Muscle blood-flow dynamics at exercise onset: do the limbs differ?

The effect of self-identified arm dominance on exercising forearm hemodynamics and skeletal muscle desaturation

The human forearm model is commonly employed in physiological investigations exploring local vascular function and oxygen delivery; however, the effect of arm dominance on exercising forearm hemodynamics and skeletal muscle oxygen saturation (SmO2) in untrained individuals is poorly understood. Therefore, the purpose of this study was to explore the effect of self-identified arm dominance on forearm hemodynamics and SmO2 in untrained individuals during submaximal, non-ischemic forearm exercise. Twenty healthy individuals (23±4 years, 50% female; 80% right-handed) completed three-minute bouts of supine rhythmic (1 second contraction: 2 second relaxation duty cycle) forearm handgrip exercise at both absolute (10kg; 98N) and relative (30% of maximal voluntary contraction) intensities in each forearm. Beat-by-beat measures of forearm blood flow (FBF; ml/min), mean arterial blood pressure (MAP; mmHg) and flexor digitorum superficialis SmO2 (%) were obtained throughout and averaged during the final 30 seconds of rest, exercise, and recovery while forearm vascular conductance was calculated (FVC; ml/min/100mmHg). Data are Δ from rest (mean±SD). Absolute force production did not differ between non-dominant and dominant arms (97±11 vs. 98±13 N, p = 0.606) whereas relative force production in females did (69±24 vs. 82±25 N, p = 0.001). At both exercise intensities, FBFRELAX, FVCRELAX, MAPRELAX, and the time constant tau for FBF and SmO2 were unaffected by arm dominance (all p>0.05). While arm dominance did not influence SmO2 during absolute intensity exercise (p = 0.506), the non-dominant arm in females experienced an attenuated reduction in SmO2 during relative intensity exercise (-14±10 vs. -19±8%, p = 0.026)-though exercise intensity was also reduced (p = 0.001). The present investigation has demonstrated that arm dominance in untrained individuals does not impact forearm hemodynamics or SmO2 during handgrip exercise.

Variability of Lower Limb Artery Systolic-Diastolic Velocities in Futsal Athletes and Non-Athletes: Evaluation by Arterial Doppler Ultrasound

Background: Sports athletes, namely high-intensity practitioners, suffer from vascular remodeling overtime. The purpose of this study was to analyze the systolic and diastolic velocities' variation between non-athletes and futsal athletes by means of arterial lower limb doppler ultrasound. Additionally, we intended to verify if the velocity variations occur primarily at the systolic or the diastolic level and in which arteries. Methods: Seventy-six young males (mean ± SD: 24.9 ± 2.8 years old) volunteered to participate in this cross-sectional study and were divided into two groups: a futsal athletes group (n = 38; 24 ± 2.78 years) in the central region of Portugal playing on the 2nd national league with the same level of practice (16 ± 2.4 years of practice) and a non-athletes group (n = 38: 26 ± 1.8 years) who did not practice sports regularly and were not federated in any sport. All the subjects agreed to participate in the study with the aim of assessing the arterial lower limb through doppler ultrasound (Philips HD7 echograph with linear transducer 7-12 MHz). Results: Differences between groups (p ≤ 0.05) in the systolic velocity of the left deep femoral artery (p = 0.022; d = 0.546, small) and in the right superficial femoral artery (p = 0.028; d = -0.515, small) were found. We also found differences in the diastolic velocity: in the left common femoral artery (p = 0.002; d = -0.748, moderate), in the right deep femoral artery (p = 0.028; d = -0.521, small), in the right superficial femoral artery (p = 0.026; d = -0.522, small), in the right popliteal artery (p = 0.002; d = -0.763, moderate), and in the left popliteal artery (p = 0.007; d = -0.655, moderate). Moreover, the athletes' group presented the highest mean values, with the exception of the systolic velocity of the left deep femoral artery. In intragroup analysis of variance referring to systolic and diastolic velocities in arterial levels in the right and left arteries, differences were found in all analyses (p ≤ 0.05). Conclusions: We conclude that futsal athletes of our sample go through a process of changes such as increased blood flow velocity in systolic and diastolic cardiac phase in all studied lower limb arteries, showing that the remodeling occurs regardless of vessel radius. Our results reinforce the existence of vascular remodeling that may vary with the sport and its intensity.

