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AGE‐RELATED EFFECTS OF FATIGUE AND RECOVERY FROM FATIGUE IN RAT MEDIAL GASTROCNEMIUS MUSCLE
Author(s) -
De Haan A.,
Lodder M. A. N.,
Sargeant A. J.
Publication year - 1989
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1989.sp003323
Subject(s) - isometric exercise , contraction (grammar) , chemistry , muscle contraction , anatomy , phosphocreatine , medicine , muscle fatigue , population , endocrinology , electromyography , energy metabolism , physical medicine and rehabilitation , environmental health
Force‐velocity, power‐velocity and unloaded shortening data were obtained from in situ medial gastrocnemius muscle‐tendon complexes (stimulated at 60 Hz) with intact circulation of mature male rats (∼ 125 days old). Measurements were carried out at the end of a long (15 s) contraction (fatigued muscles) or with a short (1 s) contraction either in the fresh state (fresh muscles) or in muscles which had recovered for 15 min after a long contraction. Compared to the fresh state fatigue reduced isometric force by 57%, maximal shortening velocity by ∼ 40% and maximal power output by 81%. These reductions were similar to data previously obtained with younger rats (40 days old). However, the velocity data of the muscles which had recovered for 15 min after a long contraction showed a greater reduction in the mature rats. This difference between the two age groups together with a difference in the changes in the initial parts of the isometric force‐time curves suggest an age‐dependent response of the fast‐fatigable fibre population of these mixed muscles. In a separate series of experiments the underlying mechanism of the recovery from fatigue was studied in a group of young rats. Fatigue was induced with five long (15 s) contractions (each at 5 min intervals). The recovery of isometric force and power output was monitored with short contractions which indicated a plateau of recovery but the absolute values were still reduced after 60 min (85 and 71% of pre‐fatigue values, respectively). Phosphocreatine concentration recovered rapidly, whereas the ATP concentration was still markedly reduced after 1 h of recovery. The time courses of recovery of inosine‐5'‐monophosphate (IMP) and lactate concentrations resembled those of force and power output. Thus it is possible that age‐dependent differences in IMP and/or lactate production may play a role in fatigue and recovery from fatigue.