Frequent low-load ischemic resistance exercise to failure enhances muscle oxygen delivery and endurance capacity

This study investigated the effects of frequent low-load ischemic resistance exercise performed to failure on quadriceps size and performance, muscle activation, oxygen kinetics and cardiovascular responses. Ten healthy males performed knee-extension exercise for 4 weeks (4 sessions/week) at 15% maximal voluntary muscle contraction (MVC). One leg was trained with free blood flow (C-leg) while in the other leg (I-leg) ischemia was induced by an inflatable cuff (≥230 mmHg). Quadriceps cross-sectional area (CSA) of the I-leg increased by 3.4% (P<0.05). A tendency for smaller increase in muscle CSAs at the cuff level was observed. MVC force did not change in either leg, whereas the number of repetitions during exercise test to failure increased (P<0.01) by 63% in I-leg and 36% in C-leg. The decrease in muscle oxygenated hemoglobin concentration acquired by NIRS was attenuated (P<0.01) by 56% in I-leg and 21% in C-leg. Electromyographic amplitude of rectus femoris in I-leg was ～45% lower (P<0.025) during the ischemic test. Also, ～9% increase (P<0.05) in pre-exercise diastolic pressure was observed. In conclusion, substantial gains in muscle endurance capacity were induced, which were associated with enhanced muscle oxygen delivery. The potential negative effects of ischemic exercise with high cuff pressure on muscle and nerve and on arterial pressure regulation need further investigation.     

Resistance exercise training in patients with heart failure

The utility, safety and physiological adaptations of resistance exercise training in patients with chronic heart failure (CHF) are reviewed and recommendations based on current research are presented. Patients with CHF have a poor clinical status and impaired exercise capacity due to both cardiac limitations and peripheral maladaptations of the skeletal musculature. Because muscle atrophy has been demonstrated to be a hallmark of CHF, the main principle of exercise programmes in such patients is to train the peripheral muscles effectively without producing great cardiovascular stress. For this reason, new modes of training as well as new training methods have been applied. Dynamic resistance training, based on the principles of interval training, has recently been established as a safe and effective mode of exercise in patients with CHF. Patients perform dynamic strength exercises slowly, on specific machines at an intensity usually in the range of 50-60% of one repetition maximum; work phases are of short duration (< or =60 seconds) and should be followed by an adequate recovery period (work/recovery ratio >1 : 2). Patients with a low cardiac reserve can use small free weights (0.5, 1 or 3 kg), elastic bands with 8-10 repetitions, or they can perform resistance exercises in a segmental fashion. Based on recent scientific evidence, the application of specific resistance exercise programmes is safe and induces significant histochemical, metabolic and functional adaptations in skeletal muscles, contributing to the treatment of muscle weakness and specific myopathy occurring in the majority of CHF patients. Increased exercise tolerance and peak oxygen consumption (V-dotO(2peak)), changes in muscle composition, increases in muscle mass, alterations in skeletal muscle metabolism, improvement in muscular strength and endurance have also been reported in the literature after resistance exercise alone or in combination with aerobic exercise. According to new scientific evidence, appropriate dynamic resistance exercise should be recommended as a safe and effective alternative training mode (supplementary to conventional aerobic exercise) in order to counteract peripheral maladaptation and improve muscle strength, which is necessary for recreational and daily living activities, and thus quality of life, of patients with stable, CHF.     

Skeletal muscle oxidative capacity and exercise tolerance in rats with heart failure

