Lower body negative pressure enhances oxygen availability in the knee extensor muscles during intense resistive exercise in supine position

Purpose

During exercise in supine posture or under microgravity in space, the gravity-dependent component of local blood pressure in leg muscles at upright posture can be simulated by lower body negative pressure (LBNP). We hypothesized that during resistive exercise LBNP favors oxygen availability in lower extremities, benefiting energy levels and performance of working muscles.

Methods

In permutated crossover design, nine subjects performed a series of fifteen slow-paced concentric (4 s) and eccentric contractions (4 s) without or with 40 mmHg LBNP and 4 s pause between repetitions. The force at knee flexion was 6% of the one repetition maximum (1-RM) and gradually increased to 60% 1RM in the first half of the individual range of motion, subsequently remaining constant until full extension.

Results

During the low force periods of continuous exercise, LBNP enhanced the refill of capillary blood measured by near infrared spectroscopy, amplifying the increase of total haemoglobin by about 20 µmol/l (p < 0.01) and oxyhaemoglobin by about 10 µmol/l (p < 0.01). During continuous exercise, LBNP induced a trend towards a lower EMG increment. This LBNP effect was not found when the periods of low forces at knee flexion were extended by 4 s pauses. Increased respiratory oxygen uptake (+ 0.1 l/min, p < 0.05) indicated overall enhanced muscle energy turn-over.

Conclusions

Our results suggest stimulation of oxidative metabolism through LBNP enables working muscles to meet the energy demands of intense exercise. Further research is needed on the consequences for energy metabolism and the molecular control of growth and differentiation.

     

Postural effect on cardiac output,oxygen uptake and lactate during cycle exercise of varying intensity

Owing to changes in cardiac output, blood volume distribution and the efficacy of the muscle pump, oxygen supply may differ during upright and supine cycle exercise. In the present study we measured, in parallel, circulatory (heart rate, stroke volume, blood pressure) and metabolic parameters (oxygen uptake, lactic acid concentration [1a]) during incremental-exercise tests and at constant power levels ranging from mild to severe exercise. In supine position, cardiac output exceeded the upright values by 1.0-1.5 1 · min^–1 during rest, light ([la] < 2 mmol · 1^–1) and moderate ([la] =2–4 mmol · 1^–1) exercise. At higher exercise intensities the cardiac output in an upright subject approached and eventually slightly exceeded the supine values. For both rest-exercise transitions and large-amplitude steps (W 140 W) the cardiac output kinetics was significantly faster in upright cycling. The metabolic parameters (VO₂ and [la]) showed no simple relationship to the circulatory data. In light to moderate exercise they were unaffected by body position. Only in severe exercise, when cardiac output differences became minimal, could significant influences be observed: with supine body posture, [la] started to rise earlier and maximal power (W=23 W) and exercise duration (64 s) were significantly reduced. However, the maximal [la] value after exercise was identical in both positions. The present findings generally show advantages of upright cycling only for severe exercise. With lower workloads the less effective muscle pump in the supine position appears to be compensated for by the improved central circulatory conditions and local vasodilatation.     

Cardiac responses to lower body negative pressure and dynamic leg exercise

Summary Cardiac responses to dynamic leg exercise at 0, 50, and 100 W in the supine position were investigated with and without the lower portion of the body exposed to a pressure of –6.6 kPa (Lower Body Negative Pressure, LBNP). Resting values for heart rate (HR) and stroke volume (SV) were considerably higher and lower, respectively, during LBNP than in the control condition. At the transition from rest to the mildest exercise during LBNP SV showed a prompt increase by about 40%, but no significant change in the control condition. HR, which increased by 17 beats · min^–1 in the control condition, showed during LBNP no change initially and subsequently a small but significant drop below its resting value. Steady-state values for HR at the various levels of exercise were not significantly affected by LBNP, whereas corresponding values for SV were considerably lowered, so that exercise values for cardiac output were about 3 l · min^–1 less during LBNP than in the control condition. The reductions in SV and cardiac output indicate residual pooling of blood in intra- and extramuscular capacitance vessels of the legs. With a change from rest to exercise at 100 W during LBNP mean systolic ejection rate (MSER) increased by 67%, the relations between SV and MSER suggesting that ventricular performance was maintained by a combination of the Frank-Starling mechanism and enhanced contractile strength.     

