Hormonal
Irisin, a myokine derived from FNDC5, promotes skeletal muscle hypertrophy and attenuates denervation-induced atrophy by activating IL-6 signaling and satellite cell elevation, although its role in human pathology remains under investigation.
Irisin shows promise in animal studies for building muscle and preventing atrophy, but its role in humans is still being defined. Exercise increases the precursor protein (FNDC5) in humans, but whether this translates to higher circulating irisin levels is debated. It is not yet a validated therapeutic target for human muscle gain.
Reza et al. reported that irisin induced skeletal muscle hypertrophy and attenuated denervation-induced atrophy by activating IL-6 signaling in rodents (Reza et al., 2017). The effects of irisin on hypertrophy were shown to be established by the activation of muscle satellite cells and elevation of protein synthesis (Reza et al., 2017).
Why this rating
Strong evidence in rodent models, but human data is conflicting or limited (e.g., lower levels in sarcopenia).
Source
Role of Myokines in Regulating Skeletal Muscle Mass and Function
Jong Han Lee et al. · Frontiers in Physiology · 2019
DOI 10.3389/fphys.2019.00042
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