PURPOSE: Past research has shown the development of exercise intolerance after myocardial infarction (MI). The purpose of this study was to test the hypothesis that reductions in oxidative enzyme activity, in a variety of skeletal muscles, coincide with the development of exercise intolerance in a rat model of chronic heart failure (CHF) induced by MI. METHODS: The animals were initially divided into two groups: sham-operated controls (Sham) and animals in which a MI was surgically induced. MI rats were then subdivided into two groups according to left ventricular end-diastolic pressure (LVEDP): <20 mm Hg [small MI (SMI)] and > 20 mm Hg [large MI (LMI)]. Exercise tolerance was measured by performing a progressive run to fatigue test (RTF). Citrate synthase (CS), 3-hydroxyacyl CoA dehydrogenase (HADH), and malate dehydrogenase (MDH) activities were measured in six hindlimb muscles. RESULTS: After approximately 6 wk of recovery, LVEDP differed among groups (P < 0.05): Sham (1 +/- 1 mm Hg, N = 7), SMI (7 +/- 2 mm Hg, N = 7), and LMI (30 +/- 2 mm Hg, N = 6). RTF was 20 +/- 1 min for Sham, 25 +/- 3 min for SMI, and 11 +/- 2 min for LMI (P < 0.05 for LMI vs Sham, SMI). Significant reductions in enzyme activity were found for all three enzymes in the red portion of the gastrocnemius muscles of LMI. However, no significant correlation was found between RTF and CS, HADH, or MDH in any muscle of the three groups of animals. DISCUSSION: The results of the present study demonstrate that severe left ventricular dysfunction is associated with reductions in exercise tolerance and modest decreases in oxidative enzyme activities in selected muscles. It does not appear, however, that the development of exercise intolerance in CHF and oxidative enzyme activities are mechanistically related to one another.     

Strength/endurance training versus endurance training in congestive heart failure

PURPOSE: The aim of this study was to compare the effects of endurance training alone (ET) with combined endurance and strength training (CT) on hemodynamic and strength parameters in patients with congestive heart failure (CHF). METHODS: Twenty male patients with CHF were randomized into one of two training regimens consisting of endurance training or a combination of endurance and resistance training. Group ET had 40-min interval cycle ergometer endurance training three times per week. Group CT combined endurance and strength training with the same interval endurance training for 20 min, followed by 20 min of strength training. Left ventricular function was assessed at baseline and after 40 training sessions by echocardiography and radionuclide ventriculography. Work capacity was measured with cardiopulmonary exercise test (CPX) and lactate determination. Strength was measured with an isokinetic dynamometer. RESULTS: After 40 sessions, the ET group improved functional class, work capacity, peak torque, and muscular endurance. However, peak O2 remained unchanged. Left ventricular ejection fraction (LVEF) and fractional shortening (FS) decreased, whereas left ventricular end-diastolic diameter (LVED) increased. The CT group improved NYHA score, working capacity, peak O2, and peak lactate; peak torque and muscular endurance, LVEF, and FS increased, whereas LVED decreased. Compared with ET, CT was significantly (P < 0.05) better in improving LV function.CONCLUSION: Combined endurance/strength training was superior to endurance training alone concerning improvement of LV function, peak VO2, and strength parameters. It appears that for stable CHF patients, a greater benefit can be derived from this training modality.     

Norepinephrine alters exercise oxygen consumption in heart failure patients

PURPOSE: The primary aim of this research was to evaluate the effect of acute norepinephrine (NE) infusion on the exercise oxygen utilization in heart failure patients as compared with healthy adults. METHODS: Eleven healthy adults and 10 patients with NYHA class II-III heart failure (ejection fraction <40%) who were not on beta-blocker therapy underwent steady state exercise under placebo or NE infusion conditions, followed by maximal ramp exercise testing. Oxygen utilization, hemodynamic responses, and serum lactate NE levels were evaluated. RESULTS: The hemodynamic effects of NE were evident in both groups with statistically significant increases in blood pressure and concomitant decreases in heart rates. Lactate levels were higher in heart failure subjects under all conditions and steady state exercise increased levels by 24% (P = 0.04). NE infusion increased lactate levels by a nonsignificant 24% (P = 0.19). NE infusion tended to increase oxygen consumption (VO2) at the end of steady state exercise in CHF subjects (4% change; P = 0.06). Compared with healthy adults, NE infusion significantly impaired (increased) the gross VO2/W relationship in heart failure subjects (P = 0.037). There was also a modest trend for a worsening (decrease) in net efficiency after NE infusion in CHF subjects. There were no significant adverse effects of low-dose NE infusion in either group. CONCLUSIONS: We conclude that 1) acute low-dose NE infusion impairs the oxygen utilization in stable heart failure patients but not in healthy adults. This may help to explain the exercise intolerance that accompanies congestive heart failure. 2) Acute infusion of low-dose NE infusion is safe and well tolerated in both healthy adults and compensated heart failure patients.     