Gentle exercise with a previously inactive muscle group hastens the decline of blood lactate concentration after strenuous exercise

Summary The aim of this study was to elucidate the mechanism by which the disappearance of blood lactate following severe exercise is enhanced during active recovery in comparison with recovery at rest. Rates of decline of arterialised venous blood lactate concentrations in man after maximal one-leg exercise were compared during four different modes of recovery: passive (PR), exercise of the muscles involved in the initial exercise (SL), exercise of the corresponding muscles in the hitherto-inactive leg (OL), or exercise of one arm (RA). Recovery exercise workloads were each 40% of the onset of blood lactate accumulation (OBLA) for the limb used. In comparison with PR, SL and OL accelerated the fall in blood lactate to similar extents whereas RA was without effect. The first-order rate constant (min^–1) for decline of arterialised venous blood lactate concentration after the intense exercise was 0.027 (0.003) in PR, 0.058 (0.025) in SL, 0.034 (0.002) in OL, and in RA was 0.028 (0.002) [mean (SEM),n = 6 subjects]. Preliminary studies had shown that RA in isolation elevated blood lactate whereas SL and OL did not. Thus, with appropriate workloads, exercise of either hitherto active or passive muscles enhanced blood lactate decline during recovery from intense exercise. This suggests that the effect resulted principally from the uptake and utilisation of lactate in the circulation by those exercising muscles rather than from increased transport of lactate to other sites of clearance by sustained high blood flow through the previously active muscles.     

Dynamic exercise in man as influenced by experimental restriction of blood flow in the working muscles

The effects of reduced muscle perfusion pressure on dynamic exercise performance and cardiovascular and respiratory functions were investigated. Eight subjects were studied during supine cycle ergometry at stepwise increasing workloads until exhaustion with and without the legs exposed to a supra-atmospheric pressure of 50 mmHg (Leg Positive Pressure, LPP), a novel and convenient means of reducing the perfusion pressure in the working muscles. In the LPP condition exercise performance was reduced by 40% which, judging from assessments of perceived exertion, was due to premature muscle fatigue, indicating local or overall underperfusion of the working muscles. At any given work load, the arterial pressure response was considerably stronger during LPP than in the control condition. LPP also caused greater increases in blood lactate concentration and pulmonary ventilation, the differences from control increasing with the work load. Furthermore, the ventilatory equivalent for O₂ at a given work load was markedly higher in the LPP than in the control condition, while exercise-induced decreases in end-tidal P_CO2 were considerably exaggerated by LPP. The augmented pressor response during flow-restricted exercise, together with the strong ventilatory response which was out of proportion to overall O₂ uptake, suggests increased activation of muscle chemoreflexes by accumulation of metabolic end products, the increased pressor response tending to reduce the local flow error in the working muscles.     

Lactate concentrations in human skeletal muscle biopsy, microdialysate and venous blood during dynamic exercise under blood flow restriction

The intramuscular microdialysate lactate concentration during dynamic exercise with various degrees of blood flow restriction and its relation to lactate concentration in skeletal muscle biopsy and venous blood were studied. Nine healthy males performed three one-legged knee extension exercises (Ex 1–3). Blood flow was restricted stepwise by applying supra-atmospheric pressure over the working leg. Microdialysate mean (range) lactate concentrations at the end of the exercise periods were 3.2 (0.5–6.6), 4.4 (1.1–9.8) and 7.9 (1.1–11.6) mmol·l^–1 during unrestricted, moderately restricted and severely restricted blood flow respectively. There was a significant correlation between microdialysate and venous lactate concentrations at the end of all three exercise periods. Microdialysate lactate concentration correlated significantly to skeletal muscle biopsy lactate concentration at the end of Ex 1. In conclusion, microdialysate lactate concentration in the working muscle increased step-wise with increasing blood flow restriction. It showed a better correlation to venous than to muscle biopsy lactate, which is possibly partly explained by the characteristics of diffusion between body compartments and differences in time resolution between the methods used.An erratum to this article can be found at     

