Inactive Leg Research Articles

Cardiovascular responses to combined mechanoreflex and metaboreflex activation in healthy adults: effects of sex and low- versus high-hormone phases in females.

Females generally have smaller blood pressure (BP) responses to isolated muscle mechanoreflex and metaboreflex activation compared with males, which may explain sex differences in BP responses to voluntary exercise. The mechanoreflex may be sensitized during exercise, but whether mechanoreflex-metaboreflex interactions differ by sex or variations in sex hormones remains unknown. Thirty-one young healthy subjects (females, n = 16) performed unilateral passive cycling (mechanoreflex), active cycling (40% peak Watts), postexercise circulatory occlusion (PECO; metaboreflex), and passive cycling combined with PECO (combined mechanoreflex and metaboreflex activation). Beat-to-beat BP, heart rate, inactive leg vascular conductance, and active leg muscle oxygenation were measured. Ten females underwent exploratory testing during low- and high-hormone phases of their self-reported menstrual cycle or oral contraceptive use. Systolic BP and heart rate responses did not differ between sexes during active cycling [Δ30 ± 9 vs. 29 ± 11 mmHg (males vs. females), P = 0.9; Δ33 ± 8 vs. 35 ± 6 beats/min, P = 0.4] or passive cycling with PECO (Δ26 ± 11 vs. 21 ± 10 mmHg, P = 0.3; Δ14 ± 7 vs. 18 ± 15 beats/min, P = 0.3). Passive cycling with PECO revealed additive, not synergistic, effects for systolic BP [males: Δ23 ± 14 vs. 26 ± 11 mmHg (sum of isolated passive cycling and PECO vs. combined activation); females: Δ26 ± 11 vs. 21 ± 12 mmHg, interaction P = 0.05]. Results were consistent in subset analyses with sex differences in active cycling BP (P > 0.1) and exploratory analyses of hormone phase (P > 0.4). Despite a lack of statistical equivalence, no differences in cardiovascular responses were found during combined mechanoreflex-metaboreflex activation between sexes or hormone levels. These results provide preliminary data regarding the involvement of muscle mechanoreflex-metaboreflex interactions in mediating sex differences in voluntary exercise BP responses.NEW & NOTEWORTHY The muscle mechanoreflex may be sensitized by metabolites during exercise. We show that cardiovascular responses to combined mechanoreflex (passive cycling) and metaboreflex (postexercise circulatory occlusion) activation are primarily additive and do not differ between males and females, or across variations in sex hormones in females. Our findings provide new insight into the contributions of muscle mechanoreflex-metaboreflex interactions as a cause for prior reports that females have smaller blood pressure responses to voluntary exercise.

One-leg inactivity induces a reduction in mitochondrial oxidative capacity, intramyocellular lipid accumulation and reduced insulin signalling upon lipid infusion: a human study with unilateral limb suspension

Aims/hypothesisPhysical inactivity, low mitochondrial function, increased intramyocellular lipid (IMCL) deposition and reduced insulin sensitivity are common denominators of chronic metabolic disorders, like obesity and type 2 diabetes. Yet, whether low mitochondrial function predisposes to insulin resistance in humans is still unknown.MethodsHere we investigated, in an intervention study, whether muscle with low mitochondrial oxidative capacity, induced by one-legged physical inactivity, would feature stronger signs of lipid-induced insulin resistance. To this end, ten male participants (age 22.4 ± 4.2 years, BMI 21.3 ± 2.0 kg/m2) underwent a 12 day unilateral lower-limb suspension with the contralateral leg serving as an active internal control.ResultsIn vivo, mitochondrial oxidative capacity, assessed by phosphocreatine (PCr)-recovery half-time, was lower in the inactive vs active leg. Ex vivo, palmitate oxidation to 14CO2 was lower in the suspended leg vs the active leg; however, this did not result in significantly higher [14C]palmitate incorporation into triacylglycerol. The reduced mitochondrial function in the suspended leg was, however, paralleled by augmented IMCL content in both musculus tibialis anterior and musculus vastus lateralis, and by increased membrane bound protein kinase C (PKC) θ. Finally, upon lipid infusion, insulin signalling was lower in the suspended vs active leg.Conclusions/interpretationTogether, these results demonstrate, in a unique human in vivo model, that a low mitochondrial oxidative capacity due to physical inactivity directly impacts IMCL accumulation and PKCθ translocation, resulting in impaired insulin signalling upon lipid infusion. This demonstrates the importance of mitochondrial oxidative capacity and muscle fat accumulation in the development of insulin resistance in humans.Trial registrationClinicalTrial.gov NCT01576250.FundingPS was supported by a ‘VICI’ Research Grant for innovative research from the Netherlands Organization for Scientific Research (Grant 918.96.618).

