Journal article

Human single muscle fibre function with 84 day bed-rest and resistance exercise.


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Publication Details

Författarlista: Tesch, Per A

Publikationsår: 2004

Startsida: 501

End page: 513

Antal sidor: 13

ISSN: 0022-3751



Muscle biopsies were obtained from the vastus lateralis before and after 84 days of bed-restfromsix control (BR) and six resistance-exercised (BRE) men to examine slow- and fast-twitchmuscle fibre contractile function. BR did not exercise during bed-rest and had a 17 and 40%decrease inwholemuscle size and function, respectively. TheBREgroup performedfour sets ofseven maximal concentric and eccentric supine squats 2–3 days perweek (every third day) thatmaintained whole muscle strength and size. Slow (MHC I) and fast (MHC IIa) muscle fibreswere studied at 15?C for diameter, peak force (Po), contractile velocity (Vo) and force–powerparameters. SDS-PAGE was performed on each single fibre after the functional experimentsto determine MHC isoform composition. MHCI and IIa BR fibres were, respectively, 15 and8% smaller, 46 and 25% weaker (Po), 21 and 6% slower (Vo), and 54 and 24% less powerfulafter bed-rest (P<0.05). BR MHCI and IIa Po and power normalized to cell size were lower(P<0.05). BRE MHCI fibres showed no change in size or Vo after bed-rest; however, Po was19%lower (P<0.05), resulting in 20 and30%declines (P<0.05) in normalizedPo and power,respectively. BREMHCIIa fibres showed no change in size, Po and power after bed-rest, whileVo waselevated13%(P<0.05).BREMHCIIanormalizedPo andpowerwere10and15%lower(P<0.05), respectively.MHCisoformcomposition shifted away fromMHCI fibres, resultingin an increase (P<0.05) inMHCI/IIa (BR and BRE) andMHCIIa/IIx (BR only) fibres. Thesedata show that the contractile function of the MHCI fibres was more affected by bed-rest andless influenced by the resistance exercise protocol than the MHCIIa fibres. Considering thelarge differences inpower ofhumanMHCIandIIamusclefibres (5- to6-fold), the maintenanceof wholemuscle function with the resistance exercise programme is probably explained by (1)the maintenance of MHCIIa power and (2) the shift from slow to fast (MHC I?MHCI/IIa)in


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