Assessment of resistance vessel function in human skeletal muscle: guidelines for experimental design, Doppler ultrasound, and pharmacology

The introduction of duplex Doppler ultrasound almost half a century ago signified a revolutionary advance in the ability to assess limb blood flow in humans. It is now widely used to assess blood flow under a variety of experimental conditions to study skeletal muscle resistance vessel function. Despite its pervasive adoption, there is substantial variability between studies in relation to experimental protocols, procedures for data analysis, and interpretation of findings. This guideline results from a collegial discussion among physiologists and pharmacologists, with the goal of providing general as well as specific recommendations regarding the conduct of human studies involving Doppler ultrasound-based measures of resistance vessel function in skeletal muscle. Indeed, the focus is on methods used to assess resistance vessel function and not upstream conduit artery function (i.e., macrovasculature), which has been expertly reviewed elsewhere. In particular, we address topics related to experimental design, data collection, and signal processing as well as review common procedures used to assess resistance vessel function, including postocclusive reactive hyperemia, passive limb movement, acute single limb exercise, and pharmacological interventions.

Habitual exercise training in older adults offsets the age-related prolongation in leg vasodilator kinetics during single-limb lower body exercise

We tested the hypothesis that aging is associated with prolonged leg vasodilator kinetics and habitual exercise training in older adults improves these responses relative to untrained older adults. Additionally, we examined the relationship between contraction-induced rapid onset vasodilation (ROV) and vasodilator kinetics. Young ( n = 10), older untrained ( n = 13), and older trained ( n = 14) adults performed single and rhythmic knee-extension contractions at 20% and 40% work-rate maximum (WR_max). Femoral artery diameter and mean blood velocity were measured by Doppler ultrasound. Vascular conductance (VC; ml·min^-1·mmHg^-1) was calculated using blood flow (ml/min) and mean arterial pressure (mmHg). The primary outcome was the kinetic response (mean response time; MRT), modeled using an exponential model, expressed as the number of duty cycles to change 63% of the steady-state amplitude. There were no age- or training-related differences in VC MRT between the groups at 20% WR_max. Older untrained adults exhibited prolonged VC MRT at 40% WR_max relative to young (37 ± 16 vs. 24 ± 10 duty-cycles; P < 0.05) and older trained adults (37 ± 16 vs. 23 ± 14 duty-cycles; P < 0.05). There were no differences in VC MRT between young and older trained adults at 40% WR_max ( P = 0.96). There were no associations between peak ROV and VC MRT at 20% or 40% WR_max ( r = -0.08 and 0.22; P = 0.67 and 0.20, respectively) in the group as a whole. Our data suggest 1) advancing age prolongs leg vasodilator kinetics; 2) habitual exercise training in older adults offsets this age-related prolongation; and 3) contraction-induced ROV is not related to vasodilator kinetics within a group of young and older adults. NEW & NOTEWORTHY Aging is associated with reductions in exercise hyperemia and vasodilation at the onset of exercise, as well as during steady-state exercise. Habitual endurance exercise training offsets these age-related reductions. We found that aging prolongs vasodilator kinetics in the leg of older untrained but not older trained adults. Finally, our results demonstrate that contraction-induced rapid vasodilation is not associated with vasodilator kinetics within the leg of young and older adults.

Sex differences in the oxygen delivery, extraction, and uptake during moderate-walking exercise transition

Previous studies in children and older adults demonstrated faster oxygen uptake (V̇O2) kinetics in males compared with females, but young healthy adults have not been studied. We hypothesized that young men would have faster aerobic system dynamics in response to the onset of exercise than women. Interactions between oxygen supply and utilization were characterized by the dynamics of V̇O2, deoxyhemoglobin (HHb), tissue saturation index (TSI), cardiac output (Q̇), and calculated arteriovenous O2 difference (a–vO2diff) in women and men. Eighteen healthy active young women and men (9 of each sex) with similar aerobic fitness levels volunteered for this study. Participants performed an incremental cardiopulmonary treadmill exercise test and 3 moderate-intensity treadmill exercise tests (at 80% V̇O2 of gas exchange threshold). Data related to the moderate exercise were submitted to exponential data modelling to obtain parameters related to the aerobic system dynamics. The time constants of V̇O2, a–vO2diff, HHb, and TSI (30 ± 6, 29 ± 1, 16 ± 1, and 15 ± 2 s, respectively) in women were statistically (p < 0.05) faster than the time constants in men (42 ± 10, 49 ± 21, 19 ± 3, and 20 ± 4 s, respectively). Although Q̇ dynamics were not statistically different (p = 0.06) between groups, there was a trend to slower Q̇ dynamics in men corresponding with the slower V̇O2 kinetics. These results indicated that the peripheral and pulmonary oxygen extraction dynamics were remarkably faster in women. Thus, contrary to the hypothesis, V̇O2 dynamics measured at the mouth at the onset of submaximal treadmill walking were faster in women compared with men.