Possibilities of Using the Angular Navigation Equipment for Space Rockets

The paper discusses the possibilities of using the navigation user equipment on the basis of determining the angular position of space rockets in flight taking into account the special features of the control process. The task statement is given on clarifying the angular position on the active trajectory leg and identifying the abnormal operation of the meters of inertial navigation systems on the inactive trajectory leg of the space rockets using navigation user equipment. Methodological ways for solving the tasks are proposed and substantiated.

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.

Effect of Time of Day on Sustained Postexercise Vasodilation Following Small Muscle-Mass Exercise in Humans.

IntroductionPrevious studies observed diurnal variation in hemodynamic responses during recovery from whole-body exercise, with vasodilation appearing greater after evening versus morning sessions. It is unclear what mechanism(s) underlie this response. Since small muscle-mass exercise can isolate peripheral effects related to postexercise vasodilation, it may provide insight into possible mechanisms behind this diurnal variation.MethodsThe study was conducted in ten healthy (5F, 5M) young individuals, following single-leg dynamic knee-extension exercise performed in the Morning (7:30–11:30 am) or the Evening (5–9 pm) on two different days, in random order. Arterial pressure (automated auscultation) and leg blood flow (femoral artery Doppler ultrasound) were measured pre-exercise and during 120 min postexercise. Net effect for each session was calculated as percent change in blood flow (or vascular conductance) between the Active Leg and the Inactive Leg.ResultsFollowing Morning exercise, blood flow was 34.9 ± 8.9% higher in the Active Leg versus the Inactive Leg (p < 0.05) across recovery. Following Evening exercise, blood flow was 35.0 ± 8.8% higher in the Active Leg versus the Inactive Leg (p < 0.05). Likewise, vascular conductance was higher in the Active Leg versus the Inactive Leg (Morning: +35.1 ± 9.0%, p < 0.05; Evening: +33.2 ± 8.2%, p < 0.05). Morning and Evening blood flow (p = 0.66) and vascular conductance (p = 0.64) did not differ.ConclusionThese data suggest previous studies which identified diurnal variations in postexercise vasodilation responses are likely reflecting central rather than peripheral modulation of cardiovascular responses.

Effects of Dynamic Arm and Leg Exercise on Muscle Sympathetic Nerve Activity and Vascular Conductance in the Inactive Leg

