Effects of isokinetic, isotonic and isometric submaximal exercise on heart rate and blood pressure

Acute responses and chronic adaptations to exercise in humans: a look from the autonomic nervous system window

The objective of this review was to give an overview on the current knowledge on the neural mechanisms of cardiovascular regulation during acute exercise and the autonomic adaptations brought about by chronic exercise, that is, exercise training. Evidence derived mainly from human studies, which supports the contribution of the different control mechanisms, namely the centralcommand, the reflex drive from active muscles and the arterial baroreflex, with the attendant modifications in autonomic nervous system activity, in determining the acute cardiovascular responses to exercise are discussed, along with some controversial issues and evolving concepts in exercise physiology. In particular, data that show how the various neural mechanisms involved in cardiovascular regulation during exercise are differently modulated by factors related to the muscular activity being performed, such as the type and intensity of exercise and the size of the active muscle masses are presented, stressing the plasticity of the neural network. Thereafter, the clinical implications pertaining neural cardiovascular adaptations to exercise training are presented and discussed, in the context of cardiac diseases. In particular, I will summarize a series of investigations performed in our laboratory that utilized a new training methodology and different exercise formats to quantify the training load in cardiac patients. The way by which individualized exercise training doses affects the autonomic nervous system and the cardiorespiratory adaptations is highlighted.

An evidence-based guide to the efficacy and safety of isometric resistance training in hypertension and clinical implications

More than 30 randomized controlled trials, supported by individual patient-level and group-level meta-analyses and a Delphi analysis of expert opinion, unequivocally show isometric resistance training (IRT) elicits antihypertensive benefits in healthy people and those with chronic illness. We aim to provide efficacy and safety evidence, and a guide for IRT prescription and delivery. Recommendations are made for the use of IRT in specific patient populations and appropriate methods for IRT delivery. Published data suggest IRT consistently elicits mean blood pressure reductions of 7.4/3.3 mmHg systolic blood pressure/diastolic blood pressure, equivalent to antihypertensive medication monotherapy. Blood pressure reductions of this size are associated with an approximate 13% to 22% reduction in major cardiovascular events. Moreover, IRT is safe in a range of patient populations. We suggest that IRT has the greatest potential benefit when used as an antihypertensive therapy in individuals unwilling and/or unable to complete aerobic exercise, or who have had limited adherence or success with it; individuals with resistant or uncontrolled hypertension, already taking at least two pharmacological antihypertensive agents; and healthy or clinical populations, as an adjunct to aerobic exercise and dietary intervention in those who have not yet attained control of their hypertension. IRT is efficacious and produces clinically meaningful blood pressure reductions (systolic blood pressure, 7 mmHg; diastolic blood pressure, 3 mmHg). IRT is safe and typical program delivery requires only about 17 min weekly. IRT should be used as an adjunct to other exercise modalities, in people unable to complete other types of exercise, or in resistant hypertension.

Metabolic and cardiovascular responses to continuous and intermittent plank exercises

BACKGROUND

Plank exercise (PE) is a whole-body isometric muscle training which is beneficial for physical health. However, none of the previous studies investigated the responses within a typical isometric muscle training or PE protocol consisting of multiple sets. The application of PE was restricted for the understudied metabolic and cardiovascular responses, especially for the patients with cardiovascular diseases. This study is to alleviate the safety concerns of PE by investigating the PE-induced metabolic and cardiovascular responses.

METHODS

Eleven male recreational-level college students completed a baseline cardiopulmonary exercise test, continuous PE (CPE) and intermittent PE (IPE). Ratio of maximal oxygen uptake per kilogram of body mass (%VO_2max/kg), ratio of maximal heart rate (%HR_max), and respiratory exchange ratio (RER) were continuously measured during PEs and divided into seven equal timepoints. Blood pressure (BP) was measured every minute during, before, and after PEs. A mixed-model repeated measures ANOVA was used to examine the interaction effect of exercise × phase.

