In vivo evidence of an age-related increase in ATP cost of contraction in the plantar flexor muscles.
Impaired skeletal muscle efficiency potentially contributes to the age-related decline in exercise capacity and may explain the altered haemodynamic response to exercise in the elderly. Thus we examined whether (i) the ATP cost of contraction increases with age, and (ii) this results in altered convective O(2) delivery to maintain microvascular oxygenation in the calf muscle. To this aim, we used an integrative experimental approach combining (31)P-MRS (magnetic resonance spectroscopy), Doppler ultrasound imaging and NIRS (near-IR spectroscopy) during dynamic plantar flexion exercise at 40% of WR(max) (maximal power output) in 20 healthy young and 20 older subjects matched for physical activity. The ATP cost of contraction was significantly higher in the old (7.2±4.1 mM/min per W) compared with the young (2.4±1.9 mM/min per W; P<0.05) and this was only significantly correlated with the plantar flexion WR(max) value in the old subjects (r=-0.52; P<0.05). Even when differences in power output were taken into account, end-exercise blood flow (old, 259±168 ml/min per W and young, 134±40 ml/min per W; P<0.05) and convective O(2) delivery (old, 0.048±0.031 l/min per W and young, 0.026±0.008 l/min per W; P<0.05) were greater in the old in comparison with the young subjects. In contrast, the NIRS oxyhaemoglobin, deoxyhaemoglobin and microvascular oxygenation indices were not significantly different between the groups (P>0.05). Therefore the present study reveals that, although the peripheral haemodynamic responses to plantar flexion exercise appear to be appropriate, the elevated energy cost of contraction and associated reduction in the WR(max) value in this muscle group may play a role in limiting exercise capacity with age.
Gwenael
G
Layec
Joel D
JD
Trinity
Corey R
CR
Hart
§Department of Radiology and Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, U.S.A.
Seong-Eun
SE
Kim
Henderik Jonathan
HJ
Groot
¶Centre de Resonance Magnetique Biologique et Medicale, UMR CNRS 7339, Faculté de Médecine de Marseille, Marseille, France.
Yann
Y
Le Fur
Jacob R
JR
Sorensen
§Department of Radiology and Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City, UT, U.S.A.
Eun-Kee
EK
Jeong
Russell S
RS
Richardson
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism / Q000502:physiology*; D001783:Blood Flow Velocity / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D018608:Ultrasonography, Doppler; D055815:Young Adult
D000255:Adenosine Triphosphate