Changes in muscle sympathetic nerve activity and calf blood flow during combined leg and forearm exercise

The Effects of 10-Week Strength Training in the Winter on Brown-like Adipose Tissue Vascular Density

There is no evidence of the effect of exercise training on human brown-like adipose tissue vascular density (BAT-d). Here, we report whether whole-body strength training (ST) in a cold environment increased BAT-d. The participants were 18 men aged 20-31 years. They were randomly assigned to two groups: one that performed ST twice a week at 75% intensity of one-repetition maximum for 10 weeks during winter (EX; n = 9) and a control group that did not perform ST (CT; n = 9). The total hemoglobin concentration in the supraclavicular region determined by time-resolved near-infrared spectroscopy was used as a parameter of BAT-d. ST volume (T_vol) was defined as the mean of the weight × repetition × sets of seven training movements. The number of occasions where the room temperature was lower than the median (NR_cold) was counted as an index of potential cold exposure during ST. There was no significant between-group difference in BAT-d. Multiple regression analysis using body mass index, body fat percentage, NR_cold, and T_vol as independent variables revealed that NR_cold and T_vol were determined as predictive of changes in BAT-d. An appropriate combination of ST with cold environments could be an effective strategy for modulating BAT.

Muscle sympathetic nerve activity during exercise

Appropriate cardiovascular adjustment is necessary to meet the metabolic demands of working skeletal muscle during exercise. The sympathetic nervous system plays a crucial role in the regulation of arterial blood pressure and blood flow during exercise, and several important neural mechanisms are responsible for changes in sympathetic vasomotor outflow. Changes in sympathetic vasomotor outflow (i.e., muscle sympathetic nerve activity: MSNA) in inactive muscles during exercise differ depending on the exercise mode (static or dynamic), intensity, duration, and various environmental conditions (e.g., hot and cold environments or hypoxic). In 1991, Seals and Victor [6] reviewed MSNA responses to static and dynamic exercise with small muscle mass. This review provides an updated comprehensive overview on the MSNA response to exercise including large-muscle, dynamic leg exercise, e.g., two-legged cycling, and its regulatory mechanisms in healthy humans.

Effects of dynamic arm and leg exercise on muscle sympathetic nerve activity and vascular conductance in the inactive leg

The influence of muscle sympathetic nerve activity (MSNA) responses on local vascular conductance during exercise are not well established. Variations in exercise mode and active muscle mass can produce divergent MSNA responses. Therefore, we sought to examine the effects of small- versus large-muscle mass dynamic exercise on vascular conductance and MSNA responses in the inactive limb. Thirty-five participants completed two study visits in a randomized order. During visit 1, superficial femoral artery (SFA) blood flow (Doppler ultrasound) was assessed at rest and during steady-state rhythmic handgrip (RHG; 1:1 duty cycle, 40% maximal voluntary contraction), one-leg cycling (17 ± 3% peak power output), and concurrent exercise at the same intensities. During visit 2, MSNA (contralateral fibular nerve microneurography) was acquired successfully in 12/35 participants during the same exercise modes. SFA blood flow increased during RHG (P < 0.0001) and concurrent exercise (P = 0.03) but not cycling (P = 0.91). SFA vascular conductance was unchanged during RHG (P = 0.88) but reduced similarly during concurrent and cycling exercise (both P < 0.003). RHG increased MSNA burst frequency (P = 0.04) without altering burst amplitude (P = 0.69) or total MSNA (P = 0.26). In contrast, cycling and concurrent exercise had no effects on MSNA burst frequency (both P ≥ 0.10) but increased burst amplitude (both P ≤ 0.001) and total MSNA (both P ≤ 0.007). Across all exercise modes, the changes in MSNA burst amplitude and SFA vascular conductance were correlated negatively (r = -0.43, P = 0.02). In summary, the functional vascular consequences of alterations in sympathetic outflow to skeletal muscle are most closely associated with changes in MSNA burst amplitude, but not frequency, during low-intensity dynamic exercise.NEW & NOTEWORTHY Low-intensity small- versus large-muscle mass exercise can elicit divergent effects on muscle sympathetic nerve activity (MSNA). We examined the relationships between changes in MSNA (burst frequency and amplitude) and superficial femoral artery (SFA) vascular conductance during rhythmic handgrip, one-leg cycling, and concurrent exercise in the inactive leg. Only changes in MSNA burst amplitude were inversely associated with SFA vascular conductance responses. This result highlights the functional importance of measuring MSNA burst amplitude during exercise.