RESULTS

The %VO_2max/kg (F_6,69=11.25, P < 0.001), %HR_max (F_6,65=7.74, P < 0.001), RER (F_6,69=11.56, P < 0.001), and BP (systolic BP, F_2,26=8.42, P = 0.002; diastolic BP, F_2,24=22.63, P < 0.001) increased by safe magnitudes. Compared with the corresponding period in the IPE group, the %VO_2max/kg (33.5 [2.2] vs. 27.7 [1.9], P = 0.043) and %HR_max (63.2 [3.9] vs. 53.3 [2.1], P = 0.019) increased more significantly from the 40% duration of CPE. Systolic BP increased by larger magnitudes during CPE than IPE (154.2 [3.8] vs. 142.3 [4.8] mmHg, P = 0.002). RERs were over 1 during PEs without cardiovascular and metabolic variables over the anaerobic threshold.

CONCLUSION

Energy was mainly supplied by anaerobic metabolism during PEs. CPE may be preferable for trainees aiming at anaerobic capacity enhancement. IPEs may be preferable to CPEs for youth patients with mild and borderline cardiovascular diseases due to their lower metabolic and cardiovascular responses.

Study on the Effects of Different Seat and Leg Support Conditions of a Trunk Rehabilitation Robot

Performance of trunk rehabilitation exercises while sitting on movable surfaces with feet on the ground can increase trunk and leg muscle activations, and constraining the feet to move with the seat isolates control of the trunk. However, there are no detailed studies on the effects of these different leg supports on the trunk and leg muscle activations under unstable and forcefully perturbed seating conditions. We have recently devised a trunk rehabilitation robot that can generate unstable and forcefully perturbed sitting surfaces, and can be used with ground-mounted or seat-connected footrests. In this study, we have evaluated the differences in balance performance, trunk movement and muscle activation (trunk and legs) of fourteen healthy adults caused by the use of these different footrest configurations under the different seating scenarios. The center of pressure and trunk movement results show that the seat-connected footrest may be a more suitable choice for use in a balance recovery focused rehabilitation protocol, while the ground-mounted footrest may be a more suitable choice for a trunk movement focused rehabilitation protocol. Although it is difficult to make a clear selection between footrests due to the mixed trends observed in the muscle activation results, it appears that the seat-connected footrest may be preferable for use with the unstable seat as it causes greater muscle activations. Furthermore, the results provide limited evidence that targeting of a particular muscle group may be possible through careful selection of the seat and footrest conditions. Therefore, it may be possible to utilize the trunk rehabilitation robot to maximize the training outcomes for a wide range of patients through careful selection of training protocols.

Blood Pressure and Heart Rate Responses to an Isokinetic Testing Protocol in Professional Soccer Players

The aim of this study was to determine blood pressure (BP) and heart rate (HR) responses triggered during an isokinetic testing protocol in professional soccer players and compare cardiovascular parameters at completion of this isokinetic protocol with those during a treadmill test. Using purposive sampling, 63 professional soccer players were recruited. Cardiovascular responses were measured noninvasively during a bilateral testing protocol of knee flexion and extension. Treadmill ergospirometry following an incremental speed protocol was performed to analyze the same cardiovascular parameters at rest and at completion of this test. There were significant differences in diastolic blood pressure (DBP) and HR according to field position. The parameters presented high homogeneity at both competitive levels. Systolic blood pressure, mean arterial pressure, HR, and rate pressure product at completion of the treadmill test were significantly higher than those at completion of the isokinetic protocol. Intermittent isokinetic testing protocol of the knee triggers normal and safe BP and HR responses in healthy professional soccer players. The HR of the defenders was higher than those of the forwards and midfielders but was independent of the competitive level. The values of cardiovascular parameters at isokinetic protocol completion were lower than those during the treadmill test.

