{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,27]],"date-time":"2026-04-27T10:16:27Z","timestamp":1777284987346,"version":"3.51.4"},"reference-count":41,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2023,1,9]],"date-time":"2023-01-09T00:00:00Z","timestamp":1673222400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Funda\u00e7\u00e3o para a Ci\u00eancia e Tecnologia","award":["UIDB\/\/2020"],"award-info":[{"award-number":["UIDB\/\/2020"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>The present study aimed to investigate the effects of a continuous visual feedback and the isometric contraction nature on the complexity and variability of force. Thirteen healthy and young male adults performed three MVCs followed by three submaximal isometric force tasks at a target force of 40% of their MVC for 30 s, as follows: (i) push isometric task with visual feedback (Pvisual); (ii) hold isometric task with visual feedback (Hvisual); (iii) hold isometric task without visual feedback (Hnon-visual). Force complexity was evaluated through sample entropy (SampEn) of the force output. Force variability was analyzed through the coefficient of variation (CV). Results showed that differences were task-related, with Pvisual showing higher complexity (i.e., higher SampEn) and decreased variability (i.e., lower CV) when compared with the remaining tasks. Additionally, no significant differences were found between the two hold isometric force tasks (i.e., no influence of visual feedback). Our results are promising as we showed these two isometric tasks to induce different motor control strategies. Furthermore, we demonstrated that visual feedback\u2019s influence is also dependent on the type of isometric task. These findings should motivate researchers and physiologists to shift training paradigms and incorporate different force control evaluation tasks.<\/jats:p>","DOI":"10.3390\/s23020726","type":"journal-article","created":{"date-parts":[[2023,1,9]],"date-time":"2023-01-09T07:05:09Z","timestamp":1673247909000},"page":"726","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Torque Regulation Is Influenced by the Nature of the Isometric Contraction"],"prefix":"10.3390","volume":"23","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2694-9639","authenticated-orcid":false,"given":"Philipp","family":"Bauer","sequence":"first","affiliation":[{"name":"Centro Interdisciplinar de Performance Humana (CIPER), Neuromuscular Research Lab, Faculty of Human Kinetics, University of Lisbon, 1495-751 Lisbon, Portugal"},{"name":"Interdisciplinary Research Centre Egas Moniz (CiiEM), Egas Moniz School of Health & Science, 2829-511 Almada, Portugal"}]},{"given":"Jo\u00e3o S\u00e1","family":"Gomes","sequence":"additional","affiliation":[{"name":"Centro Interdisciplinar de Performance Humana (CIPER), Neuromuscular Research Lab, Faculty of Human Kinetics, University of Lisbon, 1495-751 Lisbon, Portugal"},{"name":"Interdisciplinary Research Centre Egas Moniz (CiiEM), Egas Moniz School of Health & Science, 2829-511 Almada, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3244-4664","authenticated-orcid":false,"given":"Jo\u00e3o","family":"Oliveira","sequence":"additional","affiliation":[{"name":"Centro Interdisciplinar de Performance Humana (CIPER), Neuromuscular Research Lab, Faculty of Human Kinetics, University of Lisbon, 1495-751 Lisbon, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2074-722X","authenticated-orcid":false,"given":"Paulo","family":"Santos","sequence":"additional","affiliation":[{"name":"Centro Interdisciplinar de Performance Humana (CIPER), Neuromuscular Research Lab, Faculty of Human Kinetics, University of Lisbon, 1495-751 Lisbon, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6154-5563","authenticated-orcid":false,"given":"Pedro","family":"Pezarat-Correia","sequence":"additional","affiliation":[{"name":"Centro Interdisciplinar de Performance Humana (CIPER), Neuromuscular Research Lab, Faculty of Human Kinetics, University of Lisbon, 1495-751 Lisbon, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9691-5456","authenticated-orcid":false,"given":"Jo\u00e3o R.","family":"Vaz","sequence":"additional","affiliation":[{"name":"Centro Interdisciplinar de Performance Humana (CIPER), Neuromuscular Research Lab, Faculty of Human Kinetics, University of Lisbon, 1495-751 Lisbon, Portugal"},{"name":"Interdisciplinary Research Centre Egas Moniz (CiiEM), Egas Moniz School of Health & Science, 2829-511 Almada, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2023,1,9]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1007\/s00221-010-2528-4","article-title":"Visual information interacts with neuromuscular factors in the coordination of bimanual isometric force","volume":"209","author":"Hu","year":"2011","journal-title":"Exp. Brain Res."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"469","DOI":"10.1249\/mss.0b013e31802d3ad3","article-title":"Aging, visuomotor correction, and force fluctuations in large muscles","volume":"39","author":"Tracy","year":"2007","journal-title":"Med. Sci. Sport. Exerc."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"679","DOI":"10.1097\/OPX.0000000000000599","article-title":"Contributions of visuo-oculomotor abilities to interceptive skills in sports","volume":"92","author":"Gao","year":"2015","journal-title":"Optom. Vis. Sci."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"1911","DOI":"10.1093\/geronb\/gbaa081","article-title":"Conscious movement processing, fall-related anxiety, and the visuomotor control of locomotion in older adults","volume":"75","author":"Ellmers","year":"2020","journal-title":"J. Gerontol. B Psychol. Sci. Soc. Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"1022","DOI":"10.1016\/j.humov.2010.09.007","article-title":"The interaction of respiration and visual feedback on the control of force and neural activation of the agonist muscle","volume":"30","author":"Baweja","year":"2011","journal-title":"Hum. Mov. Sci."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"137","DOI":"10.1007\/s00221-007-1082-1","article-title":"Memory and coordination in bimanual isometric finger force production","volume":"182","author":"Davis","year":"2007","journal-title":"Exp. Brain Res."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"35","DOI":"10.1007\/s00221-009-1883-5","article-title":"Removal of visual feedback alters muscle activity and reduces force variability during constant isometric contractions","volume":"197","author":"Baweija","year":"2009","journal-title":"Exp. Brain Res."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1016\/j.neulet.2010.12.040","article-title":"Adaptation to bimanual asymmetric weights in isometric force coordination","volume":"490","author":"Hu","year":"2011","journal-title":"Neurosci. Lett."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"909","DOI":"10.1136\/jnnp.2006.091363","article-title":"Effects of focal hand dystonia on visually guided and internally guided force control","volume":"77","author":"Prodoehl","year":"2006","journal-title":"J. Neurol. Neurosurg. Psychiatry"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"306","DOI":"10.3758\/PP.70.2.306","article-title":"Compensatory properties of visual information in the control of isometric force","volume":"70","author":"Hong","year":"2008","journal-title":"Percept. Pyschophys."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"121","DOI":"10.1016\/j.neulet.2009.12.068","article-title":"Spatial resolution of visual feedback affects variability and structure of isometric force","volume":"470","author":"Kuznetsov","year":"2010","journal-title":"Neurosci. Lett."},{"key":"ref_12","first-page":"71","article-title":"The sensorimotor system, part I: The physiologic basis of functional joint stability","volume":"37","author":"Riemann","year":"2002","journal-title":"J. Athl. Train."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"114","DOI":"10.1152\/physiol.00027.2020","article-title":"Force Steadiness: From Motor Units to Voluntary Actions","volume":"36","author":"Enoka","year":"2021","journal-title":"Physiology"},{"key":"ref_14","doi-asserted-by":"crossref","unstructured":"Schaefer, L.V., and Bittmann, F.N. (2017). Are there two forms of isometric muscle action? Results of the experimental study support a distinction between a holding and a pushing isometric muscle function. BMC Sport. Sci. Med. Rehabil., 9.","DOI":"10.1186\/s13102-017-0075-z"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"3087","DOI":"10.1152\/jn.00232.2002","article-title":"Task differences with the same load torque alter the endurance time of submaximal fatiguing contractions in humans","volume":"88","author":"Hunter","year":"2002","journal-title":"J. Neurophysiol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"657","DOI":"10.1002\/mus.20752","article-title":"Time to failure of a sustained contraction is predicted by target torque and initial electromyographic bursts in elbow flexor muscles","volume":"35","author":"Rudroff","year":"2007","journal-title":"Muscle Nerve"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"307","DOI":"10.1007\/s00221-010-2233-3","article-title":"Muscle activity differs with load compliance during fatiguing contractions with the knee extensor muscles","volume":"203","author":"Rudroff","year":"2010","journal-title":"Exp. Brain Res."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"R1144","DOI":"10.1152\/ajpregu.00019.2016","article-title":"Loss of knee extensor torque complexity during fatiguing isometric muscle contractions occurs exclusively above the critical torque","volume":"310","author":"Pethick","year":"2016","journal-title":"Am. J. Physiol. Regul. Integr. Comp. Physiol."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"956","DOI":"10.1113\/EP086960","article-title":"Effects of ipsilateral and contralateral fatigue and muscle blood flow occlusion on the complexity of knee-extensor torque output in humans","volume":"103","author":"Pethick","year":"2018","journal-title":"Exp. Physiol."},{"key":"ref_20","first-page":"1050","article-title":"Complexity of knee extensor torque: Effect of aging and contraction intensity","volume":"35","author":"Catai","year":"2018","journal-title":"J. Strength Cond. Res."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"676","DOI":"10.1016\/j.medengphy.2014.02.017","article-title":"The effect of signal acquisition and processing choices on ApEn values: Towards a \u201cgold standard\u201d for distinguishing effort levels from isometric force records","volume":"36","author":"Forrest","year":"2014","journal-title":"Med. Eng. Phys."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"837","DOI":"10.1037\/0096-1523.25.3.837","article-title":"Noise, information transmission, and force variability","volume":"25","author":"Slifkin","year":"1999","journal-title":"J. Exp. Psychol. Hum. Percept. Perform."