Cardiovascular control during whole body exercise

It has been considered whether during whole body exercise the increase in cardiac output is large enough to support skeletal muscle blood flow. This review addresses four lines of evidence for a flow limitation to skeletal muscles during whole body exercise. First, even though during exercise the blood flow achieved by the arms is lower than that achieved by the legs (∼160 vs. ∼385 ml·min(-1)·100 g(-1)), the muscle mass that can be perfused with such flow is limited by the capacity to increase cardiac output (42 l/min, highest recorded value). Secondly, activation of the exercise pressor reflex during fatiguing work with one muscle group limits flow to other muscle groups. Another line of evidence comes from evaluation of regional blood flow during exercise where there is a discrepancy between flow to a muscle group when it is working exclusively and when it works together with other muscles. Finally, regulation of peripheral resistance by sympathetic vasoconstriction in active muscles by the arterial baroreflex is critical for blood pressure regulation during exercise. Together, these findings indicate that during whole body exercise muscle blood flow is subordinate to the control of blood pressure.

Short-term exercise training augments 2-adrenoreceptor-mediated sympathetic vasoconstriction in resting and contracting skeletal muscle

We hypothesized that exercise training (ET) would alter α2-adrenoreceptor-mediated sympathetic vasoconstriction. Sprague-Dawley rats (n = 30) were randomized to sedentary (S), mild- (M) or heavy-intensity (H) treadmill ET groups (5 days per week for 4 weeks). Following the ET component of the study, rats were anaesthetized, and instrumented for lumbar sympathetic chain stimulation, triceps surae muscle contraction and measurement of femoral vascular conductance (FVC). The percentage change of FVC in response to sympathetic stimulation was determined at rest and during contraction in control, α2 blockade (yohimbine) and combined α2 + nitric oxide (NO) synthase (NOS) blockade (N-nitro-L-arginine methyl ester hydrochloride, L-NAME) conditions. ET augmented (P < 0.05) sympathetic vasoconstrictor responses at rest and during contraction. Yohimbine reduced (P < 0.05) the vasoconstrictor response in ET rats at rest (M: 2 Hz: 8 ± 2%, 5 Hz: 9 ± 4%; H: 2 Hz: 14 ± 5%, 5 Hz: 11 ± 6%) and during contraction (M: 2 Hz: 9 ± 2%, 5 Hz: 9 ± 5%; H: 2 Hz: 8 ± 3%, 5 Hz: 6 ± 6%) but did not change the response in S rats. The addition of L-NAME caused a larger increase (P < 0.05) in the vasoconstrictor response in ET than in S rats at rest (2 Hz: S: 8 ± 2%, M: 15 ± 3%, H: 23 ± 7%; 5 Hz: S: 8 ± 5%, M: 15 ± 3%, H: 17 ± 5%) and during contraction (2 Hz: S: 9 ± 3%, M: 18 ± 3%, H: 22 ± 6%; 5 Hz: S: 9 ± 5%, M: 22 ± 4%, H:26 ± 9%). Sympatholysis was greater (P < 0.05) in ET than in S rats. Blockade of α2-adrenoreceptors and NOS reduced (P < 0.05) sympatholysis in ET rats, but had no effect on sympatholysis in S rats. In conclusion, ET increased α2-mediated vasoconstriction at rest and during contraction.