Muscle Oxygenation, Neural, and Cardiovascular Responses to Isometric and Workload-matched Dynamic Resistance Exercise

Differences in blood flow patterns and energy cost between isometric and dynamic resistance exercise may result to variant cardiovascular, neural, and muscle metabolic responses. We aimed to compare the cardiovascular, baroreceptor sensitivity, and muscle oxygenation responses between workload-matched, large muscle-mass isometric and dynamic resistance exercises. Twenty-four young men performed an isometric and a dynamic double leg-press protocol (4 sets×2 min) with similar tension time index (workload). Beat-by-beat hemodynamics, baroreceptor sensitivity, muscle oxygenation, and blood lactate were assessed. The increase in blood pressure was greater (p<0.05) in the 1^st set during dynamic than isometric exercise (by ~4.5 mmHg), not different in the 2^nd and 3^rd sets, and greater in the 4^th set during isometric exercise (by ~5 mmHg). Dynamic resistance exercise evoked a greater increase in heart rate, stroke volume, cardiac output, and contractility index (p<0.05), and a greater decline in peripheral resistance, baroreceptor sensitivity, and cardiac function indices than isometric exercise (p<0.05). Participants exhibited a greater reduction in muscle oxyhemoglobin and a greater increase in muscle deoxyhemoglobin in dynamic versus isometric exercise (p<0.001-0.05), with no differences in total hemoglobin and blood lactate. In conclusion, large muscle-mass, multiple-set isometric exercise elicits a relatively similar blood pressure but blunted cardiovascular and baroreceptor sensitivity responses compared to workload-matched dynamic resistance exercise. Differences in blood pressure responses between protocols appear small (~5 mmHg) and are affected by the number of sets. The muscle oxidative stimulus is greater during dynamic resistance exercise than workload-matched isometric exercise.

Evaluating Retinal and Choroidal Perfusion Changes after Isometric and Dynamic Activity Using Optical Coherence Tomography Angiography

Optical coherence tomography angiography (OCTA) is a non-invasive tool for imaging and quantifying the retinal and choroidal perfusion state in vivo. This study aimed to evaluate the acute effects of isometric and dynamic exercise on retinal and choroidal sublayer perfusion using OCTA. A pilot study was conducted on young, healthy participants, each of whom performed a specific isometric exercise on the first day and a dynamic exercise the day after. At baseline and immediately after the exercise, heart rate (HR), mean arterial pressure (MAP), superficial capillary plexus perfusion (SCPP), deep capillary plexus perfusion (DCPP), choriocapillaris perfusion (CCP), Sattlers’s layer perfusion (SLP), and Haller’s layer perfusion (HLP) were recorded. A total of 34 eyes of 34 subjects with a mean age of 32.35 ± 7.87 years were included. HR as well as MAP increased significantly after both types of exercise. Both SCPP and DCPP did not show any significant alteration due to isometric or dynamic exercise. After performing dynamic exercise, CCP, SLP, as well as HLP significantly increased. Changes in MAP correlated significantly with changes in HLP after the dynamic activity. OCTA-based analysis in healthy adults following physical activity demonstrated a constant retinal perfusion, supporting the theory of autoregulatory mechanisms. Dynamic exercise, as opposed to isometric activity, significantly changed choroidal perfusion. OCTA imaging may represent a novel and sensitive tool to expand the diagnostic spectrum in the field of sports medicine.