Creatine supplementation reduces muscle inosine monophosphate during endurance exercise in humans

INTRODUCTION: Creatine (Cr) supplementation has been shown to attenuate increases in plasma ammonia and hypoxanthine during intense endurance exercise lasting 1 h, suggesting that Cr supplementation may improve muscle energy balance (matching of ATP resynthesis to ATP demand) during such exercise. We hypothesized that Cr supplementation would improve muscle energy balance (as assessed by muscle inosine monophosphate (IMP) accumulation) during intense endurance exercise. METHODS: Seven well-trained men completed two experimental trials involving approximately 1 h of intense endurance exercise (cycling 45 min at 78+/-1% & OV0312;O2 peak followed by completion of 251+/-6 kJ as quickly as possible (performance ride)). Subjects ingested approximately 42 g.d dextrose for 5 d before the first experimental trial (CON), then approximately 21 g Cr monohydrate plus approximately 21 g.d dextrose for 5 d before the second experimental trial (CREAT). Trials were ordered because of the long washout time for Cr. Subjects were blinded to the order of the trials. RESULTS: Creatine supplementation significantly (P< 0.05) increased muscle total Cr (resting values: CREAT: 138.1+/-7.9; CON: 117.7+/- 6.5 mmol.kg dm). No difference was seen between treatments in any measured muscle or blood metabolite after the first 45 min of exercise. Despite the performance ride completion time being similar in the two treatments ( approximately 13.5 min, approximately 86% & OV0312;O2 peak), IMP at the end of the performance ride was significantly (P<0.05) lower in CREAT than in CON (CREAT: 1.2+/- 0.6; CON: 2.0+/- 0.7 mmol.kg dm). CONCLUSION:Raising muscle total Cr content before exercise appears to improve the ability of the muscle to maintain energy balance during intense aerobic exercise, but not during more moderate exercise intensities.     

Reduction in LBNP tolerance following prolonged endurance exercise training.

Eight young men underwent an 8-month endurance exercise training program. Prior to and following the training program, the subjects' maximal oxygen uptake (VO2max), total blood volume (TBV) and plasma volume (PV), tolerance to lower body negative pressure (LBNP) assessed by the cumulative stress index (CSI) to presyncope, and their hemodynamic responses to 0 to -45 torr LBNP was determined. Hemodynamic measures included rebreathe carbon dioxide cardiac output (Qc), heart rate (HR), directly measured arterial blood pressures (ABP), and strain gauge determination of forearm blood flow (FBF) and leg volume changes (delta LgV). Calculated values of stroke volume (SV), forearm, vascular resistance (FVR), and peripheral vascular resistance (PVR) were made. Following training, each subject had an increased VO2max (mean = +27.4%, P < 0.001), TBV (mean = +15.8%, P < 0.02), and PV (mean = +16.5%, P < 0.02) and each subject had a decreased tolerance to LBNP (mean CSI = -24%, P < 0.001). Stepwise linear regression identified that the major factors to significantly predict the decreased CSI pre- to post-training were a reduced response of PVR to LBNP from -15 to -45 torr (Model R2 = 0.853), the delta TBV (model R2 = 0.981), and the greater post-training reduction in SBP to LBNP of 0 to -45 torr (model R2 = 1.0). These data suggest that physiologic adaptations associated with the increased VO2max and TBV resulting from a prolonged endurance exercise training program can alter the reflex control of vasomotion and cardiac output during LBNP and reduce the LBNP tolerance.     

Predictors of isotonic exercise in patients with heart failure.

