Maximal Voluntary Contraction Exercise Research Articles

The impact of submaximal fatiguing exercises on the ability to generate and sustain the maximal voluntary contraction.

Neuromuscular fatigability is a failure to produce or maintain a required torque, and commonly quantified with the decrease of maximal torque production during a few seconds-long maximal voluntary contraction (MVC). The literature shows that the MVC reduction after exercises with different torque-time integral (TTI), is often similar. However, it was shown that after a fatiguing exercise, the decline in the capacity to sustain the maximal voluntary contraction for 1 min (MVC1-MIN) differs from the decrease in the capacity to perform a brief-MVC, suggesting that this latter can only partially assess neuromuscular fatigability. This study aims to highlight the relevance of using a sustained MVC to further explore the neuromuscular alterations induced by fatiguing exercises with different TTI. We used two contraction intensities (i.e., 20% and 40% MVC) to modulate the TTI, and two exercise modalities [i.e., voluntary (VOL) and electrical induced (NMES)], since the letter are known to be more fatiguing for a given TTI. Thirteen subjects performed a plantar-flexors MVC1-MIN before and after the fatiguing exercises. A similar MVC loss was obtained for the two exercise intensities despite a greater TTI at 40% MVC, regardless of the contraction modality. On the other hand, the torque loss during MVC1-MIN was significantly greater after the 40% compared to 20% MVC exercise. These findings are crucial because they demonstrate that maximal torque production and sustainability are two complementary features of neuromuscular fatigability. Hence, MVC1-MIN assessing simultaneously both capacities is essential to provide a more detailed description of neuromuscular fatigability.

Skeletal muscle blood flow and vascular conductance are enhanced in humans with high‐affinity hemoglobin during handgrip exercise in severe hypoxia

BackgroundIn humans, exercise tolerance is determined by the balance of diffusive and convective elements of oxygen transport. Mathematical models have suggested that alterations in hemoglobin‐oxygen (Hb‐O2) binding affinity (P50) have minimal effects of on oxygen delivery. However, there is limited experimental data in humans to evaluate these models during exercise in humans.PurposeWe sought to investigate skeletal muscle blood flow and vascular conductance (hyperemic response to exercise and hypoxia) during exercise in otherwise healthy participants with chronically high Hb‐O2 affinity (HAH). We hypothesized that patients with HAH would have a blunted hyperemic response to both handgrip and hypoxia due to the marked polycythemia that is typical in participants with HAH compared to controls.MethodsParticipants with HAH (n=6, 3 men, age= 37±12 yr, P50=15±2 mmHg) and control participants matched for age, sex, and BMI (CTL, n=5, 3 men, age=41±8 yr, and P50=26±1 mmHg) completed two intensities (10% and 20% maximal voluntary contraction (MVC)) of rhythmic handgrip exercise with a duty cycle of 1s contraction and 2s relaxation (20 contractions·min−1). Each exercise intensity was performed breathing three different gas mixtures: 21%, 15%, and 10% oxygen. Brachial artery mean blood velocity was measured using Doppler ultrasound. Beat‐by‐beat blood pressure was measured via arterial catheterization. Forearm blood flow (FBF) was calculated as the product of mean blood velocity (cm·s−1) and brachial artery cross‐sectional area (cm2) and expressed as milliliters per minute (mL·min−1), and forearm vascular conductance (FVC) was calculated as (FBF) × (mean arterial pressure)−1 × 100 and expressed as mL·min−1·mmHg−1. Data were analyzed using a three‐way ANOVA (Inspirate [21%, 15%, 10% O2], group [CTL, HAH], handgrip intensity [Rest, 10% and 20% MVC]).ResultsDuring normoxia (21% O2), groups were not different in FBF (P>0.05), FVC (P>0.05) or arterial saturation (SaO2, P=0.54). Similarly, the moderate hypoxia condition (15% O2), groups were not different in FBF (P>0.05), or FVC (P>0.05) despite a preservation in arterial saturation in HAH (SaO2, CTL: 89.0±0.7% vs. HAH: 95.1±1.7%, P<0.001). However, with more severe hypoxic exposure (10% O2), FBF and FVC were higher in HAH than controls during the 20% MVC exercise (P<0.05). HAH also had higher FBF (P<0.05) and trended towards higher FVC in the 10% MVC exercise (P=0.08). Interestingly, arterial saturation was drastically higher for HAH at the end of handgrip exercise (20% MVC) in 10% O2 (CTL: 69.2±4.5% vs. HAH: 89.1±1.4%, P<0.001).ConclusionAs predicted in mathematical models, Hb‐O2 binding affinity had little effect on skeletal muscle blood flow and forearm vascular conductance during light exercise under normoxic and moderate hypoxic conditions (21% and 15% O2). However, with a greater physiological stress to skeletal muscle O2 uptake in a more severe hypoxic condition (10% O2), participants with HAH, contrary to our initial hypothesis, had preserved arterial O2 saturation and a greater hyperemic response than controls.Support or Funding InformationThis work was supported by the NIH (5T32DK007352‐39 to CCW, R35HL139854 to MJJ) Rest 10% MVC 20% MVC FBF,mL·min−1 21% O2 CTL 87 ± 8 327 ± 25 589 ± 26 HAH 142 ± 19 420 ± 29 716 ± 68 15% O2 CTL 173 ± 61 357 ± 63 707 ± 62 HAH 156 ± 66 539 ± 111 930 ± 143 10% O2 CTL 154 ± 72 386 ± 81 668 ± 57 HAH 244 ± 133 703 ± 199* 932 ± 118* FVC,mL·min−1·mmHg−1 21% O2 CTL 94 ± 9 356 ± 27 621 ± 24 HAH 130 ± 19 363 ± 25 617 ± 63 15% O2 CTL 187 ± 63 384 ± 54 758 ± 53 HAH 137 ± 44 453 ± 79 764 ± 226 10% O2 CTL 171 ± 71 431 ± 73 708 ± 67 HAH 221 ± 109 718 ± 136 917 ± 172 * Abbreviations: FBF, forearm blood flow; FVC, forearm vascular conductance; MVC, maximal voluntary contraction; CTL, control group; HAH, high‐affinity Hb group. Values are presented as mean±SE. * indicates significant difference (P<0.05) from CTL group at same %MVC.