The aim of this study was to comprehensively assess the effects of rhythmic handgrip (RHG), one‐leg cycling, and concurrent arm and leg exercise on muscle sympathetic nerve activity (MSNA) and vascular conductance responses in the inactive leg. Thirty‐five participants completed two study visits in a randomized order. During visit 1, hemodynamic (Finometer) and superficial femoral artery (SFA) blood flow (Doppler ultrasound) measurements were assessed at rest and during 3 min of RHG (1:1 duty cycle; 40% MVC), one‐leg cycling (17 ± 3% peak power output), and concurrent exercise at the same intensities. During visit 2, hemodynamic and MSNA (fibular nerve microneurography) measurements were acquired during the same exercise modes (MSNA; n=12). SFA blood flow and MSNA were both acquired in the inactive leg. Heart rate, blood pressure, cardiac output, and respiration rate increased during each exercise mode (all, P&lt;0.0001), with the largest increases during concurrent exercise (all, P&lt;0.006); no differences were detected between visit 1 and 2 (all, P&gt;0.05). SFA mean blood flow increased during RHG (Δ24 ± 30 ml/min, P&lt;0.0001) and concurrent exercise (Δ10 ± 38 ml/min, P=0.03) but not cycling (Δ2.3 ± 30 ml/min, P=0.9). SFA vascular conductance was unchanged during RHG (Δ0.02 ± 0.29 ml·min−1·mmHg−1, P=0.9) but reduced similarly during concurrent and cycling exercise (Δ−0.14 ± 0.33 ml·min−1·mmHg−1; Δ−0.14 ± 0.38 ml·min−1·mmHg−1, P&lt;0.003). RHG increased MSNA burst frequency (Δ4 ± 8 burst/min, P=0.04) without altering burst amplitude (Δ7 ± 14 %, P=0.7) or total MSNA (Δ40 ± 40 %, P=0.07). In contrast, cycling and concurrent exercise had no effects on MSNA burst frequency (Δ−3 ± 6 burst/min and Δ4 ± 6 burst/min, P≥0.1) but increased burst amplitude (Δ34 ± 30 %; Δ31 ± 31 %, P≤0.001) and total MSNA (Δ59 ± 63 %; Δ94 ± 100 %, P≤0.007). In conclusion, during one‐leg cycling or concurrent exercise, reductions in inactive leg SFA vascular conductance occurred in parallel with increases in burst amplitude and total MSNA but not burst frequency. Exercise studies relying solely on measures of MSNA burst occurrence may not accurately reflect the corresponding changes in vascular conductance.Support or Funding InformationResearch was supported by a Natural Science and Engineering Research Council (NSERC) of Canada Discovery Grant (P.J.M; #06019), the Canada Foundation for Innovation (P.J.M.; #34379), and the Ontario Ministry of Research, Innovation, and Science (P.J.M. #34379).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Active and Inactive Leg Hemodynamics during Sequential Single-Leg Interval Cycling.

Leg order during sequential single-leg cycling (i.e., exercising both legs independently within a single session) may affect local muscular responses potentially influencing adaptations. This study examined the cardiovascular and skeletal muscle hemodynamic responses during double-leg and sequential single-leg cycling. Ten young healthy adults (28 ± 6 yr) completed six 1-min double-leg intervals interspersed with 1 min of passive recovery and, on a separate occasion, 12 (six with one leg followed by six with the other leg) 1-min single-leg intervals interspersed with 1 min of passive recovery. Oxygen consumption, heart rate, blood pressure, muscle oxygenation, muscle blood volume, and power output were measured throughout each session. Oxygen consumption, heart rate, and power output were not different between sets of single-leg intervals, but the average of both sets was lower than the double-leg intervals. Mean arterial pressure was higher during double-leg compared with sequential single-leg intervals (115 ± 9 vs 104 ± 9 mm Hg, P < 0.05) and higher during the initial compared with second set of single-leg intervals (108 ± 10 vs 101 ± 10 mm Hg, P < 0.05). The increase in muscle blood volume from baseline was similar between the active single leg and the double leg (267 ± 150 vs 214 ± 169 μM·cm, P = 0.26). The pattern of change in muscle blood volume from the initial to second set of intervals was significantly different (P < 0.05) when the leg was active in the initial (-52.3% ± 111.6%) compared with second set (65.1% ± 152.9%). These data indicate that the order in which each leg performs sequential single-leg cycling influences the local hemodynamic responses, with the inactive muscle influencing the stimulus experienced by the contralateral leg.