CARDIORESPIRATORY RESPONSES TO ISOKINETIC EXERCISE IN PATIENTS WITH CORONARY ARTERY DISEASE

ABSTRACT Introduction Exercise training using an isokinetic dynamometer is an alternative for improving muscle strength in patients with coronary artery disease (CAD). Few studies have shown metabolic and cardiorespiratory responses to submaximal isokinetic exercises in patients in cardiac rehabilitation programs. Objective To describe cardiorespiratory responses at two intensities of isokinetic exercise. Additionally, we compared the cardiorespiratory responses of isokinetic exercise with data from the incremental cardiopulmonary exercise test (CPET). Methods Eight individuals with CAD (61.7 ± 6.6 years) performed the following tests: 1) CPET on a treadmill; 2) Peak torque test (five repetitions) and fatigue resistance test (20 repetitions) of knee flexion-extension at angular speeds of 120°/s and 180°/s; 3) Two sets of 20 repetitions were performed at 30–40% (low-intensity, LI) and 50–60% (moderate-intensity, MI) of peak torque at angular speeds of 120°/s and 180°/s, using an isokinetic dynamometer. During the exercises, the individuals were connected to an expired gases analyzer with simultaneous monitoring of the electrocardiogram trace, heart rate (HR), oxygen consumption (VO2), carbon dioxide production, and minute ventilation (VE). The differences (∆) between the peak measurements during exercises and the baseline values were calculated. Results Both LI and MI produced cardiorespiratory responses below the anaerobic threshold (82.8 ± 8.1% of HRmax and 74.4 ± 9.6% of VO2peak) compared to the CPET data ( P < 0.01). MI showed higher ∆ HR (9.8 ± 5.5 vs. 6.3 ± 4.6 bpm; P = 0.01), ∆ rate pressure product (3015 ± 2286 vs. 1957 ± 1932 mmHg·bpm; P = 0.01), and ∆VE (10.2 ± 6.2 vs. 6.9 ± 7 L·min-1; P = 0.03) than LI at the angular velocity of 180°/s. Conclusion These results suggest that this isokinetic exercise protocol may be used as a strategy for cardiac rehabilitation programs in patients with CAD. Level of evidence IV; Case series.

Are Blood Pressure and Cardiovascular Stress Greater in Isometric or in Dynamic Resistance Exercise?

Medical and sports medicine associations are reluctant to endorse isometric exercise to the same extent as dynamic resistance exercise (RE). The major concern is the fear of greater increases in blood pressure (BP) that might be associated with isometric exercise. This review comprehensively presents all human studies that directly compared the magnitude of hemodynamic responses between isometric and dynamic RE. We also discuss possible mechanisms controlling BP-response and cardiovascular adjustments during both types of RE. The most prominent finding was that isometric and dynamic RE using small-muscle mass evoke equal increases in BP; however, the circulatory adjustments contributing to this response are different in dynamic and isometric RE. In contrast, studies using large-muscle mass report inconsistent results for the magnitude of BP-response between the two types of RE. Thus, when the same muscles and workloads are used, the increase in BP during isometric and dynamic RE is more comparable to what is commonly believed. However, it should be noted that only a few studies equalized the workload in two types of RE, most used small sample sizes, and all studies employed healthy participants. More studies are needed to compare the cardiovascular risks associated with isometric and dynamic RE, especially in individuals with chronic disease.

Eccentric versus Concentric - Which Is the Most Stressful Cardiovascularly and Metabolically?

The purpose of this study was to compare the fatigability resistance profile and the physiological responses of strenuous concentric (CON) versus eccentric (ECC) isokinetic exercises. At two different sessions, 12 healthy sedentary male subjects (24.3 ± 2.5 years) performed strenuous CON and ECC isokinetic exercises. The protocol consisted of three sets of 12 maximal repetitions, separated by 30-s intervals, at a velocity of 60°·s for both flexor and extensor knee muscles of the dominant leg. Metabolic (ventilation, oxygen uptake, blood lactate concentration) and cardiovascular (HR, mean arterial blood pressure) parameters were registered before, throughout, and after the isokinetic session. The isokinetic data analysis revealed a more pronounced fatigue in the hamstrings than in the quadriceps in the ECC mode (fatigue index, ratio between the third and the first sets, of 94.8% ± 11.8% vs 86.4% ± 10.8%; P < 0.05). All physiological responses studied increased gradually during the isokinetic evaluation, both in CON and ECC modes. For total work normalized by physiological responses, cardiovascular and metabolic variables were lower in the CON than in the ECC mode, a sign of a weaker efficiency in CON mode (ratio between performance and physiological cost). In conclusion, the study shows a specific fatigability resistance profile consisting of an early decrease of ECC hamstring performance compared with the quadriceps profile. In addition, we confirm that physiological consequences are important during strenuous isokinetic exercises but ECC exercise produces less stress on the cardiovascular and the metabolic systems than does CON exercise.

