{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T09:33:24Z","timestamp":1786440804790,"version":"build-2736575974"},"reference-count":44,"publisher":"PeerJ","license":[{"start":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T00:00:00Z","timestamp":1786406400000},"content-version":"unspecified","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/100031913","name":"Tangshan Normal University","doi-asserted-by":"crossref","award":["20263121053"],"award-info":[{"award-number":["20263121053"]}],"id":[{"id":"10.13039\/100031913","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Dalian Federation of Social Sciences Key Project","award":["2025dlskzd475"],"award-info":[{"award-number":["2025dlskzd475"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Body mass index (BMI) is routinely used in university health surveillance, but its sex- and grade-specific association with multidimensional physical fitness, including nonlinear patterns, remains unclear.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>Data from 16,292 university students (8,505 females; 7,787 males; aged 17\u201323 years) who completed the national standardized fitness assessment were analyzed in this cross-sectional study. Vital capacity, 50-m sprint, standing long jump, sit-and-reach, 800\/1,000-m run, and muscular endurance were standardized within sex to derive a Physical Fitness Index (PFI), with time-based tests reverse-scored. Two-way analyses of variance examined associations of sex, academic grade, and BMI category with PFI. Sex- and grade-specific quadratic models were used to characterize BMI\u2013PFI curves and estimate the model-derived BMI value associated with peak predicted PFI. Pearson correlations assessed associations between PFI and individual fitness components.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      Academic grade was associated with PFI, whereas no overall sex effect was observed (sex:\n                      <jats:italic>F<\/jats:italic>\n                      (1, 16,284) = 1.51,\n                      <jats:italic>p<\/jats:italic>\n                      = 0.219, partial \u03b7\n                      <jats:sup>2<\/jats:sup>\n                      = 0.000093; grade:\n                      <jats:italic>F<\/jats:italic>\n                      (3, 16,284) = 74.54,\n                      <jats:italic>p<\/jats:italic>\n                      &lt; 0.001, partial \u03b7\n                      <jats:sup>2<\/jats:sup>\n                      = 0.0136). The sex \u00d7 grade interaction was statistically significant but small (\n                      <jats:italic>F<\/jats:italic>\n                      (3, 16,284) = 20.44,\n                      <jats:italic>p<\/jats:italic>\n                      &lt; 0.001, partial \u03b7\n                      <jats:sup>2<\/jats:sup>\n                      = 0.00375). Within both sexes, normal-weight students showed the highest PFI; underweight students had higher PFI than overweight and obese peers, while PFI was lower in the overweight and obese groups. The BMI\u2013PFI association was stronger in males (partial \u03b7\n                      <jats:sup>2<\/jats:sup>\n                      = 0.1061) than in females (partial \u03b7\n                      <jats:sup>2<\/jats:sup>\n                      = 0.0287). All quadratic models showed a concave BMI\u2013PFI pattern, with lower predicted PFI at higher BMI values and model-derived peak estimates varying across sex\u2013grade subgroups. These estimates should not be interpreted as physiological optima or recommended BMI targets. Correlations indicated that PFI integrated cardiorespiratory fitness, lower-limb power, flexibility, muscular endurance, and running performance.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>BMI was associated with multidimensional physical fitness in this large cohort of university students, with lower PFI observed at both low and high BMI values. BMI showed a stronger association with PFI than academic grade, particularly in males. These findings support BMI-informed and sex-sensitive fitness monitoring, but should be interpreted as cross-sectional associations because body-composition and behavioral measures were unavailable.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.7717\/peerj.21656","type":"journal-article","created":{"date-parts":[[2026,8,11]],"date-time":"2026-08-11T08:52:51Z","timestamp":1786438371000},"page":"e21656","source":"Crossref","is-referenced-by-count":0,"title":["Body mass index and physical fitness in university students: sex differences and nonlinear patterns in a large cross-sectional study"],"prefix":"10.7717","volume":"14","author":[{"given":"Qiang","family":"Wei","sequence":"first","affiliation":[{"name":"Department of Physical Education, Tangshan Normal University, Tangshan, Hebei, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lei","family":"Wang","sequence":"additional","affiliation":[{"name":"Department of Physical Education, Tangshan Normal University, Tangshan, Hebei, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Chun","family":"Yang","sequence":"additional","affiliation":[{"name":"Department of Physical Education, Tangshan Normal University, Tangshan, Hebei, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wei","family":"Sun","sequence":"additional","affiliation":[{"name":"Department of Physical Education, Tangshan Normal University, Tangshan, Hebei, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Siqin","family":"Shen","sequence":"additional","affiliation":[{"name":"College of Physical Education, Dalian University, Dalian, Liaoning, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"4443","published-online":{"date-parts":[[2026,8,11]]},"reference":[{"issue":"3","key":"10.7717\/peerj.21656\/ref-1","doi-asserted-by":"publisher","first-page":"418","DOI":"10.1111\/j.1600-0838.2009.00959.x","article-title":"Health-related fitness in adolescents: underweight, and not only overweight, as an influencing factor. 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