Submitted on October 26, 2007
Accepted on January 11, 2008
Acute Responses in Muscle Mitochondrial and Cytosolic Enzyme Activities During Heavy Internittent Exercise
H. J. Green1*, Eric B. Bombardier2, T. A. Duhamel3, Graham Paul Holloway4, A. Russell Tupling5, and J. Ouyang6
1 Department of Kinesiology, University of Waterloo, Waterloo, Canada
2 Kinesiology, University of Waterloo, Canada
3 St.Boniface General Hospital Research Centre, University of Manitoba, Winnipeg, Canada
4 Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada; , Canada
5 Kinesiology, University of Waterloo, Waterloo, Canada
6 University of Waterloo, United States
* To whom correspondence should be addressed. E-mail: green{at}healthy.uwaterloo.ca.
To examine the effects of repetitive bouts of heavy exercise on the maximal activities of enzymes representative of the major metabolic pathways and segments, 13 untrained volunteers (VO2peak=44.3±2.3 ml.kg-1. min-1) cycled at ~ 91% for 6 min once per h for 16 h. Maximal enzyme activities (Vmax, mol.kg-1 protein .h-1) were measured in homogenates from tissue extracted from the vastus lateralis before (B) and after (A) exercise at repetitions 1 (R1), 2 (R2), 9 (R9) and 16 (R16). For the mitochondrial enzymes, exercise resulted in reductions (P
0.05) in cytochrome oxidase (COX, 14.6 %), near significant reductions in malate dehydrogenase (4.06% ; P=0.06) and succinic dehydrogenase (4.82 % ;p=0.09), near significant increases in 
-hydroxyacyl CoA dehydrogenase (4.94 %; P=0.08) and no change in citrate synthase (CS, 2.88 %; P=0.37). For the cytosolic enzymes, exercise reduced (P0.05) Vmax in hexokinase (HEX, 4.4 %), creatine phosphokinase (9.0 %), total phosphorylase ( 13.5 %), phosphofructokinase ( 16.6 %), pyruvate kinase (PK, 14.1 %) and lactate dehydrogenase (10.7%). Repetition-dependent reductions (P0.05) in Vmax were observed for CS ( 1R,2R
16R), COX ( R1,R2R16), HEX (1R,2R16R) and PK (R916R). It is concluded that heavy exercise results in transient reductions in a wide range of enzymes involved in different metabolic functions and that in the case of selected enzymes, multiple repetitions of the exercise reduce average Vmax.