Post-Activation Potentiation and Fatigue in Quadriceps Femoral Muscle after a 5 s Maximal Voluntary Isometric Contraction

Following an acute physical exercise, both post-activation potentiation and fatigue of the neuromuscular apparatus may occur. The voluntary recruitment of motor units occurs with frequencies that elicit incompletely fused tetanic contractions and these frequencies are most susceptible for post-activation potentiation as well as low-frequency fatigue. Therefore, the goal of the present study was to investigate which of the processes post-activation potentiation or low-frequency fatigue will be prevalent after 5 s maximal voluntary contraction (MVC). Eight healthy untrained men (age 24—35 years, mass 81.2 ± 5.1 kg) performed maximal sustained isometric knee extension for 5 s at a knee angle of 90 degrees. The contractile properties of quadriceps muscle evoked by electrical stimulation at 1, 7, 10, 15, 20, 50 Hz and 100 Hz, were recorded before and immediately after the exercise and 3, 5, and 10 min following the exercise. The rest interval between muscle electrical stimulation was 3 s. A significant raise of force evoked by 1—15 Hz stimulation was observed immediately after the 5 s MVC exercise (p < 0.01). Later in recovery (at 10 min) the contraction force at 15 Hz and 20 Hz significantly decreased (p < 0.05). Tetanic force at 50 Hz and 100 Hz demonstrated a significant decrease immediately after the exercise and remained depressed up to 3 min (p < 0.01). The ratio of 20 / 50 Hz recorded immediately after the 5 s MVC increased significantly (p < 0.05), however 10 min after the exercise there was a significant decrease compared to its initial level (p < 0.05). The simultaneous occurrence of post-activation potentiation at low stimulation frequencies and suppressed forces at high stimulation frequencies suggests that potentiation and fatigue mechanisms were acting concurrently. Moreover, when post-activation potentiation is lost (in 10 min after the 5 s MVC exercise), the contraction force at low stimulation frequencies decreases resulting in significant low-frequency fatigue.Keywords: isometric exercise, electrical stimulation, low-frequency fatigue, recovery.

