Daily blood flow restriction does not affect muscle fiber capillarization & satellite cell content during […] bed rest in healthy young men, 2024

[SNT Gatchaman]

Daily blood flow restriction does not affect muscle fiber capillarization and satellite cell content during two weeks of bed rest in healthy young men
Thorben Aussieker; Cas J. Fuchs; Antoine Zorenc; Lex B. Verdijk; Luc J.C. van Loon; Tim Snijders

The present study assessed whether single-leg daily blood flow restriction (BFR) treatment attenuates the decline in muscle fiber size, capillarization, and satellite cell (SC) content during 2 weeks of bed rest in healthy, young men.

Twelve healthy, young men (age: 24±3 y; BMI: 23.7±3.1 kg/m2) were subjected to 2 weeks of bed rest, during which one leg was exposed to three times daily 5 min of BFR, whereas the contralateral leg received sham treatment (CON). Muscle biopsies were obtained from the M. vastus lateralis from both the BFR and CON leg before and immediately after the 2 weeks of bed rest. Type I and II muscle fiber size, myonuclear content, capillarization, and SC content were assessed by immunohistochemistry.

No significant decline in either type I or type II muscle fiber size were observed following bedrest, with no differences between the CON and BFR leg (P>0.05). Type I muscle fiber capillary density increased in response to bed rest in both legs (P<0.05), while other muscle fiber capillarization measures remained unaltered. SC content decreased in both type I (from 7.4±3.2 to 5.9±2.7 per 100 fibers) and type II (from 7.2±3.4 to 6.5±3.2 per 100 fibers) muscle fibers (main effect of time P=0.018), with no significant differences between the BFR and CON leg (P>0.05).

In conclusion, two weeks of bed rest has no effect on muscle capillarization, decrease the SC content and daily BFR treatment does not affect skeletal muscle fiber size and SC content in healthy, young men.

Link | PDF (Journal of Applied Physiology)

 

[Hutan]

I'm struggling to make sense of this.
e.g

In conclusion, two weeks of bed rest has no effect on muscle capillarization, decrease the SC content and daily BFR treatment does not affect skeletal muscle fiber size and SC content in healthy, young men.

versus

Type I muscle fiber capillary density increased in response to bed rest in both legs (P<0.05)

SC content decreased in both type I (from 7.4±3.2 to 5.9±2.7 per 100 fibers) and type II (from 7.2±3.4 to 6.5±3.2 per 100 fibers) muscle fibers (main effect of time P=0.018)

 

[SNT Gatchaman]

I've only skim-read through once, but I think the body of the paper indicates that capillaries (numbers) do not decline with bed rest, even though the muscle fibres themselves reduce in size. So capillary density increases. They also say capillary contact points on individual fibres don't change. Findings in relation to the control leg.

Methods —

Various indices of muscle fiber capillarization (capillary contacts (CC), capillary-to-fiber ratio on an individual fiber basis (C/Fi ), capillary-to-fiber perimeter exchange (CFPE) index and capillary density (CD)) were determined

Discussion —

A period of strict bed rest results in an approximate 0.5% decline in muscle mass per day, which is accompanied by a ~0.3-4.2% decline in muscle strength (43). In line, we have previously reported a significant decline in leg lean mass and muscle strength in response to 14 days of bed rest of ~5% and ~6-10%, respectively (9). […] Despite the substantial macroscopic atrophy, type I (-5.3±14.0%) and type II (-9.1±16.3%) muscle fiber size tended (P=0.062; η2 =0.282) to decline in response to the bed rest intervention period (9). We extend on this prior work, by assessing a range of other muscle fiber characteristics in muscle tissue biopsies collected before and after 14 days of bedrest.

That passage is also a little confusing to interpret.

The muscle fiber capillary network plays a key role in delivery of nutrients, oxygen, and signaling factors that facilitate the muscle conditioning response (13, 26). Although capillary loss is well documented following prolonged periods of muscle detraining (<3 months) (18-20), discrepant findings have been reported after shorter periods of disuse. In the present study, no changes in type I or type II muscle fiber capillarization (CC, C/Fi and CFPE-index) were observed in the CON leg following 2 weeks of bed rest. The significant increase in type I muscle fiber CD can be explained by the moderate decline in type I muscle fiber size over time, whereas the number of capillary contacts remained the same. Together this shows that disuse muscle (fiber) atrophy induced over a 14-day bed rest period is not accompanied by a reduction of muscle fiber capillaries.

We should probably have a look at [9]

[9] Daily blood flow restriction does not preserve muscle mass and strength during 2 weeks of bed rest (2024, The Journal of Physiology) [Open access]
[18] Interrelationships between skeletal muscle adaptations and performance as studied by detraining and retraining (1979, Acta Physiologica Scandinavica) SciHub
[20] Adaptive changes in work capacity, skeletal muscle capillarization and enzyme levels during training and detraining (1981, Acta Physiologica Scandinavica) SciHub

 

[Hutan]

Thank you.

I've only skim-read through once, but I think the body of the paper indicates that capillaries (numbers) do not decline with bed rest, even though the muscle fibres themselves reduce in size. So capillary density increases.

That makes sense, although the abstract says

No significant decline in either type I or type II muscle fiber size were observed following bedrest, with no differences between the CON and BFR leg (P>0.05).

The abstract says that satellite cell content (volume?) decreased.

 

[SNT Gatchaman]

I haven't looked closely at the satellite cell passages, but I thought it might be useful to have this paper noted (+/- its predecessors) so we might be able to compare with LC/ME biopsy findings. Hopefully, the upcoming Wüst/Appleman paper will report on more definitive direct comparisons between ME/LC vs normals-after-bedrest.