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Effects of old age and contraction mode on knee extensor muscle ATP flux and metabolic economy in vivo.
Fitzgerald, Liam F; Bartlett, Miles F; Nagarajan, Rajakumar; Francisco, Ericber Jimenez; Sup, Frank C; Kent, Jane A.
Afiliação
  • Fitzgerald LF; Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
  • Bartlett MF; Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
  • Nagarajan R; Human Magnetic Resonance Center, Institute for Applied Life Sciences, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
  • Francisco EJ; Mechatronics and Robotics Laboratory, Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
  • Sup FC; Mechatronics and Robotics Laboratory, Department of Mechanical & Industrial Engineering, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
  • Kent JA; Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
J Physiol ; 599(12): 3063-3080, 2021 06.
Article em En | MEDLINE | ID: mdl-33876434
KEY POINTS: We used 31-phosphorus magnetic resonance spectroscopy to quantify in vivo skeletal muscle metabolic economy (ME; mass-normalized torque or power produced per ATP consumed) during three 24 s maximal-effort contraction protocols: (1) sustained isometric (MVIC), (2) intermittent isokinetic (MVDCIsoK ), and (3) intermittent isotonic (MVDCIsoT ) in the knee extensor muscles of young and older adults. ME was not different between groups during the MVIC but was lower in older than young adults during both dynamic contraction protocols. These results are consistent with an increased energy cost of locomotion, but not postural support, with age. The effects of old age on ME were not due to age-related changes in muscle oxidative capacity or ATP flux. Specific power was lower in older than young adults, despite similar total ATP synthesis between groups. Together, this suggests a dissociation between cross-bridge activity and ATP utilization with age. ABSTRACT: Muscle metabolic economy (ME; mass-normalized torque or power produced per ATP consumed) is similar in young and older adults during some isometric contractions, but less is known about potential age-related differences in ME during dynamic contractions. We hypothesized that age-related differences in ME would exist only during dynamic contractions, due to the increased energetic demand of dynamic versus isometric contractions. Ten young (Y; 27.5 ± 3.9 years, 6 men) and 10 older (O; 71 ± 5 years, 5 men) healthy adults performed three 24 s bouts of maximal contractions: (1) sustained isometric (MVIC), (2) isokinetic (120°·s-1 , MVDCIsoK ; 0.5 Hz), and (3) isotonic (load = 20% MVIC, MVDCIsoT ; 0.5 Hz). Phosphorus magnetic resonance spectroscopy of the vastus lateralis muscle was used to calculate ATP flux (mM ATP·s-1 ) through the creatine kinase reaction, glycolysis and oxidative phosphorylation. Quadriceps contractile volume (cm3 ) was measured by MRI. ME was calculated using the torque-time integral (MVIC) or power-time integral (MVDCIsoK and MVDCIsoT ), total ATP synthesis and contractile volume. As hypothesized, ME was not different between Y and O during the MVIC (0.12 ± 0.03 vs. 0.12 ± 0.02 Nm. s. cm-3. mM ATP-1 , mean ± SD, respectively; P = 0.847). However, during both MVDCIsoK and MVDCIsoT , ME was lower in O than Y adults (MVDCIsoK : 0.011 ± 0.003 vs. 0.007 ± 0.002 J. cm-3. mM ATP-1 ; P < 0.001; MVDCIsoT : 0.011 ± 0.002 vs. 0.008 ± 0.002; P = 0.037, respectively), despite similar muscle oxidative capacity, oxidative and total ATP flux in both groups. The lower specific power in older than young adults, despite similar total ATP synthesis between groups, suggests there is a dissociation between cross-bridge activity and ATP utilization with age.
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Texto completo: 1 Base de dados: MEDLINE Assunto principal: Músculo Esquelético / Contração Isométrica Tipo de estudo: Health_economic_evaluation Limite: Adult / Aged / Humans / Male Idioma: En Revista: J Physiol Ano de publicação: 2021 Tipo de documento: Article País de afiliação: Estados Unidos

Texto completo: 1 Base de dados: MEDLINE Assunto principal: Músculo Esquelético / Contração Isométrica Tipo de estudo: Health_economic_evaluation Limite: Adult / Aged / Humans / Male Idioma: En Revista: J Physiol Ano de publicação: 2021 Tipo de documento: Article País de afiliação: Estados Unidos