Abstract
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.
Highlights
Since its first description at the end of the 19th century (Fick, 1881), eccentric exercise has sparked much interest on account of distinctive features enabling high external mechanical power at reduced cost and its potential for positive rehabilitation and training outcomes (Hoppeler, 2016).In regular daily movement, concentric and eccentric muscle contractions are combined, for example, when using the stairs or when braking a fall or lowering a heavy object
In the study by MacMillan et al (2017) patients with chronic obstructive pulmonary disease (COPD) were randomly assigned to either a concentric or an eccentric exercise training protocol to contrast the effects of a rehabilitation program consisting of three weekly 30-min sessions for 10 weeks at an intensity defined by the target HR corresponding to 60–80% of peak power output established from a concentric incremental test
The few studies currently available suggest that mitochondrial biogenesis is not stimulated in response to either acute or chronic eccentric exercise, at least when performed at intensities as used in studies summarized in Tables 1–3, which is consistent with the absence of changes in mitochondrial respiration parameters
Summary
Since its first description at the end of the 19th century (Fick, 1881), eccentric exercise has sparked much interest on account of distinctive features enabling high external mechanical power at reduced cost and its potential for positive rehabilitation and training outcomes (Hoppeler, 2016). A similar observation was made during uphill and downhill running where subjects reached the same maximal HR but failed to reach concentric VO2max value under eccentric exercise modality (Lemire et al, 2020) These results are of significance, as they provide a quantifiable comparison of cardiorespiratory demands that can serve to guide exercise rehabilitation recommendations. The extent to which the degree of cytoskeletal mechanical stress and timing of the damage and repair cycle modulate the adaptive responses is not clear This point is illustrated by the report of transient alterations after one session of unaccustomed/acute eccentric exercise, which resolve spontaneously with rest, as well as evidence that after a few bouts, a repeated effect is seen such that postexercise markers of damage are no longer seen (McHugh, 2003; Hyldahl et al, 2017). Repeated large muscle mass dynamic exercise of sufficient intensity induces systemic adaptations that lead to an increase in VO2peak/max, which is a strong indicator of the aerobic,
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