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

Benedikt Gasser,Annika Frei,Walter Frey,Martin Flück,David Niederseer,Christian M Schmied,Martino Franchi,Silvio Catuogno,Daniel Fitze

doi:10.3390/s21010173

Abstract

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.

Highlights

In untrained subjects, repeated sessions of continuous muscle work produce a number of systemic reactions that enhance aerobic capacity [1,2]
Using a soft robotic device that has been designed for neuromuscular rehabilitation, we have recently demonstrated that interval-type eccentric pedaling exercise at moderate intensity reproduces physiological feature being associated with both resistance, and endurance, type eccentric exercise stimulus, including the lower cardiovascular and aerobic cost than concentric interval exercise at a work-matched intensity, and the acutely elevated glucose concentration [19]
Thirteen subjects were recruited for this study upon having credited their written informed consent to participate in this investigation into the effects of concentric compared to eccentric interval-type of training on an Allegro soft robot (Dynamic Devices, Zurich, Switzerland) [19]

Summary

Introduction

In untrained subjects, repeated sessions of continuous muscle work produce a number of systemic reactions that enhance aerobic capacity [1,2]. Typical improvements in oxygen uptake and aerobic power output in the order of 10–15% can be observed after few weeks of endurance training consisting of repeated sessions of continuous exercise at moderate intensity [1,2]. The thereby observable adaptations of systemic aerobic capacity are matched to larger increases in cardiac output and gains in skeletal muscle’s aerobic capacity [3]. Often the gains in endurance performance are limited by the inherent moderate fatigue resistance of untrained subjects that do not allow performing exercise at the high intensities or long durations that induce large degrees of adaptations [9]

Methods

Discussion

Conclusion