Mechanisms of cutaneous vasoconstriction during upright posture

The cutaneous circulation is thought to participate in the neurocirculatory adjustments during orthostatic stress, but the underlying mechanisms mediating such reflex cutaneous vasoconstriction are poorly understood. The aim of this study was to assess the relative importance of baroreceptor (cardiopulmonary and arterial) and positional (vestibular, exercise, veno-arteriolar and myogenic) reflexes in triggering cutaneous vasoconstriction during upright posture. First, hypotensive lower body negative pressure (LBNP) was compared with actual postural changes to assess the relative contributions of baroreceptor reflexes and positional reflexes. Then changes in body position were compared with changes in limb position in the absence or presence of proximal (axillary) or distal (local cutaneous) nerve blocks, to assess the relative contributions of vestibular, exercise, veno-arteriolar and myogenic reflexes. Skin sympathetic nerve activity was determined by microneurography, and skin blood flow was determined by laser Doppler velocimetry. LBNP of –50 mmHg (cardiopulmonary + arterial baroreceptors) had no effect on skin sympathetic nerve activity or skin vascular resistance. In contrast, an upright posture with the arms dependent (baroreceptor+vestibular+exercise+veno-arteriolar reflexes) caused a two- to threefold increase in skin vascular resistance. In the supine position, passive movement of the arm into a dependent position to activate veno-arteriolar reflexes alone evoked an increase in skin vascular resistance which approximated the response to normal upright posture. Blocking central sympathetic nerve impulses by application of an axillary blockade did not influence the cutaneous vasoconstrictor response to an upright posture or changes in limb position. In contrast, application of a distal nerve block by local cutaneous surface anaesthesia completely blocked vasoconstrictor responses evoked by these manoeuvres. In conclusion, these experiments in human subjects identify a primary role for veno-arteriolar reflexes in triggering vasoconstriction in the cutaneous circulation during upright posture.     

Numerical Simulation of the Influence of Gravity and Posture on Cardiac Performance

A numerical model of the cardiovascular system was used to quantify the influences on cardiac function of intrathoracic pressure and intravascular and intraventricular hydrostatic pressure, which are fundamental biomechanical stimuli for orthostatic response. The model included a detailed arterial circulation with lumped parameter models of the atria, ventricles, pulmonary circulation, and venous circulation. The venous circulation was divided into cranial, central, and caudal regions with nonlinear compliance. Changes in intrathoracic pressure and the effects of hydrostatic pressure were simulated in supine, launch, sitting, and standing postures for 0, 1, and 1.8 G. Increasing intrathoracic pressure experienced with increasing gravity caused 12% and 14% decreases in cardiac output for 1 and 1.8 G supine, respectively, compared to 0 G. Similar results were obtained for launch posture, in which the effects of changing intrathoracic pressure dominated those of hydrostatic pressure. Compared to 0 G, cardiac output decreased 0.9% for 1 G launch and 15% for 1.8 G launch. In sitting and standing, the position of the heart above the hydrostatic indifference level caused the effects of changing hydrostatic pressure to dominate those of intrathoracic pressure. Compared to 0 G, cardiac output decreased 13% for 1 G sitting and 23% for 1.8 G sitting, and decreased 17% for 1 G standing and 31% for 1.8 G standing. For a posture change from supine to standing in 1 G, cardiac output decreased, consistent with the trend necessary to explain orthostatic intolerance in some astronauts during postflight stand tests. Simulated lower body negative pressure (LBNP) in 0 G reduced cardiac output and mean aortic pressure similar to 1 G standing, suggesting that LBNP provides at least some cardiovascular stimuli that may be useful in preventing postflight orthostatic intolerance. A unifying concept, consistent with the Frank–Starling mechanism of the heart, was that cardiac output was proportional to cardiac diastolic transmural pressure for all postures and gravitational accelerations. © 2002 Biomedical Engineering Society. PAC2002: 8765+y, 8719Bb, 8719Uv, 8719Hh     