Sympathetic nervous system activation reduces contraction-induced rapid vasodilation in the leg of humans independent of age

Contraction-induced rapid vasodilation is attenuated similarly in the upper and lower limbs of older adults. In the forearm, this attenuation is in part due to a greater sympathetic vasoconstriction. We examined whether the age-related reduction in contraction-induced vasodilation in the leg is also due to a sympathetic vasoconstrictive mechanism. Thirteen young (24 ± 1 yr) and twelve older adults (67 ± 1 yr) performed single-leg knee extension at 20 and 40% of work-rate maximum (WR_max) during control and cold-pressor test (CPT) conditions. Femoral artery diameter and blood velocity were measured using Doppler ultrasound. Vascular conductance (VC; ml·min^-1·mmHg^-1) was calculated using blood flow (ml/min) and mean arterial pressure (mmHg). Peak (ΔVC from baseline) and total VC were blunted in older adults during control conditions across exercise intensities (P < 0.05). Peak and total VC were reduced during CPT in both age groups across exercise intensities (P < 0.05). The relative change (i.e., %reduction; CPT vs. control) in peak (-25 ± 5 vs. -22 ± 4% at 20% WR_max; and -21 ± 6 vs. -27 ± 5% at 40% WR_max; P = 0.42-0.55) and total VC (-28 ± 5 vs. -36 ± 6% at 20% WR_max; and -22 ± 8 vs. -33 ± 5% at 40% WR_max; P = 0.23-0.34) were similar between young and older adults. When matched for absolute workload (~10 W), age differences persisted in peak VC (P < 0.05) under both conditions, with similar relative changes in peak and total VC during CPT. Our data suggest that 1) sympathetic stimulation reduces contraction-induced rapid vasodilation in the leg of young and older adults similarly; and 2) enhanced sympathetic vasoconstriction does not fully explain age-related differences in contraction-induced vasodilation within the leg.NEW & NOTEWORTHY Aging is associated with attenuated contraction-induced rapid onset vasodilation (ROV). Within the forearm, this attenuation is partially due to enhanced sympathetic vasoconstriction. In the current study, we found that sympathetic vasoconstriction reduces contraction-induced ROV within the leg of both young and older adults, with the magnitude of change being similar between age groups. Our current results suggest that age-related attenuations in contraction-induced ROV within the leg are not fully explained by a sympathetic vasoconstrictor mechanism.

Reliability of contrast-enhanced ultrasound for the assessment of muscle perfusion in health and peripheral arterial disease

We investigated the reliability of contrast-enhanced ultrasound (CEUS) in assessing calf muscle microvascular perfusion in health and disease. Response to a post-occlusive reactive hyperaemia test was repeated on two occasions >48 h apart in healthy young (28 ± 7 y) and elderly controls (70 ± 5 y), and in peripheral arterial disease patients (PAD, 69 ± 7 y; n = 10, 9 and 8 respectively). Overall, within-individual reliability was poor (coefficient of variation [CV] range: 15-87%); the most reliable parameter was time to peak (TTP, 15-48% CV). Nevertheless, TTP was twice as long in elderly controls and PAD compared to young (19.3 ± 10.4 and 22.0 ± 8.6 vs. 8.9 ± 6.2 s respectively; p < 0.01), and area under the curve for contrast intensity post-occlusion (a reflection of blood volume) was ∼50% lower in elderly controls (p < 0.01 versus PAD and young). Thus, CEUS assessment of muscle perfusion during reactive hyperaemia demonstrated poor reliability, yet still distinguished differences between PAD patients, elderly and young controls.

