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New work out in preprint with @kevinmurachphd.bsky.social

Nathan Serrano et al. present this #Opinion piece providing a critical evaluation of muscle memory theory 💭 💪

🔗 physoc.onlinelibrary.wiley.com/doi/10.1113/...

Muscle memory theory: A critical evaluation Click on the article title to read more.

A recent opinion article providing a nuanced view on the current standing of Muscle Memory Theory physoc.onlinelibrary.wiley.com/doi/10.1113/...

Brushing up on some new confocal imaging techniques

The impact of life-long strength versus endurance training on muscle fiber morphology and phenotype composition in older men | Journal of Applied Physiology | American Physiological Society Aging is typically associated with decreased muscle strength and rate of force development (RFD), partly explained by motor unit remodeling due to denervation, and subsequent loss of fast-twitch type II myofibers. Exercise is commonly advocated to counteract this detrimental loss. However, it is unclear how life-long strength versus endurance training may differentially affect markers of denervation and reinnervation of skeletal myofibers and, in turn, affect the proportion and morphology of fast-twitch type II musculature. Thus, we compared fiber type distribution, fiber type grouping, and the prevalence of atrophic myofibers (≤1,494 µm2) in strength-trained (OS) versus endurance-trained (OE) master athletes and compared the results to recreationally active older adults (all >70 yr, OC) and young habitually active references (<30 yr, YC). Immunofluorescent stainings were performed on biopsy samples from vastus lateralis, along with leg press maximal strength and RFD measurements. OS demonstrated similar type II fiber distribution (OS: 52.0 ± 16.4%; YC: 51.1 ± 14.4%), fiber type grouping, maximal strength (OS: 170.0 ± 18.9 kg, YC: 151.0 ± 24.4 kg), and RFD (OS: 3,993 ± 894 N·s−1, YC: 3,470 ± 1,394 N·s−1) as young, and absence of atrophic myofibers (OS: 0.2 ± 0.7%; YC: 0.1 ± 0.4%). In contrast, OE and OC exhibited more atrophic fibers (OE: 1.2 ± 1.0%; OC: 1.1 ± 1.4%), more grouped fibers, and smaller proportion of type II fibers (OE: 39.3 ± 11.9%; OC: 35.0 ± 12.4%) than OS and YC (all P < 0.05). In conclusion, strength-trained master athletes were characterized by similar muscle morphology as young, which was not the case for recreationally active or endurance-trained old. These results indicate that strength training may preserve type II fibers with advancing age in older men, likely as a result of chronic use of high contractile force generation. NEW & NOTEWORTHY Aging is associated with loss of fast-twitch type II myofibers, motor unit remodeling, and grouping of myofibers. This study reveals, for the first time, that strength training preserves neural innervation of type II fibers, resulting in similar myofiber type distribution and grouping in life-long strength-trained master athletes as young moderately active adults. In contrast, life-long endurance-trained master athletes and recreationally active old adults demonstrated higher proportion of type I fibers accompanied by more marked grouping of type I myofibers, and more atrophic fibers compared with strength-trained master athletes and young individuals. Thus, strength training should be utilized as a training modality for preservation of fast-twitch musculature, maximal muscle strength, and rapid force capacity (RFD) with advancing age.

Lifelong strength training had greater muscle fiber size and type II fibers compared to endurance training. This suggests strength may be more beneficial vs endurance in old age. doi.org/10.1152/japplphysiol.00208.2023

Deficiency of α-actinin-3 is associated with increased susceptibility to contraction-induced damage and skeletal muscle remodeling Abstract. Sarcomeric α-actinins (α-actinin-2 and -3) are a major component of the Z-disk in skeletal muscle, where they crosslink actin and other structura

ACTN-3 deficiency (common in ~20% of people) weakens muscles, especially during forceful contractions. If you have the R577x mutation (deficiency) you may have weakened muscles and lack contraction ability but it comes with a trade off of increased slow fiber ACTN-2
doi.org/10.1093/hmg/...

Body fat and risk of all-cause mortality: a systematic review and dose-response meta-analysis of prospective cohort studies - International Journal of Obesity International Journal of Obesity - Body fat and risk of all-cause mortality: a systematic review and dose-response meta-analysis of prospective cohort studies

Leaner doesn't always mean healthier... specifically when considering mortality risk. Males show lowest risk around 25% body fat whereas females are around 35%

doi.org/10.1038/s413...

Muscle physiology and its relations to the whole body in health and disease Click on the article title to read more.

Along the same line as our most recent publication, here is another paper outlining similar concepts of muscle health

Muscle physiology and its relations to the whole body in health and disease - Groeneveld - Acta Physiologica - Wiley Online Library

doi.org/10.1111/apha...

Type I (slow twitch) fibers are well known as the endurance type for their high metabolic activity whereas type II fibers are more related to high power but low endurance ability due to a lower ability to metabolize fats and insulin sensitivity. Within obesity, individuals may express more type II

Muscle fiber phenotype: a culprit of abnormal metabolism and function in skeletal muscle of humans with obesity | American Journal of Physiology-Endocrinology and Metabolism | American Physiological S... The proportion of the different types of fibers in a given skeletal muscle contributes to its overall metabolic and functional characteristics. Greater proportion of type I muscle fibers is associated...

Muscle fiber types are a potential metabolic link to overall metabolism in humans with obesity. In this review we laid out the various metabolic characteristics linked to each fiber type and how they may contribute to overall metabolic status

journals.physiology.org/doi/full/10....