Accurate work-rate measurements during in vivo MRS studies of exercising human quadriceps.
BACKGROUND
Given that we have reached a point in the field of muscle energetics where absolute measurements are warranted to take the area forward, we designed an ergometer, including two force and two displacement transducers, allowing dynamic and isometric knee extension within a MR system and accurate measurements of power output.


METHODS
On the basis of repeated measurements, the force and displacement transducers accuracy was 1% for values ranging from 0 to 394 N and 4% for values ranging from 0 to 20 cm. In addition, measurements were not affected by magnetic field. MRS experiments in exercising muscle were conducted in eight subjects. They performed two standardized dynamic alternate leg extension exercises (25 and 35% of MVC) while the corresponding metabolic changes were measured using (31)P-MRS.


RESULTS
The mean power output produced during both exercises were 63 +/- 16 and 81 +/- 15 W while the eccentric work was reduced i.e. 12 +/- 14 and 21 +/- 6 W for the moderate and heavy exercise respectively. The corresponding metabolic changes were significant with a 20-40% PCr depletion and an end of exercise pH ranging from 0.02 to 0.70 pH units.


CONCLUSIONS
Overall, the present ergometer allows quadriceps exercise in a MR system and should be useful for future metabolic studies for which reliable and absolute quantification of power output is warranted.
Layec
Gwenael
G
Centre de Resonance Magnetique Biologique et Medicale, UMR CNRS 6612, Faculté de Médecine de Marseille, 27Bd Jean Moulin, 13005 Marseille, France.
Bringard
Aurélien
A
Vilmen
Christophe
C
Micallef
Jean-Paul
JP
Fur
Yann Le
YL
Perrey
Stéphane
S
Cozzone
Patrick J
PJ
Bendahan
David
D
D016552:Ergometry / Q000379:methods; D015444:Exercise / Q000502:physiology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D052097:Quadriceps Muscle / Q000502:physiology*