{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,7]],"date-time":"2026-02-07T16:52:39Z","timestamp":1770483159484,"version":"3.49.0"},"reference-count":40,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2010,1,21]],"date-time":"2010-01-21T00:00:00Z","timestamp":1264032000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Interpolated twitch technique (ITT) is a non-invasive method for assessing the completeness of muscle activation in clinical settings. Voluntary activation level (VA), measured by ITT and estimated by a conventional linear model, was reported to have a non-linear relationship with true voluntary contraction force at higher activation levels. The relationship needs to be further clarified for the correct use by clinicians and researchers. This study was to established a modified voluntary activation (modified VA) and define a valid range by fitting a non-linear logistic growth model. Eight healthy male adults participated in this study. Each subject performed three sets of voluntary isometric ankle plantar flexions at 20, 40, 60, 80 and 100% maximal voluntary contraction (MVC) with real-time feedback on a computer screen. A supramaximal electrical stimulation was applied on tibia nerve at rest and during contractions. The estimated VA was calculated for each contraction. The relationship between the estimated VA and the actual voluntary contraction force was fitted by a logistic growth model. The result showed that according to the upper and lower limit points of the logistic curve, the valid range was between the 95.16% and 10.55% MVC. The modified VA estimated by this logistic growth model demonstrated less error than the conventional model. This study provided a transfer function for the voluntary activation level and defined the valid range which would provide useful information in clinical applications.<\/jats:p>","DOI":"10.3390\/s100100796","type":"journal-article","created":{"date-parts":[[2010,1,21]],"date-time":"2010-01-21T08:53:33Z","timestamp":1264064013000},"page":"796-807","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":14,"title":["The Non-linear Relationship between Muscle Voluntary Activation Level and Voluntary Force Measured by the Interpolated Twitch Technique"],"prefix":"10.3390","volume":"10","author":[{"given":"Yi-Ming","family":"Huang","sequence":"first","affiliation":[{"name":"Physical Therapy Department and Graduate Institute of Rehabilitation Science, Chang Gung University, 259, Wen-Hwa 1st Rd, Kweishan, Tao-Yuan, Taiwan"}]},{"given":"Miao-Ju","family":"Hsu","sequence":"additional","affiliation":[{"name":"Department of Physical Therapy, College of Health Science, Kaohsiung Medical University, Kaohsiung, Taiwan"},{"name":"Department of Rehabilitation, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan"}]},{"given":"Cheng-Hsiang","family":"Lin","sequence":"additional","affiliation":[{"name":"Department of Statistics, Tunghai University, Taichung, Taiwan"}]},{"given":"Shun-Hwa","family":"Wei","sequence":"additional","affiliation":[{"name":"Graduate Institute of Rehabilitation Science and Technology, National Yang Ming University, Taipei, Taiwan"}]},{"given":"Ya-Ju","family":"Chang","sequence":"additional","affiliation":[{"name":"Physical Therapy Department and Graduate Institute of Rehabilitation Science, Chang Gung University, 259, Wen-Hwa 1st Rd, Kweishan, Tao-Yuan, Taiwan"}]}],"member":"1968","published-online":{"date-parts":[[2010,1,21]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"376","DOI":"10.1002\/(SICI)1097-4598(200003)23:3<376::AID-MUS9>3.0.CO;2-2","article-title":"Evidence of inability to fully activate human limb muscle","volume":"23","author":"Yue","year":"2000","journal-title":"Muscle Nerv"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"231","DOI":"10.1055\/s-2002-29074","article-title":"Impaired ability of voluntary quadriceps activation bilaterally interferes with function testing after knee injuries. A twitch interpolation study","volume":"23","author":"Urbach","year":"2002","journal-title":"Int. J. Sports Med"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1691","DOI":"10.1097\/00005768-199912000-00001","article-title":"Bilateral deficit of voluntary quadriceps muscle activation after unilateral ACL tear","volume":"31","author":"Urbach","year":"1999","journal-title":"Med. Sci. Sports Exerc"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"641","DOI":"10.1136\/ard.56.11.641","article-title":"Sensorimotor changes and functional performance in patients with knee osteoarthritis","volume":"56","author":"Hurley","year":"1997","journal-title":"Ann. Rheum. Dis"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"127","DOI":"10.1093\/rheumatology\/32.2.127","article-title":"The influence of arthrogenous muscle inhibition on quadriceps rehabilitation of patients with early, unilateral osteoarthritic knees","volume":"32","author":"Hurley","year":"1993","journal-title":"British J. Rheumatol"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"925","DOI":"10.1093\/rheumatology\/34.10.925","article-title":"Muscle