Human investigations into the exercise pressor reflex

During exercise, neural input from skeletal muscles reflexly maintains or elevates blood pressure (BP) despite a maybe fivefold increase in vascular conductance. This exercise pressor reflex is illustrated by similar heart rate (HR) and BP responses to electrically induced and voluntary exercise. The importance of the exercise pressor reflex for tight cardiovascular regulation during dynamic exercise is supported by studies using pharmacological blockade of lower limb muscle afferent nerves. These experiments show attenuation of the increase in BP and cardiac output when exercise is performed with attenuated neural feedback. Additionally, there is no BP response to electrically induced exercise with paralysing epidural anaesthesia or when similar exercise is evoked in paraplegic patients. Furthermore, BP decreases when electrically induced exercise is carried out in tetraplegic patients. The lack of an increase in BP during exercise with paralysed legs manifests, although electrical stimulation of muscles enhances lactate release and reduces muscle glycogen. Thus, the exercise pressor reflex enhances sympathetic activity and maintains perfusion pressure by restraining abdominal blood flow, while brain, skin and muscle blood flow may also become affected because the reflex 'resets' arterial baroreceptor modulation of vascular conductance, making BP the primarily regulated cardiovascular variable during exercise.

Blood flow in the brachial artery increases after intense cycling exercise

During cycling blood flow is redistributed from physically inactive tissues to working leg muscles. It is unknown how long this situation persists after very intense exercise or whether it differs between intense exhausting and non-exhausting exercise. It is also not known to what extent the redistribution differs between different types of non-active tissues. Therefore nine healthy young men cycled first for 2 min at 328 W (non-exhausting exercise, mean). Blood velocity in thigh and arm (ultrasound-doppler), perfusion of forearm skin (non-acral skin) and finger tip (acral skin, with arterio-venous anastomoses) were measured for 30 min after exercise (laser-doppler). To be able to study vascular resistance and central circulation, blood pressure (Finometer), heart rate (ECG), and stroke volume (ultrasound-doppler) were measured. Thereafter the subjects cycled at the same power to exhaustion (4 min), and the measurements were repeated. After both exercises mean blood pressure was unchanged (< or = 80 mm Hg) despite increased cardiac output (> or = + 30% vs. pre-exercise). Blood velocity in the brachial artery was higher during the whole recovery period than at rest (p< or =0.02; no differences between exercises). Blood perfusion of non-acral skin was unchanged from pre-exercise level after 2 min of non-exhausting exercise, but it was twice as high after 4 min cycling to exhaustion as at rest (p=0.02). Blood perfusion of acral skin rose after both exercises and did not differ between exhausting and non-exhausting exercise. In conclusion, arm blood flow increases above the pre-exercise level in the recovery period after short-lasting, strenuous exercise.

The effects of shoulder load and pinch force on electromyographic activity and blood flow in the forearm during a pinch task

The object of the current study was to determine whether static contraction of proximal musculature has an effect on the blood flow more distally in the upper extremity. Static contractions of muscles in the neck shoulder region at three levels (relaxed, shoulders elevated and shoulders elevated loaded with 4.95 kg each) were combined with intermittent pinch forces at 0, 10 and 25% of the maximum voluntary contraction (MVC). Blood flow to the forearm was measured with Doppler ultrasound. Myoelectric activity of the forearm and neck-shoulder muscles was recorded to check for the workload levels. Across all levels of shoulder load, blood flow increased significantly with increasing pinch force (21% at 10% MVC and by 44% at 25% MVC). Blood flow was significantly affected by shoulder load, with the lowest blood flow at the highest shoulder load. Interactions of pinch force and shoulder load were not significant. The myoelectric activity of forearm muscles increased with increasing pinch force. The activation of the trapezius muscle decreased with increasing pinch force and increased with increasing shoulder load. The precise mechanisms accounting for the influence of shoulder load remains unclear. The results of this study indicate that shoulder load might influence blood flow to the forearm.

Are the Arms and Legs in Competition for Cardiac Output?