Effect of Nitric Oxide Synthase Inhibition on Plasma ATP during Hypoxia and Exercise Induced Vasodilation in Humans

IntroductionAdenosine triphosphate (ATP) is postulated to be a major player in the local control of skeletal muscle vascular tone during exercise. Exercise during hypoxic conditions significantly augments skeletal muscle blood flow and elevates venous plasma levels of ATP compared to normoxic conditions in young healthy adults. This suggests that the elevated levels of ATP during hypoxic exercise contribute to the augmented vasodilation. Nitric oxide synthase (NOS) inhibition has also been shown to blunt the effects of hypoxia on exercise vasodilation. Therefore, the aim of the current study was to evaluate the effect of NOS inhibition and hypoxia on vasodilator responses and plasma ATP levels during exercise in healthy young adults.Methods10 young volunteers (age = 28 ± 1 years, 6 men/4 women) performed four minutes of forearm handgrip exercise at 20% of their maximal voluntary contraction (MVC). The forearm handgrip exercise was performed under normoxia and hypoxia (SpO2 = ~80%) with and without NOS inhibitor, LNMMA administered via a brachial artery catheter. Beat to beat blood pressure and heart rate were recorded. Forearm blood flow was measured using Doppler ultrasound and normalized for arterial pressure to determine forearm vascular conductance (FVC). Venous blood was obtained from a retrograde intravenous catheter at rest and during the last minute of each exercise bout. Plasma ATP was measured using the luciferin‐luciferase technique.ResultsDuring saline and normoxia FVC was 43.4 ± 8.4 at rest and 307.8 ± 22.6 ml/min/100mmHg during exercise. With hypoxia FVC increased to 59.35 ± 10.5 at rest and 370.9 ± 33.3 ml/min/100mmHg during exercise (both p<0.05 vs. normoxia). During LNMMA and normoxia FVC did not change significantly compared to saline 33.9 ± 4.4 at rest and 283.5 ± 23.2 ml/min/100mmHg during exercise. With hypoxia and LNMMA FVC was 35.04 ± 4.1 at rest (p>0.05 vs. normoxia) and 326.0 ± 23.9 ml/min/100mmHg during exercise (p<0.05 vs. normoxia). When changes from baseline are evaluated, hypoxia augmented the vasodilator responses exercise to exercise during both saline and LNMMA.ATP was higher during 20% MVC exercise with saline during hypoxia as compared to normoxia (65.6 ± 12.1 vs. 108.1 ± 23.2 versus nmol/L, p=0.058). It was also higher during 20% MVC exercise with LNMMA (81.7 ± 9.5 vs. 106.1 ± 14.7 nmol/L, p=0.055). When changes from baseline are evaluated, hypoxia augmented venous ATP concentration with exercise during both saline and LNMMA.ConclusionsOur results suggest that increased endogenous ATP release during hypoxic exercise continued to evoke vasodilation during NOS inhibition. A likely source of this ATP is from red blood cells and this interpretation is consistent with findings demonstrating that NOS inhibition has limited effects on ATP mediated dilation in the human forearm.Support or Funding InformationThis research was supported by National Institutes of Health Research Grants HL‐119337, CTSA UL1 TR000135 and the Caywood Professorship via the Mayo Foundation

Muscle Activation under Different Loading Conditions during the Power Clean

The power clean is a component of the clean and jerk Olympic lift and is also commonly utilised in training programs for several sports. Few studies have explored electromyographical (EMG) activation of the major muscles used during this exercise. The aim of the present study was to examine muscle activation during the power clean for the following muscles: gastrocnemius (GS), vastus lateralis (VL), transversus abdominis (TA), multifidus (MU), erector spinae (ES) and trapezius (TR). Eight experienced lifters performed five maximal voluntary contraction (MVC) exercises followed by three sets of three power clean repetitions at 70%, 80% and 90% 1RM. There was a significant increase with load for peak EMG of ES and GS and mean EMG of GS and VL. This suggests that athletes targeting the ES, GS and VL in their strength training could potentially benefit by increasing intensity from 70 to 90%. There was no evidence to suggest that this intensity increase benefits the TA and MU muscles. The power clean produced significantly higher peak values than the MVC exercises for the MU and ES muscles, suggesting that it could be used as both a strength training exercise for these muscles and an MVC exercise in future studies.

