Some research support....
The one thing in common with low and high loads, but always reaching full activation... everything from BFR with super low loads, up to heavy loads, is high rate coding...contraction is induced by intra-cellular calcium concentrations, the higher the rate coding, the higher the levels of calcium. Look at just how many things, even hypertrophy, that is stimulated purely by high calcium levels.
https://www.ncbi.nlm.nih.gov/pubmed/17332163
Prolonged or unaccustomed exercise leads to muscle cell membrane damage, detectable as release of the intracellular enzyme lactic acid dehydrogenase (LDH). This is correlated to excitation-induced influx of Ca2+, but it cannot be excluded that mechanical stress contributes to the damage. We here explore this question using N-benzyl-p-toluene sulfonamide (BTS), which specifically blocks muscle contraction. Extensor digitorum longus muscles were prepared from 4-wk-old rats and mounted on holders for isometric contractions. Muscles were stimulated intermittently at 40 Hz for 15-60 min or exposed to the Ca2+ ionophore A23187. Electrical stimulation increased 45Ca influx 3-5 fold. This was followed by a progressive release of LDH, which was correlated to the influx of Ca2+. BTS (50 microM) caused a 90% inhibition of contractile force but had no effect on the excitation-induced 45Ca influx. After stimulation, ATP and creatine phosphate levels were higher in BTS-treated muscles, most likely due to the cessation of ATP-utilization for cross-bridge cycling, indicating a better energy status of these muscles. No release of LDH was observed in BTS-treated muscles. However, when exposed to anoxia, electrical stimulation caused a marked increase in LDH release that was not suppressed by BTS but associated with a decrease in the content of ATP. Dynamic passive stretching caused no increase in muscle Ca2+ content and only a minor release of LDH, whereas treatment with A23187 markedly increased LDH release both in control and BTS-treated muscles.
In conclusion, after isometric contractions, muscle cell membrane damage depends on Ca2+ influx and energy status and not on mechanical stress.
https://www.jstage.jst.go.jp/article/jpfsm/4/2/4_171/_pdf/-char/en
Recent stud-ies suggest that Ca2+ signaling contributes to both muscle hypertrophy and atrophy, suggesting Ca2+ signaling is a regulator of muscle plasticity.
https://www.ncbi.nlm.nih.gov/pubmed/10448861
Skeletal muscle hypertrophy and regeneration are important adaptive responses to both physical activity and pathological stimuli. Failure to maintain these processes underlies the loss of skeletal muscle mass and strength that occurs with ageing and in myopathies. Here we show that stable expression of a gene encoding insulin-like growth factor 1 (IGF-1) in C2C12 skeletal muscle cells, or treatment of these cells with recombinant IGF-1 or with insulin and dexamethasone, results in hypertrophy of differentiated myotubes and a switch to glycolytic metabolism.
Treatment with IGF-1 or insulin and dexamethasone mobilizes intracellular calcium, activates the Ca2+/calmodulin-dependent phosphatase calcineurin, and induces the nuclear translocation of the transcription factor NF-ATc1. Hypertrophy is suppressed by the calcineurin inhibitors cyclosporin A or FK506, but not by inhibitors of the MAP-kinase or phosphatidylinositol-3-OH kinase pathways. Injecting rat latissimus dorsi muscle with a plasmid encoding IGF-1 also activates calcineurin, mobilizes satellite cells and causes a switch to glycolytic metabolism.
We propose that growth-factor-induced skeletal-muscle hypertrophy and changes in myofibre phenotype are mediated by calcium mobilization and are critically regulated by the calcineurin/NF-ATc1 signalling pathway.
And since calcium causes physical 'issues', possibly it causes mechanical 'issues' that stimulate the need for additional fibrils
Now add in these...a quote from Enoka's text
The sensation of tenderness appears to be triggered by the loss of cellular calcium homeostasis (Clarkson, Cyrnes, McCarmick, Turcotte, & White, 1986; Friden & Lieber, 1997' Jackson, Jones, & Edwards, 1984) due to the activity-induced disruption of sarcomeres.
A high intracellular calcium concentration activates proteolytic and lipolytic systems that initiate the degradation of cellular structures (Armstrong, 1990). Because this inflamatory process has a time course smilar to that of the heightened tenderness (Lieber, Schimtz, et al., 1994) and thre is an appropriate activation of the immune system (Malm, Lenkel, & Sjodin, 1999), the sensation of soreness is usually attributed to the inflammatory response.
And this, from this forum way back.. DOMS is seen when remodeling is occuring. (maybe we don't need to 'feel' DOMS, but the same effects..)
Ji-Guo Yu1, 2, Lena Carlsson1 and Lars-Eric Thornell1, 2 Contact Information
(1) Department of Integrative Medical Biology, Section for Anatomy, Umeå University, 901 87 Umeå, Sweden
(2) Department of Musculoskeletal Research, Gävle University, 907 13 Gävle, Sweden
Accepted: 15 January 2004 Published online: 26 February 2004
Abstract The myofibrillar and cytoskeletal alterations observed in delayed onset muscle soreness (DOMS) caused by eccentric exercise are generally considered to represent damage.
By contrast our recent immunohistochemical studies suggested that the alterations reflect myofibrillar remodeling (Yu and Thornell 2002; Yu et al. 2003). In the present study the same human muscle biopsies were further analyzed with transmission electron microscopy and immunoelectron microscopy. We show that the ultrastructural hallmarks of DOMS, Z-disc streaming, Z-disc smearing, and Z-disc disruption were present in the biopsies and were significantly more frequent in biopsies taken 2–3 days and 7–8 days after exercise than in those from controls and 1 h after exercise. Four main types of changes were observed: amorphous widened Z-discs, amorphous sarcomeres, double Z-discs, and supernumerary sarcomeres. We confirm by immunoelectron microscopy that the main Z-disc protein alpha-actinin is not present in Z-disc alterations or in the links of electron-dense material between Z-discs in longitudinal register. These alterations were related to an increase of F-actin and desmin, where F-actin was present within the strands of amorphous material. Desmin, on the other hand, was seen in less dense regions of the alterations. Our results strongly support that the myofibrillar and cytoskeletal alterations, considered to be the hallmarks of DOMS, reflect an adaptive remodeling of the myofibrils.
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Ji-Guo Yu, Dieter O. Fürst, Lars-Eric Thornell
Abstract
Myofibrillar Z-disc streaming and loss of the desmin cytoskeleton are considered the morphological hallmarks of eccentric contraction-induced injury. The latter is contradicted by recent studies where a focal increase of desmin was observed in biopsies taken from human muscles with DOMS. In order to determine the effects of eccentric contraction-induced alterations of the myofibrillar Z-disc, we examined the distribution of a-actinin, the Z-disc portion of titin and the nebulin NB2 region in relation to actin and desmin in DOMS biopsies. In biopsies taken 2–3 days and 7–8 days after exercise, we observed a significantly higher number of fibres showing focal areas lacking staining for a-actinin, titin and nebulin than in biopsies taken from control or 1 h after exercise. None of these proteins were part of Z-disc streamings but instead they were found in distinct patterns in areas characterised by altered staining for desmin and actin.
These were preferentially seen in regions with increased numbers of sarcomeres in parallel myofibrils. We propose that these staining patterns represent different stages of sarcomere formation. These findings therefore support our previous suggestion that muscle fibres subjected to eccentric contractions adapt to unaccustomed activity by the addition of new sarcomeres.