{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,11]],"date-time":"2026-09-11T10:12:43Z","timestamp":1789121563893,"version":"build-2803163510"},"reference-count":17,"publisher":"MDPI AG","issue":"9","license":[{"start":{"date-parts":[[2026,9,11]],"date-time":"2026-09-11T00:00:00Z","timestamp":1789084800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Medicina"],"abstract":"<jats:p>Background and Objectives: Stroke, a neurological disorder caused by damage to the central nervous system, is commonly accompanied by impairments in motor and sensory function and muscle strength. We compared the effects of progressive squat exercises performed under varying support-surface stability conditions on quadriceps femoris muscle thickness in patients 6 months to less than 1 year after stroke, using rehabilitative ultrasound imaging. Materials and Methods: This randomized, open-label, parallel-group controlled trial assessed 36 patients with stroke for eligibility. Four individuals were excluded before randomization; the remaining 32 participants were randomly assigned in a 1:1 ratio to either the unstable-support-surface squat exercise group (n = 16) or the stable-support-surface squat exercise group (n = 16). Both groups performed progressive squat exercises five times per week for 4 weeks. Quadriceps femoris muscle thickness was measured before and after the intervention using rehabilitative ultrasound imaging. Results: Between-group comparisons of changes from baseline showed significantly greater increases in rectus femoris and vastus medialis muscle thickness in the unstable support-surface squat exercise group than in the stable support-surface squat exercise group (p &lt; 0.05). No significant between-group differences were observed in vastus intermedius or vastus lateralis muscle thickness (p &gt; 0.05). Conclusions: Progressive squat exercise performed on an unstable support surface resulted in greater increases in rectus femoris and vastus medialis muscle thickness than the same exercise performed on a stable support surface. However, these findings are limited to muscle thickness and should not be interpreted as evidence of improved muscle strength or functional performance.<\/jats:p>","DOI":"10.3390\/medicina62091749","type":"journal-article","created":{"date-parts":[[2026,9,11]],"date-time":"2026-09-11T08:17:42Z","timestamp":1789114662000},"page":"1749","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Influence of Support Surface Stability on Changes in Quadriceps Femoris Muscle Thickness During Progressive Squat Exercise in Patients with Stroke: A Randomized Controlled Trial"],"prefix":"10.3390","volume":"62","author":[{"given":"Hui Ju","family":"Nam","sequence":"first","affiliation":[{"name":"Chungdam Hospital, 46, Samseong-ro 147-gil, Gangnam-gu, Seoul 06063, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"methodology","vocabulary":"credit"},{"role":"software","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"formal-analysis","vocabulary":"credit"},{"role":"investigation","vocabulary":"credit"},{"role":"data-curation","vocabulary":"credit"},{"role":"writing-original-draft","vocabulary":"credit"},{"role":"writing-review-editing","vocabulary":"credit"},{"role":"visualization","vocabulary":"credit"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8751-5055","authenticated-orcid":false,"given":"Ga-Yeon","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Public Health, Graduate School, Dankook University, 119 Dandae-ro, Dongnan-gu, Cheonan-si 31116, Republic of Korea"}],"role":[{"vocabulary":"crossref","role":"author"},{"role":"conceptualization","vocabulary":"credit"},{"role":"validation","vocabulary":"credit"},{"role":"resources","vocabulary":"credit"},{"role":"supervision","vocabulary":"credit"},{"role":"project-administration","vocabulary":"credit"}]}],"member":"1968","published-online":{"date-parts":[[2026,9,11]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"167","DOI":"10.1161\/hs0102.101014","article-title":"Adherence to postacute rehabilitation guidelines is associated with functional recovery in stroke","volume":"33","author":"Duncan","year":"2002","journal-title":"Stroke"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"406","DOI":"10.1016\/S0003-9993(95)80568-0","article-title":"Outcome and time course of recovery in stroke. Part II: Time course of recovery. The Copenhagen Stroke Study","volume":"76","author":"Nakayama","year":"1995","journal-title":"Arch. Phys. Med. Rehabil."