PURPOSE: Study aims were to determine the predictors of isotonic resistance exercise performance in patients with advanced heart failure and to compare the preexercise values of patients who experienced a negative physiologic response to resistance exercise with those who had minimal or no response. METHODS: A correlational design was used. After pharmacologic left ventricular unloading therapy using a pulmonary artery catheter, 34 patients with advanced heart failure performed graduated isotonic weight-lifting exercises. Measurements were made of hemodynamics and rating of perceived exertion after each test. RESULTS: The following variables, measured at baseline, were significantly correlated with the amount of weight patients were able to lift: rating of perceived exertion (RPE; r = -0.42, P = 0.014); diastolic blood pressure (DBP; r = 0.49, P = 0.03); systolic blood pressure (SBP; r = 0.40, P = 0.017); pulmonary capillary wedge pressure (PCWP; r = 0.39, P = 0.026); and right atrial pressure (RAP; r = 0.35, P = 0.041). Multiple regression analysis, using a stepwise procedure, showed that 47% of the variance in exercise performance was explained by DBP, RPE, and PCWP. There were no significant differences in baseline hemodynamics, ejection fraction, or age between the group of patients who had a negative hemodynamic response at peak exercise and the group of patients who had minimal or no response. CONCLUSIONS: Resting PCWP, DBP, and RPE can provide important information to help clinicians predict isotonic resistance exercise performance in patients with advanced heart failure. However, those patients who have a negative response to this type of exercise cannot be distinguished at baseline by clinical characteristics or age.     

Effect of endurance exercise on autonomic control of heart rate

Long-term endurance training significantly influences how the autonomic nervous system controls heart function. Endurance training increases parasympathetic activity and decreases sympathetic activity in the human heart at rest. These two training-induced autonomic effects, coupled with a possible reduction in intrinsic heart rate, decrease resting heart rate. Long-term endurance training also decreases submaximal exercise heart rate by reducing sympathetic activity to the heart. Physiological ageing is associated with a reduction in parasympathetic control of the heart; this decline in parasympathetic activity can be reduced by regular endurance exercise. Some research has indicated that females have increased parasympathetic and decreased sympathetic control of heart rate. These gender-specific autonomic differences probably contribute to a decreased cardiovascular risk and increased longevity observed in females.     

Influence of short-term endurance exercise training on heart rate variability

PURPOSE: To examine the influence of 2 wk (eight sessions) of endurance training on cardiac autonomic modulation, as measured by heart rate variability (HRV). METHODS: Twenty-four males (mean age: 23.1 yr) were randomized to an exercise (EX; N = 12) or control group (CT; N = 12). EX trained for eight sessions (4x wk-1, 40 min, 80-85% HRreserve) on a cycle ergometer. ECG tracings were collected during 5 min of paced breathing (12 breaths x min-1 (PB)), 5 min of spontaneous breathing (SB1), 5 min of 70 degrees head-up tilt (TILT), and a second 5-min period of spontaneous breathing (SB2). Data were collected before (test 1), during (tests 2-4), and 48 h after (test 5) the 2-wk period. HRV was reported as the standard deviation of RR intervals, and as natural logarithm of the normalized units (NU) of high- and low-frequency power (lnHF and lnLF). RESULTS: EX exhibited a significant increase in peak oxygen consumption (8%). During PB and TILT conditions, ANOVA revealed a group x time interaction such that EX exhibited lower lnLFNU and lnLF/lnHF during test 5 compared with test 1. CONCLUSION: These data suggest that eight endurance exercise-training sessions performed over 2 wk enhance the relative vagal modulation of the heart during PB and TILT, but not during SB.     

