Cardiovascular and Muscular Consequences of Work-Matched Interval-Type of Concentric and Eccentric Pedaling Exercise on a Soft Robot

Eccentric Contraction Enhances Healing of the Bone-Tendon Interface After Rotator Cuff Repair in Mice

BACKGROUND

Various muscle contraction modalities have differing effects on the musculoskeletal system. To understand the magnitude of these effects, the authors investigated the effects of eccentric and concentric contractions on the bone-tendon interface after rotator cuff repair in mice.

HYPOTHESIS

Eccentric contraction promotes healing of the bone-tendon interface after rotator cuff repair in mice better than other muscle contraction patterns.

STUDY DESIGN

Controlled laboratory study.

METHODS

The authors performed acute supraspinatus tendon repair of the right shoulder in 104 C57BL/6 mice. Animals were randomized into 4 groups postoperatively: control group (Con group), horizontal running group (Horz group), +15° uphill running group (Up group), and -15° downhill running group (Down group), with 26 animals in each group. At 4 and 8 weeks postoperatively, the authors removed the eyeball, collected blood samples, and extracted the supraspinatus tendon-humerus complex for histological, immunological, bone morphological, and biomechanical tests.

RESULTS

At 4 and 8 weeks postoperatively, the Down group exhibited a better collagen cell arrangement and fibrocartilage layer than the other 3 groups. At 4 weeks postoperatively, anti-inflammatory macrophages (M2 macrophages) were observed at the repair site in all groups except for the Con group. At 8 weeks postoperatively, M2 macrophages were withdrawn from the tendon site in all groups. The transforming growth factor β1 concentration in the Down group was greater than that in the other 3 groups at 4 weeks postoperatively, and it was higher than that in the Con group at 8 weeks postoperatively. The bone volume fraction, number of trabeculae, and thickness of trabeculae at the repair site in the Down group, as well as the ultimate strength and failure load in the biomechanical tests, were greater than those in the other 3 groups at 8 weeks postoperatively.

CONCLUSION

Eccentric contraction promotes healing of the bone-tendon interface after rotator cuff repair in mice better than other muscle contraction patterns.

CLINICAL RELEVANCE

After clinical rotator cuff repair, patients can be rehabilitated by eccentric training to speed up the functional recovery of the shoulder joint.

ACE-I/D Allele Modulates Improvements of Cardiorespiratory Function and Muscle Performance with Interval-Type Exercise

Background: The prominent insertion/deletion polymorphism in the gene for the major modulator of tissue perfusion, angiotensin-converting enzyme (ACE-I/D) is associated with variability in adjustments in cardiac and skeletal muscle performance with standard forms of endurance and strength type training. Here, we tested whether the ACE-I/D genotype would be associated with variability in the effects of interval-type training on peak and aerobic performance of peripheral muscle and cardio-vasculature and post-exercise recovery. Methods: Nine healthy subjects (39.0 ± 14.7 years of age; 64.6 ± 16.1 kg, 173.6 ± 9.9) completed eight weeks of interval training on a soft robotic device based on repeated sets of a pedaling exercise at a matched intensity relative to their peak aerobic power output. Prior to and post-training, peak anaerobic and aerobic power output was assessed, mechanical work and metabolic stress (oxygen saturation and hemoglobin concentrations of Musculus vastus lateralis (VAS) and Musculus gastrocnemius (GAS), blood lactate and factors setting cardiac output such as heart rate, systolic and diastolic blood pressure were monitored during ramp-incremental exercise and interval exercise with the calculation of areas under the curve (AUC), which were put in relation to the produced muscle work. Genotyping was performed based on I- and D-allele-specific polymerase chain reactions on genomic DNA from mucosal swaps. The significance of interaction effects between training and ACE I-allele on absolute and work-related values was assessed with repeated measures ANOVA. Results: Subjects delivered 87% more muscle work/power, 106% more cardiac output, and muscles experienced ~72% more of a deficit in oxygen saturation and a ~35% higher passage of total hemoglobin during single interval exercise after the eight weeks of training. Interval training affected aspects of skeletal muscle metabolism and performance, whose variability was associated with the ACE I-allele. This concerned the economically favorable alterations in the work-related AUC for the deficit of SmO2 in the VAS and GAS muscles during the ramp exercise for the I-allele carriers and opposing deteriorations in non-carriers. Conversely, oxygen saturation in the VAS and GAS at rest and during interval exercise was selectively improved after training for the non-carriers of the I-allele when the AUC of tHb per work during interval exercise deteriorated in the carriers. Training also improved aerobic peak power output by 4% in the carriers but not the non-carriers (p = 0.772) of the ACE I-allele while reducing negative peak power (-27.0%) to a lesser extent in the ACE I-allele carriers than the non-carriers. Variability in cardiac parameters (i.e., the AUC of heart rate and glucose during ramp exercise, was similar to the time to recovery of maximal tHb in both muscles after cessation of ramp exercise, only associated with the ACE I-allele but not training per se. Diastolic blood pressure and cardiac output during recovery from exhaustive ramp exercise demonstrated a trend for training-associated differences in association with the ACE I-allele. Discussion: The exercise-type dependent manifestation of antidromic adjustments in leg muscle perfusion and associated local aerobic metabolism between carriers and non-carriers of the ACE I-allele with the interval-training highlight that non-carriers of the I-allele do not present an essential handicap to improve perfusion-related aerobic muscle metabolism but that the manifestation of responsiveness depends on the produced work. Conclusions: The deployed interval-type of exercise produced ACE I-allele-related differences in the alterations of negative anaerobic performance and perfusion-related aerobic muscle metabolism, which manifestation is exercise specific. The training-invariant ACE I-allele-associated differences in heart rate and blood glucose concentration emphasize that the repeated impact of the interval stimulus, despite a near doubling of the initial metabolic load, was insufficient to overturn ACE-related genetic influences on cardiovascular function.

