{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,28]],"date-time":"2026-09-28T22:51:20Z","timestamp":1790635880284,"version":"4.1.0"},"reference-count":43,"publisher":"Wiley","issue":"16","license":[{"start":{"date-parts":[[2018,7,4]],"date-time":"2018-07-04T00:00:00Z","timestamp":1530662400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"}],"funder":[{"name":"American Society for Biomechanics"},{"name":"Rocky Mountain American College of Sports Medicine"}],"content-domain":{"domain":["physoc.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["The Journal of Physiology"],"published-print":{"date-parts":[[2018,8]]},"abstract":"<jats:sec><jats:title>Key points<\/jats:title><jats:p><jats:list list-type=\"bullet\">\n<jats:list-item><jats:p>The fluctuations in force during a steady isometric contraction (force steadiness) are associated with oscillations in common synaptic input to the involved motor neurons.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>Decreases in force steadiness are associated with increases in pegboard times in older adults, although a mechanism for this link has not been established.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>We used a state\u2010space model to estimate the variability in common synaptic input to motor neurons during steady, isometric contractions.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>The estimate of common synaptic input was derived from the discharge times of motor units as recorded with high\u2010density surface electrodes.<\/jats:p><\/jats:list-item>\n<jats:list-item><jats:p>We found that the variability in common synaptic input to motor neurons modulates force steadiness for young and older adults, as well as pegboard time for older adults.<\/jats:p><\/jats:list-item>\n<\/jats:list><\/jats:p><\/jats:sec><jats:sec><jats:title>Abstract<\/jats:title><jats:p>We investigated the associations between grooved pegboard times, force steadiness (coefficient of variation for force) and variability in an estimate of the common synaptic input to motor neurons innervating the wrist extensor muscles during steady contractions performed by young and older adults. The discharge times of motor units were derived from recordings obtained with high\u2010density surface electrodes when participants performed steady isometric contractions at 10% and 20% of maximal voluntary contraction force. The steady contractions were performed with a pinch grip and wrist extension, both independently (single action) and concurrently (double action). The variance in common synaptic input to motor neurons was estimated with a state\u2010space model of the latent common input dynamics. There was a statistically significant association between the coefficient of variation for force during the steady contractions and the estimated variance in common synaptic input in young (<jats:italic>r<\/jats:italic><jats:sup>2<\/jats:sup>\u00a0=\u00a00.31) and older (<jats:italic>r<\/jats:italic><jats:sup>2<\/jats:sup>\u00a0=\u00a00.39) adults, although not between either the mean or the coefficient of variation for interspike interval of single motor units with the coefficient of variation for force. Moreover, the estimated variance in common synaptic input during the double\u2010action task with the wrist extensors at the 20% target was significantly associated with grooved pegboard time (<jats:italic>r<\/jats:italic><jats:sup>2<\/jats:sup>\u00a0=\u00a00.47) for older adults but not young adults. These findings indicate that longer pegboard times of older adults were associated with worse force steadiness and greater fluctuations in the estimated common synaptic input to motor neurons during steady contractions.<\/jats:p><\/jats:sec>","DOI":"10.1113\/jp275658","type":"journal-article","created":{"date-parts":[[2018,6,8]],"date-time":"2018-06-08T05:55:30Z","timestamp":1528437330000},"page":"3793-3806","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":93,"title":["Variability in common synaptic input to motor neurons modulates both force steadiness and pegboard time in young and older adults"],"prefix":"10.1113","volume":"596","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6576-2346","authenticated-orcid":false,"given":"Daniel F.","family":"Feeney","sequence":"first","affiliation":[{"name":"Department of Integrative Physiology University of Colorado Boulder  CO 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