Human temperature regulation during cycling with moderate leg ischaemia

The effect of graded ischaemia in the legs on the regulation of body temperature during steady-state exercise was investigated in seven healthy males. It was hypothesised that graded ischaemia in the working muscles increases heat storage within the muscles, which in turn potentiates sweat secretion during exercise. Blood perfusion in the working muscles was reduced by applying a supra-atmospheric pressure (+6.6 kPa) around the legs, which reduced maximal working capacity by 29%. Each subject conducted three separate test trials comprising 30 min of steady-state cycling in a supine position. Exercise with unrestricted blood flow (Control trial) was compared to ischaemic exercise conducted at an identical relative work rate (Relative trial), as well as at an identical absolute work rate (Absolute trial); the latter corresponding to a 20% increase in relative workload. The average (SD) increases in both the rectal and oesophageal temperatures during steady-state cycling was 0.3 (0.2)°C and did not significantly differ between the three trials. The increase in muscle temperature was similar in the Control (2.7 (0.3)°C) and Absolute (2.4 (0.7)°C) trials, but was substantially lower (P<0.01) in the Relative trial (1.4 (0.8)°C). Ischaemia potentiated (P<0.01) sweating on the forehead in the Absolute trial (24.2 (7.3) g m^–2 min^–1) compared to the Control trial (13.4 (6.2) g m^–2 min^–1), concomitant with an attenuated (P<0.05) vasodilatation in the skin during exercise. It is concluded that graded ischaemia in working muscles potentiates the exercise sweating response and attenuates vasodilatation in the skin initiated by increased core temperature, effects which may be attributed to an augmented muscle metaboreflex.     

Effects of microgravity on interstitial muscle receptors affecting heart rate and blood pressure during static exercise

Summary Afferent nerve fibers from receptors situated in the interstitium of skeletal muscles can induce cardiovascular reflexes. It has been shown that these interstitial muscle receptors are also sensitive to the local state of hydration: increased heart rates and blood pressure values were seen during dynamic and static exercise after local dehydration on earth. Since weightlessness leads to a persisting fluid loss in the lower part of the body, we hypothesized that leg exercise in space would augment heart rate and blood pressure responses to a similar extent as during local, interstitial dehydration on earth. Initial measurements during weightlessness were obtained in one subject after 6 days of space flight. Heart rate and blood pressure responses to light static foot plantar flexion (18% of maximal voluntary contraction) were recorded in two sessions. To eliminate the influence of muscle perfusion, exercise was performed during a period of arterial occlusion obtained by means of pneumatic cuffs at mid-thigh level. Identical protocols were used in the pre- and postflight controls, which were performed both in the sitting posture and in a –90° tilted sitting posture assumed 30–40 min before arterial occlusion. During weightlessness the exercise responses of heart rate and systolic and diastolic blood pressure closely followed the tracings obtained with the tilted sitting posture on ground. The response amplitudes in these states of reduced lower limb volumes (about 20/min and 20 mmHg, respectively) exceeded the responses in the supine position by a factor of at least 2. Enhancement of cardiovascular reflexes following local fluid losses of skeletal muscles appears to be a general phenomenon that can also be seen during weightlessness.Abbreviations EMG Electromyogram - LBNP Lower body negative pressure - MVC Maximal voluntary contraction     

The influence of straining maneuvers on the pressor response during isometric exercise

Summary Experiments were performed to determine to what extent increments in esophageal and abdominal pressure would have on arterial blood pressure during fatiguing isometric exercise. Arterial blood pressure was measured during handgrip and leg isometric exercise performed with both a free and occluded circulation to active muscles. Handgrip contractions were exerted at 33 and 70% MVC (maximum voluntary contraction) by 4 volunteers in a sitting position and calf muscle contractions at 50 and 70% MVC with the subjects in a kneeling position. Esophageal pressure measured at the peak of inspirations did not change during either handgrip or leg contractions but peak expiratory pressures increased progressively during both handgrip and leg contractions as fatigue occurred. These increments were independent of the tensions of the isometric contractions exerted. Intra-abdominal pressures measured at the peak of either inspiration or expiration did not change during inspiration with handgrip contractions but increased during expiration. During leg exercise, intraabdominal pressures increased during both inspiration and expiration, reaching peak levels at fatigue. The arterial blood pressure also reached peak levels at fatigue, independent of circulatory occlusion and tension exerted, averaging 18.5–20 kPa (140–150 mm Hg) for both handgrip and leg contrations. While blood pressure returned to resting levels following exercise with a free circulation, it declined by only 2.7–3.8 kPa after leg and handgrip exercise, respectively, during circulatory occlusion. These results indicate that straining maneuvers contribute 3.5 to 7.8 kPa to the change in blood pressure depending on body position.     