A Short-Term Eccentric HIIT Induced Greater Reduction in Cardio-Metabolic Risk Markers in Comparison With Concentric HIIT in Sedentary Overweight Men

Background: Steady-state eccentric exercise training improves cardiometabolic risk (CMR) despite lesser cardiovascular demands compared with load-matched concentric training. Whether a high-intensity interval eccentric training is also effective reducing CMR is unknown. Aim: To compare the effects of a short-term high-intensity interval eccentric training (ECC-HIIT) with high-intensity interval concentric training (CONC-HIIT) on CMR in sedentary overweight men. Methods: Twenty men (age: 27.9 ± 5.3y, body massindex: 29.1 ± 3.1 kg·m-2) were randomly assigned to ECC-HIIT (n = 10) or CONC-HIIT (n = 10) delivered as six sessions, including 4 x 5:2 min work-to-rest ratio, at 80% peak concentric power output. Heart rate (HR), rate of perceived exertion (RPE) and muscle soreness weremonitored during training sessions. Training effects on lipid profile, insulin sensitivity (HOMA-IR), body composition, thigh circumference, isometric knee extensors maximal strength, resting systolic and diastolic blood pressure (SBP and DBP) were determined. Results: Average training HR and RPE were -29%and -50%lower in ECC-HIIT in comparison with CONC-HIIT. Muscle soreness was initially greater after ECC-HIIT compared with CONC-HIIT. Significant changes in total and low-density lipoprotein cholesterol (-7.0 ± 8.7%; p = .02 and -6.3 ± 14.4%; p = .03), SBP (-9.8 ± 7.8%; p = .002), and maximal thigh circumference (+2.5 ± 3.1%; p = .02) were observed following ECC-HIIT. No changes in any CMR marker were observed after CONC-HIIT. Moderate-to-large training effect sizes were obtained in thigh circumference, SBP, total cholesterol and low-density lipoprotein cholesterol in response to ECC-HIIT. Conclusion: A two-week ECC-HIIT was well-tolerated and induced rapid onset improvements in cholesterol and blood pressure compared to conventional CONC-HIIT in sedentary overweight men.

High-Intensity Interval Training for Heart Failure Patients With Preserved Ejection Fraction (HIT-HF)-Rational and Design of a Prospective, Randomized, Controlled Trial