DUPLO-PRODUTO E VARIAÇÃO DA FREQUÊNCIA CARDÍACA APÓS ESFORÇO ISOCINÉTICO EM ADULTOS E IDOSOS

RESUMO Introdução: O envelhecimento predispõe a alterações multissistêmicas, por exemplo, nos sistemas cardiovascular e musculoesquelético. A prática de exercício físico é um importante recurso terapêutico para retardar perdas de funções orgânicas. No entanto, existe pouco conhecimento sobre as respostas cardiovasculares durante e após o exercício isocinético em idosos. Objetivo: O objetivo deste estudo é analisar as respostas de frequência cardíaca, pressão arterial e duplo-produto em indivíduos de distintas faixas etárias submetidos ao esforço muscular isocinético. Método: O estudo foi constituído por 60 voluntários distribuídos em três faixas etárias - G1: 30 a 45 anos, G2: 45 a 60 anos e G3: 60 a 75 anos - submetidos a teste bilateral de flexão-extensão de joelhos em dinamômetro isocinético com velocidade angular de 60º/segundo para verificação das respostas hemodinâmicas. Os dados foram analisados por meio do Software Bioestat® 5.3, pelo teste de Kruskal-Wallis seguido pelo teste de Dunn para as amostras independentes e de Friedman para amostras dependentes, além da comparação das curvas de Kaplan-Meier por meio do teste de log-rank, considerando P ≤ 0,05. Resultados: O grupo de idosos (G3) apresentou maiores valores de pressão arterial sistólica, duplo-produto e tempo para o retorno à frequência cardíaca basal comparado com o grupo mais jovem (G1). Conclusão: O grupo de 60 a 75 anos de idade apresentou maior consumo de oxigênio pelo miocárdio durante e após o exercício, assim como maior tempo para retornar à FC basal em comparação com os mais jovens.

Muscular contraction mode differently affects autonomic control during heart rate matched exercise

The precise contributions of afferent feedback to cardiovascular and respiratory responses to exercise are still unclear. The aim of this crossover study was to assess whether and how autonomic cardiovascular and respiratory control differed in response to dynamic (DYN) and isometric contractions (ISO) at a similar, low heart rate (HR) level. Therefore, 22 healthy males (26.7 ± 3.6 yrs) performed two kinds of voluntary exercises at similar HR: ISO and DYN of the right quadriceps femoris muscle. Although HR was eqivalent (82 ± 8 bpm for DYN and ISO, respectively), rating of exertion, blood pressures, and rate pressure product were higher, whereas breathing frequency, minute ventilation, oxygen uptake and carbon dioxide output were significantly lower during ISO. Tidal volume, end-tidal partial pressures of O2 and CO2, respiratory exchange ratio and capillary blood lactate concentration were comparable between both contraction modes. Heart rate variability (HRV) indicators, SDNN, HF-Power and LF-Power, representing both vagal and sympathetic influences, were significantly higher during ISO. Sample entropy, a non-linear measure of HRV was also significantly affected by contraction mode. It can be concluded that, despite the same net effect on HR, the quality of cardiovascular control during low intensity exercise is significantly different between DYN and ISO. HRV analysis indicated a sympatho-vagal coactivation during ISO. Whether mechanoreceptor feedback alone, a change in central command, or the interaction of both mechanisms is the main contributor of the distinct autonomic responses to the different exercise modes remains to be elucidated.