Plasma renin and aldosterone changes during twenty minutes' moderate exercise

Summary The influence of posture on plasma renin and aldosterone changes during exercise performed at a constant relative work load (40%–50% maximal oxygen uptake) was studied in eight healthy men. Each subject carried out two 20-min exercises on an ergocycle at an interval of 8 days; the first exercise was performed in the normal sitting position (upright exercise), the second in a comfortable supine position (supine exercise). In both cases, heart rate and blood pressure were measured as well as plasma renin activity (PRA), aldosterone (ALDO) and osmolality, before and immediately after exercise, and 15 min following the end of exercise. An increase in heart rate, blood pressure, PRA, ALDO and osmolality was noted at the end of each exercise. This increase was greater in the supine exercise than when upright for PRA and ALDO; plasma osmolality and blood pressure showed identical increases for both types of exercise; increase in heart rate was greater when supine than when upright. PRA and ALDO were still elevated 15 min after the upright activity, but had regained their base values in that time after the supine exercise. Our results show that moderate, relatively brief periods of exercise stimulate the production of renin and aldosterone, but the response is less when supine than in the normal upright position.     

Effects of blood volume distribution on ventilatory variables at rest and during exercise

Ventilatory variables and heart rate (HR) were investigated in eight supine subjects during dynamic leg exercise at 0 and 100 W with and without the lower portion of the body exposed to a pressure of -50 mmHg (lower body negative pressure, LBNP). Resting values of inspired minute volume (V1), and respiratory drive in terms of mouth occlusion pressure (P0.1) were unchanged, whereas HR was higher during LBNP than in the control condition. Exercise values for HR in steady state were not affected by LBNP, whereas V1 was 15 and 11% lower and P0.1 was 20 and 11% lower in this condition at the 0 and 100 W workload levels, respectively. Time courses for V1 at the onset of 100 W exercise were similar with and without exposure to LBNP, indicating that the sudden increase in venous return occurring upon onset of pedalling during LBNP affords no significant stimulus in the initial development of exercise hyperpnoea. That exercise ventilation and P0.1 in steady state were reduced by LBNP suggests diminished humoral and/or locally induced chemical drive due to improved blood flow in exercising muscles resulting in reduced production of muscle metabolites or facilitation of their removal.     

Respiratory and circulatory responses to sustained positive-pressure breathing and exercise in man

To investigate the effects of sustained positive-pressure breathing (PPB) on the adaptation of respiratory and circulatory functions to exercise, 8 healthy volunteers were exposed to PPB of air at 15 and 30 cm H₂O in the supine position at rest and while performing leg exercise at 50% of individual maximal working capacity. PPB was both subjectively and objectively better tolerated when combined with exercise than it was at rest. PPB at 30 cm H_aO resulted in marked hyperventilation with alkalosis in the resting condition, but did not significantly affect respiratory minute volume, blood gases or acid-base balance during exercise. Cardiac output and left ventricular work were reduced by about one fifth and one third, respectively, both at rest and during exercise. In contrast to the case at normal airway pressure, exercise-induced increase in cardiac output was accompanied by an increment in stroke volume during PPB. Although mean arterial pressure (relative to atmospheric) was elevated by PPB at rest and during exercise, the driving pressure in systemic circuits (arterial minus central venous pressure) was reduced in both conditions. It is concluded that dynamic exercise counteracts deleterious effects of PPB by normalizing respiratory function and by improving cardiac filling by activation of the leg muscle and the abdominal pumps.     

