title: Fatigue from high- and low-frequency muscle stimulation: contractile and biochemical alterations.
abstract: This study examined the effect of high- (75 Hz, 1 min) and low- (5 Hz, 1.5 min) frequency stimulation on contractile and biochemical properties of the diaphragm. Tension was reduced to 21 +/- 1 and 54 +/- 2% (SE) of the initial value after high- and low-frequency stimulation, respectively. After 0, 0.25, 1, and 2 min of recovery from high-frequency stimulation, 5 Hz elicited more force (expressed as % of initial tension) than 75-Hz stimulation. Time 0 recovery values were 21 +/- 1 and 78 +/- 6% of the initial force for 75- and 5-Hz stimulation, respectively. By 1 min of recovery, force elicited by 5-Hz stimulation had returned to the prefatigue value. In contrast, force production with 75-Hz stimulation did not full recover until 10-15 min. After fatigue produced by low-frequency stimulation, force production with 5-Hz stimulation was reduced to 54 +/- 2% of the initial tension, a value significantly lower than the 71 +/- 2% of initial force elicited by 75-Hz stimulation. Force production with 5-Hz stimulation increased rapidly in the first 15 s of recovery (54 +/- 2% at 0 and 70 +/- 2% at 15 s) and by 5 min was significantly greater than the force elicited by 75-Hz stimulation (100 +/- 3 vs. 93 +/- 1%). As before, force production at 75-Hz stimulation did not fully recover until 10-15 min. Both fatigue protocols produced a significant prolongation in isometric twitch contraction and one-half relaxation times. Creatine phosphate (CP) concentration was reduced and muscle lactate increased by both fatigue protocols.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D003964:Diaphragm / Q000502:physiology; D004558:Electric Stimulation; D005260:Female; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007537:Isometric Contraction; D007773:Lactates / Q000378:metabolism; D019344:Lactic Acid; D009119:Muscle Contraction; D010725:Phosphocreatine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D007773:Lactates; D010725:Phosphocreatine; D019344:Lactic Acid; D000255:Adenosine Triphosphate; D002118:Calcium