Heart rate variability and blood pressure during dynamic and static exercise at similar heart rate levels

Aim was to elucidate autonomic responses to dynamic and static (isometric) exercise of the lower limbs eliciting the same moderate heart rate (HR) response. Method: 23 males performed two kinds of voluntary exercise in a supine position at similar heart rates: static exercise (SE) of the lower limbs (static leg press) and dynamic exercise (DE) of the lower limbs (cycling). Subjective effort, systolic (SBP) and diastolic blood pressure (DBP), mean arterial pressure (MAP), rate pressure product (RPP) and the time between consecutive heart beats (RR-intervals) were measured. Time-domain (SDNN, RMSSD), frequency-domain (power in the low and high frequency band (LFP, HFP)) and geometric measures (SD1, SD2) as well as non-linear measures of regularity (approximate entropy (ApEn), sample entropy (SampEn) and correlation dimension D2) were calculated. Results: Although HR was similar during both exercise conditions (88±10 bpm), subjective effort, SBP, DBP, MAP and RPP were significantly enhanced during SE. HRV indicators representing overall variability (SDNN, SD 2) and vagal modulated variability (RMSSD, HFP, SD 1) were increased. LFP, thought to be modulated by both autonomic branches, tended to be higher during SE. ApEn and SampEn were decreased whereas D₂ was enhanced during SE. It can be concluded that autonomic control processes during SE and DE were qualitatively different despite similar heart rate levels. The differences were reflected by blood pressure and HRV indices. HRV-measures indicated a stronger vagal cardiac activity during SE, while blood pressure response indicated a stronger sympathetic efferent activity to the vessels. The elevated vagal cardiac activity during SE might be a response mechanism, compensating a possible co-activation of sympathetic cardiac efferents, as HR and LF/HF was similar and LFP tended to be higher. However, this conclusion must be drawn cautiously as there is no HRV-marker reflecting “pure” sympathetic cardiac activity.

Effect of Carvedilol, Ivabradine or their combination on exercise capacity in patients with Heart Failure (the CARVIVA HF trial)

AIM

Patients with heart failure (HF) have reduced exercise capacity. The beneficial effect of beta-blocker on prognosis is not matched by an impact on exercise capacity and quality of life. We performed a randomised open blinded endpoint study to assess the effect of heart rate reduction with carvedilol, ivabradine, and their combination on exercise capacity in HF patients receiving maximal dose of ACE inhibitor.

METHODS AND RESULTS

After a run-in phase patients were randomly allocated to 3 groups: carvedilol up to 25mg bid (n=38); ivabradine up to 7.5mg bid (n=41); and carvedilol/ivabradine up to 12.5/7.5mg bid (n=42). The maximal dose of study treatment was more frequently tolerated in patients receiving ivabradine (36/41) than in those receiving carvedilol (18/38) or combination therapy (32/42) (P<0.01 ivabradine versus carvedilol). Heart rate was reduced in all three groups, but to a greater extent by the combination. The distance walked on the 6-min walking test and the exercise time on MVO(2) test significantly improved in the ivabradine and combination groups (both P<0.01 versus baseline), as did peak VO(2) and VAT (P<0.01 for ivabradine and P<0.03 for combination versus carvedilol, respectively). No changes in these parameters were found with carvedilol. The patients receiving ivabradine or the combination had better quality of life (P<0.01 versus baseline for ivabradine and P<0.02 for combination), versus no change with carvedilol.

CONCLUSION

Ivabradine alone or in combination with carvedilol is more effective than carvedilol alone at improving exercise tolerance and quality of life in HF patients.

Relief of angina pectoris when carrying heavy loads with the left hand in a patient with previous coronary artery bypass graft operation who has severe exercise angina: a case report

In patients with known coronary artery disease and/or a history of revascularization, angina pectoris or unstable coronary syndromes are usually attributed to the progression of atherosclerotic lesions rather than an unrecognized great vessel disease. However, for patients with a previous coronary artery bypass graft operation (CABG), during which a left internal mammary artery (LIMA) conduit has been used, great vessel disease, especially subclavian artery stenosis should also be suspected. We present a case of a patient with a LIMA conduit who has angina pectoris on exertion, but interestingly the pain is relieved when he carries heavy loads with his left hand, which can be due to increased blood flow to the LIMA conduit during heavy lifting because of increased peripheral resistance.