Hemodynamic responses during graded and constant-load plantar flexion exercise in middle-aged men and women with type 2 diabetes

We tested the hypotheses that type 2 diabetes (T2D) impairs the 1) leg hemodynamic responses to an incremental intermittent plantar-flexion exercise and 2) dynamic responses of leg vascular conductance (LVC) during low-intensity (30% maximal voluntary contraction, MVC) and high-intensity (70% MVC) constant-load plantar-flexion exercise in the supine posture. Forty-four middle-aged individuals with T2D (14 women), and 35 healthy nondiabetic (ND) individuals (18 women) were tested. Leg blood flow (LBF) was measured between each contraction using venous occlusion plethysmography. During the incremental test peak force (Fpeak) relative to MVC was significantly reduced ( P < 0.05) in men and women with T2D compared with their respective nondiabetic counterparts. Peak LBF and the slope of LBF relative to percentage Fpeak were also reduced ( P < 0.05) in women with T2D compared with healthy women (peak blood flow, 460.6 ± 126.8 vs. 628.3 ± 347.7 ml/min; slope, 3.78 ± 1.74 vs. 5.85 ± 3.14 ml·min−1·%Fpeak−1) and in men with T2D compared with nondiabetic men (peak blood flow, 621.7 ± 241.3 vs. 721.2 ± 359.7 ml/min; slope, 5.75 ± 2.66 vs. 6.33 ± 3.63 ml·min−1·%Fpeak−1). During constant-load contractions at 30% MVC T2D did not affect the dynamic responses of LVC (LBF/MAP). However, at 70% MVC [completed by a subgroup of participants (20 with T2D, 6 women; 13 ND, 6 women)] the time constant of the second growth phase of LVC was longer and the amplitude of the first growth phase was lower ( P < 0.05 for both) in men and women with T2D. The results suggest that the T2D-induced impairments in performance of the leg muscles are related to reductions in blood flow in both men and women.

Ultrasound elastography in children: establishing the normal range of muscle elasticity

BACKGROUND

Ultrasound elastography allows assessment of tissue elasticity. To the best of our knowledge, the elastography appearance of muscles in normal children has not been described.

OBJECTIVE

To determine the US elasticity of muscles in children at rest and following exercise.

MATERIALS AND METHODS

Cine elastography of biceps brachii and rectus femoris muscles was obtained at rest and after exercise in 42 healthy children (23 males, 19 females; mean: 11.2 ± 4.4 years, range: 2-18 years). Elastography scores were assigned to each clip based on a five-point color scale. Mean elastography scores and standard deviations were calculated and resting and postexercise elastography scores were compared.

RESULTS

Resting muscle elasticity was lower in the biceps brachii than in the rectus femoris (P = 0.008), and higher in the dominant than in the nondominant biceps brachii (P < 0.032). Rectus femoris elasticity was higher in males than females (P = 0.051). Postexercise muscle elasticity significantly increased in both the dominant and nondominant biceps brachii (P < 0.001) and in the rectus femoris (P < 0.001). There was no significant gender-related difference in postexercise muscle elasticity. Biceps brachii elasticity decreased and rectus femoris elasticity increased with increasing body mass index. Younger subjects had a greater change in muscle elasticity with exercise.

CONCLUSION

Resting muscle elasticity in children is significantly lower in the biceps brachii than in the rectus femoris and in the nondominant biceps brachii than in the dominant biceps brachii. Elasticity significantly increases immediately postexercise in both muscle groups; resting differences between biceps brachii and rectus femoris elasticity, and dominant and nondominant biceps brachii elasticity, do not persist after exercise. The change in muscle elasticity with exercise is higher in younger children.

Effect of altered arterial perfusion pressure on vascular conductance and muscle blood flow dynamic response during exercise in humans

Changes in vascular conductance (VC) are required to counter changes in muscle perfusion pressure (MPP) to maintain muscle blood flow (MBF) during exercise. We investigated the recruitment of VC as a function of peak VC measured in three body positions at two different work rates to test the hypothesis that adaptations in VC compensated changes in MPP at low-power output (LPO), but not at high-power output (HPO). Eleven healthy volunteers exercised at LPO and HPO (repeated plantar flexion contractions at 20–30% maximal voluntary contraction, respectively) in horizontal (HOR), 35° head-down tilt (HDT), and 45° head-up tilt (HUT). Muscle blood flow velocity and popliteal diameter were measured by ultrasound to determine MBF, and VC was estimated by dividing MBF flow by MPP. Peak VC was unaffected by body position. The rates of increase in MBF and VC were significantly faster in HUT and slower in HDT than HOR, and rates were faster in LPO than HPO. During LPO exercise, the increase in, and steady-state values of, MBF were less for HUT and HDT than HOR; the increase in VC was less in HUT than HOR and HDT. During HPO exercise, MBF in the HDT was reduced compared with HOR and HUT, even though VC reached 92% VC peak, which was greater than HOR, which was, in turn, greater than HUT. Reduced MBF during HPO HDT exercise had the functional consequence of a significant increase in muscle electromyographic index, revealing the effects of MPP on O2 delivery during exercise.