L-arginine supplementation enhances exhaled NO, breath condensate VEGF, and headache at 4,342 m

We examined the effect of dietary supplementation with L-arginine on breath condensate VEGF, exhaled nitric oxide (NO), plasma erythropoietin, symptoms of acute mountain sickness, and respiratory related sensations at 4,342 m through the course of 24 h in seven healthy male subjects. Serum L-arginine levels increased in treated subjects at time 0, 8, and 24 h compared with placebo, indicating the effectiveness of our treatment. L-arginine had no significant effect on overall Lake Louise scores compared with placebo. However, there was a significant increase in headache within the L-arginine treatment group at 12 h compared with time 0, a change not seen in the placebo condition between these two time points. There was a trend (p = 0.087) toward greater exhaled NO and significant increases in breath condensate VEGF with L-arginine treatment, but no L-arginine effect on serum EPO. These results suggest that L-arginine supplementation increases HIF-1 stabilization in the lung, possibly through a NO-dependent pathway. In total, our observations indicate that L-arginine supplementation is not beneficial in the prophylactic treatment of AMS.     

Oral magnesium therapy, exercise heart rate, exercise tolerance, and myocardial function in coronary artery disease patients

Background

Previous studies have demonstrated that in patients with coronary artery disease (CAD) upward deflection of the heart rate (HR) performance curve can be observed and that this upward deflection and the degree of the deflection are correlated with a diminished stress dependent left ventricular function. Magnesium supplementation improves endothelial function, exercise tolerance, and exercise induced chest pain in patients with CAD.

Purpose

We studied the effects of oral magnesium therapy on exercise dependent HR as related to exercise tolerance and resting myocardial function in patients with CAD.

Methods

In a double blind controlled trial, 53 male patients with stable CAD were randomised to either oral magnesium 15 mmol twice daily (n = 28, age 61±9 years, height 171±7 cm, body weight 79±10 kg, previous myocardial infarction, n = 7) or placebo (n = 25, age 58±10 years, height 172±6 cm, body weight 79±10 kg, previous myocardial infarction, n = 6) for 6 months. Maximal oxygen uptake (VO_2max), the degree and direction of the deflection of the HR performance curve described as factor k<0 (upward deflection), and the left ventricular ejection fraction (LVEF) were the outcomes measured.

Results

Magnesium therapy for 6 months significantly increased intracellular magnesium levels (32.7±2.5 v 35.6±2.1 mEq/l, p<0.001) compared to placebo (33.1±3.1.9 v 33.8±2.0 mEq/l, NS), VO_2max (28.3±6.2 v 30.6±7.1 ml/kg/min, p<0.001; 29.3±5.4 v 29.6±5.2 ml/kg/min, NS), factor k (−0.298±0.242 v −0.208±0.260, p<0.05; −0.269±0.336 v −0.272±0.335, NS), and LVEF (58±11 v 67±10%, p<0.001; 55±11 v 54±12%, NS).

Conclusion

The present study supports the intake of oral magnesium and its favourable effects on exercise tolerance and left ventricular function during rest and exercise in stable CAD patients.     

Abnormalities of the exercise pressor reflex in heart failure

Abnormal cardiovascular responses to exercise in heart failure contribute significantly to the morbidity and mortality in the patient population. These abnormal responses may be the result of peripheral impairment in the skeletal muscle and the neurons that innervate the muscle. We present the current literature on the role of muscle afferents in regulating the cardiovascular responses to exercise in cardiomyopathy.     

Post-exercise heart rate variability of endurance athletes after different high-intensity exercise interventions

Methodological problems have limited the number of studies on heart rate variability (HRV) dynamics immediately after exercise. We used the short-time Fourier transform method to study immediate (5 min) and slow (30 min) recovery of HRV after different high-intensity exercise interventions. Eight male athletes performed two interval interventions at 85% and 93% (IV₈₅ and IV₉₃) and two continuous interventions at 80% and 85% (CO₈₀ and CO₈₅) of the velocity at VO_2max (vVO_2max). We found no increase in high frequency power (HFP), but low frequency (LFP) and total power (TP) increased ( P <0.05) during the first 5 min of the recovery after each intervention. During the 30-min recovery, HFP, LFP and TP (1) increased slowly toward resting values, but HFP remained lower ( P <0.01) than at rest, (2) were lower ( P <0.05) after IV₉₃ and CO₈₅ when compared with IV₈₅ and CO₈₀, respectively and (3) were lower ( P <0.01) after CO₈₅ when compared with IV₈₅. HRV recovery was detected during the immediate recovery after interventions. Increased exercise intensity resulted in lower HRV both in interval and in continuous interventions. In addition, when interval and continuous interventions were performed at a similar workload, HRV was lower after continuous intervention.     