Abstract 15456: Enhanced Vasoconstrictor Sensitivity to Exercise Pressor Reflex Engagement in Peripheral Artery Disease

Exercise is associated with a rise in heart rate, blood pressure (BP) and blood flow to active skeletal muscle that is mediated by the exercise pressor reflex and modified by regional release of vasodilator factors. In peripheral artery disease (PAD) the exercise pressor reflex is enhanced and the ability to raise blood flow to the affected limb is impaired. To assess the functional impact of the enhanced exercise pressor reflex on regional blood flow in limbs affected by PAD, we determined beat-by-beat BP and mean blood velocity (MBV, Doppler) in the popliteal artery, and calculated vascular conductance index (VC, MBV/mean BP) in the exercising (ipsilateral) or contralateral resting leg during graded rhythmic plantar flexion exercise in 7 patients with symptomatic PAD (age 67±2 yrs, body-mass-index 27.9±1.1) and in 5 healthy age-matched controls (2 exercise trials with each leg). At peak exercise (2.0 kg, 1 contraction/sec), the pressor effect was greatest in PAD when exercise was performed with the “ischemic” leg (ankle-brachial index 0.58±0.05; mean ΔBP +9.1±2.0 mmHg), lower with the less affected leg (ankle brachial index 0.76±0.07; mean ΔBP +6.9±1.6 mmHg) and lowest in the controls (ankle brachial index 1.11±0.04; mean ΔBP +3.9±1.8 mmHg). In controls, VC increased in the exercising leg ( P &lt;0.05) but did not change in the inactive contralateral leg ( P =NS). Similarly, in PAD, VC increased in the exercising “ischemic” leg ( P &lt;0.05) but did not change in the inactive contralateral leg ( P =NS). In sharp contrast, while VC increased in the less affected exercising leg ( P &lt;0.05), in the contralateral resting “ischemic” leg VC decreased by 24±10% ( P &lt;0.05). Similarly, when static handgrip at 30% maximum voluntary contraction to fatigue served as the exercise stimulus, vasoconstriction was noted in the “ischemic” leg (n=5; P &lt;0.05). Thus, unlike in the exercising leg, in the resting “ischemic” leg activation of the exercise pressor reflex resulted in substantial vasoconstriction. This suggests that despite activation of peripheral vasodilator mechanisms downstream to the arterial obstruction, the vasculature of the “ischemic” leg is exquisitely sensitive to reflex vasoconstriction.

Enhanced vasoconstrictor sensitivity to exercise pressor reflex engagement in peripheral arterial disease (1156.7)

Exercise is associated with a rise in heart rate, blood pressure (BP) and blood flow to active muscle mediated by the exercise pressor reflex and regional release of vasodilators. In peripheral arterial disease (PAD) the exercise pressor reflex is enhanced. To assess the functional impact of the exercise pressor reflex, we determined BP and mean blood velocity (MBV, Doppler) in the popliteal artery and calculated vascular conductance (VC, MBV/mean BP) in the exercising and contralateral legs during graded rhythmic plantar flexion in 7 patients with PAD (age 67±2 yrs, ankle‐brachial‐index 0.6±0.1 in the ischemic leg) and in 5 controls. At peak exercise (2.0 kg, 1 Hz), the pressor effect was greatest in PAD when exercise was performed with the ischemic leg, and lowest in the controls. In controls, exercise did not affect VC in the contralateral inactive leg (P=NS). Similarly, in PAD, exercise in the ischemic leg did not affect VC in the opposite inactive leg (P=NS). In contrast, during exercise with the non‐ischemic leg, VC in the contralateral ischemic leg decreased by 24±10% (P&lt;0.05). Thus, activation of the exercise pressor reflex resulted in vasoconstriction in the inactive but diseased leg. This suggests that despite upregulation of peripheral vasodilator factors, the vasculature of the ischemic leg is exquisitely sensitive to reflex vasoconstriction.Grant Funding Source: Supported by P01 HL096570 and UL1 TR000127