Role of α-adrenergic vasoconstriction in regulating skeletal muscle blood flow and vascular conductance during forearm exercise in ageing humans.

In healthy humans, ageing is typically associated with reduced skeletal muscle blood flow and vascular conductance during exercise. Further, there is a marked increase in resting sympathetic nervous system (SNS) activity with age, yet whether augmented SNS-mediated α-adrenergic vasoconstriction contributes to the age-associated impairment in exercising muscle blood flow and vascular tone in humans is unknown. We tested the hypothesis that SNS-mediated vasoconstriction is greater in older than young adults and limits muscle (forearm) blood flow (FBF) during graded handgrip exercise (5, 15, 25% maximal voluntary contraction (MVC)). FBF was measured (Doppler ultrasound) and forearm vascular conductance (FVC) was calculated in 11 young (21±1years) and 12 older (62±2years) adults in control conditions and during combined local α- and β-adrenoreceptor blockade via intra-arterial infusions of phentolamine and propranolol, respectively. Under control conditions, older adults exhibited significantly lower FBF and FVC at 15% MVC exercise (22.6±1.3 vs. 29±3.3mlmin(-1) 100g forearm fat-free mass (FFM)(-1) and 21.7±1.2 vs. 33.6±4.0mlmin(-1) 100g FFM(-1) 100mmHg(-1); P<0.05) and 25% MVC exercise (37.4±1.4 vs. 46.0±4.9mlmin(-1) 100g FFM(-1) and 33.7±1.4 vs. 49.0±5.7mlmin(-1) 100g FFM(-1) 100mmHg(-1); P<0.05), whereas there was no age group difference at 5% MVC exercise. Local adrenoreceptor blockade increased FBF and FVC at rest and during exercise in both groups, although the increase in FBF and FVC from rest to steady-state exercise was similar in young and older adults across exercise intensities, and thus the age-associated impairment in FBF and FVC persisted. Our data indicate that during graded intensity handgrip exercise, the reduced FVC and subsequently lower skeletal muscle blood flow in older healthy adults is not due to augmented sympathetic vasoconstriction, but rather due to impairments in local signalling or structural limitations in the peripheral vasculature with advancing age.

Acute ingestion of dietary nitrate increases muscle blood flow via local vasodilation during exercise in young adults (705.9)

Dietary nitrate (NO3‐) supplementation with beetroot juice (BR) can reduce the O2 cost of submaximal exercise and increase exercise tolerance. NO3‐ is converted to nitrite and can be reduced to the vasodilator nitric oxide amid a low O2 environment and BR is observed to increase hindlimb blood flow in rats during treadmill exercise. We tested the hypothesis that BR increases forearm blood flow (FBF) via local vasodilation during handgrip exercise in young adults (n=7; 24±2 years). FBF (Doppler ultrasound) and blood pressure (finometer) were measured at rest and during graded handgrip exercise at 5, 15, and 25% maximal voluntary contraction (MVC) lasting 4 minutes each. During 25% MVC exercise, systemic hypoxia (80%SaO2) began and exercise continued for 3 additional minutes. Subjects then ingested concentrated BR (12.6 mmol nitrate) and repeated the exercise bout 2h post consumption. Compared to control, BR significantly increased FBF at 15% (183±29 vs. 165±21 ml/min), 25% (331±40 vs.293±43 ml/min), and 25% + hypoxia (393 ±59 vs. 357±49 ml/min; all P&lt;0.05), and this was due to increases in vascular conductance. Further, the increase in FBF from control was greatest at 25% MVC in normoxia and hypoxia (Δ~35‐40 ml/min) compared with 15% (Δ~18 ml/min) and 5% (Δ~5 ml/min). These findings may have important implications for aging and diseased populations that have impaired muscle perfusion and exercise intolerance.Grant Funding Source: Supported by HL095573

