About this Research Topic
Skeletal muscle contracts by either shortening or lengthening (concentrically or eccentrically, respectively). Although these two types of actions coexist in our daily movements, they completely differ from one another in terms of mechanisms of force generation, maximum force produced and energy cost. Eccentric actions generate higher forces than isometric and concentric ones for any given contraction velocity. In addition, the metabolic cost required for lengthening actions is approximately a quarter of the one required for a shortening one of the similar magnitude. Thus, eccentric training (ECC) has been advocated as particularly suitable for recovering muscle mass and strength in elderly and clinical populations.
Many medical conditions are associated with muscle wasting: cardiac failure, chronic obstructive pulmonary disease, malignant tumors and the loss of muscle mass in old age (Sarcopenia) all involve a reduction in muscle strength, mobility and exercise capacity. Thus, the application of specific exercise interventions aimed at recovering these functions could be particularly beneficial to these populations. The loss of muscle mass and strength in these conditions is associated with a reduced aerobic capacity: ECC has been shown to be particularly suitable for training these individuals since it provides a strong mechanical stress at a lower metabolic cost. Despite these advantages, the use of ECC in clinical scenarios and ageing has often been object of contrasting opinions, mainly because associated with exercise induced muscle damage and inflammation. Alterations to muscle fiber cytoskeleton, cellular damage and local inflammation, due to the high forces developed by ECC contractions, have been previously reported.
Moderate/low ECC loading has been suggested as a strategy to overcome this problem, as when meticulously monitored and progressively ramped, it effectively promotes muscle mass and strength gains without inducing muscle soreness and damage.
Further, recent investigations have highlighted the benefit of using lower loads for increasing anabolism after conventional resistance training. However, up to date, research has mainly focused on the acute and chronic effects of high-load ECC only (resistance-exercised based) while the potential of moderate/low load regimes seems to have been virtually neglected. Recent research has elucidated many ECC-specific adaptations in skeletal muscle (i.e. mechanisms of force generation, structural remodeling and cellular signaling, different neuromuscular activation strategies between loading modalities). Nonetheless, the structural, neural and metabolic adaptations to low/moderate ECC training still remain unclear as well as the comparison between ECC and CON or conventional training (mix of ECC/CON) and the molecular mechanisms orchestrating such adaptations.
Therefore, the aim of this Research Topic is to better clarify what are the main functional, morphological and molecular responses of human skeletal muscle in response to different intensities of ECC compared to conventional ECC/CON loading paradigms, to gain novel insights into this particular typology of exercise, which prove particularly useful in clinical settings and in rehabilitation.
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