strength, voluntary activation and cross-sectional muscle area in patients with fibromyalgia","volume":"34","author":"Norregaard","year":"1995","journal-title":"British J. Rheumatol"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1106","DOI":"10.1136\/jnnp.57.9.1106","article-title":"Muscle strength, voluntary activation, twitch properties, and endurance in patients with fibromyalgia","volume":"57","author":"Norregaard","year":"1994","journal-title":"J. Neurol. Neurosur. Psychiatry"},{"key":"ref_8","first-page":"85","article-title":"Muscle performance, voluntary activation, twitch properties and perceived effort in normal subjects and patients with the chronic fatigue syndrome","volume":"114","author":"Lloyd","year":"1991","journal-title":"Brain"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"1229","DOI":"10.1016\/j.jbiomech.2008.01.019","article-title":"Effect of voluntary activation on age-related muscle fatigue resistance","volume":"41","author":"Mademli","year":"2008","journal-title":"J. Biomech"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"361","DOI":"10.1046\/j.1365-201X.1998.t01-1-00358.x","article-title":"Effects of real and imagined training on voluntary muscle activation during maximal isometric contractions","volume":"163","author":"Herbert","year":"1998","journal-title":"Acta Physiol. Scand"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"41","DOI":"10.1016\/j.neulet.2007.07.018","article-title":"Effect of electrostimulation training-detraining on neuromuscular fatigue mechanisms","volume":"424","author":"Jubeau","year":"2007","journal-title":"Neurosci. Lett"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1131","DOI":"10.1152\/jappl.1981.51.5.1131","article-title":"Extent of motor unit activation during effort","volume":"51","author":"Belanger","year":"1981","journal-title":"J. Appl. Physiol"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"317","DOI":"10.1016\/j.jelekin.2006.04.008","article-title":"Methodological issues with the interpolated twitch technique","volume":"17","author":"Folland","year":"2007","journal-title":"J. Electromyogr. Kinesiol"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"553","DOI":"10.1113\/jphysiol.1954.sp005070","article-title":"Voluntary strength and fatigue","volume":"123","author":"Merton","year":"1954","journal-title":"J. Physiol"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1288","DOI":"10.1136\/jnnp.49.11.1288","article-title":"Clinical and experimental application of the percutaneous twitch superimposition technique for the study of human muscle activation","volume":"49","author":"Rutherford","year":"1986","journal-title":"J. Neurol. Neurosur. Psychiatry"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"593","DOI":"10.1002\/mus.880180605","article-title":"Reliability of measurements of muscle strength and voluntary activation using twitch interpolation","volume":"18","author":"Allen","year":"1995","journal-title":"Muscle Nerv"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"2267","DOI":"10.1152\/jappl.1996.81.5.2267","article-title":"Muscle inactivation: assessment of interpolated twitch technique","volume":"81","author":"Behm","year":"1996","journal-title":"J. Appl. Physiol"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"523","DOI":"10.1046\/j.1365-2281.1997.05555.x","article-title":"The twitch interpolation technique for the estimation of true quadriceps muscle strength","volume":"17","author":"Norregaard","year":"1997","journal-title":"Clin. Physiol. (Oxford, England)"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"462","DOI":"10.1007\/BF00376464","article-title":"Twitch interpolation technique in testing of maximal muscle strength: influence of potentiation, force level, stimulus intensity and preload","volume":"67","author":"Mehlsen","year":"1993","journal-title":"Eur. J. Appl. Physiol. Occup. Physiol"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"541","DOI":"10.1007\/s00421-002-0579-3","article-title":"EMG activity and voluntary activation during knee-extensor concentric torque generation","volume":"86","author":"Babault","year":"2002","journal-title":"Eur. J. Appl. Physiol"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"2271","DOI":"10.1152\/jn.1999.82.5.2271","article-title":"Twitch interpolation in human muscles: mechanisms and implications for measurement of voluntary activation","volume":"82","author":"Herbert","year":"1999","journal-title":"J. Neurophysiol"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1706","DOI":"10.1002\/1097-4598(200011)23:11<1706::AID-MUS6>3.0.CO;2-B","article-title":"Measurement of central activation failure of the quadriceps femoris in healthy adults","volume":"23","author":"Stackhouse","year":"2000","journal-title":"Muscle Nerv"},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1016\/0304-3940(94)90926-1","article-title":"Are humans able to voluntarily elicit maximum muscle force?","volume":"179","author":"Dowling","year":"1994","journal-title":"Neurosci. Lett"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"861","DOI":"10.1002\/(SICI)1097-4598(199607)19:7<861::AID-MUS8>3.0.CO;2-7","article-title":"Quantitation