Effect of hypoxia on the dynamic response of hyperaemia in the contracting human calf muscle

Although systemic hypoxia increases the muscle hyperaemic response during 'steady-state' exercise, its effect on the dynamic characteristics of this response is not clear. In the present study, we first established that hypoxia increases the steady-state hyperaemic response at low workloads during calf exercise. To study dynamic aspects of this response, eight subjects performed eight exercise trials while breathing a normoxic (fractional inspired O(2) = 0.2094) or hypoxic gas mixture (fractional inspired O(2) = 0.105). Subjects performed intermittent contractions (1 s) of the calf muscle at 20% maximal voluntary contraction, and the leg blood flow (LBF), leg vascular conductance (LVC) and EMG activities of the triceps surae muscles were measured during each contraction-relaxation period (3 s). The LBF and LVC responses were averaged for each subject and fitted using a four-phase, exponential growth and decay function. Hypoxia evoked significant increases in the change in LBF (15%) and LVC (23%) from the start to the end of exercise, as well as the amplitude of the rapid growth phase of LBF and LVC (21%). Similar, but non-significant, effects on the amplitude of the slow growth phase of LBF (P = 0.08) and LVC (P = 0.10) were observed. By contrast, hypoxia had no effect on temporal parameters of these growth phases, parameters defining the decay phases or EMG activities. These results suggest that the effect of hypoxia on exercise hyperaemia is targeted at the rapid and perhaps the slow growth phase of the response, and is not mediated by a change in the level of muscle activation.

Effect of type 2 diabetes on the dynamic response characteristics of leg vascular conductance during exercise

In this study we tested the hypothesis that type 2 diabetes impairs the dynamic response of leg vascular conductance (LVC) during exercise. LVC (leg blood flow/mean arterial pressure) responses were studied during intermittent contractions of the calf muscle in subjects with type 2 diabetes (n = 9), heavy controls (n = 10) and lean controls (n = 8) using a biexponential function and an estimate of the mean response time (MRT). The time constant of the second phase of LVC was significantly greater in type 2 diabetes (66.4 ± 29.2 s) than the heavy (22.2 ± 13.4 s) and lean (21.8 ± 9.3 s) controls, resulting in a significantly greater MRT in the diabetic group (median [IQR] = 30.7 [24.6-46.5] s versus 16.3 [4.3-23.2] s and 18.4 [13.7-19.3] s). These data support the hypothesis and suggest that a slowed hyperaemic response in the exercising limb might contribute to exercise intolerance in diabetic subjects.

Massage impairs postexercise muscle blood flow and "lactic acid" removal

PURPOSE

This study tested the hypothesis that one of the ways sports massage aids muscle recovery from exercise is by increasing muscle blood flow to improve "lactic acid" removal.

METHODS

Twelve subjects performed 2 min of strenuous isometric handgrip (IHG) exercise at 40% maximum voluntary contraction to elevate forearm muscle lactic acid. Forearm blood flow (FBF; Doppler and Echo ultrasound of the brachial artery) and deep venous forearm blood lactate and H+ concentration ([La-], [H+]) were measured every minute for 10 min post-IHG under three conditions: passive (passive rest), active (rhythmic exercise at 10% maximum voluntary contraction), and massage (effleurage and pétrissage). Arterialized [La-] and [H+] from a superficial heated hand vein was measured at baseline.