Tei指数预测慢性心力衰竭病人运动耐量的价值

目的　测量慢性心力衰竭病人的Tei指数 ,分析Tei指数与 6分钟步行距离的关系。方法　慢性心力衰竭住院病人 70例 ,行超声心动图检查 ,所有病人进行 6分钟步行试验 ,分析 6分钟步行距离与超声心动图各参数的相关性。结果　平均Tei指数随NYHA分级的增加而增加 ,单因素相关分析显示Tei指数与E/A比值呈正相关 ,与左室晚期充盈的A峰速度、E峰减速时间DT及左室射血分数呈负相关。Tei指数与心率、血压、年龄无相关性。与单纯反映左室收缩舒张功能的指标相比 ,Tei指数与 6分钟步行距离之间有更强的相关性 (r=- 0 .5 80 ,P <0 0 0 1)。多因素逐步回归分析显示Tei指数与A峰速度为预测心力衰竭病人 6分钟步行距离的独立因素。结论　左室舒张功能异常比左室收缩功能异常对慢性心力衰竭病人运动耐量的影响更明显。Tei指数反映整体的心肌功能 ,对于评价左室收缩功能不全病人的心肺运动耐量是一个很有价值、简便、易重复的指标     

Effects of branched-chain amino acid (BCAA) supplementation on endurance exercise performance of pregnant rats

Aims

The present study evaluated the effects of BCAA supplementation on exercise performance of pregnant rats.

Methods

In order to assess these effects, Wistar rats were divided into four groups: sedentary not-supplemented (SNS, n = 8); sedentary supplemented (SS, n = 8); trained not-supplemented (TNS, n = 8) and trained supplemented (TS, n = 8). All groups were submitted to the endurance test until exhaustion (ET) and post-effort lactate (PEL) determination before pregnancy (ET-B and PEL-B) and at the 19th day of pregnancy (ET-19 and PEL-19).

Results

The endurance training significantly increased the ET time to exhaustion (p < 0.05). Regardless of BCAA supplementation, both endurance trained groups (TS and TNS) showed a longer time to exhaustion, assessed by ET, compared with the sedentary groups (SS and SNS) (p < 0.05). In the TNS, ET-19 time to exhaustion decreased when compared with the period before pregnancy. On the other hand, ET-19 time to exhaustion was not affected in the TS at the end of the pregnancy period. In addition, TS showed a marked PEL-19 reduction when compared with PEL-B. The data presented herein suggest that BCAA supplementation plays an ergogenic role in the maintenance of exercise performance during pregnancy in rats.     

Low exercise ventilation in endurance athletes.

Previous studies have shown that endurance athletes are endowed with low ventilatory responses to chemical stimuli. The implications of this association have never been clear. Although recent evidence shows that exercise ventilation (VE) correlates with ventilatory chemoresponsiveness in a group of athletes, the extent to which non-athletes may differ from athletes in this regard is unknown. We have examined the relationship between ventilatory chemoresponsiveness and exercise VE in a group of 7 non-athletes, and contrasted these findings with those obtained previously from 8 endurance and 8 non-endurance athletes. Correlation lines of exercise VE with chemical responses were similar in slope and intercept for both athletes and non-athletes. However, we found that non-athletes had greater exercise VE per unit metabolic rate (VO2 or VCO2), and greater ventilatory responses to O2 and CO2, when compared with endurance athletes at equal relative work loads (P less than 0.05). The lower exercise VE/VCO2 of endurance athletes as compared with non-athletes persisted in hyperoxia, indicating that factors other than differences in hypoxic sensitivity explain the lower exercise VE of endurance athletes. Low exercise VE may be the link between low ventilatory chemosensitivity and outstanding endurance athletic performance.