Endurance training reduces the rate of diaphragm fatigue in vitro.
OBJECTIVE
The present study examined the effects of endurance training on the contractile and biochemical properties of the rat costal diaphragm in vitro.


METHODS
Sixty-four rats were divided into two groups: exercise trained (T) and control (C). Training consisted of treadmill running 5 d x wk(-1), 60 min x d(-1) at approximately 70% of VO2max, over a 10-wk period.


RESULTS
Control diaphragm strips produced an average of 12% less force from minute 15 to 50 of a 60-min in vitro fatigue protocol, compared with the T diaphragm strips (P < 0.01). T diaphragms had 10.1% higher citrate synthase (CS) and 12.1% higher superoxide dismutase (SOD) activities compared with the C (P < 0.05). Despite a significant decrease (P < 0.05) in Type IIb myosin heavy chains (MHC) and an increase (P < 0.05) in Type I MHC in T diaphragms, maximal shortening velocity (Vmax) in the diaphragm was not different between T and C animals. No differences were observed in specific force or the relative proportions of myosin light chains between groups.


CONCLUSIONS
These findings suggest that endurance training reduces the rate of diaphragm fatigue in vitro but has no effect on Vmax or specific force.
Vrabas
I S
IS
Department of Exercise and Sport Sciences, University of Florida, Gainesville 32611, USA.
Dodd
S L
SL
Powers
S K
SK
Hughes
M
M
Coombes
J
J
Fletcher
L
L
Demirel
H
H
Reid
M B
MB
D000818:Animals; D001696:Biomechanical Phenomena; D002950:Citrate (si)-Synthase / Q000032:analysis; D003964:Diaphragm / Q000201:enzymology / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D007537:Isometric Contraction / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D009210:Myofibrils / Q000737:chemistry; D018995:Myosin Heavy Chains / Q000032:analysis; D018994:Myosin Light Chains / Q000032:analysis; D010101:Oxygen Consumption / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012420:Running / Q000502:physiology; D013482:Superoxide Dismutase / Q000032:analysis
D018994:Myosin Light Chains; D013482:Superoxide Dismutase; D002950:Citrate (si)-Synthase; D018995:Myosin Heavy Chains