of central activation failure during maximal voluntary contractions in humans","volume":"19","year":"1996","journal-title":"Muscle Nerv"},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"M249","DOI":"10.1093\/gerona\/54.5.M249","article-title":"Older adults exhibit a reduced ability to fully activate their biceps brachii muscle","volume":"54","author":"Yue","year":"1999","journal-title":"J. Gerontol"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"712","DOI":"10.1177\/0269215507079137","article-title":"Decrease of hypertonia after continuous passive motion treatment in individuals with spinal cord injury","volume":"21","author":"Chang","year":"2007","journal-title":"Clin. Rehab"},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"128","DOI":"10.1007\/PL00013785","article-title":"Influence of complete spinal cord injury on skeletal muscle mechanics within the first 6 months of injury","volume":"81","author":"Castro","year":"2000","journal-title":"Eur. J. Appl. Physiol"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"2195","DOI":"10.1152\/jn.1995.73.6.2195","article-title":"Fatigability, relaxation properties, and electromyographic responses of the human paralyzed soleus muscle","volume":"73","author":"Shields","year":"1995","journal-title":"J. Neurophysiol"},{"key":"ref_29","unstructured":"Odum, E.P., and Barrett, G.W. (2005). Fundamentals of Ecology, Thomson Brooks\/Cole. [5th ed]."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"275","DOI":"10.1073\/pnas.6.6.275","article-title":"On the rate of growth of the population of the United States since 1790 and its mathematical representation","volume":"6","author":"Pearl","year":"1920","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_31","unstructured":"Pearl, R. (1925). The Biology of Population Growth, Alfred A. Knopf."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"34","DOI":"10.1053\/j.jfas.2007.10.008","article-title":"Effect of knee flexion angle on Achilles tendon force and ankle joint plantarflexion moment during passive dorsiflexion","volume":"47","author":"Orishimo","year":"2008","journal-title":"J. Foot Ankle Surg"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"1636","DOI":"10.1152\/jappl.1982.52.6.1636","article-title":"Influence of joint position on ankle plantarflexion in humans","volume":"52","author":"Sale","year":"1982","journal-title":"J. Appl. Physiol.: Respirat. Environ. Exerc. Physiol"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"625","DOI":"10.1007\/s00421-008-0757-z","article-title":"Relationships between voluntary activation and motor unit firing rate during maximal voluntary contractions in young and older adults","volume":"103","author":"Knight","year":"2008","journal-title":"Eur. J. Appl. Physiol"},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"M45","DOI":"10.1093\/geronj\/47.2.M45","article-title":"The weakness of old age is not due to failure of muscle activation","volume":"47","author":"Phillips","year":"1992","journal-title":"J. Gerontol"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"1470","DOI":"10.1249\/01.mss.0000228953.52473.ce","article-title":"Determining the extent of neural activation during maximal effort","volume":"38","author":"Kendall","year":"2006","journal-title":"Med. Sci. Sports Exerc"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1113\/jphysiol.1982.sp014294","article-title":"Control scheme governing concurrently active human motor units during voluntary contractions","volume":"329","author":"LeFever","year":"1982","journal-title":"J. Physiol"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"45","DOI":"10.1016\/0006-8993(81)90266-3","article-title":"Comparison of the recruitment and discharge properties of motor units in human brachial biceps and adductor pollicis during isometric contractions","volume":"219","author":"Kukulka","year":"1981","journal-title":"Brain Res"},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"113","DOI":"10.1113\/jphysiol.1982.sp014293","article-title":"Behaviour of human motor units in different muscles during linearly varying contractions","volume":"329","author":"LeFever","year":"1982","journal-title":"J. Physiol"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"563","DOI":"10.1002\/(SICI)1097-4598(199605)19:5<563::AID-MUS3>3.0.CO;2-9","article-title":"Rank-ordered regulation of motor units","volume":"19","author":"Erim","year":"1996","journal-title":"Muscle Nerv"}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/10\/1\/796\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T22:01:16Z","timestamp":1760220076000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/10\/1\/796"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2010,1,21]]},"references-count":40,"journal-issue":{"issue":"1","published-online":{"date-parts":[[2010,1]]}},"alternative-id":["s100100796"],"URL":"https:\/\/doi.org\/10.3390\/s100100796","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2010,1,21]]}}}