Training effects on peripheral muscle oxygenation and performance in children with congenital heart diseases

We investigated the effect of training on peripheral muscular performance and oxygenation during exercise and recovery in children with congenital heart diseases (CHD). Eighteen patients with CHD aged 12 to 15 years were randomly assigned into either an individualized 12-week aerobic cycling training group (TG) or a control group (CG). Maximal voluntary contraction (MVC) and endurance at 50% MVC (time to exhaustion, T(lim)) of the knee extensors were measured before and after training. During the 50% MVC exercise and recovery, near-infrared spectroscopy (NIRS) was used to assess the fall in muscle oxygenation, i.e., deoxygenation ([Formula: see text]) of the vastus lateralis, the mean rate of decrease in muscle oxygenation, the half time of recovery (T(1/2R)), and the recovery speed to maximal oxygenation (R(S)). There was no effect of time on any parameter in the CG. After training, significant improvements were observed in TG for MVC (101.6 ± 14.0 vs. 120.2 ± 19.4 N·m, p < 0.01) and T(lim) (66.2 ± 22.6 vs. 86.0 ± 23.0 s, p< 0.01). Increased oxygenation (0.20 ± 0.13 vs. 0.15 ± 0.07 a.u., p < 0.01) and faster mean rate of decrease in muscle oxygenation were also shown after training in TG (1.22 ± 0.45 vs. 1.71 ± 0.78%·s(-1), p < 0.001). Moreover, a shorter recovery time was observed in TG after training for T(1/2R) (27.2 ± 6.1 vs. 20.8 ± 4.2 s, p < 0.01) and R(S) (63.1 ± 18.4 vs. 50.3 ± 11.4 s, p < 0.01). A significant relationship between the change in [Formula: see text] and both MVC (r = 0.95, p < 0.001) and T(lim) (r = 0.90, p < 0.001) in TG was observed. We concluded that exercise training improves peripheral muscular function by enhancing strength and endurance performance in children with CHD. This improvement was associated with increased oxygenation of peripheral muscles and faster recovery.

Changes of central haemodynamic parameters during mental stress and acute bouts of static and dynamic exercise

Chronic dynamic (aerobic) exercise decreases central arterial stiffness, whereas chronic resistance exercise evokes the opposite effect. Nevertheless, there is little information available on the effects of acute bouts of exercise. Also, there is limited data showing an increase of central arterial stiffness during acute mental stress. This study aimed to determine the effect of acute mental and physical (static and dynamic exercise) stress on indices of central arterial stiffness. Fifteen young healthy volunteers were studied. The following paradigms were performed: (1) 2 min of mental arithmetic, (2) short bouts (20 s) of static handgrip at 20 and 70% of maximal voluntary contraction (MVC), (3) fatiguing handgrip at 40% MVC and (4) incremental dynamic knee extensor exercise. Central aortic waveforms were assessed using SphygmoCor software. As compared to baseline, pulse wave transit time decreased significantly for all four interventions indicating that central arterial stiffness increased. During fatiguing handgrip there was a fall in the ratio of peripheral to central pulse pressure from 1.69+/-0.02 at baseline to 1.56+/-0.05 (P<0.05). In the knee extensor protocol a non-significant trend for the opposite effect was noted. The augmentation index increased significantly during the arithmetic, short static and fatiguing handgrip protocols, whereas there was no change in the knee extensor protocol. We conclude that (1) during all types of acute stress tested in this study (including dynamic exercise) estimated central stiffness increased, (2) during static exercise the workload posed on the left ventricle (expressed as change in central pulse pressure) is relatively higher than that posed during dynamic exercise (given the same pulse pressure change in the periphery).