Age and microvascular responses to knee extensor exercise in women

This study examined the relation between femoral artery hyperemic responses to leg exercise and microvascular oxygen extraction in nine young [(mean +/- S.E.M) Y: 25 +/- 1 years] and 13 older (O: 67 +/- 1 years) healthy women. Femoral artery blood flow (FBF; Doppler ultrasound), mean arterial pressure (MAP), and femoral vascular conductance (FVC; FBF/MAP) were assessed at rest and during 9 min of approximately 17-18 W single knee extensor exercise. Near-infrared spectroscopy (NIRS) in the vastus lateralis was used to measure changes in deoxyhemoglobin (HHb) and oxyhemoglobin (O(2)Hb) to assess oxygen extraction (Delta HHb), microvascular blood volume (Delta HHb + O(2)Hb), and spatial heterogeneity of blood volume (relative dispersion, defined as the coefficient of variation of measurements from all NIR sensors). During exercise, FBF and FVC were lower (p < 0.05) in O compared to Y (Y: 1,430 +/- 101 mL min(-1) and 16.6 +/- 1.2 mL min(-1) per mmHg versus O: 1,127 +/- 64 mL min(-1) and 10.9 +/- 0.6 mL min(-1)per mmHg). While oxygen extraction increased more rapidly in Y, there were no age differences (p > 0.10) beyond the fourth min of exercise. In addition, the relative increase in microvascular blood volume was not significantly different during exercise in Y versus O (age effect: p = 0.87), although Y demonstrated an increase in blood volume heterogeneity in both the active and inactive leg (p = 0.02 and <0.05, respectively) not observed in O (p = 0.71 and 0.28, respectively). NIRS-derived measurements of changes in deoxygenated hemoglobin do not support the hypothesis that older women compensate for the blunted leg hyperemic response to knee extensor exercise through an augmentation of quadriceps oxygen extraction; knee extensor work may be accomplished by other metabolic or microvascular adjustments to exercise in older women.

Cross-Education After One Session of Unilateral Surface Electrical Stimulation of the Rectus Femoris

Thirty-six adult men were randomly assigned to a remote stimulation group (RS; n = 18) or control group (CTL; n = 18). The RS group unilaterally performed a 10-minute surface electrical stimulation program (frequency 100 Hz, impulse 300 micros, 10 seconds on/10 seconds off) on the rectus femoris of the non-dominant leg. The subjects of the CTL group relaxed for 10 minutes without performing any training. Immediately before and after the surface electrical stimulation program, the isometric strength and the electromyographic (EMG) and mechanomyographic (MMG) response of the dominant leg was measured for all subjects. The dominant leg of the RS group showed a significant increase in the isometric force (5.11%; P < 0.001) and EMG activity of the agonist muscle (4.67%; P < 0.05), whereas a decrease in EMG activity of the antagonist muscles was observed (-10.27%; P < 0.05). The MMG activity did not show any alteration. No significant changes were observed for the CTL group. These results indicate that one unilateral surface electrical stimulation session on the rectus femoris improves the efficiency of the inactive leg. At a practical level, the results open a new way to rehabilitate muscle-skeletal injuries, especially weak members that cannot do any physical work. In this case, the muscle strength (and physical efficiency) can be improved by passive electrostimulation training on the healthy member.

Comment on Point:Counterpoint “The muscle metaboreflex does/does not restore blood flow to contracting muscles”

The following letters are in response to the Point:Counterpoint series “The muscle metaboreflex does/does not restore blood flow to contracting muscles” that appeared in the January issue (vol. 100: 357–361, 2006; ). To the Editor : This letter

Blood flow response to electrically induced twitch and tetanic lower-limb muscle contractions