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"903","DOI":"10.1152\/japplphysiol.00166.2002","article-title":"Aging and the time and frequency structure of force output variability","volume":"94","author":"Vaillancourt","year":"2003","journal-title":"J. Appl. Physiol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1594","DOI":"10.1016\/S1388-2457(01)00593-4","article-title":"Regularity of force tremor in Parkinson\u2019s disease","volume":"112","author":"Vaillancourt","year":"2001","journal-title":"Clin. Neurophysiol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2085","DOI":"10.1113\/jphysiol.2015.284380","article-title":"Fatigue reduces the complexity of knee extensor torque fluctuations during maximal and submaximal intermittent isometric contractions in man","volume":"593","author":"Pethick","year":"2015","journal-title":"J. Physiol."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1042","DOI":"10.1016\/j.clinbiomech.2006.05.009","article-title":"Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks","volume":"21","author":"Schiffman","year":"2006","journal-title":"Clin. Biomech."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"592","DOI":"10.1152\/japplphysiol.00717.2017","article-title":"Improvements in force variability and structure from vision-to memory-guided submaximal isometric knee extension in subacute stroke","volume":"124","author":"Chow","year":"2018","journal-title":"J. Appl. Physiol."},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Li, K., and Wei, N. (2014, January 14\u201316). Fingertip force variability on the left and right hand during low-level sustained precision pinch. Proceedings of the IEEE 2014 7th International Conference on Biomedical Engineering and Informatics, Dalian, China.","DOI":"10.1109\/BMEI.2014.7002789"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"1307","DOI":"10.1007\/s00167-011-1425-0","article-title":"Extension and flexion torque variability in ACL deficiency","volume":"19","author":"Skurvydas","year":"2011","journal-title":"Knee Surg. Sport. Traumatol. Arthrosc."},{"key":"ref_30","unstructured":"Stergiou, N. (2003). Innovative Analyses of Human Movement, Human Kinetics."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"H2039","DOI":"10.1152\/ajpheart.2000.278.6.H2039","article-title":"Physiological time-series analysis using approximate entropy and sample entropy. American journal of physiology","volume":"278","author":"Richman","year":"2000","journal-title":"Am. J. Physiol. Heart Circ. Physiol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"349","DOI":"10.1007\/s10439-012-0668-3","article-title":"The appropriate use of approximate entropy and sample entropy with short data sets","volume":"41","author":"Yentes","year":"2013","journal-title":"Ann. Biomed. Eng."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"935","DOI":"10.2165\/00007256-200535110-00002","article-title":"A nonlinear dynamic approach for evaluating postural control: New directions for the management of sport-related cerebral concussion","volume":"35","author":"Cavanaugh","year":"2005","journal-title":"Sport. Med."},{"key":"ref_34","unstructured":"The Jamovi Project (2022, September 10). Jamovi (Version 1.6). Available online: https:\/\/www.jamovi.org."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"155","DOI":"10.1016\/j.jcm.2016.02.012","article-title":"A guideline of selecting and reporting intraclass correlation coefficients for reliability research","volume":"15","author":"Koo","year":"2016","journal-title":"J. Chiropr. Med."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1689","DOI":"10.1016\/j.jbiomech.2004.02.005","article-title":"Angle-and gender-specific quadriceps femoris muscle recruitment and knee extensor torque","volume":"37","author":"Pincivero","year":"2004","journal-title":"J. Biomech."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"3117","DOI":"10.1007\/s00421-021-04779-1","article-title":"Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle","volume":"121","author":"Pethick","year":"2021","journal-title":"Eur. J. Appl. Physiol."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"505","DOI":"10.1007\/s00221-002-1129-2","article-title":"EMG differences between concentric and eccentric maximum voluntary contractions are evident prior to movement onset","volume":"145","author":"Grabiner","year":"2022","journal-title":"Exp. Brain Res."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"104","DOI":"10.1007\/BF00626764","article-title":"Muscle activation during maximal voluntary eccentric and concentric knee extension","volume":"62","author":"Westing","year":"1991","journal-title":"Eur. J. Appl. Physiol. Occup. Physiol."},{"key":"ref_40","unstructured":"Grabiner, M.D., Owings, T.M., George, M.R., and Enoka, R.M. (1995, January 2\u20136). Eccentric Contractions are Specified a Priori by the CNS. Proceedings of the 50th Congress of the International Society of Biomechanics, Jyvaskyla, Finland."},{"key":"ref_41","doi-asserted-by":"crossref","unstructured":"Hernandez, L.R., and Camic, C.L. (2019). Fatigue-Mediated Loss of Complexity is Contraction-Type Dependent in Vastus Lateralis Electromyographic Signals. Sports, 7.","DOI":"10.3390\/sports7040078"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/23\/2\/726\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T18:03:43Z","timestamp":1760119423000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/23\/2\/726"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,1,9]]},"references-count":41,"journal-issue":{"issue":"2","published-online":{"date-parts":[[2023,1]]}},"alternative-id":["s23020726"],"URL":"https:\/\/doi.org\/10.3390\/s23020726","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,1,9]]}}}