Background: The pathophysiology of HF with preserved ejection fraction (HFpEF) has not yet been fully understood and HFpEF is often misdiagnosed. Remodeling and fibrosis stimulated by inflammation appear to be main factors for the progression of HFpEF. In contrast to patients with HF with reduced ejection fraction, medical treatment in HFpEF is limited to relieving HF symptoms. Since mortality in HFpEF patients remains unacceptably high with a 5-year survival rate of only 30%, new treatment strategies are urgently needed. Exercise seems to be a valid option. However, the optimal training regime still has to be elucidated. Therefore, the aim of the study is to investigate the effects of a high-intensity interval (HIT) training vs. a moderate continuous training (MCT) on exercise capacity and disease-specific mechanisms in a cohort of patients with HFpEF. Methods: The proposed study will be a prospective, randomized controlled trial in a primary care setting including 86 patients with stable HFpEF. Patients will undergo measurements of exercise capacity, disease-specific blood biomarkers, cardiac and arterial vessel structure and function, total hemoglobin mass, metabolic requirements, habitual physical activity, and quality of life (QoL) at baseline and follow-up. After the baseline visit, patients will be randomized to the intervention or control group. The intervention group (n = 43) will attend a supervised 12-week HIT on a bicycle ergometer combined with strength training. The control group (n = 43) will receive an isocaloric supervised MCT combined with strength training. After 12 weeks, study measurements will be repeated in all patients to quantify the effects of the intervention. In addition, telephone interviews will be performed at 6 months, 1, 2, and 3 years after the last visit to assess clinical outcomes and QoL. Discussion: We anticipate clinically significant changes in exercise capacity, expressed as VO_2peak, as well as in disease-specific mechanisms following HIT compared to MCT. Moreover, the study is expected to add important knowledge on the pathophysiology of HFpEF and the clinical benefits of a training intervention as a novel treatment strategy in HFpEF patients, which may help to improve both QoL and functional status in affected patients. Trial registration: ClinicalTrials.gov, identifier: NCT03184311, Registered 9 June 2017.

Aerobic Metabolic Adaptations in Endurance Eccentric Exercise and Training: From Whole Body to Mitochondria

A characteristic feature of eccentric as compared with concentric exercise is the ability to generate greater mechanical loads for lower cardiopulmonary demands. Current evidence concurs to show that eccentric training translates into considerable gains in muscle mass and strength. Less is known, however, regarding its impact on oxygen transport and on factors to be considered for optimizing its prescription and monitoring. This article reviews the existing evidence for endurance eccentric exercise effects on the components of the oxygen transport system from systemic to mitochondria in both humans and animals. In the studies reviewed, specially designed cycle-ergometers or downhill treadmill running were used to generate eccentric contractions. Observations to date indicate that overall, the aerobic demand associated with the eccentric training load was too low to significantly increase peak maximal oxygen consumption. By extension, it can be inferred that the very high eccentric power output that would have been required to solicit a metabolic demand sufficient to enhance peak aerobic power could not be tolerated or sustained by participants. The impact of endurance eccentric training on peripheral flow distribution remains largely undocumented. Given the high damage susceptibility of eccentric exercise, the extent to which skeletal muscle oxygen utilization adaptations would be seen depends on the balance of adverse and positive signals on mitochondrial integrity. The article examines the protection provided by repeated bouts of acute eccentric exercise and reports on the impact of eccentric cycling and downhill running training programs on markers of mitochondrial function and of mitochondrial biogenesis using mostly from animal studies. The summary of findings does not reveal an impact of training on skeletal muscle mitochondrial respiration nor on selected mitochondrial messenger RNA transcripts. The implications of observations to date are discussed within future perspectives for advancing research on endurance eccentric exercise physiological impacts and using a combined eccentric and concentric exercise approach to optimize functional capacity.

The Cardiovascular Response to Interval Exercise Is Modified by the Contraction Type and Training in Proportion to Metabolic Stress of Recruited Muscle Groups

Background: Conventional forms of endurance training based on shortening contractions improve aerobic capacity but elicit a detriment of muscle strength. We hypothesized that eccentric interval training, loading muscle during the lengthening phase of contraction, overcome this interference and potentially adverse cardiovascular reactions, enhancing both muscle metabolism and strength, in association with the stress experienced during exercise. Methods: Twelve healthy participants completed an eight-week program of work-matched progressive interval-type pedaling exercise on a soft robot under predominately concentric or eccentric load. Results: Eccentric interval training specifically enhanced the peak power of positive anaerobic contractions (+28%), mitigated the strain on muscle’s aerobic metabolism, and lowered hemodynamic stress during interval exercise, concomitant with a lowered contribution of positive work to the target output. Concentric training alone lowered blood glucose concentration during interval exercise and mitigated heart rate and blood lactate concentration during ramp exercise. Training-induced adjustments for lactate and positive peak power were independently correlated (p < 0.05, |r| > 0.7) with indices of metabolic and mechanical muscle stress during exercise. Discussion: Task-specific improvements in strength and muscle’s metabolic capacity were induced with eccentric interval exercise lowering cardiovascular risk factors, except for blood glucose concentration, possibly through altered neuromuscular coordination.