Oxygen transport to working skeletal muscles is challenged during whole-body exercise. In general, arm-cranking exercise elicits a maximal oxygen uptake (VO2max) corresponding to approximately 70% of the value reached during leg exercise. However, in arm-trained subjects such as rowers, cross-country skiers, and swimmers, the arm VO2max approaches or surpasses the leg value. Despite this similarity between arm and leg VO2max, when arm exercise is added to leg exercise, VO2max is not markedly elevated, which suggests a central or cardiac limitation. In fact, when intense arm exercise is added to leg exercise, leg blood flow at a given work rate is approximately 10% less than during leg exercise alone. Similarly, when intense leg exercise is added to arm exercise, arm blood flow and muscle oxygenation are reduced by approximately 10%. Such reductions in regional blood flow are mainly attributed to peripheral vasoconstriction induced by the arterial baroreflex to support the prevailing blood pressure. This putative mechanism is also demonstrated when the ability to increase cardiac output is compromised; during exercise, the prevailing blood pressure is established primarily by an increase in cardiac output, but if the contribution of the cardiac output is not sufficient to maintain the preset blood pressure, the arterial baroreflex increases peripheral resistance by augmenting sympathetic activity and restricting blood flow to working skeletal muscles.

The influence of inspiratory muscle work history and specific inspiratory muscle training upon human limb muscle fatigue

The purpose of this study was to assess the influence of the work history of the inspiratory muscles upon the fatigue characteristics of the plantar flexors (PF). We hypothesized that under conditions where the inspiratory muscle metaboreflex has been elicited, PF fatigue would be hastened due to peripheral vasoconstriction. Eight volunteers undertook seven test conditions, two of which followed 4 week of inspiratory muscle training (IMT). The inspiratory metaboreflex was induced by inspiring against a calibrated flow resistor. We measured torque and EMG during isometric PF exercise at 85% of maximal voluntary contraction (MVC) torque. Supramaximal twitches were superimposed upon MVC efforts at 1 min intervals (MVC(TI)); twitch interpolation assessed the level of central activation. PF was terminated (T(lim)) when MVC(TI) was <50% of baseline MVC. PF T(lim) was significantly shorter than control (9.93 +/- 1.95 min) in the presence of a leg cuff inflated to 140 mmHg (4.89 +/- 1.78 min; P = 0.006), as well as when PF was preceded immediately by fatiguing inspiratory muscle work (6.28 +/- 2.24 min; P = 0.009). Resting the inspiratory muscles for 30 min restored the PF T(lim) to control. After 4 weeks, IMT, inspiratory muscle work at the same absolute intensity did not influence PF T(lim), but T(lim) was significantly shorter at the same relative intensity. The data are the first to provide evidence that the inspiratory muscle metaboreflex accelerates the rate of calf fatigue during PF, and that IMT attenuates this effect.

Thermoregulation during Exercise in Individuals with Spinal Cord Injuries

The increased participation in wheelchair sports in conjunction with environmental challenges posed by the most recent Paralympic venues has stimulated interest into the study of thermoregulation of wheelchair users. This area is particularly pertinent for the spinal cord injured as there is a loss of vasomotor and sudomotor effectors below the level of spinal lesion. Studies within this area have examined a range of environmental conditions, exercise modes and subject populations. During exercise in cool conditions (15-25 degrees C), trained paraplegic individuals (thoracic or lumbar spinal lesions) appear to be at no greater risk of thermal injury than trained able-bodied individuals, although greater heat storage for a given metabolic rate is evident. In warm conditions (25-40 degrees C), trained subjects again demonstrate similar core temperature responses to the able-bodied for a given relative exercise load but elicit increased heat storage within the lower body and reduced whole-body sweat rates, increasing the risk of heat injury. The few studies examining a wide range of lesion levels have noted that, for paraplegic individuals where heat production is matched by available sweating capacity, excessive heat strain may be offset. Studies relating to tetraplegic subjects (cervical spinal lesions) are fewer in number but have consistently shown this population to elicit much faster rates of core and skin temperature increase and thermal imbalance in both cool and warm conditions than paraplegic individuals. These responses are due to the complete absence or severely reduced sweating capacity in tetraplegic subjects. During continuous exercise protocols, the main thermal stressor for tetraplegic subjects appears to be environmental heat gain, whereas during an intermittent-type exercise protocol it appears to be metabolic heat production. Fluid losses during exercise and heat retention during passive recovery from exercise are related to lesion level. Future research is recommended to focus on the specific role of absolute and relative metabolic rates, sweating responses, training status and more sport- and vocation-specific exercise protocols.

