{"doi":"10.1152/ajpcell.00575.2019","title":"Ca<sup>2+</sup> dependency of limb muscle fiber contractile mechanics in young and older adults","abstract":"Age-induced declines in skeletal muscle contractile function have been attributed to multiple cellular factors, including lower peak force (P o ), decreased Ca 2+ sensitivity, and reduced shortening velocity (V o ). However, changes in these cellular properties with aging remain unresolved, especially in older women, and the effect of submaximal Ca 2+ on contractile function is unknown. Thus, we compared contractile properties of muscle fibers from 19 young (24 ± 3 yr; 8 women) and 21 older adults (77 ± 7 yr; 7 women) under maximal and submaximal Ca 2+ and assessed the abundance of three proteins thought to influence Ca 2+ sensitivity. Fast fiber cross-sectional area was ~44% larger in young (6,479 ± 2,487 µm 2 ) compared with older adults (4,503 ± 2,071 µm 2 , P &lt; 0.001), which corresponded with a greater absolute P o (young = 1.12 ± 0.43 mN; old = 0.79 ± 0.33 mN, P &lt; 0.001). There were no differences in fast fiber size-specific P o , indicating the age-related decline in force was explained by differences in fiber size. Except for fast fiber size and absolute P o , no age or sex differences were observed in Ca 2+ sensitivity, rate of force development (k tr ), or V o in either slow or fast fibers. Submaximal Ca 2+ depressed k tr and V o , but the effects were not altered by age in either sex. Contrary to rodent studies, regulatory light chain (RLC) and myosin binding protein-C abundance and RLC phosphorylation were unaltered by age or sex. These data suggest the age-associated reductions in contractile function are primarily due to the atrophy of fast fibers and that caution is warranted when extending results from rodent studies to humans.","journal":"American Journal of Physiology-Cell Physiology","year":2020,"id":99882,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":29,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9565,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2020-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":490890,"name":"Christopher W. Sundberg","orcid":"0000-0002-6709-4078","position":1,"is_corresponding":false},{"id":462420,"name":"Lauren J. Kelly","orcid":null,"position":2,"is_corresponding":false},{"id":385850,"name":"Sandra K. Hunter","orcid":"0000-0001-8013-2051","position":3,"is_corresponding":false},{"id":461037,"name":"R. H. Fitts","orcid":"0000-0001-9674-1118","position":4,"is_corresponding":false},{"id":350874,"name":"Laura E. Teigen","orcid":"0000-0001-9272-074X","position":0,"is_corresponding":true}],"reference_count":80,"raw_metadata":null,"created_at":"2026-07-18T22:38:09.754371Z","pmid":"32348175","pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}