High-frequency blood flow-restricted resistance exercise results in acute and prolonged cellular stress more pronounced in type I than in type II fibers

• Myocellular stress with high-frequency blood flow-restricted resistance exercise (BFRRE) was investigated by measures of heat shock protein (HSP) responses, glycogen content, and inflammatory markers. Thirteen participants [age: 24 +/- 2 yr (means +/- SD), 9 males] completed two 5-day blocks of seven BFRRE sessions, separated by 10 days. Four sets of unilateral knee extensions to failure at 20% of one-repetition maximum (1RM) were performed. Muscle samples obtained before, 1 h after the first session in the first and second block (acute 1 and acute 2), after three sessions (day 4), during the "rest week," and at 3 (post 3) and 10 days postintervention (post 10) were analyzed for HSP70, alpha beta-crystallin, glycogen [periodic acid-Schiff (PAS) staining], mRNAs, miRNAs, and CD68(+) (macrophages) and CD661D(+) (neutrophils) cell numbers. alpha beta-crystallin translocated from the cytosolic to the cytoskeletal fraction after acute 1 and acute 2 (P < 0.05) and immunostaining revealed larger responses in type I than in type II fibers (acute 1, 225 +/- 184% vs. 92 +/- 81%, respectively, P = 0.001). HSP70 was increased in the cytoskeletal fraction at day 4 and post 3, and immunostaining intensities were more elevated in type I than in type II fibers at day 4 (206 +/- 84% vs. 72 +/- 112%, respectively, P <0.001), during the rest week (98 +/- 66% vs. 42 +/- 79%, P < 0.001), and at post 3 (115 +/- 82% vs. 28 +/- 78%, P = 0.003). Glycogen content was reduced in both fiber types, but most pronounced in type I, which did not recover until the rest week (-15% to 29%, P <= 0.001). Intramuscular macrophage numbers were increased by similar to 65% postintervention, but no changes were observed in muscle neutrophils. We conclude that high-frequency BFRRE with sets performed till failure stresses both fiber types, with type I fibers being most affected. NEW & NOTEWORTHY BFRRE has been reported to preferentially stress type I muscle fibers, as evidenced by HSP responses. We extend these findings by showing that the HSP responses occur in both fiber types but more so in type I fibers and that they can still be induced after a short-term training period. Furthermore, the reductions in glycogen content of type I fibers after strenuous frequent BFRRE in unaccustomed subjects can be prolonged (>= 5 days), probably due to microdamage.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Fysiologi (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Physiology (hsv//eng)

Nyckelord

glycogen staining

inflammation

ischemic exercise

kaatsu

muscle

damage

human skeletal-muscle

heat-shock proteins

alpha-b-crystallin

eccentric exercise

subcellular movement

glycogen resynthesis

time-course

expression

damage

hsp70

Physiology

Sport Sciences

Glycogen staining

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