Department of Kinesiology, University of Massachusetts, Amherst, MA, United States of America.
Institute for Applied Life Sciences, University of Massachusetts, Amherst, MA, United States of America.
PLoS One. 2024 Sep 25;19(9):e0308336. doi: 10.1371/journal.pone.0308336. eCollection 2024.
Although it is clear that the bioenergetic basis of skeletal muscle fatigue (transient decrease in peak torque or power in response to contraction) involves intramyocellular acidosis (decreased pH) and accumulation of inorganic phosphate (Pi) in response to the increased energy demand of contractions, the effects of old age on the build-up of these metabolites has not been evaluated systematically. The purpose of this study was to compare pH and [Pi] in young (18-45 yr) and older (55+ yr) human skeletal muscle in vivo at the end of standardized contraction protocols. Full study details were prospectively registered on PROSPERO (CRD42022348972). PubMed, Web of Science, and SPORTDiscus databases were systematically searched and returned 12 articles that fit the inclusion criteria for the meta-analysis. Participant characteristics, contraction mode (isometric, dynamic), and final pH and [Pi] were extracted. A random-effects model was used to calculate the mean difference (MD) and 95% confidence interval (CI) for pH and [Pi] across age groups. A subgroup analysis for contraction mode was also performed. Young muscle acidified more than older muscle (MD = -0.12 pH; 95%CI = -0.18,-0.06; p<0.01). There was no overall difference by age in final [Pi] (MD = 2.14 mM; 95%CI = -0.29,4.57; p = 0.08), although sensitivity analysis revealed that removing one study resulted in greater [Pi] in young than older muscle (MD = 3.24 mM; 95%CI = 1.72,4.76; p<0.01). Contraction mode moderated these effects (p = 0.02) such that young muscle acidified (MD = -0.19 pH; 95%CI = -0.27,-0.11; p<0.01) and accumulated Pi (MD = 4.69 mM; 95%CI = 2.79,6.59; p<0.01) more than older muscle during isometric, but not dynamic, contractions. The smaller energetic perturbation in older muscle indicated by these analyses is consistent with its relatively greater use of oxidative energy production. During dynamic contractions, elimination of this greater reliance on oxidative energy production and consequently lower metabolite accumulations in older muscle may be important for understanding task-specific, age-related differences in fatigue.
虽然很明显，骨骼肌疲劳的生物能量基础（收缩时峰值扭矩或功率的短暂下降）涉及细胞内酸中毒（收缩时能量需求增加导致 pH 值降低）和无机磷（Pi）的积累，但年龄对这些代谢物积累的影响尚未得到系统评估。本研究旨在比较年轻（18-45 岁）和老年（55+岁）人体骨骼肌在标准化收缩方案结束时的体内 pH 和 [Pi]。详细的研究细节已在 PROSPERO（CRD42022348972）上进行了前瞻性注册。使用 PubMed、Web of Science 和 SPORTDiscus 数据库进行了系统搜索，并返回了 12 篇符合荟萃分析纳入标准的文章。提取了参与者特征、收缩模式（等长、动态）和最终 pH 值和 [Pi]。使用随机效应模型计算 pH 值和 [Pi] 随年龄组的平均差异（MD）和 95%置信区间（CI）。还进行了收缩模式的亚组分析。年轻的肌肉酸化程度比老年肌肉大（MD = -0.12 pH；95%CI = -0.18，-0.06；p<0.01）。按年龄划分，最终 [Pi] 无总体差异（MD = 2.14 mM；95%CI = -0.29，4.57；p = 0.08），尽管敏感性分析显示，删除一项研究后，年轻肌肉中的 [Pi] 大于老年肌肉（MD = 3.24 mM；95%CI = 1.72，4.76；p<0.01）。收缩模式调节了这些影响（p = 0.02），使得年轻肌肉在等长收缩时酸化（MD = -0.19 pH；95%CI = -0.27，-0.11；p<0.01）并积累 Pi（MD = 4.69 mM；95%CI = 2.79，6.59；p<0.01）比老年肌肉多。这些分析表明，老年肌肉的能量波动较小，这与其相对更多地利用氧化能量产生相一致。在动态收缩期间，消除这种对氧化能量产生的更大依赖，以及随后在老年肌肉中积累较低的代谢物，可能对于理解与年龄相关的疲劳的特定任务差异很重要。