Effects of Vascular Occlusion on Maximal Force, Exercise-induced T2 Changes, and EMG Activities of Quadriceps Femoris Muscles

The purpose of our study was to determine the effect of vascular occlusion on neuromuscular activation and/or the energy metabolic characteristics of the quadriceps femoris (QF) muscles during muscle contractions. Seven men participated in the study. An occlusion cuff was attached to the proximal end of the right thigh, so that blood flow in the anterior medial malleolar artery was reduced to approximately 88 % of the non-occluded flow. Muscle functional magnetic resonance imaging and maximal voluntary contraction (MVC) were carried out before and immediately after 5 sets of 10 repetitions of knee extension exercises at 50 % of the 10 repetitions maximum, from which transverse relaxation times (T2) and maximal force were measured, respectively. Integrated electromyography (iEMG) activity was recorded from the belly of the rectus femoris, vastus lateralis, and vastus medialis muscles during MVC and repetitive exercises. The percentage change in T2 was significantly increased for individual QF muscles, and there was a significant increase in iEMG activity over the 5 sets of repetitive exercises under conditions of vascular occlusion, but there was no significant effect on isometric force and iEMG activity during MVC. These results are consistent with the idea that there is greater osmolite accumulation during exercise with occlusion, although increased neural activation cannot be ruled out.

The Chemoreflex in Young Boys and Girls

In order to determine the influence of the chemoreflex on the cardiovascular system of young children, 35 boys and 35 girls (all 7 - 9 years old) performed three minutes of 30 % maximal voluntary contraction (MVC) static handgrip (SHG) exercise followed by four minutes of blood flow occlusion in the previously exercised arm, and then six minutes of passive recovery. Heart rate (HR) and blood pressure (BP) were measured each minute. Twenty girls performed a second occlusion trial to determine reliability. Reliability coefficients for HR (R = 0.51 - 0.78), diastolic (R = 0.46 - 0.81) and systolic (R = 0.57 - 0.78) BP throughout the occlusion trial were moderately high. There was a similar increase in HR (19 +/- 8 vs. 16 +/- 10 %), diastolic (34 +/- 12 vs. 34 +/- 16 %) and systolic (18 +/- 9 vs. 15 +/- 7 %) BP in boys and girls, respectively, during three minutes 30 % MVC exercise. During the occlusion period, diastolic (43 +/- 31 vs. 47 +/- 26 %) and systolic (51 +/- 25 vs. 54 +/- 32 %) BP dropped similarly during minute one but remained elevated significantly above baseline in both boys and girls the entire four-minute period. During the recovery period, minute one SBP and DBP dropped similarly in boys (23 +/- 37, 20 +/- 37 %) and girls (20 +/- 38, 12 +/- 38 %), respectively. In boys and girls DBP remained significantly above baseline the entire recovery period. HR in boys and girls returned to baseline immediately following SHG exercise and remained there through recovery. In conclusion, as reported in adults, the drop in HR to baseline during post-exercise ischemia with a concomitant maintenance of BP significantly above baseline indicates that at least two separate mechanisms, with varying influence, are responsible for HR and BP control in young children. Further, the chemoreflex operates similarly in young boys and girls.

EFFECT OF HANDGRIP EXERCISE ON BLOOD PRESSURE IN BALLET DANCERS, POWER AND ENDURANCE ATHLETES

The effects of power and endurance training on blood pressure have been investigated. The haemodynamic impact of ballet training, classified as intermittent, is not well understood. PURPOSE To evaluate systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR) and forearm blood flow (FBF) responses to dynamic and static exercises in ballet dancers, power and endurance athletes. METHODS 9 ballet dancers, 10 power and 10 endurance althletes and 18 untrained subjects, 24±2 vs 21±2 vs 23±2 vs 24±3 years, 20±1 vs 24±2 vs 22±2 vs 22±2 kg/m2, underwent to a experimental protocol in which dynamic (40 contraction/minute) and static exercise handgrip were performed with dominant arm at 10% and 30% of the maximal voluntary contraction (MVC) for 3 minutes at 10% and 30% MVC. Post-handgrip forearm ischaemia (FI) was performed after 30% MVC exercises. SBP and DBP (oscilometric method -DIXTAL), HR (EKG) and FBF by venous occlusion pletismography. Forearm vascular resistance (FVR) by Mean Blood Pressure/FBF. VO2 max (mlO2/1/min-1) was measured directly on a cycle ergometer (30W/3min protocol). RESULTS VO2max values were higher in athletes than in untrained subjects (ballet dancers=42±2 mlO2/1/min-1, endurance=54±3 mlO2/1/min-1, power=44±2 mlO2/1/min-1, and untrained subjects=35±3, P < 0.05). Post-static handgrip Fl increased DBP(mmHg) significantly in power athletes (25± 4) and led to a mild rise in ballet dancers (8± 3) and untrained subjects (10± 3) P < 0.05. Dynamic handgrip at 30% MVC elicited greater SBP (mmHg) increase in endurance (15± 3) and power (13± 4) athletes when compared to ballet dancers (3± 3) and untrained subjects (4± 2), P=0.003. Dynamic exercise FI led to a SBP rise in endurance (15± 3) and power (16± 4) athletes when compared to ballet dancers (−1± 4) and untrained subjects (5± 3mmHg), P=0.003. No difference was found in HR, FBF and FVR among groups. CONCLUSION Power and endurance training may elicit higher sympathetic activation during dynamic and static exercises than intermittent training.