Janssen TW, Hopman MT. Blood flow response to electrically induced twitch and tetanic lower-limb muscle contractions. Arch Phys Med Rehabil 2003;84:982–7. Objectives:To compare the effect of electric stimulation (ES)-induced twitch with tetanic leg muscle contractions on blood flow responses and to assess blood flow responses in the contralateral inactive leg. Design:Intervention with within-subject comparisons. Setting:University research laboratory. Participants:A volunteer sample of 12 healthy men (mean age, 25.1±3.0y). Intervention:ES was applied at 1 and 3Hz to induce twitch contractions and at 35Hz to induce tetanic contractions of the lower- and upper-leg muscles. Exercise periods consisted of ES/rest cycles (6s/20s) for 5 minutes. Main Outcome Measures:Blood flow velocity changes measured by echo Doppler ultrasonography at rest and during the first 2 subsequent ES cycles. Results:Blood flow significantly increased from resting values for the tetanic 2-leg, tetanic 1-leg, and 3-Hz conditions, but not for the 1-Hz twitch condition or in the inactive leg. Conclusions:Both tetanic and 3-Hz twitch contractions, but not 1-Hz twitch contractions, increased leg blood flow in humans. Because blood flow elevations induced by the 3-Hz contractions did not differ statistically from those induced by the tetanic contractions but were realized with less discomfort, this mode is preferable for therapeutic interventions. Because stimulation of the ipsilateral leg muscles did not change blood flow in the contralateral inactive leg, the muscles in the area of desired effect must be stimulated.

Exercise.

Exercise.

Lactate and H+ uptake in inactive muscles during intense exercise in man.

1. The present study examined how uptake of lactate and H+ in resting muscle is affected by blood flow, arterial lactate concentration and muscle metabolism. 2. Six males subjects performed intermittent arm exercise in two separate 32 min periods (Part I and Part II) and in one subsequent 20 min period in which one leg knee-extensor exercise was also performed (Part III). The exercise was performed at various intensities in order to obtain different steady-state arterial blood lactate concentrations. In the inactive leg, femoral venous blood flow (draining about 7.7 kg of muscles) was measured and femoral arterial and venous blood was collected frequently. Biopsies were taken from m. vastus lateralis of the inactive leg at rest and 10 and 30 min into both Part I and Part II as well as 10 min into recovery from Part II. 3. The arterial plasma lactate concentrations were 7, 9 and 16 mmol l-1 after 10 min of Parts I, II and III, respectively, and the corresponding arterial-venous difference (a-vdiff) for lactate in the resting leg was 1.3, 1.4 and 2.0 mmol l-1. The muscle lactate concentration was 2.8 mmol (kg wet wt)-1 after 10 min of Part I and remained constant throughout the experiment. During Parts I and II, a-vdiff lactate decreased although the arterial lactate concentration and plasma-muscle lactate gradient were unaltered throughout each period. Thus, membrane transport of lactate decreased during each period. 4. Blood flow in the inactive leg was about 2-fold higher during arm exercise compared to the rest periods, resulting in a 2-fold higher lactate uptake. Thus, lactate uptake by inactive muscles was closely related to blood flow. 5. Throughout the experiment a-vdiff for actual base excess and for lactate were of similar magnitude. Thus, in inactive muscles lactate uptake appears to be coupled to the transport of H+.

Cardiovascular and metabolic responses to static contraction in man

There is substantial controversy regarding muscle blood flow and its regulation during static exercises. Major issues include (1) the relationship between developed force and muscle blood flow, (2) the ability of metabolic vasodilation to overcome neurally mediated vasoconstriction, (3) the time course and magnitude of hyperaemic flow following static exercise and (4) blood flow to the contralateral inactive limb. At rest, 15, 25 and 50% maximal voluntary contractions (MVC) femoral venous flow in four healthy young men (LBF; mean +/- 1 SD) was 0.4 +/- 0.3, 1.76 +/- 0.65, 0.90 +/- 0.32 and 1.06 +/- 0.59 1 min-1, and mean arterial pressures (MAP) were 104 +/- 13, 140 +/- 14, 160 +/- 17 and 161 +/- 11 mmHg. Thus, LBF does not increase proportionally with increasing levels of MVC, despite increased arterial pressure. Further, during both 25 and 50% MVC, which were held to exhaustion, an elevated limb vascular resistance was encountered towards the end of contraction, which suggests that neurally mediated vasoconstrictor activity overrides local vasodilation. Femoral venous effluent documented perfusion of active muscle during contractions of 15 and 25% MVC, but less so at 50% MVC. Immediately in recovery LBF reached levels of 3-3.5 1 min-1, which corresponded to 150 ml 100 g-1 min-1. When both O2 uptake and lactate release during the contractions and in recovery were taken into account, a close correlation between rate of energy turnover and exerted force was found. When MAP was raised by static contraction of the opposite quadriceps, LBF in the inactive leg increased momentarily. Within 1 min vascular resistance became elevated and the blood flow became reduced.