Effect of long-acting testosterone treatment on functional exercise capacity, skeletal muscle performance, insulin resistance, and baroreflex sensitivity in elderly patients with chronic heart failure a double-blind, placebo-controlled, randomized study

OBJECTIVES

This study investigated the effect of a 12-week long-acting testosterone administration on maximal exercise capacity, ventilatory efficiency, muscle strength, insulin resistance, and baroreflex sensitivity (BRS) in elderly patients with chronic heart failure (CHF).

BACKGROUND

CHF is characterized by a metabolic shift favoring catabolism and impairment in skeletal muscle bulk and function that could be involved in the pathophysiology of heart failure.

METHODS

Seventy elderly patients with stable CHF-median age 70 years, ejection fraction 31.8 +/- 7%-were randomly assigned to receive testosterone (n = 35, intramuscular injection every 6 weeks) or placebo (n = 35), both on top of optimal medical therapy. At baseline and at the end of the study, all patients underwent echocardiogram, cardiopulmonary exercise test, 6-min walk test (6MWT), quadriceps maximal voluntary contraction (MVC), and isokinetic strength (peak torque) and BRS assessment (sequences technique).

RESULTS

Baseline peak oxygen consumption (VO(2)) and quadriceps isometric strength showed a direct relation with serum testosterone concentration. Peak VO(2) significantly improved in testosterone but was unchanged in placebo. Insulin sensitivity was significantly improved in testosterone. The MVC and peak torque significantly increased in testosterone but not in placebo. The BRS significantly improved in testosterone but not in placebo. Increase in testosterone levels was significantly related to improvement in peak VO(2) and MVC. There were no significant changes in left ventricular function either in testosterone or placebo.

CONCLUSIONS

These results suggest that long-acting testosterone therapy improves exercise capacity, muscle strength, glucose metabolism, and BRS in men with moderately severe CHF. Testosterone benefits seem to be mediated by metabolic and peripheral effects.

The effect of eccentric strength training on heart rate and on its variability during isometric exercise in healthy older men

The purpose of this study was to investigate if chronic eccentric strength training (ST) affects heart rate (HR) and heart rate variability (HRV) during sub-maximal isometric voluntary contractions (SIVC). The training group (TG) (9 men, 62 +/- 2) was submitted to ST (12 weeks, 2 days/week, 2-4 sets of 8-12 repetitions at 75-80% peak torque (PT). The control group (CG) (8 men, 64 +/- 4) did not perform ST. The HR and the HRV (RMSSD index) were evaluated during SIVC of the knee extension (15, 30 and 40% of PT). ST increased the eccentric torque only in TG, but did not change the isometric PT and the duration of SIVC. During SIVC, the HR response pattern and the RMSSD index were similar for both groups in pre- and post-training evaluations. Although ST increased the eccentric torque in the TG, it did not generate changes in HR or HRV.

Muscle metaboreflex contribution to cardiovascular regulation during dynamic exercise in microgravity: insights from mission STS-107 of the space shuttle Columbia

One of the most important features of prolonged weightlessness is a progressive impairment of muscular function with a consequent decrease in exercise capacity. We tested the hypothesis that the impairment in musculo-skeletal function that occurs in microgravity results in a potentiation of the muscle metaboreflex mechanism and also affects baroreflex modulation of heart rate (HR) during exercise. Four astronauts participating in the 16 day Columbia shuttle mission (STS-107) were studied 72-71 days before launch and on days 12-13 in-flight. The protocol consisted of 6 min bicycle exercise at 50% of individual V(o2,max) followed by 4 min of postexercise leg circulatory occlusion (PECO). At rest, systolic (S) and diastolic (D) blood pressure (BP), R-R interval and baroreflex sensitivity (BRS) did not differ significantly between pre- and in-flight measurements. Both pre- and in-flight, SBP increased and R-R interval and BRS decreased during exercise, whereas DBP did not change. During PECO preflight, SBP and DBP were higher than at rest, whereas R-R interval and BRS recovered to resting levels. During PECO in-flight, SBP and DBP were significantly higher whereas R-R interval and BRS remained significantly lower than at rest. The part of the SBP response (delta) that was maintained by PECO was significantly greater during spaceflight than before (34.5 +/- 8.8 versus 13.8 +/- 11.9 mmHg, P = 0.03). The tachycardic response to PECO was also significantly greater during spaceflight than preflight (-141.5 +/- 25.2 versus - 90.5 +/- 33.3 ms, P = 0.02). This study suggests that the muscle metaboreflex is enhanced during dynamic exercise in space and that the potentiation of the muscle metaboreflex affects the vagally mediated arterial baroreflex contribution to HR control.

