Muscle Physiology Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
Human Magnetic Resonance Center, Institute for Applied Life Sciences, University of Massachusetts Amherst, Amherst, MA, 01003, USA.
J Physiol. 2021 Jun;599(12):3063-3080. doi: 10.1113/JP281117. Epub 2021 May 12.
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 (MVDC ), and (3) intermittent isotonic (MVDC ) 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.
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 , MVDC ; 0.5 Hz), and (3) isotonic (load = 20% MVIC, MVDC ; 0.5 Hz). Phosphorus magnetic resonance spectroscopy of the vastus lateralis muscle was used to calculate ATP flux (mM ATP·s ) through the creatine kinase reaction, glycolysis and oxidative phosphorylation. Quadriceps contractile volume (cm ) was measured by MRI. ME was calculated using the torque-time integral (MVIC) or power-time integral (MVDC and MVDC ), 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 mM ATP , mean ± SD, respectively; P = 0.847). However, during both MVDC and MVDC , ME was lower in O than Y adults (MVDC : 0.011 ± 0.003 vs. 0.007 ± 0.002 J cm mM ATP ; P < 0.001; MVDC : 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.
我们使用 31 磷磁共振波谱法来量化活体骨骼肌代谢经济学（ME；每消耗 1 个 ATP 产生的扭矩或功率与肌肉质量的比值），这是在年轻人和老年人的膝关节伸肌中进行的三种 24 秒最大努力收缩方案：（1）持续等长（MVIC），（2）间歇性等速（MVDC）和（3）间歇性等张（MVDC）。在 MVIC 期间，ME 在两组之间没有差异，但在动态收缩方案中，老年人的 ME 低于年轻人。这些结果与年龄相关的运动能量成本增加一致，但与姿势支持无关。老年人 ME 的变化不是由于肌肉氧化能力或 ATP 通量的年龄相关变化引起的。尽管两组之间的总 ATP 合成相似，但老年人的比功率低于年轻人。总的来说，这表明随着年龄的增长，横桥活性和 ATP 利用之间存在分离。
在某些等长收缩期间，年轻人和老年人的肌肉代谢经济学（ME；每消耗 1 个 ATP 产生的扭矩或功率与肌肉质量的比值）相似，但对于 ME 在动态收缩期间潜在的年龄相关差异知之甚少。我们假设，由于动态收缩比等长收缩对能量的需求更高，因此在动态收缩期间会出现与年龄相关的 ME 差异。10 名年轻（Y；27.5 ± 3.9 岁，6 名男性）和 10 名老年人（O；71 ± 5 岁，5 名男性）健康成年人进行了三种 24 秒的最大收缩：（1）持续等长（MVIC），（2）等速（120°·s-1，MVDC；0.5 Hz）和（3）等张（负荷= 20%MVIC，MVDC；0.5 Hz）。使用磷磁共振波谱法测量股外侧肌的 ATP 通量（mM ATP·s-1）通过肌酸激酶反应、糖酵解和氧化磷酸化。通过 MRI 测量股四头肌的收缩体积（cm3）。使用扭矩时间积分（MVIC）或功率时间积分（MVDC 和 MVDC）、总 ATP 合成和收缩体积来计算 ME。正如假设的那样，在 MVIC 期间，Y 和 O 之间的 ME 没有差异（分别为 0.12 ± 0.03 和 0.12 ± 0.02 Nm·s·cm·mM ATP，平均值 ± SD；P = 0.847）。然而，在 MVDC 和 MVDC 期间，O 中的 ME 低于 Y 成年人（MVDC：0.011 ± 0.003 对 0.007 ± 0.002 J·cm·mM ATP；P < 0.001；MVDC：0.011 ± 0.002 对 0.008 ± 0.002；P = 0.037），尽管两组的肌肉氧化能力、氧化和总 ATP 通量相似。尽管两组之间的总 ATP 合成相似，但老年人的比功率仍低于年轻人，这表明随着年龄的增长，横桥活性和 ATP 利用之间存在分离。
