Original articles   

The Journal of Sports Medicine and Physical Fitness 2001 June;41(2):165-9

Copyright © 2002 EDIZIONI MINERVA MEDICA

lingua: Inglese

Relationship between the slow component of oxygen uptake and the potential reduction in maximal power output during constant-load exercise

Yano T., Yunoki T., Ogata H.

From the Laboratory of Human Movement Science Faculty of Education, Hokkaido University, Sapporo, Japan

Back­ground. The pur­pose of the ­present ­study was to exam­ine the rela­tion­ship ­between the ­slow com­po­nent of oxy­gen ­uptake (.VO2) and mus­cle ­fiber ­fatigue. Max­i­mal pow­er out­put (MPO) was ­used as an ­index of mus­cle ­fiber ­fatigue.
Meth­ods. Two con­stant exer­cis­es ­were car­ried out at exer­cise inten­sities of 40% and 80% of max­i­mal oxy­gen ­uptake (.VO2max). ­Each exer­cise was repeat­ed ­three ­times, ­once for the meas­ure­ment for .VO2, and the oth­er two ­times for MPO test­ing, at 3 and 6 min­utes ­after ­work out­put.
­Results. Repro­du­cibil­ity of MPO at ­rest was ­assessed by cor­re­la­tion coef­fi­cient. Its val­ue was 0.933. At 40% .VO2max, MPO did not sig­nif­i­cant­ly ­decrease ­from the rest­ing val­ue. At 80% .VO2max, MPO sig­nif­i­cant­ly ­decreased by 129±77 ­watts at 3 min and by 178±108 ­watts at 6 min. The .VO2 kinet­ic at 40% .VO2 was ­well ­described by a mono­ex­po­nen­tial func­tion ­with a ­time con­stant of 0.432 min. How­ev­er, at 80% .VO2max, a ­slow com­po­nent of the ­form of a lin­e­ar ­drift super­im­posed on a mono­ex­po­nen­tial func­tion ­with an essen­tial­ly ­equal ­time con­stant (0.469 min) was unam­big­u­ous­ly detect­ed. ­This ­slow com­po­nent was sig­nif­i­cant­ly relat­ed to the ­decrease in MPO (r=0.567).
Con­clu­sions. The ­present ­results sug­gest­ed ­that the ­fatigue of mus­cle ­fibers may be one of the fac­tors ­that pro­duce the ­slow com­po­nent of .VO2 dur­ing ­high inten­sity exer­cise.