Exercise capacity and cardiovascular adaptations to aerobic training early after stroke

Clinicians are becoming increasingly interested in the use of aerobic training to enhance functional outcomes after stroke. Several studies have demonstrated the effectiveness of training among individuals in the chronic poststroke period. However, there is limited information on the response to training in earlier stages of recovery. The purpose of this article is to review what is known regarding the capacity of people early after stroke (<4 months) to respond to the physiological demands of exercise (exercise capacity) as well as their ability to make long-term cardiovascular adaptations to aerobic exercise. There is evidence that exercise capacity, as measured by peak oxygen consumption on maximal exercise tests, is reduced in this population. There is also evidence, albeit limited, that exercise trainability soon after stroke can be both feasible and safe, if appropriate screening and monitoring are used. Moreover, there are early indications that activity-level functions such as walking speed, mobility, and balance may be enhanced through such programs. Further research is necessary to elucidate the most appropriate timing and design of fitness programs for people early after stroke.

Comparison of heart-rate and blood-pressure increases during isokinetic eccentric versus isometric exercise in older adults

The authors compared heart-rate and blood-pressure responses to typical isometric (ISO) and isokinetic (90 degrees /s) eccentric (ECC) resistance-training protocols in older adults. Twenty healthy older adults (74 +/- 5 years old) performed randomly ordered ISO and isokinetic ECC exercise (3 sets of 10 repetitions) at a target intensity of 100 % of their peak ISO torque value. Heart rate and systolic (SBP) and diastolic (DBP) blood pressures were recorded continuously, and mean arterial pressure (MAP) and rate-pressure product (RPP) were calculated. ECC peak torque (139 +/- 33 N. m) was significantly greater than ISO peak torque (115 +/- 26 N. m; p <.001). All variables increased significantly (p <.001) during both ISO and ECC exercise. Changes in SBP, DBP, MAP, and RPP were significantly greater during ISO exercise than during ECC exercise (p <.001). Clinically, an isokinetic ECC exercise program enables older adults to work at the same torque output with less cardiovascular stress than ISO exercise.

Cardiovascular stress associated with concentric and eccentric isokinetic exercise in young and older adults

Heart rate (HR), mean arterial blood pressure (MAP), and rate-pressure product (RPP) responses to submaximal isokinetic concentric (CON) and eccentric (ECC) knee extension exercise were compared at the same absolute torque output in 20 young (mean+/-SD=23.2+/-1.7 years) and 20 older (mean+/-SD=75.2+/-4.6 years) adults. After determination of peak CON and ECC torques, subjects performed separate, randomly ordered, 2-minute bouts of isokinetic CON and ECC exercise (90 degrees/s, exercise intensity: 50% of CON peak torque). CON exercise elicited greater changes in HR, MAP, and RPP than ECC exercise (p<.001) for both age groups. There were no age-related differences in HR, MAP, or RPP responses for either CON or ECC exercise. At the same absolute torque output, isokinetic CON knee extension exercise elicited significantly greater increases in cardiovascular stress than ECC exercise in both young and older adults. This result has implications for determining appropriate fitness and rehabilitation programs.