Concentric and Eccentric Pedaling-Type Interval Exercise on a Soft Robot for Stable Coronary Artery Disease Patients: Toward a Personalized Protocol

BACKGROUND

Cardiovascular diseases are the leading causes of death worldwide, and coronary artery disease (CAD) is one of the most common causes of death in Europe. Leading cardiac societies recommend exercise as an integral part of cardiovascular rehabilitation because it reduces the morbidity and mortality of patients with CAD. Continuous low-intensity exercise using shortening muscle actions (concentric, CON) is a common training modality during cardiovascular rehabilitation. However, a growing clinical interest has been recently developed in high-intensity interval training (HIIT) for stable patients with CAD. Exercise performed with lengthening muscle actions (eccentric, ECC) could be tolerated better by patients with CAD as they can be performed with higher loads and lower metabolic cost than CON exercise.

OBJECTIVE

We developed a clinical protocol on a soft robot to compare cardiovascular and muscle effects of repeated and work-matched CON versus ECC pedaling-type interval exercise between patients with CAD during cardiovascular rehabilitation. This study aims to ascertain whether the developed training protocols affect peak oxygen uptake (VO_2peak), peak aerobic power output (P_peak), and parameters of muscle oxygen saturation (SmO₂) during exercise, and anaerobic muscle power.

METHODS

We will randomize 20-30 subjects to either the CON or ECC group. Both groups will perform a ramp test to exhaustion before and after the training period to measure cardiovascular parameters and SmO₂. Moreover, the aerobic skeletal muscle power (P_peak) is measured weekly during the 8-week training period using a simulated squat jump and a counter movement jump on the soft robot and used to adjust the training load. The pedaling-type interval exercise on the soft robot is performed involving either CON or ECC muscle actions. The soft robotic device being used is a closed kinetic chain, force-controlled interactive training, and testing device for the lower extremities, which consists of two independent pedals and free footplates that are operated by pneumatic artificial muscles.

RESULTS

The first patients with CAD, who completed the training, showed protocol-specific improvements, reflecting, in part, the lower aerobic training status of the patient completing the CON protocol. Rehabilitation under the CON protocol, more than under the ECC protocol, improved cardiovascular parameters, that is, VO_2peak (+26% vs -6%), and P_peak (+20% vs 0%), and exaggerated muscle deoxygenation during the ramp test (248% vs 49%). Conversely, markers of metabolic stress and recovery from the exhaustive ramp test improved more after the ECC than the CON protocol, that is, peak blood lactate (-9% vs +20%) and peak SmO₂ (+7% vs -7%). Anaerobic muscle power only improved after the CON protocol (+18% vs -15%).

CONCLUSIONS

This study indicates the potential of the implemented CON and ECC protocols of pedaling-type interval exercise to improve oxygen metabolism of exercised muscle groups while maintaining or even increasing the P_peak. The ECC training protocol seemingly provided a lower cardiovascular stimulus in patients with CAD while specifically enhancing the reoxygenation and blood lactate clearance in recruited muscle groups during recovery from exercise.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02845063; https://clinicaltrials.gov/ct2/show/NCT02845063.

Basic science and clinical use of eccentric contractions: History and uncertainties

The peculiar attributes of muscles that are stretched when active have been noted for nearly a century. Understandably, the focus of muscle physiology has been primarily on shortening and isometric contractions, as eloquently revealed by A.V. Hill and subsequently by his students. When the sliding filament theory was introduced by A.F. Huxley and H.E. Huxley, it was a relatively simple task to link Hill's mechanical observations to the actions of the cross bridges during these shortening and isometric contractions. In contrast, lengthening or eccentric contractions have remained somewhat enigmatic. Dismissed as necessarily causing muscle damage, eccentric contractions have been much more difficult to fit into the cross-bridge theory. The relatively recent discovery of the giant elastic sarcomeric filament titin has thrust a previously missing element into any discussion of muscle function, in particular during active stretch. Indeed, the unexpected contribution of giant elastic proteins to muscle contractile function is highlighted by recent discoveries that twitchin-actin interactions are responsible for the "catch" property of invertebrate muscle. In this review, we examine several current theories that have been proposed to account for the properties of muscle during eccentric contraction. We ask how well each of these explains existing data and how an elastic filament can be incorporated into the sliding filament model. Finally, we review the increasing body of evidence for the benefits of including eccentric contractions into a program of muscle rehabilitation and strengthening.