RESULTS

Data are presented as mean +/- SE. Venoarterial [La-] difference ([La-]v-a) at 30 s of post-IHG was the same across conditions (passive = 6.1 +/- 0.6 mmol x L(-1), active = 5.7 +/- 0.6 mmol x L(-1), massage = 5.5 +/- 0.6 mmol x L(-1), NS), whereas FBF was greater in passive (766 +/- 101 mL x min(-1)) versus active (614 +/- 62 mL x min(-1), P = 0.003) versus massage (540 +/- 60 mL x min(-1), P < 0.0001). Total FBF area under the curve (AUC) for 10 min after handgrip was significantly higher in passive versus massage (4203 +/- 531 vs 3178 +/- 304 mL, P = 0.024) but not versus active (3584 +/- 284 mL, P = 0.217). La(-)- efflux (FBF x [La-]v-a) AUC mirrored FBF AUC (passive = 20.5 +/- 2.8 mmol vs massage = 14.7 +/- 1.6 mmol, P = 0.03, vs active = 15.4 +/- 1.9 mmol, P = 0.064). H+ efflux (FBF x [H+]v-a) was greater in passive versus massage at 30 s (2.2 +/- 0.4e(-5) vs 1.3 +/- 0.2e(-5) mmol, P < 0.001) and 1.5 min (1.0 +/- 0.2e(-5) vs 0.6 +/- 0.09e(-5) mmol, P = 0.003) after IHG.

CONCLUSIONS

Massage impairs La(-) and H+ removal from muscle after strenuous exercise by mechanically impeding blood flow.

Alpha-adrenergic control of blood flow during exercise: effect of sex and menstrual phase

Sex differences exist in autonomic control of the cardiovascular system. This study was designed to directly test sex or female menstrual phase-related differences in α-adrenergic control of blood flow during exercise. We hypothesized that women would exhibit reduced α-adrenergic vasoconstriction compared with men during exercise; in addition, women would constrict less during the early luteal than the early follicular phase of the female menses. Young men (n = 10) were studied once and women (n = 9) studied twice, once during the early follicular phase and once during the early luteal phase of female menses. We measured forearm blood flow (FBF; Doppler ultrasound of the brachial artery) during rest and steady-state dynamic exercise (15 and 30% of maximal voluntary contraction, 20 contractions/min). A brachial artery catheter was inserted for the local administration of α-adrenergic agonists [phenylephrine (PE; α(1)) or clonidine (CL; α(2))]. Blood flow responses to exercise [forearm vascular conductance (FVC)] were similar between all groups. At rest, infusion of PE or CL decreased FVC in all groups (40-60% reduction). Vasoconstriction to PE was abolished in all groups at 15 and 30% exercise intensity. Vasoconstriction to CL was reduced at 15% and abolished at 30% intensity in all groups; women had less CL-induced constriction during the early luteal than early follicular phase (P < 0.017, 15% intensity). These results indicate that vasodilator responses to forearm exercise are comparable between men and women and are achieved through similar paths of α-adrenergic vascular control at moderate intensities; this control may differ at low intensities specific to the female menstrual phase.

Plasma ATP concentration and venous oxygen content in the forearm during dynamic handgrip exercise

Background

It has been proposed that adenosine triphosphate (ATP) released from red blood cells (RBCs) may contribute to the tight coupling between blood flow and oxygen demand in contracting skeletal muscle. To determine whether ATP may contribute to the vasodilatory response to exercise in the forearm, we measured arterialised and venous plasma ATP concentration and venous oxygen content in 10 healthy young males at rest, and at 30 and 180 seconds during dynamic handgrip exercise at 45% of maximum voluntary contraction (MVC).

Results

Venous plasma ATP concentration was elevated above rest after 30 seconds of exercise (P < 0.05), and remained at this higher level 180 seconds into exercise (P < 0.05 versus rest). The increase in ATP was mirrored by a decrease in venous oxygen content. While there was no significant relationship between ATP concentration and venous oxygen content at 30 seconds of exercise, they were moderately and inversely correlated at 180 seconds of exercise (r = -0.651, P = 0.021). Arterial ATP concentration remained unchanged throughout exercise, resulting in an increase in the venous-arterial ATP difference.

Conclusions

Collectively these results indicate that ATP in the plasma originated from the muscle microcirculation, and are consistent with the notion that deoxygenation of the blood perfusing the muscle acts as a stimulus for ATP release. That ATP concentration was elevated just 30 seconds after the onset of exercise also suggests that ATP may be a contributing factor to the blood flow response in the transition from rest to steady state exercise.

Femoral artery blood flow and its relationship to spontaneous fluctuations in rhythmic thigh muscle workload

BACKGROUND AND AIM

Limb femoral arterial blood flow (LBF) is known to increase linearly with increasing workload under steady-state conditions, suggesting a close link between LBF and metabolic activity. We, however, hypothesized that sudden physiological and spontaneous changes in exercise rhythm, and consequently workload temporarily alter blood flow to the working muscle. LBF and its relation to fluctuations in the contraction rhythm and workload were therefore investigated.