Effect of fitness on arm vascular and metabolic responses to upper body exercise

We investigated arm perfusion and metabolism during upper body exercise. Eight average, fit subjects and seven rowers, mean ± SE maximal oxygen uptake (V̇o2 max) 157 ± 7 and 223 ± 14 ml O2· kg–0.73·min–1, respectively, performed incremental arm cranking to exhaustion. Arm blood flow (ABF) was measured with thermodilution and arm muscle mass was estimated by dual-energy X-ray absorptiometry. During maximal arm cranking, pulmonary V̇o2 was ∼45% higher in the rowers compared with the untrained subjects and peak ABF was 6.44 ± 0.40 and 4.55 ± 0.26 l/min, respectively ( P < 0.05). The arm muscle mass for the rowers and the untrained subjects was 3.5 ± 0.4 and 3.3 ± 0.1 kg, i.e., arm perfusion was 1.9 ± 0.2 and 1.4 ± 0.1 l blood·kg–1·min–1, respectively ( P < 0.05). The arteriovenous O2 difference was 156 ± 7 and 120 ± 8 ml/l, respectively, and arm V̇o2 was 0.98 ± 0.08 and 0.60 ± 0.04 l/min corresponding with 281 ± 22 and 181 ± 12 ml/kg, while arm O2 diffusional conductance was 49.9 ± 4.3 and 18.6 ± 3.2 ml·min–1·mmHg–1, respectively ( P < 0.05). Also, lactate release in the rowers was almost three times higher than in the untrained subjects (26.4 ± 1.1 vs. 9.5 ± 0.4 mmol/min, P < 0.05). The energy requirement of an ∼50% larger arm work capacity after long-term arm endurance training is covered by an ∼60% increase in aerobic metabolism and an almost tripling of the anaerobic capacity.

Arm blood flow and metabolism during arm and combined arm and leg exercise in humans

The cardiovascular response to exercise with several groups of skeletal muscle suggests that work with the arms may decrease leg blood flow. This study evaluated whether intense exercise with the legs would have a similar effect on arm blood flow (Y(arm)) and O(2) consumption (V(O(2))(,arm)). Ten healthy male subjects (age 21 +/- 1 year; mean +/- S.D.) performed arm cranking at 80 % of maximum arm work capacity (A trial) and combined arm cranking with cycling at 60 % of maximum leg work capacity (A + L trial). The combined trial was a maximum effort for 5-6 min. Y(arm) measurement by thermodilution in the axilliary vein and arterial and venous blood samples permitted calculation of V(O(2))(,arm). During the combined trial, Y(arm) was reduced by 0.58 +/- 0.25 l min(-1) (19.1 +/- 3.0 %, P < 0.05) from the value during arm cranking (3.00 +/- 0.46 l min(-1)). The arterio-venous O(2) difference increased from 122 +/- 15 ml l(-1) during the arm trial to 150 +/- 21 ml l(-1) (P < 0.05) during the combined trial. Thus, V(O(2))(,arm) (0.45 +/- 0.06 l min(-1)) was reduced by 9.6 +/- 6.3 % (P < 0.05) and arm vascular conductance from 27 +/- 4 to 23 +/- 3 ml min(-1) (mmHg)(-1) (P < 0.05) as noradrenaline spillover from the arm increased from 7.5 +/- 3.5 to 13.8 +/- 4.2 nmol min(-1) (P < 0.05). The data suggest that during maximal whole body exercise in humans, arm vasoconstriction is established to an extent that affects oxygen delivery to and utilisation by working skeletal muscles.

