Influence of muscle dimensions on economy of isometric exercise in rat medial gastrocnemius muscles in situ.
The effect of muscle dimensions on economy (force-time integral divided by the amount of energy utilized) was investigated in male rats (body mass range 95-490 g), anaesthetized with pentobarbital. The medial gastrocnemius muscle in situ performed 6 maximal isometric contractions of 350 ms duration (1.s-1) at twitch optimum length at 35 degrees C. The areas under the 6 time-force curves were added to obtain force-time integral of the experiment. Differences of concentrations of ATP, phosphocreatine and lactate between experimental and contralateral (resting) muscles were used to calculate high-energy phosphate consumption due to stimulation. Muscle mass and cross-sectional area increased (approximately +400% and +300%, respectively) over the rat body mass range studied. Muscle length and length of the most distal fibre bundle increased by approximately 17 mm and 4 mm, respectively. Force-time integral (N.s) increased proportional to cross-sectional area whereas high-energy phosphate consumption (mumoles) increased proportional to muscle mass. The relative fraction of the total energy consumption utilized for force-independent processes was independent of rat body mass. The economy of the actomyosin system was unaffected during growth, whereas economy of the whole muscle decreased during growth by approximately 30% (p less than 0.001). The effect of muscle dimensions on economy is discussed with respect to human endurance capacity measured by voluntary isometric contractions.
de Haan
A
A
Department of Exercise Physiology and Health, Faculty of Medicine, University of Amsterdam, The Netherlands.
Rexwinkel
R
R
van Doorn
J E
JE
Westra
H G
HG
Hollander
A P
AP
Huijing
P A
PA
Woittiez
R D
RD
Sargeant
A J
AJ
D000818:Animals; D001835:Body Weight; D007537:Isometric Contraction; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000033:anatomy & histology / Q000201:enzymology / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D005082:Physical Exertion; D051381:Rats; D011919:Rats, Inbred Strains
D010710:Phosphates