Muscle reoxygenation rate after isometric exercise at various intensities in relation to muscle oxidative capacity.

The purpose of this study was to determine whether the reoxygenation rate (Reoxy-rate) immediately after static exercise at various submaximal intensities would be related to muscle oxidative capacity. Seven healthy male subjects performed isometric handgrip exercise for 10 sec at 30%, 60% and 90% of maximal voluntary contraction (MVC). The Reoxy-rate and muscle oxygen consumption during exercise (muscle VO2EX) were monitored by near infrared continuous wave spectroscopy (NIRcws). The muscle oxidative capacity was evaluated by the time constant for phosphocreatine resynthesis (PCrTc) using 31-phosphorus magnetic resonance spectroscopy (31P-MRS). The Peak blood flow of brachial artery after exercise (BABFpeak) was measured using Doppler ultrasound. There was no correlation between PCrTc and Reoxy-rate at 30% and 60% MVC. In contrast, Reoxy-rate at 90% MVC was positively correlated to PCrTC (r = 0.825, p < 0.05). The muscle VO2EX increased 5.9, 8.8 and 12.6-fold of the resting on average at 30%, 60% and 90% MVC, respectively, and the muscle VO2EX at 90% MVC was significantly higher than that at 30% and 60% MVC. On the other hand, BABFpeak increased only just 1.9, 2.4 and 2.7-fold of the resting on average at 30%, 60% and 90% MVC, respectively (Fig. 4). These results suggest that the higher oxidative capacity muscle shows slower muscle reoxygenation after 10 sec isometric exercise at 90% MVC because the Reoxy-rate after this type of exercise may be influenced more by muscle VO2 than by O2 supply. In contrast, 60% MVC and lower exercise intensities may not be severe enough to influence the muscle VO2 dependent Reoxy-rate.

Physiologic and symptomatic responses of cardiac patients to resistance exercise

The purpose of this study was to investigate the symptomatic and physiologic responses during moderate to heavy resistance exercise in a population with coronary artery disease. After at least 12 weeks of aerobic training without experiencing complications, 15 male cardiac patients were selected for the study. Approximately one week after a graded exercise test (GXT), each patient's maximal voluntary contraction (MVC) was determined on seven upper-body Nautilus machines. Resistance exercises, consisting of two sets of seven repetitions at a submaximal intensity (75% MVC) for each exercise, were then performed on two nonconsecutive occasions; symptomatic, hemodynamic, and electrocardiographic responses were recorded and analyzed for patients both on and off beta-blockers. During the MVC and submaximal exercise trials, no significant untoward hemodynamic change was noted with heart rate, systolic blood pressure, diastolic blood pressure, or rate pressure product, and no patient complained of angina or developed ischemic electrocardiographic changes. However, three incidences of premature ventricular contractions (PVCs) occurred. During the GXT, there were 13 incidences of angina, ischemia, or PVCs. Patients taking beta-blockers had significantly lower (p less than .01) values for heart rate and rate pressure product during the GXT, MVC, and submaximal trials. These results suggest that clinically stable, aerobically trained cardiac patients may perform moderate to heavy resistance exercises without experiencing complications.