Cardiovascular responses to upright and supine exercise in humans after 6 weeks of head-down tilt (−6°)

Seven healthy men performed steady-state dynamic leg exercise at 50 W in supine and upright postures, before (control) and repeatedly after 42 days of strict head-down tilt (HDT) (−6°) bedrest. Steady-state heart rate (f _c), mean arterial blood pressure, cardiac output (Q˙ _c), and stroke volume (SV) were recorded. The following data changed significantly from control values. The f _c was elevated in both postures at least until 12 days, but not at 32 days after bedrest. Immediately after HDT, SV and Q˙ _c were decreased by 25 (SEM 3)% and 19 (SEM 3)% in supine, and by 33 (SEM 5)% and 20 (SEM 3)% in upright postures, respectively. Within 2 days there was a partial recovery of SV in the upright but not in the supine posture. The SV and Q˙ _c during supine exercise remained significantly decreased for at least a month. Submaximal oxygen uptake did not change after HDT. We concluded that the cardiovascular response to exercise after prolonged bedrest was impaired for so long that it suggested that structural cardiac changes had developed during the HDT period. Accepted: 6 June 2000     

Arterial blood pressure and carotid baroreflex function during arm and combined arm and leg exercise in humans

AIM: During arm cranking (A) blood pressure is higher than during combined arm and leg exercise (A + L), while the carotid baroreflex (CBR) is suggested to reset to control a higher blood pressure in direct relation to work intensity and the engaged muscle mass. METHOD: This study evaluated the function of the CBR by using neck pressure and neck suction during upright A, L and A + L in 12 subjects and, in order to evaluate a potential influence of the central blood volume on the CBR, also during supine A in five subjects. Exercise intensities for A and L were planned to elicit a heart rate response of c. 100 and 120 beats min(-1), respectively, in the upright position and both workloads were maintained during A + L and supine A. RESULTS: The CBR operating point, corresponding to the pre-stimulus blood pressure, was 88 +/- 6 mmHg (mean +/- SE) at rest. During upright A, L and A + L and supine A it increased to 109 +/- 9, 95 +/- 7, 103 +/- 7 and 104 +/- 4 mmHg, respectively, and it was thus higher during upright A than during A + L and supine A (P < 0.05). In addition, the CBR threshold and saturation pressures, corresponding to the minimum and maximum carotid sinus pressure, respectively, were higher during upright A than during supine A, A + L, L and at rest (P < 0.05) with no significant change in the maximal reflex gain. CONCLUSION: These findings demonstrate that during combined arm and leg and exercise in the upright position the CBR resets to a lower blood pressure than during arm cranking likely because the central blood volume is enhanced by the muscle pump of the legs.     

Muscle strength during bedrest with and without muscle exercise as a countermeasure

Bedrest is known to be a useful experimental model for simulating weightlessness and studying its effects on human skeletal muscle activity. We therefore conducted a study in which 12 healthy male subjects underwent 28 days of continuous exposure to 6° head-down bedrest. Our main objective was to test a set of preventive countermeasures for maintaining the stability of the human body. Of the subjects 6 performed deadlifts in the supine position for 30 to 45 min each day. The isometric actions were performed for 5–30 s at 90, 120 and 150° knee angles and isokinetic training at speeds of 30 and 180° · s^–1 In vivo quadriceps muscle strength was measured under controlled experimental conditions with a commercial dynamometer. The hypothesis thet intense daily isometric and isokinetic leg exercise and lower body negative pressure (LBNP) might serve to maintain muscle strength under conditions of weightlessness was tested. Of the subjects 6, who did not perform any exercise; served as the control population under conditions of simulated weightlessness. The results showed that a significant reduction (P 0.0001) in the muscle force [–10.3 (SD 6.7%)] occurred in the control group whereas no significant changes were observed in the trained group [+ 3.9 (6.8%)]. From these studies we conclude that intense muscle training and LBNP constitute efficient countermeasures to compensate for the biomechanical effects of weightlessness on human lower limbs and to limit other factors such as cardiovascular deconditioning.     

Difference in human cardiovascular response between upright and supine recovery from upright cycle exercise