METHODS

LBF, measured by Doppler ultrasound, and the achieved workload, were continuously measured in nine subjects, aiming to perform steady-state, one-legged, dynamic knee-extensor exercise at 30 and 60 contractions per minute (cpm), at incremental target workloads of 10, 20, 30 and 40 W.

RESULTS

In agreement with previous findings, LBF increased positively and linearly (P<0.05) with increasing target workload. However, LBF was inversely and linearly related (P<0.05) to the actually achieved workload, when measured over 60 consecutive contraction-relaxation cycle bouts, for each target intensity at 30 and 60 cpm respectively. Thus any sudden spontaneous increase or decrease in the achieved workload transiently altered the relationship between LBF and the achieved workload. The influence upon the magnitude of LBF, due to fluctuations in the achieved workload from the target workload, was furthermore similar between target workload sessions at 30 and 60 cpm respectively. LBF was, however, not associated with variations in the contraction frequencies.

CONCLUSIONS

These findings indicate that a transient sudden increase in the workload more rapidly impedes LBF and that vasodilatation may be elicited to restore the intensity related steady-state LBF response in relation to the average metabolic activity.

Stroke volume decreases during mild dynamic and static exercise in supine humans

AIM

The contributions of cardiac output (CO) and total peripheral resistance to changes in arterial blood pressure are debated and differ between dynamic and static exercise. We studied the role stroke volume (SV) has in mild supine exercise.

METHODS

We investigated 10 healthy, supine volunteers by continuous measurement of heart rate (HR), mean arterial blood pressure, SV (ultrasound Doppler) and femoral beat volume (ultrasound Doppler) during both dynamic mild leg exercise and static forearm exercise. This made it possible to study CO, femoral flow (FF) and both total and femoral peripheral resistance beat-by-beat.

RESULTS

During a countdown period immediately prior to exercise, HR and mean arterial pressure increased, while SV decreased. During mild supine exercise, SV decreased by 5-8%, and most of this was explained by increased mean arterial pressure. Dynamic leg exercise doubled femoral beat volume, while static hand grip decreased femoral beat volume by 18%. FF is tightly regulated according to metabolic demand during both dynamic leg exercise and static forearm exercise.

CONCLUSION

Our three major findings are, firstly, that SV decreases during both dynamic and static mild supine exercise due to an increase in mean arterial pressure. Secondly, femoral beat volume decreases during static hand grip, but FF is unchanged due to the increase in HR. Finally, anticipatory responses to exercise are apparent prior to both dynamic and static exercise. SV changes contribute to CO changes and should be included in studies of central haemodynamics during exercise.

Metabolic and Vascular Limb Differences Affected by Exercise, Gender, Age, and Disease

PURPOSE

We studied previously resistance-trained men and compared the effects of concentric and eccentric training on performance and structural muscle parameters.

METHODS

Seventeen trained individuals (age 26.9 +/- 3.4 yr) participated in 12 wk of either maximum concentric (N = 8) or eccentric (N = 9) resistance training of the elbow flexors. The functional performance was measured as the maximum concentric and eccentric strength and angular velocity at standard loads. Muscle cross-sectional area and cross-sectional area of single cells were used as measures of muscular hypertrophy. Fiber-type proportions were assessed by staining cells for myofibrillar ATPase.

RESULTS

Both eccentric and concentric training increased concentric strength to a similar extent (14 vs 18%), whereas eccentric training led to greater increases in eccentric strength than concentric training did (26 vs 9%). The maximum angular velocity at all loads was enhanced equally in both training groups. The cross-sectional area of both the elbow flexors (+11%) and of the type I and type IIA fibers increased only after the eccentric training. In addition, the relative cross-sectional area occupied by the type II fibers increased from 64 to 73% after the eccentric training. There were only minor changes in the fiber-type proportions.

CONCLUSION

The present data suggest that for resistance-trained men, increases in concentric strength and velocity performance after eccentric training are largely mediated by changes in fiber and muscle cross-sectional area. However, hypertrophy alone could not explain the increase in eccentric strength. Because the increases in strength and velocity performance after concentric training could not be ascribed to muscular adaptations alone, we suggest that they may be attributable to additional neural factors.