Skeletal muscle blood flow in humans and its regulation during exercise

Regional limb blood flow has been measured with dilution techniques (cardio-green or thermodilution) and ultrasound Doppler. When applied to the femoral artery and vein at rest and during dynamical exercise these methods give similar reproducible results. The blood flow in the femoral artery is approximately 0.3 L min(-1) at rest and increases linearly with dynamical knee-extensor exercise as a function of the power output to 6-10 L min[-1] (Q= 1.94 + 0.07 load). Considering the size of the knee-extensor muscles, perfusion during peak effort may amount to 2-3 L kg(-1) min(-1), i.e. approximately 100-fold elevation from rest. The onset of hyperaemia is very fast at the start of exercise with T 1/2 of 2-10 s related to the power output with the muscle pump bringing about the very first increase in blood flow. A steady level is reached within approximately 10-150 s of exercise. At all exercise intensities the blood flow fluctuates primarily due to the variation in intramuscular pressure, resulting in a phase shift with the pulse pressure as a superimposed minor influence. Among the many vasoactive compounds likely to contribute to the vasodilation after the first contraction adenosine is a primary candidate as it can be demonstrated to (1) cause a change in limb blood flow when infused i.a., that is similar in time and magnitude as observed in exercise, and (2) become elevated in the interstitial space (microdialysis technique) during exercise to levels inducing vasodilation. NO appears less likely since NOS blockade with L-NMMA causing a reduced blood flow at rest and during recovery, it has no effect during exercise. Muscle contraction causes with some delay (60 s) an elevation in muscle sympathetic nerve activity (MSNA), related to the exercise intensity. The compounds produced in the contracting muscle activating the group IIl-IV sensory nerves (the muscle reflex) are unknown. In small muscle group exercise an elevation in MSNA may not cause vasoconstriction (functional sympatholysis). The mechanism for functional sympatholysis is still unknown. However, when engaging a large fraction of the muscle mass more intensely during exercise, the MSNA has an important functional role in maintaining blood pressure by limiting blood flow also to exercising muscles.

Altered lower limb vascular perfusion in patients with sciatica secondary to disc herniation

STUDY DESIGN

The present study attempts to document deep vascular abnormalities of the lower extremity in cases of sciatica secondary to discal herniation using Tc-99m methylene diphosphonate angiography.

OBJECTIVES

Vascular abnormalities are studied compared with the contralateral extremity and normal control subjects. An attempt is made to determine the clinical usefulness of the current technique. SUMMARY OF BACKGROUND DATA. Thermography has occasionally evidenced a decreased cutaneous temperature in patients with sciatica. There have been no studies to date looking at the total vascular flow in this condition, mainly constituted by the muscular perfusion.

METHODS

Thirty patients with sciatica secondary to discal herniation, 16 patients with chronic low back pain referred to the thigh, and 31 control subjects were examined by isotopic angiography of the posterior aspect of the thigh after intravenous injection of Tc-99m methylene diphosphonate. The affected side was compared with the nonpainful side, and the difference was expressed as a percentage. Control subjects were used as reference values.

RESULTS

Abnormality in vascularization of the lower extremity was found in 24 (80%) of patients with sciatica and in 11 (68.7%) of the patients with low back pain. The median blood flow difference was, respectively, -12.5% and +4% in these two groups versus +2.9% in the control group. The differences between the sciatica group and the other groups were statistically significant. No correlation was found with the clinical parameters studied.

CONCLUSION

Vascular perfusion abnormalities observed in patients with sciatica secondary to disc herniation may be more important than previously considered and possibly result from alteration in sympathetic vascular autoregulation.

Differential sympathetic neural control of oxygenation in resting and exercising human skeletal muscle

Metabolic products of skeletal muscle contraction activate metaboreceptor muscle afferents that reflexively increase sympathetic nerve activity (SNA) targeted to both resting and exercising skeletal muscle. To determine effects of the increased sympathetic vasoconstrictor drive on muscle oxygenation, we measured changes in tissue oxygen stores and mitochondrial cytochrome a,a3 redox state in rhythmically contracting human forearm muscles with near infrared spectroscopy while simultaneously measuring muscle SNA with microelectrodes. The major new finding is that the ability of reflex-sympathetic activation to decrease muscle oxygenation is abolished when the muscle is exercised at an intensity > 10% of maximal voluntary contraction (MVC). During high intensity handgrip, (45% MVC), contraction-induced decreases in muscle oxygenation remained stable despite progressive metaboreceptor-mediated reflex increases in SNA. During mild to moderate handgrips (20-33% MVC) that do not evoke reflex-sympathetic activation, experimentally induced increases in muscle SNA had no effect on oxygenation in exercising muscles but produced robust decreases in oxygenation in resting muscles. The latter decreases were evident even during maximal metabolic vasodilation accompanying reactive hyperemia. We conclude that in humans sympathetic neural control of skeletal muscle oxygenation is sensitive to modulation by metabolic events in the contracting muscles. These events are different from those involved in either metaboreceptor muscle afferent activation or reactive hyperemia.