Cardiovascular responses were examined in seven healthy male subjects during 10 min of recovery in the upright or supine position following 5 min of upright cycle exercise at 80% peak oxygen uptake. An initial rapid decrease in heart rate (f _c) during the early phase of recovery followed by much slower decrease was observed for both the upright and supine positions. The average f _c at the 10th min of recovery was significantly lower (P < 0.05) in the supine position than in the upright position, while they were both significantly greater than the corresponding pre-exercise levels (each P < 0.05). Accordingly, the amplitude of the high frequency (HF) component of R-R interval variability (by spectrum analysis) in both positions was reduced with a decrease in mean R-R interval, the relationship being expressed by a regression line – mean R-R interval = 0.006 × HF amplitude + 0.570 (r = 0.905, n = 28, P < 0.001). These results would suggest that the slower reduction in f _c following the initial rapid reduction in both positions is partly attributable to a retardation in the restoration of the activity of the cardiac parasympathetic nervous system. Post-exercise upright stroke volume (SV, by impedance cardiography) decreased gradually to just below the pre-exercise level, whereas post-exercise supine SV increased markedly to a level similar to that at rest before exercise. The resultant cardiac output (Q˙ _c) and the total peripheral vascular resistance (TPR) in the upright and supine positions returned gradually to their respective pre-exercise levels in the corresponding positions. At the 10th min of recovery, both average SV and Q˙ _c were significantly greater (each P < 0.005) in the supine than in the upright position, while average TPR was significantly lower (P < 0.05) in the supine than in the upright position. In contrast, immediately after exercise, mean blood pressure dropped markedly in both the supine and upright positions, and their levels at the 10th min of recovery were similar. Therefore we concluded that arterial blood pressure is maintained relatively constant through various compensatory mechanisms associated with f _c, SV, Q˙ _c, and TPR during rest and recovery in different body positions. Accepted: 4 September 1999     

Central and Regional Circulatory Effects of Adding Arm Exercise to Leg Exercise

7 young, healthy, male subjects performed exercise on bicycle ergometers in two 20 min periods with an interval of 1 h. The first 10 min of each 20 min period consisted of arm exercise (38–62% of Vdot;o₂ max for arm exercise) or leg exercise (58–78% of Vdot;o₂ max for leg exercise). During the last 10 min the subjects performed combined arm and leg exercise (71–83% of Vdot;o₂ max for this type of exercise). The following variables were measured during each type of exercise: oxygen uptake, heart rate, mean arterial blood pressure, cardiac output, leg blood flow (only during leg exercise and combined exercise), arterio-venous concentration differences for O₂ and lactate at the levels of the axillary and the external iliac vessels. Superimposing a sufficiently strenuous arm exercise (oxygen uptake for arm exercise 40% of oxygen uptake for combined exercise) on leg exercise caused a reduction in blood flow and oxygen uptake in the exercising legs with unchanged mean arterial blood pressure. Superimposing leg exercise on arm exercise caused a decrease in mean arterial blood pressure and an increased axillary arterio-venous oxygen difference. These findings indicate that the oxygen supply to one large group of exercising muscles may be limited by vasoconstriction or by a fall in arterial pressure, when another large group of muscles is exercising simultaneously.     

Post-exercise leg and forearm flexor muscle cooling in humans attenuates endurance and resistance training effects on muscle performance and on circulatory adaptation

The influence of regular post-exercise cold application to exercised muscles trained by ergometer cycling (leg muscles) or handgrip exercise using a weight-loaded handgrip ergometer (forearm flexor muscles) was studied in human volunteers. Muscle loads were applied during exercise programs three to four times a week for 4–6 weeks. Besides measuring parameters characterizing muscle performance, femoral and brachial artery diameters were determined ultrasonographically. Training effects were identified by comparing pre- and post-training parameters in matched groups separately for the trained limbs cooled after exercise by cold-water immersion and the corresponding trained limbs kept at room temperature. Significant training effects were three times more frequent in the control than in the cold group, including increases in artery diameters in the control but not in the cold group. It is concluded that training-induced molecular and humoral adjustments, including muscle hyperthermia, are physiological, transient and essential for training effects (myofiber regeneration, muscle hypertrophy and improved blood supply). Cooling generally attenuates these temperature-dependent processes and, in particular, hyperthermia-induced HSP formation. This seems disadvantageous for training, in contrast to the beneficial combination of rest, ice, compression and elevation in the treatment of macroscopic musculo-tendinous damage. Part of the results were presented at the Congress on Physiology and Pharmacology of Temperature Regulation held in Rhodes (Greece) in October 14, 2004 [Ohnishi N, Yamane M, Uchiyama N, Shirasawa S, Kosaka M, Shiono H, Okada T (2004) Adaptive changes in muscular performance and circulation by resistance training with regular cold adaptation. J Therm Biol 29: 839–843].