Injuries to Athletes with Physical Disabilities: Prevention Implications.

In brief: While athletes with disabilities may not be injured any more often than the able-bodied, the types of injuries they sustain are specific to their disabilities and sports. Wheelchair athletes, for example, are especially susceptible to hypothermia and hyperthermia due to their inactive leg muscles, vasomotor paralysis, and reduced evaporative heat loss and cooling. This review of current literature reveals that high-risk sports are track and field, basketball, and road racing, with soft-tissue injuries the most common among wheelchair athletes. Carpal tunnel syndrome is also a characteristic injury. Many preventive measures are suggested, including prescription of sport chairs tailored to an athlete's body type, disability, and sport.

Activation by exercise of human skeletal muscle pyruvate dehydrogenase in vivo.

1. The activity of pyruvate dehydrogenase in its active and inactive forms was measured in biopsy samples obtained from the vastus lateralis muscle of healthy subjects before and after exercise. 2. At rest, 40 +/- 4% (mean +/- SEM) of the enzyme was in the active form. 3. After progressive aerobic exercise to exhaustion (n = 5), 88 +/- 2.3% was in the active form. 4. After intermittent supramaximal short-term exercise (1 min exercise, 3 min rest) to exhaustion (n = 6), 60 +/- 2.2% was in the active form. 5. After isometric maximal exercise of 65 +/- 3.6 s duration (n = 3), only 39 +/- 1% of the enzyme was in the active form. 6. Muscle glycogen depletion was greatest with intermittent exercise and least with isometric maximal exercise; in contrast, the increase in muscle lactate was least with progressive exercise (1.3 to 9.4 mumol/g), intermediate in intermittent maximal exercise (1.2 to 13.1 mumol/g) and greatest after isometric exercise (1.8 to 17.6 mumol/g). There were no significant differences between the three studies in the changes in lactate/pyruvate ratios. 7. In three subjects who exercised with one leg, activation of the enzyme was twice as great in the exercise as in the inactive leg. 8. The ratio of active to total enzyme in biopsies of resting muscle was greater in four well-trained athletes than in four untrained control subjects (70% compared with 41% respectively). 9. The activation of pyruvate dehydrogenase appears to play an important part in regulating the use of glycogen and glucose during exercise in man.

下腿血流量からみた不活動の影響について : ギプス固定・非固定肢下腿の血流量比較

下腿血流量からみた不活動の影響について : ギプス固定・非固定肢下腿の血流量比較

Substrate utilization by the inactive leg during one-leg or arm exercise.

Substrate utilization by the nonexercising leg was studied in healthy subjects during one-leg exercise at an average work load of 105 W for 40 min (n equals 8) or during arm exercise at 65 W for 20 min (n equals 5). During one-leg exercise both the blood flow and the A-FV difference of oxygen for the non exercising leg rose, resulting in an approximately five fold increment in oxygen uptake. EMG activity of the leg was increased above basal. Despite unchanged or falling arterial levels of insulin, the A-FV difference for glucose across the nonexercising leg rose during exercise and the estimated glucose uptake increased approximately fourfold. Release of lactate in the basal state reverted to a significant net uptake of lactate by the nonexercising leg. During arm exercise there was a 20-70% rise in leg blood flow and the leg oxygen uptake rose 25-45% in spite of minimal EMG activity from the thigh muscles. There was a large uptake of lactate by the legs during arm exercise. We conclude that several important metabolic alterations take place in the nonexercising leg tissues during physical exertion: 1) blood flow and oxygen uptake rise, partly as a consequence of motor activation; 2) substrate utilization shifts from a predominant FFA uptake in the basal state to a greater utilization of carbohydrate; 3) nonexercising muscle, and possibly adipose tissue, play an important role in the removal of lactate during exercise.