Exhausting handgrip exercise reduces the blood flow in the active calf muscle exercising at low intensity

The calf and forearm blood flows (Qcalf and Qforearm respectively), blood pressure, heart rate and oxygen uptake of six men and women were studied during combined leg and handgrip exercise to determine whether a reduction of exercise-induced hyperaemia would occur in the active leg when exhausting rhythmic handgrip exercise at 50% maximal voluntary contraction (MVC) was superimposed upon rhythmic plantar flexion lasting for 10 min at 10% MVC (P10) prior to this combined exercise. The Qcalf and Qforearm were measured by venous occlusion plethysmography during 5-s rests interposed during every minute of P10 exercise and immediately after combined exercise. The muscle sympathetic nerve activity (MSNA) changes were also recorded during leg exercise alone and combined exercise. During plantar flexion performed 60 times.min-1 with a load equal to 10% MVC (P10), Qcalf was maintained at a constant level, which was significantly higher than the resting value (P < 0.001). When rhythmic handgrip contraction at 50% MVC (H50) and P10 were performed simultaneously, the combined exercise was concluded due to forearm exhaustion after a mean of 51.2 (SEM 5.5) s. At exhaustion, Qcalf had decreased significantly from 20.6 (SEM 3.0) ml.100 ml-1.min-1 (10th min during P10 exercise) to 15.3 (SEM) ml.100 ml-1.min-1 (P = 0.001), whereas Qforearm had increased significantly (0.001 < P < 0.01) from 8.6 (SEM 1.9) ml.100 ml-1.min-1 (10th min of P10 exercise) to 26.2 (SEM 3.2) ml.100 ml-1.min-1. The mean blood pressure remained at an almost constant level during the 3rd to 10th min of P10 exercise and increased markedly when H50 was added.(ABSTRACT TRUNCATED AT 250 WORDS)

Relative contraction force producing a reduction in calf blood flow by superimposing forearm exercise on lower leg exercise

The relative contraction force producing a reduction in exercise hyperaemia was studied by superimposing handgrip contraction at different intensities on plantar flexion of low intensity. Ten active women served as subjects. Blood flow to the forearm (Qforearm) and calf (Qcalf) was measured with mercury-in-rubber strain gauges by venous occlusion plethysmography immediately after 60 s of rhythmic plantar flexion at 10% of maximum voluntary contraction (MVC), which was expressed as P10H0, or combined plantar flexion and handgrip contraction. In the combined exercise, handgrip exercise at 30%, 50% or 70% MVC was added to plantar flexion during the last 30 s of exercise (P10H30, P10H50 and P10H70, respectively). The Qforearm increases after P10H30, P10H50 and P10H70 were significantly larger (P < 0.01) than that after P10H0, and the difference between P10H30 and P10H70 was also significant (P < 0.01). Immediate post-exercise Qcalf after P10H0 increased by 7.4 (SEM 0.9) ml x 100 ml-1 x min-1. When handgrip contraction at 70% MVC was added, the Qcalf increase after exercise [4.5 (SEM 0.7) ml x 100 ml-1 x min-1] was significantly lower than after plantar flexion alone (P < 0.05). However, no significant change was found in Qcalf when the forces of added handgrip contraction were 30% and 50% MVC, although the mean value of Qcalf increase was lower after P10H50 combined exercise. Calf vascular resistance calculated as BP/Qcalf (BP mean blood pressure) tended to increase after P10H70 to a nonsignificant extent. Heart rate and oxygen uptake in these exercises increased when handgrip contraction at 30%, 50%, or 70% MVC was added to plantar flexion at 10% MVC.(ABSTRACT TRUNCATED AT 250 WORDS)