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1046\/j.1468-1331.2002.0090s1023.x","article-title":"Gait training in hemiplegia","volume":"9","author":"Mauritz","year":"2002","journal-title":"Eur. J. Neurol."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"395","DOI":"10.1111\/j.1747-4949.2010.00467.x","article-title":"Loss of skeletal muscle mass after stroke: A systematic review","volume":"5","author":"English","year":"2010","journal-title":"Int. J. Stroke"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"792","DOI":"10.1177\/036354659602400615","article-title":"Comparison of intersegmental tibiofemoral joint forces and muscle activity during various closed kinetic chain exercises","volume":"24","author":"Stuart","year":"1996","journal-title":"Am. J. Sports Med."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Lee, J.H., Kim, S., Heo, J., Park, D.H., and Chang, E. (2022). Differences in the muscle activities of the quadriceps femoris and hamstrings while performing various squat exercises. BMC Sports Sci. Med. Rehabil., 14.","DOI":"10.1186\/s13102-022-00404-6"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"90","DOI":"10.1053\/apmr.2003.50004","article-title":"Comparison of the ankle, knee, hip, and trunk corrective action shown during single-leg stance on firm, foam, and multiaxial surfaces","volume":"84","author":"Riemann","year":"2003","journal-title":"Arch. Phys. Med. Rehabil."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"33","DOI":"10.1139\/h05-103","article-title":"Trunk muscle activity increases with unstable squat movements","volume":"30","author":"Anderson","year":"2005","journal-title":"Can. J. Appl. Physiol."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"400","DOI":"10.1123\/ijspp.2.4.400","article-title":"Effect of instability and resistance on unintentional squat-lifting kinetics","volume":"2","author":"Drinkwater","year":"2007","journal-title":"Int. J. Sports Physiol. Perform."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Akazawa, N., Harada, K., Okawa, N., Tamura, K., and Moriyama, H. (2018). Muscle mass and intramuscular fat of the quadriceps are related to muscle strength in non-ambulatory chronic stroke survivors: A cross-sectional study. PLoS ONE, 13.","DOI":"10.1371\/journal.pone.0201789"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"438","DOI":"10.1016\/j.jstrokecerebrovasdis.2016.10.006","article-title":"Validity of quadriceps muscle thickness measurement in patients with subacute stroke during hospitalization for assessment of muscle wasting and physical function","volume":"26","author":"Nozoe","year":"2017","journal-title":"J. Stroke Cerebrovasc. Dis."},{"key":"ref_12","first-page":"980","article-title":"Ultrasound imaging distinguishes between normal and weak muscle","volume":"85","author":"Hicks","year":"2004","journal-title":"Arch. Phys. Med. Rehabil."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"608","DOI":"10.2519\/jospt.2007.2418","article-title":"Intrarater and interrater reliability of assessment of lumbar multifidus muscle thickness using rehabilitative ultrasound imaging","volume":"37","author":"Wallwork","year":"2007","journal-title":"J. Orthop. Sports Phys. Ther."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"e51","DOI":"10.1016\/j.radi.2017.03.011","article-title":"Reproducibility of ultrasound-derived muscle thickness and echo-intensity for the entire quadriceps femoris muscle","volume":"23","author":"Santos","year":"2017","journal-title":"Radiography"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"259","DOI":"10.1016\/j.math.2014.02.002","article-title":"Validity of measuring distal vastus medialis muscle using rehabilitative ultrasound imaging versus magnetic resonance imaging","volume":"19","author":"Worsley","year":"2014","journal-title":"Man. Ther."},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Cheon, S., Lee, J.H., Jun, H.P., An, Y.W., and Chang, E. (2020). Acute effects of open kinetic chain exercise versus those of closed kinetic chain exercise on quadriceps muscle thickness in healthy adults. Int. J. Environ. Res. Public Health, 17.","DOI":"10.3390\/ijerph17134669"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"289","DOI":"10.1111\/j.1469-7580.2006.00619.x","article-title":"Intra- and intermuscular variation in human quadriceps femoris architecture assessed in vivo","volume":"209","author":"Blazevich","year":"2006","journal-title":"J. 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