed H-reflex amplitude. Also, all four limbs were actively engaged in locomotor movement, and this led to the speculation that the effect from the arms could be underestimated by “swamping” of the conditioning during movement of the test limb. Work from the cat suggests that descending locomotor drive may be differentially specified for different motor unit populations in the hindlimb. Accordingly, details of interlimb coordination between the arms and legs in humans require further characterization and an examination of different populations of motor units as can be obtained from H-reflex recruitment curve (RC) parameters. Using modulation of H-reflex amplitudes across the entire ascending limb as neural probes for interlimb coupling, the present study evaluated the separated influences of rhythmic activity of the arms and leg on neuronal excitability of a stationary “test leg”. This three-limb “reduced” locomotion approach was applied using a stepping ergometer during the performance of three rhythmic movement tasks: arms (A); contralateral leg (L); and arms and contralateral leg (AL). Data were sampled at four different phases of the stepping cycle (using the moving leg as reference): start power (SP); end power (EP); start recovery (SR); and end recovery (ER). The main result was a large and significant influence of rhythmic AL activity on RC parameters of the H-reflex at EP and SP phases. However, the parameters (and thus motor unit populations) were differentially affected at each phase and task. For instance, a significant contribution of arms movement was noticed for H _max (largest motor units) at EP phase (P < 0.05), but no changes was observed for other parameters related to lower reflex amplitude (e.g., H-reflex evoked with an input that elicited 50% of maximum reflex response during static condition; H@50%). On the other hand, at SR phase, the parameter H@50% was significantly affected during AL compared to L. It is suggested that the remote effect from arms rhythmic activity has been differentially manifested across motor unit populations for each phase of movement. These findings provide definitive evidence for interlimb coupling between cervical and lumbar oscillators in gating the excitability of reflex pathways to a leg muscle for different populations of motorneurons within the pool. This further supports the contention of similar functional organization for locomotor networks in the human when compared to other animals. Additionally, these data provide additional confirmation of the significant role of the output of neural control for rhythmic arm movement in modulating reflex excitability of the legs that is specifically adjusted according to the phase and task.     

A comparison of three bioelectrical impedance analyses for predicting lean body mass in a population with a large difference in muscularity

This study tested the hypothesis that, as compared to whole-body bioelectrical impedance (BI) analysis, segmental BI analysis can estimate lean body mass (LBM) more accurately in a population with a large difference in muscularity. In addition to whole-body BI, which determines impedance (Z) between the wrist and ankle, two segmental BI analyses which determine the Z value of every body segment in each of (1) the arms, legs and trunk (distal BI) and (2) the upper arms, upper legs and trunk (proximal BI) were applied to a group of 125 male athletes and 75 non-athletes. The subjects were divided into validation and cross-validation groups. Simple and multiple regression analyses were applied to (length)²/Z (BI index) values for the whole-body and each body segment, to develop the prediction equations of LBM measured using air-displacement plethysmography. In the validation group, the SE of estimation was similar in the whole-body (3.4 kg, 5.4%), distal (3.4 kg, 5.5%) and proximal BI (3.3 kg, 5.2%) analyses. However, the whole-body and distal BI analyses produced systematical errors in the estimates of LBM. Moreover, the residuals in the two methods significantly (P<0.05) correlated with the ratios of BI indices of the upper arms and upper legs to those of the arms and legs, respectively, calculated as variables approximating the relative development of lean tissues at the proximal area of limbs. On the other hand, the proximal BI analysis was validated and cross-validated. Thus, the accuracy of estimating LBM was similar in the whole-body and the two segmental BI analyses. However, the prediction equations derived from the use of the whole-body BI index and a combination of the arms, legs and trunk BI indices produced a systematical error relating to the difference between the limb segments in lean tissue development.     

Ph-positive chronic myeloid leukemia with loss of the segment distal to M-bcr.

We describe a patient with chronic myeloid leukemia (CML) and a 22q- but no 9q+ chromosome. Southern blot analysis showed a BCR rearrangement. The patient soon developed profound and superficial thrombophlebitis in arms and legs and died from pulmonary embolisation 15 days after diagnosis. Five CML cases with a deletion of 22q but no known translocation of 22q11----qter have been described earlier. The present patient is the first such case, however, in whom a BCR rearrangement has been demonstrated.